PATENT DOCUMENT

Publication Number: US-10505401-B2
Application Number: US-201715690121-A
Country: US
Kind Code: B2

Title: Wireless charging system with receiver locating circuitry and foreign object detection

Abstract:
A wireless power transmission system has a wireless power receiving device that is located on a charging surface of a wireless power transmitting device. The wireless power receiving device has a wireless power receiving coil and the wireless power transmitting device has a wireless power transmitting coil array. Control circuitry in the transmitting device uses inverter circuitry to supply alternating-current signals to coils in the coil array, thereby transmitting wireless power signals. Impulse response measurement circuitry coupled to the coil array is used to make impulse response measurements while the control circuitry uses the inverter circuitry to apply impulse signals to each of the coils. The control circuitry analyzes output from the impulse response measurement circuitry to measure inductances associated with the coils in the coil array.

Claims:
What is claimed is: 
     
       1. A wireless power transmitting device configured to transmit wireless power signals to a wireless power receiving coil in a wireless power receiving device, comprising:
 an array of wireless power transmitting coils; 
 inverter circuitry coupled to the array of wireless power transmitting coils; 
 impulse response measurement circuitry coupled to the array of wireless power transmitting coils; and 
 control circuitry configured to:
 store valid sets of coil inductances for the array, wherein each valid set of coil inductances corresponds to inductance values for the wireless power transmitting coils in the array that occur when the wireless power receiving device is present on the charging surface in the absence of foreign objects; 
 measure inductance values for at least some of the wireless power transmitting coils with the impulse response measurement circuitry; and 
 compare the measured inductance values to the valid sets of coil inductances associated with the array of wireless power transmitting coils to determine whether the wireless power receiving device is present on the array in the absence of foreign objects. 
 
 
     
     
       2. The wireless power transmitting device of  claim 1  wherein the control circuitry determines whether foreign objects overlap the wireless power receiving coil by comparing the measured inductance values to the valid sets of coil inductances and wherein the control circuitry is further configured to:
 control the transmission of the wireless power signals with the inverter circuitry and the array of wireless power transmitting coils based on whether any foreign objects are determined to be overlapping the wireless power receiving coil by comparing the measured inductance values to the valid sets of coil inductances. 
 
     
     
       3. The wireless power transmitting device of  claim 2  wherein the control circuitry is configured to:
 transmit the wireless power signals in response to determining that no foreign objects overlap the wireless power receiving coil; and 
 block transmission of the wireless power signals in response to detecting that a foreign object overlaps the wireless power receiving coil. 
 
     
     
       4. The wireless power transmitting device of  claim 3  wherein the control circuitry is configured to measure the inductance values for the wireless power transmitting coils by applying impulses to the wireless power transmitting coils with the inverter circuitry and measuring corresponding impulse responses with the impulse response measurement circuitry. 
     
     
       5. The wireless power transmitting device of  claim 4  wherein the control circuitry is further configured to control the transmission of the wireless power signals by selecting a given coil in the array of wireless power transmitting coils to transmit the wireless power signals based at least partly on the measured inductance values. 
     
     
       6. A wireless power transmitting device configured to transmit wireless power signals to a wireless power receiving device, comprising:
 an array of wireless power transmitting coils; 
 inverter circuitry coupled to the array of wireless power transmitting coils; 
 inductance measurement circuitry coupled to the array of wireless power transmitting coils; and 
 control circuitry configured to:
 measure inductance values for at least some of the wireless power transmitting coils by applying impulses to the wireless power transmitting coils with the inverter circuitry and measuring corresponding impulse responses with the inductance measurement circuitry; and 
 determine whether foreign objects are present on the array of wireless power transmitting coils at least partly by comparing the measured inductance values to coil inductance values associated with presence of the wireless power receiving device on the array of wireless power transmitting coils in absence of any foreign objects. 
 
 
     
     
       7. The wireless power transmitting device of  claim 6  wherein the control circuitry is configured to measure an inductance value for each of the wireless power transmitting coils and is configured to use the measured inductance values in determining whether any foreign objects overlap a wireless power receiving coil in the wireless power receiving device. 
     
     
       8. The wireless power transmitting device of  claim 7  wherein the control circuitry is configured to:
 store sets of the coil inductance values that are associated with the presence of the wireless power receiving device on the array of wireless power transmitting coils in the absence of any foreign objects. 
 
     
     
       9. The wireless power transmitting device of  claim 6  wherein the inductance measurement circuitry comprises impulse response measurement circuitry coupled to the array of wireless power transmitting coils. 
     
     
       10. The wireless power transmitting device of  claim 6  wherein the control circuitry is further configured to control the transmission of the wireless power signals by selecting a given coil in the array of wireless power transmitting coils to transmit the wireless power signals based at least partly on the measured inductance values. 
     
     
       11. The wireless power transmitting device of  claim 6  wherein the control circuitry is configured to block transmission of the wireless power signals in response to determining that a foreign object is present. 
     
     
       12. The wireless power transmitting device of  claim 6  wherein the control circuitry is configured to transmit the wireless power signals in response to determining that no foreign objects are present by comparing the measured inductance values to the coil inductance values. 
     
     
       13. A wireless power transmitting device configured to transmit wireless power signals to a wireless power receiving device, comprising:
 an array of wireless power transmitting coils, wherein the wireless power transmitting coils have a nominal inductance value in absence of foreign objects and the wireless power receiving device; 
 wireless power transmitter circuitry coupled to the array of wireless power transmitting coils; 
 inductance measurement circuitry coupled to the array of wireless power transmitting coils; and 
 control circuitry configured to:
 measure inductance values for at least some of the wireless power transmitting coils with the inductance measurement circuitry; and 
 compare the measured inductance values to sets of coil inductance values for the array of wireless power transmitting coils that are associated with presence of the wireless power receiving device on the array of wireless power transmitting coils in absence of foreign objects, wherein each one of the coil inductance values in each set is different than the nominal inductance value. 
 
 
     
     
       14. The wireless power transmitting device of  claim 13  wherein the control circuitry is configured to block transmission of the wireless power signals in response to determining that the measured inductance values do not match any of the sets of coil inductance values. 
     
     
       15. The wireless power transmitting device of  claim 14  wherein the control circuitry is configured to transmit the wireless power signals in response to determining that the measured inductance values match one of the sets of coil inductance values. 
     
     
       16. The wireless power transmitting device of  claim 15  wherein the control circuitry is configured to store the sets of the coil inductance values for comparing to measured inductance values. 
     
     
       17. The wireless power transmitting device of  claim 16  wherein the inductance measurement circuitry comprises impulse response measurement circuitry. 
     
     
       18. The wireless power transmitting device of  claim 15  wherein the control circuitry is further configured to control the transmission of the wireless power signals by selecting a given coil in the array of wireless power transmitting coils to transmit the wireless power signals based at least partly on the measured inductance values. 
     
