PATENT DOCUMENT

Publication Number: US-10978918-B1
Application Number: US-202016782464-A
Country: US
Kind Code: B1

Title: Wireless power devices with capacitive foreign object detection sensors

Abstract:
A wireless power transmitting device uses a wireless power transmitting coil to transmit wireless power signals to a wireless power receiving device. The wireless power transmitting coil is located in a housing. The housing has a circular outline and contains one or more magnets that couple to corresponding magnets in the wireless power receiving device to help align a wireless power receiving coil in the wireless power receiving device to the wireless power transmitting coil in the wireless power transmitting device. A circular array of capacitive sensor electrodes is supported by the housing at a location that overlaps the wireless power transmitting coil. Capacitive sensor measurements from the capacitive sensor array are analyzed to determine whether a foreign object such as a coin or paperclip is present between the housing and the wireless power receiving device.

Claims:
What is claimed is: 
     
       1. A wireless power transmitting device for transmitting wireless power to a wireless power receiving device, comprising:
 a housing; 
 wireless power transmitting circuitry in the housing, wherein the wireless power transmitting circuitry has a wireless power transmitting coil configured to transmit wireless power signals to the wireless power receiving device through a charging surface; 
 a dielectric layer; 
 a circular array of capacitive sensor electrodes that overlap the wireless power transmitting coil and that are formed from a thin-film conductive layer on the dielectric layer; and 
 control circuitry configured to:
 gather capacitance measurements from each of the capacitive sensor electrodes; and 
 determine whether a foreign object is present on the charging surface based on the capacitance measurements. 
 
 
     
     
       2. The wireless power transmitting device of  claim 1  wherein the capacitive sensor electrodes each have a thickness of less than 10 microns. 
     
     
       3. The wireless power transmitting device of  claim 1  wherein the capacitive sensor electrodes each have a direct-current sheet resistance of 10 Ω/square-100 kΩ/square. 
     
     
       4. The wireless power transmitting device of  claim 1  wherein the capacitive sensor electrodes comprise an outer ring of capacitive sensor electrodes surrounding an inner ring of capacitive sensor electrodes. 
     
     
       5. The wireless power transmitting device of  claim 1  wherein the control circuitry is configured to determine whether the foreign object is present at least partly by determining whether any two of the capacitive sensor electrodes exhibit changed capacitance values relative to baseline capacitance values. 
     
     
       6. The wireless power transmitting device of  claim 1  wherein the wireless power transmitting device is configured to determine whether the foreign object is present at least partly by determining whether capacitance measurements from the array of capacitive sensor electrodes correspond to a wireless power receiving device at the charging surface. 
     
     
       7. The wireless power transmitting device of  claim 1  wherein the control circuitry is configured to halt wireless power transmission with the wireless power transmitting circuitry in response to determining that the foreign object is present. 
     
     
       8. The wireless power transmitting device of  claim 1  further comprising a calibration electrode, wherein the control circuitry is configured to calibrate the capacitive sensor electrodes by making capacitance measurements with at least one of the capacitive sensor electrodes and the calibration electrode. 
     
     
       9. The wireless power transmitting device of  claim 1  wherein the housing has a circular outline and comprises at least one magnet configured to attract a corresponding magnet in the wireless power receiving device. 
     
     
       10. The wireless power transmitting device of  claim 1  wherein the control circuitry comprises drive circuitry and sense circuitry and wherein the control circuitry is configured to gather the capacitance measurements by driving a signal onto each of the capacitive sensor electrodes in sequence with the drive circuitry while using the sense circuitry to measure corresponding signals on remaining electrodes in the capacitive sensor electrodes. 
     
     
       11. The wireless power transmitting device of  claim 1  wherein the control circuitry comprises drive circuitry and sense circuitry and wherein the control circuitry is configured to gather the capacitance measurements by driving a signal onto successive pairs of the capacitive sensor electrodes with the drive circuitry while using the sense circuitry to measure corresponding signals on remaining electrodes in the capacitive sensor electrodes. 
     
     
       12. A wireless power transmitting device for transmitting wireless power to a wireless power receiving device, comprising:
 a wireless power transmitting coil configured to transmit wireless power signals to the wireless power receiving device; 
 a first ring of capacitive sensor electrodes; 
 a second ring of capacitive sensor electrodes surrounding the first ring of capacitive sensor electrodes; and 
 control circuitry configured to:
 gather capacitance measurements from the first and second rings of capacitive sensor electrodes; and 
 determine whether a foreign object is present on the charging surface based on the capacitance measurements. 
 
