PATENT DOCUMENT

Publication Number: US-11722016-B2
Application Number: US-202017028325-A
Country: US
Kind Code: B2

Title: Accessory insert modules with magnetic alignment components

Abstract:
A magnetic alignment system can include a primary annular magnetic alignment component and a secondary annular magnetic alignment component. The primary alignment component can include an inner annular region having a first magnetic orientation, an outer annular region having a second magnetic orientation opposite to the first magnetic orientation, and a non-magnetized central annular region disposed between the primary inner annular region and the primary outer annular region. The secondary alignment component can have a magnetic orientation with a radial component. Additional features, such as a rotational magnetic alignment component and/or an NFC coil and circuitry can be included.

Claims:
What is claimed is: 
     
       1. An alignment module comprising:
 an annular magnetic alignment component including a plurality of arcuate magnets, each arcuate magnet having:
 an inner arcuate region having a magnetic polarity oriented in a first axial direction; 
 an outer arcuate region having a magnetic polarity oriented in a second axial direction opposite the first axial direction; and 
 a non-magnetized central arcuate region disposed between the inner arcuate region and the outer arcuate region; and 
 
 an encapsulating structure surrounding and holding the arcuate magnets in an annular arrangement, the encapsulating structure having a central opening inboard of the annular magnetic alignment component. 
 
     
     
       2. The alignment module of  claim 1  further comprising:
 a rotational alignment component comprising a rectangular magnet, 
 wherein the encapsulating structure further holds the rectangular magnet in a fixed position outboard of the annular magnetic alignment component. 
 
     
     
       3. The alignment module of  claim 1  wherein the encapsulating structure has an annular shape. 
     
     
       4. The alignment module of  claim 3  wherein the encapsulating structure comprises an annular front enclosure and an annular rear enclosure joined at inner and outer edges thereof. 
     
     
       5. The alignment module of  claim 4  wherein the annular front enclosure and the annular rear enclosure are made of plastic. 
     
     
       6. The alignment module of  claim 5  where the annular front enclosure and the annular rear enclosure are joined by a weld. 
     
     
       7. The alignment module of  claim 5  where the annular front enclosure is formed in a first injection molding stage and the annular rear enclosure is injection molded onto the annular front enclosure. 
     
     
       8. The alignment module of  claim 1  wherein the encapsulating structure comprises an annular front enclosure, an annular back enclosure, an annular inner side enclosure and an annular outer side enclosure and wherein the annular front enclosure and the annular back enclosure are joined to the annular inner side enclosure and the annular outer side enclosure by adhesive. 
     
     
       9. An alignment module comprising:
 an annular magnetic alignment component including a plurality of arcuate magnets, each arcuate magnet having:
 an inner arcuate region having a magnetic polarity oriented in a first axial direction; 
 an outer arcuate region having a magnetic polarity oriented in a second axial direction opposite the first axial direction; and 
 a non-magnetized central arcuate region disposed between the inner arcuate region and the outer arcuate region; 
 
 a rotational alignment component comprising a rectangular magnet and disposed outside a perimeter of the annular magnetic alignment component; and 
 an encapsulating structure holding the annular magnetic alignment component and the rotational alignment component in a fixed spatial relationship to each other, the encapsulating structure comprising:
 a front planar layer; 
 a back planar layer; and 
 a magnet-holding layer made of a plastic material, the magnet-holding layer having a circular opening therethrough to accommodate the annular magnetic alignment component and a rectangular opening therethrough to accommodate the rectangular magnet, 
 the magnet-holding layer further including a disc of the plastic material filling a region inboard of the annular magnetic alignment component. 
 
 
     
     
       10. The alignment module of  claim 9  wherein the magnet-holding layer, the arcuate magnets, and the rectangular magnet have equal thicknesses. 
     
     
       11. The alignment module of  claim 9  further comprising:
 a first adhesive layer attaching the front planar layer to the magnet-holding layer; and 
 a second adhesive layer attaching the back planar layer to the magnet-holding layer. 
 
     
     
       12. The alignment module of  claim 9  wherein the front planar layer and the back planar layer are rectangular layers with rounded corners. 
     
     
       13. An alignment module comprising:
 an annular magnetic alignment component including a plurality of arcuate magnets, each arcuate magnet having:
 an inner arcuate region having a magnetic polarity oriented in a first axial direction; 
 an outer arcuate region having a magnetic polarity oriented in a second axial direction opposite the first axial direction; and 
 a non-magnetized central arcuate region disposed between the inner arcuate region and the outer arcuate region; 
 
 an encapsulating structure surrounding and holding the arcuate magnets in an annular arrangement; and 
 a near-field communication (NFC) coil disposed within the encapsulating structure inboard of and coaxial with the annular magnetic alignment component, the NFC coil coupled to an NFC tag circuit. 
 
     
     
       14. The alignment module of  claim 13  wherein the encapsulating structure comprises:
 a front planar layer; 
 a back planar layer; and 
 a magnet-holding layer, the magnet-holding layer having a circular opening therethrough to accommodate the annular magnetic alignment component and the NFC coil. 
 
     
     
       15. The alignment module of  claim 14  wherein the magnet-holding layer and the arcuate magnets have equal thicknesses. 
     
     
       16. The alignment module of  claim 14  wherein the magnet-holding layer includes a disc of material filling a region inboard of the annular magnetic alignment component and the NFC coil. 
     
     
       17. The alignment module of  claim 14  further comprising:
 a rotational alignment component comprising a rectangular magnet and disposed outboard of the annular magnetic alignment component, 
 wherein the magnet-holding layer has a rectangular opening therethrough to accommodate the rotational alignment component.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 62/907,332, filed Sep. 27, 2019, and of U.S. Provisional Application No. 63/061,752, filed Aug. 5, 2020. The disclosures of both provisional applications are incorporated by reference herein for all purposes. 
     The following five U.S. patent applications, filed on the same day as this application, Sep. 22, 2020, also claim the benefit of the above-referenced provisional applications: U.S. application Ser. No. 17/028,231, titled “Magnetic Alignment Systems for Electronic Devices”; U.S. application Ser. No. 17/028,275, titled “Magnetic Alignment Systems with Rotational Alignment Component for Electronic Devices”; U.S. application Ser. No. 17/028,256, titled “Magnetic Alignment Systems with NFC for Electronic Devices”; U.S. application Ser. No. 17/028,295, titled “Magnetic Alignment Systems with Proximity Detection for Electronic Devices”; and U.S. application Ser. No. 17/028,310, titled “Wireless Charging Modules with Magnetic Alignment Components.” 
    
