PATENT DOCUMENT

Publication Number: US-11909248-B2
Application Number: US-202117179647-A
Country: US
Kind Code: B2

Title: Accessory with a magnetic relay structure for wireless power transfer

Abstract:
A device in a wireless power system may be operable with a removable accessory such as a case. The device may transmit or receive wireless power through the case while the electronic device is coupled to the case. The case may have a folio shape with a front cover portion that covers the display of the electronic device. The case may have an embedded ferrimagnetic core that relays magnetic flux during wireless power transfer operations. Magnetic alignment structures in the case may position the ferrimagnetic core in the case in a high magnetic flux density region between the power transmitting device and the power receiving device. The ferrimagnetic core relays the magnetic flux between a transmitting coil in the power transmitting device and a receiving coil in the power receiving device. The ferrimagnetic core may be formed in a front portion, a sidewall, or a rear wall of a case.

Claims:
What is claimed is: 
     
       1. A cover for an electronic device having a front face, the cover comprising:
 a rear cover portion configured to receive the electronic device; 
 a front cover portion configured to move relative to the rear cover portion and configured to cover the front face of the electronic device; and 
 a ferrimagnetic core embedded in the front cover portion, wherein the ferrimagnetic core is configured to direct received magnetic flux from a first coil in the electronic device to a second coil in an additional electronic device; 
 a first magnetic alignment structure in the front cover portion; and 
 a shielding structure in the front cover portion, wherein the shielding structure is interposed between the ferrimagnetic core and the first magnetic alignment structure. 
 
     
     
       2. The cover of  claim 1 , wherein the ferrimagnetic core is a first ferrimagnetic core and wherein first ferrimagnetic core is interposed between a second ferrimagnetic core in the electronic device and a third ferrimagnetic core in the additional electronic device when the first magnetic alignment structure is magnetically coupled to a second magnetic alignment structure in the electronic device and a third magnetic alignment structure in the additional electronic device. 
     
     
       3. The cover of  claim 1 , wherein the shielding structure is a circular shielding structure that laterally surrounds the ferrimagnetic core. 
     
     
       4. The cover of  claim 1 , wherein the shielding structure comprises copper. 
     
     
       5. The cover of  claim 2 , wherein the first magnetic alignment structure is a first permanent magnet, wherein the second magnetic alignment structure is a second permanent magnet, and wherein the third magnetic alignment structure is a third permanent magnet. 
     
     
       6. The cover of  claim 1  wherein the ferrimagnetic core is positioned in a high magnetic flux density region between the electronic device and the additional electronic device when the first magnetic alignment structure is aligned with a second magnetic alignment structure in the electronic device and a third magnetic alignment structure in the additional electronic device. 
     
     
       7. The cover of  claim 1 , wherein the ferrimagnetic core is a first ferrimagnetic core and wherein the cover further comprises:
 a second ferrimagnetic core embedded in the front cover portion, wherein the second ferrimagnetic core is configured to direct received magnetic flux from a third coil in the electronic device towards a fourth coil in the additional electronic device. 
 
     
     
       8. A cover for an electronic device having a front face, the cover comprising:
 a rear cover portion configured to receive the electronic device; 
 a front cover portion configured to move relative to the rear cover portion and configured to cover the front face of the electronic device; 
 a first ferrimagnetic core embedded in the front cover portion, wherein the first ferrimagnetic core is configured to direct received magnetic flux from a first coil in the electronic device to a second coil in an additional electronic device; 
 a second ferrimagnetic core embedded in the front cover portion, wherein the second ferrimagnetic core is configured to direct received magnetic flux from a third coil in the electronic device towards a fourth coil in the additional electronic device; 
 a first permanent magnet in the front cover portion; 
 a second permanent magnet in the front cover portion; 
 a first shielding structure interposed between the first ferrimagnetic core and the first permanent magnet; and 
 a second shielding structure interposed between the second ferrimagnetic core and the second permanent magnet. 
 
     
     
       9. The cover of  claim 8 , wherein the first permanent magnet is configured to magnetically couple to a third permanent magnet in the electronic device and wherein the first permanent magnet is configured to magnetically couple to a fourth permanent magnet in the additional electronic device. 
     
     
       10. The cover of  claim 1 , wherein the additional electronic device comprises a stylus and wherein the front cover portion is interposed between the stylus and the front face of the electronic device during wireless charging when the front cover portion covers the front face. 
     
     
       11. The cover of  claim 10 , wherein the stylus is configured to overlap a display area of a screen of the electronic device during wireless charging. 
     
     
       12. The cover of  claim 10 , wherein the stylus is configured to overlap a border area of the electronic device during wireless charging and wherein the border area is interposed between a display area of a screen of the electronic device and an edge of the electronic device. 
     
     
       13. The cover of  claim 10 , wherein the stylus and the electronic device are configured to transfer wireless power to one another when the stylus is placed directly on the front face of the electronic device. 
     
     
       14. An accessory for an electronic device, the accessory comprising:
 a dielectric layer that is interposed between the electronic device and an additional electronic device during wireless power transfer operations between the electronic device and the additional electronic device; 
 a first magnetic alignment structure; 
 a first ferrimagnetic core in the dielectric layer that is interposed between a second ferrimagnetic core in the electronic device and a third ferrimagnetic core in the additional electronic device when the first magnetic alignment structure is magnetically coupled to a second magnetic alignment structure in the electronic device and a third magnetic alignment structure in the additional electronic device; and 
 a shielding structure in the dielectric layer, wherein the shielding structure is interposed between the first ferrimagnetic core and the first magnetic alignment structure. 
 
     
     
       15. The accessory of  claim 14 , wherein the accessory further comprises a rear wall and peripheral sidewalls that define a recess configured to receive the electronic device. 
     
     
       16. The accessory of  claim 15 , wherein one of the peripheral sidewalls includes the dielectric layer and the first ferrimagnetic core. 
     
     
       17. The accessory of  claim 15 , wherein the rear wall includes the dielectric layer and the first ferrimagnetic core. 
     
     
       18. The accessory of  claim 15 , wherein the first ferrimagnetic core is configured to relay received magnetic flux from a first coil in the electronic device towards a second coil in the additional electronic device. 
     
     
       19. The accessory of  claim 15 , wherein the first ferrimagnetic core is configured to relay received magnetic flux from a first coil in the additional electronic device towards a second coil in the electronic device. 
     
     
       20. The accessory of  claim 14 , wherein the first magnetic alignment structure is a circular permanent magnet having a central opening and wherein the first ferrimagnetic core is a circular magnetic core positioned in the central opening.