 
     
     
       13. The wireless power transmitting device of  claim 12 , wherein the first and second rings of capacitive sensor electrodes overlap the wireless power transmitting coil, wherein the control circuitry comprises drive circuitry and sense circuitry, and wherein the control circuitry is configured to gather the capacitance measurements by driving a signal onto successive pairs of non-adjacent capacitive sensor electrodes in the first and second rings of capacitive sensor electrodes while using the sense circuitry to measure corresponding signals on remaining capacitive sensor electrodes in the first and second rings of capacitive sensor electrodes. 
     
     
       14. The wireless power transmitting device of  claim 12  wherein the control circuitry comprises drive circuitry and sense circuitry and wherein the control circuitry is configured to gather the capacitance measurements by driving a signal onto each of the capacitive sensor electrodes in sequence with the drive circuitry while using the sense circuitry to measure corresponding signals on remaining electrodes in the capacitive sensor electrodes. 
     
     
       15. The wireless power transmitting device of  claim 12  wherein the control circuitry comprises drive circuitry and sense circuitry and wherein the control circuitry is configured to gather the capacitance measurements by driving alternating-current signals onto at least one of the capacitive sensor electrodes with the drive circuitry while gathering signals from at least one other one of the capacitive sensor electrodes with the sense circuitry and wherein the alternating-current signals have a frequency of 100 Hz to 10 MHz. 
     
     
       16. The wireless power transmitting device of  claim 15  wherein the alternating-current signals have a frequency of 100 kHz to 500 kHz. 
     
     
       17. The wireless power transmitting device of  claim 12  wherein the capacitive sensor electrodes are formed from a conductive material having a sheet resistance of at least 10 Ω/square. 
     
     
       18. A wireless power transmitting device configured to transmit wireless power to a wireless power receiving device having a coil, comprising:
 a wireless power transmitting coil configured to transmit wireless power signals to the wireless power receiving device; 
 a dielectric layer; 
 a circular array of capacitive sensor electrodes formed from a thin-film conductive layer on the dielectric layer; and 
 control circuitry configured to:
 determine whether a foreign object is present on the charging surface based on capacitance measurements from the circular array of capacitive sensor electrodes; and 
 in response to determining that a foreign object is present, halt transmission of the wireless power signals. 
 
 
     
     
       19. The wireless power transmitting device of  claim 18  further comprising a housing containing the wireless power transmitting coil and a magnet in the housing that is configured to attract a corresponding magnetic structure in the wireless power receiving device during transmission of the wireless power signals.

Description:
This application claims the benefit of provisional patent application No. 62/956,522, filed Jan. 2, 2020, which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD 
     This relates generally to power systems, and, more particularly, to wireless power systems for charging electronic devices. 
     BACKGROUND 
     In a wireless charging system, a wireless power transmitting device such as a charging mat wirelessly transmits power to a wireless power receiving device such as a portable electronic device. The wireless power receiving device has a coil and rectifier circuitry. The coil receives alternating-current wireless power signals from the wireless charging mat. The rectifier circuitry converts the received signals into direct-current power. 
     SUMMARY 
     A wireless power system has foreign object detection capabilities so that foreign objects such as coins and paper clips are detected. The wireless power system has a wireless power transmitting device and a wireless power receiving device. The wireless power transmitting device uses a wireless power transmitting coil to transmit wireless power signals to the wireless power receiving device. The wireless power transmitting coil and other components of the wireless power transmitting device are located in a housing. The housing has a circular outline and contains one or more magnets that couple to corresponding magnets in the wireless power receiving device to help align a wireless power receiving coil in the wireless power receiving device with the wireless power transmitting coil in the wireless power transmitting device. 
     Capacitive sensing is used to detect foreign objects. An array of capacitive sensor electrodes is supported by the housing at a location that overlaps the wireless power transmitting coil. Capacitive sensor measurements from the capacitive sensor array are analyzed to determine whether a foreign object such as a coin or paperclip is present between the housing and the wireless power receiving device. If a foreign object is detected, wireless power transmission with the wireless power transmitting coil is halted or other suitable action taken. 
    
    
     
