PATENT DOCUMENT

Publication Number: US-10720789-B2
Application Number: US-201916362592-A
Country: US
Kind Code: B2

Title: Wireless charging station

Abstract:
A wireless charging system including a transmitter and a receiver. The transmitter is formed of a coil of wire that includes a first loop portion, a second loop portion, and a crossing portion. The crossing portion electrically couples the first loop portion and the second loop portion such that when current is generated in the coil, electrical current flows through the first loop portion in a different rotational direction than in the second loop portion. The receiver is formed of a ferromagnetic core and multiple (e.g., three) coils disposed about the ferromagnetic core. Each coil may be disposed about a different axis of the core such that current may be induced in at least one of the coils by a magnetic field in any direction.

Claims:
What is claimed is: 
     
       1. A wireless charging receiver comprising:
 a first planar coil centered along a first axis and comprising a first loop portion wound about a first central axis and a second loop portion wound about a second central axis, different from the first central axis; 
 a second planar coil centered along a second axis, the second axis extending perpendicular to the first axis and comprising a third loop portion wound about a third central axis and a fourth loop portion wound about a fourth central axis different from the third central axis, wherein both the first planar coil and the second planar coil are coplanar; and 
 a ferromagnetic structure positioned adjacent to the first planar coil and the second planar coil. 
 
     
     
       2. The wireless charging receiver of  claim 1  further comprising a third coil disposed relative to a third axis, the third axis extending in a direction different than the first axis and the second axis. 
     
     
       3. The wireless charging receiver of  claim 2  wherein the second axis is perpendicular to the first axis, and wherein the third axis is perpendicular to the first axis and the second axis. 
     
     
       4. The wireless charging receiver of  claim 1  wherein the first planar coil is disposed around the ferromagnetic structure, and wherein the second planar coil is disposed around the ferromagnetic structure and the first planar coil. 
     
     
       5. The wireless charging receiver of  claim 1  wherein the first planar coil is disposed along the first axis, and the second planar coil is disposed along the second axis. 
     
     
       6. The wireless charging receiver of  claim 5  wherein both the first planar coil and the second planar coil each comprise a two loop portions. 
     
     
       7. The wireless charging receiver of  claim 5  wherein the ferromagnetic structure is a shielding disk positioned above the first planar coil and the second planar coil. 
     
     
       8. The wireless charging receiver of  claim 1  wherein the first loop portion is spaced apart from the second loop portion and the first central axis and second central axis are each perpendicular to the first axis and wherein the third loop portion is spaced apart from the fourth loop portion and the third central axis and fourth central axis are each perpendicular to the second axis. 
     
     
       9. The wireless charging receiver of  claim 8  wherein the first planar coil and the second planar coil overlap each other near a midpoint between respective the first loop portion and the second loop portion. 
     
     
       10. The wireless charging receiver of  claim 8  wherein the first axis and the second axis intersect at a center point such that the first, second, third and fourth loop portions are disposed symmetrically about the center point. 
     
     
       11. The wireless charging receiver of  claim 1  further comprising a third planar coil disposed relative to a third axis perpendicular to both the first axis and the second axis. 
     
     
       12. The wireless charging receiver of  claim 11  wherein the third planar coil surrounds each of the first and second planar coils. 
     
     
       13. The wireless charging receiver of  claim 1  wherein the ferromagnetic structure is disposed on top of the first and second planar coils and is sized and shaped such that outer edges of the ferromagnetic structure are adjacent to outer edges of the first and second planar coils. 
     
     
       14. A wireless charging receiver comprising:
 a first planar coil formed from a first winding of wire having a first loop portion wound about a first central axis and a second loop portion spaced apart from the first loop portion and wound about a second central axis, different from the first central axis; 
 a second planar coil coplanar with the first planar coil and formed from a second winding of wire having a third loop portion wound about a third central axis and a fourth loop portion spaced apart from the third loop portion and wound about a fourth axis different from the third central axis, wherein the first, second, third and fourth central axis are all parallel to each other; and 
 a ferromagnetic structure disposed on top of the first and second planar coils. 
 
     
     
       15. The wireless charging receiver of  claim 14  wherein the first planar coil and the second planar coil overlap each other near a midpoint between respective the first loop portion and the second loop portion. 
     
     
       16. The wireless charging receiver of  claim 14  wherein the first planar coil is centered along a first axis that bisects the first and second loop portions and the second planar coil is centered along a second axis that bisects the third and fourth loop portions and is perpendicular to the first axis. 
     
     
       17. The wireless charging receiver of  claim 16  wherein the first axis and the second axis intersect at a center point such that the first, second, third and fourth loop portions are disposed symmetrically about the center point. 
     
     
       18. The wireless charging receiver of  claim 16  further comprising a third planar coil coplanar with the first and second planar coils and disposed relative to a third axis perpendicular to both the first axis and the second axis. 
     
     
       19. The wireless charging receiver of  claim 18  wherein the third planar coil surrounds each of the first and second planar coils. 
     
     
       20. The wireless charging receiver of  claim 19  wherein the ferromagnetic structure is disposed on top of the first and second planar coils and is sized and shaped such that outer edges of the ferromagnetic structure are adjacent to outer edges of the first and second planar coils.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This patent application is a continuation of U.S. patent application Ser. No. 15/184,868, filed on Jun. 16, 2016, which claims priority from U.S. Provisional Application No. 62/180,553, filed Jun. 16, 2015, which is hereby incorporated by reference for all purposes. 
    
