PATENT DOCUMENT

Publication Number: US-11159054-B2
Application Number: US-201916513583-A
Country: US
Kind Code: B2

Title: Wireless power transmitting devices

Abstract:
A power system has a wireless power transmitting device and a wireless power receiving device. Coils in the transmitting device may include a circular coil overlapped by first and second rectangular coils at a charging surface. The rectangular coils each include straight segments extending over a central region of the circular coil. Control circuitry can activate the circular coil to transmit wireless power to a first type of wireless power receiving coil using vertical components of the magnetic field generated by the circular coil. The control circuitry can activate the rectangular coils to transmit wireless power to a second type of wireless power receiving coil using horizontal components of the magnetic field generated by the rectangular coils. The circular and rectangular coils wirelessly charge the power receiving device while located at the same position on the charging surface, regardless of the type of wireless power receiving coil that is used.

Claims:
What is claimed is: 
     
       1. A wireless power transmitting device comprising:
 a first wireless power transmitting coil that includes conductive loops surrounding a central region; 
 a second wireless power transmitting coil that is smaller than the first wireless power transmitting coil and that includes a first straight segment that overlaps the central region; 
 a third wireless power transmitting coil that is smaller than the first wireless power transmitting coil and that includes a second straight segment that overlaps the central region and extends parallel to the first straight segment; and 
 control circuitry configured to transmit wireless power through a charging surface to a first type of electronic device using the first wireless power transmitting coil and to a second type of electronic device different than the first type of electronic device using the second and third wireless power transmitting coils. 
 
     
     
       2. The wireless power transmitting device defined in  claim 1 , wherein the conductive loops in the first wireless power transmitting coil comprise circular conductive loops. 
     
     
       3. The wireless power transmitting device defined in  claim 2 , wherein the second wireless power transmitting coil comprises first rectangular conductive loops and the third wireless power transmitting coil comprises second rectangular conductive loops. 
     
     
       4. The wireless power transmitting device defined in  claim 3 , wherein the circular conductive loops wind around the central region from an inner diameter to an outer diameter, the first and second rectangular conductive loops each having a length and a width that is less than the outer diameter. 
     
     
       5. The wireless power transmitting device defined in  claim 4 , wherein the length is less than the width, the first straight segment extends across the length of the first rectangular conductive loops, and the second straight segment extends across the length of the second rectangular conductive loops. 
     
     
       6. The wireless power transmitting device defined in  claim 5 , wherein the inner diameter is between 10 mm and 30 mm and the outer diameter is between 30 mm and 70 mm. 
     
     
       7. The wireless power transmitting device defined in  claim 1 , wherein the first wireless power transmitting coil comprises a first number of conductive loops and the second and third wireless power transmitting coils each comprise a second number of conductive loops that is less than the first number of conductive loops. 
     
     
       8. The wireless power transmitting device defined in  claim 1 , wherein the second wireless power transmitting coil overlaps a portion of the third wireless power transmitting coil. 
     
     
       9. The wireless power transmitting device defined in  claim 8 , wherein the second wireless power transmitting coil comprises a third straight segment extending parallel to the first and second straight segments and the third wireless power transmitting coil comprises a fourth straight segment extending parallel to the third straight segment, wherein the second straight segment is laterally interposed between the third and first straight segments, and wherein the first straight segment is laterally interposed between the second and fourth straight segments. 
     
     
       10. The wireless power transmitting device defined in  claim 1 , wherein the second wireless power transmitting coil comprises a third straight segment extending parallel to the first and second straight segments and the third wireless power transmitting coil comprises a fourth straight segment extending parallel to the third straight segment, wherein the second straight segment is laterally interposed between the fourth and first straight segments, and wherein the first straight segment is laterally interposed between the second and third straight segments. 
     
     
       11. The wireless power transmitting device defined in  claim 1 , further comprising:
 a first inverter coupled to the second wireless power transmitting coil; and 
 a second inverter coupled to the third wireless power transmitting coil, wherein the control circuitry is configured to transmit the wireless power by controlling the first inverter to drive a first current on the second wireless power transmitting coil and by controlling the second inverter to concurrently drive a second current on the third wireless power transmitting coil that is out of phase with respect to the first current on the second wireless power transmitting coil. 
 
     
     
       12. The wireless power transmitting device defined in  claim 1  further comprising a layer, wherein the first wireless power transmitting coil is interposed between the layer and the second and third wireless power transmitting coils, and the layer comprises a material selected from the group consisting of: ferrite and a nano-crystalline material. 
     
     
       13. The wireless power transmitting device defined in  claim 1 , further comprising:
 a fourth wireless power transmitting coil that includes additional conductive loops surrounding an additional central region; 
 a fifth wireless power transmitting coil that is smaller than the first and fourth wireless power transmitting coils and that includes a third straight segment that overlaps the additional central region and that extends parallel to the first and second straight segments; and 
 a sixth wireless power transmitting coil that is smaller than the first and fourth wireless power transmitting coils and that includes a fourth straight segment that overlaps the additional central region and extends parallel to the third straight segment, wherein the control circuitry is control circuitry configured to transmit the wireless power through the charging surface using the fourth, fifth, and sixth wireless power transmitting coils. 
 
     
     
       14. The wireless power transmitting device defined in  claim 1 , wherein the first type of electronic device comprises a cellular telephone and wherein the second type of electronic device comprises a wristwatch with a wrist strap. 
     
     
       15. The wireless power transmitting device defined in  claim 1 , wherein the first type of electronic device comprises a cellular telephone having a vertical coil and wherein the second type of electronic device comprises a wristwatch having a horizontal coil. 
     
     
       16. A wireless charging mat comprising:
 a charging surface; 
 at least one unit cell of wireless power transmitting coils, wherein each unit cell in the at least one unit cell comprises:
 a circular coil that extends across a first lateral area of the charging surface and that is optimized to transmit wireless power to a first type of electronic device, 
 a first rectangular coil that at least partially overlaps the circular coil, wherein the first rectangular coil comprises a first straight segment and a second straight segment extending parallel to the first straight segment, and 
 a second rectangular coil that at least partially overlaps the circular coil, wherein the second rectangular coil comprises a third straight segment that extends parallel to the second straight segment and a fourth straight segment that extends parallel to the third straight segment, wherein the first and second rectangular coils each extend across a second lateral area of the charging surface that is smaller than the first lateral area, and wherein the first and second rectangular coils are optimized to transmit wireless power to a second type of electronic device different than the first type of electronic device; and 
 
 control circuitry configured to transmit wireless power through the charging surface using the at least one unit cell. 
 
     
     
       17. The wireless charging mat defined in  claim 16 , wherein the circular coil comprises loops of conductor that surround a central region devoid of conductive material and the second and third straight segments each overlap the central region. 
     
     
       18. The wireless charging mat defined in  claim 17 , wherein the first rectangular coil comprises fifth and sixth straight segments extending between the first and second straight segments, the second rectangular coil comprises seventh and eighth straight segments extending between the third and fourth straight segments, the first, second, third, and fourth straights segments each have a first length, and the fifth, sixth, seventh, and eighth straight segments each have a second length that is less than the first length. 
     
     
       19. The wireless charging mat defined in  claim 17 , wherein the at least one unit cell comprises first, second, and third unit cells arranged in a row along a longitudinal axis of the wireless charging mat, and wherein the first, second, third, and fourth straight segments each extend perpendicular to the longitudinal axis of the wireless charging mat. 
     
     
       20. The wireless charging mat defined in  claim 16 , wherein the control circuitry is configured to:
 identify an orientation of a wireless power receiving coil in the first or second type of electronic device; 
 activate at least one of the first and second rectangular coils in at least one of the unit cells in response to identifying that the wireless power receiving coil is in a first orientation; and 
 activate the circular coil in at least one of the unit cells in response to identifying that the wireless power receiving coil is in a second orientation that is different from the first orientation. 
 