    
     BACKGROUND 
     The present disclosure relates generally to consumer electronic devices and more particularly to magnetic alignment components and systems that facilitate establishing and maintaining a desired alignment between two (or more) devices, e.g., for purposes of enabling efficient wireless power transfer between the devices. 
     Portable electronic devices (e.g., mobile phones, media players, electronic watches, and the like) operate when there is charge stored in their batteries. Some portable electronic devices include a rechargeable battery that can be recharged by coupling the portable electronic device to a power source through a physical connection, such as through a charging cord. Using a charging cord to charge a battery in a portable electronic device, however, requires the portable electronic device to be physically tethered to a power outlet. Additionally, using a charging cord requires the mobile device to have a connector, typically a receptacle connector, configured to mate with a connector, typically a plug connector, of the charging cord. The receptacle connector includes a cavity in the portable electronic device that provides an avenue via which dust and moisture can intrude and damage the device. Further, a user of the portable electronic device has to physically connect the charging cable to the receptacle connector in order to charge the battery. 
     To avoid such shortcomings, wireless charging technologies have been developed that exploit electromagnetic induction to charge portable electronic devices without the need for a charging cord. For example, some portable electronic devices can be recharged by merely resting the device on a charging surface of a wireless charger device. A transmitter coil disposed below the charging surface is driven with an alternating current that produces a time-varying magnetic flux that induces a current in a corresponding receiver coil in the portable electronic device. The induced current can be used by the portable electronic device to charge its internal battery. Some portable electronic devices have been designed to not only receive power wirelessly but also to transmit power wirelessly to other portable electronic devices, such as accessory devices. 
     SUMMARY 
     Among other factors, the efficiency of wireless power transfer depends on the alignment between the transmitter and receiver coils. For instance, a transmitter coil and receiver coil may perform best when they are aligned coaxially. Where a portable electronic device has a flat surface with no guiding features, finding the proper alignment can be difficult. Often, alignment is achieved by trial and error, with the user shifting the relative positions of the device and charger and observing the effect on charging performance. Establishing optimal alignment in this manner can be time-consuming. Further, the absence of surface features can make it difficult to maintain optimal alignment. For example, if the portable electronic device and/or charger are jostled during charging, they may be shifted out of alignment. For these and other reasons, improved techniques for establishing and maintaining alignment between electronic devices would be desirable. 
     According to embodiments described herein, a portable electronic device and an accessory device can include complementary magnetic alignment components that facilitate alignment of the accessory device with the portable electronic device and/or attachment of the accessory device to the portable electronic device. The magnetic alignment components can include annular magnetic alignment components that, in some embodiments, can surround inductive charging transmitter and receiver coils. In the nomenclature used herein, a “primary” annular magnetic alignment component refers to an annular magnetic alignment component used in a wireless charger device or other terminal accessory. A “secondary” annular magnetic alignment component refers to an annular magnetic alignment component used in a portable electronic device. An “auxiliary” annular magnetic alignment component refers to an annular magnetic alignment component used in a charge-through accessory. 
     In some embodiments, a magnetic alignment system can also include a rotational magnetic alignment component that facilitates aligning two devices in a preferred rotational orientation. A rotational magnetic alignment component can include, for example, one or more magnets disposed outboard of an annular alignment component. It should be understood that any device that has an annular alignment component might or might not also have a rotational alignment component, and rotational alignment components may be categorized as primary, secondary, or auxiliary depending on the type of device. 
     In some embodiments, magnetic alignment components can be fixed in position within a device housing. Alternatively, any or all of the magnetic alignment components in a device (including annular and/or rotational alignment components) can be made movable in the axial and/or lateral direction. A movable magnetic alignment component can allow the magnets to be moved (e.g., axially) into closer proximity to increase magnetic forces holding the devices in alignment or moved away from each other to reduce the magnetic forces holding the devices in alignment. 
     In some embodiments, a magnetic alignment system can also include a near-field communication (NFC) coil and supporting circuitry to allow devices to identify themselves to each other using an NFC protocol. An NFC coil in a particular device can be an annular coil that is disposed inboard of the annular alignment component or outboard of the annular alignment component. For example, in a device that has an annular alignment component surrounding an inductive charging coil, the NFC coil can be disposed in an annular gap between the inductive charging coil and the annular alignment component. It should be understood that an NFC component is optional in the context of providing magnetic alignment and can be used with moving or fixed magnetic alignment components. 
     The following detailed description, together with the accompanying drawings, will provide a better understanding of the nature and advantages of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    shows a simplified representation of a wireless charging system incorporating a magnetic alignment system according to some embodiments. 
         FIG.  2 A  shows a perspective view of a magnetic alignment system according to some embodiments, and  FIG.  2 B  shows a cross-section through the magnetic alignment system of  FIG.  2 A . 
         FIG.  3 A  shows a perspective view of a magnetic alignment system according to some embodiments, and  FIG.  3 B  shows a cross-section through the magnetic alignment system of  FIG.  3 A . 
         FIG.  4    shows a simplified top-down view of a secondary alignment component according to some embodiments. 
         FIG.  5 A  shows a perspective view of a magnetic alignment system according to some embodiments, and  FIG.  5 B  shows an axial cross-section view through a portion of the system of  FIG.  5 A . 
         FIGS.  5 C- 5 E  show examples of arcuate magnets with radial magnetic orientation according to some embodiments. 
         FIGS.  6 A and  6 B  show graphs of force profiles for different magnetic alignment systems, according to some embodiments. 
         FIG.  7    shows a simplified top-down view of a secondary alignment component according to some embodiments. 
         FIG.  8 A  shows a perspective view of a magnetic alignment system according to some embodiments, and  FIGS.  8 B and  8 C  show axial cross-section views through different portions of the system of  FIG.  8 A . 
         FIGS.  9 A and  9 B  show simplified top-down views of secondary alignment components according to various embodiments. 
         FIG.  10    shows a simplified top-down view of a secondary alignment component according to some embodiments. 
         FIG.  11    illustrates an example of an annular alignment component having a gap according to some embodiments. 
         FIGS.  12 A and  12 B  show examples portable electronic devices incorporating a magnetic alignment component according to some embodiments. 
         FIG.  13    shows a simplified view of a wireless charger device incorporating a magnetic alignment component according to some embodiments. 
         FIG.  14 A  shows a simplified perspective view of a system including a portable electronic device in alignment with a wireless charger device according to some embodiments, and  FIG.  14 B  shows a simplified partial cross section view of the system of  FIG.  14 A . 
         FIG.  15    is a block diagram illustrating an exemplary wireless charging system including devices that can be aligned together via a magnetic alignment system according to some embodiments. 
         FIG.  16    shows an example of a portable electronic device and an accessory incorporating a magnetic alignment system with an annular alignment component and a rotational alignment component according to some embodiments. 
         FIGS.  17 A and  17 B  show an example of rotational alignment according to some embodiments. 
         FIGS.  18 A and  18 B  show a perspective view and a top view of a rotational alignment component having a “z-pole” configuration according to some embodiments. 
         FIGS.  19 A and  19 B  show a perspective view and a top view of a rotational alignment component having a “quad-pole” configuration according to some embodiments. 
         FIGS.  20 A and  20 B  show a perspective view and a top view of a rotational alignment component having an “annulus design” configuration according to some embodiments. 
         FIGS.  21 A and  21 B  show a perspective view and a top view of a rotational alignment component having a “triple pole” configuration according to some embodiments. 
         FIG.  22    shows graphs of torque as a function of angular rotation for magnetic alignment systems having rotational alignment components according to various embodiments. 
         FIG.  23    shows a portable electronic device having an alignment system with multiple rotational alignment components according to some embodiments. 
         FIG.  24    shows a simplified representation of a wireless charging system incorporating a magnetic alignment system according to some embodiments. 
         FIG.  25 A  shows a perspective view of a magnetic alignment system according to some embodiments, and  FIG.  25 B  shows a cross-section through the magnetic alignment system of  FIG.  25 A . 
         FIG.  26 A  shows a perspective view of a magnetic alignment system according to some embodiments, and  FIG.  26 B  shows a cross-section through the magnetic alignment system of  FIG.  26 A . 
         FIG.  27    shows a simplified rear view of an accessory device incorporating a magnetic alignment component according to some embodiments. 
         FIG.  28 A  shows a simplified perspective view of a system including a portable electronic device in alignment with an accessory device and a wireless charger device according to some embodiments, and  FIG.  28 B  shows a simplified partial cross section view of the system of  FIG.  28 A . 
         FIG.  29    is a block diagram illustrating an exemplary wireless charging system including devices that can be aligned together via a magnetic alignment system according to some embodiments. 
         FIGS.  30 A- 30 C  illustrate moving magnets according to an embodiment of the present invention. 
         FIGS.  31 A and  31 B  illustrate a moving magnetic structure according to an embodiment of the present invention. 
         FIGS.  32 A and  32 B  illustrate a moving magnetic structure according to an embodiment of the present invention. 
         FIGS.  33 - 35    illustrate a moving magnetic structure according to an embodiment of the present invention. 
         FIG.  36    illustrates a normal force between a first magnet in a first electronic device and a second magnet in a second electronic device. 
         FIG.  37    illustrates a shear force between a first magnet in a first electronic device and a second magnet in a second electronic device. 
         FIGS.  38 A and  38 B  illustrate a moving magnet in conjunction with a high friction surface according to an embodiment of the present invention. 
         FIGS.  39 A and  39 B  illustrate a moving magnet in conjunction with a high friction surface according to an embodiment of the present invention. 
         FIGS.  40 A and  40 B  illustrate a moving magnet in conjunction with a high friction surface according to an embodiment of the present invention. 
         FIGS.  41 A and  41 B  illustrate another moving magnet in conjunction with a high friction surface according to an embodiment of the present invention. 
         FIG.  42    illustrates a cutaway side view of another moving magnet structure according to an embodiment of the present invention. 
         FIG.  43    is a partially transparent view of the moving magnet structure of  FIG.  42   . 
         FIG.  44    is another cutaway side view of the electronic device of  FIG.  42   . 
         FIGS.  45  and  46    illustrate the electronic device of  FIG.  42    as it engages with a second electronic device. 
         FIGS.  47 A and  47 B  illustrate structures for constraining motions of magnets in an electronic device according to an embodiment of the present invention. 
         FIGS.  48 A and  48 B  illustrate structures for constraining motions of magnets in an electronic device according to an embodiment of the present invention. 
         FIGS.  49 A and  49 B  illustrate structures for constraining motions of magnets an electronic device according to an embodiment of the present invention. 
         FIG.  50    shows a simplified back view of a portable electronic device according to some embodiments. 
         FIG.  51    shows an exploded view of a wireless charging and alignment assembly for a portable electronic device incorporating an NFC reader according to some embodiments. 
         FIG.  52    shows a simplified cross-section view of a portion of the portable electronic device of  FIG.  50    incorporating the assembly of  FIG.  51   . 
         FIG.  53    shows an exploded view of a wireless charger device incorporating an NFC tag circuit according to some embodiments. 
         FIGS.  54 A and  54 B  show partial cross-section views of wireless charger device according to some embodiments. 
         FIG.  55    shows an example of an accessory device incorporating an auxiliary alignment component with an NFC tag circuit and coil according to some embodiments. 
         FIG.  56    shows a more detailed view of an NFC tag circuit assembly according to some embodiments. 
         FIG.  57    shows an exploded view of an NFC tag circuit assembly according to some embodiments. 
         FIG.  58    shows a partial cross section view of an accessory according to some embodiments. 
         FIG.  59    shows an example of another accessory device according to some embodiments. 
         FIG.  60    shows an enlarged view of an auxiliary annular magnetic alignment component and NFC tag circuit assembly according to some embodiments. 
         FIG.  61    shows an exploded view of an NFC tag circuit assembly according to some embodiments. 
         FIG.  62    shows a simplified partial cross-section view of a system that includes a wireless charger device, a portable electronic device, and an accessory device according to some embodiments. 
         FIG.  63    shows an example of an accessory device having an auxiliary alignment component with an NFC tag circuit and coil according to some embodiments. 
         FIG.  64    shows a simplified partial cross-section view of a system that includes a wireless charger device, a portable electronic device, and an accessory device according to some embodiments. 
         FIG.  65    shows a flow diagram of a process that can be implemented in a portable electronic device according to some embodiments. 
         FIG.  66    shows an exploded view of a wireless charger device according to some embodiments. 
         FIG.  67    shows a simplified partial cross-section view of a wireless charger device according to some embodiments. 
         FIG.  68    shows an exploded view of a cable assembly with incorporated power circuitry that can be connected to a wireless charger device according to some embodiments. 
         FIG.  69 A  shows an example of a portable electronic device having a wireless power module according to some embodiments. 
         FIG.  69 B  shows a cross section view of the wireless power module of  FIG.  69 A . 
         FIG.  70    shows a more detailed top view of a wireless power module according to some embodiments. 
         FIGS.  71 A- 71 D  show cross section views of NFC coils that can be used in a wireless power module according to various embodiments. 
         FIG.  72    shows an rear view of a case according to some embodiments. 
         FIG.  73 A  shows a simplified axial view of internal components of an annular alignment assembly for a case according to some embodiments. 
         FIG.  73 B  shows a cross section view of the annular alignment assembly of  FIG.  73 A . 
         FIG.  73 C  shows a more detailed view of an NFC tag circuit assembly according to some embodiments. 
         FIG.  74    shows an exploded view of an annular alignment assembly and rotational alignment assembly according to some embodiments. 
         FIG.  75    shows a cross-section view of a portion of a rear panel of a case according to some embodiments. 
         FIGS.  76 A and  76 B  show top and bottom perspective views of a charger alignment module according to some embodiments. 
         FIG.  77    shows an exploded view of a charger alignment module according to some embodiments. 
         FIG.  78    shows a top perspective view of a teardrop-shaped charger module according to some embodiments. 
         FIG.  79 A  is a front view and  FIG.  79 B  is a top view of an accessory insert module according to some embodiments. 
         FIG.  80    shows an exploded view of an accessory insert module according to some embodiments. 
         FIG.  81    shows an exploded view of an accessory insert module according to some embodiments. 
         FIGS.  82  and  83    show partial cross-section views of accessory insert modules according to various embodiments. 
         FIG.  84    is a partial cross section view of an annular accessory insert module according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Described herein are various embodiments of magnetic alignment systems and components thereof. A magnetic alignment system can include annular alignment components, where each annular alignment component can comprise a ring of magnets (or a single annular magnet) having a particular magnetic orientation or pattern of magnetic orientations such that a “primary” annular alignment component can attract and hold a complementary “secondary” annular alignment component. Magnetic alignment components can be incorporated into a variety of devices, and a magnetic alignment component in one device can attract another device having a complementary magnetic alignment component into a desired alignment and/or hold the other device in a desired alignment. (Devices aligned by a magnetic alignment system may be said to be “attached” to each other.) 
     For purposes of the present description, a number of different categories of devices can be distinguished. As used herein, a “portable electronic device” refers generally to any electronic device that is portable and that consumes power and provides at least some interaction with the user. Examples of portable electronic devices include: smart phones and other mobile phones; tablet computers; laptop computers; wearable devices (e.g., smart watches, headphones, earbuds); and any other electronic device that a user may carry or wear. Other portable electronic devices can include robotic devices, remote-controlled devices, personal-care appliances, and so on. 
     An “accessory device” (or “accessory”) refers generally to a device that is useful in connection with a portable electronic device to enhance the functionality and/or esthetics of the portable electronic device. Many categories of accessories may incorporate magnetic alignment. For example, one category of accessories includes wireless charger accessories. As used herein, a “wireless charger accessory” (or “wireless charger device” or just “wireless charger”) is an accessory that can provide power to a portable electronic device using wireless power transfer techniques. A “battery pack” (or “external battery”) is a type of wireless charger accessory that incorporates a battery to store charge that can be transferred to the portable electronic device. In some embodiments, a battery pack may also receive power wirelessly from another wireless charger accessory. Wireless charger accessories may also be referred to as “active” accessories, in reference to their ability to provide and/or receive power. Other accessories are “passive accessories” that do not provide or receive power. For example, some passive accessories are “cases” that can cover one or more surfaces of the portable electronic device to provide protection (e.g., against damage caused by impact of the portable electronic device with other objects), esthetic enhancements (e.g., decorative colors or the like), and/or functional enhancements (e.g., cases that incorporate storage pockets, batteries, card readers, or sensors of various types). Cases can have a variety of form factors. For example, a “tray” can refer to a case that has a rear panel covering the back surface of the portable electronic device and side surfaces to secure the portable electronic device in the tray while leaving the front surface (which may include a display) exposed. A “sleeve” can refer to a case that has front and back panels with an open end (or “throat”) into which a portable electronic device can be inserted so that the front and back surfaces of the device are covered; in some instances, the front panel of a sleeve can include a window through which a portion (or all) of a display of the portable electronic device is visible. A “folio” can refer to a case that has a retention portion that covers at least the back surface (and sometimes also one or more side surfaces) of the portable electronic device and a cover that can be closed to cover the display or opened to expose the display. It should be understood that not all cases are passive accessories. For example, a “battery case” can incorporate a battery pack in addition to protective and/or esthetic features; a battery case can be shaped generally as a tray, sleeve, or folio. Other examples of active cases can include cases that incorporate card readers, sensors, batteries, or other electronic components that enhance functionality of a portable electronic device. 
     In the present description, a distinction is sometimes made between a “charge-through accessory,” which is an accessory that can be positioned between a portable electronic device and a wireless charger device without interfering with wireless power transfer between the wireless charger device and the portable electronic device, and a “terminal accessory,” which is an accessory that is not a charge-through accessory. A wireless charging accessory is typically a terminal accessory, but not all terminal accessories provide wireless charging of a portable electronic device. For example some terminal accessories can be “mounting” accessories that are designed to hold the portable electronic device in a particular position. Examples of mounting include tripods, docking stations, other stands, or mounts that can hold a portable electronic device in a desired position and/or orientation (which might or might not be adjustable). Such accessories might or might not incorporate wireless charging capability. 
     According to embodiments described herein, a portable electronic device and an accessory device can include complementary magnetic alignment components that facilitate alignment of the accessory device with the portable electronic device and/or attachment of the accessory device to the portable electronic device. The magnetic alignment components can include annular magnetic alignment components that, in some embodiments, can surround inductive charging transmitter and receiver coils. (It will be apparent that an annular magnetic alignment component can also be used in a device that does not have an inductive charging coil.) In the nomenclature used herein, a “primary” annular magnetic alignment component refers to an annular magnetic alignment component used in a wireless charger device or other terminal accessory. A “secondary” annular magnetic alignment component refers to an annular magnetic alignment component used in a portable electronic device. An “auxiliary” annular magnetic alignment component refers to an annular magnetic alignment component used in a charge-through accessory. (In this disclosure, adjectives such as “annular,” “magnetic,” “primary,” “secondary” and “auxiliary” may be omitted when the context is clear.) The primary and secondary annular alignment components have magnetic orientations that are complementary, such that the primary and secondary annular alignment components can attract each other and attach devices containing these components in a desired alignment. For example, a primary annular alignment component can have a “quad-pole” magnetic configuration, with an inner annular region having a magnetic polarity in a first axial direction, an outer annular region having a magnetic polarity in a second axial direction opposite the first direction, and a central non-magnetized region between the inner annular region and the outer annular region. A secondary annular alignment component can have a radial magnetic configuration (e.g., with north pole oriented radially inward or radially outward, either exactly or approximately; examples are described below). When aligned, the primary and secondary annular alignment components can form a closed magnetic loop such that the DC magnetic flux is largely contained within the magnets. Alternatively, a secondary annular alignment component can also have a quad-pole magnetic configuration matching that of the primary annular alignment component. An auxiliary annular alignment component can operate as a “repeater” and can have a quad-pole configuration matching that of the primary annular alignment component. 
     In some embodiments, a magnetic alignment system can also include a rotational magnetic alignment component that facilitates aligning two devices in a preferred rotational orientation. A rotational magnetic alignment component can include, for example, one or more magnets disposed outboard of an annular alignment component. The magnet(s) of a rotational alignment component can have complementary orientations, such the rotational alignment components in two devices can attract each other and attach the two devices containing these components in a desired rotational orientation. For example, a rotational alignment component can have a quad-pole configuration with a first magnetized region (e.g., extending along one side of a rectangular magnet) having a magnetic polarity in a first axial direction, a second magnetized region (e.g., extending along the opposite side of the rectangular magnet) having a magnetic polarity in a second axial direction opposite the first direction, and a central non-magnetized region. As another example, a rotational alignment component can have a triple-pole configuration with a first magnetized region (e.g., extending along one side of a rectangular magnet) having a magnetic polarity in a first axial direction, a second magnetized region (e.g., extending along the opposite side of the rectangular magnet) also having a magnetic polarity the first axial direction, a central magnetized region having a magnetic polarity in a second axial direction opposite the first direction, and non-magnetized regions between the central magnetized region and each of the first and second magnetized regions. Other magnetic configurations can be substituted. It should be understood that any device that has an annular magnetic alignment component might or might not also have a rotational magnetic alignment component, and rotational alignment components may be categorized as primary, secondary, or auxiliary, e.g., depending on the type of device. 
     In some embodiments, magnetic alignment components can be fixed in position within a device housing. Alternatively, any or all of the magnetic alignment components in a device (including annular and/or rotational alignment components) can be made movable in the axial and/or lateral direction. A movable magnetic alignment component can allow the magnets to be moved (e.g., axially) into closer proximity to increase magnetic forces holding the devices in alignment or moved away from each other to reduce the magnetic forces holding the devices in alignment. 
     In some embodiments, a magnetic alignment system can also include a near-field communication (NFC) coil and supporting circuitry to allow devices to identify themselves to each other using an NFC protocol. An NFC coil in a particular device can be an annular coil that is disposed inboard of the annular alignment component or outboard of the annular alignment component. For example, in a device that has an annular alignment component surrounding an inductive charging coil, the NFC coil can be disposed in an annular gap between the inductive charging coil and the annular alignment component. It should be understood that an NFC component is optional in the context of providing magnetic alignment. 
     Accordingly, while the following description focuses on specific examples incorporating various combinations of components, it should be understood that any device can have has an annular magnetic alignment component, which can be, for example, any of the primary, secondary, or auxiliary annular magnetic alignment components described herein. Further, any device that has an annular magnetic alignment component can also have a rotational magnetic alignment component, which can be, for example, any of the rotational magnetic alignment components described herein. Further, any device that has an annular magnetic alignment component, regardless of whether it also has a rotational magnetic alignment component, can also have an NFC coil (and supporting reader circuitry and/or tag circuitry), which can be implemented, e.g., according to any of the examples described herein. 
     1. Primary and Secondary Annular Magnetic Alignment Components 
     1.1. Overview of Magnetic Alignment Systems 
       FIG.  1    shows a simplified representation of a wireless charging system  100  incorporating a magnetic alignment system  106  according to some embodiments. A portable electronic device  104  is positioned on a charging surface  108  of a wireless charger device  102 . Portable electronic device  104  can be a consumer electronic device, such as a smart phone, tablet, wearable device, or the like, or any other electronic device for which wireless charging is desired. Wireless charger device  102  can be any device that is configured to generate time-varying magnetic flux to induce a current in a suitably configured receiving device. For instance, wireless charger device  102  can be a wireless charging mat, puck, docking station, or the like. Wireless charger device  102  can include or have access to a power source such as battery power or standard AC power. 
     To enable wireless power transfer, portable electronic device  104  and wireless charger device  102  can include inductive coils  110  and  112 , respectively, which can operate to transfer power between them. For example, inductive coil  112  can be a transmitter coil that generates a time-varying magnetic flux  114 , and inductive coil  110  can be a receiver coil in which an electric current is induced in response to time-varying magnetic flux  114 . The received electric current can be used to charge a battery of portable electronic device  104 , to provide operating power to a component of portable electronic device  104 , and/or for other purposes as desired. (“Wireless power transfer” and “inductive power transfer,” as used herein, refer generally to the process of generating a time-varying magnetic field in a conductive coil of a first device that induces an electric current in a conductive coil of a second device.) 
     To enable efficient wireless power transfer, it is desirable to align inductive coils  112  and  110 . According to some embodiments, magnetic alignment system  106  can provide such alignment. In the example shown in  FIG.  1   , magnetic alignment system  106  includes a primary magnetic alignment component  116  disposed within or on a surface of wireless charger device  102  and a secondary magnetic alignment component  118  disposed within or on a surface of portable electronic device  102 . Primary and secondary alignment components  116  and  118  are configured to magnetically attract one another into an aligned position in which inductive coils  110  and  112  are aligned with one another to provide efficient wireless power transfer. 
     According to embodiments described herein, a magnetic alignment component (including a primary or secondary alignment component) of a magnetic alignment system can be formed of arcuate magnets arranged in an annular configuration. In some embodiments, each magnet can have its magnetic polarity oriented in a desired direction so that magnetic attraction between the primary and secondary magnetic alignment components provides a desired alignment. In some embodiments, an arcuate magnet can include a first magnetic region with magnetic polarity oriented in a first direction and a second magnetic region with magnetic polarity oriented in a second direction different from (e.g., opposite to) the first direction. As will be described, different configurations can provide different degrees of magnetic field leakage. 
     1.2. Magnetic Alignment Systems with a Single Axial Magnetic Orientation 
       FIG.  2 A  shows a perspective view of a magnetic alignment system  200  according to some embodiments, and  FIG.  2 B  shows a cross-section through magnetic alignment system  200  across the cut plane indicated in  FIG.  2 A . Magnetic alignment system  200  can be an implementation of magnetic alignment system  106  of  FIG.  1   . In magnetic alignment system  200 , the alignment components all have magnetic polarity oriented in the same direction (along the axis of the annular configuration). For convenience of description, an “axial” direction (also referred to as a “longitudinal” or “z” direction) is defined to be parallel to an axis of rotational symmetry  201  of magnetic alignment system  200 , and a transverse plane (also referred to as a “lateral” or “x” or “y” direction) is defined to be normal to axis  201 . The term “proximal side” or “proximal surface” is used herein to refer to a side or surface of one alignment component that is oriented toward the other alignment component when the magnetic alignment system is aligned, and the term “distal side” or “distal surface” is used to refer to a side or surface opposite the proximal side or surface. (The terms “top” and “bottom” may be used in reference to a particular view shown in a drawing but have no other significance.) 
     As shown in  FIG.  2 A , magnetic alignment system  200  can include a primary alignment component  216  (which can be an implementation of primary alignment component  116  of  FIG.  1   ) and a secondary alignment component  218  (which can be an implementation of secondary alignment component  118  of  FIG.  1   ). Primary alignment component  216  and secondary alignment component  218  have annular shapes and may also be referred to as “annular” alignment components. The particular dimensions can be chosen as desired. In some embodiments, primary alignment component  216  and secondary alignment component  218  can each have an outer diameter of about 54 mm and a radial width of about 4 mm. The outer diameters and radial widths of primary alignment component  216  and secondary alignment component  218  need not be exactly equal. For instance, the radial width of secondary alignment component  218  can be slightly less than the radial width of primary alignment component  216  and/or the outer diameter of secondary alignment component  218  can also be slightly less than the radial width of primary alignment component  216  so that, when in alignment, the inner and outer sides of primary alignment component  216  extend beyond the corresponding inner and outer sides of secondary alignment component  218 . Thicknesses (or axial dimensions) of primary alignment component  216  and secondary alignment component  218  can also be chosen as desired. In some embodiments, primary alignment component  216  has a thickness of about 1.5 mm while secondary alignment component  218  has a thickness of about 0.37 mm. 
     Primary alignment component  216  can include a number of sectors, each of which can be formed of one or more primary arcuate magnets  226 , and secondary alignment component  218  can include a number of sectors, each of which can be formed of one or more secondary arcuate magnets  228 . In the example shown, the number of primary magnets  226  is equal to the number of secondary magnets  228 , and each sector includes exactly one magnet, but this is not required. Primary magnets  226  and secondary magnets  228  can have arcuate (or curved) shapes in the transverse plane such that when primary magnets  226  (or secondary magnets  228 ) are positioned adjacent to one another end-to-end, primary magnets  226  (or secondary magnets  228 ) form an annular structure as shown. In some embodiments, primary magnets  226  can be in contact with each other at interfaces  230 , and secondary magnets  228  can be in contact with each other at interfaces  232 . Alternatively, small gaps or spaces may separate adjacent primary magnets  226  or secondary magnets  228 , providing a greater degree of tolerance during manufacturing. 
     In some embodiments, primary alignment component  216  can also include an annular shield  214  (also referred to as a DC magnetic shield or DC shield) disposed on a distal surface of primary magnets  226 . In some embodiments, shield  214  can be formed as a single annular piece of material and adhered to primary magnets  226  to secure primary magnets  226  into position. Shield  214  can be formed of a material that has high magnetic permeability, such as stainless steel, and can redirect magnetic fields to prevent them from propagating beyond the distal side of primary alignment component  216 , thereby protecting sensitive electronic components located beyond the distal side of primary alignment component  216  from magnetic interference. 
     Primary magnets  226  and secondary magnets  228  (and all other magnets described herein) can be made of a magnetic material such as an NdFeB material, other rare earth magnetic materials, or other materials that can be magnetized to create a persistent magnetic field. In some embodiments, the magnets can be plated with a thin layer (e.g., 7-13 μm) of NiCuNi or similar materials. Each primary magnet  226  and each secondary magnet  228  can have a monolithic structure having a single magnetic region with a magnetic polarity aligned in the axial direction as shown by magnetic polarity indicators  215 ,  217  in  FIG.  2 B . For example, each primary magnet  226  and each secondary magnet  228  can be a bar magnet that has been ground and shaped into an arcuate structure having an axial magnetic orientation. (As will be apparent, the term “magnetic orientation” refers to the direction of orientation of the magnetic polarity of a magnet or magnetized region.) In the example shown, primary magnet  226  has its north pole oriented toward the proximal surface and south pole oriented toward the distal surface while secondary magnet  228  has its south pole oriented toward the proximal surface and north pole oriented toward the distal surface. In other embodiments, the magnetic orientations can be reversed such that primary magnet  226  has its south pole oriented toward the proximal surface and north pole oriented toward the distal surface while secondary magnet  228  has its north pole oriented toward the proximal surface and south pole oriented toward the distal surface. 
     As shown in  FIG.  2 B , the axial magnetic orientation of primary magnet  226  and secondary magnet  228  can generate magnetic fields  240  that exert an attractive force between primary magnet  226  and secondary magnet  228 , thereby facilitating alignment between respective electronic devices in which primary alignment component  216  and secondary alignment component  218  are disposed (e.g., as shown in  FIG.  1   ). While shield  214  can redirect some of magnetic fields  240  away from regions below primary magnet  226 , magnetic fields  240  may still propagate to regions laterally adjacent to primary magnet  226  and secondary magnet  228 . In some embodiments, the lateral propagation of magnetic fields  240  may result in magnetic field leakage to other magnetically sensitive components. For instance, if an inductive coil having a ferromagnetic shield is placed in the interior (or inboard) region of annular primary alignment component  216  (or secondary alignment component  218 ), leakage of magnetic fields  240  may saturate the ferrimagnetic shield, which can degrade wireless charging performance. 
     It will be appreciated that magnetic alignment system  200  is illustrative and that variations and modifications are possible. For instance, while primary alignment component  216  and secondary alignment component  218  are each shown as being constructed of eight arcuate magnets, other embodiments may use a different number of magnets, such as sixteen magnets, thirty-six magnets, or any other number of magnets, and the number of primary magnets need not be equal to the number of secondary magnets. In other embodiments, primary alignment component  216  and/or secondary alignment component  218  can each be formed of a single, monolithic annular magnet; however, segmenting magnetic alignment components  216  and  218  into arcuate magnets may improve manufacturing because (for some types of magnetic material) smaller arcuate segments may be less brittle than a single, monolithic annular magnet and less prone to yield loss due to physical stresses imposed on the magnetic material during manufacturing. 
     1.3. Magnetic Alignment Systems with Closed-Loop Configurations 
     As noted above with reference to  FIG.  2 B , a magnetic alignment system with a single axial magnetic orientation may allow lateral leakage of magnetic fields, which may adversely affect performance of other components of an electronic device. Accordingly, some embodiments provide magnetic alignment systems with a “closed-loop” configuration that reduces magnetic field leakage. Examples will now be described. 
       FIG.  3 A  shows a perspective view of a magnetic alignment system  300  according to some embodiments, and  FIG.  3 B  shows a cross-section through magnetic alignment system  300  across the cut plane indicated in  FIG.  3 A . Magnetic alignment system  300  can be an implementation of magnetic alignment system  106  of  FIG.  1   . In magnetic alignment system  300 , the alignment components have magnetic components configured in a “closed loop” configuration as described below. 
     As shown in  FIG.  3 A , magnetic alignment system  300  can include a primary alignment component  316  (which can be an implementation of primary alignment component  116  of  FIG.  1   ) and a secondary alignment component  318  (which can be an implementation of secondary alignment component  118  of  FIG.  1   ). Primary alignment component  316  and secondary alignment component  318  have annular shapes and may also be referred to as “annular” alignment components. The particular dimensions can be chosen as desired. In some embodiments, primary alignment component  316  and secondary alignment component  318  can each have an outer diameter of about 54 mm and a radial width of about 4 mm. The outer diameters and radial widths of primary alignment component  316  and secondary alignment component  318  need not be exactly equal. For instance, the radial width of secondary alignment component  318  can be slightly less than the radial width of primary alignment component  316  and/or the outer diameter of secondary alignment component  318  can also be slightly less than the radial width of primary alignment component  316  so that, when in alignment, the inner and outer sides of primary alignment component  316  extend beyond the corresponding inner and outer sides of secondary alignment component  318 . Thicknesses (or axial dimensions) of primary alignment component  316  and secondary alignment component  318  can also be chosen as desired. In some embodiments, primary alignment component  316  has a thickness of about 1.5 mm while secondary alignment component  318  has a thickness of about 0.37 mm. (All numerical values herein are examples and may be varied as desired.) 
     Primary alignment component  316  can include a number of sectors, each of which can be formed of a number of primary magnets  326 , and secondary alignment component  318  can include a number of sectors, each of which can be formed of a number of secondary magnets  328 . In the example shown, the number of primary magnets  326  is equal to the number of secondary magnets  328 , and each sector includes exactly one magnet, but this is not required; for example, as described below a sector may include multiple magnets. Primary magnets  326  and secondary magnets  328  can have arcuate (or curved) shapes in the transverse plane such that when primary magnets  326  (or secondary magnets  328 ) are positioned adjacent to one another end-to-end, primary magnets  326  (or secondary magnets  328 ) form an annular structure as shown. In some embodiments, primary magnets  326  can be in contact with each other at interfaces  330 , and secondary magnets  328  can be in contact with each other at interfaces  332 . Alternatively, small gaps or spaces may separate adjacent primary magnets  326  or secondary magnets  328 , providing a greater degree of tolerance during manufacturing. 
     In some embodiments, primary alignment component  316  can also include an annular shield  314  (also referred to as a DC magnetic shield or DC shield) disposed on a distal surface of primary magnets  326 . In some embodiments, shield  314  can be formed as a single annular piece of material and adhered to primary magnets  326  to secure primary magnets  326  into position. Shield  314  can be formed of a material that has high magnetic permeability and/or high magnetic saturation value, such as stainless steel or low-carbon steel, and can redirect magnetic fields to prevent them from propagating beyond the distal side of primary alignment component  316 , thereby protecting sensitive electronic components located beyond the distal side of primary alignment component  316  from magnetic interference. 
     Primary magnets  326  and secondary magnets  328  can be made of a magnetic material such as an NdFeB material, other rare earth magnetic materials, or other materials that can be magnetized to create a persistent magnetic field. Each secondary magnet  328  can have a single magnetic region with a magnetic polarity having a component in the radial direction in the transverse plane (as shown by magnetic polarity indicator  317  in  FIG.  3 B ). As described below, the magnetic orientation can be in a radial direction with respect to axis  301  or another direction having a radial component in the transverse plane. Each primary magnet  326  can include two magnetic regions having opposite magnetic orientations. For example, each primary magnet  326  can include an inner arcuate magnetic region  352  having a magnetic orientation in a first axial direction (as shown by polarity indicator  353  in  FIG.  3 B ), an outer arcuate magnetic region  354  having a magnetic orientation in a second axial direction opposite the first direction (as shown by polarity indicator  355  in  FIG.  3 B ), and a central non-magnetized region  356  that does not have a magnetic orientation. Central non-magnetized region  356  can magnetically separate inner arcuate region  352  from outer arcuate region  354  by inhibiting magnetic fields from directly crossing through central region  356 . Magnets having regions of opposite magnetic orientation separated by a non-magnetized region are sometimes referred to herein as having a “quad-pole” configuration. 
     In some embodiments, each secondary magnet  328  can be made of a magnetic material that has been ground and shaped into an arcuate structure, and a magnetic orientation having a radial component in the transverse plane can be created, e.g., using a magnetizer. Similarly, each primary magnet  326  can be made of a single piece of magnetic material that has been ground and shaped into an arcuate structure, and a magnetizer can be applied to the arcuate structure to induce an axial magnetic orientation in one direction within an inner arcuate region of the structure and an axial magnetic orientation in the opposite direction within an outer arcuate region of the structure, while demagnetizing or avoiding creation of a magnetic orientation in the central region. In some alternative embodiments, each primary magnet  326  can be a compound structure with two arcuate pieces of magnetic material providing inner arcuate magnetic region  352  and outer arcuate magnetic region  354 ; in such embodiments, central non-magnetized region  356  can be formed of an arcuate piece of nonmagnetic (or demagnetized) material or formed as an air gap defined by sidewalls of inner arcuate magnetic region  352  and outer arcuate magnetic region  354 . DC shield  314  can be formed of a material that has high magnetic permeability and/or high magnetic saturation value, such as stainless steel or low-carbon steel, and can be plated, e.g., with 5-10 μm of matte Ni. Alternatively, DC shield  314  can be formed of a magnetic material having a radial magnetic orientation (in the opposite direction of secondary magnets  328 ). In some embodiments, DC shield  314  can be omitted entirely. 
     As shown in  FIG.  3 B , the magnetic polarity of secondary magnet  328  (shown by indicator  317 ) can be oriented such that when primary alignment component  316  and secondary alignment component  318  are aligned, the south pole of secondary magnet  328  is oriented toward the north pole of inner arcuate magnetic region  352  (shown by indicator  353 ) while the north pole of secondary magnet  328  is oriented toward the south pole of outer arcuate magnetic region  354  (shown by indicator  355 ). Accordingly, the respective magnetic orientations of inner arcuate magnetic region  352 , secondary magnet  328  and outer arcuate magnetic region  356  can generate magnetic fields  340  that exert an attractive force between primary magnet  326  and secondary magnet  328 , thereby facilitating alignment between respective electronic devices in which primary alignment component  316  and secondary alignment component  318  are disposed (e.g., as shown in  FIG.  1   ). Shield  314  can redirect some of magnetic fields  340  away from regions below primary magnet  326 . Further, the “closed-loop” magnetic field  340  formed around central non-magnetized region  356  can have tight and compact field lines that do not stray outside of primary and secondary magnets  326  and  328  as far as magnetic field  240  strays outside of primary and secondary magnets  226  and  228  in  FIG.  2 B . Thus, magnetically sensitive components can be placed relatively close to primary alignment component  316  with reduced concern for stray magnetic fields. Accordingly, as compared to magnetic alignment system  200 , magnetic alignment system  300  can help to reduce the overall size of a device in which primary alignment component  316  is positioned and can also help reduce noise created by magnetic field  340  in adjacent components or devices, such as an inductive receiver coil positioned inboard of secondary alignment component  318 . 
     While each primary magnet  326  includes two regions of opposite magnetic orientation, it should be understood that the two regions can but need not provide equal magnetic field strength. For example, outer arcuate magnetized region  354  can be more strongly polarized than inner arcuate magnetized region  352 . Depending on the particular implementation of primary magnets  326 , various techniques can be used to create asymmetric polarization strength. For example, inner arcuate region  352  and outer arcuate region  354  can have different radial widths; increasing radial width of a magnetic region increases the field strength of that region due to increased volume of magnetic material. Where inner arcuate region  352  and outer arcuate region  354  are discrete magnets, magnets having different magnetic strength can be used. 
     In some embodiments, having an asymmetric polarization where outer arcuate region  354  is more strongly polarized than inner arcuate region  352  can create a flux “sinking” effect toward the outer pole. This effect can be desirable in various situations. For example, when primary magnet  326  is disposed within a wireless charger device and the wireless charger device is used to charge a “legacy” portable electronic device that has an inductive receiver coil but does not have a secondary (or any) annular magnetic alignment component, the (DC) magnetic flux from the primary annular alignment component may enter a ferrite shield around the inductive receiver coil. The DC magnetic flux can contribute to saturating the ferrite shield and reducing charging performance. Providing a primary annular alignment component with a stronger field at the outer arcuate region than the inner arcuate region can help to draw DC magnetic flux away from the ferrite shield, which can improve charging performance when a wireless charger device having an annular magnetic alignment component is used to charge a portable electronic device that lacks an annular magnetic alignment component. 