    
     BACKGROUND 
     Electronic devices (e.g., mobile phones, media players, electronic watches, and the like) operate when there is charge stored in their batteries. Batteries charge when the electronic device is coupled to a power source, such as via a charging cord. Using charging cords to charge batteries in electronic devices, however, requires the electronic device to be physically tethered to a power outlet. In areas where there are many devices that are charging, there may be a large, disorganized grouping of cables that could easily get tangled. Additionally, using charging cords requires the mobile device to have a receptacle configured to mate with the charging cord. The receptacle is typically a cavity in the electronic device that provides avenues within which dust and moisture can intrude and damage the device. Furthermore, a user of the electronic device has to physically connect the charging cable to the receptacle in order to charge the battery. 
     To avoid such shortcomings, wireless charging stations have been developed to wirelessly charge electronic devices. Electronic devices may charge by merely resting on a charging surface of the charging station. Magnetic fields generated by transmitters disposed below the charging surface may induce corresponding currents in receivers that have a corresponding inductive coil. The induced currents may be used by the electronic device to charge an internal battery. 
     Existing wireless charging systems have a number of disadvantages. For instance, wireless charging surfaces require a specific charging region disposed on top of a transmitter coil embedded beneath the surface. This requires the electronic device to be placed in a very specific area on the charging surface. If an electronic device is placed outside of the charging region, the electronic device may not wirelessly charge due to the absence of a magnetic field. Additionally, since single axis magnetic fields require transmitter and receiver coils to be disposed on parallel planes, the electronic device must be positioned in a particular orientation (e.g., with the back face of the device resting on the surface) in order for charging to occur. 
     SUMMARY 
     Embodiments provide transmitters, receivers, and systems for wireless charging. Embodiments further provide methods of making receivers and methods of wireless charging. 
     In some embodiments, an array of transmitter coils can be disposed below a charging surface. The array of transmitter coils may generate time-varying magnetic fields across a vast majority of the charging surface. The magnetic fields can provide power to a dock (or electronic device) located at virtually any position of the surface and in any orientation by inducing current in a multi-dimensional receiver coil of the dock (or electronic device). 
     In some embodiments, a wireless charging transmitter includes a coil configured to transmit power. The coil may include a first loop portion, a second loop portion, and a crossing portion. The crossing portion may include overlapping conductive paths electrically coupling the first loop portion and the second loop portion. The first and second loop portions may be electrically coupled such that, when an electrical current is generated in the coil, the electrical current flows through the first loop portion in a first rotational direction, and through the second loop portion in a second rotational direction different than the first rotational direction. 
     In some embodiments, a wireless charging transmitter includes: a coil configured to transmit power, the coil including a first loop portion; a second loop portion; and a crossing portion comprising overlapping conductive paths that electrically couple the first loop portion and the second loop portion such that, when an electrical current is generated in the coil, the electrical current flows through the first loop portion in a first rotational direction and through the second loop portion in a second rotational direction opposite the first rotational direction. 
     The first loop portion and the second loop portion may be characterized by substantially the same shape and dimensions. In certain embodiments, when the electrical current is generated in the coil a first magnetic field may be generated by the electrical current flowing through the first loop portion, the first magnetic field being characterized by a first direction; and a second magnetic field may be generated by the electrical current flowing through the second loop portion, the second magnetic field being characterized by a second direction different than the first direction. An angle formed between the first direction and the second direction may be at least 135 degrees. In some embodiments, the first direction and the second direction may extend in opposite directions. The crossing portion may be a first crossing portion, and wherein the transmitter may further include a second coil configured to transmit power, the second coil including: a third loop portion; a fourth loop portion; and a second crossing portion comprising overlapping conductive paths that electrically couple the third loop portion and the fourth loop portion such that, when an electrical current is generated in the second coil, the electrical current flows through the third loop portion in the first rotational direction and through the fourth loop portion in the second rotational direction. When the electrical current is generated in the first coil and the second coil, a bridging magnetic field may be generated in a region between the first coil and the second coil. In certain embodiments, the bridging magnetic field may bend between the second loop portion and the third loop portion. The bridging magnetic field may bend in an orientation from the second loop portion to the third loop portion. In particular embodiments, the bridging magnetic field may bend in an orientation from the third loop portion to the second loop portion. The second coil may overlap at least a portion of the first coil. In some embodiments, the first loop portion may have a first horizontal part and a first vertical part, and the second loop portion may have a second horizontal part and a second vertical part. The first horizontal part may extend above the second vertical part, and wherein the second horizontal part extends below the first vertical part. 
     In some embodiments, a wireless charging receiver includes: a first coil disposed relative to a first axis; a second coil disposed relative to a second axis, the second axis extending in a direction different than the first axis; and a ferromagnetic structure positioned adjacent to the first coil and the second coil. 
     The wireless charging receiver may further include a third coil disposed relative to a third axis, the third axis may extend in a direction different than the first axis and the second axis. The second axis may extend in a direction between 45 to 135 degrees from the first axis, and the third may extend in a direction between 45 to 135 degrees from the first axis and the second axis. In some embodiments, the second axis may be perpendicular to the first axis, and the third axis may be perpendicular to the first axis and the second axis. The first coil may be disposed around the ferromagnetic structure, and the second coil may be disposed around the ferromagnetic structure and the first coil. In some embodiments, the third coil may be disposed around the ferromagnetic structure, the first coil, and the second coil. The wireless charging receiver may further include a first insulating layer disposed between the ferromagnetic structure and the first coil, a second insulating layer disposed between the first coil and the second coil, and a third insulating layer disposed between the second coil and the third coil. The first coil may be disposed along the first axis, and the second coil may be disposed along the second axis. In some embodiments, both the first coil and the second coil each comprise a two loop portions. The ferromagnetic structure may be a shielding disk positioned above the first coil and the second coil. 
     In particular embodiments, a method of fabricating a wireless charging receiver includes: providing a ferromagnetic structure; forming a first insulating layer around the ferromagnetic structure; forming a first coil on the first insulating layer, the first coil being disposed about a first axis of the ferromagnetic structure; forming a second insulating layer on the first coil and exposed surfaces of the first insulating layer; forming a second coil on the second insulating layer, the second coil being disposed about a second axis of the ferromagnetic structure, and the second axis being substantially perpendicular to the first axis; forming a third insulating layer on the second coil and exposed surfaces of the second insulating layer; and forming a third coil on the third insulating layer, the third coil being disposed about a third axis of the ferromagnetic structure, and the third axis being substantially perpendicular to the first axis and the second axis. 
     In certain embodiments, forming the first coil, the second coil, and the third coil each includes depositing a patterned layer of conductive material. The first insulating layer may be formed by fusing a first set of two halves together over the ferromagnetic structure, where the second insulating layer may be formed by fusing a second set of two halves together over the first insulating layer and the first coil, and where the third insulating layer may be formed by fusing a third set of two halves together over the second insulating layer and the second coil. 
     In some embodiments, a wireless charging system includes: a transmitter assembly comprising: a charging surface; and a plurality of transmitter coils disposed below the charging surface. The plurality of coils include first and second transmitter coils configured to transmit power, the first coil generating first and second magnetic fields and the second coil generating third and fourth magnetic fields when driven with electrical current, the first and second transmitter coils forming a bridging magnetic field disposed between the first and second transmitter coils; and a receiver assembly. The receiver assembly includes: a first coil disposed relative to a first axis; a second coil disposed relative to a second axis, the second axis extending in a direction different than the first axis; and a ferromagnetic structure positioned adjacent to the first coil and the second coil. 
     The wireless charging system may further include a third receiver coil disposed relative to a third axis, the third axis being substantially perpendicular to the first axis and the second axis. The charging surface may be substantially planar. The charging surface may include curved regions. In certain embodiments, the bridging magnetic field may bend between the second and third magnetic fields. A fifth magnetic field may bridge between two loop portions of the first transmitter coil, and a sixth magnetic field may bridge between two loop portions of the second coil. Each transmitter coil may have a length and a width, where the length may be correlated with a dimension of the charging surface. The length may be twice the width. 
     In some embodiments, a wireless charging table includes: a table top having an upper surface upon which one or more electronic devices can be placed; a wireless charging transmitter positioned under the upper surface of the table top, the wireless charging transmitter comprising a plurality of transmitter coils that define a charging region at the upper surface of the table top, the plurality of transmitter coils including at least a first transmitter coil including: a first loop portion; a second loop portion; and a crossing portion comprising overlapping conductive paths that electrically couple the first loop portion and the second loop portion such that, when an electrical current may be generated in the first transmitter coil, the electrical current flows through the first loop portion in a first rotational direction, and through the second loop portion in a second rotational direction opposite the first rotational direction; and a power distribution system operatively coupled to the wireless charging transmitter, the power distribution system configured to receive power from an alternating current (AC) power source and distribute power to the wireless charging transmitter. 
     When the electrical current may be generated in the first transmitter coil: a first magnetic field may be generated by the current flowing through the first loop portion, the first magnetic field being characterized by a first direction; and a second magnetic field may be generated by the current flowing through the second loop portion, the second magnetic field being characterized by a second direction different than the first direction. In certain embodiments, an angle formed between the first direction and the second direction may be at least 135 degrees. The crossing portion may be a first crossing portion, and where the plurality of transmitter coils further includes a second coil configured to transmit power, the second coil includes: a third loop portion; a fourth loop portion; and a second crossing portion comprising overlapping conductive paths that electrically couple the third loop portion and the fourth loop portion such that, when an electrical current may be generated in the second coil, the electrical current flows: through the third loop portion in the first rotational direction; and through the fourth loop portion in the second rotational direction. When the electrical current is generated in the first transmitter coil and the second coil, a bridging magnetic field may be generated in a region between the first transmitter coil and the second coil. The bridging magnetic field may bend between the second loop portion and the third loop portion. In some embodiments, the first loop portion may have a first horizontal part and a first vertical part, and the second loop portion may have a second horizontal part and a second vertical part. The first horizontal part may extend above the second vertical part, and the second horizontal part may extend below the first vertical part. The power distribution system may include a controller configured to communicate with an electronic device of the one or more electronic devices. 