Description:
This application claims priority to U.S. provisional patent application No. 63/034,544 filed Jun. 4, 2020, which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD 
     This relates generally to power systems, and, more particularly, to wireless power systems for charging electronic devices. 
     BACKGROUND 
     In a wireless charging system, a wireless power transmitting device such as a charging mat or charging puck wirelessly transmits power to a wireless power receiving device such as a portable electronic device. The portable electronic device has a coil and rectifier circuitry. The coil of the portable electronic device receives alternating-current wireless power signals from the wireless power transmitting device. The rectifier circuitry converts the received signals into direct current power. 
     SUMMARY 
     A wireless power system has a wireless power transmitting device and a wireless power receiving device. The wireless power transmitting device may include a coil and wireless power transmitting circuitry coupled to the coil. The wireless power transmitting circuitry may be configured to transmit wireless power signals with the coil. The wireless power receiving device may include a coil that is configured to receive wireless power signals from the wireless power transmitting device and rectifier circuitry that is configured to convert the wireless power signals to direct current power. 
     A device in a wireless power system may be operable with a removable accessory such as a case. The device may transmit or receive wireless power through the case while the electronic device is coupled to the case. The case may have a folio shape with a front cover portion that covers the display of the electronic device. 
     The removable accessory may have an embedded ferrimagnetic core that relays magnetic flux during wireless power transfer operations between electronic devices adjacent to the removable accessory. Magnetic alignment structures in the case may position the ferrimagnetic core in the case in a high magnetic flux density region between the power transmitting device and the power receiving device. The ferrimagnetic core relays the magnetic flux between a transmitting coil in the power transmitting device and a receiving coil in the power receiving device. 
     The ferrimagnetic core may be formed in a front portion of a case that is configured to cover a display of an electronic device. The ferrimagnetic core may also be formed in a sidewall or a rear wall of a case. The case may include copper shielding structures around the ferrimagnetic core. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram of an illustrative wireless charging system that includes a wireless power transmitting device and a wireless power receiving device in accordance with an embodiment. 
         FIG.  2    is a circuit diagram of illustrative wireless power transmitting and receiving circuitry in accordance with an embodiment. 
         FIGS.  3 A and  3 B  are top and cross-sectional side views respectively of an illustrative device in a wireless charging system in accordance with an embodiment. 
         FIG.  4    is a top view of an illustrative removable case having a front cover portion in accordance with an embodiment. 
         FIG.  5    is a cross-sectional side view of the illustrative removable case of  FIG.  4    in accordance with an embodiment. 
         FIG.  6    is a perspective view of an illustrative wireless charging system that includes an electronic device and a removable case without a front cover portion in accordance with an embodiment. 
         FIG.  7    is a side view of an illustrative wireless charging system with a wireless power transmitting device that is directly adjacent to a wireless power receiving device in accordance with an embodiment. 
         FIGS.  8 A and  8 B  are side views of an illustrative wireless charging system with a removable case that is interposed between a wireless power transmitting device and a wireless power receiving device in accordance with an embodiment. 
         FIGS.  9 A and  9 B  are top views of an illustrative removable cover with magnetic cores for relaying magnetic flux between a wireless power transmitting device and a wireless power receiving device in accordance with an embodiment. 
         FIG.  10    is a side view of an illustrative wireless charging system with a removable case having a ring-shaped magnetic core that is interposed between a wireless power transmitting device and a wireless power receiving device in accordance with an embodiment. 
         FIG.  11    is a top view of an illustrative removable cover with a ring-shaped magnetic core of the type shown in  FIG.  10    in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A wireless power system has a wireless power transmitting device that transmits power wirelessly to a wireless power receiving device. The wireless power transmitting device may be a device such as a wireless charging mat, wireless charging puck, wireless charging stand, wireless charging table, or other wireless power transmitting equipment. The wireless power transmitting device may be a stand-alone device or built into other electronic devices such as a laptop or tablet computer, cellular telephone or other electronic device. The wireless power transmitting device has one or more coils that are used in transmitting wireless power to one or more wireless power receiving coils in the wireless power receiving device. The wireless power receiving device is a device such as a cellular telephone, watch, media player, tablet computer, pair of earbuds, remote control, laptop computer, electronic pencil or stylus, other portable electronic device, or other wireless power receiving equipment. 
     During operation, the wireless power transmitting device supplies alternating-current signals to one or more wireless power transmitting coils. This causes the coils to transmit alternating-current electromagnetic signals (sometimes referred to as wireless power signals) to one or more corresponding coils in the wireless power receiving device. Rectifier circuitry in the wireless power receiving device converts received wireless power signals into direct-current (DC) power for powering the wireless power receiving device. 
     In some instances, an electronic device may be coupled to a removable case. When held by the removable case, a portion of the removable case may sometimes be interposed between the electronic device and an adjacent electronic device. In one example, the electronic device held by the case may serve as a power receiving device and the adjacent electronic device may serve as a power transmitting device. In another example, the electronic device held by the case may serve as a power transmitting device and the adjacent electronic device may serve as a power receiving device. The presence of the removable case may lead to an increased distance between coils in the wireless power receiving device and the wireless power transmitting device. To improve charging efficiency, the removable case may include one or more magnetic cores (e.g., ferrite pieces) to direct magnetic flux from the transmitting device to the receiving device. 
     An illustrative wireless power system (wireless charging system) is shown in  FIG.  1   . As shown in  FIG.  1   , wireless power system  8  includes a wireless power transmitting device such as wireless power transmitting device  12  and includes a wireless power receiving device such as wireless power receiving device  24 . Wireless power transmitting device  12  includes control circuitry  16 . Wireless power receiving device  24  includes control circuitry  30 . Control circuitry in system  8  such as control circuitry  16  and control circuitry  30  is used in controlling the operation of system  8 . This control circuitry may include processing circuitry associated with microprocessors, power management units, baseband processors, digital signal processors, microcontrollers, and/or application-specific integrated circuits with processing circuits. The processing circuitry implements desired control and communications features in devices  12  and  24 . For example, the processing circuitry may be used in selecting coils, determining power transmission levels, processing sensor data and other data, processing user input, handling negotiations between devices  12  and  24 , sending and receiving in-band and out-of-band data, making measurements, and otherwise controlling the operation of system  8 . 
     Control circuitry in system  8  may be configured to perform operations in system  8  using hardware (e.g., dedicated hardware or circuitry), firmware and/or software. Software code for performing operations in system  8  is stored on non-transitory computer readable storage media (e.g., tangible computer readable storage media) in control circuitry  8 . The software code may sometimes be referred to as software, data, program instructions, instructions, or code. The non-transitory computer readable storage media may include non-volatile memory such as non-volatile random-access memory (NVRAM), one or more hard drives (e.g., magnetic drives or solid state drives), one or more removable flash drives or other removable media, or the like. Software stored on the non-transitory computer readable storage media may be executed on the processing circuitry of control circuitry  16  and/or  30 . The processing circuitry may include application-specific integrated circuits with processing circuitry, one or more microprocessors, a central processing unit (CPU) or other processing circuitry. 
