Patent Publication Number: US-9852844-B2

Title: Magnetic shielding in inductive power transfer

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a nonprovisional patent application of and claims the benefit to U.S. Provisional Patent Application No. 61/969,337, filed Mar. 24, 2014 and titled “Magnetic Shielding in Inductive Power Transfer,” and this application is a nonprovisional patent application of and claims the benefit to U.S. Provisional Patent Application No. 62/036,685, filed Aug. 13, 2014 and titled “Inductive Power Transmission Housing Shielding,” the disclosures of which are hereby incorporated herein by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     This disclosure relates generally to connectible devices, and more specifically to magnetic shielding in inductive power transfer between connectible devices. 
     BACKGROUND 
     Many electronic devices connect to other electronic devices. For example, electronic devices such as portable digital media players, wearable devices, and/or other kinds of portable computing devices may connect to one or more docks in order to charge, transfer data, connect to one or more accessories, such as external input/output devices, and so on. A connection may mechanically couple the electronic devices and/or may electrically couple the electronic devices for the purposes of power and/or data transmission. Using some traditional coupling techniques, it may be difficult to maintain a mechanical coupling between the electronic devices in a way that does not interfere or further facilitates an electrical coupling between the electronic devices. 
     SUMMARY 
     The present disclosure includes systems and methods for magnetic shielding in an inductive power transfer system. A first electronic device with a first connection surface and an inductive power transfer receiving coil and first magnetic element positioned adjacent to the first connection surface connects in an aligned position with a second electronic device with a second connection surface and an inductive power transfer transmitting coil and second magnetic element positioned adjacent to the second connection surface. In the aligned position, the first and second electronic devices may be coupled by the first and second magnetic elements and the inductive power transfer transmitting coil may be configured to transmit power to the inductive power transfer receiving coil. The first and/or second magnetic elements and/or the inductive power transfer receiving and/or transmitting coils may be configured to minimize or reduce eddy currents caused in the first and/or second magnetic elements by the inductive power transfer receiving and/or transmitting coils. 
     The first and/or second magnetic elements and/or the inductive power transfer receiving and/or transmitting coils may be configured in one or more of a variety of different ways to minimize or reduce eddy currents caused in the first and/or second magnetic elements by the inductive power transfer receiving and/or transmitting coils. In some implementations, the inductive power transfer receiving and/or transmitting coils may be inductively coupled in the aligned position. In various implementations, the positioning of the first and/or second magnetic elements and/or the inductive power transfer receiving and/or transmitting coils may be spaced so as to minimize or reduce eddy currents caused in the first and/or second magnetic elements. In one or more implementations, the first and/or second connection surfaces may be formed of one or more nonconductive materials. 
     In some implementations, the first and/or second magnetic elements may be coated with one or more coatings. Such coatings may be formed of one or more nonconductive and/or magnetically permeable materials. Similarly, the first and/or second magnetic elements may be at least partially covered by one or more shield elements. Such shield elements may be formed of one or more electrically nonconductive materials. The inductive power transfer receiving and/or transmitting coils may also be at least partially covered by one or more shield elements. Such shield elements may be, or function as, a Faraday cage for the inductive power transfer receiving and/or transmitting coils. 
     In other embodiments, an electronic device may include an inductive coil operable to participate in an inductive power transmission system and a housing or other enclosure. The electronic device may also include one or more magnetic field directing materials (such as diamagnetic material and/or superconductive material) that block magnetic flux of the inductive power transmission from a portion of the housing and/or otherwise shape the flow of the magnetic flux. The magnetic field directing material may also be highly thermally conductive and may operate as a heat spreader. In this way, loss efficiency of the inductive power transmission system may be improved. Temperature increase of the housing may also be prevented and/or mitigated. 
     In various embodiments, a system for magnetic shielding in inductive power transfer includes a first electronic device and a second electronic device. The first electronic device includes a first connection surface, an inductive power transfer receiving coil positioned adjacent to the first connection surface, and a first magnetic element positioned adjacent to the first connection surface. At least one of the first magnetic element or the inductive power transfer receiving coil is configured to minimize or reduce eddy currents caused in the first magnetic element by the inductive power transfer receiving coil. The second electronic device includes a second connection surface, an inductive power transfer transmitting coil positioned adjacent to the second connection surface, and a second magnetic element positioned adjacent to the second connection surface. The first magnetic element and the second magnetic element connect the first electronic device and the second electronic device in an aligned position and the inductive power transfer transmitting coil is configured to inductively transmit power to the inductive power transfer receiving coil when the first electronic device and the second electronic device are in the aligned position. 
     In some embodiments, an electronic device includes a first connection surface, an inductive power transfer receiving coil positioned adjacent to the first connection surface, and a first magnetic element positioned adjacent to the first connection surface. At least one of the first magnetic element or the inductive power transfer receiving coil is configured to minimize or reduce eddy currents caused in the first magnetic element by the inductive power transfer receiving coil. The first magnetic element connects the first electronic device to a second magnetic element of a second electronic device in an aligned position. The inductive power transfer receiving coil is configured to inductively receive power from an inductive power transfer transmitting coil of the second electronic device when the first electronic device and the second electronic device are in the aligned position. 
     In one or more embodiments, an electronic device may include a housing, an inductive coil operable to participate in an inductive power transmission system, and a magnetic field directing material. The magnetic field directing material may block magnetic flux of the inductive power transmission system from a portion of the housing. 
     It is to be understood that both the foregoing general description and the following detailed description are for purposes of example and explanation and do not necessarily limit the present disclosure. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate subject matter of the disclosure. Together, the descriptions and the drawings serve to explain the principles of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front isometric view illustrating a system for magnetic shielding in inductive power transfer. 
         FIG. 2  is a cross-sectional front plan view of the system of  FIG. 1  taken along section A-A of  FIG. 1  illustrating the connectible electronic devices in an aligned position. 
         FIG. 3  illustrates the system of  FIG. 2  showing the connectible electronic devices in one possible contact position. 
         FIG. 4  is a cross sectional side view of the system of  FIG. 2  taken along section B-B of  FIG. 2 . 
         FIG. 5A  illustrates a magnetic field of the first magnetic element of  FIG. 2  removed from the first electronic device and the shield element. 
         FIG. 5B  illustrates the magnetic field of the first magnetic element including the shield element of  FIG. 2  removed from the first electronic device. 