     
     
       21. The wireless charging mat defined in  claim 20 , further comprising measurement circuitry, wherein the control circuitry is further configured to identify the orientation of the wireless power receiving coil based on data, and wherein the data comprises data selected from the group consisting of: wireless data from an in-band signal received by at least one of the unit cells from the wireless power receiving coil, and voltage data measured from at least one of the unit cells using the measurement circuitry. 
     
     
       22. A wireless power transmitting device configured to transmit wireless power to a wireless power receiving coil in a wireless power receiving device on a charging surface of the wireless power transmitting device, the wireless power transmitting device comprising:
 a first circular coil; 
 a second circular coil; 
 a first pair of rectangular coils overlapping the first circular coil; 
 a second pair of rectangular coils overlapping the second circular coil; and 
 control circuitry, wherein the control circuitry is configured to:
 identify a location of the wireless power receiving coil on the charging surface; 
 transmit the wireless power through the charging surface using a selected one of the first circular coil and the first pair of rectangular coils in response to identifying that the wireless power receiving coil overlaps the first circular coil, 
 
 transmit the wireless power through the charging surface using a selected one of the second circular coil and the second pair of rectangular coils in response to identifying that the wireless power receiving coil overlaps the second circular coil, and 
 transmit the wireless power through the charging surface using one rectangular coil from each of the first and second pairs of rectangular coils in response to identifying that the wireless power receiving coil overlaps a location on the charging surface between the first and second circular coils.