     
       19. The wireless power transmitting device of  claim 13  wherein the control circuitry is configured to determine whether the wireless power receiving device is present on the array in absence of foreign objects by comparing only those measured inductance values that differ from the nominal coil inductance value to the sets of coil inductance values.

Description:
This application claims priority to U.S. provisional patent application No. 62/453,859, filed on Feb. 2, 2017, and provisional patent application No. 62/457,743, filed on Feb. 10, 2017, which are hereby incorporated by reference herein in their entireties. 
    
    
     FIELD 
     This relates generally to wireless systems, and, more particularly, to systems in which devices are wirelessly charged. 
     BACKGROUND 
     In a wireless charging system, a wireless power transmitting device such as a device with a charging surface wirelessly transmits power to a portable electronic device. The portable electronic device receives the wirelessly transmitted power and uses this power to charge an internal battery and to power components in the portable electronic device. 
     It can be challenging to regulate the flow of wireless power in a wireless charging system. For example, in a wireless charging system having a wireless charging surface with an array of wireless power transmitting coils, it can be difficult to determine which coils to use to effectively transmit wireless power to a portable electronic device. It can also be difficult to detect the presence of foreign objects on the wireless charging surface. 
     SUMMARY 
     A wireless power transmission system has a wireless power receiving device that is located on a charging surface of a wireless power transmitting device. The wireless power receiving device has a wireless power receiving coil and the wireless power transmitting device has a wireless power transmitting coil array. Control circuitry may use inverter circuitry in the wireless power transmitting device to supply alternating-current signals to coils in the coil array, thereby transmitting wireless power signals. 
     Impulse response measurement circuitry coupled to the coil array may make impulse response measurements while the control circuitry uses the inverter circuitry to apply impulse signals to each of the coils. The control circuitry can analyze measurements made with the impulse response measurement circuitry to determine the values of inductances associated with the coils in the coil array. 
     By using processing techniques such as expression-based and look-up-table-based non-linear interpolation techniques, the control circuitry can determine the location of the wireless power receiving coil relative to the coils of the coil array. This information and additional information associated with the measured inductances of the coils in the wireless power transmitting device can be used in taking actions such as making wireless power transmission adjustments, adjusting the display of information on a display in the wireless power transmitting device, and setting maximum transmit power levels. 
     Foreign objects on the coil array such as foreign objects that are overlapped by a wireless power receiving coil in a wireless power receiving device can be detected by comparing measured inductance values to sets of coil inductances that are known to be associated with the presence of a power receiving device in the absence of foreign objects. In response to detecting that a foreign object is present, wireless power transmission operations can be blocked or other suitable action can be taken. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an illustrative wireless charging system in accordance with embodiments. 
         FIG. 2  is a circuit diagram of an illustrative wireless charging system in accordance with an embodiment. 
         FIG. 3  is a graph of an illustrative impulse response to an applied impulse signal in a wireless charging system in accordance with an embodiment. 
         FIG. 4  is a diagram of illustrative wireless power transmitting and wireless power receiving circuitry in accordance with an embodiment. 
         FIG. 5  is a top view of an illustrative wireless power transmitting device with an array of coils that forms a wireless charging surface in accordance with an embodiment. 
         FIG. 6  is a graph showing illustrative inductances produced in first and second wireless power transmitting coils in a wireless power transmitting device as a function of wireless power receiving device coil location in accordance with an embodiment. 
         FIG. 7  is a diagram showing how inductance measurements from a set of wireless power transmitting coils can be used to determine the location of a wireless power receiving coil that overlaps a wireless charging surface in accordance with an embodiment. 
         FIG. 8  is a flow chart of illustrative operations involved in operating a wireless power transfer system in accordance with an embodiment. 
         FIG. 9  is a top view of an illustrative wireless power transmitting device on which a receiving device and a foreign object that is overlapped by a receiving coil in the receiving device are present overlapping coils in a coil array in the wireless power transmitting device in accordance with an embodiment. 
         FIG. 10  is a graph showing how inductances for coils in a coil array vary in the presence of a wireless power receiving device coil at various locations relative to the coils and are perturbed due to the presence of foreign objects overlapping the coils in accordance with an embodiment. 
         FIG. 11  is a diagram showing how inductance measurements can be used to locate a wireless power receiving device coil on a wireless power transmitting device coil array in the absence of a foreign object in accordance with an embodiment. 
         FIG. 12  is a diagram showing how inductance measurements can be used to determine that a foreign object is present in the vicinity of a wireless power receiving device coil so that wireless power transmission operations can be halted or other suitable action taken in accordance with an embodiment. 
         FIG. 13  is a diagram of an illustrative coil array with fifteen coils that is being overlapped by a wireless receiving device in accordance with an embodiment. 
         FIG. 14  is a table showing how measured inductance values for the coils in the coil array (e.g., inductance values that vary from a nominal coil inductance) match a predetermined valid set of coil inductance values in accordance with an embodiment. 
         FIG. 15  is a diagram of an illustrative coil array with fifteen coils that is being overlapped by a wireless receiving device and a foreign object in accordance with an embodiment. 
         FIG. 16  is a table showing how measured inductance values for the coils in the coil array of  FIG. 15  do not match any predetermined valid set of measured inductance values indicating that the foreign object of  FIG. 15  is present on the coil array in accordance with an embodiment. 
         FIG. 17  is a flow chart of illustrative operations involved in operating a wireless power transmission system in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A wireless power system has a wireless power transmitting device that transmits power wirelessly to a wireless power receiving device. The wireless power transmitting device is a device such as a wireless charging mat, wireless charging puck, wireless charging stand, wireless charging table, or other wireless power transmitting equipment. The wireless power transmitting device has one or more coils that are used in transmitting wireless power to one or more wireless power receiving coils in the wireless power receiving device. The wireless power receiving device is a device such as a cellular telephone, watch, media player, tablet computer, pair of earbuds, remote control, laptop computer, other portable electronic device, or other wireless power receiving equipment. 
     During operation, the wireless power transmitting device supplies alternating-current drive signals to one or more wireless power transmitting coils. This causes the coils to transmit alternating-current electromagnetic signals (sometimes referred to as wireless power signals) to one or more corresponding coils in the wireless power receiving device. Rectifier circuitry in the wireless power receiving device converts received wireless power signals into direct-current (DC) power for powering the wireless power receiving device. 