         FIG. 6  is a method diagram illustrating a method for magnetic shielding in inductive power transfer. This method may be performed by the system of  FIG. 1 . 
         FIG. 7  is a close up view of the first and second magnetic elements of an alternative embodiment of the first and second electronic devices in the aligned position. 
         FIG. 8  is a simplified block diagram of an example frequency controlled inductive charging system. The example frequency controlled inductive charging system may be utilized with the system of  FIG. 2 . 
         FIG. 9  is a simplified isometric view of an inductive power transmission system in accordance with another embodiment from which a number of components have been omitted for purposes of clarity. 
         FIG. 10A  is a cross-sectional side view of a first implementation of the inductive power transmission system of  FIG. 9 , taken along the section C-C of  FIG. 9 . 
         FIG. 10B  is a cross-sectional side view of a second implementation of the inductive power transmission system of  FIG. 9 , taken along the section C-C of  FIG. 9 . 
         FIG. 10C  is a cross-sectional side view of a third implementation of the inductive power transmission system of FIG.  FIG. 9 , taken along the section C-C of  FIG. 9 . 
         FIG. 11  is a method diagram illustrating an example method for manufacturing an inductive power transmission system. This example method may be performed by the systems of  FIGS. 9, 10B , and/or  10 C. 
         FIGS. 12-14  illustrate isometric views of sample electronic devices in which various embodiments of the magnetic shielding techniques disclosed herein may be utilized. 
         FIG. 15  is a schematic cross sectional side view of the wearable device of  FIG. 14 , taken along section D-D of  FIG. 14 . 
     
    
    
     DETAILED DESCRIPTION 
     The description that follows includes sample systems, methods, and apparatuses that embody various elements of the present disclosure. However, it should be understood that the described disclosure may be practiced in a variety of forms in addition to those described herein. 
     The present disclosure includes systems and methods for magnetic shielding in inductive power transfer. In some embodiments, a first electronic device is coupled or connected in an aligned position with a second electronic device. The first electronic device may include inductive power transfer receiving coil and a first magnetic element, both positioned adjacent to the first connection surface. Similarly, a second electronic device may include an inductive power transfer transmitting coil and a second magnetic element, both positioned adjacent to the second connection surface. In the aligned position, the first and second electronic devices may be coupled or connected by the first and second magnetic elements (which may be permanent magnets) and the inductive power transfer transmitting coil may be configured to transmit power to the inductive power transfer receiving coil. The first and/or second magnetic elements and/or the inductive power transfer receiving and/or transmitting coils may be configured to minimize or reduce eddy currents caused in the first and/or second magnetic elements by the inductive power transfer receiving and/or transmitting coils. In this way, magnetic connection mechanisms may be utilized without impairing the inductive power transfer and/or causing excessive heat. 
     The first and/or second magnetic elements and/or the inductive power transfer receiving and/or transmitting coils may be configured in one or more of a variety of different ways to minimize or reduce eddy currents caused in the first and/or second magnetic elements by the inductive power transfer receiving and/or transmitting coils. In some implementations, the inductive power transfer receiving and/or transmitting coils may be inductively coupled in the aligned position. In various implementations, the positioning of the first and/or second magnetic elements and/or the inductive power transfer receiving and/or transmitting coils may be spaced so as to minimize or reduce eddy currents caused in the first and/or second magnetic elements. In one or more implementations, the first and/or second connection surfaces may be formed of one or more nonconductive materials. 
     In some implementations, the first and/or second magnetic elements may be coated with one or more coatings. Such coatings may be formed of one or more nonconductive and/or magnetically permeable materials such as a polymer including a polyurethane or other type of plastic. The coating may include a combination of a polymer and conductive fibers or particles, a combination of other nonconductive materials and conductive fibers or particles, and/or other such nonconductive and/or magnetically permeable materials. 
     Similarly, the first and/or second magnetic elements may be at least partially covered by one or more shield elements. Such shield elements may be formed of one or more electrically nonconductive materials, soft magnetic material, ferromagnetic material, ceramic materials, crystalline materials, iron cobalt, and/or other such materials. In some cases, the shield element may be at least partially positioned between the first and/or second magnetic elements and the inductive power transfer receiving and/or transmitting coils, respectively. One or more gaps may be positioned between a surface of the first and/or second magnetic elements that faces the inductive power transfer receiving and/or transmitting coils, respectively, and the portion of the shield element positioned between. Such a shield element may direct a magnetic field of the first and/or second magnetic elements toward the respective connection surface. In some cases, the shield element may be at least partially covered by a nonconductive coating. 
     The inductive power transfer receiving and/or transmitting coils may also be at least partially covered by one or more shield elements. Such shield elements may be formed of one or more crystalline materials, ceramic materials, soft magnetic material, ferromagnetic material, iron silicon, and/or other such materials and/or may function as a Faraday cage for the inductive power transfer receiving and/or transmitting coils. Such shield elements may be at least partially positioned between the inductive power transfer receiving and/or transmitting coils and the first and/or second magnetic elements, respectively. 
     In various cases, the first and/or second magnetic elements may be positioned in the center of the inductive power transfer receiving and/or transmitting coils, respectively, and/or along an axis running through the center of the inductive power transfer receiving and/or transmitting coils. 
     In other embodiment, an electronic device may include an inductive coil operable to participate in an inductive power transmission system, a housing or other enclosure, and one or more magnetic field directing materials. The magnetic field directing material may block magnetic flux of the inductive power transmission system from a portion of the housing, shaping the flow of the magnetic flux. In this way, loss efficiency of the inductive power transmission system may be improved and/or temperature increase of the housing may be prevented and/or mitigated. 
     As used herein, a “lateral magnetic force” may be used to refer to a magnetic force that moves one or both of the devices in a lateral or an X- or a Y-direction with respect to one another. In some cases, the lateral magnetic force may refer to a resistance to a shear or lateral force between the devices. In some cases, some Z-direction (height) motion may occur as a byproduct of an alignment of the adjacent surfaces with respect to each other, particularly if the adjacent surfaces are curved. Lateral magnetic force is more fully discussed with respect to  FIGS. 1-3  below. As used herein, a “transverse magnetic force” refers to a magnetic force that attracts the devices toward each other in a transverse or Z-direction, which may operate to center and align the two devices as well as resist a separation or expansion of a gap between the two devices. Transverse magnetic force is more fully discussed with respect to  FIGS. 1-3  below. As discussed herein, lateral magnetic force and transverse magnetic force may be components of the same, single magnetic field. Both may vary based on the positions of the magnetic elements. 