     Power transmitting device  12  may be a stand-alone power adapter (e.g., a wireless power transmitting device that includes power adapter circuitry), may be a wireless charging puck or other device that is coupled to a power adapter or other equipment by a cable, may be equipment that has been incorporated into furniture, a vehicle, or other system, may be a removable battery case, or may be other wireless power transfer equipment. In some cases, power transmitting device  12  may be a portable electronic device such as a cellular telephone, watch, media player, tablet computer, pair of earbuds, remote control, laptop computer, electronic pencil or stylus, or other portable electronic device. Power transmitting device  12  may also be capable of receiving wireless power (and may have similar power receiving components as power receiving device  24 ). 
     Power receiving device  24  may be a portable electronic device such as a cellular telephone, watch, media player, tablet computer, pair of earbuds, remote control, laptop computer, electronic pencil or stylus, other portable electronic device, or other wireless power receiving equipment. 
     Power transmitting device  12  may be coupled to a wall outlet (e.g., an alternating current power source), may have a battery such as battery  18  for supplying power, and/or may have another source of power. Power transmitting device  12  may have an alternating-current (AC) to direct-current (DC) power converter such as AC-DC power converter  14  for converting AC power from a wall outlet or other power source into DC power. DC power may be used to power control circuitry  16  and other components within device  12 . In some cases, a single electronic device may be configured to serve as both a power receiving device and a power transmitting device (e.g., the device has both power transmitting circuitry and power receiving circuitry). 
     The DC power may be used to power control circuitry  16 . During operation, a controller in control circuitry  16  uses power transmitting circuitry  52  to transmit wireless power to power receiving circuitry  54  of device  24 . Power transmitting circuitry  52  may have switching circuitry (e.g., inverter circuitry  61  formed from switches such as transistors) that is turned on and off based on control signals provided by control circuitry  16  to create AC current signals through one or more wireless power transmitting coils such as wireless power transmitting coils  36 . Coils  36  may be arranged in a planar coil array (e.g., in configurations in which device  12  is a wireless charging mat) or may be arranged to form a cluster of coils (e.g., in configurations in which device  12  is a wireless charging puck). In some arrangements, device  12  may have only a single coil. In other arrangements, device  12  may have multiple coils (e.g., two coils, more than two coils, four or more coils, six or more coils, 2-6 coils, fewer than 10 coils, etc.). 
     As the AC currents pass through one or more coils  36 , alternating-current electromagnetic (e.g., magnetic) fields (wireless power signals  44 ) are produced that are received by one or more corresponding receiver coils such as coil(s)  48  in power receiving device  24 . Device  24  may have a single coil  48 , at least two coils  48 , at least three coils  48 , at least four coils  48 , or other suitable number of coils  48 . 
     When the alternating-current electromagnetic fields (sometimes referred to as magnetic flux) are received by coils  48  (e.g., when magnetic flux passes through coils  48 ), corresponding alternating-current currents are induced in coils  48 . Rectifier circuitry such as rectifier circuitry  50 , which contains rectifying components such as synchronous rectification metal-oxide-semiconductor transistors arranged in a bridge network, converts received AC signals (received alternating-current signals associated with electromagnetic signals  44 ) from one or more coils  48  into DC voltage signals for powering device  24 . 
     The DC voltage produced by rectifier circuitry  50  (sometimes referred to as rectifier output voltage Vrect) can be used in charging a battery such as battery  58  and can be used in powering other components in device  24 . For example, device  24  may include input-output devices  56 . Input-output devices  56  may include input devices for gathering user input and/or making environmental measurements and may include output devices for providing a user with output. As an example, input-output devices  56  may include a display for creating visual output, a speaker for presenting output as audio signals, light-emitting diode status indicator lights and other light-emitting components for emitting light that provides a user with status information and/or other information, haptic devices for generating vibrations and other haptic output, and/or other output devices. Input-output devices  56  may also include sensors for gathering input from a user and/or for making measurements of the surroundings of system  8 . Illustrative sensors that may be included in input-output devices  56  include three-dimensional sensors (e.g., three-dimensional image sensors such as structured light sensors that emit beams of light and that use two-dimensional digital image sensors to gather image data for three-dimensional images from light spots that are produced when a target is illuminated by the beams of light, binocular three-dimensional image sensors that gather three-dimensional images using two or more cameras in a binocular imaging arrangement, three-dimensional lidar (light detection and ranging) sensors, three-dimensional radio-frequency sensors, or other sensors that gather three-dimensional image data), cameras (e.g., infrared and/or visible cameras with respective infrared and/or visible digital image sensors and/or ultraviolet light cameras), gaze tracking sensors (e.g., a gaze tracking system based on an image sensor and, if desired, a light source that emits one or more beams of light that are tracked using the image sensor after reflecting from a user&#39;s eyes), touch sensors, buttons, capacitive proximity sensors, light-based (optical) proximity sensors such as infrared proximity sensors, other proximity sensors, force sensors, sensors such as contact sensors based on switches, gas sensors, pressure sensors, moisture sensors, magnetic sensors, audio sensors (microphones), ambient light sensors, optical sensors for making spectral measurements and other measurements on target objects (e.g., by emitting light and measuring reflected light), microphones for gathering voice commands and other audio input, distance sensors, motion, position, and/or orientation sensors that are configured to gather information on motion, position, and/or orientation (e.g., accelerometers, gyroscopes, compasses, and/or inertial measurement units that include all of these sensors or a subset of one or two of these sensors), sensors such as buttons that detect button press input, joysticks with sensors that detect joystick movement, keyboards, and/or other sensors. Any of these input-output components (which form a load for device  24 ) may be powered by the DC voltages produced by rectifier circuitry  50  (and/or DC voltages produced by battery  58 ). 
     Device  12  may optionally have one or more input-output devices  60  (e.g., input devices and/or output devices of the type described in connection with input-output devices  56 ). For example, device  12  may be a tablet computer that includes a display  32  and one or more sensors. 
     Device  12  and/or device  24  may communicate wirelessly using in-band or out-of-band communications. Device  12  may, for example, have wireless transceiver circuitry  40  that wirelessly transmits out-of-band signals to device  24  using an antenna. Wireless transceiver circuitry  40  may be used to wirelessly receive out-of-band signals from device  24  using the antenna. Device  24  may have wireless transceiver circuitry  46  that transmits out-of-band signals to device  12 . Receiver circuitry in wireless transceiver  46  may use an antenna to receive out-of-band signals from device  12 . In-band transmissions between devices  12  and  24  may be performed using coils  36  and  48 . 
     It is desirable for power transmitting device  12  and power receiving device  24  to be able to communicate information such as received power, states of charge, and so forth, to control wireless power transfer. However, this process need not involve the transmission of device identification information. Out of an abundance of caution, it is noted that to the extent that any implementation of this charging technology involves the use of device identification information (or more generally, personally identifiable information), implementers 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, identification 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. Where possible, such identification information may be abstracted, such as by using some but not all bits in a byte of information, so that the resulting identification is not globally unique but still sufficient to facilitate communication under reasonable device usage scenarios. 
     Control circuitry  16  has external object measurement circuitry  41  that may be used to detect external objects adjacent to device  12  (e.g., on the top of a charging surface). Circuitry  41  may detect foreign objects such as coils, paper clips, and other metallic objects and may detect the presence of wireless power receiving devices  24  (e.g., circuitry  41  can detect the presence of one or more coils  48 ). In arrangements in which device  12  forms a charging puck, the charging puck may have a surface shape that mates with the shape of device  24 . A puck or other device  12  may, if desired, have magnets (sometimes referred to as magnetic alignment structures) that removably attach device  12  to device  24 , in the process aligning coil  48  with coil  36  for efficient wireless charging. 
     During object detection and characterization operations, external object measurement circuitry  41  can be used to make measurements on coils  36  to determine whether any devices  24  are present on device  12 . Additional coils (that are not used for power transmission) and/or other additional sensors may be used for object detection and characterization operations if desired. 