     The position at which a wireless power receiving device is located on a wireless charging surface affects electromagnetic coupling (coupling coefficient k) between the coil(s) in the wireless power receiving device and each of the coils in the charging surface. The inductance of each transmitting coil may also be affected by the placement of the wireless power receiving device on the charging surface. For example, the inductance of a particular wireless power transmitting coil will increase when a wireless power receiving coil and the corresponding ferrite or other magnetic material in that coil overlaps the power transmitting coil. By making inductance measurements on the array of wireless power transmitting coils in a wireless power transmitting device, the location of one or more wireless power receiving coils relative to each of the wireless power transmitting coils can be determined. Information on the size and orientation of the wireless power receiving device may also be determined. Based on the inductance measurements and other information, the settings of wireless power transmitting circuitry in the wireless power transmitting device may be adjusted to help enhance wireless power transfer operations. If desired, one or more coils in a wireless power transmitting device may be driven with appropriate weight(s), wireless power transmission limits may be established, content may be displayed on a display, and other actions may be taken. In some situations, incompatible objects such as coins or other foreign objects may be present in the vicinity of a wireless power receiving device. For example, a wireless power receiving device coil may overlap a foreign object. By comparing measured inductance values to predetermined valid sets of coil inductances, the presence of a foreign object may be detected so that wireless power transmission operations may be blocked or other suitable action taken. 
     An illustrative wireless power system (wireless charging system) is shown in  FIG. 1 . As shown in  FIG. 1 , wireless power system  8  includes wireless power transmitting device  12  and one or more wireless power receiving devices such as wireless power receiving device  10 . Device  12  may be a stand-alone device such as a wireless charging mat, may be built into furniture, or may be other wireless charging equipment. Device  10  is a portable electronic device such as a wristwatch, a cellular telephone, a tablet computer, or other electronic equipment. Illustrative configurations in which device  12  is a mat or other equipment that forms a wireless charging surface and in which device  10  is a portable electronic device that rests on the wireless charging surface during wireless power transfer operations are sometimes be described herein as examples. 
     During operation of system  8 , a user places one or more devices  10  on the charging surface of device  12 . Power transmitting device  12  is coupled to a source of alternating-current voltage such as alternating-current power source  50  (e.g., a wall outlet that supplies line power or other source of mains electricity), has a battery such as battery  38  for supplying power, and/or is coupled to another source of power. A power converter such as alternating-current-to-direct current (AC-DC) power converter  40  can convert power from a mains power source or other alternating-current (AC) power source into direct-current (DC) power that is used to power control circuitry  42  and other circuitry in device  12 . During operation, control circuitry  42  uses wireless power transmitting circuitry  34  and one or more coil(s)  36  coupled to circuitry  34  to transmit alternating-current electromagnetic signals  48  to device  10  and thereby convey wireless power to wireless power receiving circuitry  46  of device  10 . 
     Power transmitting circuitry  34  has switching circuitry (inverter circuitry) that supplies AC signals (drive signals) to one or more of coils  36  during wireless power transfer operations. One or more coils  36  may be used at a time for wireless power transfer. For example, a single coil  36  may supply power to a single receiving device that overlaps that coil, two coils  36  (e.g., adjacent coils) may supply power to a single device overlapping those two coils or to a pair of devices overlapping those coils, three or more coils may be driven to supply power to a single overlapping receiving device or to multiple overlapping receiving devices, two or more coils or three or more coils that are not adjacent to each other may be driven simultaneously to supply power to two or more or three or more devices at different respective locations on the coil array, etc. 
     The inverter circuitry that supplies the drive signals to coils  36  may include a single pair of transistors or other inverter circuit coupled to multiple coils  36  through multiplexer circuitry (e.g., to allow those transistors to be shared between multiple coils), may include a pair of transistors or other inverter circuit associated with each coil, and/or may include other inverter circuit arrangements that allow alternating-current drive signals to be supplied to one or more selected coils  36 . 
     During power transfer operations, transistors in the inverter circuitry are turned on and off based on control signals provided by control circuitry  42 . In configurations in which multiple coils have multiple respective inverter circuits, the transistors in the active coils (coils selected for wireless power transfer) may be turned on and off without turning on and off the transistors in the inactive coils. In configurations in which multiplexing circuitry is used to couple the inverter circuitry to selected coils, the multiplexing circuitry is configured appropriately to route AC signals from the inverter circuitry to the selected coils. As the AC signals pass through one or more coils  36  that have been selected for supplying wireless power, alternating-current electromagnetic fields (wireless power signals  48 ) are produced that are received by corresponding coil(s)  14  coupled to wireless power receiving circuitry  46  in receiving device  10 . When the alternating-current electromagnetic fields are received by coil  14 , corresponding alternating-current currents and voltages are induced in coil  14 . Rectifier circuitry in circuitry  46  converts received AC signals (received alternating-current currents and voltages associated with wireless power signals) from coil(s)  14  into DC voltage signals for powering device  10 . The DC voltages are used in powering components in device  10  such as display  52 , touch sensor components and other sensors  54  (e.g., accelerometers, force sensors, temperature sensors, light sensors, pressure sensors, gas sensors, moisture sensors, magnetic sensors, etc.), wireless communications circuits  56  for communicating wirelessly with corresponding wireless communications circuitry  58  in control circuitry  42  of wireless power transmitting device  12  and/or other equipment, audio components, and other components (e.g., input-output devices  22  and/or control circuitry  20 ) and are used in charging an internal battery in device  10  such as battery  18 . 