     It will be appreciated that magnetic alignment system  300  is illustrative and that variations and modifications are possible. For instance, while primary alignment component  316  and secondary alignment component  318  are each shown as being constructed of eight arcuate magnets, other embodiments may use a different number of magnets, such as 16 magnets, 18 magnets, 32 magnets, 36 magnets, or any other number of magnets, and the number of primary magnets need not be equal to the number of secondary magnets. In other embodiments, secondary alignment component  318  can be formed of a single, monolithic annular magnet. Similarly, primary alignment component  316  can be formed of a single, monolithic annular piece of magnetic material with an appropriate magnetization pattern as described above, or primary alignment component  316  can be formed of a monolithic inner annular magnet and a monolithic outer annular magnet, with an annular air gap or region of nonmagnetic material disposed between the inner annular magnet and outer annular magnet. In some embodiments, a construction using multiple arcuate magnets may improve manufacturing because smaller arcuate magnets are less brittle than a single, monolithic annular magnet and are less prone to yield loss due to physical stresses imposed on the magnetic material during manufacturing. It should also be understood that the magnetic orientations of the various magnetic alignment components or individual magnets do not need to align exactly with the lateral and axial directions. The magnetic orientation can have any angle that provides a closed-loop path for a magnetic field through the primary and secondary alignment components. 
     1.4. Magnetic Orientation for a Closed-Loop Magnetic Alignment System 
     1.4.1. Radially Symmetric Orientation 
     As noted above, in embodiments of magnetic alignment systems having closed-loop magnetic orientations, such as magnetic alignment system  300 , secondary alignment component  318  can have a magnetic orientation with a radial component. For example, in some embodiments, secondary alignment component  318  can have a magnetic polarity in a radial orientation.  FIG.  4    shows a simplified top-down view of a secondary alignment component  418  according to some embodiments. Secondary alignment component  418 , like secondary alignment component  318 , can be formed of arcuate magnets  428   a - h  having radial magnetic orientations as shown by magnetic polarity indicators  417   a - h . In this example, each arcuate magnet  428   a - h  has a north magnetic pole oriented toward the radially outward side and a south magnetic pole toward the radially inward side; however, this orientation can be reversed, and the north magnetic pole of each arcuate magnet  428   a - h  can be oriented toward the radially inward side while the south magnetic pole is oriented toward the radially outward side. 
       FIG.  5 A  shows a perspective view of a magnetic alignment system  500  according to some embodiments. Magnetic alignment system  500 , which can be an implementation of magnetic alignment system  300 , includes a secondary alignment component  518  having a radially outward magnetic orientation (e.g., as shown in  FIG.  4   ) and a complementary primary alignment component  516 . In this example, magnetic alignment system  500  includes a gap  507  between two of the sectors; however, gap  507  is optional and magnetic alignment system  500  can be a complete annular structure. Also shown are components  502 , which can include, for example an inductive coil assembly or other components located within the central region of primary magnetic alignment component  516  or secondary magnetic alignment component  518 . Magnetic alignment system  500  can have a closed-loop configuration similar to magnetic alignment system  300  (as shown in  FIG.  3 B ) and can include arcuate sectors  501 , each of which can be made of one or more arcuate magnets. In some embodiments, the closed-loop configuration of magnetic alignment system  500  can reduce or prevent magnetic field leakage that may affect components  502 . 
       FIG.  5 B  shows an axial cross-section view through one of arcuate sectors  501 . Arcuate sector  501  includes a primary magnet  526  and a secondary magnet  528 . As shown by orientation indicator  517 , secondary magnet  528  has a magnetic polarity oriented in a radially outward direction, i.e., the north magnetic pole is toward the radially outward side of magnetic alignment system  500 . Like primary magnets  326  described above, primary magnet  526  includes an inner arcuate magnetic region  552 , an outer arcuate magnetic region  554 , and a central non-magnetized region  556  (which can include, e.g., an air gap or a region of nonmagnetic or non-magnetized material). Inner arcuate magnetic region  552  has a magnetic polarity oriented axially such that the north magnetic pole is toward secondary magnet  528 , as shown by indicator  553 , while outer arcuate magnetic region  554  has an opposite magnetic orientation, with the south magnetic pole oriented toward secondary magnet  528 , as shown by indicator  555 . As described above with reference to  FIG.  3 B , the arrangement of magnetic orientations shown in  FIG.  5 B  results in magnetic attraction between primary magnet  526  and secondary magnet  528 . In some embodiments, the magnetic polarities can be reversed such that the north magnetic pole of secondary magnet  528  is oriented toward the radially inward side of magnetic alignment system  500 , the north magnetic pole of outer arcuate region  554  of primary magnet  526  is oriented toward secondary magnet  528 , and the north magnetic pole of inner arcuate region  552  is oriented away from secondary magnet  528 . 
     When primary alignment component  516  and secondary alignment component  518  are aligned, the radially symmetrical arrangement and directional equivalence of magnetic polarities of primary alignment component  516  and secondary alignment component  518  allow secondary alignment component  518  to rotate freely (relative to primary alignment component  516 ) in the clockwise or counterclockwise direction in the lateral plane while maintaining alignment along the axis. 
     As used herein, a “radial” orientation need not be exactly or purely radial. For example,  FIG.  5 C  shows a secondary arcuate magnet  538  according to some embodiments. Secondary arcuate magnet  538  has a purely radial magnetic orientation, as indicated by arrows  539 . Each arrow  539  is directed at the center of curvature of magnet  538 ; if extended inward, arrows  539  would converge at the center of curvature. However, achieving this purely radial magnetization requires that magnetic domains within magnet  538  be oriented obliquely to neighboring magnetic domains. For some types of magnetic materials, purely radial magnetic orientation may not be practical. Accordingly, some embodiments use a “pseudo-radial” magnetic orientation that approximates the purely radial orientation of  FIG.  5 C .  FIG.  5 D  shows a secondary arcuate magnet  548  with pseudo-radial magnetic orientation according to some embodiments. Magnet  548  has a magnetic orientation, shown by arrows  549 , that is perpendicular to a baseline  551  connecting the inner corners  552 ,  553  of arcuate magnet  548 . If extended inward, arrows  549  would not converge. Thus, neighboring magnetic domains in magnet  548  are parallel to each other, which is readily achievable in magnetic materials such as NdFeB. The overall effect in a magnetic alignment system, however, can be similar to the purely radial magnetic orientation shown  FIG.  5 C .  FIG.  5 E  shows a secondary annular alignment component  558  made up of magnets  548  according to some embodiments. Magnetic orientation arrows  549  have been extended to the center point  561  of annular alignment component  558 . As shown the magnetic field direction can be approximately radial, with the closeness of the approximation depending on the number of magnets  548  and the inner radius of annular alignment component  558 . In some embodiments, 18 magnets  548  can provide a pseudo-radial orientation; in other embodiments, more or fewer magnets can be used. It should be understood that all references herein to magnets having a “radial” magnetic orientation include pseudo-radial magnetic orientations and other magnetic orientations that are approximately but not purely radial. 
     In some embodiments, a radial magnetic orientation in a secondary alignment component  518  (e.g., as shown in  FIG.  5 B ) provides a magnetic force profile between secondary alignment component  518  and primary alignment component  516  that is the same around the entire circumference of the magnetic alignment system. The radial magnetic orientation can also result in greater magnetic permeance, which allows secondary alignment component  518  to resist demagnetization as well as enhancing the attractive force in the axial direction and improving shear force in the lateral directions when the two components are aligned. 
       FIGS.  6 A and  6 B  show graphs of force profiles for different magnetic alignment systems, according to some embodiments. Specifically,  FIG.  6 A  shows a graph  600  of vertical attractive (normal) force in the axial (z) direction for different magnetic alignment systems of comparable size and using similar types of magnets. Graph  600  has a horizontal axis representing displacement from a center of alignment, where 0 represents the aligned position and negative and positive values represent displacements from the aligned position in opposite directions (in arbitrary units), and a vertical axis showing the normal force (F NORMAL ) as a function of displacement in the lateral plane (also in arbitrary units). For purposes of this description, F NORMAL  is defined as the magnetic force between the primary and secondary alignment components in the axial direction; F NORMAL &gt;0 represents attractive force while F NORMAL &lt;0 represents repulsive force. Graph  600  shows normal force profiles for three different types of magnetic alignment systems. A first type of magnetic alignment system uses “central” alignment components, such as a pair of complementary disc-shaped magnets placed along an axis; a representative normal force profile for a central magnetic alignment system is shown as line  601  (dot-dash line). A second type of magnetic alignment system uses annular alignment components with axial magnetic orientations, e.g., magnetic alignment system  200  of  FIGS.  2 A and  2 B ; a representative normal force profile for such an annular-axial magnetic alignment system is shown as line  603  (dashed line). A third type of magnetic alignment system uses annular alignment components with closed-loop magnetic orientations and radial symmetry (e.g., magnetic alignment system  500  of  FIGS.  5 A and  5 B ); a representative normal force profile for a radially symmetric closed-loop magnetic alignment system is shown as line  605  (solid line). 
     Similarly,  FIG.  6 B  shows a graph  620  of lateral (shear) force in a transverse direction for different magnetic alignment systems. Graph  620  has a horizontal axis representing lateral displacement in opposing directions from a center of alignment, using the same convention as graph  600 , and a vertical axis showing the shear force (F SHEAR ) as a function of direction (in arbitrary units). For purposes of this description, F SHEAR  is defined as the magnetic force between the primary and secondary alignment components in the lateral direction; F SHEAR &gt;0 represents force toward the left along the displacement axis while F SHEAR &lt;0 represents force toward the right along the displacement axis. Graph  620  shows shear force profiles for the same three types of magnetic alignment systems as graph  600 : a representative shear force profile for a central magnetic alignment system is shown as line  621  (dot-dash line); a representative shear force profile for an annular-axial magnetic alignment system is shown as line  623  (dashed line); and a representative normal force profile for a radially symmetric closed-loop magnetic alignment system is shown as line  625  (solid line). 
     As shown in  FIG.  6 A , each type of magnetic alignment system achieves the strongest magnetic attraction in the axial direction (i.e., normal force) when the primary and secondary alignment components are in the aligned position ( 0  on the horizontal axis), as shown by respective peaks  611 ,  613 , and  615 . While the most strongly attractive normal force is achieved in the aligned positioned for all systems, the magnitude of the peak depends on the type of magnetic alignment system. In particular, a radially-symmetric closed-loop magnetic alignment system (e.g., magnetic alignment system  500  of  FIG.  5   ) provides stronger magnetic attraction when in the aligned position than the other types of magnetic alignment systems. This strong attractive normal force can overcome small misalignments and can help to hold devices in the aligned position, thereby can achieving a more accurate and robust alignment between the primary and secondary alignment components, which in turn can provide a more accurate and robust alignment between a portable electronic device and a wireless charger device within which the magnetic alignment system is implemented. 
     As shown in  FIG.  6 B , the strongest shear forces are obtained when the primary and secondary alignment components are laterally just outside of the aligned position, e.g., at −2 and +2 units of separation from the aligned position, as shown by respective peaks  631   a - b ,  633   a - b , and  635   a - b . These shear forces act to urge the alignment components toward the aligned position. Similarly to the normal force, the peak strength of shear force depends on the type of magnetic alignment system. In particular, a radially-symmetric closed-loop magnetic alignment system (e.g., magnetic alignment system  500  of  FIG.  5   ) provides higher magnitude of shear force when just outside of the aligned position than the other types of magnetic alignment systems. This strong shear force can provide tactile feedback (sometimes described as a sensation of “snappiness”) to help the user identify when the two components are aligned. In addition, like the normal force, the shear force can overcome small misalignments due to frictional force and can achieve a more accurate and robust alignment between the primary and secondary alignment components, which in turn can provide a more accurate and robust alignment between a portable electronic device and a wireless charger device within which the magnetic alignment system is implemented. 
     Depending on the particular configuration of magnets, various design choices can be used to increase the sensation of snappiness for a closed-loop magnetic alignment system. For example, reducing the amount of magnetic material in the devices in areas near the magnetic alignment components—e.g., by using less material or by increasing the distance between the magnetic alignment component and the other magnetic material—can reduce stray fields and increase the perceived “snapping” effect of the magnetic alignment components. As another example, increasing the magnetic-field strength of the alignment magnets (e.g., by increasing the amount of material) can increase both shear and normal forces. As yet another example, the widths of the magnetized regions in the primary annular alignment component (and/or the relative strength of the magnetic field in each region) can be optimized based on the particular magnetic orientation pattern for the secondary annular alignment component (e.g., whether the secondary annular alignment components have the purely radial magnetic orientation of  FIG.  5 C  or the pseudo-radial magnetic orientation of  FIG.  5 D ). Another consideration can be the coefficient of friction between the surfaces of the devices containing primary and secondary alignment components; lower friction decreases resistance to the shear force exerted by the annular magnetic alignment components. 
     A radially-symmetric closed-loop magnetic alignment system (e.g., magnetic alignment system  500  of  FIGS.  5 A and  5 B ) can provide accurate and robust alignment in the axial and lateral directions. Further, because of the radial symmetry, the alignment system does not have a preferred rotational orientation in the lateral plane about the axis; the shear force profile can be the same regardless of relative rotational orientation of the electronic devices being aligned. 
     1.4.2. Alternating Radial Orientation 
     In some embodiments, a closed-loop magnetic alignment system can be designed to provide one or more preferred rotational orientations.  FIG.  7    shows a simplified top-down view of a secondary alignment component  718  according to some embodiments. Secondary alignment component  718  includes sectors  728   a - h  having radial magnetic orientations as shown by magnetic polarity indicators  717   a - h . Each of sectors  728   a - h  can include one or more secondary arcuate magnets. In this example, secondary magnets in sectors  728   b ,  728   d ,  728   f , and  728   h  each have a north magnetic pole oriented toward the radially outward side and a south magnetic pole toward the radially inward side, while secondary magnets in sectors  728   a ,  728   c ,  728   e , and  728   g  each have a north magnetic pole oriented toward the radially inward side and a south magnetic pole toward the radially outward side. In other words, magnets in adjacent sectors  728   a - h  of secondary alignment component  718  have alternating magnetic orientations. 
     A complementary primary alignment component can have sectors with correspondingly alternating magnetic orientations. For example,  FIG.  8 A  shows a perspective view of a magnetic alignment system  800  according to some embodiments. Magnetic alignment system  800  includes a secondary alignment component  818  having alternating radial magnetic orientations (e.g., as shown in  FIG.  7   ) and a complementary primary alignment component  816 . Some of the arcuate sections of magnetic alignment system  800  are not shown in order to reveal internal structure; however, it should be understood that magnetic alignment system  800  can be a complete annular structure. Also shown are components  802 , which can include, for example, inductive coil assemblies or other components located within the central region of primary annular alignment component  816  and/or secondary annular alignment component  818 . Magnetic alignment system  800  can be a closed-loop magnetic alignment system similar to magnetic alignment system  300  described above and can include arcuate sectors  801   b ,  801   c  of alternating magnetic orientations, with each arcuate sector  801   b ,  801   c  including one or more arcuate magnets in each of primary annular alignment component  816  and secondary annular alignment component  818 . In some embodiments, the closed-loop configuration of magnetic alignment system  800  can reduce or prevent magnetic field leakage that may affect component  802 . Like magnetic alignment system  500 , magnetic alignment system  800  can include a gap  803  between two sectors. 
       FIG.  8 B  shows an axial cross-section view through one of arcuate sectors  801   b , and  FIG.  8 C  shows an axial cross-section view through one of arcuate sectors  801   c . Arcuate sector  801   b  includes a primary magnet  826   b  and a secondary magnet  828   b . As shown by orientation indicator  817   b , secondary magnet  828   b  has a magnetic polarity oriented in a radially outward direction, i.e., the north magnetic pole is toward the radially outward side of magnetic alignment system  800 . Like primary magnets  326  described above, primary magnet  826   b  includes an inner arcuate magnetic region  852   b , an outer arcuate magnetic region  854   b , and a central non-magnetized region  856   b  (which can include, e.g., an air gap or a region of nonmagnetic or non-magnetized material). Inner arcuate magnetic region  852   b  has a magnetic polarity oriented axially such that the north magnetic pole is toward secondary magnet  828   b , as shown by indicator  853   b , while outer arcuate magnetic region  854   b  has an opposite magnetic orientation, with the south magnetic pole oriented toward secondary magnet  828   b , as shown by indicator  855   b . As described above with reference to  FIG.  3 B , the arrangement of magnetic orientations shown in  FIG.  8 B  results in magnetic attraction between primary magnet  826   b  and secondary magnet  828   b.    
     As shown in  FIG.  8 C , arcuate sector  801   c  has a “reversed” magnetic orientation relative to arcuate sector  801   b . Arcuate sector  801   c  includes a primary magnet  826   c  and a secondary magnet  828   c . As shown by orientation indicator  817   c , secondary magnet  828   c  has a magnetic polarity oriented in a radially inward direction, i.e., the north magnetic pole is toward the radially inward side of magnetic alignment system  800 . Like primary magnets  326  described above, primary magnet  826   c  includes an inner arcuate magnetic region  852   c , an outer arcuate magnetic region  854   c , and a central non-magnetized region  856   c  (which can include, e.g., an air gap or a region of nonmagnetic or non-magnetized material). Inner arcuate magnetic region  852   c  has a magnetic polarity oriented axially such that the south magnetic pole is toward secondary magnet  828   c , as shown by indicator  853   c , while outer arcuate magnetic region  854   c  has an opposite magnetic orientation, with the north magnetic pole oriented toward secondary magnet  828   c , as shown by indicator  855   c . As described above with reference to  FIG.  3 B , the arrangement of magnetic orientations shown in  FIG.  8 C  results in magnetic attraction between primary magnet  826   c  and secondary magnet  828   c.    
     An alternating arrangement of magnetic polarities as shown in  FIGS.  7  and  8 A- 8 C  can create a “ratcheting” feel when secondary alignment component  818  is aligned with primary alignment component  816  and one of alignment components  816 ,  818  is rotated relative to the other about the common axis. For instance, as secondary alignment component  816  is rotated relative to primary alignment component  816 , each radially-outward magnet  828   b  alternately comes into proximity with a complementary magnet  826   b  of primary alignment component  816 , resulting in an attractive magnetic force, or with an anti-complementary magnet  826   c  of primary alignment component  816 , resulting in a repulsive magnetic force. If primary magnets  826   b ,  826   c  and secondary magnets  828   b ,  828   c  have the same angular size and spacing, in any given orientation, each pair of magnets will experience similar net (attractive or repulsive) magnetic forces such that alignment is stable and robust in rotational orientations in which complementary magnet pairs  826   b ,  828   b  and  826   c ,  828   c  are in proximity. In other rotational orientations, a torque toward a stable rotational orientation can be experienced. 
     In the examples shown in  FIGS.  7  and  8 A- 8 C , each sector includes one magnet, and the direction of magnetic orientation alternates with each magnet. In some embodiments, a sector can include two or more magnets having the same direction of magnetic orientation. For example,  FIG.  9 A  shows a simplified top-down view of a secondary alignment component  918  according to some embodiments. Secondary alignment component  918  includes secondary magnets  928   b  with radially outward magnetic orientations and secondary magnets  928   c  with radially inward orientations, similarly to secondary alignment component  818  described above. In this example, the magnets are arranged such that a pair of outwardly-oriented magnets  928   b  (forming a first sector  901 ) are adjacent to a pair of inwardly-oriented magnets  928   c  (forming a second sector  903  adjacent to first sector  901 ). The pattern of alternating sectors (with two magnets per sector) repeats around the circumference of secondary alignment component  918 . Similarly,  FIG.  9 B  shows a simplified top-down view of another secondary alignment component  918 ′ according to some embodiments. Secondary alignment component  918 ′ includes secondary magnets  928   b  with radially outward magnetic orientations and secondary magnets  928   c  with radially inward orientations. In this example, the magnets are arranged such that a group of four radially-outward magnets  928   b  (forming a first sector  911 ) is adjacent to a group of four radially-inward magnets  928   c  (forming a second sector  913  adjacent to first sector  911 ). The pattern of alternating sectors (with four magnets per sector) repeats around the circumference of secondary alignment component  918 ′. Although not shown in  FIGS.  9 A and  9 B , the structure of a complementary primary alignment component for secondary alignment component  918  or  918 ′ should be apparent in view of  FIGS.  8 A- 8 C . A shear force profile for the alignment components of  FIGS.  9 A and  9 B  can be similar to the ratcheting profile described above, although the number of rotational orientations that provide stable alignment will be different. 
     1.4.3. Other Magnetic Orientations 
     In other embodiments, a variety of force profiles can be created by changing the magnetic orientations of different sectors within the primary and/or secondary alignment components. As just one example,  FIG.  10    shows a simplified top-down view of a secondary alignment component  1018  according to some embodiments. Secondary alignment component has sectors  1028   a - h  with sector-dependent magnetic orientations as shown by magnetic polarity indicators  1017   a - h . In this example, secondary alignment component  1018  can be regarded as bisected by bisector line  1001 , which defines two halves of secondary alignment component  1018 . In a first half  1003 , sectors  1028   e - h  have magnetic polarities oriented radially outward, similarly to examples described above. 
     In the second half  1005 , sectors  1028   a - d  have magnetic polarities oriented substantially parallel to bisector line  1001  rather than radially. In particular, sectors  1028   a  and  1028   b  have magnetic polarities oriented in a first direction parallel to bisector line  1001 , while sectors  1028   c  and  1028   d  have magnetic polarities oriented in the direction opposite to the direction of the magnetic polarities of sectors  1028   a  and  1028   b . A complementary primary alignment component can have an inner annular region with magnetic north pole oriented toward secondary alignment component  1018 , an outer annular region with magnetic north pole oriented away from secondary alignment component  1018 , and a central non-magnetized region, providing a closed-loop magnetic orientation as described above. The asymmetric arrangement of magnetic orientations in secondary alignment component  1018  can modify the shear force profile such that secondary alignment component  1018  generates less shear force resisting motion in the direction toward second half  1005  (upward in the drawing) than in the direction toward first half  1003  (downward in the drawing). In some embodiments, an asymmetrical arrangement of this kind can be used where the primary alignment component is mounted in a docking station and the secondary alignment component is mounted in a portable electronic device that docks with the docking station. Assuming secondary annular alignment component  1018  is oriented in the portable electronic device such that half-annulus  1005  is toward the top of the portable electronic device, the asymmetric shear force can facilitate an action of sliding the portable electronic device downward to dock with the docking station or upward to remove it from the docking station, while still providing an attractive force to draw the portable electronic device into a desired alignment with the docking station. 
     In the embodiments described above, the secondary annular magnetic alignment component has a magnetic orientation that is generally aligned in the transverse plane. In some alternative embodiments, a secondary annular magnetic alignment component can instead have a quad-pole configuration similar to that of primary annular magnetic alignment component  316  of  FIGS.  3 A and  3 B , with or without a DC shield (which, if present, can be similar to DC shield  314  of  FIGS.  3 A and  3 B ) on the distal surface of the secondary arcuate magnets. Using quad-pole magnetic configurations in both the primary and secondary alignment components can provide a closed-loop DC magnetic flux path and a strong sensation of “snappiness”; however, the thickness of the secondary magnetic alignment component may need to be increased to accommodate the quad-pole magnets and DC shield, which may increase the overall thickness of a portable electronic device that houses the secondary magnetic alignment component. To reduce thickness, the DC shield on the distal surface of the secondary alignment component can be omitted; however, omitting the DC shield may result in increased flux leakage into neighboring components. 
     It will be appreciated that the foregoing examples are illustrative and not limiting. Sectors of a primary and/or secondary alignment component can include magnetic elements with the magnetic polarity oriented in any desired direction and in any combination, provided that the primary and secondary alignment components of a given magnetic alignment system have complementary magnetic orientations that exert forces toward the desired position of alignment. Different combinations of magnetic orientations may create different shear force profiles, and the selection of magnetic orientations may be made based on a desired shear force profile (e.g., high snappiness), avoidance of DC flux leakage into other components, and other design considerations. 
     1.5. Annular Magnetic Alignment Components with Gaps 
     In examples described above, the primary alignment component and secondary alignment component have annular shapes. As described above (e.g., with reference to  FIG.  3 A ), the annulus can be completely closed. In other embodiments (e.g., as shown in  FIGS.  5 A and  8 A ), a primary or secondary annular alignment component can include one or more gaps, where each gap can be a section of an annulus where magnetic material (or indeed any material) is absent. 
       FIG.  11    illustrates an example of an alignment component  1118  (which can be a primary or secondary annular magnetic alignment component) having a gap according to some embodiments. As shown, alignment component  1118  can include a number of arcuate magnets  1128  forming an annular shape. In this embodiment, a gap  1101  between two magnets is created by omitting one of arcuate magnets  1128 . More generally, a gap such as gap  1101  can be created using various techniques. For example, the angle ϕ subtended by each arcuate magnet can be selected such that 360°/ϕ is not an integer. Thus, the size of gap  1101  may be equal to or smaller than (or larger than) the size of an arcuate magnet  1128 . In various embodiments of a magnetic alignment system, a gap such as gap  1101  may be formed in either or both of a secondary alignment component and a primary alignment component, and the size, number, and location of gaps can be different between the primary and secondary alignment components. To provide reliable magnetic alignment, the size of gap  1101  or other gaps can be limited, e.g., to 20° of arc or less. 
     In some embodiments, a gap such as gap  1101  may provide a convenient path for electrical connections to components located in interior region  1103  inboard of alignment component  1118 . For example, as described above, an inductive coil (or other electronic component) may be disposed in interior region  1103 , and gap  1101  in alignment component  1118  may provide a convenient path for electrical connections between the inductive coil (or other component) and a battery (or other components) located outboard of alignment component  1118 . It should be understood that electrical connections can also be made by routing connection paths over or under magnets  1128  (into or out of the plane of  FIG.  11   ); however, routing connection paths over or under the magnets may result in increased thickness of the device in which alignment component  1118  is disposed. 
     It should be understood that a gap such as gap  1101  can be included in a primary alignment component, a secondary alignment component, or both. In some embodiments where gaps are provided in both the primary alignment component and the secondary alignment component, the presence of the gaps may alter the shear force profile in a manner that creates a preferred rotational orientation. The extent to which a preferred orientation arises may depend on the size of the gaps and the particular configuration of magnets. 
     1.6. Portable Electronic Devices Incorporating Magnetic Alignment Components 
       FIGS.  12 A and  12 B  show simplified rear views of portable electronic devices incorporating magnetic alignment components according to some embodiments. In the examples shown, the portable electronic devices incorporate secondary magnetic alignment components having a radial magnetic orientation, which can allow for a thinner device profile; however, it should be understood that a portable electronic device can instead incorporate a primary magnetic alignment component. 
       FIG.  12 A  shows a smart phone  1200  as an example of a portable electronic device that can incorporate a magnetic alignment component according to some embodiments. Smart phone  1200  can support a variety of computing and communication activities and can draw operating power from an onboard battery (not shown). In some embodiments, the battery can be recharged using wireless power transfer. For example, smart phone  1200  can include a coil assembly  1210 , which can be configured as an inductive receiver coil for wireless power transfer. Such time-varying magnetic fields can be provided by a transmitter coil in a wireless charger device (not shown in  FIG.  12 A ). In addition or instead, coil assembly  1210  may be operable as an inductive transmitter coil for wireless power transfer and may be operable to generate time-varying magnetic fields that can be used to charge an accessory device such as a wireless headset, an external battery, or another portable electronic device (e.g., another smart phone). Coil assembly  1210  can include an inductive receiver coil (e.g., a wound coil of electrically conductive wire) coupled to a power storage device (e.g., a battery) or power consuming device. In some embodiments, coil assembly  1210  can also include electromagnetic shielding (e.g., one or more pieces of ferrite) placed over the distal surface, inner annular surface, and/or outer annular surface of the coil. 
     For optimal wireless charging performance, it is desirable to align coil  1210  with a coil in the transmitting (or receiving) device. Annular magnetic alignment component  1218  can be, for example, an implementation of any of the secondary magnetic alignment components described above and can include an annular arrangement of magnets  1228  with interfaces  1232 , which can be air gaps or surfaces where adjacent magnets contact one another. The magnetic polarities of magnets  1228  can be oriented in varying directions in the lateral plane, e.g., in a radial direction as described above with reference to  FIG.  4   . In the example shown, magnetic alignment component  1218  includes a gap  1201 , which can provide electrical connection paths for wires (or conductive traces) to connect between coil  1210  and components outboard of magnetic alignment component  1218 . 
     Coil  1210  can be optimized to support wireless power transfer between devices. In some embodiments, it may also be desirable to support wireless data transfer between devices, for instance to allow different devices that incorporate magnetic alignment systems to identify themselves. Accordingly, in some embodiments, a near-field communication (NFC) coil  1260  can be provided in the region between coil  1210  and magnets  1228 . An NFC reader circuit and/or other components (not shown) can connect to termination ends  1262   a ,  1226   b  of NFC coil  1260  through gap  1201 . Example embodiments of NFC coil  1210  are described in section 5 below. 
     In some embodiments, a magnetic alignment component such as component  1218  can be modified to fit portable electronic devices of different sizes while preserving a constant outer diameter and radial width of the annulus. By way of example,  FIG.  12 B  shows a smart phone  1200 ′ as another example of a portable electronic device that can incorporate a magnetic alignment component according to some embodiments. Like smart phone  1200  of  FIG.  12 A , smart phone  1200 ′ can support a variety of computing and communication activities and may draw operating power from an onboard battery (not shown). One difference between smart phone  1200  and smart phone  1200 ′ can be that smart phone  1200 ′ has a smaller form factor than smart phone  1200 . For instance smart phone  1200 ′ may be narrower (in the x direction) and/or shorter (in the y direction) than smart phone  1200 . However, it may be desirable for these smart phones of different form factors to interoperate with the same wireless charger devices and/or other accessories. Accordingly, smart phone  1200 ′ can include a wireless charging coil  1210 ′ that can be identical to wireless charging coil  1210  of smart phone  1200 . 
     To provide alignment of coil  1210 ′ with a coil in another device, smart phone  1200 ′ can include a magnetic alignment component  1218 ′. Magnetic alignment component  1218 ′ can be for example, an implementation of any of the secondary magnetic alignment components described above and can include an annular arrangement of arcuate magnets  1228 ′ with interfaces  1232 ′, which can be air gaps or surfaces where adjacent magnets  1228 ′ contact one another. The magnetic polarities of magnets  1228 ′ can be oriented in varying directions in the lateral plane, e.g., in a radial direction as described above. In addition, NFC coil  1260 ′ can be provided in the region between coil  1210 ′ and magnets  1228 ′, similarly to NFC coil  1260  of  FIG.  12 A . 
     In the example shown, to accommodate the narrower width of smart phone  1200 ′ magnetic alignment component  1218 ′ includes diametrically opposed gaps  1201   a ,  1201   b . In addition to decreasing the width (in the x direction) of magnetic alignment component  1218 ′, gaps  1201   a  and/or  1201   b  can also provide electrical connection paths for wires (or conductive traces) to connect between coil  1210 ′ and components outboard of magnetic alignment component  1218 ′. In some embodiments, the arcuate magnet sections  1228 ′ adjacent to gaps  1201   a ,  1201   b  can have beveled corners  1229   a - b  and  1231   a - b , which can further reduce the width of alignment component  1218 ′ without reducing the outer diameter. 
     It should be understood that smart phones  1200  and  1200 ′ are just examples, and a variety of portable electronic devices having a range of different form factors can accommodate an annular alignment component of a given diameter and width. Further, while  FIGS.  12 A and  12 B  show alignment components  1218 ,  1218 ′ and coils  1210 ,  1210 ′ on the rear of smart phones  1200 ,  1200 ′, it should be understood that these components can be inside the rear housing of smart phones  1200 ,  1200 ′ and that the rear housing may be opaque so that alignment components  1218 ,  1218 ′ and coils  1210 ,  1210 ′ need not be visible to users. 
     1.7. Wireless Charger Devices Incorporating Magnetic Alignment Components 
       FIG.  13    shows a simplified view of a wireless charger device  1300  incorporating a magnetic alignment component according to some embodiments. In the example shown, the wireless charger device incorporates a primary alignment component; however, it should be understood that a wireless charger device can instead incorporate a secondary magnetic alignment component. 
     Wireless charger device  1300  can support inductive power transfer for charging a portable electronic device (such as smart phone  1200  of  FIG.  12 A  or smart phone  1200 ′ of  FIG.  12 B ). In this example, wireless charger device  1300  has a housing  1302  surrounding a transmitter coil assembly  1312 . Although not shown in  FIG.  13   , it should be understood that transmitter coil assembly  1312  can include an inductive transmitter coil having wires that can be connected to an external power source (e.g., via cable  1304 ). In some embodiments, transmitter coil assembly  1312  can also include electromagnetic shielding (e.g., one or more pieces of ferrite placed over the distal surface, inner annular surface, and/or outer annular surface of the transmitter coil and/or a thin layer of metal placed over the proximal surface of the transmitter coil to reduce parasitic electric fields). Control circuitry to control the transmitter coil can be disposed within housing  1302  or elsewhere as desired. A primary magnetic alignment component  1316  is disposed around transmitter coil assembly  1312 . 
     Components of wireless charger device  1300  can be enclosed in housing  1302 , which can be made of aluminum, plastic, ceramic, or other durable material. Housing  1302  is shown as puck-shaped; however, other shapes can also be used. For instance, housing  1302  can be rectangular, elliptical, or any other shape that provides a charging surface. In some embodiments, housing  1302  can be a two-piece housing that includes an enclosure for the distal and side surfaces of wireless charger device  1300  and a top cap covering the proximal surface of transmitter coil assembly  1312 . The top cap (not shown in  FIG.  13   ) can be made of ceramic or other material that is permeable to electromagnetic fields, while the enclosure can be made of aluminum, plastic or other materials. The top cap and enclosure can be sealed together using an appropriate adhesive. Although  FIG.  13    shows a view into the interior of wireless charger device  1300 , it should be understood that housing  1302  can be opaque. Housing  1302  can include an opening to permit connection of cable  1304  to transmitter coil assembly  1312 . In some embodiments, one end of cable  1304  is captively coupled to electronic components of transmitter coil assembly  1312  while the other end of cable  1304  (not shown) is coupled to a plug connector (e.g., a USB type A or USB-C connector) that can be used to draw power from the grid or other power source via an adapter. 
     For optimal wireless charging performance, it is desirable to align the transmitter coil of coil assembly  1312  with a corresponding coil in a receiving device such as smart phone  1200 . Magnetic alignment component  1316  can be, for example, an implementation of any of the primary magnetic alignment components described above and can include an annular arrangement of magnets  1326  with interfaces  1330  between adjacent magnets  1326 , which can be air gaps or surfaces where adjacent magnets  1326  contact one another. Magnets  1326  can provide a closed loop configuration as described above; for instance, each magnet  1326  can include an inner arcuate region having an axial magnetic orientation in a first direction, an outer arcuate region having an axial magnetic orientation in a second direction opposite the first direction, and a central arcuate region having no distinct magnetic orientation. In the example shown, magnetic alignment component  1316  includes a gap  1301 , which can provide electrical connection paths for wires (or conductive traces) to connect between coil assembly  1312  and cable  1304  without adding to the axial thickness of wireless charger device  1300 . 
     Coil assembly  1312  can be optimized to support wireless power transfer between devices. In some embodiments, it may also be desirable to support wireless data transfer between devices, for instance to allow different devices that incorporate magnetic alignment systems to identify themselves. Accordingly, in some embodiments, a near-field communication (NFC) coil  1364  can be provided in the region between coil assembly  1312  and magnetic alignment component  1316 . In some embodiments, NFC coil  1364  can couple to a passive NFC tag that can be read by a suitably configured NFC reader (e.g., in smart phone  1200  of  FIG.  12 A ). Example embodiments of NFC coil  1364  are described in section 5 below. 
     In various embodiments, primary magnetic alignment component  1316  can be used to facilitate alignment between wireless charger device  1300  and a variety of different portable electronic devices having different form factors (e.g., including portable electronic device  1200  and portable electronic device  1200 ′). As long as the portable electronic device being aligned with primary magnetic alignment component  1316  includes a complementary secondary alignment component having an annular shape matching primary alignment component  1316  and a magnetic field orientation complementary to primary alignment component  1316 , primary alignment component  1316  can facilitate alignment of wireless charger device  1300  with the portable electronic device, regardless of any other dimensions of either device. It should also be understood that some embodiments of wireless charger device  1300  can be used to charge a portable electronic device that does not have a magnetic alignment component; however, in such instances, primary alignment component  1316  might not facilitate optimal alignment with the portable electronic device, and the user would need to align the devices using other techniques (e.g., manual adjustment based on charging performance or placing the devices in a cradle that holds the devices such that their respective charging coils are in alignment). 
     1.8. Wireless Charging Systems with Magnetic Alignment 
       FIG.  14 A  shows a simplified perspective view of a system  1400  including portable electronic device  1200  (of  FIG.  12 A ) in alignment with wireless charger device  1300  (of  FIG.  13   ) according to some embodiments. In  FIG.  14 A , portions of wireless charger device  1300  are shown using dashed lines to avoid obscuring other details. As shown, wireless charger device  1300  can be placed with its charging (or proximal) surface against the rear (or proximal) surface  1403  of portable electronic device  1200 . When the devices are placed in this arrangement, secondary alignment component  1218  in portable electronic device  1200  can attract and hold primary magnetic alignment component  1316  of wireless charger device  1300  in alignment so that transmitter coil assembly  1312  of wireless charger device  1300  is aligned with coil assembly  1210  of portable electronic device  1200 . As shown, wireless charger device  1300  can have any rotational orientation about an axis defined by the centers of primary magnetic alignment component  1316  and secondary magnetic alignment component  1218 ; for instance gap  1201  in secondary magnetic alignment component  1218  need not align with gap  1301  in primary magnetic alignment component  1316 . 
       FIG.  14 B  shows a simplified partial cross section view of system  1400  according to some embodiments. Portable electronic device  1200  has a rear housing  1402  (which can be made of a material such as glass or plastic that is permeable to electromagnetic fields and to DC magnetic fields) and a front housing  1404  (which can include a touch screen display). Coil assembly  1210  can include an inductive receiver coil  1410  (which can be made, e.g., of stranded wire wound into a coil) and shielding  1412  (which can include, e.g., a ferrimagnetic shield). Secondary magnet  1428  forms a portion of secondary magnetic alignment component  1218  and can have a magnetic field oriented in a radially inward direction (as shown by the arrow). It should be understood that, although alignment component  1218  is shown in  FIG.  14 A , rear housing  1402  can be opaque and alignment component  1218  need not be visible to a user. 
     Wireless charger device  1300  has a housing  1302  that includes a single-piece enclosure  1406  forming distal and side surfaces of housing  1302  and a top cap  1408  forming a proximal surface of housing  1302 . As described above, enclosure  1406  and top cap  1408  can be made of the same material or different materials, and top cap  1408  can be made of a material that is permeable to AC electromagnetic fields and to DC magnetic fields. Transmitter coil assembly  1312  can include an inductive transmitter coil  1416  (which can be made, e.g., of stranded wire wound into a coil) and electromagnetic shielding  1415  (which can include, e.g., a ferrimagnetic shield). Primary magnet  1426  forms a portion of primary magnetic alignment component  1316  and can include an inner arcuate region  1452  having a magnetic field oriented in a first axial direction, an outer arcuate region  1454  having a magnetic field oriented in a second axial direction opposite the first axial direction, and a non-magnetized central arcuate region  1456 . As described above, a DC shield  1414  can be disposed on the distal surface of primary magnet  1426 . It should be understood that, although alignment component  1316  is shown in  FIG.  14 A , housing  1302  can be opaque and alignment component  1316  need not be visible to a user. 
     When aligned, primary magnet  1426  and secondary magnet  1428  produce a closed-loop magnetic flux as shown by lines  1440 . Magnetic flux  1440  can attract primary annular alignment component  1318  and secondary annular alignment component  1216  into alignment such that the respective centers of primary annular alignment component  1318  and secondary annular alignment component  1216  are aligned along a common axis. Since transmitter coil  1416  is fixed in a position concentric with primary alignment component  1316  and receiver coil  1410  is fixed in position concentric with secondary alignment component  1218 , a result of aligning primary annular alignment component  1318  and secondary annular alignment component  1216  along a common axis is that transmitter coil  1416  and receiver coil  1410  are also aligned along a common axis, thereby enabling efficient wireless power transfer. For instance, transmitter coil  1416  can be driven with an alternating current to generate time-varying magnetic fields that induce a time-varying current in receiver coil  1416 . Electromagnetic shielding (e.g., shielding  1415  and  1412 ) can confine the AC fields to the immediate vicinity of coils  1416  and  1410 . 
     In particular, some embodiments provide a gap region  1411  between secondary magnet  1428  and receiver coil assembly  1210  that may experience low DC magnetic flux and may also experience low AC electromagnetic fields due to electromagnetic shielding  1412  around coil  1410 . Similarly, some embodiments provide a gap region  1413  between primary magnet  1426  and transmitter coil assembly  1312  that may experience low DC magnetic flux and may also experience low AC electromagnetic fields due to electromagnetic shielding  1418  around transmitter coil  1416 . In some embodiments, NFC antenna coils (not shown) may be placed in gap region  1411  and/or  1413 , e.g., to support identification of wireless charger device  1300  by portable electronic device  1200 . Example embodiments of NFC coil  1260  are described in section 5 below. It is noted that a similar gap region may be created when using a z-pole magnetic alignment system of the kind shown in  FIG.  2   ; however, a larger space between the charging coils and magnets would be required. 
     As can be appreciated with reference to  FIG.  14 B , each secondary alignment magnet  1428  of secondary alignment component  1218  can have a thin axial dimension so that secondary alignment component  1218  does not require an increased thickness of portable electronic device  1200 . For instance, the axial thickness of each secondary alignment magnet  1428  can be less than or equal to the thickness of receiver coil assembly  1210  (including coil  1410  and shielding  1412 ). Primary alignment component  1426  can have a thicker axial dimension, e.g., occupying all of the axial space between enclosure  1406  and top cap  1408 . In some embodiments, primary alignment component  1426  can also have a radial width that is slightly larger than a radial width of secondary alignment component  1428 . 
       FIG.  15    is a block diagram illustrating an exemplary wireless charging system  1500  including a portable electronic device  1504  (which can be, e.g., portable electronic device  1200  or any other portable electronic device described herein) and a wireless charger device  1502  (which can be, e.g., wireless charger device  1300  or any other wireless charger device described herein) that can be aligned together via a magnetic alignment system  1506  according to some embodiments. Magnetic alignment system  1506  can include a primary alignment component  1516  within wireless charger device  1502  and a secondary alignment component  1518  within portable electronic device  1504 . Primary alignment component  1516  and secondary alignment component  1516  can be constructed according to any of the embodiments described herein. Portable electronic device  1504  can also include a computing system  1541  coupled to a memory bank  1542 . Computing system  1541  can include control circuitry configured to execute instructions stored in memory bank  1542  for performing various functions for operating portable electronic device  1504 . The control circuitry can include one or more programmable integrated logic circuits, such as microprocessors, central processing units (CPUs), graphics processing units (GPUs), field programmable gate arrays (FPGAs), or the like. 
     Computing system  1541  can also be coupled to a user interface system  1543 , a communication system  1544 , and a sensor system  1545  for enabling portable electronic device  1504  to perform one or more functions. For instance, user interface system  1543  can include a display, speaker, microphone, actuator for enabling haptic feedback, and one or more input devices such as a button, switch, capacitive screen for enabling the display to be touch sensitive, and the like. Communication system  1544  can include wireless telecommunication components, NFC components, Bluetooth components, and/or Wi-Fi components for enabling portable electronic device  1504  to make phone calls, interact with wireless accessories, and access the Internet. In some embodiments, communication system  1544  can include NFC reader circuitry that is used in connection with magnetic alignment system  1506  to identify an aligned device; examples are described in section 5 below. Sensor system  1545  can include light sensors, accelerometers, gyroscopes, temperature sensors, magnetometers, and/or any other type of sensor that can measure a parameter of an external entity and/or environment. 