     In an illustrative arrangement, measurement circuitry  41  of control circuitry  16  contains signal generator circuitry (e.g., oscillator circuitry for generating AC probe signals at one or more probe frequencies, a pulse generator that can create impulses so that impulse responses can be measured to gather inductance information, Q-factor information, etc.) and signal detection circuitry (e.g., filters, analog-to-digital converters, impulse response measurement circuits, etc.). During measurement operations, switching circuitry in device  12  (e.g., in the puck of device  12 ) may be adjusted by control circuitry  16  to switch each of coils  36  into use. As each coil  36  is selectively switched into use, control circuitry  16  uses the signal generator circuitry of signal measurement circuitry  41  to apply a probe signal to that coil while using the signal detection circuitry of signal measurement circuitry  41  to measure a corresponding response. Measurement circuitry  43  in control circuitry  30  and/or in control circuitry  16  may also be used in making current and voltage measurements (e.g., so that this information can be used by device  24  and/or device  12 ). 
       FIG.  2    is a circuit diagram of illustrative wireless charging circuitry for system  8 . As shown in  FIG.  2   , circuitry  52  may include inverter circuitry such as one or more inverters  61  or other drive circuitry that produces wireless power signals that are transmitted through an output circuit that includes one or more coils  36  and capacitors such as capacitor  70 . In some embodiments, device  12  may include multiple individually controlled inverters  61 , each of which supplies drive signals to a respective coil  36 . In other embodiments, an inverter  61  is shared between multiple coils  36  using switching circuitry. 
     During operation, control signals for inverter(s)  61  are provided by control circuitry  16  at control input  74 . A single inverter  61  and single coil  36  is shown in the example of  FIG.  2   , but multiple inverters  61  and multiple coils  36  may be used, if desired. In a multiple coil configuration, switching circuitry (e.g., multiplexer circuitry) can be used to couple a single inverter  61  to multiple coils  36  and/or each coil  36  may be coupled to a respective inverter  61 . During wireless power transmission operations, transistors in one or more selected inverters  61  are driven by AC control signals from control circuitry  16 . The relative phase between the inverters can be adjusted dynamically (e.g., a pair of inverters  61  may produce output signals in phase or out of phase (e.g., 180 degrees out of phase). 
     The application of drive signals using inverter(s)  61  (e.g., transistors or other switches in circuitry  52 ) causes the output circuits formed from selected coils  36  and capacitors  70  to produce alternating-current electromagnetic fields (signals  44 ) that are received by wireless power receiving circuitry  54  using a wireless power receiving circuit formed from one or more coils  48  and one or more capacitors  72  in device  24 . 
     If desired, the relative phase between driven coils  36  (e.g., the phase of one of coils  36  that is being driven relative to another adjacent one of coils  36  that is being driven) may be adjusted by control circuitry  16  to help enhance wireless power transfer between device  12  and device  24 . Rectifier circuitry  50  is coupled to one or more coils  48  (e.g., a pair of coils) and converts received power from AC to DC and supplies a corresponding direct current output voltage Vrect across rectifier output terminals  76  for powering load circuitry in device  24  (e.g., for charging battery  58 , for powering a display and/or other input-output devices  56 , and/or for powering other components). A single coil  48  or multiple coils  48  may be included in device  24 . In an illustrative configuration, device  24  may be a stylus or other portable device with at least two coils  48 . These two (or more) coils  48  may be used together when receiving wireless power. Other configurations may be used, if desired. 
     As previously mentioned, in-band transmissions using coils  36  and  48  may be used to convey (e.g., transmit and receive) information between devices  12  and  24 . With one illustrative configuration, frequency-shift keying (FSK) is used to transmit in-band data from device  12  to device  24  and amplitude-shift keying (ASK) is used to transmit in-band data from device  24  to device  12 . Power may be conveyed wirelessly from device  12  to device  24  during these FSK and ASK transmissions (e.g., at least some wireless power is conveyed during the in-band communications, whether or not devices  12  and  24  have completed a handshake process and agreed upon a sustained power transfer level). While power transmitting circuitry  52  is driving AC signals into one or more of coils  36  to produce signals  44  at the power transmission frequency, wireless transceiver circuitry  40  may use FSK modulation to modulate the power transmission frequency of the driving AC signals and thereby modulate the frequency of signals  44 . In device  24 , coil  48  is used to receive signals  44 . Power receiving circuitry  54  uses the received signals on coil  48  and rectifier  50  to produce DC power. At the same time, wireless transceiver circuitry  46  monitors the frequency of the AC signal passing through coil(s)  48  and uses FSK demodulation to extract the transmitted in-band data from signals  44 . This approach allows FSK data (e.g., FSK data packets) to be transmitted in-band from device  12  to device  24  with coils  36  and  48  while power is simultaneously being wirelessly conveyed from device  12  to device  24  using coils  36  and  48 . 
     In-band communications between device  24  and device  12  may use ASK modulation and demodulation techniques. Wireless transceiver circuitry  46  transmits in-band data to device  12  by using a switch (e.g., one or more transistors in transceiver  46  that are coupled coil  48 ) to modulate the impedance of power receiving circuitry  54  (e.g., coil  48 ). This, in turn, modulates the amplitude of signal  44  and the amplitude of the AC signal passing through coil(s)  36 . Wireless transceiver circuitry  40  monitors the amplitude of the AC signal passing through coil(s)  36  and, using ASK demodulation, extracts the transmitted in-band data from these signals that was transmitted by wireless transceiver circuitry  46 . The use of ASK communications allows ASK data bits (e.g., ASK data packets) to be transmitted in-band from device  24  to device  12  with coils  48  and  36  while power is simultaneously being wirelessly conveyed from device  12  to device  24  using coils  36  and  48 . 
     The example of FSK modulation being used to convey in-band data from power transmitting device  12  to power receiving device  24  and ASK modulation being used to convey in-band data from power receiving device  24  to power transmitting device  12  is merely illustrative. In general, any desired communication techniques may be used to convey information from power transmitting device  12  to power receiving device  24  and from power receiving device  24  to power transmitting device  12 . 
     In the illustrative configuration of  FIGS.  3 A and  3 B , which is sometimes described herein as an example, device  12  is a tablet computer or other device with a display. Device  12  may transmit wireless power to an additional device such as a computer stylus. A user can use the stylus to draw or write on tablet computer  12  and to provide other input to tablet computer  12 . 
       FIG.  3 A  is a top view of device  12  and  FIG.  3 B  is a cross-sectional side view of device  12 . As shown in  FIG.  3 A , tablet computer  12  may include a housing such as housing  164  in which display  32  is mounted. Additional input-output devices (such as a button) may also be used to supply input to tablet computer  12 . Display  32  may be a capacitive touch screen display or a display that includes other types of touch sensor technology. The touch sensor of display  32  may be configured to receive input from a stylus. The stylus may also receive wireless power from device  12 . 
     The stylus may have a cylindrical shape or other elongated body that extends along a longitudinal axis. The body of the stylus may be formed from metal and/or plastic tubes and other elongated structures. The stylus may have a tip that contains a conductive elastomeric member that is detected by a touch sensor of the display in tablet computer  12 . If desired, the tip may contain active electronics (e.g., circuitry that transmits signals that are capacitively coupled into the touch sensor of the display and that are detected as touch input on the touch sensor). 
     The stylus may include a shaft portion that couples the tip to an opposing end of the stylus. The end opposite the tip may contain a conductive elastomeric member, active electronics (e.g., circuitry that transmits signals that are capacitively coupled into the touch sensor of the tablet display and that are detected as touch input on the touch sensor), buttons, a metal connector that mates with an external plug, or other input-output components. 
     A force sensor may be incorporated into the stylus tip and/or the opposing end of the stylus. A force sensor may be used to measure how forcefully a user is pressing the stylus against the outer surface of the display of device  12 . Force data may then be wirelessly transmitted from the stylus to tablet  12  so that the thickness of a line that is being drawn on the tablet display can be adjusted accordingly or so that device  12  may take other suitable action. 