     In some embodiments, a wireless charging receiver for interacting with a wireless charging retail table includes: a first coil disposed relative to a first axis; a second coil disposed relative to a second axis, the second axis extending in a direction different than the first axis; and a ferromagnetic structure positioned adjacent to the first coil and the second coil, where the first coil, the second coil, and the ferromagnetic structure are configured to receive magnetic fields generated by a transmitter for the wireless charging retail table. 
     The wireless charging receiver may be encased within a docking station. The docking station may be configured to rest on a charging surface of the wireless charging retail table. The docking station may be configured to connect to an electronic device to provide power to the electronic device. The wireless charging receiver may further include a third coil disposed relative to a third axis, the third axis extending in a direction different than the first axis and the second axis. The second axis may extend in a direction between 45 to 135 degrees from the first axis, and the third axis may extend in a direction between 45 to 135 degrees from the first axis and the second axis. The second axis may be perpendicular to the first axis, and the third axis may be perpendicular to the first axis and the second axis. 
     In some embodiments, a wireless charging system includes: a table top having an upper surface upon which one or more electronic devices can be placed; a wireless charging transmitter positioned under the upper surface of the table top, the wireless charging transmitter comprising a plurality of transmitter coils that define a charging region at the upper surface of the table top, the plurality of transmitter coils including at least a first transmitter coil includes: a first loop portion; a second loop portion; and a crossing portion comprising overlapping conductive paths that electrically couple the first loop portion and the second loop portion such that, when an electrical current is generated in the first transmitter coil, the electrical current flows through the first loop portion in a first rotational direction, and through the second loop portion in a second rotational direction opposite the first rotational direction; and a power distribution system operatively coupled to the wireless charging transmitter, the power distribution system may be configured to receive power from an alternating current (AC) power source and distribute power to the wireless charging transmitter. The wireless charging system also includes a wireless charging receiver including: a first coil disposed relative to a first axis; a second coil disposed relative to a second axis, the second axis extending in a direction different than the first axis; and a ferromagnetic structure positioned adjacent to the first coil and the second coil, where the first coil, the second coil, and the ferromagnetic structure are configured to receive magnetic fields generated by the plurality of transmitter coils. 
     The wireless charging system may also include a plurality of sensors configured to detect a presence of an electronic device. The power distribution system may include a controller coupled to the plurality of sensors and the plurality of transmitter coils. The controller may be configured to selectively energize one or more transmitter coils in response to the detected presence of the electronic device. The wireless charging receiver may be encased within a docking station. 
     A better understanding of the nature and advantages of embodiments of the present disclosure may be gained with reference to the following detailed description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified diagram illustrating a wireless charging station, in accordance with embodiments of the present disclosure. 
         FIG. 2A  is a simplified diagram illustrating a transmitter coil in accordance with some embodiments of the present disclosure. 
         FIG. 2B  is a simplified diagram illustrating a transmitter coil in accordance with embodiments of the present disclosure. 
         FIG. 3A  is a simplified diagram illustrating a pair of transmitter coils according to  FIG. 2A  arranged in a parallel configuration, in accordance with embodiments of the present disclosure. 
         FIG. 3B  is a simplified diagram illustrating a pair of transmitter coils according to  FIG. 2A  arranged in a perpendicular configuration, in accordance with embodiments of the present disclosure. 
         FIG. 4  is a simplified diagram illustrating a pair of transmitter coils according to  FIG. 2B  arranged in a parallel configuration, in accordance with embodiments of the present disclosure. 
         FIG. 5  is a simplified diagram illustrating a side-view cross-section of a wireless charging station, in accordance with embodiments of the present disclosure. 
         FIG. 6A  is a simplified diagram illustrating a receiver including a core and coils wrapped around the core, in accordance with embodiments of the present disclosure. 
         FIG. 6B  is a simplified diagram illustrating a receiver including a core and coils wrapped around the core and disposed underneath the core, in accordance with embodiments of the present disclosure. 
         FIG. 7A  is a simplified diagram illustrating a receiver including coils having oval-shaped loop portions and a shielding disk disposed above the coils, in accordance with embodiments of the present disclosure. 
         FIG. 7B  is a simplified diagram illustrating a receiver including coils having bow tie-shaped loop portions and a shielding disk disposed above the coils, in accordance with embodiments of the present disclosure. 
         FIG. 7C  is a simplified diagram illustrating a cross-sectional view of a receiver including coils having loop portions and a shielding disk, in accordance with embodiments of the present disclosure. 
         FIG. 7D  is a simplified diagram illustrating a cross-sectional view of a magnetic field propagating through a receiver including coils having loop portions and a shielding disk, in accordance with embodiments of the present disclosure. 
         FIG. 8  is a simplified diagram illustrating a receiver interacting with a transmitter in a wireless charging station in the X and Z directions, in accordance with embodiments of the present disclosure. 
         FIG. 9  is a simplified diagram illustrating a receiver interacting with a transmitter in a wireless charging station in the X and Y directions, in accordance with embodiments of the present disclosure. 
         FIG. 10  is a simplified diagram illustrating a charging surface configured to selectively energize certain transmitters closest to an electronic device, in accordance with embodiments of the present disclosure. 
         FIG. 11  is a simplified diagram of a stacked transmitter, in accordance with embodiments of the present disclosure. 
         FIG. 12  is a simplified diagram illustrating a cross-sectional view of an exemplary stacked transmitter and the interaction of its generated magnetic fields with a receiver placed in various positions, in accordance with embodiments of the present disclosure. 
         FIG. 13  is a simplified diagram of a stacked receiver, in accordance with embodiments of the present disclosure. 
         FIG. 14  is a simplified diagram of a charging system including stacked receivers positioned over a plurality of stacked transmitters, in accordance with embodiments of the present disclosure. 
         FIG. 15  is a flow diagram illustrating a method of forming a receiver, in accordance with embodiments of the present disclosure. 
         FIG. 16  is a flow diagram illustrating a method of charging an electronic device using a wireless charging station, in accordance with embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments describe a wireless charging system where an electronic device may be charged across a vast majority, if not an entire area, of a charging surface. An array of transmitter coils disposed below a charging surface may generate time-varying magnetic fields capable of inducing current in a receiver of the electronic device or of a docking station with which the electronic device is coupled. In certain embodiments, each transmitter coil can generate magnetic fields in different directions simultaneously. For instance, each transmitter coil can generate two magnetic fields in opposite directions. Portions of transmitter coils may also interact with one another such that magnetic fields generated in one portion of a coil can bend into another portion of the same coil. 
     In some embodiments, magnetic fields generated by each transmitter may also bridge between transmitter coils. For instance, magnetic fields generated by current traveling through a portion of one transmitter coil may bend into a portion of another adjacent transmitter coil. Accordingly, magnetic fields may be formed between transmitter coils such that magnetic fields are present across an entire charging surface including an array of embedded transmitter coils with little or no drop-off in field strength above regions in between adjacent coils. 
     In some embodiments, the receiver can include coils in which current is induced when in the presence of the magnetic fields generated by the array of transmitters to generate current for charging electronic devices. Specifically, in some embodiments, the receiver may be configured to utilize the magnetic fields generated by individual transmitter coils in addition to magnetic fields flowing between adjacent transmitter coils to generate current for charging electronic devices. Details of such a wireless charging system is discussed in further detail herein. 
     I. Wireless Charging Station 
       FIG. 1  illustrates an exemplary wireless charging station  100  in accordance with some embodiments of the present disclosure. Wireless charging station  100  includes a charging surface  102 . Charging surface  102  may be a surface upon which a device having a receiver may rest to wirelessly charge its battery. In some embodiments, charging surface  102  may be a top surface of a charging structure (e.g., a table having charging surface  102  and a plurality of legs supporting charging surface  102 ) that is substantially planar. In other embodiments, charging surface  102  may include curvature such that regions of charging surface  102  are substantially non-planar. The curvature may be convex or concave, or may include multiple convex and concave profiles organized in a predetermined or random arrangement. 
     In some embodiments, wireless charging station  100  also includes sets of transmitters  104  and  106 . Sets of transmitters  104  and  106  may each include a plurality of coils. For instance, sets of transmitters  104  and  106  may each contain N number of coils as illustrated in  FIG. 1 . The number N may be any suitable number capable of allowing the set of transmitters to generate magnetic fields across a vast majority, if not the entire area, of charging surface  102 . In embodiments, sets of transmitters  104  and  106  may be disposed underneath charging surface  102  and embedded within charging station  100 . Although embodiments discuss two sets of transmitters  104  and  106 , other embodiments are not limited to such arrangements. For instance, embodiments may be formed of more or less than two sets of transmitters. 
     In certain embodiments, sets of transmitters  104  and  106  may have identical coil arrangements. In other embodiments, sets of transmitters  104  and  106  may have different coil arrangements. For instance, set of transmitters  104  may have more or less coils than set of transmitters  106 . Furthermore, set of transmitters  104  may have a different coil arrangement (e.g., perpendicular or parallel arrangements) than set of transmitters  106 , as will be discussed further herein with respect to  FIGS. 3A and 3B . 
     Magnetic fields may be generated by each of the coils in sets of transmitters  104  and  106  when a time-varying current is generated in the coils. For instance, each coil may be configured to generate a time-varying magnetic field when an AC current is generated in the coil. In some embodiments, the aggregate time-varying magnetic fields generated by the sets of transmitters  104  and  106  at charging surface  102  may create charging regions  108  and  80  that span across a vast majority of charging surface  102 . For instance, in some embodiments, charging regions  108  and  80  may occupy 50% to 100% of the total surface area of charging surface  102 . In  FIG. 1 , a gap is shown between charging regions  108  and  80 . This, however, is not intended to be limiting. In some embodiments, magnetic fields generated by set of transmitters  104  and set of transmitters  106  can overlap (or even travel between each set) at charging surface  102 . 