       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 circuit diagram of illustrative capacitive sensing circuitry for a wireless power system in accordance with an embodiment. 
         FIG. 3  is a top view of an illustrative wireless power transmitting device with a sensor array in accordance with an embodiment. 
         FIG. 4  is a cross-sectional side view of an illustrative wireless power system in accordance with an embodiment. 
         FIG. 5  is a flow chart of illustrative operations involves in operating a wireless power system in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A wireless power system includes a wireless power transmitting device such as a wireless charging mat or wireless charging puck. The wireless power transmitting device wirelessly transmits power to a wireless power receiving device. The wireless power receiving device may be a device such as a wrist watch, cellular telephone, tablet computer, laptop computer, or other electronic equipment. The wireless power receiving device uses power from the wireless power transmitting device for powering the device and for charging an internal battery. 
     Wireless power is transmitted from the wireless power transmitting device to the wireless power receiving device using one or more wireless power transmitting coils. The wireless power receiving device has one or more wireless power receiving coils coupled to rectifier circuitry that converts received wireless power signals into direct-current power. 
     If a foreign object such as a paperclip, coin, or other metallic object is present near the wireless power transmitting coil, there may be a risk of eddy current generation in the foreign object that could elevate the temperature of the foreign object. To determine whether a foreign object such as a paperclip or coin is present in the vicinity of the wireless power transmitting device, the wireless power transmitting device uses a capacitive sensor to make capacitance measurements. In the presence of a metallic object such as a paperclip or coin, the capacitance measurements will deviate from expected values (e.g., capacitance readings will increase/decrease). 
     An illustrative wireless power system (wireless charging system) is shown in  FIG. 1 . As shown in  FIG. 1 , wireless power system  8  includes a wireless power transmitting device such as wireless power transmitting device  12  and includes a wireless power receiving device such as wireless power receiving device  24 . Wireless power transmitting device  12  includes control circuitry  16 . Wireless power receiving device  24  includes control circuitry  30 . Control circuitry in system  8  such as control circuitry  16  and control circuitry  30  is used in controlling the operation of system  8 . This control circuitry may include processing circuitry associated with microprocessors, power management units, baseband processors, digital signal processors, microcontrollers, and/or application-specific integrated circuits with processing circuits. The processing circuitry implements desired control and communications features in devices  12  and  24 . For example, the processing circuitry may be used in selecting coils, determining power transmission levels, processing sensor data and other data to detect foreign objects and perform other tasks, processing user input, handling negotiations between devices  12  and  24 , sending and receiving in-band and out-of-band data, making measurements, and otherwise controlling the operation of system  8 . 
     Control circuitry in system  8  may be configured to perform operations in system  8  using hardware (e.g., dedicated hardware or circuitry), firmware and/or software. Software code for performing operations in system  8  is stored on non-transitory computer readable storage media (e.g., tangible computer readable storage media) in control circuitry  8 . The software code may sometimes be referred to as software, data, program instructions, instructions, or code. The non-transitory computer readable storage media may include non-volatile memory such as non-volatile random-access memory (NVRAM), one or more hard drives (e.g., magnetic drives or solid state drives), one or more removable flash drives or other removable media, or the like. Software stored on the non-transitory computer readable storage media may be executed on the processing circuitry of control circuitry  16  and/or  30 . The processing circuitry may include application-specific integrated circuits with processing circuitry, one or more microprocessors, a central processing unit (CPU) or other processing circuitry. 
     Power transmitting device  12  may be a stand-alone power adapter (e.g., a wireless charging mat or charging puck that includes power adapter circuitry), may be a wireless charging mat or puck that is coupled to a power adapter or other equipment by a cable, may be a portable device, may be equipment that has been incorporated into furniture, a vehicle, or other system, may be a removable battery case, or may be other wireless power transfer equipment. Illustrative configurations in which wireless power transmitting device  12  is a wireless charging mat or puck that has a wireless power transmission coil and housing with a circular footprint are sometimes described herein as an example. 