Description:
This application claims the benefit of provisional patent application No. 62/702,709, filed Jul. 24, 2018, which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD 
     This relates generally to power systems, and, more particularly, to wireless power systems. 
     BACKGROUND 
     Portable electronic devices such as cellular telephones, wristwatch devices, tablet computers, wireless earbuds, and other portable devices use batteries. The batteries in these devices can be charged using a battery charging system. To enhance convenience for users, wireless power systems have been provided that allow batteries in portable electronic devices to be charged wirelessly. 
     SUMMARY 
     A power system has a wireless power transmitting device and a wireless power receiving device. Coils in the power transmitting and receiving devices are used to transmit and receive wireless power signals. Good coupling between transmitting and receiving coils promotes wireless power transfer efficiency. 
     Embodiments of power transmission coils in the power transmitting devices may include a circular coil that is overlapped by first and second rectangular coils at a charging surface. The rectangular coils each include straight vertical segments that extend over a central region of the circular coil that is devoid of conductive material. The rectangular coils each extend across a smaller lateral area of the charging surface than the circular coil. 
     Control circuitry can selectively activate the circular coil to transmit wireless power to a first type of wireless power receiving coil using vertical components of the magnetic field generated by the circular coil. The control circuitry can selectively activate one or both of the rectangular coils to transmit wireless power to a second type of wireless power receiving coil using horizontal components of the magnetic field generated by the rectangular coils. The circular coil and the rectangular coils wirelessly charge the power receiving device while located at the same position on the charging surface regardless of the type of wireless power receiving coil used on the power receiving device. 
     In some embodiments, the first and second rectangular coils may overlap each other on the charging surface. The first and second rectangular coils and the circular coil can form a unit cell of wireless power transmitting coils that is repeated across the charging surface. 
     In some embodiments, two, three, or more than three unit cells of wireless power transmitting coils are distributed across the charging surface. The unit cells can be distributed within a single row extending along a longitudinal axis of the wireless power transmitting device. The straight vertical segments of the rectangular coils are longer than the horizontal segments of the rectangular coils and extend perpendicular to the longitudinal axis of the wireless power transmitting device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an illustrative wireless power system in accordance with an embodiment. 
         FIG. 2  is a schematic diagram of illustrative wireless power transmitting circuitry in accordance with an embodiment. 
         FIG. 3  is a perspective view of an illustrative wireless power receiving device with coils for receiving wireless power in accordance with an embodiment. 
         FIG. 4  is a top view of an illustrative wireless power transmitting device having multiple coils for charging different types of wireless power receiving coils in accordance with an embodiment. 
         FIG. 5  is a plot in which wireless charging performance (coupling constant) has been plotted as a function of distance across a wireless power transmitting device of the type shown in  FIG. 4  in accordance with an embodiment. 
         FIG. 6  is a top view of an illustrative wireless power transmitting device having multiple overlapping coils for charging the same type of wireless power receiving coils in accordance with an embodiment. 
         FIG. 7  is a plot in which wireless charging performance (coupling constant) has been plotted as a function of distance across a wireless power transmitting device of the type shown in  FIG. 6  in accordance with an embodiment. 
         FIG. 8  is a top view of an illustrative wireless power transmitting device having multiple unit cells of overlapping coils for charging multiple wireless power receiving devices in accordance with an embodiment. 
         FIG. 9  is a plot in which wireless charging performance (coupling constant) has been plotted as a function of rotational angle for a wireless power receiving device with respect to a wireless power transmitting device of the types shown in  FIGS. 4, 6, and 8  in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Portable electronic devices have batteries. Wired and wireless charging systems may be used in charging the batteries. For example, a user may place devices such as wristwatch devices and cellular telephones on a wireless charging mat to wirelessly charge these devices. 
     An illustrative wireless power system is shown in  FIG. 1 . Wireless power system  8  (sometimes referred to as a wireless charging system) has wireless power transmitting equipment that is used for supplying wireless power. The wireless power is used for charging batteries in electronic devices and in supplying power to other device components. 
     As shown in  FIG. 1 , wireless power system  8  includes electronic devices  10 . Electronic devices  10  include electronic devices that provide power (e.g., charging mats, charging pucks, charging stands, tablet computers, and other portable electronic devices with wireless power transmitting capabilities, etc.). Electronic devices  10  also include electronic devices that receive power. These power receiving devices may include, for example, portable electronic devices such as cellular telephones, wireless earbuds, and wristwatch devices (as examples). 
     Power can be used for powering circuitry in a power receiving device other than a battery and can be used for charging a battery in a power receiving device. Because battery charging is a common use of received power, wireless power transfer operations in system  8  are sometimes referred to as battery charging operations. Power can also be provided to a receiving device to operate a display or other circuitry in the receiving device without battery charging, if desired. 
     Charging can be performed by transferring power from a power transmitting device such as device  12  to a power receiving device such as device  24 . Power may be transferred between device  12  and device  24  wirelessly (e.g., using inductive charging). In the example of  FIG. 1 , power is being transferred wirelessly using wireless power signals  44 . 
     During operation of system  8 , wireless power transmitting device  12  wirelessly transmits power to one or more wireless power receiving devices such as device  24 . The wireless power receiving devices may include electronic devices such as wristwatches, cellular telephones, tablet computers, laptop computers, ear buds, battery cases for ear buds and other devices, tablet computer pencils (e.g., styluses) and other input-output devices (e.g., accessory devices), wearable devices, or other electronic equipment. The wireless power transmitting device may be an electronic device such as a wireless charging mat that has a charging surface (e.g., a planar charging surface) that receives portable devices to be charged, a tablet computer or other portable electronic device with wireless power transmitting circuitry (e.g., one of devices  24  that has wireless power transmitting circuitry), or other wireless power transmitting device. The wireless power receiving devices use power from the wireless power transmitting device for powering internal components and for charging internal batteries. 
     As shown in  FIG. 1 , wireless power transmitting device  12  includes control circuitry  16 . Wireless power receiving device  24  includes control circuitry  30 . Control circuitry in system  8  such as control circuitry  16  and control circuitry  30  (and/or control circuitry in other devices  10 ) is used in controlling the operation of system  8 . This control circuitry may include processing circuitry associated with microprocessors, power management units, baseband processors, digital signal processors, microcontrollers, and/or application-specific integrated circuits with processing circuits. The processing circuitry implements desired control and communications features in devices  12  and  24 . For example, the processing circuitry may be used in selecting coils, adjusting the phases and magnitudes of coil drive signals, determining power transmission levels, processing sensor data and other data, processing user input, handling negotiations between devices  12  and  24 , sending and receiving in-band and out-of-band data, making measurements, starting and stopping charging operations, turning devices  10  on and off, placing devices  10  in low-power sleep modes, and otherwise controlling the operation of system  8 . 
     Control circuitry in system  8  may be configured to perform operations in system  8  using hardware (e.g., dedicated hardware or circuitry), firmware and/or software. Software code for performing operations in system  8  is stored on non-transitory computer readable storage media (e.g., tangible computer readable storage media) in control circuitry  8 . The software code may sometimes be referred to as software, data, program instructions, instructions, or code. The non-transitory computer readable storage media may include non-volatile memory such as non-volatile random-access memory (NVRAM), one or more hard drives (e.g., magnetic drives or solid state drives), one or more removable flash drives or other removable media, or the like. Software stored on the non-transitory computer readable storage media may be executed on the processing circuitry of devices  10  (e.g., control circuitry  16  and/or  30 ). The processing circuitry may include application-specific integrated circuits with processing circuitry, one or more microprocessors, a central processing unit (CPU) or other processing circuitry. 