     Wireless charging can occur when a receiver is placed on or near charging surface  102 . The receiver may be disposed within a receiving device  112 , such as an electronic device that can be charged directly by the receiver or a docking station that can use energy received by the receiver to charge another electronic device operatively coupled to the docking station. For example, if the receiver is disposed within a docking station, an electronic device to be charged may be operatively coupled to the docking station by a physical connector through which charge from the docking station can be transferred to the electronic device. In some embodiments, an electronic device may receive power from the docking station via a second, separate inductive charging system. That is, the docking station can include both a first receiver to wirelessly receive energy from one or more of transmitters  104 ,  106  and a docking station wireless transmitter that wireless transmits energy from the docking station to a second receiver in the electronic device. 
     When receiving device  112  is placed on charging surface  102 , time-varying magnetic fields generated by one or more coils in the sets of transmitters  104  and  106  may induce a current in the receiver disposed within the receiving device  112 . The induced current may then be rectified by the receiving device  112  to generate DC power and charge a battery. Due to the continuous magnetic fields generated across charging surface  102 , receiving device  112  can generate power when placed on virtually any region the charging surface  102 . Unlike conventional wireless charging arrangements, receiving device  112  can generate power even when it is located between coils, such as between coils  104 - 1  and  104 - 2 , due to magnetic fields traveling between coils. In embodiments, another receiving device  116  may also generate power when placed above a coil, such as coil  104 - 3 , because magnetic fields generated by coil  104 - 3  may exist there as well. Additionally, the receiver of receiving device  112  can be configured to receive power in the form of magnetic fields generated in virtually any direction, thereby allowing receiving device  112  to be placed on charging surface in many different orientations. Details of the transmitter and receiver design that can facilitate such charging capabilities will be discussed further herein. 
     II. Transmitter 
     In embodiments of the present disclosure, a “transmitter” may include a coil of wire that generates a magnetic field when current is generated in the coil. The direction of the magnetic field may depend on the rotational direction of the current flowing through the coil (e.g., clockwise or counter-clockwise). For instance, according to the right hand rule (RHR), a counter-clockwise flow of current will generate an upward magnetic field inside the coil. Conversely, a clockwise flow of current will generate a downward magnetic field inside the coil. The shape and configuration of the coil may directly affect the characteristics of the magnetic field generated by the transmitter. 
     A. Transmitter Coil Structure 
       FIG. 2A  is a simplified diagram illustrating an exemplary transmitter  200 , according to embodiments of the present disclosure. Transmitter  200  may be used in the sets of transmitters  104  and  106  discussed herein with respect to  FIG. 1 . Transmitter  200  may be formed of a coil  202  that crosses over itself to form multiple loop portions. For instance, coil  202  may form two loop portions: a first loop portion  204  and a second loop portion  206 . First and second loop portions  204  and  206  may be substantially similar in size and shape. In some embodiments, first and second loop portions  204  and  206  may be mirror images of one another. In some embodiments, coil  202  may comprise one turn (e.g., as seen in  FIG. 2A ). In some other embodiments, coil  202  may have more than one turns with each turn comprising a first and second loop portion. 
     In some embodiments, first and second loop portions  204  and  206  may be electrically coupled together by a crossing portion  208 . Crossing portion  208  may be a point at which coil  202  overlaps itself such that current flowing through first loop portion  204  may continue to flow through second loop portion  206 . Accordingly, a single current may flow from node A to node B through coil  202 , as illustrated in  FIG. 2A . In some embodiments, overlapping wire portions at crossing portion  208  may be insulated from one another to minimize interference and/or prevent occurrence of short circuiting. For instance, coil  202  may be an insulated wire, or a patterned wire insulated by an insulating layer disposed between the crossing portion  208 . 
     As a current  210  is driven through transmitter  200 , magnetic fields may be generated by coil  202 . As an example, magnetic fields  216  and  218  may be generated by transmitter  200  as current  210  is driven through coil  202 . Magnetic fields  216  and  218  may be generated in a direction according to the direction of current flow around coil  202  as established by the RHR. In some embodiments, the rotational direction of current flow around second loop portion  206  may be opposite the rotational direction of the same current flow around first loop portion  204 . For instance, nodes A and B can be connected to a power source, and as shown in  FIG. 2A  current  210  may flow into the coil  202  from node A, across crossing portion  208 , around second loop portion  206 , across crossing portion  208  again, around first loop portion  204 , and out of the coil at node B. Thus, a counter-clockwise current flow  212  may be formed in first loop portion  204 , and a clockwise current flow  214  may be formed in second loop portion  206 . When the bias of the power source is reversed, current can flow through the coil  202  in the opposite direction, thereby creating a clockwise current flow in first loop portion  204  and a counter-clockwise current flow in second loop portion  206 . 
     As a result of the current flow, first magnetic field  216  may be generated within first loop portion  204 , and second magnetic field  218  may be generated in second loop portion  206 . In some embodiments, first magnetic field  216  is generated in a direction different than second magnetic field  218 . As an example, according to the RHR, when the applied bias generates current  210  shown in  FIG. 2A , first magnetic field  216  may be generated in a direction out of the page (as indicated by a circle with a dot in the center) due to counter-clockwise current flow  212 , and second magnetic field  218  may be generated in a direction into the page (as indicated by a circle with an “X” in the center) due to clockwise current flow  214 . When the bias applied by the power source is reversed, the change in current direction may generate magnetic fields in opposite directions as described herein. 
     In some embodiments, first magnetic field  216  and second magnetic field  218  may be generated in completely opposite directions. Thus, an angle between first and second magnetic fields  216  and  218  may be approximately 180 degrees. However, in some embodiments, first and second magnetic fields  216  and  218  may not be generated in completely opposite directions. This may be because the transmitter  200  is not completely flat as a result of manufacturing variations. In such embodiments, an angle between first and second magnetic fields  216  and  218  may be more or less than 180 degrees. In some embodiments, the angle between first and second magnetic fields  216  and  218  may be at least 135 degrees. In some other embodiments, the angle between first and second magnetic fields  216  and  218  may be between 175 and 185 degrees. 
     Portions of first magnetic field  216  may bridge across transmitter  200 . For instance, as shown in  FIG. 2A , bridging field  220  of first magnetic field  216  may bend across crossing portion  208  and down into the region of second magnetic field  218  as a result of the opposite polarity of magnetic fields  216  and  218 . In some embodiments, bridging field  220  may extend a distance H away from transmitter  200 . Distance H may be set according to the distance between transmitter  200  and a charging surface disposed above transmitter  200 . Distance H may be tall enough to project above the charging surface such that a receiver on the surface can be within the generated magnetic fields. 
     In some embodiments, distance H may be altered by changing a distance D of the first and second loop portions  204  and  206 . Distance D may represent the horizontal spacing between edges of a loop portion, such as loop portions  204  and  206 . A greater distance D can result in a magnetic field that projects farther away (e.g., greater distance H). Conversely, a lesser distance D can result in a magnetic field that projects closer to transmitter  200  (e.g., lesser distance H). Accordingly, distance D may be designed according to a target distance H, which may be determined based upon the distance between transmitter  200  and the charging surface. The target distance H may be directly related to the thickness of a charging surface. For instance, thicker charging surfaces may require greater distances D. In certain embodiments where, for example, the charging surface is part of a relatively thick upper surface (e.g., between one half inch and two inches thick) of a charging table sized and shaped to simultaneously charge multiple devices, distance D can range between 1 and 12 inches. In a particular embodiment, distance D can be approximately 3 inches for a charging surface approximately 1 inch thick. 
     As further illustrated in  FIG. 2A , embodiments of transmitter  200  may have a bow tie shape. That is, portions of first and second loop portions  204  and  206  may taper toward crossing portion  208 . Additionally, other portions of first and second loop portions  204  and  206  may have a straight-edged profile with relatively sharp corners. In some embodiments, transmitter  200  may have an overall length L and an overall width W. In certain embodiments, transmitter  200  may have a length ranging between 1 and 24 inches, such as approximately 6 inches. Overall width W for transmitter  200  may range between 1 and 12 inches, such as approximately 12 inches. In an embodiment, transmitter  200  may have a square-shape profile where the length L and width W are equal. In another embodiment, transmitter  200  may have a rectangular-shape profile where the length L is different than width W. For example, transmitter  200  may have a length L that is twice its width W. 
     Although  FIG. 2A  illustrates an exemplary transmitter having a bow tie profile, other profiles are envisioned herein as well. For instance, other embodiments may have curved-edge profiles and/or curved corners. In some embodiments, a transmitter structure may have loop portions that have a bent profile, e.g., L-shaped loop portions, as shown in  FIG. 2B . 
       FIG. 2B  illustrates an exemplary transmitter  222  having loops configured in a bent, L-shaped profile, according to an embodiment of the present disclosure. Similar to transmitter  200 , transmitter  222  may be formed of a coil  224  that crosses over itself to form multiple loop portions, e.g., two loop portions: a first loop portion  226  and a second loop portion  228 . First and second loop portions  226  and  228  are electrically coupled together by a crossing portion  530 , which may be a point at which transmitter  222  overlaps itself such that current flowing through first loop portion  226  may continue to flow through second loop portion  228 . 
     As a current  532  is driven through transmitter  222 , magnetic fields may be generated by transmitter  222 . As an example, first and second magnetic fields  534  and  536  may be generated by transmitter  222  as current  532  is driven through coil  224 . According to the RHR, when the applied bias generates current  532  shown in  FIG. 2B , first magnetic field  534  may be generated in a direction out of the page due to counter-clockwise current flow  538 , and second magnetic field  536  may be generated in a direction into the page due to clockwise current flow  540 . 
     As shown in  FIG. 2B , first and second loop portions  226  and  228  have bent profiles. Accordingly, a horizontal part of first loop portion  226  may extend over a vertical part of second loop portion  228  as shown in  FIG. 2B , and vice versa. Having the horizontal part of first loop portion  226  extend over the vertical part of second loop portion  228  causes the left and right edges of transmitter  222  to include parts of first and second loop portions  226  and  228 . Thus, each of the left and right edges of transmitter  222  may generate magnetic fields that extend in opposite directions. The opposite polarity of the magnetic fields minimizes detrimental coupling between neighboring transmitter coils, as will be discussed further herein. 
     Similar to transmitter  200  in  FIG. 2A , transmitter  222  may also have an overall length L, an overall width W, and a distance D. In some embodiments, the dimensions of each transmitter  222  can be related to the dimensions of a charging surface. For instance, in an embodiment where a charging surface has a length that is two times greater than its width, a transmitter  222  can have a length L that is also two times larger than its width. Furthermore, the thickness of the charging surface may dictate distance D of transmitter  222 . A larger distance D may result in a magnetic field projecting a greater distance H away from transmitter  222 . Thus, transmitter  222  may have a distance D ranging between 1-12 inches for a charging surface approximately 1 inch thick. In a particular embodiment, the distance D is approximately 3 inches. Accordingly, transmitter  222  may project a magnetic field above a charging surface such that receivers may interact with the magnetic field. 