     Housing  164  of tablet  12 , which may sometimes be referred to as an enclosure or case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of any two or more of these materials. Housing  164  may be formed using a unibody configuration in which some or all of housing  164  is machined or molded as a single structure or may be formed using multiple structures (e.g., an internal frame structure, one or more structures that form exterior housing surfaces, etc.). In the example of  FIGS.  3 A and  3 B , housing  164  includes a conductive peripheral sidewall structure  164 W that surrounds a periphery of tablet  12 . Housing  164  may, if desired, include a conductive rear wall structure  164 R that opposes display  32  (e.g., conductive rear wall structure  164 R may form the rear exterior face, side, or surface of tablet  12 ). If desired, rear wall  164 R and sidewalls  164 W may be formed from a continuous structure (e.g., in a unibody configuration) or from separate structures. Openings may be formed in housing  164  to form communications ports, holes for buttons, and other structures if desired. Rear wall  164 R and/or sidewalls  164 W may be formed from metal or dielectric materials such as ceramics, plastic, or glass. 
     Display  32  may be a touch screen display that incorporates a layer of conductive capacitive touch sensor electrodes or other touch sensor components (e.g., resistive touch sensor components, acoustic touch sensor components, force-based touch sensor components, light-based touch sensor components, etc.) or may be a display that is not touch-sensitive. Capacitive touch screen electrodes may be formed from an array of indium tin oxide pads or other transparent conductive structures. 
     Display  32  (sometimes referred to as a screen) may have an active area that includes an array of display pixels. The array of pixels may be formed from liquid crystal display (LCD) components, an array of electrophoretic pixels, an array of plasma display pixels, an array of organic light-emitting diode display pixels or other light-emitting diode pixels, an array of electrowetting display pixels, or display pixels based on other display technologies. 
     Display  32  may be protected using a display cover layer such as a layer of transparent glass, clear plastic, transparent ceramic, sapphire, or other transparent crystalline material, or other optically transparent layer(s). The display cover layer may have a planar shape, a convex curved profile, a shape with planar and curved portions, a layout that includes a planar main area surrounded on one or more edges with a portion that is bent out of the plane of the planar main area, or other suitable shapes. The display cover layer may cover the entire front face of tablet  12  (e.g., extending across an entirety of a length dimension of tablet  12  parallel to the y-axis and a width dimension of tablet  12  parallel to the x-axis of  FIGS.  3 A and  3 B ). Sidewalls  164 W may extend from a rear face of tablet  12  formed by rear wall  164 R to the display cover layer (e.g., extending across a height dimension of tablet  12  parallel to the z-axis of  FIGS.  3 A and  3 B ). In another suitable arrangement, the display cover layer may cover substantially all of the front face of tablet  12  or only a portion of the front face of tablet  12 . Openings may be formed in the display cover layer. For example, an opening may be formed in the display cover layer to accommodate a button. An opening may also be formed in the display cover layer to accommodate ports such as a speaker port. 
     Housing  164  may have four peripheral edges (e.g., sidewalls  164 W). One or more wireless power transmitting coils  36  may be mounted within housing  164  behind display  32 . If desired, one or more wireless power transmitting coils  36  may be mounted behind display  32  and adjacent to one of the four peripheral edges. For example, one or more coils  36  may be mounted behind display  32  within peripheral edge region  166 , within peripheral edge region  168 , within peripheral edge region  170 , and/or within peripheral edge region  172 . When mounted behind display  32 , coils  36  may wirelessly convey power to a stylus through display  32  when the stylus is placed onto the surface of display  32 . In these examples, transmitting coils are positioned behind the screen such that the stylus is placed on a display area (active area) of the screen (e.g., a light-emitting area of the screen) and receives wireless power through the display area during wireless charging. These examples are merely illustrative. In another possible embodiment, the stylus may be placed in a border area (inactive area) of the screen (e.g., an area of the screen without light-emitting pixels that extends around one or more sides of the periphery of the screen) during charging and may receive wireless power from transmitting coils through the border area. The border area may be interposed between the display area of the screen and an edge of the electronic device. 
     Consider an example in which a wireless power transmitting coil  36  is formed within region  168  of tablet  12 . In this scenario, when it is desired to charge a stylus, a user may place the stylus onto the surface of display  32  within region  168  (e.g., so that the stylus shaft lies on the surface of display  32  and is aligned with the y-axis of  FIG.  3 A ). When the stylus is placed onto display  32  within region  168  (e.g., directly on the front face of the electronic device), a wireless power receiving coil in the stylus (e.g., coil  48  in  FIG.  1   ) may be aligned with a wireless power transmitting coil  36  in region  168 . When aligned, wireless power signals  44  may be transmitted from tablet computer  12  to the stylus. The wireless power received by the stylus may be used to charge a battery (e.g., battery  58  in  FIG.  1   ). Once battery  58  has become sufficiently charged, the user may pick up the stylus and continue to use the stylus to provide user input to tablet  12 . 
     If desired, alignment structures may be formed within regions  166 ,  168 ,  170 , and/or  172  to help ensure that receiving coil(s)  48  on the stylus are aligned with transmitting coil(s)  36  on tablet  12  when the stylus is placed on the surface of display  32 . Examples of such alignment structures include magnetic alignment structures, indentations or grooves formed on the front face of display  32 , clip structures, adhesive structures, or any other desired alignment structures. In the example where transmitting coils are located within region  168 , magnetic alignment structures may be formed within or adjacent to region  168  and under display  32  if desired. The magnetic alignment structures may attract conductive or magnetic structures on the stylus to snap and hold the stylus into a position at which coils  36  and  48  are aligned. 
     If desired, one or more wireless power transmitting coils  36  may be mounted within tablet  12  adjacent to housing sidewalls  164 W such as within region  174  of  FIG.  3 B . In scenarios where housing sidewalls  164 W are formed from conductive material, a dielectric window may be formed within the sidewalls. Transmitting coils  36  may be mounted behind the dielectric windows to allow wireless power to be transferred to the stylus when the stylus is placed adjacent to the dielectric window or adjacent to the dielectric sidewall. 
     The example of  FIGS.  3 A and  3 B  is merely illustrative. If desired, one or more wireless power transmitting coils  36  may be formed adjacent to rear housing wall  164 R for charging stylus  24  through rear wall  164 R. In scenarios where rear housing wall  164 R is formed from conductive materials, dielectric windows may be formed within rear housing wall  164 R and coils  36  may transmit wireless power to a stylus through the dielectric windows in rear housing wall  164 R. In another suitable arrangement, rear housing wall  164 R may be formed from dielectric (e.g., a dielectric cover layer that forms the rear face of the tablet). In general, wireless power transmitting coils  36  may be formed at any desired location along display  32 , along housing sidewalls  164 W, and/or along rear housing wall  164 R. Locating transmitting coils  36  along the periphery of display  32  such as in regions  166 ,  168 ,  170 , and  172  may allow the stylus to be placed on the surface of display  32  without blocking an excessive amount of the viewing region of display  32  (e.g., so that a user can still view images displayed using display  32  while the stylus is being charged). However, in general, wireless power transmitting coils  36  may be located at any desired location along the surface of display  32 . Wireless power transmitting coils  36  may be located along any of the four peripheral sidewalls  164 W of tablet  12 . 
     In this example, a tablet computer serves as a wireless power transmitting device that transmits wireless power to an external device such as a stylus. This example is merely illustrative. Instead, or in addition, a tablet computer may include power receiving coils for receiving wireless power. The power receiving coils (e.g., coils  48 ) may be positioned adjacent to a dielectric portion of rear housing wall  164 R, as one example. 
     As shown in  FIG.  4   , the wireless charging system may also include a removable cover  102 . Removable cover  102  (sometimes referred to as removable case) may have any suitable shape that allows cover  102  to mate with device  12 . In the example of  FIG.  4   , cover  102  has a folio shape (sometimes referred to as a folio cover) with a rear portion  102 R and front portion  102 F (sometimes referred to as first and second portions). Rear portion  102 R may have a rectangular recess with a rear wall surrounded by peripheral sidewalls  102 W or other suitable structures (straps, clips, a sleeve, corner pockets, etc.) that allow cover  102  to receive and couple to device  12 . 