       FIG. 1  is a front isometric view illustrating a system for magnetic shielding in inductive power transfer. The system  100  may include a first electronic device  101  and a second electronic device  102 . Although  FIG. 1  illustrate the first electronic device  101  as a cordless electronic device of a particular shape and the second electronic device  102  as a dock for the cordless electronic device, it is understood that this is merely an example. In various implementations, either the first electronic device  101  or the second electronic device  102  may be any kind of electronic device such as a laptop computer, a tablet computer, a mobile computing device, a smart phone, a cellular telephone, a digital media player, a dock that connects to another electronic device for the purposes of charging and/or connecting the electronic device to one or more external components, and/or any other such electronic device. 
     As illustrated in  FIG. 1 , the first electronic device  101  includes a first connection surface  103  that is operable to contact a second connection surface  104  of the second electronic device  102 . As such, the first and second electronic devices  101 ,  102  may be positionable with respect to each other in at least lateral  199  and transverse  198  relative directions. 
       FIG. 2  is a cross-sectional front plan view of the system  100  of  FIG. 1  taken along section A-A of  FIG. 1  illustrating the first and second connectible electronic devices  101  and  102  in an aligned position.  FIG. 3  illustrates the system of  FIG. 2  showing the first and second connectible electronic devices  101  and  102  in one possible contact position. The first and second connection surfaces  103  and  104  may contact at any number of different points. As such, any number of different contact positions may be possible, of which  FIG. 3  is an example. However, the first and second connectible electronic devices  101  and  102  may have a single aligned position, illustrated in  FIG. 2 , where a first magnetic element  105  connects with a second magnetic element  111  and an inductive power transfer transmitting coil  113   a  and  113   b  (cross-sectional portions of a single coil) is aligned with an inductive power transfer receiving coil  107   a  and  107   b  (cross-sectional portions of a single coil). In the aligned position, the first and second electronic devices  101  and  102  may be participants in an inductive power transfer system where the second electronic device  102  functions as a charging dock for the first electronic device  101  by inductively transmitting power to the first electronic device  101 , which the first electronic device  101  stores in the power source  110 .  FIG. 4  is a cross-sectional side view of the system of  FIG. 2  taken along section B-B of  FIG. 2 . 
     As illustrated in  FIG. 2 , the first electronic device  101  may include one or more first magnetic elements  105  (which may be a permanent magnet and may include a shield element  106 ), inductive power transfer receiving coil  107   a  and  107   b  (cross-sectional portions of a single coil that respectively include shield elements  140   a  and  140   b ), processing units  108 , one or more non-transitory storage media  109  (which may take the form of, but is not limited to, a magnetic storage medium; optical storage medium; magneto-optical storage medium; read only memory; random access memory; erasable programmable memory; flash memory; and so on), and/or one or more power sources  110  (such as one or more batteries). The processing unit  108  may execute one or more instructions stored in the non-transitory storage medium  109  to perform one or more first electronic device operations such as one or more receiving operations utilizing the receiving component, communication operations, calculation operations, storage operations, input/output operations, time operations, charging operations, and so on. 
     Similarly, the second electronic device  102  may include one or more second magnetic elements  111  (which may be a permanent magnet and may include a shield element  112 ), inductive power transfer transmitting coil  113   a  and  113   b  (cross-sectional portions of a single coil that respectively include shield elements  141   a  and  141   b ), processing units  114 , one or more non-transitory storage media  115 , and/or one or more power sources  116  (such as one or more alternating current or direct current power sources). The processing unit  114  may execute one or more instructions stored in the non-transitory storage medium  115  to perform one or more second electronic device operations such as one or more transmitting operations utilizing the transmitting component, calculation operations, storage operations, and so on. 
     When the first and second electronic devices  101  and  102  are placed into one of the possible contact positions (such as shown in  FIG. 3 ), lateral  199  magnetic force between the first and second magnetic elements  105  and  111  may bring the electronic devices into the aligned position (shown in  FIG. 2 ) where transverse  198  magnetic force between the first and second magnetic elements may connect the two devices. In the aligned position, the inductive power transfer transmitting coil  113   a  and  113   b  may be configured to inductively transmitting power to the inductive power transfer receiving coil  107   a  and  107   b.    
     As illustrated in  FIG. 2 , the first magnetic element  105  may be positioned within the center, or along an axis (corresponding to the transverse direction  198  in this example implementation) running through the center, of the inductive power transfer receiving coil  107   a  and  107   b . Similarly, the second magnetic element  111  may be positioned within the center, or along an axis (corresponding to the transverse direction  198  in this example implementation) running through the center, of the inductive power transfer transmitting coil  113   a  and  113   b.    
     When conductive materials, such as magnetic elements, are positioned within the induction field of a transmitting coil and receiving coil of an inductive power transfer system, eddy currents may be formed in the conductive materials. Such eddy currents may result in less current being received by the receiving coil, thus less inductive power transfer system efficiency. Such eddy currents may also cause undesired heating in the conductive materials. As such, the first and/or second magnetic elements and/or the inductive power transfer transmitting and/or receiving coils may be configured to minimize or reduce eddy currents caused in the first and/or second magnetic elements by the inductive power transfer transmitting and/or receiving coils. 
     The first and/or second magnetic elements ( 105 ,  111 ) and/or the inductive power transfer transmitting and/or receiving coils ( 113   a - b ,  107   a - b ) may be configured to minimize or reduce eddy currents in a variety of different ways. As illustrated, the inductive power transfer transmitting coil  113   a  and  113   b  and the inductive power transfer receiving coil  107   a  and  107   b  may be inductively coupled in the aligned position. Transmitting and receiving coils in an inductive power transfer system may be inductively coupled when they are centered with respect to each other and sufficiently adjacent that the receiving coil is within the majority of the inductive current field generated by the transmitting coil. This results in more of the inductive current field influencing the receiving coil, resulting in increased transmission efficiency and less generated heat, as opposed to being available for influencing other conductive materials and thus reducing transmission efficiency and more generated heat. As such, tightly coupling the coils may reduce eddy currents that might otherwise be caused in one or more of the magnetic elements. 