     Power transmitting device  12  may be a stand-alone power adapter (e.g., a wireless charging mat that includes power adapter circuitry), may be a wireless charging mat that is coupled to a power adapter or other equipment by a cable, may be a portable electronic device (cellular telephone, tablet computer, laptop computer, etc.), may be equipment that has been incorporated into furniture, a vehicle, or other system, or may be other wireless power transfer equipment. Illustrative configurations in which wireless power transmitting device  12  is a wireless charging mat or portable electronic device are sometimes described herein as an example. 
     Power receiving device  24  may be a portable electronic device such as a wristwatch, a cellular telephone, a laptop computer, a tablet computer, an accessory such as an earbud, a tablet computer input device such as a wireless tablet computer pencil, a battery case, or other electronic equipment. Power transmitting device  12  may be coupled to a wall outlet (e.g., an alternating current power source), may have a battery for supplying power, and/or may have another source of power. Power transmitting device  12  may have an alternating-current (AC) to direct-current (DC) power converter such as AC-DC power converter  14  for converting AC power from a wall outlet or other power source into DC power. In some configurations, AC-DC power converter  14  may be provided in an enclosure (e.g., a power brick enclosure) that is separate from the enclosure of device  12  (e.g., a wireless charging mat enclosure or portable electronic device enclosure) and a cable may be used to couple DC power from the power converter to device  12 . DC power may be used to power control circuitry  16 . 
     During operation, a controller in control circuitry  16  may use power transmitting circuitry  52  to transmit wireless power to power receiving circuitry  54  of device  24 . Power transmitting circuitry  52  may have switching circuitry (e.g., inverter circuitry  60  formed from transistors) that is turned on and off based on control signals provided by control circuitry  16  to create AC current signals through one or more transmit coils  42 . Coils  42  may be arranged in a planar coil array (e.g., in configurations in which device  12  is a wireless charging mat) or may be arranged in other configurations. In some arrangements, device  12  may have only a single coil. In arrangements in which device  12  has multiple coils, the coils may be arranged in one or more layers. Coils in different layers may or may not overlap with each other. 
     In some configurations, coils  42  are formed from coils that help direct magnetic fields vertically (e.g., parallel to the surface normal of a charging mat). In other configurations, coils  42  may include coils that help direct magnetic fields horizontally (e.g., parallel to the surface of a charging mat). These coils may, for example, generate magnetic fields having substantial horizontal components running parallel to the surface of device  12 . If desired, coils  42  may include multiple different types of coils such as both coils that help direct magnetic fields vertically and coils that help direct magnetic fields horizontally. These different types of coils may be formed in different layers and may overlap each other if desired. 
     Coils  48  in device  24  can also be formed from solenoids. The solenoids in a charging mat may be formed in an array that lies under the charging surface of the charging mat and that extends across the charging surface of the charging mat. In some configurations, coils  42  and/or  48  may be implemented using pot cores formed of magnetic material with circular grooves or grooves of other shapes. 
     As the AC currents pass through one or more coils  42 , a time varying electromagnetic (e.g., magnetic) field (signals  44 ) is produced that is received by one or more corresponding receiver coils such as coil  48  in power receiving device  24 . When the time varying electromagnetic field is received by coil  48 , corresponding alternating-current currents are induced in coil  48 . Rectifier circuitry such as rectifier  50 , which contains rectifying components such as synchronous rectification metal-oxide-semiconductor transistors arranged in a bridge network, converts received AC signals (received alternating-current signals associated with electromagnetic signals  44 ) from coil  48  into DC voltage signals for powering device  24 . 
     The DC voltages produced by rectifier  50  can be used in powering (charging) an energy storage device such as battery  58  and can be used in powering other components in device  24 . For example, device  24  may include input-output devices  56  such as a display, touch sensor, communications circuits, audio components, sensors, components that produce electromagnetic signals that are sensed by a touch sensor in a tablet computer or other device with a touch sensor (e.g., to provide pencil input, etc.), and other components and these components may be powered by the DC voltages produced by rectifier  50  (and/or DC voltages produced by battery  58  or other energy storage device in device  24 ). 
     Device  12  and/or device  24  may communicate wirelessly (e.g., using in-band and out-of-band communications). Device  12  may, for example, have wireless transceiver (TX/RX) circuitry  40  that wirelessly transmits out-of-band signals to device  24  using an antenna. Wireless transceiver circuitry  40  may be used to wirelessly receive out-of-band signals from device  24  using the antenna. Device  24  may have wireless transceiver circuitry  46  that transmits out-of-band signals to device  12 . Receiver circuitry in wireless transceiver  46  may use an antenna to receive out-of-band signals from device  12 . In some configurations, devices  10  can communicate through local area networks and/or wide area networks (e.g., the internet). 
     Wireless transceiver circuitry  40  can use one or more coils  42  to transmit in-band signals to wireless transceiver circuitry  46  that are received by wireless transceiver circuitry  46  using coil  48 . Any suitable modulation scheme may be used to support in-band communications between device  12  and device  24 . With one illustrative configuration, frequency-shift keying (FSK) is used to convey in-band data from device  12  to device  24  and amplitude-shift keying (ASK) is used to convey in-band data from device  24  to device  12 . Power may be conveyed wirelessly from device  12  to device  24  during these FSK and ASK transmissions. Other types of communications (e.g., other types of in-band communications) may be used, if desired. 
     During wireless power transmission operations, circuitry  52  supplies AC drive signals to one or more coils  42  at a given power transmission frequency. The power transmission frequency may be, for example, a predetermined frequency of about 125 kHz, at least 80 kHz, at least 100 kHz, less than 500 kHz, less than 300 kHz, less than 150 KHz, between 80 kHz and 150 kHz, or other suitable wireless power frequency. In some configurations, the power transmission frequency may be negotiated in communications between devices  12  and  24 . In other configurations, the power transmission frequency may be fixed. 
     During wireless power transfer operations, while power transmitting circuitry  52  is driving AC signals into one or more of coils  42  to produce signals  44  at the power transmission frequency, wireless transceiver circuitry  40  uses FSK modulation to modulate the power transmission frequency of the driving AC signals and thereby modulate the frequency of signals  44 . In device  24 , coil  48  is used to receive signals  44 . Power receiving circuitry  54  uses the received signals on coil  48  and rectifier  50  to produce DC power. At the same time, wireless transceiver circuitry  46  uses FSK demodulation to extract the transmitted in-band data from signals  44 . This approach allows FSK data (e.g., FSK data packets) to be transmitted in-band from device  12  to device  24  with coils  42  and  48  while power is simultaneously being wirelessly conveyed from device  12  to device  24  using coils  42  and  48 . Other types of in-band communications between device  12  and device  24  may be used, if desired. 
     In-band communications between device  24  and device  12  uses ASK modulation and demodulation techniques or other suitable in-band communications techniques. Wireless transceiver circuitry  46  transmits in-band data to device  12  by using a switch (e.g., one or more transistors in transceiver  46  that are coupled coil  48 ) to modulate the impedance of power receiving circuitry  54  (e.g., coil  48 ). This, in turn, modulates the amplitude of signal  44  and the amplitude of the AC signal passing through coil(s)  42 . Wireless transceiver circuitry  40  monitors the amplitude of the AC signal passing through coil(s)  42  and, using ASK demodulation, extracts the transmitted in-band data from these signals that was transmitted by wireless transceiver circuitry  46 . The use of ASK communications allows a stream of ASK data bits (e.g., a series of ASK data packets) to be transmitted in-band from device  24  to device  12  with coils  48  and  42  while power is simultaneously being wirelessly conveyed from device  12  to device  24  using coils  42  and  48 . 
     Control circuitry  16  has external object measurement circuitry  41  (sometimes referred to as foreign object detection circuitry or external object detection circuitry) that detects external objects on a charging surface associated with device  12 . Circuitry  41  can detect foreign objects such as coils, paper clips, and other metallic objects and can detect the presence of wireless power receiving devices  24 . During object detection and characterization operations, external object measurement circuitry  41  can be used to make measurements on coils  42  to determine whether any devices  24  are present on device  12  (e.g., whether devices  24  are suspected to be present on device  12 ). Measurement circuitry  43  in control circuitry  30  and/or measurement circuitry  41  in control circuitry  16  may also be used in making current and voltage measurements, and/or may be used in making other measurements on wireless power receiving circuitry  54 . In scenarios where device  12  includes multiple coils  42 , control circuitry  16  can perform measurements using each coil  42  in sequence and/or in parallel. Control circuitry  16  can compare measurements made using measurement circuitry  41  to predetermined characteristics associated with device  24  (e.g., predetermined characteristics associated with different types of devices  24  that control circuitry  16  uses to identify the type of device  24  that is being charged). 