     All of these electrical components require a power source to operate. Accordingly, portable electronic device  1504  also includes a battery  1546  that can discharge stored energy to power the electrical components of portable electronic device  1504 . To replenish the energy discharged to power the electrical components, portable electronic device  1504  includes charging circuitry  1547  and an inductive coil  1510  that can receive power from wireless charger device  1502  coupled to an external power source  1522 . 
     Wireless charger device  1502  can include a transmitter coil  1512  for generating time-varying magnetic flux capable of inducing an electrical current in coil  1510  of portable electronic device  1504 . The induced current can be used by charging circuitry  1547  to charge battery  1546 . Wireless charger device  1502  can further include a computing system  1521  coupled to a communication system  1524  and wireless charging circuitry  1523 . Wireless charging circuitry can include circuit components to convert standard AC power having a first set of voltage and frequency characteristics (e.g., standard AC wall power) to AC power suitable for operating coil  1510 . Suitable circuit components, including rectifiers (AC-to-DC converters), boost circuits (DC-to-DC voltage boosting circuits), inverters (DC-to-AC converters), and the like, are known in the art. Computing system  1521  can include logic circuitry (such as a microprocessor, microcontroller, FPGA, or the like) configured to control the operation of wireless charger device  1502 , such as to control wireless charging circuitry  1523  to use power received from external power source  1522  to generate time-varying magnetic flux to induce current in coil  1510  to charge portable electronic device  1504 . In some embodiments, computing system  1521  can implement functionality confirming to the Qi standard for wireless charging (promulgated by the Wireless Power Consortium). 
     In some embodiments, components implementing computing system  1521  and wireless charging circuitry  1523  can be disposed within the housing that holds coil  1512  and primary alignment component  1516  (e.g., within puck-shaped housing  1302  of  FIGS.  13  and  14 A- 14 B ). In other embodiments, some or all of the components implementing computing system  1521  and wireless charging circuitry  1523  can be disposed elsewhere, e.g., at the distal end of cable  1304  in  FIGS.  13  and  14 A . For example, the logic circuitry implementing computing system  1521  can be disposed within housing  1302  while wireless charging circuitry  1532  is disposed in a boot of a plug connector at the distal end of cable  1304 . (In this case, cable  1304  can provide AC power to wireless charger device  1300 .) As another example, the logic circuitry implementing computing system  1521  and circuit components implementing portions of wireless charging circuitry  1523  can be disposed within housing  1302  while circuit components implementing other portions of wireless charging circuitry  1523  are disposed in a boot of a plug connector at the distal end of cable  1304 . For instance, an inverter may be disposed within housing  1302  while a rectifier and boost circuit are disposed in the boot. (In this case, cable  1304  can provide DC power to wireless charger device  1300 .) 
     While system  1500  is described with reference to particular blocks, it is to be understood that these blocks are defined for convenience of description and are not intended to imply a particular physical arrangement of component parts. The blocks need not correspond to physically distinct components, and the same physical components can be used to implement aspects of multiple blocks. Blocks can be configured to perform various operations, e.g., by programming a processor or providing appropriate control circuitry, and various blocks might or might not be reconfigurable depending on how the initial configuration is obtained. Embodiments of the present invention can be realized in a variety of apparatus including electronic devices that use using any combination of circuitry and software to enable wireless charging operations and/or other operations where physical alignment between devices is desired. 
     2. Rotational Alignment Components 
     In various embodiments described above, a magnetic alignment system can provide robust alignment in a lateral plane and may or may not provide rotational alignment. For example, radially symmetric magnetic alignment system  500  of  FIGS.  5 A- 5 B  may not define a preferred rotational orientation. Radially alternating magnetic alignment system  800  of  FIGS.  8 A- 8 C  can define multiple equally preferred rotational orientations. For some applications, such as alignment of a portable electronic device with a wireless charger puck or mat, rotational orientation may not be a concern. In other applications, such as alignment of a portable electronic device in a docking station or other mounting accessory, a particular rotational alignment may be desirable. Accordingly, in some embodiments an annular magnetic alignment component can be augmented with one or more rotational alignment components positioned outboard of and spaced apart from the annular magnetic alignment components. The rotational alignment component(s) can help guide devices into a target rotational orientation relative to each other. 
       FIG.  16    shows an example of a magnetic alignment system with an annular alignment component and a rotational alignment component according to some embodiments.  FIG.  16    shows respective proximal surfaces of a portable electronic device  1604  and an accessory  1602 . In this example, primary alignment components of the magnetic alignment system are included in an accessory device  1602 , and secondary alignment components of the magnetic alignment system are included in a portable electronic device  1604 . Portable electronic device  1604  can be, for example, a smart phone whose front surface provides a touchscreen display and whose back surface is designed to support wireless charging. Accessory device  1602  can be, for example, a charging dock that supports portable electronic device  1604  such that its display is visible and accessible to a user. For instance, accessory device  1602  can support portable electronic device  1604  such that the display is vertical or at a conveniently tilted angle for viewing and/or touching. In the example shown, accessory device  1602  supports portable electronic device  1604  in a “portrait” orientation (shorter sides of the display at the top and bottom); however, in some embodiments accessory device  1602  can support portable electronic device  1604  in a “landscape” orientation (longer sides of the display at the top and bottom). Accessory device  1602  can also be mounted on a swivel, gimbal, or the like, allowing the user to adjust the orientation of portable electronic device  1604  by adjusting the orientation of accessory device  1602 . 
     As described above, components of a magnetic alignment system can include a primary annular alignment component  1616  disposed in accessory  1602  and a secondary annular alignment component  1618  disposed in portable electronic device  1604 . Primary annular alignment component  1616  can be similar or identical to any of the primary alignment components described above. For example, primary annular alignment component  1616  can be formed of arcuate magnets  1626  arranged in an annular configuration. Although not shown in  FIG.  16   , one or more gaps can be provided in primary annular alignment component  1616 , e.g., by omitting one or more of arcuate magnets  1626  or by providing a gap at one or more interfaces  1630  between adjacent arcuate magnets  1626 . In some embodiments, each arcuate magnet  1626  can include an inner arcuate region having a first magnetic orientation (e.g., axially oriented in a first direction), an outer arcuate region having a second magnetic orientation opposite the first magnetic orientation (e.g., axially oriented opposite the first direction), and a central non-magnetized arcuate region between the inner and outer regions (as described above, the non-magnetized central region can include an air gap or a nonmagnetic material). In some embodiments, primary annular alignment component  1616  can also include a DC shield (not shown) on the distal side of arcuate magnets  1626 . 
     Likewise, secondary annular alignment component  1618  can be similar or identical to any of the secondary alignment components described above. For example, secondary annular alignment component  1618  can be formed of arcuate magnets  1628  arranged in an annular configuration. Although not shown in  FIG.  16   , one or more gaps can be provided in secondary annular alignment component  1618 , e.g., by omitting one or more arcuate magnets  1628  or by providing a gap at one or more interfaces  1632  between adjacent magnets  1628 . As described above, arcuate magnets  1628  can provide radially-oriented magnetic polarities. For instance, all sectors of secondary annular alignment component  1618  can have a radially-outward magnetic orientation or a radially-inward magnetic orientation, or some sectors of secondary annular alignment component  1618  may have a radially-outward magnetic orientation while other sectors of secondary annular alignment component  1618  have a radially-inward magnetic orientation. 
     As described above, primary annular alignment component  1616  and secondary annular alignment component  1618  can provide shear forces that promote alignment in the lateral plane so that center point  1601  of primary annular alignment component  1616  aligns with center point  1603  of secondary annular alignment component  1618 . However, primary annular alignment component  1616  and secondary annular alignment component  1618  might not provide torque forces that favor any particular rotational orientation, such as portrait orientation. 
     Accordingly, in some embodiments, a magnetic alignment system can incorporate one or more rotational alignment components in addition to the annular alignment components. The rotational alignment components can include one or more magnets that provide torque about the common axis of the (aligned) annular alignment components, so that a preferred rotational orientation can be reliably established. For example, as shown in  FIG.  16   , a primary rotational alignment component  1622  can be disposed outboard of and spaced apart from primary annular alignment component  1616  while a secondary rotational alignment component  1624  is disposed outboard of and spaced apart from secondary annular alignment component  1618 . Secondary rotational alignment component  1624  can be positioned at a fixed distance (y 0 ) from center point  1603  of secondary annular alignment component  1618  and centered between the side edges of portable electronic device  1604  (as indicated by distance xo from either side edge). Similarly, primary rotational alignment component  1622  can be positioned at the same distance y 0  from center point  1601  of primary annular alignment component  1616  and located at a rotational angle that results in a torque profile that favors the desired orientation of portable electronic device  1604  relative to accessory  1602  when secondary rotational alignment component  1624  is aligned with primary rotational alignment component  1622 . It should be noted that the same distance y 0  can be applied in a variety of portable electronic devices having different form factors, so that a single accessory can be compatible with a family of portable electronic devices. A longer distance y 0  can increase torque toward the preferred rotational alignment; however, the maximum distance y 0  may be limited by design considerations, such as the size of the smallest portable electronic device in a family of portable electronic devices that incorporate mutually compatible magnetic alignment systems. 
     According to some embodiments, each of primary rotational alignment component  1622  and secondary rotational alignment component  1624  can be implemented using one or more magnets (e.g., rare earth magnets such as NdFeB) each of which has each been magnetized such that its magnetic polarity is oriented in a desired direction. In the example of  FIG.  16   , the magnets have rectangular shapes; however, other shapes (e.g., rounded shapes) can be substituted. The magnetic orientations of rotational alignment components  1622  and  1624  can be complementary so that when the proximal surfaces of rotational alignment components  1622  and  1624  are near each other, an attractive magnetic force is exerted. This attractive magnetic force can help to rotate portable electronic device  1604  and accessory  1602  into a preferred rotational orientation in which the proximal surfaces of rotational alignment components  1622  and  1624  are aligned with each other. Examples of magnetic orientations for rotational alignment components  1622  and  1624  that can be used to provide a desired attractive force are described below. In some embodiments, primary rotational alignment component  1622  and secondary rotational alignment component  1624  can have the same lateral (xy) dimensions and the same thickness. The dimensions can be chosen based on a desired magnetic field strength and/or torque, the dimensions of devices in which the rotational alignment components are to be deployed, and other design considerations. In some embodiments, the lateral dimensions can be about 6 mm (x direction) by about 16 mm (y direction), and the thickness can be anywhere from about 0.3 mm to about 1.5 mm; the particular dimensions can be chosen based on the sizes of the devices that are to be aligned. In some embodiments, the thickness of the rotational alignment component for a given device can be chosen to match the thickness of an annular alignment component in that device. In some embodiments, each of primary rotational alignment component  1622  and secondary rotational alignment component  1624  can be implemented using two or more rectangular blocks of magnetic material positioned adjacent to each other. As in other embodiments, a small gap may be present between adjacent magnets, e.g., due to manufacturing tolerances. 
       FIGS.  17 A and  17 B  show an example of rotational alignment according to some embodiments. In  FIG.  17 A , accessory  1602  is placed on the back surface of portable electronic device  1604  such that primary annular alignment component  1616  and secondary alignment component  1618  are aligned with each other in the lateral plane such that, in the view shown, center point  1601  of primary annular alignment component  1616  overlies center point  1603  of secondary annular alignment component  1618 . A relative rotation is present such that rotational alignment components  1622  and  1624  are not aligned. In this configuration, an attractive force between rotational alignment components  1622  and  1624  can urge portable electronic device  1604  and accessory  1602  toward a target rotational orientation. In  FIG.  17 B , the attractive magnetic force between rotational alignment components  1622  and  1624  has brought portable electronic device  1604  and accessory  1602  into the target rotational alignment with the sides of portable electronic device  1604  parallel to the sides of accessory  1602 . In some embodiments, the attractive magnetic force between rotational alignment components  1622  and  1624  can also help to hold portable electronic device  1604  and accessory  1602  in a fixed rotational alignment. 
     Rotational alignment components  1622  and  1624  can have various patterns of magnetic orientations. As long as the magnetic orientations of rotational alignment components  1622  and  1624  are complementary to each other, a torque toward the target rotational orientation can be present when the devices are brought into lateral alignment and close to the target rotational orientation.  FIGS.  18 A- 21 B  show examples of magnetic orientations for a rotational alignment component according to various embodiments. While the magnetic orientation is shown for only one rotational alignment component, it should be understood that the magnetic orientation of a complementary rotational alignment component can be complementary to the magnetic orientation of shown. 
       FIGS.  18 A and  18 B  show a perspective view and a top view of a rotational alignment component  1824  having a “z-pole” configuration according to some embodiments. It should be understood that the perspective view is not to any particular scale and that the lateral (xy) dimensions and axial (z) thickness can be varied as desired. As shown in  FIG.  18 A , rotational alignment component  1824  can have a uniform magnetic orientation along the axial direction, as indicated by arrows  1805 . Accordingly, as shown in  FIG.  18 B , a north magnetic pole (N) may be nearest the proximal surface  1803  of rotational alignment component  1824 . A complementary z-pole alignment component can have a uniform magnetic orientation with a south magnetic pole nearest the proximal surface. The z-pole configuration can provide reliable alignment. 
     Other configurations can provide reliable alignment as well as a stronger, or more salient, “clocking” sensation for the user. A “clocking sensation,” in this context, refers to a user-perceptible torque about the common axis of the annular alignment components that urges toward the target rotational alignment and/or resists small displacements from the target rotational alignment. A greater variation of torque as a function of rotational angle can provide a more salient clocking sensation. Following are examples of magnetization configurations for a rotational alignment component that can provide more salient clocking sensations than the z-pole configuration of  FIGS.  18 A and  18 B . 
       FIGS.  19 A and  19 B  show a perspective view and a top view of a rotational alignment component  1924  having a “quad-pole” configuration according to some embodiments. It should be understood that the perspective view is not to any particular scale and that the lateral (xy) dimensions and axial (z) thickness can be varied as desired. As shown in  FIG.  19 A , rotational alignment component  1924  has a first magnetized region  1925  with a magnetic orientation along the axial direction such that the north magnetic pole (N) is nearest the proximal (+z) surface  1903  of rotational alignment component  1924  (as indicated by arrow  1905 ) and a second magnetized region  1927  with a magnetic orientation opposite to the magnetic orientation of the first region such that the south magnetic pole (S) is nearest to proximal surface  1903  (as indicated by arrows  1907 ). Between magnetized regions  1925  and  1927  is a central region  1929  that is not magnetized. In some embodiments, rotational alignment component  1924  can be formed from a single piece of magnetic material that is exposed to a magnetizer to create regions  1925 ,  1927 ,  1929 . Alternatively, rotational alignment component  1924  can be formed using two pieces of magnetic material with a nonmagnetic material or an air gap between them. As shown in  FIG.  19 B , the proximal surface of rotational alignment component  1924  can have one region having a “north” polarity and another region having a “south” polarity. A complementary quad-pole rotational alignment component can have corresponding regions of south and north polarity at the proximal surface. 
       FIGS.  20 A and  20 B  show a perspective view and a top view of a rotational alignment component  2024  having an “annulus design” configuration according to some embodiments. It should be understood that the perspective view is not to any particular scale and that the lateral (xy) dimensions and axial (z) thickness can be varied as desired. As shown in  FIG.  20 A , rotational alignment component  2024  has an annular outer magnetized region  2025  with a magnetic orientation along the axial direction such that the north magnetic pole (N) is nearest the proximal (+z) surface  2003  of rotational alignment component  2024  (as shown by arrows  2005 ) and an inner magnetized region  2027  with a magnetic orientation opposite to the magnetic orientation of the first region such that the south magnetic pole (S) is nearest to proximal surface  2003 . Between magnetized regions  2025  and  2027  is a neutral annular region  2029  that is not magnetized. In some embodiments, rotational alignment component  2024  can be formed from a single piece of magnetic material that is exposed to a magnetizer to create regions  2025 ,  2027 ,  2029 . Alternatively, rotational alignment component  2024  can be formed using two or more pieces of magnetic material with a nonmagnetic material or an air gap between them. As shown in  FIG.  20 B , the proximal surface of rotational alignment component  2024  can have an annular outer region having a “north” polarity and an inner region having a “south” polarity. The proximal surface of a complementary annulus-design rotational alignment component can have an annular outer region of south polarity and an inner region of north polarity. 
       FIGS.  21 A and  21 B  show a perspective view and a top view of a rotational alignment component  2124  having a “triple pole” configuration according to some embodiments. It should be understood that the perspective view is not to any particular scale and that the lateral (xy) dimensions and axial (z) thickness can be varied as desired. As shown in  FIG.  21 A , rotational alignment component  2124  has a central magnetized region  2125  with a magnetic orientation along the axial direction such that the south magnetic pole (S) is nearest the proximal (+z) surface  2103  of rotational alignment component  2124  (as shown by arrow  2105 ) and outer magnetized regions  2127 ,  2129  with a magnetic orientation opposite to the magnetic orientation of central region  2125  such that the north magnetic pole (N) is nearest to proximal surface  2103  (as shown by arrows  2107 ,  2109 ). Between central magnetized region  2125  and each of outer magnetized regions  2127 ,  2129  is a neutral region  2131 ,  2133  that is not strongly magnetized. In some embodiments, rotational alignment component  2124  can be formed from a single piece of magnetic material that is exposed to a magnetizer to create regions  2125 ,  2127 ,  2129 . Alternatively, rotational alignment component  2124  can be formed using three (or more) pieces of magnetic material with nonmagnetic materials or air gaps between them. As shown in  FIG.  21 B , the proximal surface may have a central region having a “south” polarity with an outer region having “north” polarity to either side. The proximal surface of a complementary triple-pole rotational alignment component can have a central region of north polarity with an outer region of south polarity to either side. 
     It should be understood that the examples in  FIGS.  18 A- 21 B  are illustrative and that other configurations may be used. The selection of a magnetization pattern for a rotational alignment component can be independent of the magnetization pattern of an annular alignment component with which the rotational alignment component is used. 
     In some embodiments, the selection of a magnetization pattern for a rotational alignment component can be based on optimizing the torque profile. For example, as noted above, it may be desirable to provide a salient clocking sensation to a user when close to the desired rotational alignment. The clocking sensation can be a result of torque about a rotational axis defined by the annular alignment components. The amount of torque depends on various factors, including the distance between the axis and the rotational alignment component (distance y 0  in  FIG.  16   ) and the length (in the y direction as defined in  FIG.  16   ) of the rotational alignment component, as well as the strength of the magnetic fields of the rotational alignment components (which may depend on the size of the rotational alignment components), the coefficient of friction between the surfaces being aligned, and whether the annular alignment components exert any torque toward a preferred rotational orientation. 
       FIG.  22    shows a graph of torque as a function of angular rotation (in degrees) for an alignment system of the kind shown in  FIG.  16   , for different magnetization configurations of the rotational alignment component according to various embodiments. Angular rotation is defined such that zero degrees corresponds to the target rotational alignment (where the proximal surfaces of rotational angular components  1622  and  1624  are in closest proximity, e.g., as shown in  FIG.  17 B ). Torque is defined such that positive (negative) values indicate force in the direction of decreasing (increasing) rotational angle. For purpose of generating the torque profiles, it is assumed that annular alignment components  1616  and  1618  are rotationally symmetric and do not exert torque about the z axis defined by center points  1601  and  1603 . Three different magnetization configurations are considered. Line  2204  corresponds to the quad-pole configuration of  FIGS.  19 A and  19 B . Line  2205  corresponds to the annulus design configuration of  FIGS.  20 A and  20 B . Line  2206  corresponds to the triple-pole configuration of  FIGS.  21 A and  21 B . As shown, the annulus design (line  2205 ) and triple-pole (line  2206 ) configurations provide a sharper peak in the torque and therefore a more salient clocking sensation for the user, as compared to the quad-pole configuration (line  2204 ). In addition, the triple-pole configuration provides a stronger peak torque and therefore a more salient clocking sensation than the annulus-design configuration. (The triple-pole configuration can also provide reduced flux leakage as compared to other configurations.) It should be understood that the numerical values in  FIG.  22    are illustrative, and that torque in a particular embodiment may depend on a variety of other factors in addition to the magnetization configuration, such as the magnet volume, aspect ratio, and distance y0 from the center of the annular alignment component. 
     In the example shown in  FIG.  16   , a single rotational alignment component is placed outboard of the annular alignment component at a distance y 0  from the center of the annular alignment component. This arrangement allows a single magnetic element to generate torque that produces a salient clocking sensation for a user aligning devices. In some embodiments, other arrangements are also possible. For example,  FIG.  23    shows a portable electronic device  2304  having an alignment system  2300  with multiple rotational alignment components according to some embodiments. In this example, alignment system  2300  includes an annular alignment component  2318  and a set of rotational alignment components  2324  positioned at various locations around the perimeter of annular alignment component  2318 . In this example, there are four rotational alignment components  2324  positioned at angular intervals of approximately 90 degrees. In other embodiments, different numbers and spacing of rotational alignment components can be used. Each rotational alignment component  2324  can have any of the magnetization configurations described above, including z-pole, quad-pole, triple-pole, or annulus-design configurations, or a different configuration. Further, different rotational alignment components  2324  can have different magnetization configurations from each other. It should be noted that rotational alignment components  2324  can be placed close to the perimeter of annular alignment component  2318 , and the larger number of magnetic components can provide sufficient torque with a shorter lever arm. Complementary rotational alignment components can be disposed around the outer perimeter of any type of annular alignment component (e.g., primary alignment components, secondary alignment components, or annular alignment components as described herein). 
     It will be appreciated that the foregoing examples of rotational alignment components are illustrative and that variations or modifications are possible. In some embodiments, a rotational alignment component can be provided as an optional adjunct to an annular alignment component, and a device that has both an annular alignment component and a rotational alignment component can align laterally to any other device that has a complementary annular alignment component, regardless of whether the other device has or does not have a rotational alignment component. Thus, for example, portable electronic device  1604  of  FIG.  16    can align rotationally to accessory  1602  (which has both annular alignment component  1616  and rotational alignment component  1622 ) as well as aligning laterally to another accessory (such as wireless charger device  400  of  FIG.  4   ) that has annular alignment component  1616  but not rotational alignment component  1622 . In the latter case, lateral alignment can be achieved, e.g., to support efficient wireless charging, but there may be no preferred rotational alignment, or rotational alignment may be achieved using a nonmagnetic feature (e.g., a mechanical retention feature such as a ledge, a clip, a notch, or the like). A rotational magnetic alignment component can be used together with any type of annular magnetic alignment component (e.g., primary annular magnetic alignment components, secondary annular magnetic alignment components, or auxiliary annular magnetic alignment components as described below). 
     3. Primary, Secondary, and Auxiliary Annular Magnetic Alignment Components 
     3.1. Overview of Three-Component Magnetic Alignment Systems 
     In some embodiments, a magnetic alignment system can align more than two devices. Examples of magnetic alignment systems with three annular alignment components (referred to as primary, secondary, and auxiliary annular magnetic alignment components) will now be described. It should be understood that the primary and secondary annular magnetic alignment components described in this section can be identical to primary and secondary annular magnetic alignment components described above and that a given pair primary and secondary annular magnetic alignment components can be used with or without an auxiliary annular magnetic alignment component. It should also be understood that a system where alignment is desired may include more than three devices and that additional auxiliary annular alignment components can be provided to facilitate alignment of more than three devices. 
       FIG.  24    shows a simplified representation of a wireless charging system  2400  incorporating a three-component magnetic alignment system  2406  according to some embodiments. Wireless charging system  2400  includes a portable electronic device  2404 , a wireless charger device  2402 , and an accessory  2420  positioned between portable electronic device  2404  and wireless charger device  2402 . Portable electronic device  2404  can be a consumer electronic device, such as a smart phone, tablet, wearable device, or the like, or any other electronic device for which wireless charging is desired. Wireless charger device  2402  can be any device that is configured to generate time-varying magnetic flux to induce a current in a suitably configured receiving device. For instance, wireless charger device  2402  can be a wireless charging mat, puck, docking station, or the like. Wireless charger device  2402  can include or have access to a power source such as battery power or standard AC power. 
     To enable wireless power transfer, portable electronic device  2404  and wireless charger device  2402  can include inductive coils  2410  and  2412 , respectively, which can operate to transfer power between them. For example, inductive coil  2412  can be a transmitter coil that generates a time-varying magnetic flux  2414 , and inductive coil  2410  can be a receiver coil in which an electric current is induced in response to time-varying magnetic flux  2414 . The received electric current can be used to charge a battery of portable electronic device  2404 , to provide operating power to a component of portable electronic device  2404 , and/or for other purposes as desired. In some embodiments, wireless power transfer between wireless charger device  2402  and portable electronic device  2404  can occur regardless of whether accessory  2420  is present. 
     Accessory  2420  can be an accessory that is used with portable electronic device  2404  to protect, enhance, and/or supplement the aesthetics and/or functions of portable electronic device  2404 . For example, accessory  2420  can be a protective case, an external battery pack, a camera attachment, or any other charge-through accessory. In some embodiments, accessory  2420  can include one or more wireless charging coils  2438 . For example, accessory  2420  can be a portable external battery pack that can be attached to and carried together with portable electronic device  2404 . In some embodiments, accessory  2420  can operate wireless charging coil  2438  as a receiver coil to charge its onboard battery (e.g., from wireless charger device  2402 ) or as a transmitter coil to provide power to portable electronic device  2404 . In some embodiments, accessory  2420  cam include separate transmitter and receiver coils  2438 . Accessory  2420  can operate coil(s)  2438  to transmit power or to receive and store power depending on current conditions. In still other embodiments, accessory  2420  can be an “unpowered” or “passive” accessory such as a case that contains no active circuitry, and wireless charging coil  2438  can be omitted. In such cases, accessory  2420  can be designed not to inhibit wireless power transfer between wireless charger device  2402  and portable electronic device  2404 . For instance, relevant portions of accessory  2420  can be made of a material such as plastic, leather, or other material that is transparent to time-varying magnetic flux  2414 . 
     To enable efficient wireless power transfer, it is desirable to align inductive coils  2412  and  2410  (and coil  2438  in embodiments where coil  2438  is present). According to some embodiments, magnetic alignment system  2406  can provide such alignment. In the example shown in  FIG.  24   , magnetic alignment system  2406  includes a primary magnetic alignment component  2416  disposed within or on a surface of wireless charger device  2402 , a secondary magnetic alignment component  2418  disposed within or on a surface of portable electronic device  2402 , and an auxiliary magnetic alignment component  2470  disposed within or on a surface of accessory  2420 . Primary, secondary, and auxiliary magnetic alignment components  2416 ,  2418 , and  2470  are configured to magnetically attract one another into an aligned position in which inductive coils  2410  and  2412  (and/or  2438  if present) are aligned with one another to provide efficient wireless power transfer. 
     Magnetic alignment system  2406  can enable modularity in that various types of accessories  2420  can align with primary and/or secondary magnetic alignment components  2416 ,  2418 , provided that accessory  2420  includes auxiliary alignment component  2470 . For instance, in some embodiments (e.g., where accessory  2420  is a protective case), accessory  2420  can mechanically couple to portable electronic device  2404  in a fixed position such that auxiliary magnetic alignment component  2470  is aligned with secondary magnetic alignment component  2418 , and portable electronic device  2404  can rely wholly or partially on auxiliary magnetic alignment component  2470  to align with primary alignment component  2418  of wireless charger device  2402 . Accordingly, when accessory  2420  is positioned on charging surface  2408  of wireless charger device  2402  such that primary alignment component  2416  is aligned with auxiliary alignment component  2470 , secondary alignment component  2418  of portable electronic device  2404  is also aligned with primary alignment component  2416 , and efficient wireless power transfer is supported. 
     As another example, in some embodiments where accessory  2420  is an external battery, auxiliary alignment component  2470  can attract to and align with secondary alignment component  2418  so that power from an internal power source (not shown) within accessory  2420  can be wirelessly transferred to portable electronic device  2404  using inductive coil  2438  and inductive coil  2410 . The modularity of magnetic alignment system  2406  can also enable wireless charger device  2402  to stack with portable electronic device  2404  and accessory  2420 . For example, auxiliary alignment component  2470  can attract and align to secondary alignment component  2418  and at the same time can attract and align to primary alignment component  2416 . Accordingly, when portable electronic device  2404 , accessory  2420 , and wireless charger device  2402  are all stacked together, power can be transmitted wirelessly from wireless charger device  2402  to accessory  2420  (e.g., to charge an internal battery of accessory  2420 ) and from accessory  2420  to portable electronic device  2404 . Both power transfers can be performed simultaneously; i.e., wireless charger device  2402  can provide power to accessory  2420  at the same time that accessory  2420  provides power to portable electronic device  2404 . In some embodiments, to enable simultaneous power transfers, accessory  2420  can include two inductive coils  2438 , one for receiving power and one for transmitting power. In other embodiments, the power transfers can be performed sequentially; e.g., wireless charger device  2402  can provide power to accessory  2420 , and at a time when wireless charger device  2402  is not providing power, accessory  2420  can provide power to portable electronic device  2404 . 
       FIG.  24    is illustrative and not limiting. For example, while  FIG.  24    shows three devices stacked together, it should be understood that the same principles can be applied to form systems of four or more devices. For instance, a wireless charging system can include a portable electronic device coupled to a protective case that is attached to and magnetically aligned with an external battery, which is attached to and magnetically aligned to a wireless charger device. All the inductive coils within the respective devices can be aligned together, and wireless power can be transmitted between the wireless charger device and the external battery, between the battery and the portable electronic device, and/or between the wireless charger device and the portable electronic device. It is to be appreciated that any number of devices can be stacked together without departing from the spirit and scope of the present disclosure. 
     According to embodiments described herein, an alignment component (including a primary, secondary, or auxiliary alignment component) of a magnetic alignment system can be formed of arcuate magnets arranged in an annular configuration. In some embodiments, each magnet can have its magnetic polarity oriented in a desired direction so that magnetic attraction between the primary, secondary, and auxiliary alignment components provides a desired alignment. In some embodiments, an arcuate magnet can include a first magnetic region with magnetic polarity oriented in a first direction and a second magnetic region with magnetic polarity oriented in a second direction different from the first direction. As will be described, different configurations can provide different degrees of magnetic field leakage. 
     3.2. Magnetic Alignment Systems with a Single Axial Magnetic Orientation 
       FIG.  25 A  shows a perspective view of a magnetic alignment system  2500  according to some embodiments, and  FIG.  25 B  shows a cross-section through magnetic alignment system  2500  across the cut plane indicated in  FIG.  25 A . Magnetic alignment system  2500  can be an implementation of magnetic alignment system  2406  of  FIG.  24   . In magnetic alignment system  2500 , the alignment components all have magnetic polarity oriented in the same direction (along the axis of the annular configuration). 
     As shown in  FIG.  25 A , magnetic alignment system  2500  can include a primary alignment component  2516  (which can be an implementation of primary alignment component  2416  of  FIG.  24   ), a secondary alignment component  2518  (which can be an implementation of secondary alignment component  2418  of  FIG.  24   ), and an auxiliary alignment component  2570  (which can be an implementation of auxiliary alignment component  2470  described above). Primary alignment component  2516 , secondary alignment component  2518 , and auxiliary alignment component  2570  have annular shapes and may also be referred to as “annular” alignment components. The particular dimensions can be chosen as desired. In some embodiments, the dimensions can be similar to example values given above in section 1. 
     Primary alignment component  2516  can include a number of sectors, each of which can be formed of one or more primary arcuate magnets  2526 . Secondary alignment component  2518  can include a number of sectors, each of which can be formed of one or more secondary arcuate magnets  2528 . Auxiliary alignment component  2470  can include a number of sectors, each of which can be formed of one or more auxiliary arcuate magnets  2572 . In the example shown, the number of primary magnets  2526  is equal to the number of secondary magnets  2528  and to the number of auxiliary magnets  2572 , and each sector includes exactly one magnet, but this is not required. Primary magnets  2526 , secondary magnets  2528 , and auxiliary magnets  2572  can have arcuate (or curved) shapes in the transverse plane such that when primary magnets  2526  (or secondary magnets  2528  or auxiliary magnets  2572 ) are positioned adjacent to one another end-to-end, primary magnets  2526  (or secondary magnets  2528  or auxiliary magnets  2572 ) form an annular structure as shown. In some embodiments, primary magnets  2526  can be in contact with each other at interfaces  2530 , secondary magnets  2528  can be in contact with each other at interfaces  2532 , and auxiliary magnets  2572  can be in contact with each other at interfaces  2574 . Alternatively, small gaps or spaces may separate adjacent primary magnets  2526  or adjacent secondary magnets  2528  or adjacent auxiliary magnets  2572 , providing a greater degree of tolerance during manufacturing. 
     In some embodiments, primary alignment component  2516  can also include an annular shield  2514  disposed on a distal surface of primary magnets  2526 . In some embodiments, shield  2514  can be formed as a single annular piece of material and adhered to primary magnets  2526  to secure primary magnets  2526  into position. Shield  2514  can be formed of a material that has high magnetic permeability and/or high magnetic saturation value, such as stainless steel or low-carbon steel, and can redirect magnetic fields to prevent them from propagating beyond the distal side of primary alignment component  2516 , thereby protecting sensitive electronic components located beyond the distal side of primary alignment component  2516  from magnetic interference. 
     Primary magnets  2526 , secondary magnets  2528 , and auxiliary magnets  2572  can be made of a magnetic material such as an NdFeB material, other rare earth magnetic materials, or other materials that can be magnetized to create a persistent magnetic field. Each primary magnet  2526 , each secondary magnet  2528 , and each auxiliary magnet  2572  can have a monolithic structure having a single magnetic region with a magnetic polarity aligned in the axial direction as shown by magnetic polarity indicators  2515 ,  2517 ,  2519  in  FIG.  25 B . For example, each primary magnet  2526 , each secondary magnet  2528 , and each auxiliary magnet  2572  can be a bar magnet that has been ground and shaped into an arcuate structure having an axial magnetic orientation. In the example shown, primary magnet  2526  has its north pole oriented toward the proximal surface and south pole oriented toward the distal surface, secondary magnet  2528  has its south pole oriented toward the proximal surface and north pole oriented toward the distal surface, and auxiliary magnet  2572  has a corresponding magnetic orientation such that the north pole of auxiliary magnet  2572  is oriented toward the proximal surface of secondary magnet  2528  and the south pole of auxiliary magnet  2572  is oriented toward the proximal surface of primary magnet  2526 . In other embodiments, the magnetic orientations can be reversed such that primary magnet  2526  has its south pole oriented toward the proximal surface and north pole oriented toward the distal surface while secondary magnet  2528  has its north pole oriented toward the proximal surface and south pole oriented toward the distal surface and auxiliary magnet  2572  has a corresponding magnetic orientation such that the south pole of auxiliary magnet  2572  is oriented toward the proximal surface of secondary magnet  2528  and the north pole of auxiliary magnet  2572  is oriented toward the proximal surface of primary magnet  2526 . 
     As shown in  FIG.  25 B , the axial magnetic orientations of primary magnet  2526 , auxiliary magnet  2572 , and secondary magnet  2528  can generate magnetic fields  2540  that exert attractive forces between primary magnet  2526  and auxiliary magnet  2572  and between auxiliary magnet  2572  and secondary magnet  2528 , thereby facilitating alignment between respective devices in which primary alignment component  2516 , auxiliary alignment component  2570 , and secondary alignment component  2518  are disposed (e.g., as shown in  FIG.  24   ). While shield  2514  can redirect some of magnetic fields  2540  away from regions below primary magnet  2526 , magnetic fields  2540  may still propagate to regions laterally adjacent to primary magnet  2526  and secondary magnet  2528 . In some embodiments, the lateral propagation of magnetic fields  2540  may result in magnetic field leakage to other magnetically sensitive components. For instance, if an inductive coil having a ferromagnetic shield is placed in the interior (or inboard) region of annular primary alignment component  2516  (or secondary alignment component  2518 ), leakage of magnetic fields  2540  may saturate the ferrimagnetic shield, which can degrade wireless charging performance. 
     It will be appreciated that magnetic alignment system  2500  is illustrative and that variations and modifications are possible. For instance, while primary alignment component  2516 , auxiliary alignment component  2570 , and secondary alignment component  2518  are each shown as being constructed of eight arcuate magnets, other embodiments may use a different number of magnets, such as sixteen magnets, thirty-six magnets, or any other number of magnets, and the number of primary magnets need not be equal to the number of secondary magnets. Similarly, the number of auxiliary magnets need not be equal to either the number of primary magnets or the number of secondary magnets. In other embodiments, primary alignment component  2516  and/or secondary alignment component  2518  and/or auxiliary alignment component  2570  can each be formed of a single, monolithic annular magnet; however, segmenting alignment components  2516 ,  2518 , and  2570  into arcuate magnets may improve manufacturing, as described above with reference to  FIGS.  3 A and  3 B . 
     3.3. Magnetic Alignment Systems with Closed-Loop Magnetic Configurations 
     As noted above with reference to  FIG.  25 B , a magnetic alignment system with a single axial magnetic orientation may allow lateral leakage of magnetic fields, which may adversely affect performance of other components of an electronic device. Accordingly, some embodiments provide magnetic alignment systems with a closed-loop magnetic configuration that reduces magnetic field leakage. Examples will now be described. 
       FIG.  26 A  shows a perspective view of a magnetic alignment system  2600  according to some embodiments, and  FIG.  26 B  shows a cross-section through magnetic alignment system  2600  across the cut plane indicated in  FIG.  26 A . Magnetic alignment system  2600  can be an implementation of magnetic alignment system  2406  of  FIG.  24   . In magnetic alignment system  2600 , the alignment components have magnetic components configured in a “closed loop” configuration as described below. 
     As shown in  FIG.  26 A , magnetic alignment system  2600  can include a primary alignment component  2616  (which can be an implementation of primary alignment component  2416  of  FIG.  24   ), a secondary alignment component  2618  (which can be an implementation of secondary alignment component  2418  of  FIG.  24   ), and an auxiliary alignment component  2670  (which can be an implementation of auxiliary alignment component  2470  of  FIG.  24   ). Primary alignment component  2616 , secondary alignment component  2618 , and auxiliary alignment component  2670  have annular shapes and may also be referred to as “annular” alignment components. The particular dimensions can be chosen as desired. In some embodiments, the dimensions can be similar to example values given above in section 1. 
     Primary alignment component  2616  can include a number of sectors, each of which can be formed of a number of primary magnets  2626 ; secondary alignment component  2618  can include a number of sectors, each of which can be formed of a number of secondary magnets  2628 ; and auxiliary alignment component  2670  can include a number of sectors, each of which can be formed of a number of auxiliary magnets  2672 . In the example shown, the number of primary magnets  2626  is equal to the number of secondary magnets  2628  and to the number of auxiliary magnets  2672 , and each sector includes one magnet, but this is not required. Primary magnets  2626 , secondary magnets  2628 , and auxiliary magnets  2672  can have arcuate (or curved) shapes in the transverse plane such that when primary magnets  2626  (or secondary magnets  2628  or auxiliary magnets  2672 ) are positioned adjacent to one another end-to-end, primary magnets  2626  (or secondary magnets  2628  or auxiliary magnets  2672 ) form an annular structure as shown. In some embodiments, adjacent primary magnets  2626  can be in contact with each other at interfaces  2630 , adjacent secondary magnets  2628  can be in contact with each other at interfaces  2632 , and adjacent auxiliary magnets  2672  can be in contact with each other at interfaces  2680 . Alternatively, small gaps or spaces may separate adjacent primary magnets  2626 , adjacent secondary magnets  2628 , or adjacent auxiliary magnets  2672 , providing a greater degree of tolerance during manufacturing. 
     In some embodiments, primary alignment component  2616  can also include an annular shield  2614  disposed on a distal surface of primary magnets  2626 . In some embodiments, shield  2614  can be formed as a single annular piece of material and adhered to primary magnets  2626  to secure primary magnets  2626  into position. Shield  2614  can be formed of a material that has high magnetic permeability, such as stainless steel, and can redirect magnetic fields to prevent them from propagating beyond the distal side of primary alignment component  2616 , thereby protecting sensitive electronic components located beyond the distal side of primary alignment component  2616  from magnetic interference. In some embodiments, auxiliary alignment component  2670  does not include a similar shield, so that a stronger magnetic attraction with primary alignment component  2616  can be provided. 
     Primary magnets  2626 , secondary magnets  2628 , and auxiliary magnets  2672  can be made of a magnetic material such as an NdFeB material, other rare earth magnetic materials, or other materials that can be magnetized to create a persistent magnetic field. Each secondary magnet  2628  can have a single magnetic region with a magnetic polarity having a component in the radial direction in the transverse plane (as shown by magnetic polarity indicator  2617  in  FIG.  26 B ). As described below, the magnetic orientation can be in a radial direction with respect to axis  2601  or another direction having a radial component in the transverse plane. Each primary magnet  2626  can include two magnetic regions having opposite magnetic orientations. For example, each primary magnet  2626  can include an inner arcuate magnetic region  2652  having a magnetic orientation in a first axial direction (as shown by polarity indicator  2653  in  FIG.  26 B ), an outer arcuate magnetic region  2654  having a magnetic orientation in a second axial direction opposite the first direction (as shown by polarity indicator  2655  in  FIG.  26 B ), and a central non-magnetized region  2656  that does not have a magnetic orientation. Central non-magnetized region  2656  can magnetically separate inner arcuate region  2652  from outer arcuate region  2654  by inhibiting magnetic fields from directly crossing through center region  2656 . Similarly, each auxiliary magnet  2672  can include two magnetic regions having opposite magnetic orientations. For example, each auxiliary magnet  2672  can include an inner arcuate magnetic region  2674  having a magnetic orientation in a first axial direction (as shown by polarity indicator  2673  in  FIG.  26 B ), an outer arcuate magnetic region  2676  having a magnetic orientation in a second axial direction opposite the first direction (as shown by polarity indicator  2675  in  FIG.  26 B ), and a central non-magnetized region  2678  that does not have a magnetic orientation. Central non-magnetized region  2678  can magnetically separate inner arcuate region  2674  from outer arcuate region  2676  by inhibiting magnetic fields from directly crossing through center region  2678 . 