     As also illustrated in  FIG. 2 , the inductive power transfer transmitting coil  113   a  and  113   b , the inductive power transfer receiving coil  107   a  and  107   b , and the first and second magnetic elements  105  and  111  may be spaced in relation to each other in order to minimize creation of eddy currents in the first and/or second magnetic elements. Positioning of either magnetic element too closely, such as immediately adjacent, to either coil may cause creation of eddy currents. However, spacing as illustrated may reduce the eddy currents that may otherwise be created by proximity of the magnetic elements and the coils. 
     In various implementations, the first and/or second connection surfaces  103  and  104  may be formed of one or more nonconductive materials. This may prevent formation of eddy currents in the connection surfaces and may further increase transmission efficiency and reduce generated heat. 
     In some implementations, the first and second magnetic elements  105  and  111  may include shield elements  106  and  112 , respectively. Each magnetic element may have a face surface and an opposite surface that are joined by at least two side surfaces wherein the face surface faces the respective connection surface. The respective shield element may at least partially cover the opposite surface and the two side surfaces. A gap  117  or  118  may be present between the respective shield element and the at least two side surfaces. 
     Such shield elements may be formed of one or more electrically nonconductive materials, soft magnetic material, ferromagnetic material, ceramic materials, crystalline materials, iron cobalt, and/or other such materials. In some cases, a soft magnetic material may be electrically conductive, such as a nonconductive ceramic material that includes ferrous metal fibers or particles suspended therein. As the fibers or particles are separated by nonconductive material, the combination may itself be nonconductive even though the presence of the ferrous metal fibers or particles may cause the combination to be a soft magnetic material. In various cases, whether formed of a conductive material, nonconductive material, or a combination thereof, such a shield element may be at least partially coated with a nonconductive coating such as those discussed in further detail below. 
     The shield element  106  or  112  may be at least partially positioned between the first or second magnet  105  and  111  and the inductive power transfer transmitting coil  113   a  and  113   b  or the inductive power transfer receiving coil  107   a  and  107   b , respectively. The gap  117  or  118  may be positioned between a surface of the respective magnetic element and the respective coil. 
     The shield element  106  or  112 , which may be formed of ferromagnetic material, a soft magnetic material, or other material that demonstrates the ability to easily become magnetic such as iron cobalt, may direct a magnetic field of the magnetic element in a direction of the connection surface. Such direction of the magnetic field may enable use of smaller magnetic elements than would otherwise be possible and may prevent the magnetic fields of the first and/or second magnetic elements  105  and  111  from interfering with (thus causing eddy currents in the magnetic elements) the inductive current field between the inductive power transfer transmitting coil  113   a  and  113   b  and the inductive power transfer receiving coil  107   a  and  107   b.    
     Although the shielding elements  106  and  112  are illustrated as having a single, solid structure, it is understood that this is an example. In some cases, one or more of the shielding elements may be formed to have one or more “cutouts,” or intermittent breaks in the material of the shield. Such cutouts may interrupt electrical conductivity through portions of such a shield and may further minimize the formation of eddy currents while still allowing for a highly permeable volume. 
       FIG. 5A  illustrates a magnetic field  120 A of the first magnetic element  105  of  FIG. 2  removed from the first electronic device  101  and the shield element  106 . By way of contrast,  FIG. 5B  illustrates the magnetic field  120 A of the first magnetic element including the shield element of  FIG. 2  removed from the first electronic device. As can be seen by comparing  FIGS. 5A and 5B , the inclusion of the shield element may direct the magnetic field  120 A toward the first connection surface (item  103  in  FIGS. 2-4 ). 
     Although  FIGS. 5A and 5B  illustrate the magnetic field  120 A as circulating in one sample direction, it is understood that this is an example. In other embodiments, the magnetic field  120 A may be reversed without departing from the scope of the present disclosure. 
     In various implementations, the inductive power transfer transmitting coil  113   a  and  113   b  or the inductive power transfer receiving coil  107   a  and  107   b  may include shield elements  140   a  and  140   b  or  141   a  and  141   b , respectively. Each coil may have a collective face surface and an collective opposite surface that are joined by at least two collective side surfaces wherein the collective face surface faces the respective connection surface. The respective shield element may at least partially cover the collective opposite surface and the collective two side surfaces. 
     As illustrated, shield elements  140   a  and  140   b  or  141   a  and  141   b  may be at least partially positioned between the inductive power transfer transmitting coil  113   a  and  113   b  or the inductive power transfer receiving coil  107   a  and  107   b  and the first or second magnetic elements  105  and  111 , respectively. These shield elements may function as a Faraday cage, blocking electromagnetic radiation. As such, these shield elements may block one or more of the magnetic elements from the inductive current field between the inductive power transfer transmitting coil and the inductive power transfer receiving coil, thus reducing eddy currents that may otherwise be caused in the magnetic elements. Such shield elements may be formed of one or more crystalline materials, ceramic materials, soft magnetic material, ferromagnetic materials, iron silicon, and/or other such materials. 
     Although the shielding elements  140   a  and  140   b  or  141   a  and  141   b  are illustrated as having a single, solid structure, it is understood that this is an example. In some cases, one or more of the shielding elements may be formed to have one or more “cutouts,” or intermittent breaks in the material of the shield. Such cutouts may interrupt electrical conductivity through portions of such a shield and may further minimize the formation of eddy currents while still allowing for a highly permeable volume. 
     In some implementations, one or more of the first and/or second magnetic elements  105  and  111  may be at least partially coated with one or more nonconductive coatings.  FIG. 7  illustrates an example implementation that includes such nonconductive coatings  131  and  132 . Such nonconductive coatings may reduce eddy currents that may otherwise be caused in the first and/or second magnetic element by the inductive power transfer transmitting coil  113   a  and  113   b  or the inductive power transfer receiving coil  107   a  and  107   b.    
     Such coatings may be formed of one or more nonconductive and/or magnetically permeable materials such as polyurethane, plastic, a combination of polyurethane and/or plastic and conductive fibers or particles, a combination of other nonconductive materials and conductive fibers or particles, and/or other such nonconductive and/or magnetically permeable materials. For example, in cases where ferrous metal fibers or particles are combined with nonconductive materials, the separation of the ferrous fibers or particles by nonconductive material may result in the combination being nonconductive even though the presence of the ferrous metal fibers or particles may cause the combination to be magnetically permeable. 