     Devices  12  and  10  include control circuitry  42  and  20 . Control circuitry  42  and  20  includes storage and processing circuitry such as microprocessors, power management units, baseband processors, digital signal processors, microcontrollers, and/or application-specific integrated circuits with processing circuits. Control circuitry  42  and  20  is configured to execute instructions for implementing desired control and communications features in system  8 . For example, control circuitry  42  and/or  20  may be used in determining power transmission levels, processing sensor data, processing user input, processing other information such as information on wireless coupling efficiency from transmitting circuitry  34 , processing information from receiving circuitry  46 , using sensing circuitry to measure coil inductances and other parameters, processing measured inductance values, using information from circuitry  34  and/or  46  such as signal measurements on output circuitry in circuitry  34  and other information from circuitry  34  and/or  46  to determine when to start and stop wireless charging operations, adjusting charging parameters such as charging frequencies, coil settings (e.g., which coils are active and weights for active coils) in a multi-coil array, and wireless power transmission levels, and performing other control functions. Control circuitry  42  and  20  may be configured to support wireless communications between devices  12  and  10  (e.g., control circuitry  20  may include wireless communications circuitry such as circuitry  56  and control circuitry  42  may include wireless communications circuitry such as circuitry  58 ). Control circuitry  42  and/or  20  may be configured to perform these operations using hardware (e.g., dedicated hardware or circuitry) and/or software (e.g., code that runs on the hardware of system  8 ). Software code for performing these operations is stored on non-transitory computer readable storage media (e.g., tangible computer readable storage media). 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, other computer readable media, or combinations of these computer readable media or other storage. Software stored on the non-transitory computer readable storage media may be executed on the processing circuitry of control circuitry  42  and/or  20 . The processing circuitry may include application-specific integrated circuits with processing circuitry, one or more microprocessors, or other processing circuitry. 
     Device  12  and/or device  10  may communicate wirelessly during operation of system  8 . Devices  10  and  12  may, for example, have wireless transceiver circuitry in control circuitry  20  and  42  (see, e.g., wireless communications circuitry such as circuitry  56  and  58  of  FIG. 1 ) that allows wireless transmission of signals between devices  10  and  12  (e.g., using antennas that are separate from coils  36  and  14  to transmit and receive unidirectional or bidirectional wireless signals, using coils  36  and  14  to transmit and receive unidirectional or bidirectional wireless signals, etc.). 
     A circuit diagram of illustrative circuitry for wireless power transfer (wireless power charging) system  8  is shown in  FIG. 2 . As shown in  FIG. 2 , wireless power transmitting circuitry  34  includes an inverter such as inverter  70  or other drive circuit that produces alternating-current drive signals such as variable-duty-cycle square waves or other drive signals. These signals are driven through an output circuit such as output circuit  71  that includes coil(s)  36  and capacitor(s)  72  to produce wireless power signals that are transmitted wirelessly to device  10 . 
     Coil(s)  36  are electromagnetically coupled with coil(s)  14 . A single coil  36  and single corresponding coil  14  are shown in the example of  FIG. 2 . In general, device  12  may have any suitable number of coils (1-100, more than 5, more than 10, fewer than 40, fewer than 30, 5-25, etc.) and device  10  may have any suitable number of coils. Switching circuitry (sometimes referred to as multiplexer circuitry) that is controlled by control circuitry  42  can be located before and/or after each coil (e.g., before and/or after each coil  36  and/or before and/or after the other components of output circuit  71  in device  12 ) to couple the array of coils to inverter  70  and can be used to switch desired sets of one or more coils (e.g., coils  36  and output circuits  71  in device  12 ) into or out of use. For example, if it is determined that device  10  is located in a position that overlaps a particular coil  36  in device  12 , the coil  36  overlapping device  10  may be activated during wireless power transmission operations while other coils  36  (e.g., coils not overlapped by device  10  in this example) are turned off. 
     Control circuitry  42  and control circuitry  20  contain wireless transceiver circuits (e.g., circuits such as wireless communication circuitry  56  and  58  of  FIG. 1 ) for supporting wireless data transmission between devices  12  and  10 . In device  10 , control circuitry  20  (e.g., communications circuitry  56 ) can use path  91  and coil  14  to transmit data to device  12 . In device  12 , paths such as path  74  may be used to supply incoming data signals that have been received from device  10  using coil  36  to demodulating (receiver) circuitry in communications circuitry  58  of control circuitry  42 . If desired, path  74  may be used in transmitting wireless data to device  10  with coil  36  that is received by receiver circuitry in circuitry  56  of circuitry  20  using coil  14  and path  91 . Configurations in which circuitry  56  of circuitry  20  and circuitry  58  of circuitry  42  have antennas that are separate from coils  36  and  14  may also be used for supporting unidirectional and/or bidirectional wireless communications between devices  12  and  10 , if desired. 
     During wireless power transmission operations, transistors in inverter  70  are controlled using AC control signals from control circuitry  42 . Control circuitry  42  uses control path  76  to supply control signals to the gates of the transistors in inverter  70 . The duty cycle and/or other attributes of these control signals and therefore the corresponding characteristics of the drive signals applied by inverter  70  to coil  36  and the corresponding wireless power signals produced by coil  36  can be adjusted dynamically. Using switching circuitry, control circuitry  42  selects which coil or coils to supply with drive signals. Using duty cycle adjustments and/or other adjustments (e.g., drive frequency adjustments, etc.), control circuitry  42  can adjust the strength of the drive signals applied to each coil. A single selected coil may be used in transmitting power wirelessly from device  12  to device  10  or multiple coils  36  may be used in transmitting power. One or more devices  10  may receive wireless power and each of these devices may have one or more wireless power receiving coils that receive power from one or more corresponding wireless power transmitting coils. 
     Wireless power receiving device  10  has wireless power receiving circuitry  46 . Circuitry  46  includes rectifier circuitry such as rectifier  80  (e.g., a synchronous rectifier controlled by signals from control circuitry  20 ) that converts received alternating-current signals from coil  14  (e.g., wireless power signals received by coil  14 ) into direct-current (DC) power signals for powering circuitry in device  10  such as load  100 . Load circuitry such as load  100  may include battery  18 , a power circuit such as a battery charging integrated circuit or other power management integrated circuit(s) that receives power from rectifier circuitry  80  and regulates the flow of this power to battery  18 , and/or other input-output devices  22 . One or more capacitors C 2  are used to couple coil  14  in input circuit  90  of device  10  to input terminals for rectifier circuitry  80 . Rectifier circuitry  80  produces corresponding output power at output terminals that are coupled to load  100 . If desired, load  100  may include sensor circuitry (e.g., current and voltage sensors) for monitoring the flow of power to load  100  from rectifier  80 . 
     The inductance L of each wireless power transmitting coil  36  in device  12  can be affected (e.g., increased) by the presence of overlapping coil(s)  14  and associated magnetic material (e.g., ferrite core material, etc.) in device  10 . The location(s) of coil(s)  14  can therefore be determined by making inductance measurements on each of coils  36  and processing these measurements (e.g., using interpolation techniques, etc.). In situations in which a metal coin or other foreign object is present on the coil array (e.g., under coil  14  or elsewhere on the coil array), the presence of the foreign object may be detected by comparing the measured inductances of coils  36  to predetermined valid sets of coil inductances. If a match between a set of measured inductances and valid set of previously measured inductances is detected, it can be concluded that only device  10  is present and that no foreign objects are present, so wireless power transmission operations may be performed. If no match is detected, it can be concluded that a foreign object is likely to be present and wireless power transmission operations may be blocked (e.g., no wireless power transmission operations may be performed) or other suitable action may be taken (e.g., a visual alert may be issued for a user using a light-emitting component such as a status indicator light-emitting diode, a display, etc., an audible alert may be issued using a sound-emitting component such as a tone generator or speaker, a haptic alert may be issued using a haptic device such as a vibrator), and/or other actions may be taken. 