     Power receiving device  24  may be a portable electronic device such as a wrist watch, a cellular telephone, a laptop computer, a tablet computer, an accessory such as an earbud, 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. DC power may be used to power control circuitry  16 . During operation, a controller in control circuitry  16  uses power transmitting circuitry  52  to transmit wireless power to power receiving circuitry  54  of device  24 . Power transmitting circuitry  52  may have switching circuitry (e.g., inverter circuitry  61  formed from transistors) that is turned on and off based on control signals provided by control circuitry  16  to create AC current signals through one or more wireless power transmitting coils such as wireless power transmitting coils  36 . These coil drive signals cause coil(s)  36  to transmit wireless power. Coils  36  may be arranged in a planar coil array (e.g., in configurations in which device  12  is a wireless charging mat) or may be arranged to form a cluster of coils (e.g., in configurations in which device  12  is a wireless charging puck). In some arrangements, device  12  (e.g., a charging mat, puck, etc.) may have only a single coil. In other arrangements, a wireless charging device may have multiple coils (e.g., two or more coils, 5-10 coils, at least 10 coils, 10-30 coils, fewer than 35 coils, fewer than 25 coils, or other suitable number of coils). 
     As the AC currents pass through one or more coils  36 , alternating-current electromagnetic (e.g., magnetic) fields (wireless power signals  44 ) are produced that are received by one or more corresponding receiver coils such as coil(s)  48  in power receiving device  24 . Device  24  may have a single coil  48 , at least two coils  48 , at least three coils  48 , at least four coils  48 , or other suitable number of coils  48 . When the alternating-current electromagnetic fields are received by coil(s)  48 , corresponding alternating-current currents are induced in coil(s)  48 . The AC signals that are used in transmitting wireless power may have any suitable frequency (e.g., 100-250 kHz, etc.). Rectifier circuitry such as rectifier circuitry  50 , which contains rectifying components such as synchronous rectification metal-oxide-semiconductor transistors arranged in a bridge network, converts received AC signals (received alternating-current signals associated with electromagnetic signals  44 ) from one or more coils  48  into DC voltage signals for powering device  24 . 
     The DC voltage produced by rectifier circuitry  50  (sometime referred to as rectifier output voltage Vrect) can be used in charging a battery such as battery  58  and can be used in powering other components in device  24 . For example, device  24  may include input-output devices  56 . Input-output devices  56  may include input devices for gathering user input and/or making environmental measurements and may include output devices for providing a user with output. As an example, input-output devices  56  may include a display for creating visual output, a speaker for presenting output as audio signals, light-emitting diode status indicator lights and other light-emitting components for emitting light that provides a user with status information and/or other information, haptic devices for generating vibrations and other haptic output, and/or other output devices. Input-output devices  56  may also include sensors for gathering input from a user and/or for making measurements of the surroundings of system  8 . Illustrative sensors that may be included in input-output devices  56  include three-dimensional sensors (e.g., three-dimensional image sensors such as structured light sensors that emit beams of light and that use two-dimensional digital image sensors to gather image data for three-dimensional images from light spots that are produced when a target is illuminated by the beams of light, binocular three-dimensional image sensors that gather three-dimensional images using two or more cameras in a binocular imaging arrangement, three-dimensional lidar (light detection and ranging) sensors, three-dimensional radio-frequency sensors, or other sensors that gather three-dimensional image data), cameras (e.g., infrared and/or visible cameras with respective infrared and/or visible digital image sensors and/or ultraviolet light cameras), gaze tracking sensors (e.g., a gaze tracking system based on an image sensor and, if desired, a light source that emits one or more beams of light that are tracked using the image sensor after reflecting from a user&#39;s eyes), touch sensors, buttons, capacitive proximity sensors, light-based (optical) proximity sensors such as infrared proximity sensors, other proximity sensors, force sensors, sensors such as contact sensors based on switches, gas sensors, pressure sensors, moisture sensors, magnetic sensors, audio sensors (microphones), ambient light sensors, optical sensors for making spectral measurements and other measurements on target objects (e.g., by emitting light and measuring reflected light), microphones for gathering voice commands and other audio input, distance sensors, motion, position, and/or orientation sensors that are configured to gather information on motion, position, and/or orientation (e.g., accelerometers, gyroscopes, compasses, and/or inertial measurement units that include all of these sensors or a subset of one or two of these sensors), sensors such as buttons that detect button press input, joysticks with sensors that detect joystick movement, keyboards, and/or other sensors. Device  12  may optionally have one or more input-output devices  70  (e.g., input devices and/or output devices of the type described in connection with input-output devices  56 ). 
     Device  12  and/or device  24  may communicate wirelessly using in-band or out-of-band communications. Device  12  may, for example, have wireless transceiver circuitry  40  that wirelessly transmits out-of-band signals to device  24  using an antenna. Wireless transceiver circuitry  40  may be used to wirelessly receive out-of-band signals from device  24  using the antenna. Device  24  may have wireless transceiver circuitry  46  that transmits out-of-band signals to device  12 . Receiver circuitry in wireless transceiver  46  may use an antenna to receive out-of-band signals from device  12 . In-band transmissions between devices  12  and  24  may be performed using coils  36  and  48 . 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. 