     B. Transmitter Arrangement 
     According to some embodiments, a transmitter having more than one coil may be used to generate magnetic fields at a charging surface, such as charging surface  102  in  FIG. 1 . For instance, more than one coil may be placed proximate to one another such that a magnetic fields exists between the coils. 
       FIG. 3A  illustrates an exemplary transmitter arrangement where two coils having bow tie profiles are arranged proximate to one another. As shown, a first coil  301  may be disposed laterally proximate to a second coil  302  such that both coils are arranged parallel to one another. First coil  301  may include a first loop portion  304  and second loop portion  306 . Current  318  flowing through first coil  301  may generate a first magnetic field  308  and a second magnetic field  310 . A portion  326  of magnetic field  308  may bridge between first and second loop portions  304  and  306 . Second coil  302  may include a third loop portion  312  and fourth loop portion  314 . Current  320  flowing through second coil  302  may generate a third magnetic field  322  and a fourth magnetic field  324 . In some embodiments, the rotational flow of the current through third loop portion  312  may be the same as the rotational flow of the current through first loop portion  304 . Accordingly, a portion  328  of the magnetic field  322  may bridge between third and fourth loop portions  312  and  314 . 
     In some embodiments, the direction of the magnetic fields generated by loop portions in adjacent coils may be opposite one another. For example, magnetic field  310  generated by second loop portion  306  may be in an opposite direction to magnetic field  322  generated by third loop portion  312 . Due to their opposite polarities, a portion  316  of magnetic field  322  may bridge between coils  301  and  302  and bend downward into the second loop portion  306 . Accordingly, a magnetic field may exist in a space X between adjacent coils  301  and  302 . In some embodiments, a receiver may generate power when placed on a region of a charging surface above a space between coils as well as above the center of a coil, as will be discussed further herein. 
     In some embodiments, as shown in  FIG. 3A , adjacent coils can be arranged in a parallel configuration. In some other embodiments, adjacent coils can be arranged in a perpendicular configuration.  FIG. 3B  illustrates such a transmitter arrangement where two coils are arranged perpendicular to one another. As shown, a second coil  332  is arranged at an angle offset from a first coil  331  of approximately 60 degrees. By placing the two coils perpendicular to one another, undesirable coupling effects between adjacent coils can be alleviated in some embodiments. Additionally, coils  331  and  332  may be arranged to have different geometries to minimize coupling. In embodiments where there are more than two coils, the transmitter arrangement may include an alternating geometry arrangement between two different coil geometries. Other embodiments may minimize coupling by isolating resonant components. Isolating resonant components may be performed by turning off those components that resonate with one another. 
     Although modifying the transmitter arrangement may decrease coupling between transmitters, other modifications may be performed instead. For instance, modifying the profile of the loop portions may minimize detrimental coupling. In an embodiment, transmitter coils may be modified to have bent L-shaped loop profiles (i.e., profile in  FIG. 2B ) to minimize detrimental coupling, as will be discussed herein with respect to  FIG. 4 . 
       FIG. 4  illustrates an exemplary transmitter arrangement where two coils having bent L-shaped loop profiles are arranged proximate to one another. As shown, a first coil  401  may be disposed laterally proximate to a second coil  402  such that both coils are arranged parallel to one another. First coil  401  may include a first loop portion  404  and a second loop portion  406 ; and second coil  402  may include a first loop portion  408  and a second loop portion  410 . As shown in  FIG. 4 , only those parts of second loop portion  406  of first coil  401  that are laterally adjacent to parts of first loop portion  408  of second coil  402  may interact with one another. Thus, less than the entire edge of coils  401  and  402  may interact with one another. In some embodiments, approximately half of the entire edges of coils  401  and  402  may interact with one another. Due to the decreased interaction between first and second coils  401  and  402 , detrimental coupling may be less than other instances where the entire edges of first and second coils are interacting with one another (e.g., coils in  FIG. 3A ), thereby minimizing coupling between first and second coils  401  and  402 . 
     Although  FIGS. 3A, 3B, and 4  illustrate first/second coils  301 / 631 ,  302 / 632 , and  701 / 702  as being substantially identical, embodiments are not so limited. For instance, first and second coils may have different cross-sectional shapes and/or have different sizes. Thus, in some embodiments, first and second coils may have different orientations and also have different shapes. Furthermore, although  FIGS. 3A, 3B, and 4  illustrate first and second coils  301 ,  331  and  302 ,  332  being adjacent to one another, one skilled in the art will understand that a transmitter may have more than two coils. Thus, first and second coils may not be adjacent to one another, but be far away from one another with one or more intermediate coils disposed between them. Further, in some embodiments, transmitters may further include ferromagnetic material (e.g., ferrite sheet material) used to concentrate magnetic fields and direct them in accordance with selected geometry based upon the arrangement of the receiver described in further detail herein. 
     In yet other embodiments, a differential coil  412 / 414  may be disposed around the outside of each transmitter coil  401  and  402 . Differential coil  412 / 414  may enhance the efficiency of magnetic field generation of each transmitter coil  401  and  402 . Additionally, differential coil  412 / 714  may minimize far-field magnetic fields, but enhance near-field magnetic fields in relation to the z-direction (i.e., the direction into and out of the page) of transmitter coils  401  and  402 . Thus, conductive entities that are far from the transmitter coils may not be exposed, or nominally exposed, to the magnetic fields generated by transmitter coils  401  and  402 , while conductive entities that are close to the transmitter coils may be substantially exposed to the magnetic fields. 
     C. Transmitter Operation 
       FIG. 5  illustrates a side-view cross-sectional perspective of a charging structure  500  that includes an upper charging surface  502  and a transmitter  504  having a plurality of transmitting coils  504   a - 504   d  according to some embodiments of the present disclosure. With reference to a three-dimensional space, Z and X directions of magnetic fields are observable in  FIG. 5 , while magnetic fields in the Y direction, although existing in the embodiment of  FIG. 5 , are not shown for ease of description. Charging structure  500  is illustrated in  FIG. 5  as a table having a table top  503  supported by multiple legs  505 . In some embodiments, the table can be located in a retail environment and used to display and charge multiple electronic devices for potential purchase. A charging width  506  across charging surface  502  can represent all of or less than the upper surface of table top  503  depending on the placement and number of individual transmitting coils included in transmitter  504 . Additionally, in some embodiments, the dimensions of one or more individual transmitting coils, such as coils  504   a - 504   d , are related to the dimensions of charging surface  502  as discussed above with respect to  FIGS. 2A and 2B . 
     Although charging structure  500  is shown in  FIG. 5  as a table having a charging surface  502  supported by a plurality of legs, it is to be appreciated that charging structure  500  can be any structure having a charging surface  502  upon which an electronic device may be placed. For example, in other embodiments, charging structure  500  can be a charging mat that is sized and shaped for personal use (e.g., to be placed on a desktop or similar surface). Additionally, while coils  504   a - 504   d  are shown in  FIG. 5  as being embedded within table top  503  of charging structure  500 , in other embodiments the coils can be placed below the table top or embedded in other portions of charging structure  500  (e.g., if charging structure  500  is a charging mat, coils  504   a - 504   d  can be embedded in the mat). In embodiments where coils  504   a - 504   b  are placed below table top  503 , table top  503  may include an apron (not shown) that surrounds the edges of table top  503  that extend far enough down such that coils  504   a - 504   b  are hidden from view. Additionally, coils  504   a - 504   d  may be embedded within a protective structure (not shown) that is attached to table top  503  having a single inlet to accept AC power. When current is driven to coils  504   a - 504   d , magnetic fields  512  and  514  may be generated. Near-field may be maximized and far-field may be minimized to maximize the strength of magnetic fields at charging surface  502 . As discussed herein, dimension D of the coils as discussed in  FIG. 2A , can be designed to maximize magnetic fields in the near-field regions. 
     According to some embodiments of the disclosure, magnetic fields  512  generated over the transmitter  504 , and magnetic fields  514  generated between transmitters  504  can form a charging width  506  that spans across a vast majority of the charging surface  502 . Magnetic fields  512  and  514  can be generated such that at least a portion of magnetic fields  512  and  514  are detectable above charging surface  502  across charging width  506 . Thus, unlike conventional charging regions, charging width  506  can be substantially continuous across the surface and allows an electronic device to be charged in areas of charging surface  502  where a coil is not disposed directly underneath, such as regions between coils  504   a - 504   d.    
     In some embodiments, coils  504   a - 504   d  are coupled to a single power source. The power source may be an AC (or pulsed DC) voltage or current source that produces time-varying current. The time-varying current may thus generate time-varying magnetic fields  512  and  514 . According to some embodiments of the present disclosure, a single power source signal may be provided to coils  504   a - 504   d . Additionally, coils  504   a - 504   d  may all be driven by a same clock source such that coils  504   a - 504   d  operate at the same frequency in a single phase. Thus, in some embodiments, there may be no need to create multiple signals having different phases, as required in a phased-array system where multiple clock sources are used to drive current to an array of antennas. Accordingly, the arrangement of coils  504   a - 504   d  may result in a simpler magnetic field generation system. In some embodiments, a receiver having one or more coils may be configured to capture magnetic fields  512  and  514  generated by transmitters  504 , with magnetic fields  512  and  514  inducing current in the receiver coils. Details of such receivers are discussed further herein. 
     In some embodiments, coils  504   a - 504   d  are coupled to more than one power source. Any coupling arrangement of coils  504   a - 504   d  and the power sources for suitable operation of the transmitter is envisioned in embodiments described herein. For instance, coils  504   a - 504   b  may be coupled to a first power source, and coils  504   c - 504   d  may be coupled to a second power source. The power sources may all have the same configurations and operate synchronously. Or, alternatively, the power sources may have different types of configurations and operate asynchronously. For instance, the first power source may provide a time-varying current at a different frequency than the second power source. As an example, the first and second power sources may operate at frequencies that are offset by one or more kHz from one another. 
     III. Receiver 
     In embodiments of the present disclosure, a “receiver” may be an electrical component including one or more coils of wire in which a current can be induced in the presence of a time-varying magnetic field. In some embodiments, a receiver can be incorporated directly into an electronic device which can use the induced current to charge a battery. In some embodiments, a receiver can be part of a docking station configured to transfer the generated power to a coupled electronic device by way of inductive charging or a wired connection. 
     As described herein, a power source may drive time-varying current to a transmitter coil. In response, the transmitter coil may generate a time-varying magnetic field. The time-varying magnetic field may induce current in one or more coils of the receiver. The current may then be converted from AC to DC for use in charging a battery of an electronic device. 
     A. Receiver Structure 