     Illustrative wireless power transmitting circuitry  52  in a configuration in which wireless power transmitting device  12  has multiple coils  42  is shown in  FIG. 2 . With the illustrative arrangement of  FIG. 2 , circuitry  52  has inverter circuitry formed from multiple inverters  60 , each controlled by control circuitry  16  and each supplying drive signals to a corresponding wireless power transmitter circuit having a respective coil  42  and capacitance (e.g., capacitor  62 ). The phase and magnitude of the alternating-current drive signal supplied by each inverter  60  to its associated coil  42  can be adjusted independently by control circuitry  16 . As a result, one or more of coils  42  (e.g., coils in a cluster overlapped by coil  48  in device  24 ) can be activated while remaining coils are not driven and remain inactive. If desired, switching circuitry can be used to decouple inactive coils from the corresponding inverter  60  and/or ground (e.g., inactive coils can be held at a floating potential). 
     The phase of each active coil  42  can also be varied. For example, one coil may have a first phase and a second coil (e.g., an adjacent coil) may be driven with opposite phase (e.g., the second coil may have a second phase that is 180° out of phase with the first phase). Using arrangements such as these, control circuitry  16  can control the strength and orientation of the magnetic fields produced by coils  42 . 
       FIG. 3  is a rear perspective view of an exemplary wireless power receiving device  24 . As shown in  FIG. 3 , wireless power receiving device  24  includes a housing such as housing  64 . Housing  64  has a surface  74  (sometimes referred to herein as rear surface  74 ) that is placed on or over a charging surface of device  12  for wirelessly charging device  24  (e.g., both rear surface  74  and the charging surface of device  12  lie substantially parallel to the X-Y plane of  FIG. 3  during wireless charging). On devices where one surface is substantially defined by a display screen (e.g., OLED display), the rear surface is opposite the surface defined by the display screen. 
     In some configurations (e.g., in scenarios where device  24  is a wrist watch or other wearable device), device  24  includes a wrist strap  72  coupled to housing  64 . In these scenarios, wrist strap  72  may contact the charging surface while device  24  is being wirelessly charged. In practice, wrist strap  72  can serve to hold housing  64  over (and separate from) the charging surface and/or can mechanically bias housing  64  away from the charging surface. Wrist strap  72  can be omitted if desired. 
     Device  24  includes one or more coils  48  on or within housing  64 . Housing  64  can include metal materials, dielectric materials, or combinations of these and/or other materials. A display or other input-output devices can be mounted to housing  64  if desired (e.g., on the side of housing  64  opposite to surface  74 ). In scenarios where coils  48  are mounted within housing  64 , housing  64  can include dielectric portions in the vicinity of the coils to allow external magnetic fields to interact with coils  48 . 
     Coils  48  can be mounted at different possible orientations within device  24 . In some scenarios, device  24  includes a vertically-oriented coil such as coil  48 A. Coil  48 A wraps around a central (longitudinal) axis  68  oriented within a plane normal (perpendicular) to surface  74  (e.g., parallel to the Z-axis of  FIG. 3 ). In other scenarios, device  24  includes a horizontally-oriented coil such as coil  48 B. Coil  48 B wraps around a central (longitudinal) axis  70  oriented within a plane parallel to surface  74  (e.g., parallel to the X-Y plane of  FIG. 3 ). Central axis  70  of coil  48 B is oriented perpendicular to central axis  68  of coil  48 A and can extend parallel to a sidewall of housing  64  if desired (e.g., coil  48 B has a transverse axis  80  that extends perpendicular to central axis  70  and that can extend parallel to a normal vector of a sidewall of housing  64 ). Device  24  can include one or more coils  48 A and/or one or more coils  48 B. Coils such as coils  48 A and  48 B can be mounted at any desired locations on or within housing  64 . 
     Coil  48 A can be confined to a single plane (e.g., a plane parallel to the X-Y plane as shown in the example of  FIG. 3 ) or can extend vertically along central axis  68  (e.g., in a cylindrical shape). Similarly, coil  48 B can be confined to a single plane or can extend horizontally along central axis  70  (as shown in the example of  FIG. 3 ). Coil  48 A is sometimes referred to herein as vertical coil  48 A (e.g., because central axis  68  is oriented vertically with respect to surface  74 ). Coil  48 B is sometimes be referred to herein as horizontal coil  48 B (e.g., because central axis  70  is oriented horizontally with respect to surface  74 ). 
     Vertical coil  48 A includes one or more turns of wire or other conducive structures that wind (wrap) around central axis  68 . Coil  48 B includes one or more turns of wire or other conductive structures that wind (wrap) around central axis  70 . The wire in vertical coil  48 A can be wrapped around a central core formed from a magnetic material such as ferrite if desired. Similarly, the wire in vertical coil  48 A can be wrapped around a central core formed from magnetic material if desired. Wire in coils  48 A and  48 B can be formed from solid copper wire or other suitable conductive strands of material. 
     In some situations, a user may place device  24  on a charging surface of device  12  so that rear surface  74  of housing  64  lies flat on the charging surface. In this configuration (e.g., in scenarios where device  10  includes vertical coil  48 A), central axis  68  of coil vertical  48 A extends parallel to the central axis of coil(s)  42  in device  12  and magnetic field  76  from coil(s)  42  may pass vertically through coil  48 A. The vertical component of magnetic field  76  induces current on coil  48 A that is used to wirelessly charge device  24 . 
     In scenarios where device  10  includes horizontal coil  48 B, central axis  70  of coil  48 B may extend perpendicular to the central axis of coil(s)  42  in device  12  and magnetic field  76  from coil(s)  42  on device  12  may pass laterally (horizontally in the configuration of  FIG. 3 ) through coil  48 B. The horizontal component of magnetic field  76  induces current on coil  48 B that is used to wirelessly charge device  24 . 
     Some types of devices  24  include vertical coils such as coil  48 A of  FIG. 3  whereas other types of devices  24  include horizontal coils such as coil  48 B of  FIG. 3 . For example, in scenarios where device  24  is a cellular telephone, device  24  may include only vertical coils such as coil  48 A. However, in other scenarios such as scenarios where device  12  includes wrist strap  72  (e.g., in scenarios where device  12  is a wristwatch), strap  72  may extend parallel to surface  74 . If strap  72  is an elastomeric loop and has no clasps, it may be impossible for a user to place rear surface  74  of housing  64  directly on the charging surface and strap  72  may hold device  12  in a position that is separated from (e.g., raised slightly above) the charging surface. In these scenarios, vertical coils such as coil  48 A may not receive adequate magnetic flux from coil(s)  42  on device  12  to sufficiently charge device  24 . However, horizontal coils such as coil  48 B can receive enough flux from coil(s)  42  on device  12  to sufficiently charge device  24  in these scenarios. These types of devices (e.g., devices having wrist strap  72 ) may include only horizontal coils such as coil  48 B if desired. 
     Device  12  is configured to transfer a sufficient amount of wireless power to wirelessly charge device  24  regardless of whether device  24  has vertical or horizontal coils. Device  12  includes different types of coils  42  that are optimized for transferring wireless power to vertical coils or for transferring wireless power to horizontal coils. For example, device  12  can include a first set of coils  42  that are arranged to maximize wireless power transfer for vertical coils  48 A and can include a second set of coils  42  that are arranged to maximize wireless power transfer for horizontal coils  48 B. 
       FIG. 4  is a top-down view of wireless power transmitting device  12  in an illustrative configuration in which device  12  has different coils  42  at charging surface  82  for transferring wireless power to vertical coils  48 A and horizontal coils  48 B. The coils  42  in device  12  include a first set of coils  42 A that are configured to optimize wireless power transfer to vertical coils  48 A and a second set of coils  42 B that are configured to optimize wireless power transfer to horizontal coils  48 B. In the example of  FIG. 4 , device  12  includes a first coil  42 A for transferring wireless power to vertical coils  48 A and a pair of coils  42 B (e.g., a first coil  42 B- 1  and a second coil  42 B- 2 ) for transferring wireless power to horizontal coils  48 B. 
     With one illustrative configuration, device  12  is a wireless charging mat (e.g., a wireless charging mat having a planar surface that opposes charging surface  82  and that rests on an underlying surface such as a tabletop or other surface). A user may place device  24  onto charging surface  82  for charging device  24 . Rear surface  74  of device  24  ( FIG. 3 ) and charging surface  82  lie within planes that are substantially parallel to the X-Y plane of  FIG. 4  during wireless charging. 
     Coils  42 B- 1  and  42 B- 2  are formed over coil  42 A in device  12  (e.g., coils  42 B- 1  and  42 B- 2  are interposed between coil  42 A and device  24  during charging). A ferrite or nano-crystalline layer can be formed under coil  42 A if desired. One or more dielectric layers can be used to prevent coils  42 B- 1  and  42 B- 2  from shorting to coil  42 A if desired. 
     As shown in  FIG. 4 , coil  42 A is a circular coil extending around a central axis that runs parallel to the Z-axis of  FIG. 4 . Coil  42 A includes a number of windings extending from inner diameter  88  of coil  42 A to outer diameter  86  of coil  42 A. Inner diameter  88  surrounds a central region  91  of coil  42 A that is free from the conductive material (e.g., wire) used to form coil  42 A. 