     Returning to  FIG. 2 , although the inductive power transfer receiving coil  107   a  and  107   b  is shown as being generally parallel to a top surface of the first electronic device  101  and the inductive power transfer transmitting coil  113   a  and  113   b  is shown as being generally parallel to a bottom surface of the second electronic device  102  such that they are not flush aligned with the first and second connection surfaces  103  and  104 , it is understood that this is an example. In other implementations, the inductive power transfer receiving coil  107   a  and  107   b  may be flush with the first connection surface and the inductive power transfer transmitting coil  113   a  and  113   b  may be flush with the second connection surface without departing from the scope of the present disclosure. In such an implementation, the inductive power transfer receiving coil  107   a  and  107   b  and the inductive power transfer transmitting coil  113   a  and  113   b  may be angled with respect to the top surface of the first electronic device and/or the bottom surface of the second electronic device. 
       FIG. 6  is a method diagram illustrating a method  600  for magnetic shielding in inductive power transfer. This method may be performed, for example, by the system of  FIG. 1 . The flow may begin at block  601  where an inductive power transfer receiving coil and first magnetic element of a first electronic device may be positioned adjacent to a connection surface of the first electronic device. The flow may then proceed to block  602  where the inductive power transfer receiving coil and the first magnetic element may be configured to minimize or reduce eddy currents caused in the first magnetic element by the inductive power transfer receiving coil. 
     At block  603 , the first electronic device may be coupled or connected to a second electronic device utilizing the first magnetic element and the second magnetic element of the second electronic device. The flow may then proceed to block  604  where power may be inductively received utilizing inductive power transfer receiving coil from inductive power transfer transmitting coil of the second electronic device. 
     Although the method  600  is illustrated and described above as including particular operations performed in a particular order, it is understood that this is an example. In various implementations, various configurations of the same, similar, and/or different operations may be performed without departing from the scope of the present disclosure. 
     For example, block  602  is shown and described above as configuring the inductive power transfer receiving coil and the first magnetic element may to minimize or reduce eddy currents caused in the first magnetic element by the inductive power transfer receiving coil. However, in some implementations, either the inductive power transfer receiving coil or first magnetic element may be so configured. Further, in various implementations, the inductive power transfer receiving and/or transmitting coils and/or the first and/or second magnetic elements may be configured to minimize or reduce eddy currents caused in either magnetic element caused by either of the coils without departing from the scope of the present disclosure. 
     Referring now to  FIG. 8 , a simplified block diagram of an example frequency controlled inductive charging system  800  is shown that may be utilized with inductive power transfer transmitting coil (e.g.,  113   a  and  113   b  of  FIGS. 2-4 ) and inductive power transfer receiving coil (e.g.,  107   a  and  107   b  of  FIGS. 2-4 ). The inductive charging system  800  includes a clock circuit  802  operatively connected to a controller  804  and a direct-current converter  806 . The clock circuit  802  can generate the timing signals for the inductive charging system  800 . 
     The controller  804  may control the state of the direct-current converter  806 . In one embodiment, the clock circuit  802  generates periodic signals that are used by the controller  804  to activate and deactivate switches in the direct-current converter  806  on a per cycle basis. Any suitable direct-current converter  806  can be used in the inductive charging system  800 . For example, in one embodiment, an H bridge may be used in the direct-current converter  806 . H bridges are known in the art, so only a brief summary of the operation of an H bridge is described herein. 
     The controller  804  controls the closing and opening of four switches S 1 , S 2 , S 3 , S 4  (not illustrated). When switches S 1  and S 4  are closed for a given period of time and switches S 2  and S 3  are open, current may flow from a positive terminal to a negative terminal through a load. Similarly, when switches S 2  and S 3  are closed for another given period of time while switches S 1  and S 4  are open, current flows from the negative terminal to the positive terminal. This opening and closing of the switches produces a time-varying current by repeatedly reversing the direction of the current through the load same load. In an alternate embodiment, an H bridge may not be required. For example, a single switch may control the flow of current from the direct-current converter  806 . In this manner, the direct-current converter  806  may function as a square wave generator. 
     The time-varying signal or square wave signal produced by the direct-current converter  806  may be input into a transformer  808 . Typically, a transformer such as those used in the above-referenced tethered charging systems includes a primary coil coupled to a secondary coil, with each coil wrapped about a common core. However, an inductive charging system as described herein includes a primary and a secondary coil separated by an air gap and the respective housings containing each coil. Thus, as illustrated, transformer  808  may not necessarily be a physical element but instead may refer to the relationship and interface between two inductively proximate electromagnetic coils such as a primary coil  810  (which may be the transmitting component  113   a  and  113   b  of the system  100  of  FIG. 2 ) and a secondary coil  812  (which may be the receiving component  107   a  and  107   b  of the system  100  of  FIG. 2 ). 
     The foregoing is a simplified description of the transmitter and its interaction with a secondary coil  812  of an inductive power transfer system. The transmitter may be configured to provide a time-varying voltage to the primary coil  810  in order to induce a voltage within the secondary coil  812 . Although both alternating currents and square waves were pointed to as examples, one may appreciate that other waveforms are contemplated. In such a case, the controller  804  may control a plurality of states of the direct-current converter  806 . For example, the controller  804  may control the voltage, current, duty cycle, waveform, frequency, or any combination thereof. 
     The controller  804  may periodically modify various characteristics of the waveforms applied to the primary coil  810  in order to increase the efficiency of the operation of the power transmitting circuitry. For example, in certain cases, the controller  804  may discontinue all power to the primary coil  810  if it is determined that the secondary coil  812  may not be inductively proximate the primary coil  810 . This determination may be accomplished in any number of suitable ways. For example, the controller  804  may be configured to detect the inductive load on the primary coil  810 . If the inductive load falls below a certain selected threshold, the controller  804  may conclude that the secondary coil  812  may not be inductively proximate the primary coil  810 . In such a case, the controller  804  may discontinue all power to the primary coil  810 . 
     In other cases, the controller  804  may set the duty cycle to be at or near a resonance frequency of the transformer  808 . In another example, the period of the waveform defining the active state of the duty cycle (i.e., high) may be selected to be at or near the resonance frequency of the transformer  808 . One may appreciate that such selections may increase the power transfer efficiency between the primary coil  810  and the secondary coil  812 . 