     Unlike conventional receivers that have only one coil for generating power from a magnetic field along one axis, a receiver according to some embodiments described herein may have more than one coil for generating power from a time-varying magnetic field in more than one direction.  FIG. 6A  illustrates an exemplary receiver  600  according to embodiments of the present disclosure. In some embodiments, receiver  600  may include three coils: a first coil  602 , a second coil  604 , and a third coil  606 . Each coil may be disposed about a core  608  in different directions such that current may be induced in at least one of coils  602 ,  604 , and  606  when exposed to an anisotropic magnetic field. For instance, as shown in  FIG. 6A , first coil  602  may be disposed about a first axis of core  608  extending in an X-direction, second coil  604  may be disposed about a second axis of core  608  extending in a Y-direction, and third coil  606  may be disposed about a third axis of core  608  extending in a Z-direction. In some embodiments, each of the first, second, and third axis can be substantially perpendicular to one another. As further shown in  FIG. 6A , coils  602 ,  604 , and  606  can be disposed over each other in a particular order. This, however, is not intended to be limiting as coils  602 ,  604 , and  606  can be disposed in any suitable configuration. 
     In some embodiments, coils  602 ,  604 , and  606  of receiver  600  are wound about core  608 . As shown in  FIG. 6A , core  608  may be in the form of a rectangular prism in some embodiments. The rectangular prism may have dimensions that range between 1 to 10 mm thick  610 , 20 to 100 mm wide  612 , and 1 to 50 mm long  614 . In some embodiments, the rectangular prism may have dimensions that range between 4-5 mm thick  610 , 50-70 mm wide  612 , and 10-30 mm long  614 . In various embodiments, core  608  can have any other suitable shape and dimensions. 
     Core  608  may be formed of any suitable material capable of concentrating magnetic fields. For instance, core  608  may comprise a ferromagnetic material such as ferrite in one example. The amount of magnetic material in the core may be tailored to result in a core that has a magnetic permeability (μ) ranging between 50 and 250, e.g., between 100 and 200. 
     Coils  602 ,  604 , and  606  may be wound around core  608  any suitable number of times such that a sufficient power is generated when subjected to a magnetic field. Power may be generated by the induced current and the resulting voltage established by the number of turns. The number of turns may be a function of a voltage-over-current ratio in a corresponding receiver of an electronic device (e.g., if the receiver  600  is disposed in a dock that wirelessly charges the electronic device), as well as a configuration of impedance matching networks (i.e., Z matching networks). In some embodiments, coils  602 ,  604 , and  606  may be wound around the core between 1 to 10 times, such as 4 to 7 times. Each of coils  602 ,  604 , and  606  may be wound around core  608  the same number of times in some embodiments. In other embodiments, one or more of coils  602 ,  604 , and  606  may be wrapped around core  608  a different number of times than the other coils. Coils  602 ,  604 , and  606  may be insulated from one another as well as from core  608 . In some instances, coils  602 ,  604 , and  606  are in the form of insulated wires. In other instances, coils  602 ,  604 , and  606  are formed of patterned wires insulated by layers of insulating material. Details of how receiver  600  is formed according to some embodiments is discussed in more detail further herein. 
     Although  FIG. 6A  illustrates a receiver  600  as having all three coils wrapped around a core, embodiments are not limited to such configurations. For instance, one or more coils may not be wrapped around the core.  FIG. 6B  illustrates an exemplary receiver  620  where one coil is not wrapped around a core  628 . As shown, a first coil  622  may be disposed about a first axis of core  628  extending in an X-direction and a second coil  624  may be disposed about a second axis of core  628  extending in a Y-direction. First coil  622  and second coil  624  can be wrapped around core  628 . A third coil  626  may be disposed about a third axis of core  628  extending in a Z-direction but with third coil  626  being disposed below core  628 . In certain embodiments, a ferromagnetic plate (not shown) may be disposed between core  628  and third coil  626 . The magnetic plate may help concentrate magnetic fields in the Z-direction to enhance power generation by third coil  626 . Any of coils  622 ,  624 , and  626  can be disposed adjacent to but not wrapped around core  628 . 
       FIG. 7A  is a simplified diagram of an alternative exemplary receiver  710  according to embodiments of the present disclosure. Receiver  710  may include three coils: a first coil  712 , a second coil  714 , and a third coil  716 . First coil  712  may be formed of a winding of wire having a first loop portion  718  and a second loop portion  720 , and second coil  714  may be formed of a winding of wire having a first loop portion  722  and a second loop portion  724 . In embodiments, first coil  712  and second coil  714  may each overlap itself near a midpoint between respective first and second loop portions  718 ,  720  and  722 ,  724 . The overlapping wire portions near the midpoint may be insulated from one another to minimize interference and/or prevent occurrence of short circuiting. Accordingly, a single current may flow through both first and second loop portions of each coil. Additionally, each coil  712 ,  714 , and  716  may be electrically isolated from one another such that there is minimal interference between them. 
     In embodiments, third coil  716  may be positioned around both first and second coils  712  and  714 . For instance, third coil  716  may encircle both first and second coils  712  and  714 . In certain embodiments, third coil  716  may encircle both first and second loop portions  718  and  720  of first coil  712  and both first and second loop portions  722  and  724  of second coil  714 . A diameter of third coil  916  may be greater than the largest distance between ends of first coil  712  or second coil  714 . 
     In embodiments, first coil  712  and second coil  714  may each be centered along an axis. For example, first coil  712  may be centered along first axis  728 , and second coil  714  may be centered along second axis  730 . First and second axis  728  and  730  may be offset from one another at an angle, such as a 90 degree angle as shown in  FIG. 7A . In some embodiments, first and second axis  728  and  730  may intersect at a center of receiver  710  such that loop portions  718 ,  720 ,  722 , and  724  may be disposed symmetrically around the center of receiver  710 . In embodiments, third coil  716  may be disposed about a third axis  732  positioned through the center of receiver  710  and extending in a direction perpendicular to both first and second axis  728  and  730 . 
     As illustrated in  FIG. 7A , first and second coils  712  and  714  may each have first and second loops that are arranged in an oval-shaped profile. However, embodiments are not limited to such profiles. For instance, first and second loops may have profiles that are non-oval, circular, square, rectangular, or any other loop profile. As an example, first and second coils  712  and  714  may have first and second loop profiles arranged in a bow tie profile, as shown in  FIG. 7B , which illustrates an exemplary receiver  711 . Receiver  711  may have a first coil  734  and a second coil  736 . Similar to  FIG. 7A , a third coil (not shown) may encompass first and second coils  734  and  736 . In some embodiments, the third coil is substantially planar with first and/or second coils  734  and  736 . First coil  734  may include a first loop portion  740  and a second loop portion  742 , and second coil  736  may include a first loop portion  744  and a second loop portion  746 . The first and second loop portions of both coils may have bow tie profiles that taper towards a midpoint between respective first and second loop portions. In such embodiments, the bow tie loop profiles minimize air gaps between first and second coils  734  and  736 , thereby increasing the efficiency at which receiver  711  generates current from magnetic fields. It is to be appreciated that any suitable loop profile for interacting with magnetic fields are envisioned herein. 
     With reference back to  FIG. 7A , in embodiments, receiver  710  may also include a shielding disk  726  positioned on top of first and second coils  712  and  714 . Shielding disk  726  may have a structure that complements the overall structure of first and second coils  712  and  714 . For example, shielding disk  726  may have a circular structure such that its outer edges are adjacent to the outer radial edges of first and second coils  712  and  714 , as shown in  FIG. 7A . In embodiments, shielding disk  726  may be formed of a ferromagnetic material (e.g., ferrite sheet material) used to concentrate magnetic fields and direct them in accordance with the selected geometry based upon the arrangement of the receiver. Shielding disk  726  may be used to guide magnetic fields through first and second coils  712  and  714 ; additionally, shielding disk  726  may have a thin structure to minimize the size of receiver  710 , as will be discussed further herein with respect to  FIG. 7C . 
       FIG. 7C  is a simplified diagram illustrating a cross-sectional view of receiver  710  according to an embodiment of the present disclosure. As shown, first and second coils  712  and  714  may be embedded in a substrate  730  disposed below shielding disk  726 . Substrate  730  may be any suitable substrate capable of housing and electrically isolating embedded coils of wire. As an example, substrate  730  may be a printed circuit board (PCB). First and second coils  712  and  714  are illustrated as a series of circles due to the cross-sectional perspective of the illustration of  FIG. 7C . Accordingly, first loop portion  722  of coil  712  may be represented by circles  712   a  and  712   b , and second loop portion  724  of coil  712  may be represented by circles  712   c  and  712   d . Second coil  714  may be represented by circles  714   a  and  714   b , and third coil  716  may be represented by circles  716   a  and  716   b . First, second, and third coils may be arranged such that a current may be generated in respective coils upon interaction with magnetic fields. 
     In embodiments, at least two of coils  712 ,  714 , and  716  may be positioned in the same plane. As an example, coils  712  and  716  may be positioned in the same plane. In other examples, all three coils  712 ,  714 , and  716  may be positioned in the same plane. Positioning coils  712 ,  714 , and  716  in the same plane enables the structure of receiver  710  to be substantially low profile, meaning the Z-height of receiver  710  may be substantially small. For instance, the overall Z-height of receiver  710  may be less than a millimeter thick. In an embodiment, the overall Z-height of receiver  710  may be approximately 0.5 mm. In such embodiments, the thickness of shielding disk  726  may be less than the overall Z-height of receiver  710 . It is to be appreciated that although the thickness of shielding disk  726  is less than the overall Z-height of receiver  710 , it is not too thin such that it is not capable of concentrating and redirecting magnetic fields. An example of such redirection of magnetic fields is illustrated in  FIG. 7D . When a magnetic field  748  propagates at an angle with respect to the plane of first or second coil  712  or  714 , respectively, shielding disk  726  may redirect magnetic field  748  through its structure. Accordingly, magnetic field  748  may propagate through loops of first and second coils  712  and  714  to induce a current in first and second coils  712  and  714 . In embodiments, the thickness of shielding disk  726  may range between 0.2 to 0.5 mm. In a particular embodiment, the thickness of shielding disk  726  is 0.3 mm. 
     B. Receiver Operation 
     According to some embodiments herein, the arrangement of three coils disposed about a core in three different directions enables power to be generated by a receiver in a magnetic field when the receiver is placed in any orientation.  FIGS. 8 and 9  illustrate the operation of a receiver when placed against a charging surface according to embodiments of the present disclosure. Specifically,  FIG. 8  illustrates receiver operation in the X and Z directions, and  FIG. 9  illustrates receiver operation in the X and Y directions. The receiver in  FIGS. 8 and 9  are illustrated as receiver  600  in  FIG. 6A ; however, it is to be appreciated that any other type of receiver may be used instead. For instance, receiver  710  or receiver  711  in  FIGS. 7A and 7B , respectively, may be used in place of the receiver in  FIGS. 8 and 9 . 
     As shown in  FIG. 8 , receivers  801   a - 801   d  disposed in a dock or an electronic device (neither of which are not shown for ease of explanation) may be placed on a charging surface  811  of a charging structure  813 . Receiver coils  804  and  806  may be disposed about core  808  in the X and Z directions, respectively. Transmitter coils  805   a - 805   c , each having loop portions  807   a  and  807   b , may generate time-varying magnetic fields, such as magnetic fields  809   a - 809   e , that extend above charging surface  811 . Charging structure  813  is illustrated as a table having a substantially planar top surface, but any other charging structure  813  may be used. Additionally, transmitter coils  805   a - 805   c  are illustrated as embedded within the table, but may be disposed underneath charging structure  813  in other embodiments. Each of receivers  801   a - 801   d  is placed in a different location and/or orientation on charging surface  811  to illustrate how the receivers can receive power from magnetic fields  809   a - 809   e.    