     Inner diameter  88  and outer diameter  86  are selected to match the size of the vertical coils  48 A on device  24  and to thereby optimize wireless power transfer to vertical coils  48 A on device  24 . As an example, inner diameter  88  may be between 15 mm and 25 mm, between 10 mm and 30 mm, between 5 mm and 35 mm, between 18 mm and 22 mm, greater than 35 mm, less than 5 mm, or other sizes. In one suitable arrangement, inner diameter  88  is approximately 20 mm. Outer diameter  86  may be between 45 mm and 55 mm, between 40 mm and 60 mm, between 35 mm and 65 mm, less than 35 mm, greater than 65 mm, or other sizes greater than inner diameter  88 . In one suitable arrangement, outer diameter  86  is approximately 50 mm. 
     Device  12  drives coil  42 A (e.g., using a corresponding inverter  60  of  FIG. 2 ) to produce magnetic field  100 . The vertical component of magnetic field  100  passes through vertical coil  48 A while device  24  is placed on charging surface  82  and induces current on vertical coil  48 A that serves to wirelessly charge device  24  (e.g., as shown by magnetic field  76  of  FIG. 3 ). Electromagnetic coupling between coil  42 A and vertical coil  48 A is maximal when vertical coil  48 A is centered about coil  42 A. However, the size of coil  42 A allows for some positional tolerance along the X and Y axes of  FIG. 4  for the placement of device  24  on charging surface  82  (e.g., device  24  may exhibit sufficient wireless charging efficiency while placed on charging surface  82  within a few millimeters or centimeters about the center of coil  42 A). 
     If desired, device  12  can include alignment structures such as visual markings that indicate the location on charging surface  82  at which the user should place device  24  to maximize wireless power transfer between coil  42 A and vertical coil  48 A. In another suitable arrangement, device  12  includes magnetic or mechanical alignment structures that serve to hold device  24  in place over the location on charging surface  82  that maximizes wireless power transfer between coil  42 A and vertical coil  48 A. Device  12  can include both visual and mechanical alignment structures if desired. 
     In the example of  FIG. 4 , coils  42 B- 1  and  42 B- 2  are rectangular coils having straight horizontal segments  92  (e.g., extending parallel to the X-axis of  FIG. 4 ) and straight vertical segments  90  (e.g., extending parallel to the Y-axis of  FIG. 4 ) that collectively wind around respective central axes parallel to the Z-axis of  FIG. 4 . Coils  42 B- 1  and  42 B- 2  each completely or partially overlap the underlying coil  42 A. Coils  42 B- 1  and  42 B- 2  each include a corresponding straight vertical segment  90  that overlaps central region  91  of coil  42 A (e.g., the portions of coils  42 B- 1  and  42 B- 2  overlapping central region  91  are straight and extend parallel to the Y-axis of  FIG. 4 ). 
     Coils  42 B- 1  and  42 B- 2  each have an inner rectangular length  94  that is equal to the length of vertical segments  90  and that is greater than inner diameter  88  of coil  42 A. Coils  42 B- 1  and  42 B- 2  each have an inner rectangular width that is equal to the length of horizontal segments  92 . The length of vertical segments  90  (e.g., length  94 ) is greater than or equal to the length of horizontal segments  92 . Coils  42 B- 1  and  42 B- 2  also have rectangular outer dimensions that are defined by the number of coil windings (loops) and the length of segments  90  and  92 . The rectangular outer dimensions of coils  42 B- 1  and  42 B- 2  are less than outer diameter  86  of coil  42 A (e.g., the lengths of segments  92  and  90  are each less than outer diameter  86 ). In one illustrative arrangement, the number of windings in each of coils  42 B- 1  and  42 B- 2  (e.g., the number of rectangular loops of conductor in coils  42 B- 1  and  42 B- 2 ) is less than the number of windings in coil  42 A (e.g., the number of circular loops in coil  42 A). In general, coils  42 B- 1  and  42 B- 2  each extend across a smaller lateral area of charging surface  82  than coil  42 A (e.g., coils  42 B- 1  and  42 B- 2  are each smaller than coil  42 A). The rectangular dimensions and number of windings of coils  42 B- 1  and  42 B- 2  are selected to optimize wireless power transfer to horizontal coils  48 B on device  24  without significantly blocking or attenuating wireless power transmitted by coil  42 A while coil  42 A is active. 
     Device  12  drives one or both of coils  42 B- 1  and  42 B- 2  (e.g., using corresponding inverters  60  of  FIG. 2 ) to produce a magnetic field having horizontal components  93  that run perpendicular to vertical segments  90  and parallel to the X-axis of  FIG. 4  (e.g., parallel to charging surface  82  and the X-Y plane of  FIG. 4 ). Horizontal components  93  of the magnetic field are generated by vertical segments  90  of coils  42 B- 1  and  42 B- 2  and pass through horizontal coil  48 B while device  24  is placed on charging surface  82  (e.g., as shown by magnetic field  76  passing through horizontal coil  48 B of  FIG. 3 ). 
     Electromagnetic coupling between coils  42 B- 1  or  42 B- 2  and horizontal coil  48 B is maximal when horizontal coil  48 B is centered over a vertical segment  90  and oriented so that central axis  70  of horizontal coil  48 B ( FIG. 3 ) extends substantially parallel to (e.g., within 25 degrees of) horizontal components  93  of the magnetic field generated by coils  42 B- 1  and  42 B- 2 . In the example of  FIG. 4 , electromagnetic coupling for horizontal coil  48 B is maximal within regions  98  and  96  of charging surface  82 . A user may therefore place a device  24  having horizontal coil  48 B along the X-axis of  FIG. 4  within regions  98  or  96  for wireless charging. The example of  FIG. 4  is merely illustrative and, if desired, regions  98  can be continuous with region  96 . 
     If desired, device  12  can concurrently use both coils  42 B- 1  and  42 B- 2  to wirelessly charge device  24 . In this scenario, device  12  drives coils  42 B- 1  and  42 B- 2  with currents that are 180 degrees out of phase with each other (e.g., using respective inverters  60  of  FIG. 2 ). This ensures that horizontal component  93  of the magnetic field generated by the right-most vertical segment  90  of coil  42 B- 1  adds with (instead of canceling out with) horizontal component  93  of the magnetic field generated by the left-most vertical segment  90  of coil  42 B- 2 . This may also serve to increase wireless power transfer within region  96  (as well as the lateral area that can be used for wireless charging) relative to scenarios where only one of coils  42 B- 1  and  42 B- 2  is active at a given time. 
     In this way, device  12  can transfer wireless power to horizontal coil  48 B on device  24  even if device  24  is not placed precisely over the center of coil  42 A. In addition, the length  94  of vertical segments  90  is selected to allow device  24  to be placed at different locations along the Y-axis of  FIG. 4 , while still allowing for satisfactory wireless coupling to horizontal coil  48 B on device  24 . For example, device  24  can be placed at any desired location along the Y-axis of  FIG. 4  so long as horizontal coil  48 B overlaps at least one vertical segment  90 . 
     By aligning at least one vertical segment  90  of coils  42 B- 1  and  42 B- 2  with central region  91  of the underlying coil  42 A, coils  42 A,  42 B- 1 , and  42 B- 2  each exhibit maximum wireless power transfer efficiency within the same lateral region of charging surface  82  (e.g., within region  96  of  FIG. 4 ). This may allow a user to place different types of devices  24  over the same location on device  12  without sacrificing wireless charging efficiency, regardless of whether the device  24  includes horizontal coils  48 B or vertical coils  48 A. This may, for example, reduce the likelihood that the user will place device  24  over an inappropriate location for the given type of device  24 . At the same time, this also serves to minimize the amount of space required in device  10  to accommodate coils for wirelessly charging different types of devices. If desired, alignment structures on charging surface  82  may serve to guide or position device  24  over the location on charging surface  82  that optimizes wireless power transfer regardless of the type coil used on device  24  (e.g., because coils  42 A,  42 B- 1 , and  42 B- 2  each exhibit maximum wireless power transfer at the same location on charging surface  82 ). 
     Coil  42 B- 1 , coil  42 B- 2 , and the underlying coil  42 A may sometimes be referred to herein as unit cell  102 . Device  12  may include only a single unit cell  102  at charging surface  82  or may include multiple unit cells  102  at charging surface  82  (e.g., two unit cells  102 , three unit cells  102 , or more than three unit cells  102 ). In scenarios where device  10  includes multiple unit cells  102 , the unit cells can be arranged in an array or grid having rows and columns or in any other desired pattern (e.g., hexagonal patterns or other patterns that do not include rows and columns). In these scenarios, different unit cells  102  can be used to concurrently charge multiple different devices  24  placed on charging surface  82 . 
     The wireless charging efficiency of device  24  is determined in part by the coupling constant between coils  42  on device  12  and coil  48  on device  24 .  FIG. 5  is an illustrative plot of coupling constant between rectangular coils  42 B- 1  and  42 B- 2  and horizontal coil  48 B on device  24  as a function of position along the X-axis of  FIG. 4 . The X=0 position of  FIG. 5  corresponds to the location of the central axis of coil  42 A (e.g., a location half-way between the right-most vertical segment  90  of coil  42 B- 1  and the left-most vertical segment  90  of coil  42 B- 2 ). 
     As shown in  FIG. 5 , curve  104  plots the coupling constant between coil  42 B- 2  and horizontal coil  48 B as horizontal coil  48 B is moved along the X-axis of  FIG. 4 . Curve  104  exhibits a peak magnitude K M  at the location along the X-axis of the left-most vertical segment  90  of coil  42 B- 2 . At this location, horizontal coil  48 B is located directly over the left-most vertical segment  90  of coil  42 B- 2  and generates current in response to horizontal component  93  of the magnetic field generated by that vertical segment  90 . 