     The portion of cover  102  that extends along fold axis  122  between rear portion  102 R and front portion  102 F may have hinge structures (e.g., flexible cover material that serves as a hinge or other hinge structures that couple portions  102 F and  102 R while allowing these portions to rotate relative to each other). In some configurations, additional bendable portions may be provided. For example, front portion  102 F may have one or more flexible strips. Each flexible strip allows additional folds to be formed in cover  102  (e.g., to manipulate the cover into one or more stand configurations and prop device  12  at a desired angle while cover  102  is coupled to device  12 ). Each flexible strip may extend parallel to fold axis  122  from one side of the front portion  102 F to another side of front portion  102 F. 
     When it is desired to protect device  12  in cover  102 , device  12  (e.g., housing  164  of device  12 ) may be press fit into a recess formed by the sidewalls  102 W and/or rear wall of cover  102 , coupled to cover  102  using magnets, clips, or straps, or otherwise coupled to cover  102 . Cover  102  may be formed from fabric, leather, polymer, other materials, and/or combinations of these materials. 
       FIG.  5    is a cross-sectional side view showing device  12  held in removable cover  102 . In  FIG.  5   , the front portion  102 F of cover  102  is folded over and covers the front face of device  12 . Accordingly, front portion  102 F of cover  102  covers the display ( 32 ) of device  12 . This may protect the display from damage. In certain arrangements, device  12  may need to transmit and/or receive wireless charging signals through cover  102 . For example, a stylus may be configured to be placed on the display for wireless charging (e.g., in one of regions  166 ,  168 ,  170 , and  172  in  FIG.  3 A ). Since front portion  102 F covers the display, the stylus may instead be placed on the front portion  102 F of the cover  102  instead of directly on the front face of the electronic device. Wireless power signals are then conveyed from device  12  to the stylus (e.g., receiving device  24 ) through cover  102 . 
     The presence of dielectric cover  102  between devices  12  and  24  during wireless charging may decrease charging efficiency (due to an increased distance between devices  12  and  24 ). To maintain charging efficiency between devices  12  and  24  with or without the presence of cover  102 , cover  102  may include ferrite pieces in front cover portion  102 F. The ferrite pieces may overlap a wireless charging area and serve to relay magnetic flux between the transmitting device and receiving device, as will be discussed later in greater detail. 
     The example in  FIGS.  4  and  5    of removable case  102  being a removable cover having a cover portion ( 102 F) configured to fold over and cover the display of device  12  is merely illustrative. In some arrangements, the front cover portion  102 F may be omitted from the removable case. An arrangement of this type is shown in  FIG.  6   . 
     As shown in  FIG.  6   , removable case  102  may include a rear portion  102 R (e.g., configured to cover a rear housing wall of device  12 , sometimes referred to as rear wall) and sidewalls  102 W (e.g., four peripheral sidewalls that extend from the rear wall). The sidewalls  102 W may form a recess that is configured to receive and secure device  12  within the removable case  102 . When it is desired to protect device  12  in case  102 , device  12  (e.g., housing  164  of device  12 ) may be press fit into a recess formed by the sidewalls  102 W of case  102 , coupled to case  102  using magnets, clips, or straps, or otherwise coupled to case  102 . Case  102  may be formed from fabric, leather, polymer, metal other materials, and/or combinations of these materials. 
     In general, wireless power signals may be conveyed (e.g., transmitted or received) through cover  102 . Consider an example where device  12  transmits wireless power signals to a stylus through an edge of the device housing (e.g., region  174  in  FIG.  3 B ). When the device is coupled to removable case  102 , the stylus may be placed on corresponding region  176  on sidewall  102 W of case  102 . Device  12  may transmit wireless power signals to the stylus through region  176  of cover  102 . Device  12  may also transmit wireless power signals to the stylus through a display area or border area of the screen and then through the front portion of the cover. 
     In another example, a tablet computer may include a wireless power receiving coil at a rear surface. In this situation, the tablet computer serves as a wireless power receiving device and may receive wireless power from a wireless power transmitting device such as a wireless charging mat or wireless charging puck. The tablet computer may still be coupled to a case  102  (e.g., of the type shown in  FIGS.  4  and  5    or  FIG.  6   ). When the tablet computer is coupled to a case  102 , rear portion  102 R of the case may be interposed between the tablet computer and the wireless charging mat. The tablet computer may therefore receive wireless power signals through a region  178  on rear portion  102 R of case  102 . 
       FIG.  7    shows an example of a wireless charging system  8  with a wireless power receiving device that is directly adjacent to a wireless power transmitting device (without an intervening case). As shown, a power transmitting assembly  202  (e.g., part of power transmitting circuitry  52 ) is included within wireless power transmitting device  12 . The power transmitting assembly (sometimes referred to as an inductive power transmitting assembly) includes a magnetic core  203  having a base  204 , a first limb  206 , and a second limb  208 . A first coil  36 - 1  is wound about the first limb  206  and a second coil  36 - 2  is wound about the second limb  208 . Coils  36 - 1  and  36 - 2  may be coupled to inverter circuitry (e.g., inverter  61  in  FIG.  1   ). The inverter circuitry can drive the coils  36 - 1  and  36 - 2  to generate magnetic flux. During operation, the first coil  36 - 1  and second coil  36 - 2  can be driven to generate magnetic flux having opposing polarity. 
     Magnetic core base  204  has a front surface  210  and a rear surface  212 . The coils  36 - 1  and  36 - 2  may each be wound about the respective limbs  206  and  208  circumferentially along the axis of the respective limb (e.g., in the direction that the limb extends from the front surface  210  of the base  204 ). The coils may be wound from a single-strand conductor, a multiple strand conductor having multiple wires connected in parallel, braided wire, Litz wire, a conductive ink or conductive trace such as multilayer tracks on a printed circuit board, or other conductive elements suitable for forming coils. 
     A power receiving assembly  222  (e.g., part of power receiving circuitry  54 ) is included within wireless power receiving device  24 . The power receiving assembly (sometimes referred to as an inductive power receiving assembly) includes a magnetic core  223  having a base  224 , a first limb  226 , and a second limb  228 . A first coil  48 - 1  is wound about the first limb  226  and a second coil  48 - 2  is wound about the second limb  228 . Coils  48 - 1  and  48 - 2  may be coupled to rectifier circuitry (e.g., rectifier  50  in  FIG.  1   ). The rectifier circuitry converts received AC signals from coils  48 - 1  and  48 - 2  into DC voltage signals for powering device  24 . 
     Magnetic core base  224  has a front surface  230  and a rear surface  232 . The coils  48 - 1  and  48 - 2  may each be wound about the respective limbs  226  and  228  circumferentially along the axis of the respective limb (e.g., in the direction that the limb extends from the front surface  230  of the base  224 ). Coils  48 - 1  and  48 - 2  may be wound from a single-strand conductor, a multiple strand conductor having multiple wires connected in parallel, braided wire, Litz wire, a conductive ink or conductive trace such as multilayer tracks on a printed circuit board, or other conductive elements suitable for forming coils. 
     Alignment structures such as magnetic alignment structures  214  and  234  may optionally be included in the system. As shown in  FIG.  7   , wireless power transmitting device  12  may have magnetic alignment structures  214 . Wireless power receiving device  24  may have magnetic alignment structures  234 . Each magnetic alignment structure  214  in the transmitting device may magnetically couple with a corresponding magnetic alignment structure  234  in the receiving device. When the transmitter alignment structures  214  are coupled to the receiver alignment structures  234 , the transmitting coils  36  may be aligned with the receiving coils  48 . Therefore, the magnetic alignment structures ensure proper alignment of the receiving coils relative to the transmitting coils. Magnetic alignment structures  214  and  234  may be permanent magnets (e.g., formed from hard magnetic materials that retain their magnetism over time). 
     The example of a power transmitting assembly and power receiving assembly shown in  FIG.  7    is merely illustrative. In general, the power transmitting assembly and power receiving assembly may have any desired design. In one alternative possible arrangement, the magnetic core of the power transmitting assembly and/or power receiving assembly may have a pot-core design (e.g., an enclosure with a ring-shaped hollow portion that receives the coil). In yet another possible arrangement, the power transmitting assembly and/or power receiving assembly may include a winding on a bar-shaped ferrite. Any desired magnetic core and coil design may be used (e.g., a U-shaped core, a C-shaped core, an E-shaped core, a toroidal core, etc.). 