     In an alternate example, the controller  804  may discontinue all power to the primary coil  810  if a spike in inductive load is sensed. For example, if the inductive load spikes at a particular rate above a certain selected threshold the controller  804  may conclude that an intermediate object may be placed inductively proximate the primary coil  810 . In such a case, the controller  804  may discontinue all power to the primary coil  810 . 
     In still further examples, the controller  804  may modify other characteristics of the waveforms applied to the primary coil  810 . For example, if the receiver circuitry requires additional power, the controller  804  may increase the duty cycle of the waveform applied to the primary coil  810 . In a related example, if the receiver circuitry requires less power, the controller  804  may decrease the duty cycle of the waveform applied to the primary coil  810 . In each of these examples, the time average power applied to the primary coil  810  may be modified. 
     In another example, the controller  804  may be configured to modify the magnitude of the waveform applied to the primary coil  810 . In such an example, if the receiver circuitry requires additional power, the controller  804  may amplify the maximum voltage of the waveform applied to the primary coil  810 . In the related case, the maximum voltage of the waveform may be reduced if the receiver circuitry requires less power. 
     With regard to  FIG. 8 , and as noted above, the transmitter portion of the inductive power transfer system may be configured to provide a time-varying signal to the primary coil  810  in order to induce a voltage within the secondary coil  812  in the receiver through inductive coupling between the primary coil  810  and the secondary coil  812 . In this manner, power may be transferred from the primary coil  810  to the secondary coil  812  through the creation of a varying magnetic flux by the time-varying signal in the primary coil  810 . 
     The time-varying signal produced in the secondary coil  812  may be received by an direct-current converter  814  that converts the time-varying signal into a DC signal. Any suitable direct-current converter  814  can be used in the inductive charging system  800 . For example, in one embodiment, a rectifier may be used as an direct-current converter. The DC signal may then be received by a programmable load  816 . 
     In some embodiments, the receiver direct-current converter  814  may be a half bridge. In such examples, the secondary coil  812  may have an increased number of windings. For example, in some embodiments, the secondary coil may have twice as many windings. In this manner, as one may appreciate, the induced voltage across the secondary coil  812  may be reduced by half, effectively, by the half bridge rectifier. In certain cases, this configuration may require substantially fewer electronic components. For example, a half bridge rectifier may require half as many transistors as a full wave bridge rectifier. As a result of fewer electronic components, resistive losses may be substantially reduced. 
     In certain other embodiments, the receiver may also include circuitry to tune out magnetizing inductance present within the transmitter. As may be known in the art, magnetizing inductance may result in losses within a transformer formed by imperfectly coupled coils. This magnetizing inductance, among other leakage inductance, may substantially reduce the efficiency of the transmitter. One may further appreciate that because magnetizing inductance may be a function of the coupling between a primary and secondary coil, that it may not necessarily be entirely compensated within the transmitter itself. Accordingly, in certain embodiments discussed herein, tuning circuitry may be included within the receiver. For example, in certain embodiments, a capacitor may be positioned parallel to the programmable load  816 . 
     In still further examples, a combination of the above-referenced sample modifications may be made by the controller. For example, the controller  804  may double the voltage in addition to reducing the duty cycle. In another example, the controller may increase the voltage over time, while decreasing the duty cycle over time. One may appreciate that any number of suitable combinations are contemplated herein. 
     Other embodiments may include multiple primary coils  810 . For example, if two primary coils are present, each may be activated or used independently or simultaneously. In such an embodiment, the individual coils may each be coupled to the controller  804 . In further examples, one of the several individual primary coils  810  may be selectively shorted. For example, a switch may be positioned in parallel to the coil such that when the switch is off current may run through the inductor. On the other hand, when the switch is on, no current will run through the coil. The switch may be any suitable type of manual, solid state, or relay based switch. In this manner, the amount of increase in current through each of the several coils may be electively controlled. For example, in a circumstance with a high inductive load, the switch may be turned off to include the coil in the circuit with the primary coil  810 . 
       FIG. 9  is a simplified isometric view of an inductive power transmission system  900  in accordance with another embodiment from which a number of components have been omitted for purposes of clarity. As illustrated, a first electronic device  901  may be operable to receive power inductively transmitted from a second electronic device  902 ; the first electronic device may store the power in one or more batteries (not shown). The first electronic device may include a housing  903  and the second electronic device may include a housing  904 . 
     The first electronic device  901  is illustrated as a smart phone and the second electronic device  902  is illustrated as a charging dock for the smart phone. However, it is understood that this is an example. In various implementations the first and/or second electronic devices may be any kind of electronic devices. Further, although the first electronic device  901  is described as receiving power inductively transmitted from the second electronic device  902 , it is understood that this is an example and that other transmission configurations may be utilized without departing from the scope of the present disclosure. 
       FIG. 10A  is a cross-sectional side view of a first implementation of the inductive power transmission system  900  of  FIG. 9 , taken along the section C-C of  FIG. 9 . As illustrated, the first electronic device  901  may include an inductive receive coil  907  and an alignment magnet  905 . As also illustrated, the second electronic device  902  may include an inductive transmit coil  908  and an alignment magnet  906 . The alignment magnets  905  and  906  may be operable to assist in aligning the inductive transmit and receive coils for inductive power transmission and to keep the coils aligned during transmission. 
     As illustrated, magnetic flux  1001   a  may be generated by and flow through the inductive transmit and receive coils  907  and  908  during inductive power transmission. Such magnetic flux  1001  may interact with the housing  903  and/or the housing  904 . This interaction may cause eddy currents to form in the housing  903  and/or the housing  904 . Such eddy currents may cause efficiency losses in the inductive power transmission and/or may increase the temperature of one or more portions of the housing  903  and/or the housing  904 . 
       FIG. 10B  is a cross-sectional side view of a second implementation of the inductive power transmission system  900  of  FIG. 9 , taken along the section C-C of  FIG. 9 . To contrast with  FIG. 10A , one or more magnetic field directing materials  909   a ,  909   b ,  910   a , and  910   b  or shields may be positioned between the inductive receive coil  907  and the housing  903  and/or the inductive transmit coil  908  and the housing  904 . These magnetic field directing materials may block or direct the magnetic flux  1001   b  from portions of the respective housings. 