     It is desirable for power transmitting device  12  and power receiving device  24  to be able to communicate information such as received power, battery states of charge, and so forth, to control wireless power transfer. However, the above-described technology need not involve the transmission of personally identifiable information in order to function. Out of an abundance of caution, it is noted that to the extent that any implementation of this charging technology involves the use of personally identifiable information, implementers should follow privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining the privacy of users. In particular, personally identifiable information data should be managed and handled so as to minimize risks of unintentional or unauthorized access or use, and the nature of authorized use should be clearly indicated to users. 
     Control circuitry  16  has external object measurement circuitry  41  that may be used to detect external objects on the charging surface of the housing of device  12  (e.g., on the top of a charging mat or, if desired, to detect objects adjacent to the coupling surface of a charging puck). The housing of device  12  may have polymer walls, walls of other dielectric, metal structures, fabric, and/or other housing wall structures that enclose coil(s)  36  and other circuitry of device  12 . The charging surface may be formed by a planer outer surface of the upper housing wall of device  12  or may have other shapes (e.g., concave or convex shapes, etc.). In arrangements in which device  12  forms a charging puck, the charging puck may have a surface shape that mates with the shape of device  24 . A puck or other device  12  may, if desired, have magnets that removably attach device  12  to device  24  (e.g., so that coil  48  aligns with coil  36  during wireless charging). 
     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  (e.g., circuitry  41  can detect the presence of one or more coils  48  and/or magnetic core material associated with coils  48 ). During object detection and characterization operations, external object (foreign object) measurement circuitry  41  can be used to make measurements on coil(s)  36  such as Q-factor measurements, resonant frequency measurements, and/or inductance measurements that can indicate whether coil  48  is present and/or whether foreign objects such as coins or paperclips are present. Measurement circuitry can also be used to make sensor measurements using a capacitive sensor, can be used to make temperature measurements, and/or can otherwise be used in gathering information indicative of whether a foreign object or other external object (e.g., device  24 ) is present on device  12 . 
     In some configurations, the control circuitry of device  12  (e.g., circuitry  41  and/or other control circuitry  16 ) can implement a power counting foreign object detection scheme. With this approach, device  12  receives information from device  24  (e.g., via in-band communications) indicating the amount of power that device  24  is wirelessly receiving (e.g., 4.5 W). Device  12  knows how much power (e.g., 5.0 W) is being transmitted (e.g., because device  12  knows the magnitude of the signal being used to drive coil  36  from inverter  61 ). By comparing the transmitted power (e.g., 5.0 W) to the received power (e.g., 4.5 W), device  12  can determine whether wireless power is being dissipated due to eddy currents flowing in a foreign object. If the dissipated power (e.g., 0.5 W in this example) is more than a predetermined threshold amount or if the efficiency of the wireless power transfer process is lower than expected, device  12  can conclude that a foreign object is present. Power counting techniques such as these may be used in conjunction with capacitive sensing foreign object detection techniques and/or other external object measurement operations performed using circuitry  41 . 
     In some embodiments, measurement circuitry  41  of control circuitry  16  contains signal generator circuitry (e.g., oscillator circuitry for generating AC probe signals at one or more probe frequencies, a pulse generator that can create impulses so that impulse responses can be measured) and/or uses the transmission of wireless power signals from device  12  to energize the coils in system  8 . Circuitry  41  may also include circuits (e.g., analog-to-digital converter circuits, filters, analog combiners, digital processing circuitry, etc.) to measure the response of system  8 . In an illustrative embodiment, which is sometimes described herein as an example, measurement circuitry  41  includes capacitive sensing circuitry and an array of capacitive sensor electrodes for making capacitive sensor measurements of external objects (e.g., foreign objects). 
     An illustrative capacitive sensor for foreign object detection is shown in  FIG. 2 . As shown in  FIG. 2 , measurement circuitry  41  includes capacitive sensing circuitry  80  and an array of capacitive sensing electrodes  86 . Capacitive sensing circuitry  80  may include drive circuitry  84  for applying a drive signal to one or more of electrodes  86  and sensing circuitry such as sense circuitry  82  for measuring the amount of the drive signal that is received on one, some, or all of the remaining electrodes  86 . In an illustrative embodiment, the drive signal is an AC signal with a frequency of at least 10 Hz, at least 100 Hz, at least 1 kHz, at least 10 kHz, at least 100 kHz, less than 100 MHz, less than 10 MHz, less than 1 MHz, less than 500 kHz, less than 100 kHz, 1 kHz to 100 kHz, 10 kHz to 100 kHz, 100 kHz to 500 kHz, etc. 