     Receiver  801   a  is positioned above a loop portion, e.g.,  807   b , of a transmitter coil, e.g.,  805   a . Magnetic fields generated by loop portion  807   b  may include a substantially vertical component, i.e., along the Z-direction. Accordingly, a current may be induced from these fields in receiver coil  804   a  and may be used to generate power. Because the magnetic field may not be substantially disposed along the X-direction at this location, a current may not be generated in receiver coil  804   a , thus causing receiver coil  804   a  to generate little to no power. 
     Receiver  801   c  is positioned between transmitter coils  805   b  and  805   c . Unlike conventional systems, receiver  804   c  can receive power from magnetic fields disposed between transmitter coils  805   b  and  805   c . As shown, bridging magnetic field  809   d  may be disposed between transmitter coils  805   b  and  805   c  and may include a substantially horizontal component. Accordingly, a current may be induced in receiver coil  804   c  and may be used to generate power. Because the magnetic field  809   d  may not be substantially disposed along the Z-direction at this location, a current may not be generated in receiver coil  806   c , thus causing receiver coil  806   c  to generate little to no power. 
     In addition to being placed flush against charging surface  811  to generate power, receiver  801  can be tilted or even placed on its side and still generate power. For instance, receiver  801   b  is tilted at an angle  810  that is less than 60 degrees (e.g., 45 degrees) to the charging surface  811 . When tilted, currents may be induced by magnetic field  809   c  in both receiver coils  804   b  and  806   b . In some embodiments, portions of magnetic field  809   d  proportionally induce corresponding currents in both receiver coils  804   b  and  806   b . As angle  810  increases to a point where it is completely perpendicular to charging surface  811  (e.g., the position of receiver  801   d ), current may cease to be induced in receiver coil  804   d , but may be more strongly induced in receiver coil  806   d . Thus, magnetic field  809   e  may induce a current in receiver coil  806   d , such that receiver coil  806   d  can be used to generate power from magnetic field  809   e . Even though receiver coil  806   d  is disposed about the Z-direction relative to core  808   d , receiver coil  806   d  is positioned about the X-direction relative to charging surface  811 . Accordingly, receiver coil  806   d  may generate power from magnetic field  809   e.    
     With reference now to  FIG. 9 ,  FIG. 9  illustrates receivers  901   a - 901   c  resting on a charging surface  911  in the X and Y direction. Receivers  901   a - 901   c  may rest on charging surface  911  in different locations and in different orientations. Receiver coils  904   a - 904   c  and  902   a - 902   c  may each be disposed about their respective cores  908   a - 908   c  in the X and Y directions, respectively. Transmitter coils  905   a - 905   h , each having loop portions  907   a  and  907   b , may generate time-varying magnetic fields (including magnetic fields  909   a - 909   c ) that extend above charging surface  911 . All magnetic fields may operate in concert to form charging regions  912   a  and  912   b  which can overlap in some embodiments. In some embodiments, transmitter coils  905   a - 905   h  may be arranged in an N×M array that is capable of generating a substantially rectangular charging region. In other embodiments it may be possible to form circular, oval or other shaped charging regions by arranging coils  905   a - 905   h  in different patterns. 
     Each of receivers  901   a - 901   c  is placed in a different location and/or orientation to illustrate how the receiver can generate power from magnetic fields in charging regions  912   a  and  912   b.    
     Receiver  901   a  is positioned between transmitter coils  905   a  and  905   b . Unlike conventional systems, receiver  901   a  can receive power from magnetic fields disposed between transmitter coils  905   a  and  905   b . As shown, bridging magnetic field  909   a  may be disposed between transmitter coils  905   a  and  905   b  and may include a substantially horizontal component. Accordingly, a current may be induced in receiver coil  904   a  and may be used to generate power. Because magnetic field  909   a  may not be substantially disposed along the Y-direction at this location, a current may not be generated in receiver coil  902   a , thus causing receiver coil  902   a  to generate little to no power. 
     In some embodiments, receivers can also be rotated at an angle less than or equal to 60 degrees and still generate power. Receiver  901   b  is rotated at an angle that is less than 60 degrees (e.g., 45 degrees) to the X-direction. When rotated, currents may be induced by magnetic field  909   b  in both receiver coils  902   b  and  904   b . In some embodiments, a portion of magnetic field  909   b  induces corresponding currents in both receiver coils  902   b  and  904   b . As the angle increases to a point where it is completely perpendicular to the X-direction (e.g., the position of receiver  901   c ), current may cease to be induced in receiver coil  904   c , but may be more strongly induced in receiver coil  902   c . Thus, magnetic field  909   c  may induce a current in receiver coil  902   c , such that receiver coil  902   c  can be used to generate power from magnetic field  909   c . Even though receiver coil  902   c  is disposed about the Y-direction relative to core  908   c , receiver coil  902   c  is positioned about the X-direction relative to charging surface  911 . Accordingly, receiver coil  902   c  may generate power from magnetic field  909   c.    
     Although embodiments illustrate receivers  901   a - 901   c  located between transmitter coils  905   a - 905   h , any of receivers  901   a - 901   c  may be placed in regions above transmitter coils  905   a - 905   h  to generate power as well. For instance, receiver  901   c  may be placed on transmitter  905   c  such that receiver  901   c  may generate power from magnetic field  909   d.    
     Accordingly, as shown in  FIGS. 8 and 9 , receivers discussed herein may generate power in any orientation on a charging surface, according to embodiments of the present disclosure. This allows a docking station or electronic device, embedded with such a receiver, to not have to be placed above a transmitter coil in any particular orientation in some embodiments. 
     It should also be noted that in some embodiments, only certain transmitter coils  905   a - 905   h  that are close enough to a receiver, e.g., any of receivers  901   a - 901   c , can be selectively energized to generate a magnetic field that induces a current in at least one of the coils of the receiver. A location of the receiver with respect to transmitter coils  905   a - 905   h  can be determined in any number of ways. In some embodiments, charging surface  911  can include a sensor configured to identify a location and orientation of an electronic device within which the receiver is housed. For example, a capacitive sensor can be configured to detect contact between a housing of the electronic device and the capacitive sensor. In some embodiments, a power expenditure can be measured when all of transmitter coils  905   a - 905   h  are energized and then only those transmitter coils  905   a - 905   h  with the largest variations caused by interaction with a receiving coil of an electronic device can remain energized. 
     One such example is shown in  FIG. 10 . Specifically,  FIG. 10  illustrates an exemplary charging surface  1000  configured to enable selective energizing of transmitter coils  1005   a - 1005   h . Charging surface  1000  can be part of a wireless charging table, such as charging structure  500  shown in  FIG. 5  or table  800  shown in  FIGS. 8 and 9  or can be part of a wireless charging mat or other wireless charging structure. As shown in  FIG. 10 , charging surface  1000  may include transmitter coils  1005   a - 1005   h  and a plurality of sensors  1022   a - 1022   h . Charging surface  1000  may also include a power distribution system  1007  configured to receive power from an alternating current (AC) power source  1021  (e.g., from a wall outlet) and distribute the AC power to one or more transmitter coils  1005   a - 1005   h . In embodiments, the power distribution system includes a controller  1020  coupled to transmitter coils  1005   a - 1005   h  and sensors  1022   a - 1022   h . Controller  1020  may be configured to receive information from sensors  1022   a - 1022   h  and/or transmitter coils  1005   a - 1005   h  and control the operation of transmitter coils  1005   a - 1005   h  in response to the received information. Sensors  1022   a - 1022   h  can be any type of sensor that enables the charging surface to detect the presence and location of one or more electronic devices, such as electronic devices  1004  and  1006  on the charging surface. As one example, sensors  1022   a - 1022   h  can be capacitive sensors. 
     As shown in  FIG. 10 , individual electronic devices to be charged can be placed at various locations on charging surface  1000 . Sometimes a device may be placed directly over or very near an individual coil—illustrated in  FIG. 10  as device  1004  placed directly over coil  1005   c . At other times a device may be placed in between two or more coils—illustrated in  FIG. 10  as device  1006  placed between coils  1005   g  and  1005   h . In the first situation, the presence of electronic device  1004  can be detected by sensor  1022   c  and cause sensor  1022   c  to send information to controller  1020 . Controller  1020  can then use this information and determine that transmitter  1005   c  should be turned on to provide power to device  1004 , as transmitter  1005   c  is closest to electronic device  1004 . In the second situation, the presence of electronic device  1006  can be detected by both sensors  1022   g  and  1022   h , each of which can send information to controller  1020 , which may then use the information to determine that transmitter  1005   g  and  1005   h  should be turned on to provide power to device  1006 . 
     Once presence of the electronic device is detected, one or more verification procedures may be performed to ensure that the electronic device is a device that is suitable for receiving power from the transmitter coils. For instance, after detecting the presence of the electronic device, a communication channel may be established between controller  1020  and one or more electronic device, e.g., electronic devices  1004  and  1006 . The electronic device may then be queried for its identification to verify that the device is suitable for receiving power from the transmitter coils. After receiving and verifying the identification of the electronic device, magnetic fields may be generated by transmitter coils close enough to the electronic device. If no communication channel can be established with the electronic device, then it may be determined that the electronic device is in fact not an electronic device, or not an electronic device that is suitable for receiving power from the transmitter coils. In which case, no transmitter coils may be activated to generate magnetic fields to the electronic device. Performing verification procedures ensures that magnetic fields are not generated for objects that are not electronic devices that can receive the generated magnetic fields, and ensures that if the object is an electronic device, it is an electronic device that is configured to receive the generated magnetic fields. In this way, no additional energy need to be expended energizing transmitter coils that are not being utilized. 
     IV. Stacked Transmitter and Receiver Coils 
     In certain embodiments, transmitter coils may be stacked upon one another to provide a continuous charging region with minimal dead zones.  FIG. 11  is a simplified diagram illustrating a top-down view of a stacked transmitter  1102  according to embodiments of the present disclosure. The structure, current flow, and generation of magnetic fields may be similar to transmitter coil  200  discussed herein with respect to  FIG. 2A . Stacked transmitter  1102  may include a first transmitter coil  1104  and a second transmitter coil  1106  positioned over at least a portion of first transmitter coil  1104 . First and second transmitter coils  1104  may each be a transmitter coil having any suitable transmitter profile discussed herein, such as a bow tie profile, bent L-shaped profile, or a rectangular profile as shown in  FIG. 11 . 
     First and second transmitter coils  1104  and  1106  may be horizontally offset from one another by a distance D, which may be selected to be a distance that enables stacked transmitter  1102  to generate overlapping magnetic fields to form a charging region, e.g., charging regions  912   a  and  912   b  in  FIG. 9 , with minimal dead zones. In an embodiment, distance D is a fraction of an entire width of a transmitter coil. For instance, distance D is a quarter of a width W of first transmitter coil  1104 . Although  FIG. 11  shows first and second transmitter coils  1104  and  1106  offset from one another in a horizontal direction, embodiments are not so limited. First and second transmitter coils  1104  and  1106  may be offset from one another in a horizontal direction, vertical direction, or both horizontal and vertical directions, as long as at least a portion of second transmitter coil  1106  overlaps a portion of first transmitter coil  1104 . 