     In general, each device may have only 1 coil, two coils (as in  FIG.  7   ), three coils, more than three coils, etc. One or both devices may include a transverse coil (e.g., a coil extending along the magnetic core base between the two magnetic core limbs). The precise geometry of the coils and magnetic cores in devices  12  and  24  may be tailored to the specific design. Wireless power receiving device  24  may be designed to cooperate specifically with wireless power transmitting device  12 . This is, however, merely illustrative. Power receiving device  24  may, in comes cases, not be specifically designed to cooperate with power transmitting device  12 . In general, each device may have different coil arrangements, different (or no) magnetic elements (e.g., magnetic cores), different coil and magnetic element sizes, different coil and magnetic element shapes, and other different characteristics. 
     In  FIG.  7   , wireless power receiving device  24  is placed directly on wireless power transmitting device  12 . For example, as shown, outer surface  236  of power receiving device  24  may be directly adjacent to and in direct contact with outer surface  216  of power transmitting device  12 . This may occur when, for example, a stylus is placed on an outer surface of a tablet computer for charging (as discussed in connection with  FIGS.  3 A and  3 B ). 
     When either power receiving device  24  or power transmitting device  12  is contained within a removable case, there may be an intervening layer between the outer surfaces of power receiving device  24  and power transmitting device  12  during charging. An arrangement of this type is shown in  FIG.  8 A . 
     As shown in  FIG.  8 A , case  102  may be interposed between wireless power transmitting device  12  and wireless power receiving device  24 . The case may include a dielectric material  262  (e.g., a bulk dielectric material) such as fabric, leather, polymer (e.g., polyurethane), other materials, and/or combinations of these materials. Dielectric material  262  of case  102  may have a thickness  260  between the power transmitting device  12  and power receiving device  24 . The larger the magnitude of thickness  260 , the greater the separation between the power transfer assembly  202  in power transmitting device  12  and the power receiving assembly  222  in power receiving device  24 . Without any additional components in case  102 , this increased separation leads to a drop in wireless power transfer efficiency between devices  12  and  24 . However, as shown in  FIG.  8 A , case  102  may include embedded components to maintain the wireless power transfer efficiency even when case  102  is present. 
     Case  102  includes a magnetic core  252  that is interposed between transmitting coil  36 - 1  and limb  206  in transmitting device  12  and receiving coil  48 - 1  and limb  226  in receiving device  24 . Case  102  also includes a magnetic core  254  that is interposed between transmitting coil  36 - 2  and limb  208  in transmitting device  12  and receiving coil  48 - 2  and limb  228  in receiving device  24 . Magnetic cores  252  and  254  have a high magnetic permeability and therefore lower the magnetic reluctance between the transmitting device and the receiving device. The magnetic field lines are concentrated in the magnetic cores  252  and  254  through case  102 . In other words, magnetic cores  252  and  254  route magnetic flux from one surface of the case (adjacent to the power transmitting device) to another surface of the case (adjacent to the power receiving device). Magnetic cores  252  and  254  may therefore sometimes be referred to as magnetic relays  252  and  254  (because they form a low reluctance path that relays magnetic flux between the transmitter and receiver). 
     Magnetic cores  252  and  254  may be positioned in areas of case  102  that have a high magnetic flux density during power transfer operations between devices  12  and  24 . As shown, magnetic core  252  may overlap limb  206  in device  12  and limb  226  in device  24 , which may be an area of high magnetic flux density. Magnetic core  254  may overlap limb  208  in device  12  and limb  228  in device  24 , which may be an area of high magnetic flux density. The magnetic cores may be embedded in dielectric material  262  such that the magnetic cores  252  and  254  are entirely surrounded by and in direct contact with dielectric material  262 . This example is merely illustrative. In an alternate arrangement, the cores may be laterally surrounded by dielectric material  262  and may have one or more exposed surfaces on the upper/lower surfaces of case  102 . 
     Case  102  may include magnetic alignment structures  264  to ensure proper alignment between the power transfer assembly  202  and power reception assembly  222 . Magnetic alignment structures  264  (which may be permanent magnets) magnetically couple with a corresponding magnetic alignment structure  214  in the transmitting device. Magnetic structures  264  may also magnetically couple with a corresponding magnetic alignment structure  234  in the receiving device. When the alignment structures  264  in the case are coupled to the alignment structures  214  and  234 , the transmitting coils  36 , magnetic cores  252 , and receiving coils  48  may all be aligned. Therefore, the magnetic alignment structures ensure proper alignment of the receiving coils relative to the transmitting coils and proper alignment of the magnetic relays  252  and  254  relative to the coils. 
     In general, magnetic relays  252  and  254  may have any desired thickness and shape. The thickness and shape of each magnetic relay may be optimized to achieve targeted magnetic performance within the system. 
     The example of using magnetic alignment structures in case  102  to ensure proper alignment between the power transfer assembly  202  and power reception assembly  222  is merely illustrative. If desired, other types of alignment structures may be used for alignment structures  264  (e.g., indentations or grooves, clip structures, adhesive structures, or any other desired alignment structures). 
     The magnetic cores herein (e.g.,  203 ,  223 ,  252 ,  254 ,  272 ,  274 , and  276 ) may be formed from a soft magnetic material such as ferrite. The magnetic cores may have a high magnetic permeability, allowing them to guide the magnetic fields in the system. The example of using ferrite cores is merely illustrative. Other ferromagnetic and/or ferrimagnetic materials such as iron, mild steel, mu-metal (a nickel-iron alloy), a nanocrystalline magnetic material, rare earth metals, or other magnetic materials having a sufficiently high magnetic permeability to guide magnetic fields in the system may be used for one or more of the cores if desired. The magnetic cores may sometimes be referred to as ferrimagnetic cores. Magnetic cores  203 ,  223 ,  252 ,  254 ,  272 ,  274 , and  276  may be a single piece or made from separate pieces. The cores may be molded, sintered, formed from laminations, formed from particles (e.g., ceramic particles) distributed in a polymer, or manufactured by other processes. 
     Case  102  may also optionally include shielding around each embedded magnetic core.  FIG.  8 A  shows an example with shielding structure  256  formed in a circular ring around magnetic core  252  and shielding structure  258  formed in a ring around magnetic core  254 . Shielding structures  256  and  258  (sometimes referred to as shielding, shielding rings, etc.) may be formed from an electromagnetic shielding material such as copper, brass, nickel, silver, steel, etc. The shielding structure may be ring-shaped and may laterally surround the magnetic cores. In other words, magnetic core  252  is formed in an opening (sometimes referred to as a central opening) defined by shielding ring  256  and magnetic core  254  is formed in an opening defined by shielding ring  258 . 
     The example of shielding  256  and  258  being ring-shaped in  FIG.  8 A  is merely illustrative. The presence of the shielding impacts the magnetic performance of the system. Therefore, the shape and thickness of each shielding portion may be selected to optimize performance of the system. As one example, shielding interposed between the cores  252  and  254  may be unnecessary. Therefore, in an alternate embodiment, shielding may be included only between the cores and adjacent permanent magnets  264 .  FIG.  8 B  is a cross-sectional side view showing an example of this type. 
     As shown in  FIG.  8 B , shielding  256  is interposed between magnetic core  252  and permanent magnet  264 . Shielding  258  is interposed between magnetic core  254  and permanent magnet  264 . Positioning the shielding in this way may help isolate cores  252  and  254  from the permanent magnets without adversely affecting the transfer of magnetic flux within the system. 
       FIG.  8 B  shows how shielding may also be incorporated in power transmitting device  12  and/or power receiving device  24 . As shown, shielding pieces such as shielding  282 ,  284 , and  286  may be incorporated around power transmitting assembly  202 . Shielding  282  is interposed between magnetic core  206  and coil  36 - 1  and permanent magnet  214 . Shielding  286  is interposed between magnetic core  208  and coil  36 - 2  and permanent magnet  214 . Similarly, shielding pieces such as shielding  288 ,  290 , and  292  may be incorporated around power receiving assembly  222 . Shielding  288  is interposed between magnetic core  226  and coil  48 - 1  and permanent magnet  234 . Shielding  292  is interposed between magnetic core  228  and coil  48 - 2  and permanent magnet  234 . Similar to shielding  256  and  258 , shielding structures  282 ,  284 ,  286 ,  288 ,  290 , and  292  may be formed from an electromagnetic shielding material such as copper, brass, nickel, silver, steel, etc. 