     By applying drive signals to each of electrodes  86  in sequence while measuring the resulting signal on the remaining (undriven) electrodes  86 , circuitry  80  can be used to measure the capacitance of each electrode  86 . Unexpected patterns of capacitances can indicate that a foreign object is present. For example, a foreign object may be detected if the measured capacitances have a pattern in which a particular pair of electrodes  86  exhibits elevated capacitances relative to the rest of electrodes  86 . In some situations, the capacitances of all of electrodes  86  are elevated. In this situation, circuitry  41  can compare the measured pattern of the elevated capacitances to a database of acceptable elevated capacitances that are expected in the presence of certain cellular telephones or other valid power receiving devices and thereby discriminate between external objects such as cellular telephones and other valid objects and foreign objects. 
     Electrodes  86  may all have the same size and shape or different electrodes  86  may have different sizes and/or shapes. In some embodiments, electrodes  86  may arranged in rows and columns (e.g., to form a rectangular array of electrodes  86 ). In other embodiments, electrodes  86  are arranged in a circular pattern (e.g., to form rings of electrodes exhibiting rotational symmetry about a center point).  FIG. 3  is a top view of device  12  in an illustrative configuration in which electrodes  86  are arranged in a circular array (e.g., an array of electrodes having rotational symmetry and a circular outline). Individual electrodes  86  have pie-slice shapes. This is an example. Other layouts for electrodes  86  may be used, if desired. 
     In the illustrative configuration of  FIG. 3 , device  12  has a circular housing such as housing  90  (e.g., a housing having a circular outline when viewed from above). Housing  90  may be formed from polymer, ceramic, glass, other dielectrics, fabric, metal, other materials, and/or combinations of such materials. Housing  90  may include housing walls (e.g., upper and lower walls, sidewalls, etc.), may include internal support structures (e.g., frame members, etc.), and/or other structural components. Coil  36  and electrodes  86  may be mounted in housing  90  (e.g., so that that electrode array overlaps coil  36  and detects whether a foreign object is overlapping coil  36 ). Device  12  may receive power from a cable coupled to housing  90  (e.g., cable  93  of  FIG. 3 , which may be coupled to a source of DC or AC power) and/or an internal battery in housing  90 . In some configurations, device  12  may receive power wirelessly (e.g., to charge an internal battery). 
     In device  12  of  FIG. 3 , electrodes  86  are formed from sectors of two rings: an inner ring surrounding center  92  of device  12  and an outer ring that surrounds the inner ring. There may be any suitable number of rings of electrodes  86  (e.g., at least three rings, at least two rings, a single ring, etc.) and each ring may contain any suitable number of conductive sectors forming electrodes  86  (e.g., at least 4, at least 8, at least 16, 10-30, 5-25, 14-40, fewer than 30, etc.). The area of each electrode may be at least 0.05 cm 2 , at least 0.2 cm 2 , at least 0.5 cm 2 , at least 1 cm 2 , at least 2 cm 2 , less than 5 cm 2 , less than 2.5 cm 2 , less than 1.5 cm 2 , less than 1 cm 2 , less than 0.3 cm 2 , or less than 0.1 cm 2  (as examples). In some embodiments, the size of electrodes  86  is selected such that typical foreign objects (e.g., common coins) will necessarily at least partially overlap at least two electrodes. In this way, situations in which a coin lies completely within the outline of a single electrode (which might produce small perturbations to the measured capacitance for that electrode that are challenging to detect) can be avoided. 
     Electrodes  86  may be formed from conductive material such as metal, semiconductor (e.g., amorphous silicon, etc.), conductive polymer, other conductive materials, alloys and/or multi-layer stacks of such materials (e.g., a metal thin-film layer or other conductive thin-film layer). Electrodes  86  may cover some or all of the charging surface of device  12  and may partly or fully overlap the turns of coil  36 . 
     During wireless power transmission, AC magnetic fields produced by coil  36  may generate small eddy currents in electrodes  86 . Eddy currents tend to produce opposing magnetic flux that can reduce wireless power transfer efficiency and undesirably heat electrodes  86 . To help suppress eddy currents in electrodes  86  and thereby avoid these effects, the resistance of electrodes  86  may be elevated. For example, electrodes  86  may be formed from a thin film with a thickness that is sufficiently small to help elevate the sheet resistance of electrodes  86  and/or electrodes  86  may be formed from conductive material(s) with relatively high resistivity. As an example, the thickness of electrodes  86  may be 0.05 microns to 2 microns, less than 100 microns, less than 10 microns, less than 1 micron, less than 0.5 microns, at least 0.1 microns, or other suitable thickness. In an illustrative configuration, electrodes  86  may be configured to exhibit a DC sheet resistance of 10 Ω/square-100 kΩ/square, at least 20 Ω/square, at least 200 Ω/square, at least 2 kΩ/square, at least 5 kΩ/square, less than 10 kΩ/square, less than 1000 Ω/square, or less than 300 Ω/square (as examples). The AC resistance of electrodes  86  will be determined by the DC sheet resistance and the geometry of electrodes  86  and the structures forming device  12 . Using a material with a sufficiently high DC resistance to form electrodes  86  helps to suppress eddy currents. 