     During wireless power transmission operations, transistors in inverter  70  are driven by AC control signals from control circuitry  42 . Control circuitry  42  may also use inverter  70  to apply square wave impulse pulses or other impulses to each coil  36  during impulse response measurements. Impulse response measurement circuitry  102  is coupled to output circuit  71 . For example, circuitry  102  may be coupled to node N in output circuit  102  using path  104 . Control circuitry  42  uses impulse response measurement circuitry  102  to make measurements on output circuit  71  (e.g., measurements on the inductance L of coil  36 , measurements of quality factor Q, etc.). 
     Each coil  36  in device  12  (e.g., a coil such as coil  36  of  FIG. 2  that has been selected by control circuitry  42  using multiplexing circuitry in wireless transmitter circuitry  34 ) has an inductance L. One or more capacitors in output circuit  71  such as capacitor  72  exhibit a capacitance C 1  that is coupled in series with inductance L in output circuit  71 . When supplied with alternating-current drive signals from inverter  70 , the output circuit formed from coil  36  and capacitor  72  will produce alternating-current electromagnetic fields that are received by coil(s)  14  in device  10 . The inductance L of each coil  36  is influenced by magnetic coupling with external objects, so measurements of inductance L for each coil  36  in device  12  can reveal information on device(s)  10  on the charging surface of device  12 . 
     During impulse response measurements, circuitry  42  uses impulse response measurement circuitry  102  (sometimes referred to as inductance measurement circuitry and/or Q factor measurement circuitry) to perform measurements of inductance L and quality factor Q. Impedance measurements and other measurements with circuitry  102  may be initiated in response to detection of an external object on device  12  using a foreign object detection sensor (e.g., a sensor using coils  36  and/or other coils, a sensor using light-based sensing, capacitive based sensing, or other sensing techniques, etc.). Impedance measurements and other measurements with circuitry  102  may also be initiated in response to manual input, based on wirelessly received commands, etc. During the measurements, control circuitry  42  directs inverter  70  to supply one or more excitation pulses (impulses) to each coil  36 , so that the inductance L and capacitance C 1  of the capacitor  72  in the output circuit  71  that includes that coil  36  form a resonant circuit. The impulses may be, for example, square wave pulses of 1 μs in duration. Longer or shorter pulses and/or pulses of other shapes may be applied, if desired. The resonant circuit resonates at a frequency near to the normal wireless charging frequency of coil  36  (e.g., about 120 kHz, 50-300 kHz, about 240 kHz, 100-500 kHz, more than 75 kHz, less than 400 kHz, or other suitable wireless charging frequency) or may resonate at other frequencies. 
     The impulse response (e.g., the voltage V(N) at node N of circuit  71 ) to the applied pulse(s) is as shown in  FIG. 3 . The frequency of the impulse response signal of  FIG. 3  is proportional to 1/sqrt(LC 1 ), so L can be obtained from the known value of C 1  and the measured frequency of the impulse response signal. Q may be derived from L and the measured decay of the impulse response signal. As shown in  FIG. 3 , if signal V(N) decays slowly, Q is high (e.g., HQ) and if signal V(N) decays more rapidly, Q is low (e.g., SQ). Measurement of the decay envelope of V(N) and frequency of V(N) of the impulse response signal of  FIG. 3  with circuitry  102  will therefore allow control circuitry  42  to determine Q and L. 
       FIG. 4  shows how wireless power transmitting circuitry  34  includes switching circuitry  110 . Signals from inverter circuitry  70  are applied to switching circuitry  110  at input  112 . Switching circuitry  110  forms part of wireless power transmitting circuitry  34  (sometimes referred to as inverter circuitry). Control signals applied to control input  116  by control circuitry  42  direct switching circuitry  110  to route the signals from input  112  to a selected one of coils  36  in an array of coils  36  in device  12 . Wireless power receiving circuitry  46  of device  10  includes one or more coils  14 . In configurations for device  10  that include multiple coils  14 , coils  14  are coupled to switching circuitry  120 . Control circuitry  20  applies control signals to control input  122  that direct switching circuitry  120  to route signals from a selected one of coils  14  to rectifier  80  via output terminals  124 . 
     With one illustrative configuration for wireless transmitting device  12 , wireless transmitting device  12  is a wireless charging mat or other wireless power transmitting equipment that has an array of coils  36  that supply wireless power over a wireless charging surface. This type of arrangement is shown in  FIG. 5 . In the example of  FIG. 5 , device  12  has an array of coils  36  that lie in the X-Y plane. Coils  36  of device  12  are covered by a planar dielectric structure such as a plastic member or other structure forming charging surface  60 . The lateral dimensions (X and Y dimensions) of the array of coils  36  in device  36  may be 1-1000 cm, 5-50 cm, more than 5 cm, more than 20 cm, less than 200 cm, less than 75 cm, or other suitable size. Coils  36  may overlap or may be arranged in a non-overlapping configuration. Coils  36  can be placed in a rectangular array having rows and columns and/or may be tiled using a hexagonal tile pattern, a pattern with square tiles, or other pattern. 
     When a user places device  10  on charging surface  60 , coil  14  (or multiple coils  14  in configurations in which device  10  contains multiple coils) will overlap one or more coils  36 . In the example of  FIG. 5 , coil  14  of device  10  is overlapping coil  36 ′ (e.g., the center of coil  14  is aligned with the center of coil  36 ′). Device  10  in the example of  FIG. 5  has a rectangular footprint (outline when viewed from above) and is characterized by longitudinal axis  130 . Axis  130  is aligned at an angle A with respect to horizontal axis X in  FIG. 5  (e.g., an angle of 0-360°). Knowledge of the location of the center of coil  14  and the value of angle A (the angular orientation of device  10  relative to device  12 ) can be used to adjust charging system parameters (e.g., to make transmitting coil selections, to adjust maximum transmit powers, and/or to adjust other system settings). 
     Control circuitry  42  uses impedance measurement circuitry such as impulse response measurement circuitry  102  and switching circuitry  110  to measure L for each of coils  36  under charging surface  60 . If the measured value of L for a given coil matches the normal (nominal) L value expected for each of coils  36  in the array of coils  36  overlapping surface  60  (e.g., when the measured L value is not influenced by the presence of coil  14  or other portions of device  10 ), control circuitry  42  can conclude that no external object is present. If a given measured value of L is different than the nominal value of L, control circuitry  42  can conclude that a portion of the housing of device  10  is present (e.g., if a decrease in L has been measured) or that coil  14  is present (e.g., if an increase in L has been measured). The locations and L values of each measured coil  36  can be analyzed by control circuitry  42  to help detect which type of device  10  is present (e.g., impedance-change patterns can be used to help identify a watch or other small device, a cellular telephone, a tablet computer, etc.), to determine the location (center of coil  14  and/or center of device  10 ) of device  12 , and to determine the angular orientation A of device  12 . 