     As illustrated, the magnetic field directing materials  909   a ,  909   b ,  910   a , and  910   b  may shape the magnetic flux  1001   b  to block the magnetic flux from the sides of the respective housings  903  and  904 . This may reduce interaction between the magnetic flux and the side portions of the housing, thereby reducing or preventing the formation of eddy currents in the side portions, efficiency losses in the inductive power transmission, and/or increases in temperature at the side portions. 
     In various implementations, the magnetic field directing materials  909   a ,  909   b ,  910   a , and  910   b  may be formed of a diamagnetic material. A diamagnetic material is a material that creates a magnetic field in opposition to an externally applied magnetic field, thus causing a repulsive effect. Such diamagnetic materials may include graphite, bismuth, graphene, pyrolytic carbon, and so on. 
     In some implementations, the magnetic field directing materials  909   a ,  909   b ,  910   a , and  910   b  may be formed of a superconductive material. A superconductive material is a material that exhibits zero electrical resistance and expels magnetic fields when cooled below a characteristic critical temperature. Such superconductive materials may include a lanthanum-based cuprate perovskite material, yttrium barium copper oxide, lanthanum oxygen fluorine iron arsenide, and so on. 
     In various implementations, such as implementations where the magnetic field directing materials  909   a ,  909   b ,  910   a , and  910   b  are formed of a relatively highly thermally conductive material such as graphite, the magnetic field directing materials may operate as a heat spreader. In such implementations, the magnetic field directing materials may dissipate heat generated by the inductive power transmission and/or from other heat generation sources (such as heat generated by power dissipating components, solar loading, and so on). 
     Further, in implementations where the magnetic field directing materials  909   a ,  909   b ,  910   a , and  910   b  operate as a heat spreader, the magnetic field directing materials may be configured to optimize their heat dissipation properties. In general, the amount of heat that the magnetic field directing materials are able to dissipate in a particular period of time may be related to the surface area of the magnetic field directing materials, the thickness of the magnetic field directing materials, and/or other such factors. 
     For instance, in some examples the magnetic field directing materials  909   a ,  909   b ,  910   a , and  910   b  may be configured to increase length (shown vertically in  FIG. 10B ) and/or width (not shown in  FIG. 10B  as  FIG. 10B  is a cross sectional view) with respect to thickness (shown horizontally in  FIG. 10B ) such that the magnetic field directing materials have a large surface area in relation to the amount of material, in order to increase heat dissipation and reduce the time required to dissipate heat while still blocking the magnetic flux  1001   b  from as much of the housings  903  and/or  904  as possible. 
     By way of another example, the magnetic field directing materials  909   a ,  909   b ,  910   a , and  910   b  may form one or more projections, such as fins or extensions, in order to increase the surface area of the magnetic field directing materials beyond that occupied by the length and width of the materials. Such projections may enable the magnetic field directing materials to dissipate more heat in a shorter amount of time than embodiments without such structures, and without altering the housings  903  and/or  904  shielded from the magnetic flux  1001   b.    
     As illustrated, the magnetic field directing materials  909   a ,  909   b  may be positioned between one or more surfaces of the inductive receive coil  907  and one or more internal portions of the housing  903 . As similarly illustrated, the magnetic field directing materials  910   a  and  910   b  may be positioned between one or more surfaces of the inductive transmit coil  908  and one or more internal portions of the housing  904 . However, it is understood that this is an example. In various implementations, magnetic field directing material may be positioned between inductive coils and internal housing portions, located within housings, and/or located on one or more external housing surfaces. 
     In some implementations, the housings  903  and/or  904  themselves may be formed of magnetic field directing materials (such as diamagnetic materials and/or superconductive materials). Alternatively, in various implementations the housings may be formed of paramagnetic materials, combinations of magnetic field directing materials and paramagnetic materials (materials are attracted by an externally applied magnetic field), conductive materials, and/or any other materials. 
     As illustrated, the magnetic field directing materials  909   a ,  909   b ,  910   a , and  910   b  are positioned on both internal sides of both housings  903  and  904 . However, it is understood that this is an example. In various implementations, any number, or amount, of magnetic field directing materials may be variously positioned without departing from the scope of the present disclosure. 
     For example, in some implementations the first electronic device  901  may include the magnetic field directing materials  909   a  and  909   b  whereas the magnetic field directing materials  910   a  and  910   b  may be omitted from the second electronic device  902 . By way of another example, in various implementations the first electronic device may include the magnetic field directing materials  909   b  but omit the magnetic field directing material  909   a  and the second electronic device may include the magnetic field directing material  910   b  but omit the magnetic field directing material  910   a . By way of another example, magnetic field directing material may be included on just one side/region of the first and/or second electronic device  901  and  902 , on a top internal surface of the housing  903  and/ 04   904 , and so on. Various configurations are possible and contemplated. 
     By way of yet another example, in some implementations the first electronic device  901  and/or the second electronic device  902  may include magnetic field directing material in addition to the magnetic field directing materials  909   a ,  909   b ,  910   a , and  910   b . In some instances of this example the additional magnetic field directing material may be positioned within and/or on one or more external surfaces of the housings  903  and/or  904 . 
     In still another example, in various implementations magnetic field directing material may be positioned to surround all surfaces of the inductive receive coil  907  and/or the inductive transmit coil  908  without departing from the scope of the present disclosure. For example,  FIG. 10C  is a cross-sectional side view of a third implementation of the inductive power transmission system  900  of  FIG. 9 , taken along the section C-C of  FIG. 9 . 
     In this implementation, the magnetic field directing material  909   c  may surround all surfaces of the inductive receive coil  907  other than the surface facing the magnetic path toward the inductive transmit coil  908 . Similarly, the magnetic field directing material  910   c  may surround all surfaces of the inductive transmit coil other than the surface facing the magnetic path toward the inductive receive coil. As such, the magnetic field directing materials  909   c  and  910   c  may shape the magnetic flux  1001   c  to block the magnetic flux  1001   c  from all surfaces of the housings  903  and  904  that are not in the magnetic path of the inductive power transmission. 
     Although  FIGS. 10A-10C  illustrate the magnetic fields  100   a - 1000   c  as circulating in one sample direction, it is understood that this is an example. In other embodiments, one or more of the magnetic fields  100   a - 1000   c  may be reversed without departing from the scope of the present disclosure. 
       FIG. 11  is a method diagram illustrating an example method  1100  for manufacturing an inductive power transmission system. This example method may be performed by the systems of  FIGS. 9, 10B , and/or  10 C. 