     Periodically (e.g., during startup and, if desired, at later intervals after wireless power transmission has commenced), capacitive sensor calibration operations may be performed to compensate for capacitance sensor drift (e.g., sensitivity drift due to temperature fluctuations). In an illustrative configuration, device  12  has one or more calibration electrodes such as electrode  86 D. During calibration operations, calibrating capacitance measurements are made using electrode  86 D (e.g., by driving electrode  86 D with a drive signal from drive circuitry  84  while sensing the resulting signal on one or more remaining electrodes  86  using sense circuitry  82 , by driving one or more of electrodes  86  while sensing signals with electrode  86 D, etc.). Electrode  86 D may be located in a portion of housing  12  where electrode  86 D is not affected by the presence or absence of objects on the charging surface of device (e.g., under a portion of a sidewall near to the outer periphery of the outer ring of electrodes  86 , under electrodes  86 , etc.). Data gathered during the calibration measurements may indicate that the sensitivity of electrodes  86  has increased or decreased relative to the nominal sensitivity of electrodes  86  and this measured offset between the expected and actual sensitivity of electrodes  86  can be used by measurement circuitry  41  in calibrating the capacitance sensor so that accurate readings are produced during subsequent capacitance measurements of external objects. 
       FIG. 4  is a cross-sectional side view of device  12  and device  24  in system  8  in an illustrative scenario in which a foreign object is present on the charging surface of device  12 . As shown in  FIG. 4 , device  24  may be placed on the surface of device  12  so that wireless power signals transmitted by coil  36  of device  12  are received by coil  48  of device  24 . Optional magnetic structures  91  (e.g., permanent magnets and/or members formed form magnetic material such as iron members that are attracted by opposing permanent magnets) can be included in the housing of device  12  and corresponding locations in the housing of device  24  to help removably hold device  24  against the charging surface of device  12  with coil  36  in alignment with coil  48 . 
     In some situations, a foreign object such as a coin, paperclip, or other conductive object may be present on the charging surface, as shown by illustrative foreign object  100  of  FIG. 4 . As wireless power signals are transmitted by device  12 , there is a possibility that the temperature of foreign object  100  will become elevated. Using foreign object detection sensor circuitry such as a capacitive sensor formed from electrodes  86 , object  100  can be detected and appropriate action taken (e.g., wireless power transmission can be halted or the maximum wireless power level can be restricted). In some embodiments, a foreign object can be detected before transmission of power with coil  36 . 
     As shown in  FIG. 4 , electrodes  86  may be mounted on a dielectric substrate such as dielectric layer  96 . Layer  96  may be formed from polymer, glass, ceramic, and/or other dielectric materials. Electrodes  86  may be formed on the upper surface of layer  96  and optionally covered with a protective coating layer such as coating  98  (e.g., a polymer layer, inorganic dielectric layer, and/or other covering layer) and/or may be formed on the opposing lower surface of layer  96  (see, e.g., illustrative electrodes  86 ′). The outer surface of coating  98  of device  12  of  FIG. 3  forms a charging surface for device  12  against which wireless power receiving devices such as device  24  may be placed to receive wireless power from coil  36 . 
     Layer  96  and the other structures of device  12  may be mounted in housing  90 . Housing  90  may include a rear wall, sidewalls, and a front surface (e.g., layer  96  and the structures on layer  96  such as coating layer  98 , which may be considered to form a front or upper housing wall for the housing of device  12 ). Coil  36  may be separated from electrodes  86  by an optional insulating layer such as layer  94  (e.g., a layer of polymer or other dielectric). Ferrite layer  102  and/or a structure of other magnetic material may be formed under coil  36  to help control the magnetic flux emitted downwardly from coil  36  during wireless power transmission. 
       FIG. 5  is a flow chart of illustrative operations involved in using system  8  to transfer wireless power from device  12  to device  24  while monitoring for the presence of foreign objects. The operations of  FIG. 5  involve using capacitive sensor measurements (e.g., measurements with electrodes  86 ) to detect capacitance variations indicative of a foreign object. If desired, one or more additional foreign object detection techniques may be used in conjunction with these capacitive sensor measurements (e.g., to help confirm that a foreign object is present before taking action or to serve as an independent trigger for foreign object detection). For example, device  12  may have an array of temperature sensors under the charging surface of device  12  to detect elevated temperatures that may be present when eddy currents are induced in a foreign object, device  12  may receive information from device  24  wirelessly that indicates the level of wireless power that is received by device  24  from device  12  (e.g., so that device  12  can compare this level to the known level of transmitted power and thereby use power counting techniques to determine whether sufficient power is being lost during transmission to indicate that a foreign object is present), device  12  may use radio-frequency measurements to detect foreign objects (e.g., measurements of the Q-factor, coil inductance, resonant frequency behavior and/or other characteristics of coil  36  and/or additional foreign object detection coils), device  12  may use optical sensor measurements to detect foreign objects (e.g., proximity sensor measurements), and/or device  12  may use other circuitry for foreign object detection 