       FIG. 6  is a graph showing how measured inductance L varies as a function of the position of coil  14  on charging surface  60 . In the example of  FIG. 6 , a first of coils  36  is located at position (X,Y)=(0,0) and a second of coils  36  is located at position (X,Y)=(X1, 0). Curve  150  shows how the inductance of the first coil is highest when coil  14  is aligned with the first coil  36  and decreases as coil  14  is located at increasing distances X from the first coil. Curve  152  shows how the inductance of the second coil is highest when coil  14  is aligned with the second coil and decreases as coil  14  is located at increasing distances from the second coil (e.g., decreasing values of X). Curves  150  and  152  represent the non-linear relationships between L and receiver coil position relative to transmitter coil position. These non-linear relationships may be stored in device  12  using non-linear equations (e.g., non-linear expressions such as curve-fit nth-order polynomials where n is 2-7, more than 3, more than 2, less than 5, or other suitable value) and/or numerical look-up table entries. During non-linear interpolation operations, control circuitry  42  measures the inductance of the first and second coils and uses these inductance measurements to determine the locations of coil  14 . In the example of  FIG. 6 , the measured inductance of the first coil is L 1  and the measured inductance of the second coil is L 2 . Control circuitry  42  uses interpolation (e.g., expression-based non-linear interpolation or look-up-table-based non-linear interpolation) to determine coil position XD (e.g., the position of coil  14  relative to the first and second coils  36 ) from the measured values of L 1  and L 2 . 
     In the  FIG. 6  example, device  10  has a coil  14  that partly overlaps two coils  36 . If desired, interpolation techniques may be used to determine the position of coil  14  (X,Y) on charging surface  60  from more than two coil inductance measurements. For example, the position of coil  14  can be determined by measuring the changes in inductance of three of coils  36  that are affected by the presence of coil  14 , as illustrated in  FIG. 7 . 
     In the configuration of  FIG. 7 , a first of wireless power transmitting coils  36  has center point CP 1 , a second of wireless power transmitting coils  36  has center point CP 2 , and a third of wireless power transmitting coils  36  has center point CP 3 . The center of wireless power receiving coil  14  is located at center point RXCP. The amount of inductance increase due to the overlap of coil  14  and the first of coils  36  is related to the distance R 1  between center point CP 1  and center point RXCP. The inductance increases experienced by the second and third of coils  36  are likewise correspondingly related to the distance R 2  between center points CP 2  and RXCP and the distance R 3  between center points CP 3  and RXCP. By measuring the first, second, and third inductances (L 1 , L 2 , and L 3 ) of the first, second, and third coils, and by using control circuitry  42  to apply the non-linear relationships of curves such as illustrative inductance-versus-distance curve  150  of  FIG. 6  (e.g., using non-linear curve-fit polynomials or other non-linear expressions, using look-up table entries, etc.), control circuitry  42  can determine the values of R 1 , R 2 , and R 3  from the measured inductances of the first, second, and third coils  36  in  FIG. 7  and can therefore compute the location (in X, Y) of center point RXCP for coil  14 . Determining the location of coil  14  relative to coils  36  in this way allows control circuitry  42  to determine the location of device  10  relative to device  14  and the array of coils  36  in charging surface  60 . 
     Inductance measurements can also be made to determine the location and orientation of the housing for device  10  and therefore the value of angular orientation A. For example, device  10  may have a housing formed from metal or other material that tends to lower the measured inductance for transmitting coils  36  that are overlapped by the housing. In scenarios in which the outline of device  10  is rectangular, the array of coils  36  under surface  60  may experience a corresponding rectangular set of inductance decreases. The outline of device  10  can be measured by using control circuitry  42  to recognize a rectangular pattern of lowered L values or other changed L values. By measuring the location of a rectangular set of reduced inductance values (e.g., a pattern of reduced coil inductances that have the shape of a known device  10 , which may surround a measured increase in inductance for a particular coil or coils such as the three coils of  FIG. 6 ), the location (X,Y position) and angular orientation (angle A of  FIG. 5 ) may be determined. Information on the location and angular orientation of device  10  can be used by control circuitry  42  to adjust system parameters (e.g., to set maximum charging powers, to select a coil or coils for transmitting wireless power, etc.). Additional actions that may be taken based on inductance measurements, recognized patterns of inductance changes, and other measurements on coils  36  include coordinating the display of information on the display of device  12  (e.g., controlling the angular orientation of on-screen content based on a measured value of angular orientation A), moving displayed information seamlessly between different devices  10  and different locations and orientations on charging surface  60 , facilitating communications between devices  10 , etc. 
       FIG. 8  is a flow chart of illustrative operations involved in using charging system  8 . 
     During the operations of block  200 , control circuitry  42  applies impulses (square wave pulses or other pulses) to output circuit  71  and an associated wireless power transmitting coil  36  in output circuit  71  using inverter  70 . This process is performed for each coil  36  in the array of wireless power transmitting coils in wireless charging surface  60 . Switching circuitry  110  is adjusted by control circuitry  42  so that each coil  36  is provided with a respective impulse from control circuitry  42 . As each impulse is applied to the output circuit associated with a respective coil  36 , control circuit  42  uses impulse response measurement circuit  102  to determine parameters such as coil inductance L, resonant frequency, Q-factor, etc. For example, control circuitry  42  can derive inductance L from a measurement of the resonant frequency of the signal measured at node N by circuitry  102  in response to an impulse applied to output circuit  71 . 
     After measuring L and, if desired, other parameters associated with each output circuit  71  and coil  36  in charging surface  60 , control circuitry processes these measurements using techniques such as non-linear interpolation. In particular, during the operations of block  202 , control circuitry  42  uses non-linear relationships such as the non-linear curves of  FIG. 6  to determine the distance of coil  14  from each of multiple coils  36  that have experienced respective inductance increases. The non-linear L-versus-distance relationships of the  FIG. 6  curves may be embodied in expressions maintained by control circuitry  42  and/or look-up tables that are maintained by control circuitry  42 . 
     The operations of block  202  may also involve pattern detection operations. If, as an example, the inductances L of a set of coils  36  decrease along a rectangular path, control circuitry  42  can conclude that a wireless power receiving device is present on charging surface  60  that has a matching rectangular outline with a corresponding rectangular metal peripheral housing member. The size of the rectangular outline and the angular orientation of the rectangular outline (e.g., the angular orientation A of device  10  of  FIG. 5 ) may be determined. As another example, control circuitry  42  can detect that a wristwatch or other small device is present. When multiple devices  10  are present, control circuitry  42  detects the coil locations and angular orientations of each device relative to surface  60  and relative to each other. 