     Curve  106  plots the coupling constant between coil  42 B- 1  and horizontal coil  48 B as horizontal coil  48 B is moved along the X-axis of  FIG. 4 . Curve  106  exhibits a peak magnitude K M  at the location along the X-axis of the right-most vertical segment  90  of coil  42 B- 1 . At this location, horizontal coil  48 B is located directly over this right-most vertical segment  90  of coil  42 B- 1  and generates current in response to horizontal component  93  of the magnetic field generated by that vertical segment  90 . 
     Curves  104  and  106  have magnitudes greater than threshold level TH 1  for positions between X=−X 2  and X=+X 2 . Threshold level TH 1  may be a minimum coupling constant for which device  24  exhibits a sufficient wireless charging efficiency while being charged using only one of coils  42 B- 1  and  42 B- 2 . Threshold level TH 1  may be between 0.10 and 0.18, between 0.11 and 0.13, greater than 0.1, greater than 0.18, approximately 0.12, or another threshold level, as examples. By forming both coils  42 B- 1  and  42 B- 2  over coil  42 A, unit cell  102  can exhibit a satisfactory coupling constant greater than threshold level TH 1  even as horizontal coil  48 B is moved along the X-axis of  FIG. 4 . 
     For example, one of coils  42 B- 1  and  42 B- 2  can be active at a given time such that a satisfactory coupling constant is achieved if horizontal coil  48 B is placed at any desired location between X=−X 2  and X=X 2 . In other words, device  12  can exhibit a lateral area ΔX over which device  24  can be charged using horizontal coil  48 B with sufficient wireless charging efficiency. In one arrangement, lateral area ΔX corresponds to region  96  of  FIG. 4 . Lateral area ΔX is larger than the lateral area that would be available in scenarios where unit cell  102  includes only a single coil for charging horizontal coil  48 B (e.g., the arrangement of  FIG. 4  allows for more positional freedom along the X-axis than in scenarios where only a single coil is used). In scenarios where both coils  42 B- 1  and  42 B- 2  are active at a given time, the coupling constant for each coil need only be greater than a lower threshold value TH 2  (e.g., because both coils will contribute to the magnetic field used to charge device  24 ). 
     The examples of  FIGS. 4 and 5  are merely illustrative. In practice, curves  104  and  106  can have other shapes. Coils  42 B- 1  and  42 B- 2  can have other shapes (e.g., hexagonal shapes, “D” shapes having straight and curved segments, square shapes, or other shapes), so long as coils  42 B- 1  and  42 B- 2  each include straight segments that overlap central region  91  and that extend parallel to the Y-axis of  FIG. 4  (e.g., segments such as vertical segments  90  of  FIG. 4 ). The presence of vertical segments  90  in coils  42 B- 1  and  42 B- 2  allows for wireless charging of horizontal coil  48 B in addition to the wireless charging capabilities provided for vertical coils  48 A by coil  42 A. Coil  42 A can have other shapes if desired (e.g., a hexagonal shape, a “D” shape, a square shape, a rectangular shape, an elliptical shape, etc.). 
     In one illustrative arrangement, coil  42 B- 1  overlaps coil  42 B- 2  in unit cell  102 .  FIG. 6  is a top-down view of device  12  showing how coil  42 B- 1  can overlap coil  42 B- 2 . As shown in  FIG. 6 , coil  42 B- 1  overlaps a portion of coil  42 B- 2  (e.g., a portion of coil  42 B- 2  is interposed between a portion of coil  42 B- 1  and coil  42 A). This is merely illustrative and, if desired, coil  42 B- 2  can overlap a portion of coil  42 B- 1 . 
     In the example of  FIG. 6 , the right-most vertical segment  90  of coil  42 B- 1  is laterally located (interposed) between the left-most vertical segment  90  of coil  42 B- 2  and the right-most vertical segment  90  of coil  42 B- 2 . Similarly, the left-most vertical segment  90  of coil  42 B- 2  is laterally located between the left-most vertical segment  90  of coil  42 B- 1  and the right-most vertical segment  90  of coil  42 B- 1 . Using overlapping coils  42 B can adjust the coupling constant and positional freedom along the X-axis as well as the overall footprint of unit cell  102  relative to scenarios where coils  42 B do not overlap (e.g., as shown in  FIG. 4 ). 
       FIG. 7  is an illustrative plot of coupling constant between rectangular coils  42 B- 1  and  42 B- 2  and horizontal coil  48 B on device  24  as a function of position along the X-axis of  FIG. 6  (e.g., in scenarios where coils  42 B- 1  and  42 B- 2  are overlapping). As shown in  FIG. 7 , dashed curve  112  plots the coupling constant between coil  42 B- 2  and horizontal coil  48 B as horizontal coil  48 B is moved along the X-axis of  FIG. 6 . Curve  112  exhibits peak magnitude K M  at the locations along the X-axis of each vertical segment  90  of coil  42 B- 2  (e.g., at X=−X 3  and X=X 4 ). 
     Curve  110  of  FIG. 7  plots the coupling constant between coil  42 B- 1  and horizontal coil  48 B as horizontal coil  48 B is moved along the X-axis of  FIG. 6 . Curve  110  exhibits peak magnitude K M  at the locations along the X-axis of each vertical segment  90  of coil  42 B- 1  (e.g., at X=−X 4  and X=X 3 ). Curves  110  and  112  collectively exhibit magnitudes greater than threshold level TH 1  for any position across lateral area ΔX 2 . One or both of coils  42 B- 1  and  42 B- 2  may be activated at a given time to ensure that a coupling constant greater than threshold level TH 1  is achieved regardless of where horizontal coil  48 B of device  24  is located within lateral area ΔX 2 . 
     Lateral area ΔX 2  can be greater than, less than, or equal to lateral area ΔX 1  of  FIG. 5 . Lateral area ΔX 2  is larger than the lateral area that would be available in scenarios where unit cell  102  includes only a single coil for charging horizontal coil  48 B (e.g., the arrangement of  FIG. 6  allows for more positional freedom along the X-axis than in scenarios where only a single coil is used). In scenarios where both coils  42 B- 1  and  42 B- 2  are active at a given time, the coupling constant for each coil need only be greater than a lower threshold value TH 2  (e.g., because both coils will contribute to the magnetic field used to charge device  24 ). 
     The examples of  FIGS. 6 and 7  are merely illustrative. In practice, curves  110  and  112  can have other shapes. Coils  42 B- 1  and  42 B- 2  can have other shapes (e.g., hexagonal shapes, “D” shapes having straight and curved sides, square shapes, or other shapes) while still having portions that overlap each other. Any desired number of unit cells  102  of the type shown in  FIG. 4  and/or  FIG. 6  can be arranged across charging surface  82  of device  12 . 
       FIG. 8  is a top-down view showing how device  12  can include three unit cells  102  arranged across charging surface  82 . In the example of  FIG. 8 , device  12  includes a first unit cell  102  such as unit cell  102 - 1 , a second unit cell  102  such as unit cell  102 - 2 , and a third unit cell  102  such as unit cell  102 - 3  arranged in a single row (e.g., along a longitudinal axis of device  12  parallel to the X-axis of  FIG. 8 ). This is merely illustrative and unit cells  102  can be arranged in any desired pattern (e.g., a triangular pattern or other patterns). Each unit cell  102  includes an underlying coil  42 A and overlying coils  42 B- 1  and  42 B- 2 . If desired, one or more (e.g., all) of unit cells  102  can include overlapping coils  42 B- 1  and  42 B- 2  (e.g., as shown in  FIG. 6 ). 
     Devices  24  having vertical coils  48 A can be placed over the center of coils  42 A in unit cells  102 - 1 ,  102 - 2 , and/or  102 - 3  for receiving wireless power from coils  42 A. If desired, alignment structures can be formed on one or more of unit cells  102 - 1 ,  102 - 2 , and  102 - 3  to help guide a user to place device  24  at a location on charging surface  82  that optimizes coupling coefficient with coils  42 A (e.g., over the center of coils  42 A). 
     Devices  24  having horizontal coils  48 B can be placed over the center of coils  42 A (e.g., within central charging regions  124 ) in unit cells  102 - 1 ,  102 - 2 , and/or  102 - 3  for receiving wireless power from coils  42 B- 1  and/or  42 B- 2 . When device  24  is placed over a central charging region  124 , magnetic fields generated by the right-most vertical segment  90  of coil  42 B- 1  and/or the left-most vertical segment  90  of coil  42 B- 2  in that unit cell  102  are used to transfer wireless power to horizontal coil  48 B. 
     If desired, the same alignment structures that are used to help guide a user to place device  24  at a location on charging surface  82  that optimizes coupling coefficient with coils  42 A can be used to help guide the user to place device  24  at a location that optimizes coupling coefficient with coils  42 B- 1  and  42 B- 2  (e.g., because central charging regions  124  overlap the center of the underlying coils  42 A). 
     When configured in this way, device  12  allows for positional tolerance in the placement of devices  24  across charging surface  82 . For example, device  24  can be placed at any desired location on charging surface  82  such that horizontal coil  48 B is located within a corresponding central charging region  124  (e.g., device  24  need not be placed precisely over the center of coil  42 A or location X=0 of  FIGS. 5 and 7 ). 
     The arrangement of  FIG. 8  allows for further positional tolerance along the X-axis of device  12 . For example, devices  24  having horizontal coils  48 B can also be placed over regions  126  between adjacent unit cells  102  (sometimes referred to herein as inter-cell regions  126 ). When device  24  is placed over an inter-cell region  126 , magnetic fields generated by the right-most vertical segment  90  of coil  42 B- 2  and/or the left-most vertical segment  90  of coil  42 B- 1  in the adjacent unit cell  102  can be used to transfer wireless power to horizontal coil  48 B. Devices  24  can also be placed over regions  128  at the ends of charging surface  82 . When device  24  is placed over regions  128 , magnetic fields generated by the one vertical segment  90  from unit cells  102  can be used to transfer wireless power to horizontal coil  48 B. 