     In some embodiments, each secondary magnet  2626  can be made of a magnetic material that has been ground and shaped into an arcuate structure, and a magnetic orientation having a radial component in the transverse plane can be created, e.g., using a magnetizer. Similarly, each primary magnet  2626  can be made of a single piece of magnetic material that has been ground and shaped into an arcuate structure, and a magnetizer can be applied to the arcuate structure to induce an axial magnetic orientation in one direction within an inner arcuate region of the structure and an axial magnetic orientation in the opposite direction within an outer arcuate region of the structure, while demagnetizing or avoiding creation of a magnetic orientation in the central region. In some alternative embodiments, each primary magnet  2626  can be a compound structure with two arcuate pieces of magnetic material providing inner arcuate magnetic region  2652  and outer arcuate magnetic region  2654 ; in such embodiments, central non-magnetized region  2656  can be formed of an arcuate piece of nonmagnetic material or formed as an air gap defined by sidewalls of inner arcuate magnetic region  2652  and outer arcuate magnetic region  2654 . Any manufacturing technique that can be used to form primary magnets  2626  can also be used to form auxiliary magnets  2672 . Thus, each auxiliary magnet  2672  can be made of a single piece of magnetic material that has been ground and shaped into an arcuate structure, and a magnetizer can be applied to the arcuate structure to induce an axial magnetic orientation in one direction within an inner arcuate region of the structure and an axial magnetic orientation in the opposite direction within an outer arcuate region of the structure, while demagnetizing or avoiding creation of a magnetic orientation in the central region. In some alternative embodiments, each auxiliary magnet  2672  can be a compound structure with two arcuate pieces of magnetic material providing inner arcuate magnetic region  2674  and outer arcuate magnetic region  2676 ; in such embodiments, central non-magnetized region  2678  can be formed of an arcuate piece of nonmagnetic (or demagnetized) material or formed as an air gap defined by sidewalls of inner arcuate magnetic region  2674  and outer arcuate magnetic region  2676 . It should be understood that in some embodiments one manufacturing technique can be used for primary magnets  2626  while a different manufacturing technique can be used for auxiliary magnets  2672 ; for example, each auxiliary magnet  2672  can be monolithic while each primary magnet  2626  is a compound structure. As long as the magnetic fields of the various magnets align as described, alignment between devices can be provided. Further, as described above with reference to  FIGS.  3 A and  3 B , the inner and outer arcuate magnetic regions of a quad-pole primary or auxiliary arcuate magnet can but need not have equal magnetic field strength; asymmetric polarization as described above can be applied. 
     As shown in  FIG.  26 B , inner arcuate magnetic region  2652  of primary magnet  2626  and inner arcuate magnetic region  2674  of auxiliary magnet  2672  can have the same magnetic orientation, as shown by polarity indictors  2653  and  2673 . Similarly, outer arcuate magnetic region  2654  of primary magnet  2626  and outer arcuate magnetic region  2676  of auxiliary magnet  2672  can have the same magnetic orientation, as shown by polarity indictors  2655  and  2675 . This configuration creates a magnetic attraction between primary magnet  2626  and auxiliary magnet  2672 , which can facilitate alignment between them. The magnetic polarity of secondary magnet  2628  (shown by indicator  2617 ) can be oriented such that when secondary magnetic alignment component  2618  is aligned with auxiliary magnetic alignment component  2670 , the south pole of secondary magnet  2628  is oriented toward the north pole of inner arcuate magnetic region  2674  of auxiliary magnet  2672  (and also toward the north pole of inner arcuate magnetic region  2652  of primary magnet  2626 ) while the north pole of secondary magnet  2628  is oriented toward the south pole of outer arcuate magnetic region  2676  of auxiliary magnet  2672  (and also toward the south pole of outer arcuate magnetic region  2654  of primary magnet  2626 ). 
     Accordingly, the respective magnetic orientations of inner arcuate magnetic regions  2652 ,  2674 , secondary magnet  2628  and outer arcuate magnetic region  2676 ,  2678  can generate magnetic fields  2640  that exert an attractive force between primary magnet  2626  and auxiliary magnet  2672  and between auxiliary magnet  2672  and secondary magnet  2628 , thereby facilitating alignment between respective electronic devices in which primary alignment component  2616 , auxiliary alignment component  2670 , and secondary alignment component  2618  are disposed (e.g., as shown in  FIG.  24   ). Shield  2614  at the distal surface of primary magnet  2626  can redirect some of magnetic fields  2640  away from regions below primary magnet  2626 . Further, the “closed-loop” magnetic field  2640  formed around central non-magnetized regions  2656  and  2678  can have tight and compact field lines that do not stray outside of primary, auxiliary, and secondary magnets  2626 ,  2672 ,  2628  as far as magnetic field  2540  strays outside of primary, auxiliary, and secondary magnets  2526 ,  2572 ,  2528  in  FIG.  25 B . Thus, magnetically sensitive components can be placed relatively close to primary alignment component  2616  with reduced concern for stray magnetic fields. Accordingly, as compared to magnetic alignment system  2500 , magnetic alignment system  2600  can help to reduce the overall size of a device in which primary alignment component  2616  is positioned and can also help reduce noise created by magnetic field  2640  in adjacent components, such as an inductive receiving coil positioned inboard of secondary alignment component  2618 . 
     It will be appreciated that magnetic alignment system  2600  is illustrative and that variations and modifications are possible. For instance, while primary alignment component  2616 , auxiliary alignment component  2672 , and secondary alignment component  2618  are each shown as being constructed of eight arcuate magnets, other embodiments may use a different number of magnets, such as sixteen magnets, thirty-six magnets, or any other number of magnets, and the number of primary magnets need not be equal to the number of secondary magnets. Similarly, the number of auxiliary magnets need not be equal to either the number of primary magnets or the number of secondary magnets. In other embodiments, secondary alignment component  2618  can be formed of a single, monolithic annular magnet. Similarly, primary alignment component  2616  and/or auxiliary alignment component  2672  can each be formed of a single, monolithic annular piece of magnetic material with an appropriate magnetization pattern as described above, or primary alignment component  2616  and/or auxiliary alignment component  2672  can each be formed of a monolithic inner annular magnet and a monolithic outer annular magnet, with an annular air gap or region of nonmagnetic material disposed between the inner annular magnet and outer annular magnet. However, a construction using multiple arcuate magnets may improve manufacturing because smaller arcuate magnets are less brittle than a single, monolithic annular magnet and are less prone to yield loss due to physical stresses imposed on the magnetic material during manufacturing. It should also be understood that the magnetic orientations of the various components or individual magnets do not need to align exactly with the lateral and axial directions. The magnetic orientation can have any angle that provides a closed-loop path for a magnetic field through the primary and secondary alignment components. 
     3.4. Magnetic Orientation for a Closed-Loop Magnetic Alignment System 
     Any of the magnetic orientations described above with reference to  FIGS.  4 ,  5 ,  7 ,  8 A- 8 C,  9 A- 9 B , or  10  can also be applied to systems that include an auxiliary alignment component. The magnetic orientation of the auxiliary magnets can be made to match that of corresponding primary magnets. 
     3.5. Annular Magnetic Alignment Components with Gaps 
     In examples described above, the primary magnetic alignment component, secondary magnetic alignment component, and auxiliary magnetic alignment component have annular shapes. As described above (e.g., with reference to  FIG.  3 A ), the annulus can be completely closed. In other embodiments, the annulus can include one or more gaps, where each gap can be a section of an annulus where magnetic material (or any material) is absent. An example magnetic alignment component with a gap is described above with reference to  FIG.  11   , and it should be understood that an auxiliary alignment component can also include one or more gaps, e.g., to accommodate a form factor of an accessory device in which an auxiliary magnetic alignment component is present and/or to accommodate electronic circuit components that may be present in the accessory device. Further, compatible annular alignment components in different devices can differ as to the number, size, and/or position of gaps. 
     3.6. Accessory Devices Incorporating Magnetic Alignment Components 
       FIG.  27    shows a simplified rear view of an accessory device  2700  incorporating an auxiliary magnetic alignment component according to some embodiments. In the example shown, the accessory device incorporates an auxiliary alignment component; however, it should be understood that an accessory device can instead incorporate a primary or secondary magnetic alignment component. 
     Accessory device  2700  can be, for example, a protective or esthetic case for a portable electronic device such as smart phone  1200  of  FIG.  12 A . Accordingly, accessory device  2700  can have a housing  2702 , which can be the same size as (or slightly larger than) smart phone  1200 . In some embodiments, housing  2702  can be shaped as a tray that covers the side and rear surfaces of smart phone  1200 , leaving the front (display) surface of smart phone  1200  exposed. Housing  2702  (or portions thereof) can be made of plastic, rubber, silicone, leather, and/or other materials. An auxiliary alignment component  2770  can be disposed within housing  2702 , in a position such that, when smart phone  1200  is inserted into accessory device  2700  in the preferred orientation, auxiliary alignment component  2770  is coaxially aligned with secondary alignment component  1218  of smart phone  1200 . 
     Auxiliary alignment component  2770  can be, for example, an implementation of any of the auxiliary alignment components described above and can include an annular arrangement of magnets  2772  with interfaces  2780 , which can be air gaps or interfaces where adjacent magnets contact one another. Magnets  2772  can have a quad-pole configuration as described above; for instance, each magnet  2772  can include an inner arcuate region having an axial magnetic orientation in a first direction, an outer arcuate region having an axial magnetic orientation in a second direction opposite the first direction, and a central arcuate region having no distinct magnetic orientation. Although not shown in  FIG.  27   , auxiliary magnetic alignment component  2770  can include one or more gaps between adjacent magnets  2772 . In some embodiments, the gap(s) can provide electrical connection paths for wires (or conductive traces) to connect between regions inboard of and outboard of auxiliary magnetic alignment component  2770 , and in some embodiments, the gap(s) can be arranged to allow housing  2702  to have a reduced lateral size for use with a smart phone having a smaller form factor. For instance, the pattern of gaps can match that of magnetic alignment component  1218 ′ of smart phone  1200 ′ of  FIG.  12 B . 
     In some embodiments, it may be desirable to support wireless data transfer between accessory device  2700  and smart phone  1200 , for instance to allow accessory device  2700  to identify itself to smart phone  1200 . Accordingly, in some embodiments, a near-field communication (NFC) coil  2766  can be provided in the region inboard of magnetic alignment component  2766 . In some embodiments, NFC coil  2766  can couple to a passive NFC tag that can be read by a suitably configured NFC reader (e.g., in smart phone  1200  of  FIG.  12   ). Example embodiments of NFC coil  2766  are described in section 5 below. 
     In the example shown, accessory device  2700  is a passive device whose function may be protective and/or esthetic. As such, it may be desirable to make accessory device  2700  thin and to provide smooth inner and outer surfaces. In some embodiments, magnets  2772  can have a thin axial dimension so that accessory device  2700  can have smooth surfaces and a desired thinness. Accessory device  2700  can have a variety of shapes and features. For example, accessory device  2700  can be a tray that covers the side and rear surfaces of smart phone  1200 , leaving the front (display) surface of smart phone  1200  exposed. Alternatively, accessory device  2700  can include a cover that can be folded over the front surface of smart phone  1200  and unfolded to allow access to the display. As another example, accessory device  2700  can be formed as a sleeve having an opening at one end (e.g., the top end or a side) to allow smart phone  1200  to be inserted into the sleeve when not in use and removed from the sleeve for use. 
     In the example shown, accessory device  2700  can a passive device that does not contain power-consuming components. Accordingly, the region  2711  inboard of annular alignment component  2770  can be made of the same material as the surrounding housing  2702 , providing a continuous back surface for accessory device  2700 . Alternatively, part or all of region  2711  may be devoid of material, allowing the corresponding portion of the rear surface of smart phone  1200  to be exposed. In some embodiments, housing  2702  of accessory device  2700  (or portions thereof) can be made of transparent material so that the rear surface of smart phone  1200  (or portions thereof) can be seen through accessory device  2700 . In the absence of transparent magnetic material, an annular region of opaque material can be disposed over magnetic alignment component  2770  so that the individual magnets are not visible. The opaque material can have a color (or colors) selected for a desired esthetic effect. 
     In some embodiments, accessory  2700  can be an active device. For example, accessory  2700  can include an external battery that can provide power to smart phone  1200 . Accordingly, central region  2711  can include one or more wireless charging coils, which can be arranged and operated as described above with reference to accessory  2420  of  FIG.  24   . 
     3.7. Wireless Charging Systems with Magnetic Alignment 
       FIG.  28 A  shows a simplified perspective view of a system  2800  including portable electronic device  1200  (of  FIG.  12 A ) in alignment with accessory device  2700  (of  FIG.  27   ) and wireless charger device  1300  (of  FIG.  13   ) according to some embodiments. In  FIG.  28 A , portions of wireless charger device  1300  and accessory device  2700  are shown using dashed lines to avoid obscuring other details. As shown, accessory device  2700  can be placed adjacent to portable electronic device  1200 , for example by inserting portable electronic device  1200  into accessory device  2700 , and wireless charger device  1300  can be placed with its charging (or proximal) surface against the rear (or proximal) surface  2803  of accessory device  2700 . When the devices are placed in this arrangement, secondary alignment component  1218  in portable electronic device  1200  is aligned with auxiliary alignment component  2770  of accessory device  2700  and with primary alignment component  1316  of wireless charger device  1300 . Accordingly, auxiliary alignment component  2770  in accessory device  2700  and secondary alignment component  1218  in portable electronic device  120  can attract and hold primary magnetic alignment component  1316  of wireless charger device  1300  in alignment so that transmitter coil assembly  1312  of wireless charger device  1300  is aligned with coil assembly  1210  of portable electronic device  1200 . As shown, wireless charger device  1300  can have any rotational orientation about an axis defined by the centers of primary magnetic alignment component  1316  and secondary magnetic alignment component  1218 ; for instance, gap  1201  in secondary magnetic alignment component  1218  need not align with gap  1301  in primary magnetic alignment component  1316 . 
       FIG.  28 B  shows a simplified partial cross section view of system  2800  according to some embodiments. Portable electronic device  1200  has a rear housing  2802  (which can be made of a material such as glass or plastic that is permeable to electromagnetic fields and to DC magnetic fields) and a front housing  2804  (which can include a touch screen display). Coil assembly  1210  can include an inductive receiver coil  2810  (which can be made, e.g., of stranded wire wound into a coil) and shielding  2812  (which can include, e.g., a ferrimagnetic shield). Secondary magnet  2828  forms a portion of secondary magnetic alignment component  1218  and can have a magnetic field oriented in a radially inward direction (as shown by the arrow). It should be understood that although secondary alignment component  1218  is shown in  FIG.  28 A , rear housing  2802  can be opaque and secondary alignment component  1218  need not be visible to a user. 
     Wireless charger device  1300  has a housing  1302  that includes a single-piece enclosure  2806  forming distal and side surfaces of housing  1302  and a top cap  2808  forming a proximal surface of housing  1302 . As described above, enclosure  2806  and top cap  2808  can be made of the same material or different materials, and top cap  2808  can be made of a material that is permeable to AC electromagnetic fields and to DC magnetic fields. Transmitter coil assembly  1312  can include an inductive transmitter coil  2816  (which can be made, e.g., of stranded wire wound into a coil) and electromagnetic shielding  2814  (which can include, e.g., a ferrimagnetic shield). Primary arcuate magnet  2826  forms a portion of primary magnetic alignment component  1316  and can include an inner arcuate region  2852  having a magnetic field oriented in a first axial direction, an outer arcuate region  2854  having a magnetic field oriented in a second axial direction opposite the first axial direction, and a non-magnetized central arcuate region  2856 . As described above, a shield  2814  can be disposed on the distal surface of primary magnet  2826 . It should be understood that although primary alignment component  1316  is shown in  FIG.  28 A , housing  1302  can be opaque and primary alignment component  1316  need not be visible to a user. 
     Accessory device  2700  has a rear housing  2702  that includes a back layer  2805  (forming back surface  2803 ) and a front layer  2807  that contacts rear housing  2802  of portable electronic device  1200  at a surface  2809 . Back layer  2805  and front layer  2807  can be made of the same material or different materials as desired. Auxiliary arcuate magnet  2872  forms a portion of auxiliary alignment component  2770  and can include an inner arcuate section  2874  having a magnetic field oriented in a first axial direction, an outer arcuate section  2876  having a magnetic field oriented in a second axial direction opposite the first axial direction, and a non-magnetized central arcuate section  2878 . It should be understood that although auxiliary alignment component  2770  is shown in  FIG.  28 A , rear housing  2702  can be opaque and auxiliary alignment component  2770  need not be visible to a user. 
     When aligned, primary magnet  2826 , auxiliary magnet  2872 , and secondary magnet  2828  produce a closed-loop magnetic flux as shown by lines  2840 . Magnetic flux  2840  can attract primary annular alignment component  1318 , auxiliary annular alignment component  2770  and secondary annular alignment component  1216  into alignment such that the respective centers of primary annular alignment component  1318 , auxiliary annular alignment component  2770 , and secondary annular alignment component  1216  are aligned along a common axis. Since transmitter coil  2816  is fixed in a position concentric with primary alignment component  1316  and receiver coil  2810  is fixed in position concentric with secondary alignment component  1218 , a result of aligning primary annular alignment component  1318 , auxiliary annular alignment component  2770 , and secondary annular alignment component  1216  along a common axis is that transmitter coil  2816  and receiver coil  2810  are also aligned along a common axis, thereby enabling efficient wireless power transfer. For instance, transmitter coil  2816  can be driven with an alternating current to generate time-varying magnetic fields that induce a time-varying current in receiver coil  2816 . Electromagnetic shielding (e.g., shielding  2814  and  2812 ) can confine the AC fields to the immediate vicinity of coils  2816  and  2812 . Further, in embodiments where accessory device  2700  includes one or more wireless charging coils, such wireless charging coils can also be aligned along a common axis with coils  2816  and  2810 . 
     Some embodiments provide a gap region  2811  between secondary magnet  2828  and coil assembly  1210  that may experience low DC magnetic flux and may also experience low AC electromagnetic fields due to electromagnetic shielding  2812  around coil  2810 . Similarly, some embodiments provide a gap region  2813  between primary magnet  2826  and transmitter coil assembly  1312  that may experience low DC magnetic flux and may also experience low AC electromagnetic fields due to electromagnetic shielding  2818  around transmitter coil  2816 . In some embodiments, NFC antenna coils (not shown) may be placed in gap region  2811  and/or  2813 , e.g., to support identification of wireless charger device  1300  by portable electronic device  1200 . Similarly, an NFC antenna coil (not shown) may be placed in a corresponding region  2815  between back layer  2805  and front layer  2807  of accessory device  2700 , e.g., to support identification of accessory device  2700  by portable electronic device  1200 . Example embodiments of NFC antenna coils that may be placed in gap regions  2811 ,  2813  and/or  2815  are described in section 5 below. 
     As can be appreciated with reference to  FIG.  28 B , arcuate magnets  2828  of secondary alignment component  1218  can have a thin axial dimension so that secondary alignment component  1218  does not require an increased thickness of portable electronic device  1200 . For instance, the axial thickness of each secondary alignment magnet  2828  can be less than or equal to the thickness of receiver coil assembly  1210  (including coil  2810  and shielding  2812 ). Primary alignment magnets  2826  can have a thicker axial dimension, e.g., occupying all of the axial space between enclosure  2806  and top cover  2808 . 
     Similarly, each arcuate magnet  2872  of auxiliary alignment component  2770  can have a thin axial dimension so that the overall thickness of accessory device  2700  can be kept small. Back layer  2805  and front layer  2807  can be planar layers. Space between layers  2805  and  2807  that is not occupied by auxiliary alignment magnets  2872  can be an air gap, or portions or all of the space may be filled with material. In some embodiments, surfaces  2803  and  2809  do not evince a local deviation from flatness due to the presence of auxiliary alignment magnets  2872 . In some embodiments, accessory device  2700  (or a back housing element thereof) can be formed as a single piece of material with auxiliary alignment component  2770  embedded therein. Auxiliary alignment magnets  2872  and primary alignment magnets  2826  can have the same radial width; in some embodiments, the radial width of auxiliary alignment magnets  2872  and primary alignment magnets  2826  can be slightly larger than the radial width of secondary alignment magnets  2828 . 
     It should be understood that auxiliary alignment component  2770  is optional, and a charge-through accessory that does not have an auxiliary alignment component may be positioned between portable electronic device  1200  and wireless charger device  1300 . Depending on the thickness and material composition of the accessory, primary annular alignment component  1316  and secondary annular alignment component  1218  may still experience sufficient attraction to provide reliable alignment between coils  2816  and  2810 . However, for DC magnets, the attractive force diminishes sharply with increasing distance between magnets, so the alignment may be less strong. Accordingly, auxiliary alignment component  2770  can be used as a “repeater” that decreases the distance between adjacent magnets and thus increases the magnetic force that urges toward alignment. 
       FIG.  29    is a block diagram illustrating an exemplary wireless charging system  2900  including a portable electronic device  2904  (which can be, e.g., portable electronic device  1200  or any other portable electronic device described herein), a wireless charger device  2902  (which can be, e.g., wireless charger device  1300  or any other wireless charger device described herein), and an accessory device  2906  (which can be, e.g., accessory device  2800  or any other accessory device described herein) that can be aligned together via a magnetic alignment system  2908  according to some embodiments. Magnetic alignment system  2908  can include a primary alignment component  2916  within wireless charger device  2902 , a secondary alignment component  2918  within portable electronic device  2904 , and an auxiliary alignment component  2970  within accessory device  2906 . Primary alignment component  2916 , secondary alignment component  2918 , and auxiliary alignment component  2970  can be constructed according to any of the embodiments described herein. Portable electronic device  2904  can include a computing system  2941  coupled to a memory bank  2942 . Computing system  2941  can include control circuitry configured to execute instructions stored in memory bank  2942  for performing various functions for operating portable electronic device  2904 . The control circuitry can include one or more programmable integrated logic circuits, such as microprocessors, central processing units (CPUs), graphics processing units (GPUs), field programmable gate arrays (FPGAs), or the like. 
     Computing system  2941  can also be coupled to a user interface system  2943 , a communication system  2944 , and a sensor system  2945  for enabling portable electronic device  2904  to perform one or more functions. For instance, user interface system  2943  can include a display, speaker, microphone, actuator for enabling haptic feedback, and one or more input devices such as a button, switch, capacitive screen for enabling the display to be touch sensitive, and the like. Communication system  2944  can include wireless telecommunication components, NFC components, Bluetooth components, and/or Wi-Fi components for enabling portable electronic device  2904  to make phone calls, interact with wireless accessories, and access the Internet. In some embodiments, communication system  2944  can include NFC reader circuitry that is used in connection with magnetic alignment system  2906  to identify one or more aligned devices; examples are described in section 5 below. Sensor system  2945  can include light sensors, accelerometers, gyroscopes, temperature sensors, magnetometers, and/or any other type of sensor that can measure a parameter of an external entity and/or environment. 
     All of these electrical components require a power source to operate. Accordingly, portable electronic device  2904  also includes a battery  2946  that can discharge stored energy to power the electrical components of portable electronic device  2904 . To replenish the energy discharged to power the electrical components, portable electronic device  2904  includes charging circuitry  2947  and an inductive coil  2910  that can receive power from wireless charger device  2902  coupled to an external power source  2922 . 
     Wireless charger device  2902  can include a transmitter coil  2912  for generating time-varying magnetic flux capable of inducing an electrical current in coil  2910  of portable electronic device  2904 . The induced current can be used by charging circuitry  2947  to charge battery  2946 . Wireless charger device  2902  can further include a computing system  2921  coupled to a communication system  2922  and wireless charging circuitry  2923 . Wireless charging circuitry can include circuit components to convert standard AC power having a first set of voltage and frequency characteristics (e.g., standard AC wall power) to AC power suitable for operating coil  2910 . Suitable circuit components, including rectifiers (AC-to-DC converters), boost circuits (DC-to-DC voltage boosting circuits), inverters (DC-to-AC converters), and the like, are known in the art. Computing system  2921  can include logic circuitry (such as a microprocessor, microcontroller, FPGA, or the like) configured to control the operation of wireless charger device  2902 , such as to control wireless charging circuitry  2923  to use power received from external power source  2922  to generate time-varying magnetic flux to induce current in coil  2910  to charge portable electronic device  2904 . In some embodiments, computing system  2921  can implement functionality confirming to the Qi standard for wireless charging (promulgated by the Wireless Power Consortium). 
     In some embodiments, components implementing computing system  2921  and wireless charging circuitry  2923  can be disposed within the housing that holds coil  2912  and primary alignment component  2916  (e.g., within puck-shaped housing  1302  of  FIGS.  13  and  14 A- 14 B ). In other embodiments, some or all of the components implementing computing system  2921  and wireless charging circuitry  2923  can be disposed elsewhere, e.g., at the distal end of cable  1304  in  FIGS.  13  and  14 A . For example, the logic circuitry implementing computing system  2921  can be disposed within housing  1302  while wireless charging circuitry  2932  is disposed in a boot of a plug connector at the distal end of cable  1304 . (In this case, cable  1304  can provide AC power to wireless charger device  1300 .) As another example, the logic circuitry implementing computing system  2921  and circuit components implementing portions of wireless charging circuitry  2923  can be disposed within housing  1302  while circuit components implementing other portions of wireless charging circuitry  2923  are disposed in a boot of a plug connector at the distal end of cable  1304 . For instance, an inverter may be disposed within housing  1302  while a rectifier and boost circuit are disposed in the boot. (In this case, cable  1304  can provide DC power to wireless charger device  1300 .) 
     As described above, accessory device  2906  can be a passive accessory such as protective case for portable electronic device  1002  and need not include any components other than auxiliary alignment component  2970 . In some embodiments, accessory device  2906  can be an active device. For instance, accessory device  2906  can include a computing system  2961  coupled to a memory bank  2962  and a communication system  2963 . Computing system  2961  can execute instructions stored in memory bank  2962  to perform one or more functions using communication system  2963 . In some embodiments, computing system  2961  can be configured to send data from memory bank  2962  through communication system  2963  to portable electronic device  2904  regarding a user interface theme for portable electronic device  2904  so that portable electronic device  2904  can use this data to modify its user interface. As an example, accessory device  2906  can be a protective case that has a picture of a car on it, and memory bank  2962  has information stored for configuring a user interface to include a car theme with car-related icons, animations, and/or sounds. Thus, when accessory device  2906  is installed on portable electronic device  2902 , computing system  2941  can receive the car-themed user interface from accessory device  2906  and can modify user interface system  2943  according to the received car-themed data (e.g., changing what is displayed, what sounds are played to signal events, etc.). In some embodiments, accessory device  2906  can also include a wireless charging component  2964  that can aid in wireless charging between portable electronic device  2904  and wireless charger device  2902 . For instance, wireless charging component  2964  can include a block of magnetic material that can help guide magnetic flux through accessory device  2906 . Or, wireless charging component  2964  can include a pair of inductor coils where one inductor coil positioned proximate to wireless charger device  2902  can receive magnetic flux, which can be relayed to the other inductor coil positioned proximate to portable electronic device  2904  so that the received flux can be retransmitted to portable electronic device  2904 . In some embodiments, accessory device  2906  can include a battery (not shown) to store power received from wireless charger device  2902  at a first time for delivery to portable electronic device  2904  at a later time. 
     While system  2900  is described with reference to particular blocks, it is to be understood that these blocks are defined for convenience of description and are not intended to imply a particular physical arrangement of component parts. The blocks need not correspond to physically distinct components, and the same physical components can be used to implement aspects of multiple blocks. Blocks can be configured to perform various operations, e.g., by programming a processor or providing appropriate control circuitry, and various blocks might or might not be reconfigurable depending on how the initial configuration is obtained. Embodiments of the present invention can be realized in a variety of apparatus including electronic devices that use using any combination of circuitry and software to enable wireless charging operations and/or other operations where physical alignment between devices is desired. 
     4. Systems with Movable Magnetic Alignment Components 
     In embodiments described above, it is assumed (though not required) that the magnetic alignment components (including annular magnetic alignment components, and, where applicable, rotational magnetic alignment components) are fixed in position relative to the device housing (or enclosure) and do not move in the axial or lateral direction. This provides a fixed magnetic flux. In some embodiments, it may be desirable for one or more of the magnetic alignment components to move in the axial direction. For example, in various embodiments of the present invention, it can be desirable to limit the magnetic flux provided by these magnetic structures. Limiting the magnetic flux can help to prevent the demagnetization of various charge and payment cards that a user might be carrying with an electronic device that incorporates one of these magnetic structures. But in some circumstances, it can be desirable to increase this magnetic flux in order to increase a magnetic attraction between an electronic device and an accessory or a second electronic device. Also, it can be desirable for one or more of the magnetic alignment components to move laterally. For example, an electronic device and an attachment structure or wireless device can be offset from each other in a lateral direction. The ability of a magnetic alignment component to move laterally can compensate for this offset and improve coupling between devices, particularly where a coil moves with the magnetic alignment component. Accordingly, embodiments of the present invention can provide structures where some or all of the magnets in these magnetic structures are able to change positions or otherwise move. Examples of magnetic structures having moving magnets are shown in the following figures. 
       FIGS.  30 A- 30 C  illustrate examples of moving magnets according to an embodiment of the present invention. In this example, first electronic device  3000  can be a wireless charger device or other device having a magnet  3010  (which can be, e.g., any of the annular or rotational magnetic alignment components described herein). In  FIG.  30 A , moving magnet  3010  can be housed in a first electronic device  3000 . First electronic device  3000  can include device enclosure  3030 , magnet  3010 , and shield  3020 . Magnet  3010  can be in a first position (not shown) adjacent to nonmoving shield  3020 . In this position, magnet  3010  can be separated from device enclosure  3030 . As a result, the magnetic flux  3012  at a surface of device enclosure  3030  can be relatively low, thereby protecting magnetic devices and magnetically stored information, such as information stored on payment cards. As magnet  3010  in first electronic device  3000  is attracted to a second magnet (not shown) in a second electronic device (not shown), magnet  3010  can move, for example it can move away from shield  3020  to be adjacent to device enclosure  3030 , as shown. With magnet  3010  at this location, magnetic flux  3012  at surface of device enclosure  3030  can be relatively high. This increase in magnetic flux  3012  can help to attract the second electronic device to first electronic device  3000 . 
     With this configuration, it can take a large amount of magnetic attraction for magnet  3010  to separate from shield  3020 . Accordingly, these and other embodiments of the present invention can include a shield that is split into a shield portion and a return plate portion. For example, in  FIG.  30 B , line  3060  can be used to indicate a split of shield  3020  into a shield  3040  and return plate  3050 . 
     In  FIG.  30 C , moving magnet  3010  can be housed in first electronic device  3000 . First electronic device  3000  can include device enclosure  3030 , magnet  3010 , shield  3040 , and return plate  3050 . In the absence of a magnetic attraction, magnet  3010  can be in a first position (not shown) such that shield  3040  can be adjacent to return plate  3050 . Again, this configuration, magnetic flux  3012  at a surface of device enclosure  3030  can be relatively low. As magnet  3010  and first electronic device is attracted to a second magnet (not shown) in a second electronic device (not shown), magnet  3010  can move, for example it can move away from return plate  3050  to be adjacent to device enclosure  3030 , as shown. In this configuration, shield  3040  can be separate from return plate  3050  and the magnetic flux  3012  at a surface of device enclosure  3030  can be increased. As before, this increase in magnetic flux  3012  can help to attract the second electronic device to the first electronic device  3000 . 
     In these and other embodiments of the present invention, various housings and structures can be used to guide a moving magnet. Also, various surfaces can be used in conjunction with these moving magnets. These surfaces can be rigid. Alternatively, these surfaces can be compliant and at least somewhat flexible. Examples are shown in the following figures. 
       FIGS.  31 A and  31 B  illustrate a moving magnetic structure according to an embodiment of the present invention. In this example, first electronic device  3100  can be a wireless charger device or other device having a first magnet  3110  (which can be, e.g., any of the annular or rotational magnetic alignment components described herein).  FIG.  31 A  illustrates a moving first magnet  3110  in a first electronic device  3100 . First electronic device  3100  can include first magnet  3110 , protective surface  3112 , housings  3120  and  3122 , compliant structure  3124 , shield  3140 , and return plate  3150 . In this figure, first magnet  3110  is not attracted to a second magnet (not shown), and therefore shield  3140  is magnetically attracted to or attached to return plate  3150 . In this position, compliant structure  3124  can be expanded or relaxed. Compliant structure  3124  can be formed of an elastomer, silicon rubber open cell foam, silicon rubber, polyurethane foam, or other foam or other compressible material. 
     In  FIG.  31 B , second electronic device  3160  has been brought into proximity of first electronic device  3100 . Second magnet  3170  can attract first magnet  3110 , thereby causing shield  3140  and return plate  3150  to separate. Housings  3120  and  3122  can compress compliant structure  3124 , thereby allowing protective surface  3112  of first electronic device  3100  to move towards or adjacent to housing  3180  of second electronic device  3160 . Second magnet  3170  can be held in place in second electronic device  3160  by housing  3190  or other structure. As second electronic device  3160  is removed from first electronic device  3100 , first magnet  3110  and shield  3140  can be magnetically attracted to return plate  3150 , as shown in  FIG.  31 A . 
       FIGS.  32 A and  32 B  illustrate moving magnetic structures according to an embodiment of the present invention. In this example, first electronic device  3200  can be a wireless charger device or other device having a first magnet  3210  (which can be, e.g., any of the annular or rotational magnetic alignment components described herein).  FIG.  32 A  illustrates a moving first magnet  3210  in a first electronic device  3200 . First electronic device  3200  can include first magnet  3210 , pliable surface  3212 , housing portions  3220  and  3222 , shield  3240 , and return plate  3250 . In this figure, first magnet  3210  is not attracted to a second magnet, and therefore shield  3240  is magnetically attached or attracted to return plate  3250 . In this position, pliable surface  3212  can be relaxed. Pliable surface  3212  can be formed of an elastomer, silicon rubber open cell foam, silicon rubber, polyurethane foam, or other foam or other compressible material. 
     In  FIG.  32 B , second electronic device  3260  has been brought into the proximity of first electronic device  3200 . Second magnet  3270  can attract first magnet  3210 , thereby causing shield  3240  and return plate  3250  to separate from each other. First magnet  3210  can stretch pliable surface  3212  towards second electronic device  3260 , thereby allowing first magnet  3210  of first electronic device  3200  to move towards housing  3280  of second electronic device  3260 . Second magnet  3270  can be held in place in second electronic device  3260  by housing  3290  or other structure. As second electronic device  3260  is removed from first electronic device  3200 , first magnet  3210  and shield  3240  can be magnetically attracted to return plate  3250  as shown in  FIG.  32 A . 
       FIGS.  33 - 35    illustrate a moving magnetic structure according to an embodiment of the present invention. In this example, first electronic device  3300  can be a wireless charger device or other device having a first magnet  3310  (which can be, e.g., any of the annular or rotational magnetic alignment components described herein). In  FIG.  33   , first magnet  3310  and shield  3340  can be magnetically attracted or attached to return plate  3350  in first electronic device  3300 . First electronic device  3300  can be at least partially housed in device enclosure  3320 . In  FIG.  34   , housing  3380  of second electronic device  3360  can move laterally across a surface of device enclosure  3320  of first electronic device  3300  in a direction  3385 . Second magnet  3370  in second electronic device  3360  can begin to attract first magnet  3310  in first electronic device  3300 . This magnetic attraction  3315  can cause first magnet  3310  and shield  3340  to pull away from return plate  3350  by overcoming the magnetic attraction  3345  between shield  3340  and return plate  3350 . In  FIG.  35   , second magnet  3370  in second electronic device  3360  has become aligned with first magnet  3310  in first electronic device  3300 . First magnet  3310  and shield  3340  have pulled away from return plate  3350  thereby reducing the magnetic attraction  3345 . First magnet  3310  has moved nearby or adjacent to device enclosure  3320 , thereby increasing the magnetic attraction  3315  to second magnet  3370  in second electronic device  3360 . 
     As shown in  FIGS.  33 - 35   , the magnetic attraction between first magnet  3310  in first electronic device  3300  and the second magnet  3370  in the second electronic device  3360  can increase when first magnet  3310  and shield  3340  pull away from return plate  3350 . This is shown graphically in the following figures. 
       FIG.  36    illustrates a normal force between a first magnet in first electronic device and a second magnet in a second electronic device as a function of a lateral offset between them. As shown in  FIGS.  33 - 36   , with a large offset between first magnet  3310  and second magnet  3570 , first magnet  3310  and shield  3340  can remain attached to return plate  3350  in first electronic device  3300  and the magnetic attraction  3315  can be minimal. The shear force necessary to overcome this magnetic attraction is illustrated here as curve  3610 . As shown in  FIG.  34   , as the offset or lateral distance between first magnet  3310  and second magnet  3370  decreases, first magnet  3310  and shield  3340  can pull away or separate from return plate  3350 , thereby increasing the magnetic attraction  3315  between first magnet  3310  and second magnet  3370 . This is illustrated here as discontinuity  3620 . As shown in  FIG.  35   , as first magnet  3310  and second magnet  3370  come into alignment, the magnetic attraction  3315  increases along curve  3630  to a maximum  3640 . The difference between curve  3610  and curve  3630  can show the increase in magnetic attraction between a phone or other electronic device, such as second electronic device  3360 , and an attachable wireless charging device or other accessory device, such as first electronic device  3300 , that results from first magnet  3310  being able to move axially. It should also be noted that in this example first magnet  3310  does not move in a lateral direction, though in other examples it is capable of such movement. Where first magnet  3310  is capable of moving in a lateral direction, curve  3630  can have a flattened peak from an offset of zero to an offset that can be overcome by a range of possible lateral movement of first magnet  3310 . 
       FIG.  37    illustrates a sheer force between a first magnet in a first electronic device and a second magnet in a second electronic device as a function of a lateral offset between them. With no offset between first magnet  3310  and second magnet  3360 , there it is no shear force to move second magnet  3370  relative to first magnet  3310 , as shown in  FIG.  33   . As the offset is increased, the shear force, that is the force attempting to realign the magnets, can increase along curve  3740 . At discontinuity  3710 , first magnet  3310  and shield  3340  can return to return plate  3350  (as shown in  FIGS.  33 - 42   ), thereby decreasing the magnetic shear force to point  3720 . The magnetic sheer force can continue to drop off along curve  3730  as the offset increases. The difference between curve  3730  and curve  3740  can show the increase in magnetic attraction between a phone or other electronic device, such as second electronic device  3360  and an attachable wireless charging device or other accessory device, such as first electronic device  3300 , that results from first magnet  3310  being able to move axially. It should also be noted that in this example first magnet  3310  does not move in a lateral direction, though in other examples it is capable of such movement. Where first magnet  3310  is capable of moving in a lateral direction, curve  3730  can remain at zero until the lateral movement of the second magnet  3370  overcomes the range of possible lateral movement of first magnet  3310 . 
     In these and other embodiments of the present invention, it can be desirable to further increase this sheer force. Accordingly, embodiments of the present invention can provide various high friction or high stiction surfaces, suction cups, pins, or other structures to increase this sheer force. Examples are shown in the following figures. 
       FIGS.  38 A and  38 B  illustrate a moving magnet in conjunction with a high friction or high stiction surface according to an embodiment of the present invention. In this example, first electronic device  3800  can be a wireless charger device or other device having a first magnet  3810  (which can be, e.g., any of the annular magnetic alignment components described above). In  FIG.  38 A , first magnet  3810  and shield  3840  can be magnetically attracted or attached to return plate  3850  in first electronic device  3800 . First electronic device  3800  can be housed in device enclosure  3820 . Some or all of a surface of device enclosure  3820  can have a coating, layer, or other structure  3822 . Structure  3822  can provide a high friction or high stiction surface. In  FIG.  38 B , first magnet  3810  and shield  3840  can be attracted to a second magnet (not shown) in a second electronic device (not shown). As before, the separation of first magnet  3810  and shield  3840  from return plate  3850  can provide an increased amount of magnetic flux to hold the second electronic device in place relative to first electronic device  3800 . Structure  3822  can increase the friction or stiction between first electronic device  3800  and the second electronic device in a lateral or shear direction. 
       FIGS.  39 A and  39 B  illustrate a moving magnet in conjunction with a high friction or high stiction surface according to an embodiment of the present invention. In this example, first electronic device  3900  can be a wireless charger device or other device having a first magnet  3910  (which can be, e.g., any of the annular or rotational magnetic alignment components described herein). In  FIG.  39 A , first magnet  3910  and shield  3940  can be magnetically attracted or attached to return plate  3950  in first electronic device  3900 . First electronic device  3900  can be housed in device enclosure  3920 . Some or all of a surface of device enclosure  3920  can have a coating, layer, or other structure  3922 , in this example over first magnet  3910 . Structure  3922  can provide a high friction or high stiction surface. In  FIG.  39 B , first magnet  3910  and shield  3940  can be attracted to a second magnet (not shown) in a second electronic device (not shown.) This can cause first magnet  3910  and shield  3940  to separate from return plate  3850 , thereby deforming structure  3922 , which can be pliable or compliant. As before, first magnet  3910  can provide an increased amount of magnetic flux to hold the second electronic device in place relative to first electronic device  3900 . Structure  3922  can increase the friction or stiction between first electronic device  3900  and the second electronic device in a lateral or sheer direction. 
       FIGS.  40 A and  40 B  illustrate a moving magnet in conjunction with a high friction surface according to an embodiment of the present invention. In this example, first electronic device  4000  can be a wireless charger device or other device having a first magnet  4010  (which can be, e.g., any of the primary annular magnetic alignment components described above). In  FIG.  40 A , first magnet  4010  and shield  4040  can be magnetically attracted or attached to return plate  4050  in first electronic device  4000 . First electronic device  4000  can be housed in device enclosure  4020 . Some or all of a surface of device enclosure  4020  can have a coating, layer, or other structure  4022 , in this example over a top surface of first electronic device  4000 . Structure  4022  can provide a high friction or high stiction surface. In  FIG.  40 B , first magnet  4010  and shield  4040  can be attracted to a second magnet (not shown) in a second electronic device (not shown.) The separation of first magnet  4010  and shield  4040  from return plate  4050  can push the top surface formed by structure  4022  upward where it can engage the second electronic device with a high-friction surface. As before, first magnet  4010  can provide an increased amount of magnetic flux to hold the second electronic device in place relative to first electronic device  4000 . Structure  4022  can increase the friction or stiction between first electronic device  4000  and the second electronic device in a lateral or sheer direction. 
       FIGS.  41 A and  41 B  illustrate another moving magnet in conjunction with a high friction or high stiction surface according to an embodiment of the present invention. In this example, first electronic device  4100  can be a wireless charger device or other device having a first magnet  4110  (which can be, e.g., any of the annular magnetic alignment components described above). In  FIG.  41 A , first magnet  4110  and first shield  4150  can be fixed in place in device enclosure  4120  of first electronic device  4100 . Some or all of a surface of device enclosure  4120  can have a coating, layer, or other structure  4122 . Structure  4122  can provide a high friction or high stiction surface. First electronic device  4100  can further include a moving second magnet  4191  and second shield  4192 , which can be attached to sliding mechanism  4190 . In  FIG.  41 B , as a second electronic device (not shown) comes into contact with first electronic device  4100 , sliding mechanism  4190  can be depressed, thereby moving second magnet  4191  away from second shield  4192  and the top surface of device enclosure  4120 . The polarity of second magnet  4191  can be in opposition to, or the opposite of, the polarity of first magnet  4110 , such that the net magnetic flux at a top surface of device enclosure  4120  is increased as sliding mechanism  4190  is depressed. Structure  4122  can increase the friction or stiction between first electronic device  4100  and the second electronic device in a lateral or sheer direction. 