     During the operations of block  204 , control circuitry  42  takes actions based on the information gathered during the operations of blocks  200  and  202 . For example, if it is determined that a small device with a correspondingly small maximum wireless power capability is present, control circuitry  42  can set a maximum wireless power transmission limit for device  12  at an appropriately low value. If, on the other hand, control circuitry  42  recognizes from the processing operations of block  202  that device  10  is a larger device with a larger maximum wireless power capability, control circuitry can set the maximum wireless power transmission limit to a higher value to help reduce charging time. The location of the center point RXCP of coil  14  may be used to determine which of coils  36  should be used in transmitting wireless power to device  10 . For example, control circuitry  42  may use the coil  36  that is closest and therefore best coupled to coil  14  to perform wireless charging. Configurations in which a set of multiple coils  36  (e.g., those coils  36  that are overlapped by coil  14  such as the three coils  36  that are overlapped by coil  14  in  FIG. 7 ) are activated at the same time based on processed inductance information may also be used. If desired, some of coils  36  may be deactivated based on measured inductance information (e.g., those coils  36  that do not exhibit inductance increases due to overlap with coil  14  may be decoupled from inverter  70  and thereby deactivated during wireless power transmission operations with device  12 ). As these examples demonstrate, actions can be taken based on measured inductance information (e.g., wireless power can be transmitted based on this information and/or other wireless power transmission adjustments may be made, etc.). 
     If desired, information on the orientation of device  10  (e.g., angular orientation A of  FIG. 5 ) may be used in determining which coil(s)  36  to use in supplying power, may be used to coordinate the display of information on displays in multiple adjacent devices  10  (e.g., so that an icon or other visual item is displayed with the same upright orientation as that visual item is moved across each of several differently oriented devices  10  on charging surface  60 ), and/or may be used in performing other operations in system  8 . 
     Eddy currents may be induced in foreign objects such as coins that are present on the coil array. These eddy currents have the potential to undesirably heat the foreign objects. To avoid undesired heating, device  12  can automatically detect when a metal coin or other foreign object is present on the coil array (e.g., under coil  14 ). Device  12  may, for example, detect the presence of a foreign object by comparing the measured inductances of coils  36  to predetermined valid sets of coil inductances associated with coils  36  in the presence of device  10  and in the absence of any foreign objects. During characterization operations, a computer-controlled positioner or other positioner may move a power receiving device such as device  10  across the surface of the coil array while device  12  gathers inductance measurements from each of the coils. These characterization operations may produce a set of known valid sets of inductance values (e.g., sets of inductance values that are known to arise when device  10  is present on the coil array in the absence of any foreign objects). Unless device  12  detects a valid set of inductance values, device  12  can prevent wireless power transmission operations. In this way, device  12  can transit wireless power only when coil  14  is overlapping the coil array in the absence of foreign objects. 
       FIG. 9  is a top view of an illustrative wireless power transmitting device. In the example of  FIG. 9 , receiving device  10  with coil  14  is overlapping some of coils  36  in the coil array (e.g., coils C 1 , C 2 , C 6  and C 7 ). Foreign object  160  is also present in the vicinity of coil  14 . In particular, foreign object  160  is present on coil C 1 . Because object  160  overlaps coil C 1 , object  160  perturbs the inductance of coil C 1 . As a result, no valid set of coil inductances will be measured. Valid sets of coil inductances will also not be measured in scenarios in which only a foreign object overlaps the coil array (and device  10  is not present), because only coil  14  in device  10  will alter the inductances of coils  36  appropriately to match a valid set of coil inductances. 
       FIG. 10  is a graph showing how coil inductances (L) for coils  36  vary as a function of the position (in dimension X) of coil  14 . Curves  162  and  166  show how inductances L of coil C 1  and C 2  vary respectively as a function of the position of coil  14  in the absence of foreign object  160 . When coil  14  is aligned with coil C 1 , inductance L of coil C 1  will increase, as shown by the rising value of curve  162  at decreasing values of X. When coil  14  is aligned with coil C 2 , inductance L of coil C 2  will increase, as shown by the rising value of curve  166  at increasing values of X. At intermediate locations, the measured inductances of coils C 1  and C 2  will have intermediate values. 
     Curves  164  and  168  correspond to the respective measured inductance values L for coils C 1  and C 2  in the presence of foreign object  160 . Due to the presence of foreign object  160 , the expected valid values of inductance L for coils C 1  and C 2  will be perturbed. For example, the expected inductances of coil C 1  at each position of coil  14  will change from that of curve  162  to that of curve  164  and the expected inductances of coil C 2  at each position of coil  14  will change from that of curve  166  to that of curve  168 . 
     As a result of the perturbations of the coil inductances due to the presence of foreign object  160 , device  12  can detect whether foreign objects are present even when coil  14  overlaps a foreign object. Known valid inductance values (e.g., curves  162  and  166 ) can be stored in device  12 . When device  12  is preparing to transmit wireless power, the inductances of coils  36  can be measured and compared to the valid sets of coil inductances. A match will indicate that device  10  is present and that no foreign object is present, so charging can proceed. 
     Consider, as an example, a scenario in which the measured inductance of coil C 1  is given by inductance  170  of  FIG. 10  and in which the measured inductance of coil C 1  is given by inductance  172  of  FIG. 10 . Because these inductance measurements fall on valid inductance curves  162  and  166 , device  12  can conclude that foreign object  160  is not overlapping coil  14  (e.g., object  160  is not located between coil  14  and coil C 1  or is not otherwise present at a location that would perturb the measured inductance values). If, however, foreign object  160  is present at a location that overlaps coil C 1  and coil  14 , the values of inductance measured at coils C 1  and C 2  will not match any valid set of inductances for coils C 1  and C 2 . In particular, as the example of  FIG. 10  demonstrates, the presence of object  160  will cause the inductance of coil C 1  to drop significantly to the inductance of point  176 , whereas the inductance of coil C 2  will vary slightly (e.g., to the inductance of point  174  as opposed to the expected value of point  172 ). The set of measured inductances of coil C 1  and C 2  in this example (points  176  and  174 ) do not match any valid set of inductances on curves  162  and  166 , so device  12  can conclude that foreign object  160  is present and can take suitable action (e.g., power transmission operations can be blocked). 
     The top view diagram of  FIG. 11  illustrates how non-linear interpolation techniques may be used to ascertain the location of center point  156  of coil  14 . In the example of  FIG. 11 , the measured inductances of four coils has been used to establish estimated distances (radiuses) from respective coil center points CA, CB, CC, and CD to the center of coil  14 . Each inductance measurement has some measurement uncertainty and there is some measurement tolerance allowed when matching measured coil inductances to valid sets of coil inductances, so each radius in  FIG. 11  is represented by a band of possible distances (e.g., a circular ring of finite thickness). Overlap area  154  between each ring represents the area in which the center point of coil  14  may be located. Device  12  takes the center of this area (point  156 ) as the center of coil  14 . 