       FIG. 12  is a simplified diagram illustrating a cross-sectional view of an exemplary stacked transmitter  1202  and the interaction of its generated magnetic fields with a receiver  1208  placed in various positions. As shown, receiver  1208  is placed in three positions: first receiver position  1210 , second receiver position  1212 , and third receiver position  1214 . It is to be appreciated that although  FIG. 12  illustrates the three receiver positions stacked upon one another, it is not intended to disclose that receiver  1208  includes three individual receiver stacked upon one another. Rather, it is intended to disclose that receiver  1208  is a single receiver that can be placed in three receiver positions that are offset from one another in the horizontal direction, i.e., translationally offset from one another, within the same horizontal plane. 
     In embodiments, stacked transmitter  1202  may include a ferrite shield  1203  and two transmitter coils: a first transmitter coil  1204  and a second transmitter coil  1206 . Second transmitter coil  1206  may overlap at least a portion of first transmitter coil  1204 . Each coil may be embedded within a flexible substrate  1205 , such as a printed circuit board. In embodiments, first transmitter coil  1204  may be operated at a frequency that is orthogonal to the frequency at which second transmitter coil  1206  operates such that magnetic fields generated by first transmitter coil  1204  propagate in an opposite direction to magnetic fields generated by second transmitter coil  1206 . In the example shown in  FIG. 12 , first transmitter coil  1204  may operate in the 0° and 180° phases while second transmitter coil  1206  may operate in the 90° and 270° phases. In some embodiments, stacked transmitter  1202  may be carrying significant current during operation. Thus, dimensions of ferrite shield  1203  may affect ferrite losses incurred by stacked transmitter  1202 . In particular embodiments, increasing a thickness of ferrite shield  1203  and/or increasing separation between ferrite shield  1203  and first transmitter  1204  may minimize ferrite losses. In certain embodiments, the thickness of ferrite shield  1203  may range between 3-5 mm, and the separation may range between 15 to 25 mm. In an embodiment, the thickness of ferrite shield  1203  is approximately 4 mm, and the separation is approximately 20 mm. 
     When receiver  1208  is placed in any one of receiver positions  1210 ,  1212 , and  1214 , a corresponding current may be generated in one or more coils of the receiver when interacting with the magnetic fields generated by stacked transmitter  1202 . The phase of the generated current in receiver  1208  may depend on the position of receiver  1208  relative to stacked coils  1204  and  1206  in stacked transmitter  1202 . As an example, when receiver  1208  is placed in first receiver position  1210 , receiver  1208  may be vertically aligned with first transmitter coil  1204  such that the phases of the generated current in receiver  1208  are 0° and 180°. When receiver  1208  is placed in second receiver position  1212 , receiver  1208  may be vertically aligned with second transmitter coil  1206  such that the phases of the generated current in receiver  1208  are 90° and 270°. Additionally, when receiver  1208  is placed in third receiver position  1214 , receiver  1208  may be vertically positioned between first and second transmitter coils  1204  and  1206  such that the phases of the generated current in receiver  1208  are 45° and 225°. 
     In addition to stacking transistor coils as discussed herein with respect to  FIG. 11 , a receiver may also include stacked receiver coils, as shown in  FIG. 13 .  FIG. 13  is a simplified diagram of a stacked receiver  1300  having a first receiver coil  1302  and a second receiver coil  1304  overlapping first receiver coil  1302 . Similar to receiver  710 , each receiver coil  1302  and  1304  may include first and second loop portions for receiving magnetic fields. In embodiments, first and second receiver coils  1302  and  1304  may be centered with one another and oriented at an offset angle. The degree of offset angle may be selected to maximize current generation when stacked receiver  1300  is positioned in magnetic fields generated by a transmitter, such as stacked transmitter  1102  in  FIG. 11 . As an example, the degree of offset angle may be 90° such that a center line  1303  of first coil  1302  is perpendicular to a center line  1305  of second coil  1304 . It is to be noted that any other degree of offset angle is envisioned herein to maximize generation of current in transmitter coils  1302  and  1024  when positioned in a magnetic field. 
       FIG. 14  is a simplified diagram illustrating a charging system  1400  including stacked receivers  1402  and  1404  positioned over a plurality of stacked transmitter coils  1405 . Stacked receivers  1402  and  1404  may each include two overlapping receiver coils that are positioned at a 90° offset angle from one another. For instance, stacked receiver  1402  may include a first receiver coil  1406  and a second receiver coil  1408 , and stacked receiver  1404  may include a first receiver coil  1410  and a second receiver coil  1412 . Stacked receivers having this coil arrangement are capable of receiving power from stacked transmitter coils  1405  in different rotational orientations. Depending on the angle of rotation, one or both receiver coils of the stacked receiver may be receiving power. For instance, if a stacked receiver is positioned at an angle that is a multiple of 90° with respect to stacked transmitter coils  1405 , one of its receiver coils will receiver power. If the stacked receiver is positioned in any other angle that is not a multiple of 90°, then both of its receiver coils may receiver power. 
     As shown in  FIG. 14 , stacked receiver  1402  is positioned parallel to stacked transmitter coils  1405 , which is an angle that is a multiple of 90°. Thus, one receiver coil, e.g., receiver coil  1406  of stacked receiver  1402 , will receive power from stacked transmitter coils  1405 . Stacked receiver  1404 , is positioned at an angle that is not a multiple of 90° with respect to stacked transmitter coils  1405 . As shown in  FIG. 14 , stacked receiver  1404  is positioned at an angle of 45° with respect to stacked transmitter coils  1405 . Thus, both first and second receiver coils  1410  and  1412  may receiver power from stacked transmitter coils  1405 . 
     V. Method of Forming Receiver 
       FIG. 15  illustrates a flow chart for fabricating a wireless charging receiver according to some embodiments of the present disclosure. At block  1502 , a core, such as core  608  in  FIG. 6A , may be provided. In some embodiments, the core may be a ferromagnetic core that can concentrate magnetic fields. The core may be in the shape of a rectangular prism, or any other shape suitable for maximizing concentration of magnetic fields and compatible with desired coil geometries. 
     At block  1504 , a first insulating layer may be formed around the core. In some embodiments, the insulating layer may be a dielectric film having a dielectric constant suitable to electrically isolate conductive materials from one another. The insulating layer may be formed by a lamination process that presses a layer of insulating film around the core and subsequently cures the insulating film. In other embodiments, the insulating layer may be formed by fusing a first set of two halves together. The two halves may each be a shell formed of an insulating material shaped to cover half of an underlying structure, such as the core. When the two halves are fused together, an insulating layer may be formed around the entire core. 
     At block  1506 , a first coil may be formed on the first insulating layer. The first coil may be any of the three coils  602 ,  604 , and  606  described herein with respect to  FIG. 6A . In some embodiments, the first coil may be formed by any suitable patterning process. For instance, the first coil may be formed by a Laser Direct Structuring (LDS) process. In other embodiments, the first coil may be formed by depositing and etching a patterned seed layer and subsequently performing an electroplating process to build up the structure of the first coil. One skilled in the art will understand that any process capable of patterning a coil on an insulating layer may be utilized in embodiments herein. 
     At block  1508 , a second insulating layer may then be formed on the first coil and exposed surfaces of the first insulating layer. As described herein, the second insulating layer may be laminated or may be formed by fusing a second set of two halves of insulating shells. Thereafter, at block  1510 , a second coil may be formed on the second insulating layer. The second coil may be any of the three coils  602 ,  604 , and  606  described herein with respect to  FIG. 6A . The second coil may be formed by any suitable deposition or patterning process such as those described herein with respect to forming the first coil. 
     Once the second coil is formed, at block  1512 , a third insulating layer may be formed on the second coil and exposed surfaces of the second insulating layer. Similar to first and second insulating layers, the third insulating layer may be laminated or formed by fusing a third set of two halves of insulating shells. Then, at block  1514 , a third coil may be formed on the third insulating layer. The third coil may be any of the three coils  602 ,  604 , and  606  discussed herein with respect to  FIG. 6A , and may be formed by any suitable deposition or patterning process described herein with respect to forming the first and second coils. 
     Optionally, a fourth insulating layer may be formed over the third coil and exposed surfaces of the third insulating layer to electrically insulate the third coil and/or protect the third coil from damage during subsequent fabrication steps. The fourth insulating layer may prevent inadvertent shorting between the third coil and other conductive structures. That way, the receiver may be properly protected and insulated from the external environment. 
     VI. Method of Charging a Device 
       FIG. 16  illustrates a flow chart  1600  for charging an electronic device according to embodiments of the present disclosure. At block  1602 , a charging surface including transmitter having a plurality of transmitter coils may be provided. The plurality of transmitter coils may be disposed below the charging surface and may be configured to generate a plurality of magnetic fields in more than one direction when a current is supplied. The generated magnetic fields may penetrate through the charging surface such that the magnetic fields exist above the charging surface and are accessible to the electronic device when placed on the charging surface. In some embodiments, a single AC (or pulsed DC) power source and clock may be used to drive the plurality of transmitter coils. 
     At block  1604 , the electronic device may be placed on the charging surface. The electronic device may contain a receiver having a core and a plurality of receiver coils disposed about the core in different directions. The receiver may be configured to receive power from any orientation when placed in a magnetic field. 
     Once placed on the charging surface, at block  1606 , the electronic device may be left on the charging surface such that at least one of the plurality of magnetic fields induces a current in at least one of the plurality of receiver coils. For instance, a magnetic field may induce a current in two coils: one coil being disposed about a Y-direction, and another coil being disposed about an X-direction. The current may be rectified in the electronic device and then used to charge an internal battery. 
     After a desired amount of charge has been stored on the battery, then at block  1606 , the electronic device may be removed from the charging surface. In some embodiments, the electronic device can be coupled to a docking station that includes the receiver, and that performs some or all of the functions performed by the electronic device described herein with respect to flow chart  1600 . 
     Although the disclosure has been described with respect to specific embodiments, it will be appreciated that the disclosure is intended to cover all modifications and equivalents within the scope of the following claims.

Metadata:
Filing Date: 20190322
Publication Date: 20200721
Grant Date: 20200721
Priority Date: 20150616
Inventors: RITTER, DAVID W.
KOSECOFF, DAVID B.
KUMKA, David S.
SAMPATH, Madhusudanan Keezhveedi
MICHALSKE, STEVEN CHARLES
ASHCROFT, Tavys Q.
RAO, Aditya
SMITH, Ariadne
Assignee: APPLE INC
CPC Classifications: [{"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/28", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/402", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/00304", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/00302", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/402", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/402", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J7/0044", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/00302", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/025", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F41/122", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/2804", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/28", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F41/046", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/00304", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/40", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/025", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F27/28", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/0044", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 56297114