     The flow may begin at block  1101  where an inductive coil of an electronic device may be configured for use in an inductive power transmission system. The inductive coil may be a transmit coil and/or a receive coil. In some implementations, configuring the inductive coil for use in an inductive power transmission system may include configuring the inductive coil to inductively transmit and/or receive power. In other implementations, configuring the inductive coil for use in an inductive power transmission system may include configuring the inductive coil to inductively transmit and/or receive power from another inductive coil. 
     The flow may then proceed to block  1102  where a magnetic field directing mechanism is positioned to block magnetic flux of the inductive power transmission system from a housing of the electronic device. Such a magnetic field directing mechanism may include materials such as diamagnetic materials, superconductive materials, and so on that are operable block the magnetic flux. 
     Although the method  1100  is illustrated and described above as including particular operations performed in a particular order, it is understood that this is an example. In various implementations, various orders of the same, similar, and/or different operations may be performed without departing from the scope of the present disclosure. 
     For example, block  1102  is illustrated and described as positioning a magnetic field directing mechanism to block magnetic flux of the inductive power transmission system from a housing of the electronic device. However, in some implementations the interaction between the magnetic flux and the housing portion may be reduced as opposed to entirely blocked without departing from the scope of the present disclosure. Such reducing of the interaction between the magnetic flux and the housing portion may be performed utilizing materials such as diamagnetic materials, superconductive materials, and so on. 
     By way of another example, in various implementations an additional operation of configuring the magnetic field directing mechanism to dissipate heat as a heat spreader may be performed without departing from the scope of the present disclosure. Such heat may be generated by the inductive power transmission and/or by other factors such as heat generated by power dissipating components, solar loading, and so on. 
     Although  FIGS. 1-11  are discussed in the context of various embodiments, it is understood that these are examples. In various implementations, various features of various different discussed embodiments may be utilized together without departing from the scope of the present disclosure. 
       FIGS. 12-14  illustrate isometric views of sample electronic devices  1201 - 1401  in which various embodiments of the magnetic connection and alignment techniques disclosed herein may be utilized. As illustrated,  FIG. 12  illustrates a smart phone  1201 ,  FIG. 13  illustrates a tablet computer  1301 , and  FIG. 14  illustrates a wearable device  1401 . However, it is understood that these are examples and that embodiments of the magnetic connection and alignment techniques disclosed herein may be utilized in a wide variety of different electronic devices without departing from the scope of the present disclosure. 
     Although  FIGS. 1-11  illustrate various configurations of components (such as inductive power receiving coil  107   a  and  107   b , inductive power transmitting coil  113   a  and  113   b , and magnetic elements  105  and  111 ), it is understood that these are examples. Various other configurations are possible in various implementations without departing from the scope of the present disclosure. 
     For example,  FIG. 15  is a schematic cross sectional side view of the wearable device  1401  of  FIG. 14 , taken along section D-D of  FIG. 14 , illustrating another sample configuration of inductive power receiving coil  1407   a  and  1407   b , first magnetic element  1405 , first connection surface  1403 , shield elements  1440   a  and  1440   b , and shield element  1406 . However, it is understood that this configuration is also an example and that still other configurations are possible without departing from the scope of the present disclosure. 
     For example, in various implementations one or more magnetic field directing materials such as the magnetic field directing materials  909   a ,  909   b , and/or  909   c  of  FIGS. 10A-10C  may be positioned on various portions of and/or inside the housing of the wearable device  1401  without departing from the scope of the present disclosure. 
     As described above and illustrated in the accompanying figures, the present disclosure discloses systems and methods for magnetic shielding in inductive power transfer. A first electronic device with a first connection surface and an inductive power transfer receiving coil and first magnetic element positioned adjacent to the first connection surface connects in an aligned position with a second electronic device with a second connection surface and an inductive power transfer transmitting coil and second magnetic element positioned adjacent to the second connection surface. In the aligned position, the relative position of first and second electronic devices may be maintained by magnetic coupling between the first and second magnetic elements. In the aligned position the inductive power transfer transmitting coil may be configured to transmit power to the inductive power transfer receiving coil. The first and/or second magnetic elements and/or the inductive power transfer receiving and/or transmitting coils may be configured to minimize or reduce eddy currents caused in the first and/or second magnetic elements by the inductive power transfer receiving and/or transmitting coils. In this way, magnetic connection mechanisms may be utilized without impairing the inductive power transfer and/or causing excessive heat. 
     In the present disclosure, the methods disclosed may be implemented utilizing sets of instructions or software readable by a device. Further, it is understood that the specific order or hierarchy of steps in the methods disclosed are examples of sample approaches. In other embodiments, the specific order or hierarchy of steps in the method can be rearranged while remaining within the disclosed subject matter. The accompanying method claims present elements of the various steps in a sample order, and are not necessarily meant to be limited to the specific order or hierarchy presented. 
     The described disclosure may utilize a computer program product, or software, that may include a non-transitory machine-readable medium having stored thereon instructions, which may be used to program a computer system (such as a computer controlled manufacturing system and/or other electronic devices) to perform a process utilizing techniques of the present disclosure. A non-transitory machine-readable medium includes any mechanism for storing information in a form (e.g., software, processing application) readable by a machine (e.g., a computer). The non-transitory machine-readable medium may take the form of, but is not limited to, a magnetic storage medium (e.g., floppy diskette, video cassette, and so on); optical storage medium (e.g., CD-ROM); magneto-optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROM and EEPROM); flash memory; and so on. 
     It is believed that the present disclosure and many of its attendant advantages will be understood by the foregoing description, and it will be apparent that various changes may be made in the form, construction and arrangement of the components without departing from the disclosed subject matter or without sacrificing all of its material advantages. The form described is merely explanatory, and it is the intention of the following claims to encompass and include such changes. 
     While the present disclosure has been described with reference to various embodiments, it will be understood that these embodiments are illustrative and that the scope of the disclosure is not limited to them. Many variations, modifications, additions, and improvements are possible. More generally, embodiments in accordance with the present disclosure have been described in the context or particular embodiments. Functionality may be separated or combined in blocks differently in various embodiments of the disclosure or described with different terminology. These and other variations, modifications, additions, and improvements may fall within the scope of the disclosure as defined in the claims that follow.