     The example in  FIG.  8 B  of separate shielding pieces surrounding the power transmitting/receiving assemblies is merely illustrative. In general, the power transmitting/receiving devices may include one or more shielding pieces in any desired configuration. For example, shielding  282 ,  284 , and  286  in  FIG.  8 B  may be formed integrally as one unitary shielding piece. One or more shielding pieces in power transmitting assembly  202  and/or power receiving assembly  222  may optionally have the same footprint as the shielding pieces in accessory  102 . The shielding pieces may overlap in the vertical direction, as shown in  FIG.  8 B . 
       FIG.  9 A  is a top view of case  102  in  FIG.  8 A , showing an illustrative arrangement for the components that are embedded in the case. In the example of  FIG.  9 A , shielding structure  256  forms a ring around magnetic core  252 . Shielding structure  258  forms a ring around magnetic core  254 . When interposed between a power transmitting device and power receiving device, permanent magnets  264  may couple to permanent magnets in the adjacent devices and position magnetic cores  252  and  254  in an appropriate alignment. Magnetic cores  252  and  254  may be sized to accommodate potential alignment variations relative to the adjacent devices. 
     The example of magnetic alignment structures  264  being formed as two discrete pieces on either side of the magnetic cores is merely illustrative. If desired, magnetic alignment structures  264  may include a ring-shaped permanent magnet that laterally surrounds magnetic cores  252 / 254  and shielding structures  256 / 258 . 
     As previously mentioned, shielding structures  256  and  258  may have shapes other than ring-shapes.  FIG.  9 B  is a top view of case  102  in  FIG.  8 B , showing an illustrative arrangement for components that are embedded in the case. As shown, shielding piece  256  may be interposed between core  252  and a magnetic alignment structure  264 . Shielding piece  258  may be interposed between core  254  and a magnetic alignment structure  264 . This example is merely illustrative. In another possible configuration, a single ring-shaped (e.g., rectangular ring-shaped) shielding structure may be formed around magnetic cores  252  and  254 . However, in this embodiment, there is still no shielding material formed between magnetic cores  252  and  254  (as shielding in this area may not be advantageous to the magnetic performance of the system). 
     It should be noted that the specific examples of the embedded components in case  102  shown in  FIGS.  8 A,  8 B,  9 A, and  9 B  are merely illustrative. In general, the size, shape, and positioning of the magnetic cores in case  102  depends on the design of the transmitting and receiving devices with which the magnetic cores are intended to operate. The magnetic cores may be embedded at various locations within case  102 . For example, the magnetic cores may be embedded in a front cover portion  102 F of a removable cover having a folio shape (as shown in  FIGS.  4  and  5   ). The magnetic cores may be embedded in the front cover portion  102 F to overlap region  166 ,  168 ,  170 , or  172  of a tablet computer. In this type of design, the embedded magnetic cores increase charging efficiency of a tablet computer transferring charge to a stylus placed on the front of the tablet computer. 
     However, the magnetic cores may instead be embedded in a sidewall of case  102  (e.g. in region  176  in  FIG.  6   ) to enhance charging efficiency in an embodiment where the stylus is placed on the sidewall of the tablet computer for wireless charging. In general, the magnetic cores may be formed in any portion of a removable case that is interposed between devices transferring wireless power (e.g., a front portion of a removable case, a sidewall of a removable case, or a rear wall of a removable case). 
     An alternate example for the design of an embedded magnetic core in case  102  is shown in  FIGS.  10  and  11   . In  FIG.  10   , power transmitting device  12  includes a single coil  36  and a magnetic core  271 . Magnetic core  271  may have a base  272  and limbs such as limb  280  (e.g., a ring-shaped limb) that protrudes away from a base portion of the core towards the outer surface of device  12 . Power receiving device  24  also includes a single coil  48  with an associated magnetic core  274 . A circular, ring-shaped magnetic core  276  is embedded in dielectric material  262  of cover  102  to relay flux from the transmitting device towards the receiving device. Magnetic core  276  may have a ring shape that aligns with the limb  280  of magnetic core  271  in the transmitting device. Similar to as in  FIG.  8   , magnetic core  276  in  FIG.  10    is positioned in an area in the system with a high magnetic flux density (e.g., in a high magnetic flux density region between devices  12  and  24 ). This way, the magnetic core  276  serves as a relay and guides the magnetic field between transmitter  12  and receiver  24 . Cover  102  again includes permanent magnets  264  to align the magnetic core  276  in the desired position and align coil  36  with coil  48 . In some examples, core  276  is a continuous ring. In some examples, core  276  comprises multiple discrete core portions arranged in an arcuate manner such as to form a circular ring. 
     As an example, the arrangement of  FIG.  10    may be used in a system where transmitting device  12  is a wireless charging mat or wireless charging puck. Wireless power receiving device  24  may be a portable electronic device such as a cellular telephone, tablet computer, etc. A portion of case  102  may be interposed between devices  12  and  24  during charging (e.g., rear portion  102 R in  FIG.  6   ). 
       FIG.  11    is a top view of a case including a ring-shaped magnetic core as in  FIG.  10   . As shown, magnetic core  276  is shaped in a ring (e.g., that aligns with limb  280  of core  271  in the transmitting device). Permanent magnet  264  may also have a ring shape that is concentric with the ring of magnetic core  276 . If desired, one or more rings of shielding material (e.g., copper shielding material or another shielding material similar to as discussed in connection with  FIG.  8   ) may be incorporated into the case. The ring(s) of shielding material may be concentric with the magnetic core  276  and magnetic alignment structure  264 . 
     To summarize, a removable case may be coupled to an electronic device to protect and/or cover the electronic device. A portion of the removable case may be interposed between the electronic device and an additional electronic device during wireless power transfer operations. For example, the electronic device may transmit wireless power signals to the additional electronic device through a portion of the removable case. The electronic device may, instead or in addition, receive wireless power signals from the additional electronic device through a portion of the removable case. Wireless power signals may be transmitted and/or received through any desired portion of the removable case (e.g., a rear portion, a front portion, a sidewall portion, etc.). The wireless power signals may be transmitted and/or received through a portion of the removable case that overlaps a display area or border area of the screen of the electronic device. To improve efficiency of wireless power transfer when the removable case is interposed between the two devices, the removable case may include one or more magnetic cores that relay magnetic flux from a first surface of the case adjacent the transmitting device to a second surface of the case adjacent the receiving device. A removable cover of any desired type and shape may include one or more magnetic cores to relay magnetic flux during wireless power transfer operations of two adjacent devices. 
     The foregoing is merely illustrative and various modifications can be made to the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20210219
Publication Date: 20240220
Grant Date: 20240220
Priority Date: 20200604
Inventors: XU, Zelin
LIU, NAN
MOUSSAOUI, ZAKI
LISI, GIANPAOLO
BHARGAVA, KUNAL
KEEZHVEEDI SAMPATH, Madhusudanan
CHABALKO, MATTHEW J.
SCRITZKY, ROBERT
Assignee: APPLE INC
CPC Classifications: [{"code": "H02J7/02", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/03545", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F7/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/0042", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/0017", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/03", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K9/0007", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F7/0247", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/50", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J7/02", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/03545", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/38", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F3/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/90", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/005", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02J50/50", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02J50/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/90", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F7/0247", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/0042", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F3/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F7/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/03545", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/38", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/03", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K9/0007", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/0042", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/03545", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F7/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K9/0007", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/0017", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/03", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 78817956