       FIG.  43    is a partially transparent view of the moving magnet structure of  FIG.  42   . First electronic device  4200  can be housed in device enclosure  4220 . As before, first electronic device  4200  can include inductive charging, near field communication complements, or other electronic circuits for components  4278 . Return plates  4250  (shown in  FIG.  42   ) can be attached to beams  4270 . 
       FIG.  44    is another cutaway side view of the electronic device of  FIG.  42   . First electronic device  4200  can be housed in device enclosure  4220 . As before, first electronic device  4200  can include inductive charging, near field communication components, or other electronic circuits for components  4278 . Return plates  4250  can be attached to beams  4270 . First magnets  4210  and shield  4240  can be attracted or attached to return plate  4250 . A high friction or high stiction structure  4222  can cover some or all of a top surface of first electronic device  4200 . Beams  4270  can be attached to return plates  4250 , can be anchored at points  4274 , and can have a tip  4272  extending above top surface of device enclosure  4220 . 
       FIGS.  45  and  46    illustrate the electronic device of  FIG.  42    as it engages with a second electronic device. In  FIG.  45   , second electronic device  4280  can include second magnets  4290 . Second electronic device  4280  can engage with first electronic device  4200 . First electronic device  4200  can include first magnets  4210 , shields  4240 , and return plates  4250 . Return plates  4250  can be attached to beams  4270 . Beams  4270  can include tips  4272  which can extend above a top surface of device enclosure  4220 . Tips  4272  can prevent second electronic device  4280  from engaging with the high friction or high stiction structure  4222  of first electronic device  4200  until the second electronic device  4280  is aligned, or nearly aligned, with first electronic device  4200 . Beams  4270  can be attached at points  4274  to device enclosure  4220 . First electronic device  4200  can include components  4278 . 
     In  FIG.  46   , second electronic device  4280  can be aligned with the first electronic device  4200 . When this occurs, first magnets  4210  and shields  4240  can detach from return plates  4250 . This can increase magnetic flux between second magnets  4290  in second electronic device  4280  and first magnets  4210  and first electronic device  4200 . Tips  4272  can become depressed into device enclosure  4220  due to this increase magnetic attraction, thereby further pushing return plates  4250  away from shields  4240 . High friction or high stiction structure  4222  can engage with second electronic device  4280  to increase the shear force necessary for a detachment of second electronic device  4280  from first electronic device  4200 . 
     In these and other embodiments of the present invention, various structures can be used to constrain movement of magnets in an electronic device. Examples are shown in the following figures. 
       FIGS.  47 A and  47 B  illustrate structures for constraining motions of magnets in an electronic device according to an embodiment of the present invention. In this example, first electronic device  4700  can be a wireless charger device or other device having a first magnet  4710  (which can be, e.g., any of the annular magnetic alignment components described above). In  FIG.  47 A , magnet  4710 , shield  4740 , and structure  4770  can be housed by device enclosure  4720  in electronic device  4700 . Structure  4770  can include notch  4772 , which can fit in tab  4724 . In  FIG.  47 B , magnet  4710  has moved, taking along with it shield  4740  and structure  4770 . Notch  4772  accepts tab  4724  as shield  4740  detaches from return plate  4750 . This can constrain the motion of magnets  4710  in electronic device  4700 . Electronic device  4700  can include a top device enclosure portion  4722 . Tab  4724  can be formed as part of or separate from top device enclosure portion  4722 . 
       FIGS.  48 A and  48 B  illustrate structures for constraining motions of magnets in an electronic device according to an embodiment of the present invention. In this example, first electronic device  4800  can be a wireless charger device or other device having a first magnet  4810  (which can be, e.g., any of the annular magnetic alignment components described above). In  FIG.  48 A , magnet  4810 , shield  4840 , and return plate  4850  can be housed in device enclosure  4820  of electronic device  4800 . Top device enclosure portion  4822  can include guide  4824 . Guide  4824  can constrain motion of magnet  4810  in electronic device  4800 . In  FIG.  48 B , magnet  4810  and shield  4840  have detached from return plate  4850  and have been guided into position by guide  4824 . Guide  4824  can include one or more chamfered edges  4825 . Again, guide  4824  can be formed along with or separate from top device enclosure portion  4822  of electronic device  4800 . 
       FIGS.  49 A and  49 B  illustrate structures for constraining motions of magnets in an electronic device according to an embodiment of the present invention. In this example, first electronic device  4900  can be a wireless charger device or other device having a first magnet  3010  (which can be, e.g., any of the annular magnetic alignment components described above). In  FIG.  49 A , magnet  4910 , shield  4940 , and return plate  4950  can be housed in device enclosure  4920  of electronic device  4900 . Magnet  4910  and shield  4940  can be supported by structure  4970 . Structure  4970  can be attached to anchor  4974  through actuators  4972 . Actuators  4972  can have hinges  4973  and  4975  at each end to allow structure  4970  to move relative to anchor  4974 . Anchor  4974  can be attached to, or formed as either part of, top device enclosure portion  4922  or device enclosure  4920 . In  FIG.  49 B , magnet  4910  and shield  4940  have detached from return plate  4950 . Actuators  4972  have changed positions but continued to connect structure  4970  to anchor  4974 . Anchor  4974  can be attached to, or formed as either part of, top device enclosure portion  4922  or device enclosure  4920 . 
     5. NFC Circuitry in a Magnetic Alignment System 
     For various applications, it may be desirable to enable a device having a magnetic alignment component to identify other devices that are brought into alignment. In some embodiments where the devices support a wireless charging standard that defines a communication protocol between devices, the devices can use that protocol to communicate. For example, the Qi standard for wireless power transfer defines a communication protocol that enables a power-receiving device (i.e., a device that has an inductive coil to receive power transferred wirelessly) to communicate information to a power-transmitting device (i.e., a device that has an inductive coil to generate time-varying magnetic fields to transfer power wirelessly to another device) via a modulation scheme in the inductive coils. The Qi communication protocol or similar protocols can be used to communicate information such as device identification or charging status or requests to increase or decrease power transfer from the power-receiving device to the power-transmitting device. 
     In some embodiments, a separate communication subsystem, such as a Near-Field Communication (NFC) subsystem can be provided to enable additional communication, including device identification, from a tag circuit located in one device to a reader circuit located in another device. (As used herein, “NFC” encompasses various protocols, including known standard protocols, that use near-field electromagnetic radiation to communicate data between antenna structures, e.g., coils of wire, that are in proximity to each other.) For example, each device that has an annular magnetic alignment component can also have an NFC coil that can be disposed inboard of and concentric with the annular magnetic alignment component. Where the device also has an inductive charging coil (which can be a transmitter coil or a receiver coil), the NFC coil can be disposed in an annular gap between the inductive charging coil and the annular magnetic alignment component. In some embodiments, an NFC protocol can be used to allow a portable electronic device to identify an accessory device when the respective magnetic alignment components of the portable electronic device and the accessory device are brought into alignment. For example, the NFC coil of a portable electronic device can be coupled to an NFC reader circuit while the NFC coil of an accessory device is coupled to an NFC tag circuit. When devices are brought into proximity, the NFC reader circuit of the portable electronic device can be activated to read the NFC tag of the accessory device. In this manner, the portable electronic device can obtain information (e.g., device identification) from the accessory device. 
     In some embodiments, an NFC reader in a portable electronic device can be triggered by detecting a change in a DC (or static) magnetic field within the portable electronic device that corresponds to a change expected when an accessory device having a complementary magnetic alignment component is brought into alignment. When the expected change is detected, the NFC reader can be activated to read an NFC tag in the other device, assuming the other device is present. 
     Examples of devices incorporating NFC circuitry and magnetic alignment components will now be described. 
     5.1. Portable Electronic Device with NFC Reader Circuitry 
       FIG.  50    shows a simplified back view of a portable electronic device  5004  according to some embodiments. In this example, portable electronic device  5004  is a smart phone, but other devices having different form factors can be substituted. Portable electronic device  5004  can include a wireless receiver coil assembly  5012 . Wireless receiver coil assembly  5012  can include a wireless receiver coil for inductive power transfer from another device as well as AC magnetic and/or electric shield(s) disposed around some or all surfaces of the wireless receiver coil. A secondary annular magnetic alignment component  5018  can be disposed around wireless receiver coil assembly  5012 . Secondary annular magnetic alignment component  5018  can include a number of arcuate magnets  5028  arranged in an annular configuration as shown. Each arcuate magnet  5028  can have a magnetic orientation having a radial component, e.g., radially inward or radially outward. (Examples of secondary annular magnetic alignment components that can be included in portable electronic device  5004  are described above in sections 1 and 3.) In some embodiments, secondary annular magnetic alignment component  5018  can include a gap  5001  (e.g., as described above with reference to  FIG.  11   ), which can provide a space for electrical connections to wireless receiver coil assembly  5012  without adding to the thickness of portable electronic device  5004 . In some embodiments, portable electronic device  5004  can also include a rotational alignment component  5024 , which can be implemented as described above in section 2. It should also be understood that portable electronic device  5004  may have an opaque rear housing (not shown in  FIG.  50   ) so that components such as wireless receiver coil assembly  5012  and secondary annular magnetic alignment component  5018  are not visible to a user. 
     According to some embodiments, an NFC coil  5060  can be disposed in an annular gap region between secondary annular magnetic alignment component  5018  and wireless receiver coil assembly  5012 . NFC coil  5060  can be, for example, a single turn of a double-stranded wire (which can be made, e.g., of copper or other conductive material) having terminals  5062   a ,  5062   b  connected to an NFC reader circuit (not shown). The NFC reader circuit, which can be of generally conventional design, can be disposed on a main logic board of portable electronic device  5004 , away from secondary annular magnetic alignment component  5018 . In some embodiments, positioning NFC coil  5060  in the annular gap region between secondary annular magnetic alignment component  5018  and wireless receiver coil assembly  5012  can allow NFC coil  5060  to be shielded from AC electromagnetic fields generated in wireless receiver coil assembly  5012  and from DC magnetic fields of secondary annular magnetic alignment component  5018 . For instance, shielding can be provided by a combination of AC shielding in receiver coil assembly  5012  and the closed-loop configuration of the arcuate magnet sections when coupled to a primary magnetic alignment component (as described above in sections 1 and 3). 
       FIG.  51    shows an exploded view of a wireless charging and alignment assembly  5100  for a portable electronic device incorporating an NFC reader according to some embodiments. Wireless charging and alignment assembly  5100  can include wireless receiver coil assembly  5012  and secondary annular magnetic alignment component  5018 . Wireless receiver coil assembly  5012  and secondary annular magnetic alignment component  5018  can be disposed on a layer  5101  of a pressure-sensitive adhesive (PSA). In some embodiments, an electric shield  5103  for wireless receiver coil assembly  5012  can be disposed on a portion of PSA layer  5101 , e.g., by depositing silver or other conductive material in an appropriate pattern. As is known in the art, electric shield  5103  can block AC electric fields emitted by wireless transmitter coil  5012  during operation while permitting AC magnetic fields to pass through. NFC coil  5060  can be disposed on PSA layer  5101  in the space between the outer edge of electric shield  5103  and the inner edge of secondary annular magnetic alignment component  5018 . NFC coil  5060  can be, for example, a single-turn multi-stranded wire coil. An electromagnetic shield assembly  5107  can be disposed over the distal surface of wireless receiver coil assembly  5012 , NFC coil  5060 , and secondary annular magnetic alignment component  5018 , thereby shielding other components of portable electronic device  5004  from electromagnetic fields generated by wireless receiver coil assembly  5012  and NFC coil  5060 . 
       FIG.  52    shows a simplified cross-section view of a portion of portable electronic device  5004  of  FIG.  50    incorporating assembly  5104  of  FIG.  51   . As shown, wireless charging and alignment assembly  5100  can be disposed between a front housing  5203  and a back housing  5205  of portable electronic device  5001 . In some embodiments, front housing  5203  can be or incorporate a touchscreen display. Back housing  5205  can be made of glass or plastic or any other material that does not interfere with wireless power or data transfer or with the magnetic fields of the annular alignment components such as secondary annular alignment component  5012 . Assembly  5100  can be oriented with PSA layer  5101  and electric shield  5103  toward back housing  5205  and shield assembly  5107  toward front housing  5203  to enable wireless charging through back housing  5205 . 
     It should be understood that portable electronic device  5004  is illustrative and that variations and modifications are possible. An assembly such as wireless charging and alignment assembly  5104  can be incorporated into a variety of electronic devices. In some embodiments, NFC coil  5060  and an NFC reader circuit coupled thereto are dedicated to identifying accessory devices having a primary magnetic alignment component that is complementary to secondary magnetic alignment component  5018 , and portable electronic device  5004  can include one or more other NFC coils and associated circuitry for other applications involving NFC technology (such as point-of-sale payment transactions). 
     5.2. Wireless Charger Device with NFC Tag Circuit 
     In some embodiments, an NFC tag may be located in a device that includes a wireless charger and an annular alignment structure. The NFC tag can be positioned and configured such that when the wireless charger device is aligned with a portable device having a complementary annular alignment structure and an NFC reader, the NFC tag is readable by the NFC reader of the portable electronic device. 
       FIG.  53    shows an exploded view of a wireless charger device  5302  incorporating an NFC tag according to some embodiments, and  FIG.  54 A  shows a partial cross-section view of wireless charger device  5302  according to some embodiments. As shown in  FIG.  53   , wireless charger device  5302  can include an enclosure  5304 , which can be made of plastic or metal (e.g., aluminum), and a charging surface  5306 , which can be made of silicone, plastic, glass, or other material that is permeable to AC and DC magnetic fields. Charging surface  5306  can be shaped to fit within a circular opening  5303  at the top of enclosure  5304 . 
     A wireless transmitter coil assembly  5311  can be disposed within enclosure  5304 . Wireless transmitter coil assembly  5311  can include a wireless transmitter coil  5312  for inductive power transfer to another device as well as AC magnetic and/or electric shield(s)  5313  disposed around some or all surfaces of wireless transmitter coil  5312 . Control circuitry  5314  (which can include, e.g., a logic board and/or power circuitry) to control wireless transmitter coil  5312  can be disposed in the center of coil  5312  and/or underneath coil  5312 . In some embodiments, control circuitry  5314  can operate wireless transmitter coil  5312  in accordance with a wireless charging protocol such as the Qi protocol or other protocols. 
     A primary annular magnetic alignment component  5316  can surround wireless transmitter coil assembly  5311 . Primary annular magnetic alignment component  5316  can include a number of arcuate magnet sections arranged in an annular configuration as shown. Each arcuate magnet section can include an inner arcuate region having a magnetic polarity oriented in a first axial direction, an outer arcuate region having a magnetic polarity oriented in a second axial direction opposite the first axial direction, and a central arcuate region that is not magnetically polarized. (Examples are described above in sections 1 and 3.) In some embodiments, the diameter and thickness of primary annular magnetic alignment component  5316  is chosen such that arcuate magnet sections of primary annular magnetic alignment component  5316  fit under a lip  5309  at the top surface of enclosure  5304 , as best seen in  FIG.  54 A . For instance, each arcuate magnet section can be inserted into position under lip  5309 , either before or after magnetizing the inner and outer regions. In some embodiments, primary annular magnetic alignment component  5316  can have a gap  5336  between two adjacent arcuate magnet sections. Gap  5336  can be aligned with an opening  5307  in a side surface of enclosure  5304  to allow external wires to be connected to wireless transmitter coil  5312  and/or control circuitry  5314 . 
     A support ring subassembly  5340  can include an annular frame  5342  that extends in the axial direction and a friction pad  5344  at the top edge of frame  5342 . Friction pad  5344  can be made of a material such as silicone or thermoplastic elastomers (TPE) such as thermoplastic urethane (TPU) and can provide support and protection for charging surface  5306 . Frame  5342  can be made of a material such as polycarbonate (PC), glass-fiber reinforced polycarbonate (GFPC), or glass-fiber reinforced polyamide (GFPA). Frame  5342  can have an NFC coil  5364  disposed thereon. For example, NFC coil  5364  can be a four-turn or five-turn solenoidal coil made of copper wire or other conductive wire that is wound onto frame  5342 . NFC coil  5364  can be electrically connected to NFC tag circuitry (not shown) that can be part of control circuitry  5314 . The relevant design principles of NFC circuits are well understood in the art and a detailed description is omitted. Frame  5342  can be inserted into a gap region  5317  between primary annular magnetic alignment component  5316  and wireless transmitter coil assembly  5311 . In some embodiments, gap region  5317  is shielded by AC shield  5313  from AC electromagnetic fields generated in wireless transmitter coil  5312  and is also shielded from DC magnetic fields of primary annular magnetic alignment component  5316  by the closed-loop configuration of the arcuate magnet sections. 
       FIG.  54 B  shows a partial cross-section view of another wireless charger device  5402  according to some embodiments. Wireless charger device  5402  can be generally similar to wireless charger device  5302  of  FIGS.  53  and  54 A . For example, wireless charger device  5402  can include an enclosure  5404 , which can be made of plastic or metal (e.g., aluminum), and a charging surface  5406 , which can be made of silicone, plastic, glass, or other material that is permeable to AC and DC magnetic fields. Charging surface  5406  can be shaped to fit within a circular opening at the top of enclosure  5404 . A wireless transmitter coil assembly  5411  can be disposed within enclosure  5304 . Wireless transmitter coil assembly  5411  be similar or identical to wireless transmitter coil assembly  5311 . Control circuitry  5414 , which can be similar or identical to control circuitry  5314  can be disposed, e.g., under coil assembly  5411 . 
     A primary annular magnetic alignment component  5416  can surround wireless transmitter coil assembly  5411 . Primary annular magnetic alignment component  5416  can be similar or identical to primary annular magnetic alignment component  5316 . In some embodiments, the diameter and thickness of primary annular magnetic alignment component  5416  is chosen such that arcuate magnet sections of primary annular magnetic alignment component  5416  fit under a lip  5409  at the top surface of enclosure  5404 , similarly to the arrangement shown in  FIG.  54 A . 
     A support frame  5442  can extend between enclosure  5404  and top cap  5406 . Support ring subassembly can be made of a material such as polycarbonate (PC), glass-fiber reinforced polycarbonate (GFPC), or glass-fiber reinforced polyamide (GFPA). Frame  5442  can have an NFC coil  5464  disposed thereon on an upper surface thereof. For example, NFC coil  5464  can be a four-turn or five-turn planar coil made of concentric turns of copper wire or other conductive wire that is wound onto frame  5442 . (Alternatively, a solenoidal wound NFC coil similar to coil  5364  can be used.) NFC coil  5464  can be electrically connected to NFC tag circuitry (not shown) that can be part of control circuitry  5414 . Frame  5442  can be inserted into a gap region between primary annular magnetic alignment component  5416  and wireless transmitter coil assembly  5411 . In some embodiments, gap region  5417  is shielded by AC shield  5413  from AC electromagnetic fields generated in wireless transmitter coil  5412  and is also shielded from DC magnetic fields of primary annular magnetic alignment component  5416  by the closed-loop configuration of the arcuate magnet sections. 
     5.3. Accessory Device with NFC Tag Circuit 
     As described above in section 3, an accessory device such as a case for a mobile phone may include an auxiliary magnetic alignment component, with or without a wireless charging coil. The auxiliary magnetic alignment component can act as a “repeater” to support the use of a primary magnetic alignment component and a secondary alignment component to align the wireless charging transmitter coil of a charger device with the wireless charging receiver coil of a portable electronic device while the portable electronic device is attached to (e.g., inserted into) the accessory device. 
     In some embodiments, an NFC tag circuit and coil may be incorporated into an accessory device having an auxiliary magnetic alignment component. The NFC tag can be read by the NFC reader of the portable electronic device (e.g., using NFC coil  5060  and associated NFC reader circuit of portable electronic device  5004  as described above), allowing the portable electronic device to identify the accessory device when the accessory device is in proximity and aligned with the portable electronic device. 
       FIG.  55    shows an example of an accessory device  5500  incorporating an auxiliary alignment component with an NFC tag circuit and coil according to some embodiments. Accessory device  5500  can be, for example, a case for portable electronic device  5004  (which can be, e.g., a smart phone). Accessory device  5500  can be shaped as a tray, sleeve, or other form factor as desired that covers and protects one or more surfaces of portable electronic device  5004 . In particular, accessory device  5500  can have a rear (or back) panel  5502  that covers the rear surface of portable electronic device  5004 . It should be understood that rear panel  5502  need not cover the entire rear surface of portable electronic device  5004 ; for example, a cutout area  5503  can be provided to expose a rear camera lens of portable electronic device  5004 . 
     Rear surface  5502  can include an auxiliary annular magnetic alignment component  5570 . Auxiliary annular magnetic alignment component  5570  can include a number of arcuate magnets  5572  arranged in an annular configuration as shown. Each arcuate magnet  5572  can include an inner arcuate region having a magnetic polarity oriented in a first axial direction, an outer arcuate region having a magnetic polarity oriented in a second axial direction opposite the first axial direction, and a central arcuate region that is not magnetically polarized. (Examples are described above in section 3.) Auxiliary annular magnetic alignment component  5570  can align with secondary annular magnetic alignment component  5018  of electronic device  5002 . 
     An NFC tag circuit assembly  5566  can be disposed inboard of auxiliary annular magnetic alignment component  5316 . In some embodiments, all or part of region  5505  of rear surface  5502 , inboard of NFC tag circuit assembly  5566 , can be a cutout area.  FIG.  56    shows a more detailed view of NFC tag circuit assembly  5566  according to some embodiments. NFC tag circuit assembly  5566  can include a printed circuit on a printed circuit board (PCB)  5602  (which can be, e.g., a flexible PCB) having a circular outer perimeter that fits within the inner diameter of auxiliary annular magnetic alignment component  5572  as shown in  FIG.  55   . In some embodiments, PCB  5602  can be a disc. In other embodiments, PCB  5602  can have a central opening  5603 , which can have various shapes. In some embodiments, the size of opening  5603  can be based on the area needed to accommodate NFC tag circuit components. 
     An NFC antenna coil  5604  can be disposed on a peripheral portion of PCB  5602  NFC antenna coil  5604  can be an etched planar coil on PCB  5602  and can include, e.g., four or five turns of copper or other electrically conductive material. NFC antenna coil  5604  can be coupled to an NFC tag chip  5606  (shown in inset  5620 ) and capacitors  5608 , which can be disposed on PCB  5602  inward of NFC antenna coil  5604 . NFC tag chip  5606  can be, for example, a passively powered NFC tag chip or other passively powered NFC tag circuit that is compatible with the NFC reader of a portable electronic device. Capacitors  5608  can be, for example, multilayer ceramic capacitors that support operation of NFC tag chip  5606 . A particular selection and configuration of supporting capacitors depends on the NFC tag chip and coil configuration; the relevant design principles of NFC circuits are well understood in the art and a detailed description is omitted. 
     In general, NFC tag circuit  5606  and capacitors  5608  have height that extends above PCB  5602 . To provide a flat profile for NFC tag circuit assembly  5566 , additional tape layers may be added to PCB  5602 .  FIG.  57    shows an exploded view of NFC tag circuit assembly  5566  including tape layers stacked on PCB  5602  to provide uniform height according to some embodiments. PCB  5602  is shown at the bottom. Tape layers  5702  and  5703  can each be layers of polyester tape (PET) with a pressure-sensitive adhesive (PSA), and each layer can be, e.g., about 150 μm thick. As shown, each of tape layers  5702  and  5703  can be shaped to match the shape of PCB  5602  and may have holes  5705  therethrough to accommodate the height of NFC tag chip  5606  and capacitors  5608 . The sum of the thicknesses of tape layers  5702  and  5703  can equal or exceed the height of NFC tag chip  5606  and capacitors  5608 . (While two tape layers are shown, it should be understood that any number of tape layers can be used depending on the thickness of the tape layers and the height of the NFC circuit components.) Top layer  5710  can be, e.g., PSA, and need not have holes therethrough. In some embodiments, the total height of NFC tag circuit assembly  5566  can be less than half a millimeter. 
       FIG.  58    shows a partial cross section view of charge-through accessory  5500  of  FIG.  55    incorporating NFC tag circuit assembly  5566  and auxiliary alignment component  5570  according to some embodiments. Charge-through accessory  5500  can be, e.g., a tray or other case for a portable electronic device, and the portion shown in  FIG.  58    can form part of rear panel  5502  of charge-through accessory  5500 . (A back surface of a portable electronic device can be positioned adjacent to surface  5801 .) Rear panel  5502  can have an internal structure with an inner layer  5804  and an outer layer  5806 , which can be made of or incorporate silicone, plastic, leather, or other materials that are permeable to DC and AC magnetic fields. In some embodiments, inner layer  5804  and outer layer  5806  provide flat surfaces for rear panel  5502 . A central layer  5808  can be disposed between inner layer  5804  and outer layer  5806 . Central layer  5808  can define a recess region  5809  to accommodate NFC tag circuit assembly  5566  and an auxiliary annular magnetic alignment component  5870 . Auxiliary annular magnetic alignment component  5870  can be similar or identical to auxiliary annular magnetic alignment component  5570  or other examples described above. As shown, the height of NFC tag circuit assembly  5566  can be less than or equal to the height of auxiliary alignment component  5870 , and recess region  5809  can be shaped appropriately. 
     As shown in  FIG.  56   , NFC tag circuit assembly  5566  extends inward from NFC coil  5604  to provide space for NFC tag chip  5606  and capacitors  5608 . Since both NFC tag circuit assembly  5566  and auxiliary annular alignment component  5570  include opaque elements, it is not possible to make all portions of rear panel  5502  of accessory  5500  transparent to reveal the rear surface of a portable electronic device held in accessory  5500 . For esthetic purposes it may be desirable to minimize the width of the non-transparent region of rear panel  5502 . 
       FIG.  59    shows an example of another accessory device  5900  having an auxiliary alignment component with an NFC tag circuit and coil according to some embodiments. Accessory device  5900  can be, for example, a case for portable electronic device  5004  (which can be, e.g., a smart phone). Like accessory device  5500  described above, accessory device  5900  can be shaped as a tray, sleeve, or other form factor as desired that covers and protects one or more surfaces of portable electronic device  5004 . In particular, accessory device  5900  can have a rear (or back) panel  5902  that covers the rear surface of portable electronic device  5004 . It should be understood that rear panel  5902  need not cover the entire rear surface of portable electronic device  5004 ; for example, a cutout area  5903  can be provided to expose a rear camera lens of portable electronic device  5004 . 
     Rear panel  5902  can include an auxiliary annular magnetic alignment component  5970  and an NFC tag circuit assembly  5966 . Auxiliary annular magnetic alignment component  5970  can include a number of arcuate magnets  5972  arranged in an annular configuration as shown. Each arcuate magnet  5972  can include an inner arcuate region having a magnetic polarity oriented in a first axial direction, an outer arcuate region having a magnetic polarity oriented in a second axial direction opposite the first axial direction, and a central arcuate region that is not magnetically polarized. (Examples are described above with reference to section 3.) Auxiliary annular magnetic alignment component  5970  can align with secondary annular magnetic alignment component  5018  of portable electronic device  5002 . 
       FIG.  60    shows an enlarged view of auxiliary annular magnetic alignment component  5970  and NFC tag circuit assembly  5966  of  FIG.  59    according to some embodiments. Annular alignment component  5970  can include a number of arcuate magnets  5972  arranged in an annular configuration, with gaps  6001  between selected pairs of adjacent magnets  5972 . In the example shown, each gap  6001  can be created by omitting an arcuate magnet  5972 . Other techniques, examples of which are described above, can be used to create gaps  6001 . Gaps  6001  can accommodate components of NFC tag circuit assembly  5966 , which can reduce the inward extension of NFC tag circuit assembly  5966  and increase the component-free area in center region  6003 . 
     NFC tag circuit assembly  5966  can include a printed circuit on a PCB  6002  (e.g., a flexible PCB) having a circular inner perimeter and a circular outer perimeter with projections  6022  that extend into gaps  6001  in annular magnetic alignment component  5970 . An NFC antenna coil  6004  can be disposed on the circular portion of PCB  6002 . NFC antenna coil  6004  can be an etched planar coil on PCB  6002  or a wound wire coil and can include, e.g., four or five turns of copper or other electrically conductive material. NFC antenna coil  6004  can be coupled to an NFC tag chip  6006  and capacitors  6008 , each of which can be disposed on a different one of projections  6022  of PCB  6002  between magnets  5972  of annular alignment component  5970 . NFC tag chip  6006  and capacitors  6008  can include standard NFC tag circuit components as described above. As can be seen, PCB  6002  can add less to the width of auxiliary annular alignment component  5970  than PCB  5602  of  FIG.  56   . The narrower opaque assembly may be esthetically desirable in instances where rear panel  5902  of accessory  5900  is generally made of transparent material and/or in instances where the region  6003  inboard of NFC tag circuit assembly  5966  provides a hole through rear panel  5902 . 
       FIG.  61    shows an exploded view of NFC tag circuit assembly  5966  according to some embodiments. PCB  6002  can have a layer of PSA underneath and a tape layer  6104  on top. Tape layer  6104  can be a layer of PET with a PSA. In some embodiments, magnets  5972  of annular alignment component  5960  provide uniform height, and tape layer  6104  can overlie and encapsulate NFC tag chip  6006  and capacitors  6008 . 
     As described above, a portable electronic device can include an annular magnetic alignment component and an NFC reader circuit, while each accessory device can include an annular magnetic alignment component and an NFC tag circuit. The NFC reader and tag circuits can be arranged such that, when the portable electronic device is brought into alignment with one or more accessory devices, the NFC reader circuit in the portable electronic device is brought into near enough proximity to the NFC tag circuit(s) of the accessory device(s) to allow the NFC reader circuit to read the NFC tag(s), thereby allowing the portable electronic device to identify the accessory device(s). The NFC tag circuits can be passive tags that are energized by the near-field of the NFC reader coil, so that an accessory device incorporating an NFC tag circuit need not have its own power supply. 
       FIG.  62    shows a simplified partial cross-section view of a system  6200  that includes a wireless charger device  6202 , a portable electronic device  6204 , and an accessory device  6220  according to some embodiments. Portable electronic device  6204  includes a secondary annular magnetic alignment component  6218  (which can be similar or identical to secondary magnetic alignment component  5018 ), a wireless receiver coil assembly  6212  (which can be similar or identical to wireless receiver coil assembly  5012  described above), and NFC coil  6260  (which can be similar to NFC coil  5060  described above) that connects to an NFC reader circuit (not shown). NFC coil  6260  can be disposed between secondary annular magnetic alignment component  6218  and wireless receiver coil assembly  6212 . 
     Wireless charger device  6202  includes a primary annular magnetic alignment component  6216  (which can be similar or identical to primary annular magnetic alignment component  5316  described above), a wireless transmitter coil assembly  6211  (which can be similar to wireless transmitter coil assembly  5311  described above), and NFC tag circuit assembly  6240 , which can be similar to support ring subassembly  5340  described above and can include NFC coil  6264  and an associated NFC tag circuit (not shown). NFC coil  6264  can be disposed between primary annular alignment component  6216  and wireless transmitter coil assembly  6211 . 
     Accessory device  6220  includes an auxiliary annular magnetic alignment component  6270  (which can be similar or identical to auxiliary annular magnetic alignment component  5570  described above) and an NFC tag circuit assembly  6266 , which can be similar or identical to NFC tag circuit assembly  5566  or NFC tag circuit assembly  5966  described above. NFC tag circuit assembly  6266  can be disposed inboard of auxiliary annular magnetic alignment component  6270 . 
     Wireless charger device  6202  includes a primary annular magnetic alignment component  6216  (which can be similar or identical to primary annular magnetic alignment component  5316  described above), a wireless transmitter coil assembly  6211  (which can be similar to wireless transmitter coil assembly  5311  described above), and NFC tag circuit assembly  6240 , which can be similar to support ring subassembly  5340  described above and can include NFC coil  6264  and an associated NFC tag circuit (not shown). NFC coil  6264  can be disposed between primary annular alignment component  6216  and wireless transmitter coil assembly  6211 . 
     Accessory device  6220  includes an auxiliary annular magnetic alignment component  6270  (which can be similar or identical to auxiliary annular magnetic alignment component  5570  described above) and an NFC tag circuit assembly  6266 , which can be similar or identical to NFC tag circuit assembly  5566  or NFC tag circuit assembly  5966  described above. NFC tag circuit assembly  6266  can be disposed inboard of auxiliary annular magnetic alignment component  6270 . 
     As shown in  FIG.  62   , NFC coil  6260  of portable electronic device  6204  is in proximity to NFC coil  6266  of accessory device  6220  and to NFC coil  6264  of wireless charger device  6202 . Accordingly, portable electronic device  6204  can read the NFC tags of both accessory device  6220  and wireless charger device  6202  whenever either is attached. It should be understood that at different times, accessory device  6220  may be present while wireless charger device  6202  is absent, or wireless charger device  6202  may be present while accessory device  6220  is absent. At any given time, portable electronic device  6204  can read the NFC tag of any device that happens to be present and aligned with secondary annular magnetic alignment component  6216 . In some embodiments, portable electronic device  6204  can include a low-power proximity sensor that detects when an accessory device or wireless charger device is brought into alignment, and portable electronic device  6204  can activate its NFC reader circuit in response to a proximity detection event. Specific examples are described below. 
     In the example of  FIG.  62   , accessory device  6220  has its NFC coil  6266  disposed inboard of secondary annular alignment component  6270 . In some alternative embodiments, an NFC coil of an accessory device can be disposed outboard of the auxiliary annular alignment component.  FIG.  63    shows an example of an accessory device  6300  having an auxiliary alignment component with an NFC tag circuit and coil according to some embodiments. Accessory device  6300  can be, for example, a case for portable electronic device  5004  (which can be, e.g., a smart phone). Like accessory devices  5500  and  5900  described above, accessory device  6300  can be shaped as a tray, sleeve, or other form factor as desired that covers and protects one or more surfaces of portable electronic device  5004 . In particular, accessory device  6300  can have a rear (or back) panel  6302  that covers the rear surface of portable electronic device  5004 . It should be understood that rear panel  6302  need not cover the entire rear surface of portable electronic device  5004 ; for example, a cutout area  6303  can be provided to expose a rear camera lens of portable electronic device  5004 . 
     Rear panel  6302  can include an auxiliary annular magnetic alignment component  6370  and an NFC tag circuit assembly  6366 . Auxiliary annular magnetic alignment component  6370  can include a number of arcuate magnets  6372  arranged in an annular configuration as shown. Each arcuate magnet  6372  can include an inner arcuate region having a magnetic polarity oriented in a first axial direction, an outer arcuate region having a magnetic polarity oriented in a second axial direction opposite the first axial direction, and a central arcuate region that is not magnetically polarized. (Examples are described above in section 3.) Auxiliary annular magnetic alignment component  6370  can align with secondary annular magnetic alignment component  5018  of portable electronic device  5002 . NFC tag circuit assembly  6366  can be disposed outboard (i.e., outside the outer perimeter) of auxiliary annular magnetic alignment component  6370 . Although not shown in detail, it should be understood that NFC tag circuit assembly  6366  can be constructed similarly to NFC tag circuit assembly  5566  described above. For instance, NFC tag circuit assembly  6366  can include a ring-shaped PCB with an etched NFC coil. A peripheral extension of the PCB (e.g., at region  6371 ) can provide an area for mounting of NFC tag circuit components (e.g., an NFC tag chip and capacitors). 
       FIG.  64    shows a system  6400  that includes a wireless charger device  6402 , a portable electronic device  6404 , and an accessory device  6420  according to some embodiments. Portable electronic device  6404  includes a secondary annular magnetic alignment component  6418  (which can be similar or identical to secondary magnetic alignment component  5018 ), a wireless receiver coil assembly  6412  (which can be similar or identical to wireless receiver coil assembly  5012  described above), and NFC coil  6460  (which can be similar to NFC coil  5060  described above) that connects to an NFC reader circuit (not shown). NFC coil  6460  can be disposed between secondary annular magnetic alignment component  6418  and wireless receiver coil assembly  6412 . 
     Wireless charger device  6402  includes a primary annular magnetic alignment component  6416  (which can be similar or identical to primary annular magnetic alignment component  5316  described above), a wireless transmitter coil assembly  6411  (which can be similar to wireless transmitter coil assembly  5511  described above), and NFC tag circuit assembly  6440 , which can be similar to support ring subassembly  5540  described above and can include NFC coil  6464  and an associated NFC tag circuit (not shown). NFC coil  6464  can be disposed between primary annular alignment component  6416  and wireless transmitter coil assembly  6411 . 
     Accessory device  6420  includes an auxiliary annular magnetic alignment component  6470  (which can be similar or identical to auxiliary annular magnetic alignment component  5570  described above) and an NFC tag circuit assembly  6466 , which can be similar or identical to NFC tag circuit assembly  6366  described above; in particular, NFC tag circuit assembly  6466  can be disposed outboard of auxiliary annular magnetic alignment component  6470 . 
     As shown in  FIG.  64   , NFC coil  6460  of portable electronic device  6404  is in proximity to NFC coil  6466  of accessory device  6420  and to NFC coil  6464  of wireless charger device  6402 . Accordingly, portable electronic device  6404  can read the NFC tags of both accessory device  6420  and wireless charger device  6402  whenever either is attached. It should be understood that at different times, accessory device  6420  may be present while wireless charger device  6402  is absent, or wireless charger device  6402  may be present while accessory device  6420  is absent. At any given time, portable electronic device  6404  can read the NFC tag of any device that happens to be present and aligned with secondary annular magnetic alignment component  6416 . In some embodiments, portable electronic device  6404  can include a low-power proximity sensor that detects when an accessory device or wireless charger device is brought into alignment, and portable electronic device  6204  can activate its NFC reader circuit in response to a proximity detection event. Specific examples are described below. 
     5.4. Proximity Detection to Trigger NFC Reader Circuit 
     Referring again to  FIG.  50   , as noted above, it may be desirable to selectively trigger the NFC reader circuit in portable electronic device  5004  when a compatible accessory comes into proximity with portable electronic device  5004 . Proximity-based triggering of the NFC reader circuit can allow considerable power savings as compared to periodically polling the NFC reader circuit and can also avoid the need for the user to take any action to trigger the NFC reader circuit, other than bringing devices into proximity. 
     In some embodiments, an electromagnetic sensor can be used to detect when a device having an annular alignment component complementary to secondary annular alignment component  5018  is brought into alignment. For example, a three-axis magnetometer  5080  can be positioned within the rear enclosure of portable electronic device  5004  in an area near secondary annular alignment component  5018  and coupled to control logic located in a main logic board of portable electronic device  5004 . Magnetometer  5080  can be a low-power component that can be periodically polled to measure a magnetic field at the location of magnetometer  5080 . In particular, based on periodic polling, a “baseline” magnetic field can be established, which can include a contribution from secondary annular alignment component  5018  and from any other devices that are currently aligned with secondary annular alignment component  5018 . When a device having an annular magnetic alignment component complementary to secondary annular magnetic alignment component  5018  (e.g., wireless charger device  5302  or accessory device  5500 ) is brought into alignment with secondary annular magnetic alignment component  5018 , the magnetic field at the location of magnetometer  5080  changes abruptly relative to the baseline in a specific and predictable manner. Accordingly, a change in the measured magnetic field (relative to baseline) having a particular magnitude can be used to detect when a device with a complementary magnetic alignment component is brought into proximity with portable electronic device  5004 . In some embodiments, the change can be defined as a three-dimensional vector, and detection of a device being brought into proximity can be triggered based on changes in magnitude and/or direction of the field measured by magnetometer  5080 . Further, aligning different types of devices may result in different changes in the magnetic field measured by magnetometer  5080 . For instance, as shown in  FIG.  62   , primary annular magnetic alignment component  6216  may be thicker than auxiliary annular magnetic alignment component  6270 , and this difference may result in different effects on the magnetic field measured by magnetometer  5080 . In addition, the change in magnetic field measured by magnetometer  5018  when a wireless charger device (e.g., wireless charger device  5302 ) is brought into alignment while portable electronic device  5004  is already aligned with an accessory (e.g., accessory  5500 ) may be different from the change measured when a wireless charger device (e.g., wireless charger device  5302 ) is brought into alignment while no accessory is present. Control logic (e.g., logic circuits located on a main logic board of portable electronic device  5500 ) can periodically (e.g., every few milliseconds or a few times per second) monitor changes in the magnetic field detected by magnetometer  5018  and can determine, based on the changes, whether a device having a complementary magnetic alignment component has been brought into proximity (or, if one such device is already known to be present, whether another such device has also been brought into proximity). In response to determining that a device has been brought into proximity, the control logic can trigger operation of NFC coil  5060  and the associated NFC reader circuit to read an NFC tag that may be present in a newly-proximate device. It should be understood that detachment (or removal from proximity) of an active or passive accessory device can also be detected by detecting changes in the magnetic field measured by magnetometer  5080 . 
     In some embodiments, based on the information in the NFC tag of the aligned device, portable electronic device  5004  may modify some aspect of its behavior. In some embodiments, an NFC tag in an accessory device may indicate a property of the accessory device, such as its color or design style. Portable electronic device  5004  can modify its color scheme or other elements of its user interface accordingly. For instance, portable electronic device  5004  may generate a transient color wash effect on the screen in a color matching the color of the accessory device. As another example, the accessory device may be a sleeve having an opaque front panel, in which a window is provided to expose a portion of the display of portable electronic device  5004 , and when portable electronic device is aligned inside the sleeve, portable electronic device  5004  can switch to a mode that displays specific content (e.g., current time or notifications) on the portion of the display that aligns with the window. In some embodiments, the accessory identification may provide context information about the environment in which the accessory is present: for example, a docking accessory may be located in a vehicle or positioned in a particular room, and portable electronic device  5004  can modify its behavior based on the context information (e.g., by switching to an in-vehicle display mode when docked in a vehicle dock). As yet another example, the accessory may be a detachable pack; when portable electronic device  5004  detects (e.g., based on magnetometer signals) that the accessory has been attached or detached, portable electronic device  5004  can store information about the attachment or detachment event (e.g., location information indicating where portable electronic device  5004  was when attachment or detachment occurred). In some embodiments, portable electronic device  5004  can provide the stored information to a user (e.g., providing location information indicating where detachment occurred to assist the user in locating the detached accessory). As a further example, accessory identification may result in portable electronic device  5004  launching a particular app associated with the accessory or unlocking certain functionality of a particular app. It should be understood from these examples that many aspects of device behavior can be modified in response to information received from an NFC tag. As a still further example, if an accessory is identified via its NFC tag as a battery pack but portable electronic device  5004  is unable to draw power from the accessory, portable electronic device  5004  can determine that the battery is dead and can alert the user accordingly. It should be understood that many aspects of behavior of a portable electronic device can be modified in response to detecting that a particular accessory has become attached or detached. 
       FIG.  65    shows a flow diagram of a process  6500  that can be implemented in portable electronic device  5004  according to some embodiments. In some embodiments, process  6500  can be performed iteratively while portable electronic device  5004  is powered on. At block  6502 , process  6500  can determine a baseline magnetic field, e.g., using magnetometer  5080 . At block  6504 , process  6500  can continue to monitor signals from magnetometer  5080  until a change in magnetic field is detected. At block  6506 , process  6500  can determine whether the change in magnetic field matches a magnitude and direction of change associated with alignment of a complementary magnetic alignment component. If not, then the baseline magnetic field can be updated at block  6502 . If, at block  6506 , the change in magnetic field matches a magnitude and direction of change associated with alignment of a complementary alignment component, then at block  6508 , process  6500  can activate the NFC reader circuitry associated with NFC coil  5060  to read an NFC tag of an aligned device. In some embodiments, NFC tags associated with different types of devices (e.g., a passive accessory versus an active accessory such as a wireless charger) are tuned to respond to different stimulating signals from the NFC reader circuitry, and information about the particular change in magnetic field can be used to determine a particular stimulating signal to be generated by the NFC reader circuitry. At block  6510 , process  6500  can receive identification information read from the NFC tag. At block  6512 , process  6500  can modify a behavior of portable electronic device  5004  based on the identification information, for example, generating a color wash effect as described above. After block  6512 , process  6500  can optionally return to block  6502  to provide continuous monitoring of magnetometer  5080 . It should be understood that process  6500  is illustrative and that other processes may be performed in addition to or instead of process  6500 . 