     In the presence of a foreign object, the set of measured inductances of the four coils will not match any valid set of inductances for the four coils. The foreign object may, as an example, overlap the lower right coil, causing the radius RD′ that is calculated from the measured inductance of the lower right coil to be perturbed. In this situation, the bands of possible radiuses RA, RB, RC, and RD′ established from the measured inductances of the coils will not overlap as expected. This lack of overlap is indicative that the set of measured inductances do not correspond to any predetermined valid set of coil inductances. Because there is no match between the set of measured inductances and a set of valid inductances, device  12  can conclude that a foreign object is present and  12  can block wireless power transmission operations. 
       FIG. 13  is a diagram of an illustrative coil array with fifteen coils C 1  . . . C 15 . In the scenario of  FIG. 13 , coil  14  of device  10  is overlapping coils C 2 , C 3 , C 7 , and C 8 . Device  12  measures coil inductances L 2 , L 3 , L 7 , and L 8  for coils C 2 , C 3 , C 7 , and C 8 , respectively, as shown in the last row of the table of  FIG. 14 . Coils C 2 , C 3 , C 7 , and C 8  may be, for example, the only coils in the coil array that have inductances that vary from a nominal coil inductance value. After measuring the inductances, device  12  compares this set of measured coil inductances to the known stored set of valid coil inductances L 2 , L 3 , L 7 , and L 8  shown in the first row of the table of  FIG. 14 . Because the measured and stored values matched (within the measurement tolerances depicted in  FIGS. 11 and 12 , for example), device  12  can conclude that no foreign object is present on charging surface  60  of  FIG. 13 . 
       FIG. 15  is a diagram of the illustrative array of coils  36  of  FIG. 13  in a scenario in which foreign object  160  is present at a location that overlaps coil  14 . As in the scenario of  FIG. 13 , coil  14  of device  10  is overlapping coils C 2 , C 3 , C 7 , and C 8  in the  FIG. 15  configuration. Device  12  measures coil inductances L 2 , L 3 , L 7 , and L 8  for coils C 2 , C 3 , C 7 , and C 8 , respectively, as shown in the last row of the table of  FIG. 16 . After measuring the inductances, device  12  compares this set of measured coil inductances to all known stored sets of valid coil inductances such as coil inductances L 2 , L 3 , L 7 , and L 8  shown in the first row of the table of  FIG. 16  (which are the same as the set of valid inductances in the first row of the table of  FIG. 14 ). Because the measured and stored values do not match (within the measurement tolerances depicted in  FIGS. 11 and 12 , for example), device  12  can conclude that foreign object  160  is present on charging surface  60  of  FIG. 15 . 
       FIG. 17  is a flow chart of illustrative operations involved in operating wireless power transmission system  8 . 
     During the operations of block  250  (e.g., in a factory or other calibration environment), device  12  (or a representative device of similar or identical construction) is characterized. During characterization measurements, the inductances of coils  36  are measured while placing device  10  and coil  14  (or a representative device and/or coil of similar or identical construction) at various locations across the surface of the coil array of device  12  (e.g., a grid of closely spaced locations covering all of the coil array or a representative subarea of the coil array). In this way, all of the possible valid combinations of measured inductances for coils  36  can be measured and each of these valid sets of inductances can be stored in storage in device  12 . 
     During normal operation (e.g., the operations of block  252 ), a user places device  10  on charging surface  60  of device  12 . Foreign object  160  may or may not be present at a location that overlaps coil  14  or other portion of the coil array. A foreign object detection sensor (e.g., a measurement circuit such as measurement circuit  104  or other suitable impedance measurement circuitry coupled to coils  36 , a separate foreign object detection sensor, and/or other object detection circuitry) is used by control circuitry  42  to monitor the coil array of device  12  for the presence of objects. So long as no objects are detected (e.g., the measured inductances and/or other electrical attributes of coils  36  remain constant), monitoring can continue, as illustrated by line  254 . If an object is detected (e.g., if circuitry  42  detects an increase in the inductance of one or more of coils  36 , etc.), processing may continue to the operations of block  256 . 
     During block  256 , control circuitry  42  uses measurement circuitry  102  to measure the inductance of coils  36  (e.g., all of coils  36  or a subset of coils adjacent to the location of the detected object, etc.). Within the measured inductances, a set of inductances with values that differ from the nominal inductance values of coils  36  can be identified (see, e.g., the measured inductances in the tables of  FIGS. 14 and 16 ). These inductance values are potentially indicative of the presence of device  10  and are accordingly analyzed by device  12 . 
     During the operations of block  258 , the set of inductance values measured at block  256  (e.g., the inductances that deviate from the nominal coil inductance) is compared to the sets of valid inductances stored in device  12  during the characterization operations of block  250 . The stored valid sets of inductances can be stored in a look-up table or may be stored in the form of equations that dynamically compute valid inductance sets to conserve storage space. The set of measured inductance values that is compared during the operations of block  258  may include only those measured inductance values that differ from a nominal coil inductance value (e.g., inductances that appear to be associated with an overlapping coil in a power receiving device). This may help to reduce the amount of processing involved in comparing measured inductances to sets of valid inductances. 
     The results of the comparison operations of block  258  are used by control circuitry  42  to control the transmission of wireless power to device  10 . 
     If a matching set of valid inductances is identified, device  12  can conclude that device  10  and coil  14  are present and that no foreign objects are present. Non-linear interpolation operations may be used to identify the center of coil  14  and suitable wireless power transmission operations may be performed (block  260 ). Initially, as an example, device  12  may transmit power using default settings to ensure that device  10  receives power sufficient for operating its communications circuitry. This allows device  10  and device  12  to establish a communications link and allows devices  10  and  12  to establish appropriate operating settings for device  12  and device  10  based on the measured location of coil  14  (block  262 ). A coil or multiple coils  36  in the coil array may be selected based at least partly on the measured inductance values. For example, the coil(s)  36  selected for wireless power transmission can be identified by determining the center of coil  14  using non-linear interpolation techniques or other coil location measurement techniques (e.g., techniques that use the measured inductance values of coils  36 ). 
     In response to determining that the measured set of inductances does not match any valid set of coil inductances, device  12  can halt wireless power transmission or take other appropriate action (block  264 ). For example, in addition to or instead of preventing device  12  from transmitting wireless power to device  10 , device  12  may alert a user of device  12  and device  10  that a foreign object is present (e.g., using a light-emitting device, an audio alert device, a haptic alert device, or other device on device  10  and/or device  12 , using wireless notifications, using notifications displayed on a display in device  10 , and/or using other alert mechanisms). 
     The foregoing is 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: 20170829
Publication Date: 20191210
Grant Date: 20191210
Priority Date: 20170202
Inventors: YANG, HENG
QIU, WEIHONG
MOUSSAOUI, ZAKI
Assignee: APPLE INC
CPC Classifications: [{"code": "H02J50/60", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/60", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/60", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/025", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02J50/90", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/60", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B5/79", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B5/24", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 62980771