     In this way, regions  128 ,  124 , and  126  can each be used to provide wireless power to devices  24  having horizontal coils  48 B (e.g., using coils  42 B- 1  and  42 B- 2 ), whereas regions  124  can be used to provide wireless power to devices  24  having vertical coils  48 A (e.g., using coils  42 A). In the example of  FIG. 8 , regions  128 ,  124 , and  126  are continuous such that devices  24  having horizontal coils  48 B can be placed at any desired location along the width of charging surface  82  (e.g., where horizontal coil  48 B overlaps the region defined by dimensions  118  and  94 ). 
     In this way, the same locations on charging surface  82  (e.g., regions  126 ) can be used to charge different types of devices  24  regardless of whether device  24  includes a horizontal coil  48 B or a vertical coil  48 A. For example, the user need not keep track of the precise location across charging surface  82  that is used to charge each type of device and the user need not precisely place devices  24  having horizontal coils  48 B on charging surface  82 . If desired, different unit cells  102  can be used to concurrently charge multiple different devices  24  at once, regardless of whether the devices  24  have vertical coils  48 A or horizontal coils  48 B. For example, unit cell  102 - 1  can wirelessly charge a first device  24  having a horizontal coil  48 B (e.g., using horizontal components of the magnetic field generated by coils  42 B- 1  and/or  42 B- 2  within a corresponding region  128 ,  126 , or  124 ) while unit cell  102 - 2  wirelessly charges a second device  24  having a vertical coil  48 A (e.g., using vertical components of the magnetic field generated by coil  42 A within the corresponding region  124 ) and unit cell  102 - 3  wirelessly charges a third device having a horizontal coil  48 B. 
     Control circuitry  16  can identify a location of device  24  (coil  48 ) over charging surface  82  and/or the type or orientation of coil  48  over charging surface  82  and can activate selected sets of antennas  42  accordingly. For example, if control circuitry  16  identifies that a vertical coil  48 A is located within a given region  124 , control circuitry  16  activates the coil  42 A within that unit cell  102  to transmit wireless power to device  24 . If control circuitry  16  identifies that a horizontal coil  48 B is located within region  124 , control circuitry  16  activates one or both of coils  42 B- 1  and  42 B- 2  in that unit cell  102  to transmit wireless power to device  24 . If control circuitry  16  identifies that a horizontal coil  48 B is located within region  126 , control circuitry  16  activates one or both of coils  42 B- 1  and  42 B- 2  in adjacent unit cells  102  to transmit power to device  24 . 
     The example of  FIG. 8  is merely illustrative. Charging surface  82  may include any desired number of unit cells  102  arranged in any desired pattern. Device  12  can have any desired shape (e.g., shapes having curved and/or straight edges). 
     An arrangement of the type shown in  FIG. 8  also allows for rotational tolerance in the placement of devices  24  on charging surface  82 . For example, devices  24  having vertical coils  48 A can be placed at any desired angle θ with respect to axis  120  of  FIG. 8  while exhibiting sufficient wireless charging efficiency (e.g., so long as surface  74  of  FIG. 3  is placed on charging surface  82 ). 
     Ideally, devices  24  having horizontal coils  48 B should be oriented such that central axis  70  of horizontal coil  48 B ( FIG. 3 ) is aligned with the X-axis of  FIG. 8  (e.g., such that transverse axis  80  of  FIG. 3  is parallel to axis  120  and the Y-axis of  FIG. 8 ). This alignment maximizes coupling between the horizontal component of the magnetic field generated by vertical segments  90  and horizontal coil  48 B. 
     However, the presence of adjacent coils  42 B across charging surface  82  also allows devices  24  having horizontal coils  48 B to be rotated across a range of other angles while still exhibiting a sufficiently high coupling constant and thus sufficient wireless charging efficiency. For example, device  24  can be placed on charging surface  82  such that transverse axis  80  ( FIG. 3 ) is oriented parallel to axis  122  (e.g., at angle θ with respect to axis  120 ). 
       FIG. 9  is an illustrative plot of coupling constant between rectangular coils  42 B- 1  and  42 B- 2  and horizontal coil  48 B on device  24  as a function of the angle θ between transverse axis  80  ( FIG. 3 ) and axis  120  ( FIG. 8 ). As shown in  FIG. 9 , curve  130  plots the coupling constant between coils  42 B- 1  and/or  42 B- 2  and horizontal coil  48 B as horizontal coil  48 B (device  24 ) is rotated about the Z-axis of  FIG. 8  (e.g., from a fixed location such as X=X 3  of  FIG. 7 ). 
     Curve  130  exhibits peak magnitude K M  when angle θ=0 degrees because central axis  70  of horizontal coil  48 B is aligned with the horizontal component of the magnetic field produced by coils  42 B- 1  and/or  42 B- 2 . As horizontal coil  48 B is rotated and angle θ increases, the coupling constant decreases because central axis  70  becomes misaligned with the horizontal component of the magnetic field. When horizontal coil  48 B is rotated to a maximum angle θ TH , the coupling constant reaches minimum threshold value TH 1 . At greater angles, the coupling constant drops below a level required to obtain sufficient wireless charging efficiency. By arranging coils  42  on device  12  as shown in the examples of  FIGS. 4, 6, and 8 , maximum angle θ TH  may be relatively large. For example, maximum angle θ TH  can be between 20 degrees and 35 degrees, between 15 degrees and 40 degrees, between 30 degrees and 40 degrees, between 20 degrees and 30 degrees, or less than 20 degrees. In one particular arrangement, maximum angle θ TH  is approximately 25 degrees. In this way, a user need not focus on placing devices  24  on charging surface  82  with a precise orientation, regardless of whether device  24  has horizontal coils  48 B or vertical coils  48 A. 
     Control circuitry  16  on device  12  ( FIG. 1 ) can use measurement circuitry  41  to gather measurements such as voltage and/or impedance measurements from each of the coils  42  in device  12 . Different measurements are associated with different types of environments over coils  42 . For example, measurement circuitry  41  may gather first measurement values in the presence of horizontal coils  48 B over coils  42 , second measurement values in the presence of vertical coils  48 A over coils  42 , third measurement values in the absence of material over coils  42 , etc. Control circuitry  16  can use these measurements to determine whether to activate or deactivate each coil  42  across charging surface  82  in real time. 
     For example, control circuitry  16  can store predetermined or calibrated measurements associated with different types of environments over coils  42  (e.g., first set of predetermined measurements associated with the presence of horizontal coil  48 B over coil  42 , a second set of predetermined measurements associated with the presence of vertical coil  48 A, a third set of predetermined measurements associated with free space, a fourth set of predetermined measurements associated with a foreign object, etc.). Control circuitry  16  compares measurements gathered using measurement circuitry  41  to the stored measurements to identify the presence, type of material, or type (orientation) of coil  48  located over each coil  42 . If desired, control circuitry  16  can also use in-band communications to help identify the type of device  24  (e.g., the type or orientation of coil  48 ) that is present over a given coil  42  (e.g., by transmitting and/or receiving in-band signals using that coil  42 ). Control circuitry  16  can activate one or both coils  42 B in a given unit cell  102  in response to determining that a horizontal coil  48 B is located over that unit cell and may activate coil  42 A in response to determining that a vertical coil  48 A is located over that unit cell. 
     Control circuitry  16  can gather these measurements sequentially and/or in parallel for each coil  42  across charging surface  82 . Control circuitry  16  can identify changes in the measurements over time to identify when device  24  has moved away from coils  42  (e.g., when a user has removed device  24  from charging surface  82 ) and may take appropriate action in response to such an identification (e.g., control circuitry  16  can disable coils  42  in response to determining that no coils  48  are present over coils  42 ). In this way, control circuitry  16  can control device  12  to selectively charge one or more devices  24  as the devices are placed onto or moved across charging surface  82  over time, regardless of whether the devices include horizontal coils  48 B, vertical coils  48 A, or no coils  48 . If desired, one or more dedicated coils  42  on device  12  can be used solely for detecting the presence and type of objects placed on charging surface  82  (e.g., without wirelessly charging any devices  24 ). 
     The foregoing is merely illustrative and various modifications can be made to the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20190716
Publication Date: 20211026
Grant Date: 20211026
Priority Date: 20180724
Inventors: PINCIUC, Christopher M.
BERDNIKOV, DMITRY
SJOEROOS, JUKKA-PEKKA J.
RANGANATHAN, SUMANT
QIU, WEIHONG
MOUSSAOUI, ZAKI
Assignee: APPLE INC
CPC Classifications: [{"code": "H02J50/60", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J7/007", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/80", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/402", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/007", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/90", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/60", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/40", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/80", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/402", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/40", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/90", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/60", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J7/025", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 69178840