     It will be appreciated that the NFC tag and NFC reader circuits described above are illustrative and that variations and modifications are possible. For example, coil designs can be modified by replacing wound wire coils with etched coils (or vice versa) and solenoidal coils with flat coils (or vice versa). “Wound wire” coils can be made using a variety of techniques, including by winding a wire, by stamping a coil from a copper sheet and molding plastic over the stamped part, or by using a needle dispenser to deposit wire on a plastic part; the wire can be heated so that it embeds into the softened plastic. Etched coils can be made by coating a surface with metal and etching away the unwanted metal. The number of turns in various NFC coils can be modified for a particular application. The choice of wound wire coils or etched coils for a particular device may depend on various design considerations. For instance, in devices that have an internal logic board, a wound wire NFC coil can terminate to the logic board; where a logic board is absent, an etched coil may simplify termination of the coil. Other design considerations may include the Q factor of the coil (a wound coil can provide higher Q in a smaller space) and/or ease of assembly. 
     Further, where a device that has an NFC tag circuit also has active circuitry (such as wireless charger devices that have active circuitry to control charging behavior), the NFC tag circuit is not limited to being a passive tag; an active NFC tag circuit can be provided to enable two-way communication with a compatible portable electronic device. For example, active NFC circuits in a portable electronic device and a wireless charger device can be used to support delivery of firmware updates to the wireless charger device. 
     Proximity-detection techniques can also be varied. For example, a different type of magnetometer (e.g., a single-axis magnetometer) can be used, or multiple magnetometers in different locations relative to the magnetic alignment components can be used. In some embodiments, a Hall effect sensor can be used instead of a magnetometer, although false positives may increase because a Hall effect sensor can generally only indicate a change or no-change rather than measuring a magnitude or direction of change. It should also be understood that proximity detection as described herein can be used for other purposes in addition to or instead of triggering an NFC reader circuit. 
     6. Example Devices Incorporating Magnetic Alignment Components 
     6.1. Wireless Charger Devices 
     Examples of wireless charger devices (or wireless chargers) incorporating annular magnetic alignment components are described above, e.g., with reference to  FIGS.  13  and  53 - 54   . As another example,  FIG.  66    shows an exploded view of a wireless charger device  6600  according to some embodiments, and  FIG.  67    shows a simplified partial cross-section view of wireless charger device  6600  according to some embodiments. Wireless charger device  6600  is similar to wireless charger device  1300  described above and can incorporate a magnetic alignment component (e.g., a primary annular alignment component as described above) as well as other features related to optimizing charging performance. 
     Wireless charger device  6600  can have a two-piece puck-shaped housing that includes a cap  6602  and an enclosure  6606 . Cap  6602 , which provides a charging surface for wireless charger device  6600 , can be made of polycarbonate or other plastic and coated on the proximal side (the top side in  FIGS.  66  and  67   ) with soft-touch silicone or the like to provide a durable surface. Other materials that are permeable to electromagnetic fields can also be used. In some embodiments, the proximal surface of top cap  6602  can be a low-friction surface (e.g., textured silicone), as wireless charger device  6600  can rely on magnetic forces rather than friction for maintaining alignment with a device to be charged. Enclosure  6606  can be made of aluminum, other electrically conductive materials, or a plastic material. As best seen in  FIG.  67   , enclosure  6606  can include a rear housing  6601 , a sidewall  6603 , and an overhanging lip  6605  with a recessed ledge  6609  on which top cap  6602  can rest. Top cap  6602  can have a small offset (e.g., 150 μm) above the upper surface of lip  6605 , to prevent ferrous particles that may stick to lip  6605  from scratching the surface of a device placed in proximity to top cap  6602 . In some embodiments, top cap  6602  can be sealed to recessed ledge  6609  using a suitable sealing material. Enclosure  6606  can include an opening  6607  through sidewall  6603  to allow electrical conduits (e.g., wires) to be connected between the interior and exterior of wireless charger device  6600 . 
     An annular magnetic alignment component  6616  can include arcuate magnets  6626  disposed on an annular DC shield  6614 . Magnetic alignment component  6616  can be an implementation of any of the primary annular alignment components described above. For example, each arcuate magnet  6626  can have a quad-pole configuration with an inner arcuate region having magnetic polarity oriented in a first axial direction, an outer arcuate region having magnetic polarity oriented in a second axial direction opposite the first direction, and a central non-magnetized region between the inner arcuate region and the outer arcuate region. In some embodiments, DC shield  6614  can be segmented, e.g., into four arcuate segments, and each segment of DC shield  6614  can have one or more arcuate magnets  6626  mounted thereon. The segments can be individually inserted into enclosure  6606  such that each segment fits under lip  6605  and the segments are adjacent to each other (either abutting or having small gaps to accommodate manufacturing tolerances). Fiducial surface features may be provided on the inner surface of enclosure  6606  to facilitate correct positioning of each segment. A gap  6617  that is large enough to accommodate electrical connection paths can be provided between two adjacent segments of annular magnetic alignment component  6616 , and gap  6617  can be aligned with opening  6607  in enclosure  6606 . To maximize the magnetic alignment force exerted by annular magnetic alignment component  6616  on a portable electronic device placed adjacent to the top surface of cap  6603 , annular magnetic alignment component  6616  can be positioned such that the proximal surfaces of magnets  6626  are adjacent to (e.g., in contact with) the inner surface of lip  6605 . In some embodiments, DC shield  6614  can rest on the inner surface of rear housing  6601  of enclosure  6606 , and annular magnetic alignment component  6616  can extend to the full height of the inner side of sidewall  6603  so that the proximal surfaces of magnets  6626  are adjacent to the inner surface of lip  6605 . In other embodiments, annular magnetic alignment component  6616  can be shorter than the inner side of sidewall  6603 , and a spacer  6615  (shown in  FIG.  67   ) can be positioned between DC shield  6614  and rear housing  6601  so that magnets  6626  are adjacent to the underside of lip  6605 . In any event, adhesives (not shown) can be used to hold magnetic alignment component  6616  (or sectors thereof) in position. 
     A charging coil assembly  6612  can include a coil  6620 , an electric shield  6622 , electromagnetic shields  6626 ,  6628 , and a shim  6624 . Coil  6620  can be a coil of wound copper wire with terminals toward the center of the coil, having a proximal surface oriented toward top cap  6601  and an opposing distal surface. An upper electromagnetic shield  6626  and a lower electromagnetic shield  6628  can be made of ferrimagnetic material (e.g., MnZn). Upper electromagnetic shield  6626 , which provides primary field shaping for coil  6620 , can be contoured to surround the distal surface and outer sides of coil  6620  and can have a slit  6627  to provide space for a wire extending from the outer edge of coil  6620  to the terminal point in the center region of coil  6620 . Lower electromagnetic shield  6628 , which acts as a spacer for a main logic board  6632 , can be flat and shaped to underlie coil  6620  with a trench to accommodate the wire extending from the outer edge of coil  6620  to the terminal point in the center region of coil  6620 . Lower electromagnetic shield  6628  can be grounded to enclosure  6606 . In some alternative embodiments, lower electromagnetic shield  6628  can be replaced with a plastic spacer. In other alternative embodiments, upper electromagnetic shield  6626  and lower magnetic shield  6628  can be formed from a single piece of ferrite material. An electric shield  6622  can be positioned over the proximal surface of coil  6620 . Electric shield  6622  can be made of a flexible printed circuit board patterned with conductive material to block electric fields while being permeable to magnetic fields. Electric shield  6622  can include peripheral conductive protrusions that can be in contact with enclosure  6606  to provide grounding. Shim  6624  can be made of a polycarbonate material and can be used to provide a uniform height across the proximal surface of charging coil assembly  6612 , helping to support cap  6602 . 
     A support ring subassembly  6640  can be positioned between annular magnetic alignment component  6616  and coil assembly  6612  (as best seen in  FIG.  67   ). Support ring subassembly  6640  can be an implementation of support ring subassembly  5340  described above with reference to  FIGS.  53  and  54   . For example, support ring subassembly  6640  can include an annular frame  6642  and an NFC coil  6664 . Annular frame  6642  can be made, e.g., of glass-reinforced polycarbonate or other plastics. NFC coil  6664  can be, e.g., a wound copper coil of 4 or 5 turns. NFC coil  6664  can be coupled to NFC tag circuitry that can be disposed on main logic board  6632 . NFC coil  6664  and associated tag circuitry can be used for device identification as described in section 5 above. 
     Main logic board  6632  can be disposed on a central portion of rear housing  6601  of enclosure  6606  and secured in place with a pressure-sensitive adhesive  6634 . Main logic board  6632  can include contact pads for connecting to external wires through opening  6607  of enclosure  6606  and additional ground contacts for grounding enclosure  6606  and electric shield  6622 . Main logic board  6632  can also include circuit components to control operation of coil  6620 . For example, depending on implementation, main logic board  6632  can be coupled to receive DC power via the contact pads and can include power circuitry for driving coil  6620  (e.g., a boost circuit and an inverter). In addition or instead, main logic board  6632  can include logic circuits (e.g., a microcontroller, ASIC, FPGA, or the like) to monitor the behavior of coil  6620  and to control current supplied to coil  6620  based on the monitoring. Examples of control logic for operating a wireless charging coil are known in the art; for instance, the logic circuits can implement functionality confirming to the Qi standard for wireless charging. In some embodiments, main logic board  6632  can also include NFC tag circuit components coupled to NFC coil  6664 . In some embodiments, logic circuits, power circuits, and/or NFC tag circuits can be implemented as integrated circuits mounted on main logic board  6632 , and the integrated circuits may be covered by shield cans to avoid electrical interference. 
     In some embodiments, thermal performance of wireless charger device  6600  can be improved by placing some or all of the power circuitry at a location external to enclosure  6606 . For example,  FIG.  68    shows an exploded view of a cable assembly  6800  with incorporated power circuitry that can be connected to wireless charger device  6600  according to some embodiments. (Portions of wireless charger device  6600 , in particular enclosure  6606  and annular alignment component  6616  are shown to facilitate understanding of the connection.) Cable assembly  6800  can include a cable  6802 , which can be of any length desired and can include multiple wires (or other electrical conductors) that are electrically insulated from each other to carry power, ground, and data signals. Cable  6802  has a proximal end  6804  that can be captively coupled to wireless charger device  6600 . For example, proximal end  6804  of cable  6802  can be inserted through opening  6607  in enclosure  6606  and secured using a crimp  6806 . In various embodiments, crimp  6808  can be welded to enclosure  6606  or to DC shield  6614 . 
     Cable  6802  has a distal end  6808  that can be captively coupled to a boot assembly  6810 . Boot assembly  6810  can include a boot housing  6812  made of a plastic such as polycarbonate, polybutylene terephthalate (PBT), or the like. A crimp  6814  (e.g., made of stainless steel) can secure distal end  6808  of cable  6802  to the interior of boot housing  6812 . 
     A circuit board  6822  can be disposed inside boot housing  6812 . Circuit board  6822  can include power circuitry such as a DC boost circuit and optionally an inverter. Circuit board  6822  can also include logic circuitry to control operation of the power circuitry. Similarly to main logic board  6632  described above, the power and/or logic circuitry can be implemented using integrated circuits mounted on the surface(s) of logic board  6632 . Circuit board  6822  can be connected to a connector  6824 , which can be, e.g., a USB-C plug connector or other standard connector. Connector  6824  can be removably connected to an external power source (not shown) such as a USB-C adapter module that can be plugged into a standard power outlet. 
     An electromagnetic interference (EMI) shell  6818  can line the interior of boot housing  6812  around circuit board  6822 . EMI shell  6818  can be made of a copper alloy (e.g., brass) or other conductive material and can reduce electromagnetic interference that may be caused by operation of circuitry on circuit board  6822 . In some embodiments, crimp  6814  can be laser-welded to EMI shell  6818 . Electrical isolation between circuit board  6822  and EMI shell  6818  can be provided using electrically insulating components such as board brace  6820  and clamshells  6826 . Faceplate  6828  can be disposed over the distal end of circuit board  6822  and secured to boot housing  6812  such that connector  6824  protrudes through the opening in faceplate  6828 . In some embodiments, the interior of boot housing  6812  can be filled with a thermally conductive potting material prior to attaching faceplate  6828  to improve heat transfer away from circuit board  6822 . 
     In some embodiments, all power circuitry can be disposed on circuit board  6822 , and cable  6802  can carry alternating current to wireless charger device  6600 . In these embodiments, main logic board  6632  within wireless charger device  6600  can couple the AC wires of cable  6802  to coil  6620 . In other embodiments, circuit board  6822  may include a portion of the power circuitry, e.g., a DC boost circuit, while other portions of the power circuitry (e.g., an inverter) are disposed on main logic board  6632 . It will be appreciated that power circuitry can generate significant amounts of heat and that placing some or all of the power circuitry in boot assembly  6810  rather than within enclosure  6606  can reduce the amount of heat generated within enclosure  6606 . In some embodiments, logic circuitry on main logic board  6632  can monitor the temperature locally, in boot assembly  6810  (e.g., based on signals from circuit board  6822 ), and in the portable electronic device being charged (e.g., using Qi communication protocols) and can reduce the charging current if temperature at any monitored location exceeds a preset upper limit. Providing high thermal conductivity in boot assembly  6810  can avoid having boot assembly  6810  become a limiting factor for charging performance. 
     Regardless of where the power circuitry is located, main logic board  6632  within enclosure  6606  can include logic circuits to monitor the behavior of coil  6620  and to control any power circuitry that may be located on main logic board  6632  and/or to send control signals to circuit board  6822  via data wires included in cable  6802  (e.g., implementing FC or other point-to-point communication protocols). Circuit board  6822  can include logic circuits to respond to control signals received from main logic board  6632 , e.g., by controlling power circuitry located on circuit board  6822 . 
     It will be appreciated that wireless charger device  6600  and associated cable assembly  6800  are illustrative and that variations and modifications are possible. For example, the particular configuration of the charging coil assembly, the annular magnetic alignment component, and NFC coil assembly can be modified, e.g., according to any of the embodiments described herein. In some embodiments, an NFC coil can be omitted entirely. In some embodiments, all power and logic circuitry can be located on main logic board  6632 , and boot assembly  6810  can be replaced by a standard cable boot assembly with a plug connector, such as a USB-C boot assembly. Further, the puck shape is not required, and a wireless charger device can have a larger form factor and/or a different shape. For example, a wireless charger device can be rectangular and can incorporate a rotational alignment component as described in section 2 above. A wireless charger device can be designed to meet various standards for avoiding demagnetization of magnetic-stripe cards placed on it; for example, the wireless charger device may be HiCo safe (i.e., does not demagnetize cards that were magnetized to the HiCo standard) but not LoCo safe (i.e., may demagnetize cards that were magnetized to the LoCo standard). 
     6.2. Portable Electronic Devices 
     Examples of portable electronic devices incorporating annular magnetic alignment components are described above, e.g., with reference to  FIGS.  12 A- 12 B,  16 , and  50 - 52   . Another example will now be described. 
       FIG.  69 A  shows an example of a portable electronic device  6900 . In this example, portable electronic device  6900  is a smart phone that has a wireless charging module  6902  that incorporates an inductive receiver coil assembly, annular alignment magnets, and an NFC reader coil. Wireless charging module  6902  is described further below. A conduit  6904  provides a pathway for electrical connections between wireless charging module  6902  and other device components  6906 , which can include, e.g., a main logic board for the portable electronic device, power management circuitry, battery, and the like. The particular configuration of components  6906  is not relevant to understanding the present disclosure. Portable electronic device  6900  can also include a rotational alignment component  6908 , which can be implemented according to any of the embodiments described in section 2 above. 
       FIG.  69 B  shows a cross section view of wireless charging module  6902  through cut line A-A of  FIG.  69 A . Wireless charging module  6902  can include a charging coil assembly  6912 , which can include an inductive charging coil  6913  and shielding components  6914 . The particular design of charging coil assembly  6912  is not critical to understanding the present disclosure. Wireless charging module  6902  can also include an annular magnetic alignment component  6916 , which can be an implementation of any of the secondary annular magnetic alignment components described above. Wireless charging module  6902  can also include an NFC coil  6960 , which can be disposed in a gap between annular magnetic alignment component  6916  and charging coil assembly  6912 . NFC coil  6960  can be, e.g., a single-turn two-stranded copper wire disposed on or within a shim  6962 , which can be made of polycarbonate or the like. In some embodiments, shim  6962  can facilitate manufacturing of NFC coil  6960  and alignment of NFC coil  6960  with other components of wireless charging module  6902 . 
       FIG.  70    shows a more detailed top view of wireless charging module  6902  according to some embodiments. As described in sections 1 and 3 above, annular alignment component  6916  can include a number of arcuate magnets  6918  arranged in an annular configuration, and each arcuate magnet  6918  can have a magnetic orientation with a radial component. A gap  6940  can be provided between arcuate magnets  6918   a  and  6918   b  to facilitate electrical connections to NFC coil  6960  and to wireless charging module  6902 . In particular, terminals  6962   a ,  6962   b  of NFC coil  6960  can extend into gap  6940 . Likewise, outer terminal  6912   a  of the inductive coil of charging assembly  6912  can also extend into gap  6940 . Inner terminal  6912   b  of the inductive charging coil of coil assembly  6912  can be exposed through a central opening in the coil shield. As shown in  FIG.  69 A , conduit  6904  can extend to gap  6940  and over the center of wireless charging module  6902  and can include conductive traces or wires to provide electrical connections between wireless charging module  6902  and other components  6906 . In some embodiments, other components  6906  can include NFC reader circuit components coupled to NFC coil  6960  and a magnetometer (or other sensor) and associated control logic to trigger operation of NFC coil  6960  when an accessory having a complementary annular magnetic alignment component comes into proximity. 
     NFC coil  6960  can be implemented in various ways, including single-turn coils fabricated using a variety of manufacturing techniques.  FIGS.  71 A- 71 D  show cross section views of NFC coils that can be used in wireless charging module  6902  according to various embodiments.  FIG.  71 A  shows a double-stranded wire  7102  disposed in a coil shim  7104  (similar to the embodiment of  FIG.  69 B ).  FIG.  71 B  shows a triple-stranded wire  7112  disposed in a coil shim  7114 . In some embodiments, one strand of wire  7112  can be a nonconductive (or dummy) strand, which may provide improved RF performance for the NFC coil.  FIG.  71 C  shows an embodiment in which coil  7122  is insert-molded into a shim  7124 . For example, a single-turn coil  7122  can be stamped from a copper foil, after which shim  7124  can be molded around coil  7122 . Stamping and insert molding can allow custom shaping of the NFC coil, e.g., varying width or thickness of the stamped coil along its length, which may provide performance improvements.  FIG.  71 D  shows an embodiment in which coil strands  7122   a ,  7122   b  are needle-dispensed into a shim  7134 . A needle dispenser can deposit wires  7122   a ,  7122   b  onto molded plastic shim  7134 ; the wires can be heated during deposition so that they embed into the softened plastic. As with stamping and insert molding, needle-dispensing can allow custom shaping of the NFC coil, e.g., varying the strand cross-section and/or separation distance between strands along the length of the coil. Any of these or other techniques for forming an NFC coil can be used. 
     It will be appreciated that portable electronic device  6900  and wireless charging module  6902  are illustrative and that variations and modifications are possible. For example, it is assumed that coil assembly  6912  operates as a receiver coil to receive power via wireless power transfer. In some embodiments, coil assembly  6912  can be reconfigurable as a transmitter coil to provide power to another device. Moreover, the particular configuration of the charging coil assembly, the annular magnetic alignment component, and NFC coil assembly can be modified to suit a specific application, e.g., according to any of the embodiments described herein. In some embodiments, an NFC coil can be omitted entirely. 
     6.3. Cases 
     Examples of cases for a portable electronic device are described above, e.g., with reference to  FIGS.  27 ,  55 - 61 , and  63   . Another example will now be described. For purposes of description, it is assumed that the case is a tray that covers the back and side surfaces of the portable electronic device, leaving the front surface (which may include a display) exposed. It is also assumed that at least the rear panel of the tray is made of a transparent material (e.g., transparent plastic) so that the back surface of the portable electronic device is visible through the back panel. It should be understood that neither of these assumptions is required; a case can have a variety of form factors, can be made of a variety of materials, and may or may not have a transparent portion. 
       FIG.  72    shows an rear view of a case  7200  according to some embodiments. Case  7200  can be a case for a smart phone (e.g., smart phone  6900  of  FIG.  69   ) or other portable electronic device. Case  7200  can be shaped as a tray and can have a rear panel  7202  that covers the back surface of the portable electronic device when case  7200  is placed on the portable electronic device. Rear panel  7202  can be made of a rigid material such as plastic, and the material can be a transparent material. Rear panel  7202  need not cover all of the rear surface of the portable electronic device; for example, a cutout area  7203  can be provided to expose a rear camera lens of the portable electronic device. Side panels  7204  of case  7200  can be made of a more pliant material with a higher coefficient of friction and can include lips or other surface features that can facilitate securing a phone into case  7200 . The particular construction of side panels  7204  is not relevant to understanding the present disclosure. 
     Rear panel  7202  can include an annular magnetic alignment assembly  7206  and a rotational alignment assembly  7210 . Annular magnetic alignment assembly  7206  can include implementation of any of the auxiliary annular magnetic alignment components described above, as well as an NFC coil and tag circuit. Rotational alignment assembly  7210  can include an implementation of any of the rotational alignment components described above. In some embodiments, case  7200  can be a charge-through accessory that allows a portable electronic device to receive power from a wireless charger device without removing case  7200 . 
     In the absence of transparent magnetic materials, annular magnetic alignment assembly  7206  and rotational alignment assembly  7210  are assumed to include opaque elements, and rear panel  7202  would not be transparent in the regions occupied by annular magnetic alignment assembly  7206  and rotational alignment assembly  7210 . In some embodiments, the magnetic alignment components can be designed to reduce disruption of the transparent esthetic of back panel  7202 . For example, as shown in  FIG.  72   , rotational alignment assembly  7210  can be shaped with rounded corners to echo the round shape of annular alignment assembly  7206 . Annular alignment assembly  7206  can be constructed using design techniques that minimize the radial width of the opaque annulus. In some embodiments, some or all surfaces of annular alignment assembly  7206  and rotational alignment assembly  7210  can be covered with an opaque cosmetic material (e.g., a plastic or adhesive that is white or colored to match the side surfaces  7204  of case  7200 . This opaque cosmetic material can conceal the internal structures of annular alignment assembly  7206  and rotational alignment assembly  7210  from view when case  7200  is in use. 
     In various embodiments, annular alignment assembly  7206  can be implemented using techniques described in section 5.3 above (e.g., with reference to  FIGS.  59 - 61  and  63   ). In other embodiments, the design can be modified to further reduce the radial width of annular alignment assembly  7206 .  FIG.  73 A  shows a simplified axial view of internal components of an annular alignment assembly  7206  according to some embodiments, and  FIG.  73 B  shows a cross section through cut line  7322  of  FIG.  73 A . 
     Annular alignment assembly  7206  can include an annular magnetic alignment component  7370 , which can be an implementation of any of the auxiliary magnetic alignment components described above. For example, auxiliary magnetic alignment component  7370  can include a number of arcuate magnets  7372  arranged in an annular configuration. Each arcuate magnet  7372  can have a quad-pole configuration with an inner arcuate region having magnetic polarity oriented in a first axial direction, an outer arcuate region having magnetic polarity oriented in a second axial direction opposite the first direction, and a central non-magnetized region between the inner arcuate region and the outer arcuate region. An NFC tag circuit subassembly  7366  can include an annular NFC antennal coil  7304  disposed inboard and near the inner edge of annular magnetic alignment component  7370  and an NFC tag circuit  7302  disposed in a gap between magnets  7372   a ,  7372   b .  FIG.  73 B  shows the positioning of NFC antenna coil  7304  relative to annular alignment component  7370 . NFC antenna coil  7304  can be a wound wire coil of, e.g., 5 or 6 turns, formed on a tape layer  7306 . 
       FIG.  73 C  shows a more detailed view of NFC tag circuit  7302  according to some embodiments. As shown, NFC tag circuit  7302  can include tag circuit components  7332  disposed on a flexible PCB  7334 . Like other NFC tag circuit components referred to herein, tag circuit components  7332  can be of conventional design and can include a tag chip and supporting components such as capacitors. NFC antenna coil  7304  can terminate into flexible PCB  7334 . 
     As shown in  FIG.  73 B , using wound NFC antenna coil  7304  can allow the radial width of NFC antenna coil  7304  to be reduced relative to etched-coil embodiments described in section 5.3 above. To further reduce width, arcuate magnets  7372  can be made with a reduced radial width. In some embodiments, to compensate for the reduction in magnetic field strength resulting from reduced width, the thickness of arcuate magnets  7372  can be increased. 
       FIG.  74    shows an exploded view of annular alignment assembly  7206  and rotational alignment assembly  7210  according to some embodiments. Shown at the bottom and top of  FIG.  74    are a carrier sheet  7402  and pull tab  7404 . Carrier sheet  7402  and pull tab  7404  can be made of silicone-coated PET or the like. In some embodiments, carrier sheet  7402  and pull tab  7404  are used to facilitate construction of annular alignment assembly  7206  and rotational alignment assembly  7210  and are removed before or during installation of annular alignment assembly  7206  and rotational alignment assembly  7210  into an accessory. Annular alignment assembly  7206  can include a bottom film  7410 , a coil shim  7412 , NFC antenna coil  7304 , PCB  7334 , annular alignment component  7370 , and a cosmetic cap  7414 . Rotational alignment assembly  7210  can include a bottom film  7420 , one or more rotational alignment magnets  7422 , and a cosmetic cap  7424 . Rotational alignment magnet(s)  7422  can implement a rotational alignment component as described in section 2 above; various magnetization patterns can be used. 
     Bottom films  7410 ,  7420  can be made of materials such as an industrial film coated with pressure-sensitive adhesive. Coil shim  7412  can provide height alignment for NFC coil  7304  and PCB  7334  with annular alignment component  7370 . In some embodiments, coil shim  7412  can have a patterned section  7413  that has openings corresponding to the locations of tag circuit components  7332  (which are on the underside of PCB  7334  in the view shown in  FIG.  74   ). Patterned section  7413  can help to provide uniform thickness for annular alignment assembly  7206 , avoiding bumps or dimples associated with tag circuit components  7332 . Terminal ends  7415   a ,  7415   b  of NFC coil  7304  can connect to pads on PCB  7334 . PCB  7334  can fit into gap  7417  in annular alignment component  7370 . Cosmetic caps  7414 ,  7424  can be made of polycarbonate and adhered to magnetic alignment components  7370 ,  7422  using pressure-sensitive adhesive. As noted above, cosmetic caps  7414 ,  7424  can have a color and/or pattern selected for esthetic effect. 
       FIG.  75    shows a cross-section view of a portion of rear panel  7202  of case  7200  according to some embodiments, showing a portion of annular alignment assembly  7206 . Rear panel  7202  has an inner surface  7501  that would be oriented toward the interior of the case, contacting the back surface of a portable electronic device that is inserted into the case. Rear panel  7202  also has an outer surface  7503 , which is an exterior surface that is visible when a portable electronic device is inserted into the case. In this example, outer surface  7503  has a raised area in the vicinity of annular alignment assembly  7206 ; however a raised area is not required, and outer surface  7503  of rear panel  7202  can be flat. Annular alignment assembly  7206  can be inset into outer surface  7503  with cosmetic cap  7414  facing outward. Gaps between the sides of annular alignment assembly  7206  and rear panel  7202  can be filled, e.g., by an opaque liquid adhesive  7520 . 
     It will be appreciated that case  7200 , annular alignment assembly  7206 , and rotational alignment assembly  7210  are illustrative and that variations and modifications are possible. For example, an alignment assembly similar to assembly  7206  can be constructed for any of the combinations of NFC tag circuits and annular magnetic alignment components described in section 5 above, and an annular alignment assembly can be inserted into a rear panel of a case, which might be transparent, translucent, or opaque. A rotational alignment component or assembly can be included or omitted as desired. Further, an annular alignment assembly can be inserted into other types of accessories, not limited to cases, with or without a rotational alignment assembly. 
     Annular alignment assembly  7206  is designed for use in a rigid case or other accessory. However, cases and other accessories need not be rigid. For example, a case can be formed as a sleeve having front and rear panels with an open end (or “throat”) into which a portable electronic device can be inserted so that the front and back sides of the portable electronic device are covered. For ease of insertion and removal, it can be helpful to construct the front and rear panels with at least some degree of flexibility. In some embodiments, a flexible annular magnetic alignment component can be provided by constructing the annular magnetic alignment component from a thin magnet made of polymers infused with a powdered ferromagnetic material or the like. Flexible or rubberized polymers can be used so that the resulting magnet has some flexibility. In some embodiments, a single flexible annular magnet can be formed, or a flexible annular magnetic alignment component can be formed of multiple arcuate sections. The axial thickness may be kept small to optimize flexibility. Flexible magnets, however, tend to have lower magnetic field strength than rare earth magnets. In some embodiments where portable electronic device uses a magnetometer to detect proximity of an accessory having an annular alignment component (e.g., as described in section 5.4 above), the magnetometer may not be able to reliably sense the field of the flexible magnet without setting thresholds so low as to result in a high rate of false positives. Accordingly, in some embodiments, a flexible annular alignment component can be modified to increase its magnetic field strength. For example, the radial width of the flexible annular alignment component can be increased, either around the entire circumference or just in a region (e.g., a quadrant) close to the magnetometer. The latter option may create a rotational asymmetry of magnetic field that can result in a “clocking” effect. As another technique to increase sensed magnetic field, an additional flexible magnet (referred to herein as a “triggering” magnet) can be placed outboard of the annular alignment component. For example, a small square or rectangular triggering magnet can be placed at a location that would be close to the magnetometer (e.g., magnetometer  5080  in  FIG.  50   ) when the sleeve is in alignment with the mobile device. In some embodiments, the sleeve may be a charge-through accessory, and it may be desirable to avoid having the triggering magnet interfere with detection of a second accessory attaching to the distal surface of the charge-through accessory. Accordingly, a triggering magnet can have a weak magnetic field that can be sensed due to short distance to the magnetometer. 
     7. Alignment Modules 
     As described above, magnetic alignment components can be incorporated into a variety of devices, including portable electronic devices and accessories such as cases and wireless charger devices. In some embodiments, a magnetic alignment component can be provided in an alignment module (optionally with other components such as an inductive charging coil) that can be incorporated into a device. An alignment module can include an annular alignment component (which can be a primary, secondary, or auxiliary alignment component) enclosed in a package that is sized and shaped to facilitate incorporation into a variety of devices in which an alignment component can be included. In some embodiments, the alignment module can also include a rotational alignment component (as described in section 2 above) enclosed in the same package and held in the desired position relative to the annular alignment component. In some embodiments, the package may also enclose a wireless charging coil and/or an NFC tag circuit as described above. In embodiments where the alignment module includes active circuitry (such as an inductive charging coil assembly and/or logic board), electrical contacts may be provided at the exterior of the package to enable connection to the included active circuitry. Examples will now be described. 
     7.1. Charger Alignment Modules 
     Alignment modules according to some embodiments may include a wireless charging coil and an annular alignment component.  FIGS.  76 A and  76 B  show top and bottom perspective views of a charger alignment module  7600  according to some embodiments. Charger alignment module  7600  has a two-piece housing that includes a cap  7601  (best seen in  FIG.  76 A ) and a rear enclosure  7606  (best seen in  FIG.  76 B ). Cap  7601  can provide a cosmetic face that may be visible to a user when charger alignment module  7600  is incorporated into an accessory device such as a docking station. Cap  7601  can include a charging surface  7604  and a surrounding rim region  7602 . Charging surface  7604  can be made of silicone or plastic with a hard-touch coating, or any other material that is permeable to AC and DC magnetic fields. Rim region  7602  can be made of plastic or other material that is permeable to DC magnetic fields. Rear enclosure  7606  can be made of metal (e.g., aluminum) and shaped to accommodate an inductive charging coil and a logic board as described below. In some embodiments, it is assumed that rear enclosure  7606  will not be visible to a user when charger alignment module  7600  is incorporated into an accessory device such as a docking station. Rear enclosure  7606  can include an opening  7608  with exposed electrical contacts  7610 . As described below, exposed electrical contacts  7610  can be disposed on a logic board and coupled by conductive traces to components housed inside charger alignment module  7600 . In some embodiments, exposed electrical contacts  7610  include contacts for electrical power for the charging coil and contacts for USB data signals (D+ and D−), power, and ground; however, any combination of contacts may be provided. In addition, coil calibration contacts  7612  may also be exposed within rear enclosure  7606 . In some embodiments, coil calibration contacts  7612  are exposed during manufacture of charger alignment module  7600  to support calibration of the inductive charging coil inside charger alignment module  7600  (e.g., testing of coil resistance); after calibration, contacts  7612  can be covered with an encapsulating sealant material prior to delivering charger alignment module  7600  to a third party for incorporation into an accessory device. 
       FIG.  77    shows an exploded view of charger alignment module  7600  according to some embodiments. Cap  7601  is shown at the top, and rear enclosure  7606  is shown at the bottom. A primary annular alignment component  7716  is disposed under cap  7601 , e.g. under rim region  7602 . Primary annular alignment component  7716  can be an implementation of any of the primary annular alignment components described above. For example, primary annular alignment component  7716  can include primary arcuate magnets  7717  arranged in an annular configuration with each primary arcuate magnet  7717  having a quad-pole configuration with an inner arcuate magnetic region having magnetic polarity oriented in a first axial direction, an outer arcuate magnetic region having magnetic polarity oriented in a second axial direction opposite the first direction, and a central non-magnetized region between the inner arcuate magnetic region and the outer arcuate magnetic region. An annular DC magnetic shield  7719  can be disposed on the distal surface of primary arcuate magnets  7717 . As described above, DC magnetic shield  7719  can be made of steel or other material having high magnetic permeability and can redirect magnetic fields to prevent them from propagating beyond the distal side of primary annular alignment component  7716 . 
     An inductive charging coil assembly  7712  can be disposed inboard of primary annular alignment component  7716 . Inductive charging coil assembly  7712  can include an inductive charging coil  7720 , an electric shield  7722  disposed on a proximal side of inductive charging coil  7720 , an electromagnetic shield  7726  disposed on a distal side of inductive charging coil  7720 , and a shim  7724 . Inductive charging coil  7720  can be a wound wire coil. Electric shield  7722  can include a thin layer of conductive material to block or reduce AC electric fields during operation of coil  7720  while being permeable to magnetic flux. Electromagnetic shield  7726  can be a ferrite or the like that extends over the distal surface and outer sides of coil  7720 . Shim  7724  can be made of plastic or other nonconductive material and can be provided to level coil  7720  with the top of electromagnetic shield  7726 , providing additional support for charging surface  7604 . A variety of inductive charging coil assemblies can be used as inductive charging coil assembly  7712 . 
     A fence  7728  can be formed of aluminum or the like and interposed between the outer side of electromagnetic shield  7726  and the inner side of DC shield  7719 . Fence  7728  can provide isolation of electromagnetic shield  7726  from DC shield  7719 , helping to keep DC magnetic flux from entering the region of coil  7720 , which may improve charging efficiency. 
     DC shield  7718 , fence  7728 , and electromagnetic shield  7726  can be mounted on a midplate  7730 . Midplate  7730  can be made of aluminum or other electrically conductive material. An opening  7731  through midplate  7730  can be provided to allow electrical connections to the end terminals of coil  7720 . In some embodiments, midplate  7730  can be welded to rear enclosure  7606  and to fence  7728 . In some embodiments, the thickness of annular alignment component  7716  can be equal to the thickness of coil assembly  7712 . In embodiments where annular alignment component  7716  is thinner than coil assembly  7712 , spacers (similar to spacers  6615  of  FIG.  67   ) can be used to position magnets  6626  adjacent to cap  6602 . 
     A logic board  7732  can be mounted on the distal surface of midplate  7730  using an adhesive  7734 , which can be, e.g., a temperature sensitive adhesive. Logic board  7732  can be a printed circuit board with electronic components mounted on the underside (not shown in  FIG.  77   ). The electronic components can include power circuitry (e.g., boost circuit, inverter) to drive inductive charging coil  7720  and control circuitry (e.g., a microcontroller, FPGA, ASIC, or the like) to control operation of the power circuitry. Examples of suitable components and circuits are known in the art, and a detailed description is omitted. Rear enclosure  7606  can be shaped to accommodate the electronic components on the underside of logic board  7732 , and midplate  7730  can provide shielding between logic board  7732  and coil  7720 . The underside of logic board  7732  can also include external electrical contacts that align with opening  7608  in rear enclosure  7606  (e.g., contacts  7610 ,  7612  as shown in  FIG.  76 B ). The top surface of logic board  7732  (shown in  FIG.  77   ) can be partially covered by adhesive  7734 , leaving certain regions exposed. For example, exposed region  7735  can align with opening  7731  in midplate  7730  and may include contacts  7736  for connecting to the terminals of coil  7720 . As another example, a grounded region  7738  can be exposed at the periphery of logic board  7732 . Grounded region  7738  can provide electrical grounding for midplate  7730 . 
     It will be appreciated that charger module  7600  is illustrative and that variations and modifications are possible. A variety of inductive coils and shielding arrangements can be used, and any of the annular alignment components described above may also be included. Further, while charger module  7600  is not shown as including an NFC tag circuit and coil, those skilled in the art with access to the present disclosure will appreciate that an NFC tag circuit and coil can be incorporated similarly to other examples of wireless charger devices described above. In some embodiments, charger module  7600  can include a wound NFC coil terminates to external electrical contacts  7608 , and a third-party accessory manufacturer can couple the NFC coil to an external NFC tag circuit, allowing the accessory manufacturer to control the tag data. Exposed contacts are helpful to enable a third party to connect external wiring or other components to charger module  7600 . In the embodiment shown, the external contacts are exposed through the rear surface of the housing; however external contacts can be exposed through any surface of the housing. For cosmetic reasons, it may be undesirable to expose the external contacts through the front surface of the charger module and to instead use surfaces (such as the rear surface or a side surface) that are expected to be hidden from view when the charger module is incorporated into an accessory. 
     In addition, a puck shape is not required, and a charger module can have a larger form factor. For example, a charger module can have a rectangular or teardrop-shaped top surface and can incorporate a rotational alignment component as described in section 2 above.  FIG.  78    shows a top perspective view of a teardrop-shaped charger module  7800  according to some embodiments. Charger module  7800  can be similar or identical to charger module  7600  except for the shape of the housing  7801 . Top cap  7802  can include a charging area  7804  under which an assembly including a charging coil assembly, annular magnetic alignment component (e.g., as shown in  FIG.  77   ), and control circuitry can be provided. Top cap  7802  can also include an extension portion  7810 , and a rotational magnetic alignment component  7812  can be disposed in extension portion  7810  at an appropriate distance from the center of the annular magnetic alignment component as described above in section 2. The bottom enclosure of charger module  7800  can also extend similarly to top cap  7802 . Other shapes, including rectangular shapes (e.g., as shown in  FIG.  16   ), can also be provided. 
     7.2. Accessory Insert Modules 
     In some embodiments, an alignment module is provided for insertion into a “passive” accessory that does not include an inductive charging circuit.  FIG.  79 A  is a front view and  FIG.  79 B  is a top view of an accessory insert module  7900  according to some embodiments. As shown in  FIG.  79 A , accessory insert module  7900  can be shaped as a rectangle with rounded corners as shown (or with square corners if desired) and can have flat front and back surfaces. As shown in  FIG.  79 B , accessory insert module  7900  can have a layered structure with front and back outer layers  7902 ,  7904 , which can be made of encapsulant material (e.g., plastic) and a central magnet-holding layer  7910 . Adhesive layers  7906 ,  7908  can be disposed between front and back outer layers  7902 ,  7904  and central magnet-holding layer  7910 . 
       FIG.  80    shows an exploded view of accessory insert module  7900  according to some embodiments. Central magnet-holding layer  7910  can be made of plastic with an annular opening  8026  and a rectangular opening  8032 . Annular opening  8026  can be sized and shaped such that an annular alignment component  8070  fits within annular opening  8026 . Annular alignment component  8070  can be an implementation of any of the auxiliary annular alignment components described above. For example, auxiliary annular alignment component  8070  can include primary arcuate magnets  8072  arranged in an annular configuration with each primary arcuate magnet  8072  having a quad-pole configuration with an inner arcuate magnetic region having magnetic polarity oriented in a first axial direction, an outer arcuate magnetic region having magnetic polarity oriented in a second axial direction opposite the first direction, and a central non-magnetized region between the inner arcuate magnetic region and the outer arcuate magnetic region. Rectangular opening  8032  can be sized and shaped such that a rotational alignment component  8022  fits within rectangular opening  8032 . Rotational alignment component  8022  can be an implementation of a rotational alignment component as described above and can include, for example, one or more magnets having a z-pole, quad-pole, triple-pole, or annulus design configuration. 
     In some embodiments, magnet-holding layer  7910 , annular alignment component  8070 , and rotational alignment component  8022  can all have the same z-height, which can help to keep accessory insert module  7900  flat in the lateral (xy) plane, particularly where the overall z-height of accessory insert module  7900  is small. In the example shown, magnet-holding layer  7910  includes a region  8030  inboard of annular alignment component  8070  that is detached from the rest of magnet-holding layer  7910 . As shown, region  8030  can be occupied by a discrete disc of material having the same thickness as the rest of magnet-holding layer  7910 , and this too can help to preserve the lateral flatness of accessory insert module  7910 . In other embodiments, region  8030  can be empty. 
     Accessory insert module  7900  can be used in an accessory such as a case for a portable electronic device. To reduce bulk of the case, it may be desirable for accessory insert module  7900  to be quite thin, e.g., a total thickness of about 1 mm. For example, front and back outer layers  7902  and  7904  and magnet-holding layer  7910  can be made of a polycarbonate film such as LEXAN™ SD8B24 film (a product of SABIC Innovative Plastics). Front and back outer layers  7902  and  7904  can each have a thickness of about 0.2 mm while magnet-holding layer  7910  can have a thickness of about 0.5 mm. (As noted above, the thickness of annular alignment component  8070  and rotational alignment component  8072  can be the same as the thickness of magnet-holding layer  7910 .) Adhesive layers  7906  and  7908  can be, e.g., pressure sensitive adhesive with a thickness of about 0.2 mm. It should be understood that these dimensions can be modified as desired. In general, thinner front and back outer layers allow a given annular alignment component  8070  and rotational alignment component  8072  to exert stronger magnetic forces on complementary devices, and thinner magnets (and magnet-holding layer  7910 ) allow the overall thickness of an accessory incorporating insert module  7900  to be reduced. 
     In some embodiments, accessory insert module  7900  can be made of opaque materials and can be inserted into a variety of accessories such as protective cases, sleeves, trays, and the like. The opacity of accessory insert module  7900  may interfere with certain esthetic options, such as a transparent case back. Some embodiments of accessory insert modules can provide a reduced region of opacity as compared to accessory insert module  7900 .  FIG.  81    shows an exploded view of an accessory insert module  8100  according to some embodiments. Accessory insert module  8100  has an annular shape, with an annular front enclosure  8102  and an annular rear enclosure  8104  surrounding annular alignment component  8170  Annular alignment component  8170  can be an implementation of any of the auxiliary annular alignment components described above. For example, auxiliary annular alignment component  8170  can include primary arcuate magnets  8172  arranged in an annular configuration with each primary arcuate magnet  8172  having a quad-pole configuration with an inner arcuate magnetic region having magnetic polarity oriented in a first axial direction, an outer arcuate magnetic region having magnetic polarity oriented in a second axial direction opposite the first direction, and a central non-magnetized region between the inner arcuate magnetic region and the outer arcuate magnetic region. Adhesive layers  8106 ,  8108 , each of which can be, e.g., a pressure-sensitive adhesive, can hold annular alignment component in place within an enclosure formed by front enclosure  8102  and rear enclosure  8104 . Front enclosure  8102  and rear enclosure  8104  can be made, e.g., of injection molded polycarbonate or other similar material. Accessory insert module  8100  can be opaque, but because of its reduced opaque area relative to accessory insert module  7900 , accessory insert module  8100  may be more esthetically appealing in transparent cases and other applications where a transparent surface is desired. 