     During the operations of block  110 , control circuitry  16  of device  12  gathers capacitance measurements from the capacitive sensor in device  12  (e.g., see, e.g., measurement circuitry  41  of  FIG. 2 , which shows capacitance sensing circuitry using electrodes  86  to gather capacitance measurements). The capacitance measurements of block  110  may be performed upon startup (e.g., when device  12  is powered up and potentially before any power is wirelessly transmitted), and/or may be performed periodically during normal use of device  12  (e.g., to ensure that no foreign objects unexpectedly are placed on the charging surface of device  12  after wireless power transmission operations have begun). During capacitance measurement operations, device  12  may drive signals onto each of electrodes  86  in sequence using drive circuitry  84  while sensing resulting signals on one, some, or all remaining electrodes  86  using sensing circuitry such as circuitry  82 . If desired, the total time required to perform a scan of all electrodes  86  may be reduced by driving signals onto more than one of electrodes  86  in parallel. for example, drive circuitry  84  may simultaneously provide drive signals to a pair of electrodes  86  (e.g., non-adjacent electrodes  86  such as electrodes on opposing sides of device  12 ) while sensing resulting signals on some or all remaining electrodes  86  using sense circuitry  82 . 
     The measurements of block  110  (e.g., the capacitance value measured for each of electrodes  86 ) are processed by control circuitry  16  to determine whether a foreign object is present. In the illustrative embodiment of  FIG. 5 , control circuitry  16  compares each of the capacitance measurements from electrodes  86  to baseline values (e.g., default values that have been optionally adjusted based on calibration operations performed using calibration electrodes such as electrode  86 D of  FIG. 3 ). As a result of this comparison, control circuitry  16  determines whether any of electrodes  86  exhibit elevated capacitances and whether any adjacent pair of electrodes  86  exhibits elevated capacitances. Capacitances may be considered to be elevated if the measured capacitance for an electrode exceeds the baseline capacitance for that electrode by more than a predetermined threshold amount. If a pair of electrodes  86  are adjacent to each other (whether adjacent electrodes from the inner ring, adjacent electrodes from the outer ring, or adjacent inner and outer ring electrodes), processing continues at block  114 . If no pair of adjacent electrodes have elevated values, processing returns to block  110 . 
     During the operations of block  114 , control circuitry  16  determines whether all electrode  86  have exhibited elevated capacitance values. If foreign object  100  is present, capacitance changes will be localized in the vicinity of object  100  (e.g., the electrodes that are overlapped by object  100  will have elevated capacitances). Accordingly, all of electrodes  86  will not experience elevated capacitances and device  24  can conclude that a foreign object is present and take appropriate action in response at block  116  (e.g., device  24  can halt wireless power transfer and optionally returns to the operations of block  110  for further monitoring of the capacitive sensor). 
     If, however, it is determined during the operations of block  114  that all of electrodes  86  exhibit an elevated capacitance, operations may proceed to block  118  to discriminate between a first scenario in which a cellular telephone or other authorized wireless power receiving device is present (e.g., whether the wireless power receiving device with a coil for receiving wireless power is adjacent to the charging surface and is optionally coupled to device  12  using magnets in device  12  and/or device  24  such as magnets  91  of  FIG. 4 ) and a second scenario in which a foreign object such as a coin or paperclip is present (and device  24  is or is not present on top of the foreign object). 
     When device  24  is present and foreign object  100  is absent, the capacitance changes exhibited by electrodes  86  will have a predefined pattern. As an example, the capacitances of the inner ring will increase by 15% (within a tolerance of 2%, or other suitable tolerance) and the capacitances of the outer ring will increase by 10% (within a tolerance of 2% or other suitable tolerance). This predefined pattern and the predefined patterns associated with other authorized wireless power receiving devices  24  are stored in device  12  (e.g., during manufacturing) and are used by control circuitry  16  during the operations of block  118  to identify when authorized devices are present in the absence of foreign objects. If the elevated capacitances detected during block  114  match the elevated capacitance pattern of an authorized device, processing may return to block  110  (e.g., additional monitoring may be performed). If, however, the elevated capacitances detected during block  114  do not match the elevated capacitance pattern associated with an authorized device, device  12  can conclude that foreign object  100  is present (e.g., in the center of device  12  aligned with center  92  of  FIG. 3 ). Accordingly, device  12  can take appropriate action at block  116  (e.g., wireless power transmission can be halted). 
     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: 20200205
Publication Date: 20210413
Grant Date: 20210413
Priority Date: 20200102
Inventors: REN, SAINING
ILLENBERGER, PATRIN
LEUNG, HO FAI
Assignee: APPLE INC
CPC Classifications: [{"code": "H02J50/60", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01V3/088", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01V3/088", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/60", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/005", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02J50/60", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01V3/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01V3/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/60", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 75394454