     In the embodiment shown in  FIG.  81   , front enclosure  8102  and/or rear enclosure  8104  can have sidewalls so that magnets  8172  are surrounded on all sides. The joint where front enclosure  8102  and rear enclosure  8104  meet can be formed in several ways.  FIGS.  82  and  83    show partial cross-section views of accessory insert modules according to various embodiments, illustrating options for joining front enclosure  8102  and rear enclosure  8104 . In  FIG.  82   , front enclosure  8102  and rear enclosure  8104  of accessory insert module  8100  can be joined by an ultrasonic or laser weld  8210 , fully enclosing annular alignment component  8170 .  FIG.  83    shows a variation in which a front enclosure  8102 ′ of accessory insert module  8100  includes a notch  8310  while rear enclosure  8104 ′ includes a projection  8312  that fits into notch  8310 . For example, front enclosure  8102 ′ with notch  8310  can be formed in a first injection molding process, after which magnets are arranged in front enclosure  8102 ′ to form annular alignment component  8170 . Thereafter, a second injection molding process can be used to form rear enclosure  8104 ′, filling in notch  8310 . 
     In still other embodiments, sidewalls can be formed separately from front enclosure  8102  and rear enclosure  8104 , providing a “stacked” construction similar to accessory insert module  7900  described above.  FIG.  84    is a partial cross section view of an annular accessory insert module  8100 ″ according to some embodiments with a “stacked” construction. Annular accessory insert module  8100 ″ can have the same annular shape as accessory insert module  8100 . In this embodiment, however, front enclosure  8102 ″ and rear enclosure  8104 ″ can be planar annular structures formed of polycarbonate or the like. Sidewalls  8410   a  and  8410   b  can be formed as concentric annular rings of polycarbonate having a thickness that can be the same as (or slightly greater than) the thickness of annular alignment component  8170 . Adhesive layers  8406 ,  8408 , which can be, e.g., pressure-sensitive adhesive, can hold the structure together. 
     It will be appreciated that these accessory insert modules are illustrative and that variations and modifications are possible. A variety of materials can be used, and any of the annular alignment components described above may be included. Further, while the various accessory insert modules are not shown as including an NFC tag circuit and coil, those skilled in the art with access to the present disclosure will appreciate that an NFC tag circuit and coil can be incorporated similarly to examples of accessory devices described above. 
     8. Additional Embodiments 
     While the invention has been described with reference to specific embodiments, those skilled in the art will appreciate that variations and modifications are possible. For instance, although the annular alignment modules are described as being made from arcuate magnets that form sectors, it will be understood that if the magnets are sufficiently small relative to the dimensions of the annular structure, trapezoidal or square magnets can approximate the behavior of arcuate magnets. Magnetic alignment components can have any dimensions, and annular magnetic alignment components can be used with or without rotational alignment components and with or without NFC circuitry. Where NFC circuitry is present, a given device can have NFC reader circuitry or NFC tag circuitry (or both) in combination with any of a primary, secondary, or auxiliary annular magnetic alignment component, and a variety of NFC coil geometries can be implemented. Magnetic alignment components can be used with an inductive charging coil to facilitate alignment of the coils as described above, or a magnetic alignment component can be present in a device that does not have an inductive charging coil. Further, a portable electronic device that has a magnetic alignment component around an inductive charging coil can be charged by a wireless charger device that does not have a magnetic alignment component, and conversely, a wireless charger device that has a magnetic alignment component can be used to charge a portable electronic device that has an inductive charging coil but not a magnetic alignment component. In these situations, the magnetic alignment component may not facilitate alignment between the devices, but it need not interfere with wireless power transfer. 
     In addition, while a portable electronic device has been described as receiving power wirelessly, those skilled in the art will appreciate that an inductive power coil may be operable to transmit as well as receive power wirelessly, and in some embodiments a portable electronic device can be reconfigurable to operate either as a transmitter or receiver for wireless power transfer. 
     Further, while it is contemplated that magnetic alignment components of the kind described herein can be used to facilitate alignment between transmitter and receiver coils for wireless power transfer between devices, use of magnetic alignment components is not so limited, and magnetic alignment components can be used in a variety of contexts to hold one device in relative alignment with another, regardless of whether either or both devices have wireless charging coils. Thus, for instance, a tripod (or other type of stand), which can hold a portable electronic device in a particular positon and orientation, can include a primary annular magnetic alignment component (and a rotational alignment component) to hold the portable electronic device in place; the magnetic alignment component can be used in addition to or instead of mechanical retention features to secure the portable electronic device to the tripod. 
     Accordingly, ecosystems of devices are contemplated. The ecosystem can include a variety of portable electronic devices having various form factors, such as smart phones, tablets, or other devices that can operate on battery power and can receive power via wireless power transfer. The ecosystem can also include a variety of wireless charger devices such as pucks, mats, docks, or the like. The ecosystem can also include “charge-through” accessories (such as cases) that may be interposed between a portable electronic device and a wireless charger device; the charge-through accessory is designed to permit magnetic flux to pass through the interposed portion of the accessory to allow wireless charging while the accessory is present. In such an ecosystem, each portable electronic device can be manufactured to include a secondary annular magnetic alignment component (e.g., having a radial or transverse magnetic orientation as described above) having dimensions of radial width and outer diameter that are constant across the ecosystem. Each wireless charger device can be manufactured to include a primary annular magnetic alignment component complementary to the secondary annular magnetic alignment components of the portable electronic devices (e.g., having a quad-pole configuration as described above), allowing wireless charger devices to be used interchangeably with different portable electronic devices. Each charge-through accessory can be manufactured to include an auxiliary annular magnetic alignment component complementary to the primary and secondary annular magnetic alignment components, again allowing interchangeable use of wireless charger devices with different charge-through accessories (and portable electronic devices). 
     Such ecosystems can also include other passive accessory devices (i.e., accessory devices that do not include inductive charging coils) that may be designed to attach to a portable electronic device using magnetic alignment components but that do not support charge-through operation. Examples include tripods or other stands, attachable accessory cases that may hold credit cards or other magnetized items that may be susceptible to demagnetization during wireless power transfer, or other accessories that are intended for use with a portable electronic device that is not being charged. Such accessory devices can be manufactured to include either a secondary annular magnetic alignment component or an auxiliary annular magnetic alignment component and may or may not include a rotational alignment component. 
     Such ecosystems can also include a “retrofitting” accessory device that may be used to provide magnetic alignment capability for a portable electronic device that was originally manufactured without a magnetic alignment component. A retrofitting accessory can have one or more mechanical retention features (e.g., sides and lips of a case shaped as a tray) that hold the smart phone (or other portable electronic device) in a fixed relative alignment with the housing of the accessory. The accessory can include a secondary magnetic alignment component (matching the specifications of the secondary alignment component for the ecosystem), and the secondary magnetic alignment component can be positioned in the retrofitting accessory so that when the portable electronic device is held in place by the mechanical retention feature(s), the inductive charging coil is centered within the secondary magnetic alignment component. Such an accessory can allow a portable electronic device that was manufactured without a magnetic alignment component to enjoy the benefits of magnetic alignment when used with devices in the magnetic alignment ecosystem. 
     It should be understood that, within a given ecosystem, any or all of the devices that include annular alignment components may also include rotational alignment components as described above. For instance, within an ecosystem, all portable electronic devices having a secondary annular alignment component that are large enough to accommodate a rotational alignment component outboard of the secondary annular alignment component can have a rotational alignment component. Devices having a primary alignment component or auxiliary alignment component might or might not have a rotational alignment component, depending on form factor and intended use. 
     It should also be understood that, within a given ecosystem, any or all of the devices that include annular alignment components may also include NFC circuitry for device identification as described above. For instance, within an ecosystem, any portable electronic device can have an NFC reader circuit as described above, while any device having a primary annular alignment component or auxiliary annular alignment component can have an NFC tag circuit as described above. 
     It should also be understood that some devices may include multiple annular alignment components. For instance, a wireless charger device may be designed with two or more separate wireless charging coils spaced apart from each other to allow multiple portable electronic devices to be charged at the same time. Each wireless charging coil can have a surrounding primary annular alignment component, and each primary alignment component can have an associated rotational alignment component and/or NFC coil. 
     In some embodiments, an alignment module that includes an annular alignment component can be packaged for easy installation into an accessory device, wireless charger device, or portable electronic device. For example, an alignment module can include a primary, secondary, or auxiliary annular magnetic alignment component as described above in an enclosing structure (or housing) that protects the magnets and holds them in position In some embodiments, a rotational magnetic alignment component can be included along with the annular magnetic alignment component, and in some embodiments, an NFC circuit can be included. The enclosing structure can be, for instance, a plastic structure, at least part of which can be transparent. As another example, the alignment module can include a wireless charging coil (e.g., a transmitter coil) centered within the annular alignment component. The enclosing structure can provide exposed electrical contacts for making electrical connections to the wireless charging coil. Such alignment modules can be made by one entity and sold to a different entity to incorporate into devices such as cases, wireless charging docks, or the like. 
     Various features described herein related to detection of devices and exchange of information (e.g., using NFC) can be realized using any combination of dedicated components and/or programmable processors and/or other programmable devices. The various processes described herein can be implemented on the same processor or different processors in any combination. Where components are described as being configured to perform certain operations, such configuration can be accomplished, e.g., by designing electronic circuits to perform the operation, by programming programmable electronic circuits (such as microprocessors) to perform the operation, or any combination thereof. Further, while the embodiments described above may make reference to specific hardware and software components, those skilled in the art will appreciate that different combinations of hardware and/or software components may also be used and that particular operations described as being implemented in hardware might also be implemented in software or vice versa. Computer programs incorporating various features described herein may be encoded and stored on various computer readable storage media; suitable media include magnetic disk or tape, optical storage media such as compact disk (CD) or DVD (digital versatile disk), flash memory, and other non-transitory media. Computer readable media encoded with the program code may be packaged with a compatible electronic device, or the program code may be provided separately from electronic devices (e.g., via Internet download or as a separately packaged computer-readable storage medium). Further, in regard to any collection or exchange of information or data by or between devices, it is well understood that the use of personally identifiable information should follow privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining the privacy of users. In particular, personally identifiable information data should be managed and handled so as to minimize risks of unintentional or unauthorized access or use, and the nature of authorized use should be clearly indicated to users. 
     Embodiments of the invention can include, but are not limited to, any of the following. 
     In some embodiments, an electronic device (e.g., a portable electronic device) can comprise: a housing having an interface surface; an inductive coil disposed within the housing and having an axis normal to the interface surface, the inductive coil being configured to transfer power wirelessly through the interface surface; and an annular magnetic alignment component disposed within the housing coaxial with and outboard of the inductive coil. The annular magnetic alignment component can have a magnetic orientation in a radial direction. The annular magnetic alignment component can comprise a plurality of arcuate magnets, and each of the arcuate magnets can have a magnetic polarity that is oriented in a radially inward (or radially outward) direction. The annular magnetic alignment component can include a gap, and an electrically conductive path connected to the inductive coil can pass through the gap. The annular magnetic alignment component can include a first gap and a second gap on opposite sides of the annular magnetic alignment component. A battery can be disposed within the housing, and the inductive coil can be coupled to the battery. The inductive coil can be configured to receive and/or transmit power wirelessly through the interface surface. 
     In some embodiments, an electronic device (e.g., a wireless charger device) can comprise: a housing having a charging surface; an inductive coil disposed within the housing and having an axis normal to the charging surface, the inductive coil being configured to transfer power wirelessly through the charging surface; and an annular magnetic alignment component disposed within the housing coaxial with and outboard of the inductive coil. The annular magnetic alignment component can comprise: an inner arcuate region having a magnetic polarity oriented in a first axial direction; an outer arcuate region having a magnetic polarity oriented in a second axial direction opposite the first axial direction; and a non-magnetized central arcuate region disposed between the inner arcuate region and the outer arcuate region. The annular magnetic alignment component can comprise a plurality of arcuate magnets, and each arcuate magnet can have a first region with a magnetic polarity oriented in the first axial direction, a second region with a magnetic polarity oriented in the second axial direction, and a non-magnetized region between the first region and the second region. The annular magnetic alignment component can include a gap, and an electrically conductive path connected to the inductive coil can pass through the gap. The inductive coil can be configured to transmit and/or receive power wirelessly through the charging surface. 
     In some embodiments, an accessory for use with a portable electronic device can comprise: a housing having a first interface surface and a second interface surface opposite the first interface surface; an annular magnetic alignment component disposed within the housing and having an axis normal to the first interface surface and the second interface surface. The annular magnetic alignment component can comprise: an inner arcuate region having a magnetic polarity oriented in a first axial direction; an outer arcuate region having a magnetic polarity oriented in a second axial direction opposite the first axial direction; and a non-magnetized central arcuate region disposed between the inner arcuate region and the outer arcuate region. The annular magnetic alignment component can comprise a plurality of arcuate magnets. Each arcuate magnet can have a first region with a magnetic polarity oriented in the first axial direction, a second region with a magnetic polarity oriented in the second axial direction, and a non-magnetized region between the first region and the second region. The annular magnetic alignment component can include a gap. The annular magnetic alignment component can include a first gap and a second gap on opposite sides of the annular magnetic alignment component. 
     In some embodiments, a magnetic alignment system can comprise: a primary alignment component formed of a plurality of primary arcuate magnets arranged in an annular configuration defining an axis and a secondary alignment component formed of a plurality of secondary arcuate magnets arranged in an annular configuration. Each primary arcuate magnet can comprise: a primary inner arcuate magnetic region having a magnetic orientation in a first direction along the axis; a primary outer arcuate magnetic region having a magnetic orientation in a second direction opposite the first direction; and a non-magnetized primary central arcuate region disposed between the primary inner arcuate region and the primary outer arcuate region. Each secondary arcuate magnet having a magnetic orientation that is in a radial direction with respect to a center of the secondary alignment component. The primary alignment component can be disposed in a first electronic device surrounding a first inductive charging coil, and the secondary alignment component can be disposed in a second electronic device surrounding a second inductive charging coil; when the primary alignment component and the secondary alignment component are aligned along a common axis, the first inductive charging coil and the second inductive charging coil can be also aligned along the common axis. 
     In some embodiments, an electronic device (e.g., a portable electronic device) can comprise: a housing having an interface surface; an inductive coil disposed within the housing and having an axis normal to the interface surface, the inductive coil being configured to transfer power wirelessly through the interface surface; an annular magnetic alignment component disposed within the housing coaxial with and outboard of the inductive coil, the annular magnetic alignment component having a magnetic orientation in a radial direction; and a rotational alignment component comprising a magnet disposed outside an outer perimeter of the annular magnetic alignment component. The rotational alignment component can comprises a magnet having at least two different regions of opposing magnetic orientations. In these and other embodiments, the magnet can have a rectangular shape in a plane transverse to an axis defined by the annular magnetic alignment component. For example, the at least two different regions of opposing magnetic orientations can include: a first region extending along a first long side of the rectangular shape and having a first magnetic orientation; and a second region extending along a second long side of the rectangular shape and having a second magnetic orientation opposite the first magnetic orientation. As another example, the at least two different regions of opposing magnetic orientations can include: a first region extending along a first long side of the rectangular shape and having a first magnetic orientation; a second region extending along a second long side of the rectangular shape and having the first magnetic orientation; and a third region extending along the rectangular shape and positioned midway between the first region and the second region, the third region having a second magnetic orientation opposite the first magnetic orientation. In these and other embodiments, the annular magnetic alignment component can comprise a plurality of arcuate magnets, each having a magnetic polarity that is oriented in a radially inward direction. In these and other embodiments, a battery can be disposed within the housing, and the inductive coil can be coupled to the battery. In these and other embodiments, the inductive coil can be configured to receive and/or transmit power wirelessly through the interface surface. 
     In some embodiments, an electronic device (e.g., a wireless charger device) can comprise: a housing having a charging surface; an inductive coil disposed within the housing and having an axis normal to the charging surface, the inductive coil being configured to transfer power wirelessly through the charging surface; an annular magnetic alignment component disposed within the housing coaxial with and outboard of the inductive coil; and a rotational alignment component comprising a magnet disposed outside a perimeter of the annular magnetic alignment component. In these and other embodiments, the annular magnetic alignment component can comprise: an inner arcuate region having a magnetic polarity oriented in a first axial direction; an outer arcuate region having a magnetic polarity oriented in a second axial direction opposite the first axial direction; and a non-magnetized central arcuate region disposed between the inner arcuate region and the outer arcuate region. In these and other embodiments, the rotational alignment component can comprise a magnet having at least two different regions of opposing magnetic orientations. For example, the magnet can have a rectangular shape in a plane transverse to an axis defined by the annular magnetic alignment component, and the at least two different regions of opposing magnetic orientations can include: a first region extending along a first long side of the rectangular shape and having a first magnetic orientation; and a second region extending along a second long side of the rectangular shape and having a second magnetic orientation opposite the first magnetic orientation. As another example, the magnet can have a rectangular shape in a plane transverse to an axis defined by the annular magnetic alignment component, and the at least two different regions of opposing magnetic orientations can include: a first region extending along a first long side of the rectangular shape and having a first magnetic orientation; a second region extending along a second long side of the rectangular shape and having the first magnetic orientation; and a third region extending along the rectangular shape and positioned midway between the first region and the second region, the third region having a second magnetic orientation opposite the first magnetic orientation. In these and other embodiments, the annular magnetic alignment component can comprise a plurality of arcuate magnets. Each arcuate magnet can have a first region with a magnetic polarity oriented in the first axial direction, a second region with a magnetic polarity oriented in the second axial direction, and a non-magnetized region between the first region and the second region. In these and other embodiments, the inductive coil can be configured to transmit power wirelessly through the charging surface. 
     In some embodiments, an accessory for use with a portable electronic device can comprise: a housing having a first interface surface and a second interface surface opposite the first interface surface; an annular magnetic alignment component disposed within the housing and having an axis normal to the first interface surface and the second interface surface; and a rotational alignment component comprising a magnet disposed outside a perimeter of the annular magnetic alignment component. In these and other embodiments, the annular magnetic alignment component can comprise: an inner arcuate region having a magnetic polarity oriented in a first axial direction; an outer arcuate region having a magnetic polarity oriented in a second axial direction opposite the first axial direction; and a non-magnetized central arcuate region disposed between the inner arcuate region and the outer arcuate region. In these and other embodiments, the rotational alignment component comprises a magnet having at least two different regions of opposing magnetic orientations. For example, the magnet can have a rectangular shape in a plane transverse to an axis defined by the annular magnetic alignment component, and the at least two different regions of opposing magnetic orientations can include: a first region extending along a first long side of the rectangular shape and having a first magnetic orientation; and a second region extending along a second long side of the rectangular shape and having a second magnetic orientation opposite the first magnetic orientation. As another example, the magnet can have a rectangular shape in a plane transverse to an axis defined by the annular magnetic alignment component, and the at least two different regions of opposing magnetic orientations can include: a first region extending along a first long side of the rectangular shape and having a first magnetic orientation; a second region extending along a second long side of the rectangular shape and having the first magnetic orientation; and a third region extending along the rectangular shape and positioned midway between the first region and the second region, the third region having a second magnetic orientation opposite the first magnetic orientation. In these and other embodiments, the annular magnetic alignment component can comprise a plurality of arcuate magnets. Each arcuate magnet can have a first region with a magnetic polarity oriented in the first axial direction, a second region with a magnetic polarity oriented in the second axial direction, and a non-magnetized region between the first region and the second region. 
     In some embodiments, a portable electronic device (or other electronic device) can comprise: a housing having an interface surface; an inductive coil disposed within the housing and having an axis normal to the interface surface, the inductive coil being configured to transfer power wirelessly through the interface surface; an annular magnetic alignment component disposed within the housing coaxial with and outboard of the inductive coil, the annular magnetic alignment component including a plurality of sectors, each sector having a magnetic orientation with a radial component; and a near-field communication (NFC) coil disposed within the housing and coaxial with the inductive coil, the NFC coil configured to wirelessly exchange signals with another device through the interface surface. In these and other embodiments, the NFC coil can be coupled to an NFC reader circuit. In these and other embodiments, the NFC coil is positioned in a gap (which can be an annular gap) between the inductive coil and the annular magnetic alignment component. In these and other embodiments, each sector of the annular magnetic alignment component can comprise one or more arcuate magnets, each arcuate magnet having a magnetic polarity oriented in a radial direction. In these and other embodiments, alternating sectors of the annular magnetic alignment component can have opposite magnetic orientations. In these and other embodiments, the annular magnetic alignment component can include a gap between two of the sectors. An electrically conductive path connecting the NFC coil to an NFC reader circuit can pass through the gap, as can an electrically conductive path connecting to the inductive coil. In these and other embodiments, a rotational alignment component comprising a magnet can be disposed within the housing and outboard of (or outside a perimeter of) the annular magnetic alignment component. 
     In some embodiments, a wireless charging device can comprise: a housing having a charging surface; an inductive coil disposed within the housing and having an axis normal to the charging surface, the inductive coil being configured to transfer power wirelessly through the charging surface; an annular magnetic alignment component disposed within the housing coaxial with and outboard of the inductive coil; and a near-field communication (NFC) coil disposed within the housing and coaxial with the inductive coil, the NFC coil configured to wirelessly exchange signals with another device through the charging surface. In these and other embodiments, the annular magnetic alignment component can include a plurality of sectors, each sector comprising: an inner arcuate region having a magnetic polarity oriented in a first axial direction (e.g., having a south magnetic pole oriented toward the charging surface); an outer arcuate region having a magnetic polarity oriented in a second axial direction opposite the first axial direction; and a non-magnetized central arcuate region disposed between the inner arcuate region and the outer arcuate region. In these and other embodiments, an annular magnetic shield can be disposed at a distal surface of the annular magnetic alignment component. In these and other embodiments, the NFC coil is coupled to an NFC tag circuit, which can be a passive NFC tag circuit or an active NFC tag circuit. In these and other embodiments, the NFC coil is positioned between the inductive coil and the annular magnetic alignment component, e.g., in an annular gap between the inductive coil and the annular magnetic alignment component. In these and other embodiments, the first axial direction can be the same direction for all of the sectors. Alternatively, alternating sectors can have opposite first axial directions. In these and other embodiments, each sector of the annular magnetic alignment component includes one or more arcuate magnets each having a quad-pole configuration. In these and other embodiments, the annular magnetic alignment component can include a gap between two of the sectors. An electrically conductive path connected to the inductive coil can pass through the gap, as can an electrically conductive path connecting the NFC coil to an NFC tag circuit. 
     In some embodiments, an accessory device can comprise: a housing having an interface surface; an annular magnetic alignment component disposed within the housing and having an axis normal to the interface surface; and a near-field communication (NFC) coil disposed within the housing and coaxial with the annular magnetic alignment component, the NFC coil configured to wirelessly exchange signals with another device through the interface surface. In these and other embodiments, the annular magnetic alignment component including a plurality of sectors, each sector comprising: an inner arcuate region having a magnetic polarity oriented in a first axial direction; an outer arcuate region having a magnetic polarity oriented in a second axial direction opposite the first axial direction; and a non-magnetized central arcuate region disposed between the inner arcuate region and the outer arcuate region. In these and other embodiments, the NFC coil can be coupled to an NFC tag circuit. In these and other embodiments, the NFC coil can be positioned inboard of the annular magnetic alignment component, and other components of an NFC tag circuit can be positioned inboard of the annular magnetic alignment component and/or in one or more gaps between sectors of the annular magnetic alignment component. Alternatively, the NFC coil can be positioned outboard of the annular magnetic alignment component. 
     In some embodiments, a portable electronic device can comprise: a housing having an interface surface; an inductive coil disposed within the housing and having an axis normal to the interface surface, the inductive coil being configured to transfer power wirelessly through the interface surface; an annular magnetic alignment component disposed within the housing coaxial with and outboard of the inductive coil, the annular magnetic alignment component including a plurality of sectors, each sector having a magnetic orientation with a radial component; a near-field communication (NFC) coil disposed within the housing and coaxial with the inductive coil, the NFC coil coupled to an NFC reader circuit and configured to wirelessly exchange signals with another device through the interface surface; a magnetometer disposed near the interface surface and outboard of the annular magnetic alignment component; and control circuitry coupled to the magnetometer and configured to trigger operation of the NFC reader circuit based at least in part on a change in a magnetic field detected by the magnetometer. In these and other embodiments, the magnetometer can be a three-axis magnetometer and the change in the magnetic field can includes a change in either or both of a magnitude or a direction of the magnetic field. In these and other embodiments, the control circuitry can be further configured to trigger operation of the NFC reader circuit in the event that the change in the magnetic field corresponds to an expected change associated with an accessory device having a second magnetic alignment component complementary to the annular magnetic alignment component of the portable electronic device becoming aligned with the portable electronic device. In these and other embodiments, the NFC reader circuit can be operable in a plurality of operating modes associated with different types of accessory devices, and the control circuitry is further configured to select one of the operating modes for the NFC reader circuit based at least in part on the change in the magnetic field detected by the magnetometer. In these and other embodiments, the control circuitry can be further configured to receive NFC tag data from the NFC reader circuit and to modify a behavior of the portable electronic device based on the received NFC tag data. In these and other embodiments, the NFC coil can be positioned in a gap between the inductive coil and the annular magnetic alignment component. In these and other embodiments, the annular magnetic alignment component can include a plurality of sectors, each sector having a magnetic orientation with a radial component, and the control circuitry can be further configured to trigger operation of the NFC reader circuit in the event that the change in the magnetic field corresponds to an expected change associated with an accessory device having a second magnetic alignment component becoming aligned with the portable electronic device, wherein the second magnetic alignment component is a second annular magnetic alignment component having a quad-pole magnetic configuration that is complementary to the annular magnetic alignment component of the portable electronic device. 
     In some embodiments, a portable electronic device can comprise: a housing having an interface surface; an annular magnetic alignment component disposed within the housing; a near-field communication (NFC) coil disposed within the housing and coaxial with the annular magnetic alignment component, the NFC coil coupled to an NFC reader circuit and configured to wirelessly exchange signals with another device through the interface surface; a magnetometer disposed near the interface surface and outboard of the annular magnetic alignment component; and control circuitry coupled to the magnetometer and configured to trigger operation of the NFC reader circuit based at least in part on a change in a magnetic field detected by the magnetometer. In these and other embodiments, the magnetometer can be a three-axis magnetometer and the change in the magnetic field can include a change in either or both of a magnitude or a direction of the magnetic field. In these and other embodiments, the control circuitry can be further configured to trigger operation of the NFC reader circuit in the event that the change in the magnetic field corresponds to an expected change associated with an accessory device having a second magnetic alignment component complementary to the annular magnetic alignment component of the portable electronic device becoming aligned with the portable electronic device. In these and other embodiments, the NFC reader circuit can be operable in a plurality of operating modes associated with different types of accessory devices and wherein the control circuitry can be further configured to select one of the operating modes for the NFC reader circuit based at least in part on the change in a magnetic field detected by the magnetometer. In these and other embodiments, the control circuitry can be further configured to receive NFC tag data from the NFC reader circuit and to modify a behavior of the portable electronic device based on the received NFC tag data. In these and other embodiments, the annular magnetic alignment component includes a plurality of sectors, each sector having a magnetic orientation with a radial component. In these and other embodiments, the control circuitry can be further configured to trigger operation of the NFC reader circuit in the event that the change in the magnetic field corresponds to an expected change associated with an accessory device having a second magnetic alignment component becoming aligned with the portable electronic device, wherein the second magnetic alignment component is a second annular magnetic alignment component having a quad-pole magnetic configuration that is complementary to the annular magnetic alignment component of the portable electronic device. 
     In some embodiments, a method of identifying an accessory can comprise: operating, by a portable electronic device having a first annular magnetic alignment component, a magnetometer to monitor a magnetic field near the first annular magnetic alignment component; detecting, by the portable electronic device, a change in the magnetic field indicative that an accessory having a second annular magnetic alignment component complementary to the first annular magnetic alignment component has come into proximity with the portable electronic device; and in response to detecting the change in the magnetic field, operating, by the portable electronic device, an NFC reader circuit that includes an NFC coil coaxial with the first annular magnetic alignment component to read an NFC tag of the accessory. In these and other embodiments, the change in the magnetic field can include a change in either or both of a magnitude or a direction of the magnetic field. In these and other embodiments, the NFC reader circuit is operable in a plurality of operating modes associated with different types of accessory devices, and the method can further comprise selecting one of the operating modes for the NFC reader circuit based at least in part on the change in a magnetic field detected by the magnetometer. In these and other embodiments, the method can further comprise modifying a behavior of the portable electronic device based on identification data read from the NFC tag of the accessory, such as changing an element displayed on a display of the portable electronic device. 
     In some embodiments, a wireless charging module can comprise: a housing having a charging surface and a second surface having an opening therethrough (the opening can be opposite the charging surface or elsewhere on the housing); an inductive coil assembly disposed within the housing, the inductive coil assembly including an electrically conductive coil; an annular magnetic alignment component disposed within the housing and surrounding the inductive coil assembly; and control circuitry disposed within the housing, the control circuitry being coupled to the electrically conductive coil and to a plurality of external electrical contacts and being configured to operate the electrically conductive coil to transfer power wirelessly through the charging surface using input power received from the external electrical contacts, where the external electrical contacts are exposed through the opening in the second surface of the housing. In these and other embodiments, the annular magnetic alignment component can include a plurality of sectors, each sector comprising: an inner arcuate region having a magnetic polarity oriented in a first axial direction; an outer arcuate region having a magnetic polarity oriented in a second axial direction opposite the first axial direction; and a non-magnetized central arcuate region disposed between the inner arcuate region and the outer arcuate region. In these and other embodiments, a conductive midplate can be disposed within the housing. The midplate can have a proximal surface oriented toward the charging surface and a distal surface opposite the proximal surface, and the inductive coil assembly can be mounted on the proximal surface of the midplate. In these and other embodiments, the control circuitry can comprise a logic board having circuit components mounted thereon. Where a midplate is present, the logic board can be mounted on the distal surface of the midplate. For instance, the midplate can have an opening therethrough, and the logic board can be coupled to the electrically conductive coil through the opening in the midplate. In these and other embodiments, an annular magnetic shield can be disposed at a distal surface of the annular magnetic alignment component. In these and other embodiments, the external electrical contacts include a calibration contact, which can be covered with a sealant material following calibration. In these and other embodiments, the inductive coil assembly can further include: an electric shield disposed between the electrically conductive coil and the charging surface; and an electromagnetic shield covering a surface of the electrically conductive coil opposite the electric shield. 
     In some embodiments, a wireless charging module can comprise: a housing having a charging surface and a second surface having an opening therethrough (the opening can be opposite the charging surface or elsewhere on the housing); an inductive coil assembly disposed within the housing, the inductive coil assembly including an electrically conductive coil and an electromagnetic shield; an annular magnetic alignment component disposed within the housing and surrounding the inductive coil assembly; a near-field communication (NFC) coil disposed within the housing and coaxial with the inductive coil assembly, the NFC coil configured to wirelessly exchange signals with another device through the charging surface; and control circuitry disposed within the housing, the control circuitry being coupled to the electrically conductive coil and to a plurality of external electrical contacts and being configured to operate the electrically conductive coil to transfer power wirelessly through the charging surface using input power received from the external electrical contacts, and the external electrical contacts can be exposed through the opening in the second surface of the housing. In these and other embodiments, the annular magnetic alignment component can include a plurality of sectors, each sector comprising: an inner arcuate region having a magnetic polarity oriented in a first axial direction; an outer arcuate region having a magnetic polarity oriented in a second axial direction opposite the first axial direction; and a non-magnetized central arcuate region disposed between the inner arcuate region and the outer arcuate region. In these and other embodiments, the NFC coil can be coupled to an NFC tag circuit. In these and other embodiments, the NFC coil can be positioned between the inductive coil assembly and the annular magnetic alignment component (e.g., in an annular gap between the inductive coil assembly and the annular magnetic alignment component). In these and other embodiments, a conductive midplate can be disposed within the housing, the midplate having a proximal surface oriented toward the charging surface and a distal surface opposite the proximal surface. The inductive coil assembly can be mounted on the proximal surface of the midplate with the electromagnetic shield oriented toward the midplate. In these and other embodiments, the control circuitry can comprise a logic board, and the NFC coil can be terminated into the logic board. Where a midplate is present, the logic board is mounted on the distal surface of the midplate. For instance, the midplate can have an opening therethrough, and the logic board can be coupled to the electrically conductive coil through the opening in the midplate. 
     In some embodiments, a wireless charging module can comprise: a housing having a charging surface and a second surface having an opening therethrough; an inductive coil assembly disposed within the housing, the inductive coil assembly including an electrically conductive coil and an electromagnetic shield; an annular magnetic alignment component disposed within the housing and surrounding the inductive coil assembly; a rotational alignment component comprising a magnet disposed within the housing outside a perimeter of the annular magnetic alignment component; and control circuitry disposed within the housing, the control circuitry being coupled to the electrically conductive coil and to a plurality of external electrical contacts and being configured to operate the electrically conductive coil to transfer power wirelessly through the charging surface using input power received from the external electrical contacts, where the external electrical contacts are exposed through the opening in the second surface of the housing. In these and other embodiments, the annular magnetic alignment component can include a plurality of sectors, each sector comprising: an inner arcuate region having a magnetic polarity oriented in a first axial direction; an outer arcuate region having a magnetic polarity oriented in a second axial direction opposite the first axial direction; and a non-magnetized central arcuate region disposed between the inner arcuate region and the outer arcuate region. In these and other embodiments, a conductive midplate can be disposed within the housing, the midplate having a proximal surface oriented toward the charging surface and a distal surface opposite the proximal surface. The inductive coil assembly can be mounted on the proximal surface of the midplate with the electromagnetic shield oriented toward the midplate. In these and other embodiments, the control circuitry can comprise a logic board. Where a midplate is present, the logic board can be mounted on the distal surface of the midplate. For instance, the midplate can have an opening therethrough, and the logic board can be coupled to the electrically conductive coil through the opening in the midplate. In these and other embodiments, the rotational alignment component can comprise a magnet having at least two different regions of opposing magnetic orientations. 
     In some embodiments, an alignment module can include: an annular magnetic alignment component including a plurality of arcuate magnets; and an encapsulating structure surrounding and holding the arcuate magnets in an annular arrangement. Each arcuate magnet can have, for example: an inner arcuate region having a magnetic polarity oriented in a first axial direction; an outer arcuate region having a magnetic polarity oriented in a second axial direction opposite the first axial direction; and a non-magnetized central arcuate region disposed between the inner arcuate region and the outer arcuate region. In these and other embodiments, the encapsulating structure can have an annular shape. For instance, the encapsulating structure can comprise an annular front enclosure and an annular rear enclosure joined at inner and outer edges thereof. The annular front enclosure and the annular rear enclosure can made of plastic or other materials. Joining of the annular front enclosure and the annular rear enclosure can be by a weld, or the annular front enclosure can be formed in a first injection molding stage after which the annular rear enclosure is injection molded onto the annular front enclosure (or vice versa). In these and other embodiments, the encapsulating structure can comprise an annular front enclosure, an annular back enclosure, an annular inner side enclosure and an annular outer side enclosure and wherein the annular front enclosure and the annular back enclosure are joined to the annular inner side enclosure and the annular outer side enclosure by adhesive. In these and other embodiments, an alignment module can also comprise: a rotational alignment component comprising a rectangular magnet, and the encapsulating structure can hold the rectangular magnet in a fixed position outboard of the annular magnetic alignment component. 
     In some embodiments, an alignment module can comprise: an annular magnetic alignment component including a plurality of arcuate magnets; a rotational alignment component comprising a rectangular magnet and disposed outside a perimeter of the annular magnetic alignment component; and an encapsulating structure holding the annular magnetic alignment component and the rotational alignment component in a fixed spatial relationship to each other. Each arcuate magnet can have: an inner arcuate region having a magnetic polarity oriented in a first axial direction; an outer arcuate region having a magnetic polarity oriented in a second axial direction opposite the first axial direction; and a non-magnetized central arcuate region disposed between the inner arcuate region and the outer arcuate region. In these and other embodiments, the encapsulating structure can comprise: a front planar layer; a back planar layer; and a magnet-holding layer, the magnet-holding layer having a circular opening therethrough to accommodate the annular magnetic alignment component and a rectangular opening therethrough to accommodate the rectangular magnet. In these and other embodiments, the magnet-holding layer, the arcuate magnets, and the rectangular magnet can have equal thicknesses, and the magnet-holding layer includes a disc of material filling a region inboard of the annular magnetic alignment component. In these and other embodiments, a first adhesive layer can attach the front planar layer to the magnet-holding layer, and a second adhesive layer can attach the back planar layer to the magnet-holding layer. In these and other embodiments, the front planar layer and the back planar layer can be rectangular layers with rounded corners. In these and other embodiments, the encapsulating structure can have an opening through a region inside an inner perimeter of the annular magnetic alignment component. 
     In some embodiments, an alignment module can comprise: an annular magnetic alignment component including a plurality of arcuate magnets, an encapsulating structure surrounding and holding the arcuate magnets in an annular arrangement; and a near-field communication (NFC) coil disposed within the encapsulating structure and coaxial with the annular magnetic alignment component, the NFC coil coupled to an NFC tag circuit. In these and other embodiments, each arcuate magnet can have: an inner arcuate region having a magnetic polarity oriented in a first axial direction; an outer arcuate region having a magnetic polarity oriented in a second axial direction opposite the first axial direction; and a non-magnetized central arcuate region disposed between the inner arcuate region and the outer arcuate region. In these and other embodiments, the NFC coil can be disposed inboard of the annular magnetic alignment component, and other NFC tag circuit components can be disposed inboard of the annular magnetic alignment component and or in gaps between certain arcuate magnets of the annular magnetic alignment component. In these and other embodiments, the encapsulating structure can comprise: a front planar layer; a back planar layer; and a magnet-holding layer, the magnet-holding layer having a circular opening therethrough to accommodate the annular magnetic alignment component (and the NFC coil). In these and other embodiments, the magnet-holding layer and the arcuate magnets can have equal thicknesses. In these and other embodiments, the magnet-holding layer can include a disc of material filling a region interior to the annular magnetic alignment component and the NFC coil. In these and other embodiments, an alignment module can further comprise: a rotational alignment component comprising a rectangular magnet and disposed outboard (or outside a perimeter) of the annular magnetic alignment component, and the magnet-holding layer can have a rectangular opening therethrough to accommodate the rotational alignment component. 
     Accordingly, although the invention has been described with respect to specific embodiments, it will be appreciated that the invention is intended to cover all modifications and equivalents within the scope of the following claims.

Metadata:
Filing Date: 20200922
Publication Date: 20230808
Grant Date: 20230808
Priority Date: 20190927
Inventors: JOL, ERIC S.
LARSSON, KARL RUBEN F.
Oro, Aaron A.
RASMUSSEN, Timothy J.
GRAHAM, Christopher S.
WU, James C.
KARANIKOS, DEMETRIOS B.
DALY, Miranda L.
THOMPSON, PAUL J.
MENDOZA, JOSHUA A.
Assignee: APPLE INC
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Family ID: 72752535