PATENT DOCUMENT

Publication Number: US-12014857-B2
Application Number: US-202117179603-A
Country: US
Kind Code: B2

Title: Wireless charging system with a switchable magnetic core

Abstract:
An electronic device in a wireless power system may be operable with a removable accessory such as a case. The device may convey wireless power to, from, or through the case while the device is coupled to the case. The device may have coplanar power transmitting and power receiving coils. The removable accessory may have an embedded switchable ferrimagnetic core and a coil that overlaps the switchable ferrimagnetic core. The switchable ferrimagnetic core may be operable in a first state where the switchable ferrimagnetic core is unsaturated. The switchable ferrimagnetic core may be operable in a second state where the switchable ferrimagnetic core is saturated by a magnetic field from a permanent magnet in a wireless power transmitting device. In the second state, the switchable ferrimagnetic core may have a lower magnetic permeability and higher magnetic reluctance than in the first state.

Claims:
What is claimed is: 
     
       1. An electronic device comprising:
 a first planar wireless charging coil having windings wound about a central region, wherein the first planar wireless charging coil is configured to transmit first wireless power signals; 
 a second planar wireless charging coil having windings positioned in the central region, wherein the second planar wireless charging coil is configured to receive second wireless power signals; 
 a first ferrimagnetic core overlapping the first planar wireless charging coil; and 
 a second ferrimagnetic core overlapping the second planar wireless charging coil, the second ferrimagnetic core positioned to direct received magnetic flux towards the second planar wireless charging coil, wherein the second ferrimagnetic core has a different magnetic reluctance than the first ferrimagnetic core. 
 
     
     
       2. The electronic device of  claim 1 , wherein the first planar wireless charging coil is configured to operate at a first maximum power level and wherein the second planar wireless charging coil is configured to operate at a second maximum power level that is greater than the first maximum power level. 
     
     
       3. The electronic device of  claim 1 , wherein the first planar wireless charging coil is configured to cease transmission of the first wireless power signals when the second planar wireless charging coil receives the second wireless power signals. 
     
     
       4. The electronic device of  claim 1 , wherein the first planar wireless charging coil is configured to transmit the first wireless power signals when the electronic device is coupled to a removable accessory. 
     
     
       5. The electronic device of  claim 1 , wherein the second planar wireless charging coil is configured to receive the second wireless power signals when the electronic device is coupled to a wireless power transmitting device. 
     
     
       6. The electronic device of  claim 1 , wherein the second planar wireless charging coil is configured to receive the second wireless power signals when the electronic device is coupled to a removable accessory and a wireless power transmitting device. 
     
     
       7. The electronic device of  claim 1 , wherein the first planar wireless charging coil and the second planar wireless charging coil are coplanar. 
     
     
       8. The electronic device of  claim 1 , wherein the first ferrimagnetic core and the second ferrimagnetic core are coplanar. 
     
     
       9. The electronic device of  claim 1 , wherein the first ferrimagnetic core and the second ferrimagnetic core are formed from different materials. 
     
     
       10. The electronic device of  claim 1 , wherein the first ferrimagnetic core and the second ferrimagnetic core have different thicknesses. 
     
     
       11. An electronic device comprising:
 a first planar wireless charging coil having windings wound about a central region; 
 a second planar wireless charging coil having windings positioned in the central region; 
 a first ferrimagnetic core overlapping the first planar wireless charging coil; 
 a second ferrimagnetic core overlapping the second planar wireless charging coil, the second ferrimagnetic core positioned to direct received magnetic flux towards the second planar wireless charging coil, wherein the second ferrimagnetic core has a different magnetic reluctance than the first ferrimagnetic core; and 
 a ring-shaped permanent magnet having a central opening, wherein the first planar wireless charging coil and the second planar wireless charging coil are positioned in the central opening of the ring-shaped permanent magnet. 
 
     
     
       12. The electronic device of  claim 1 , wherein the second planar wireless charging coil is configured to receive the second wireless power signals from a wireless power transmitting device when the electronic device and a removable accessory are inductively coupled to the wireless power transmitting device and a ferrimagnetic core in the removable accessory is in a first state. 
     
     
       13. The electronic device defined in  claim 12 , wherein the first planar wireless charging coil is configured to transmit the first wireless power signals to a wireless power receiving coil in the removable accessory when the electronic device and the removable accessory are not inductively coupled to the wireless power transmitting device and the ferrimagnetic core is in a second state that is different than the first state. 
     
     
       14. The electronic device of  claim 11 , wherein the first planar wireless charging coil is configured to operate at a first maximum power level and wherein the second planar wireless charging coil is configured to operate at a second maximum power level that is greater than the first maximum power level. 
     
     
       15. The electronic device of  claim 11 , wherein the first planar wireless charging coil is configured to transmit first wireless power signals and wherein the second planar wireless charging coil is configured to receive second wireless power signals. 
     
     
       16. The electronic device of  claim 11 , wherein the first planar wireless charging coil and the second planar wireless charging coil are coplanar. 
     
     
       17. The electronic device of  claim 11 , wherein the first ferrimagnetic core and the second ferrimagnetic core are formed from different materials. 
     
     
       18. The electronic device of  claim 11 , wherein the first ferrimagnetic core and the second ferrimagnetic core have different thicknesses. 
     
     
       19. The electronic device of  claim 11 , wherein the second planar wireless charging coil is configured to receive the second wireless power signals from a wireless power transmitting device when the electronic device and a removable accessory are inductively coupled to the wireless power transmitting device and a ferrimagnetic core in the removable accessory is in a first state and wherein the first planar wireless charging coil is configured to transmit the first wireless power signals to a wireless power receiving coil in the removable accessory when the electronic device and the removable accessory are not inductively coupled to the wireless power transmitting device and the ferrimagnetic core is in a second state that is different than the first state.

Description:
This application claims priority to U.S. provisional patent application No. 63/041,729 filed Jun. 19, 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 may include one or more wireless power transmitting devices, one or more wireless power receiving devices, and one or more wireless power transmitting and receiving devices. The wireless power transmitting device may include a coil and wireless power transmitting circuitry coupled to the coil. The wireless power transmitting circuitry may be configured to transmit wireless power signals with the coil. The wireless power receiving device may include a coil that is configured to receive wireless power signals from the wireless power transmitting device and rectifier circuitry that is configured to convert the wireless power signals to direct current power. The wireless power transmitting and receiving device may include at least one coil and both wireless power transmitting circuitry and wireless power receiving circuitry. 
     A device in a wireless power system may be operable with a removable accessory such as a case. The device may transmit or receive wireless power through the case while the electronic device is coupled to the case. The device may also transmit wireless power to the case or receive wireless power from the case while the electronic device is coupled to the case. The case may have a folio shape with a front cover portion that covers the display of the electronic device. 
     The removable accessory may have an embedded switchable ferrimagnetic core and a coil that overlaps the switchable ferrimagnetic core. In one scenario, the removable accessory may be coupled to the device without being coupled to a separate wireless power transmitting device (such as a wireless charging mat). In this scenario, the switchable ferrimagnetic core may be operable in a first state where the switchable ferrimagnetic core is unsaturated and has a high magnetic permeability and low magnetic reluctance. In the first state, the switchable ferrimagnetic core may direct received magnetic flux from the device towards the coil that is embedded in the removable accessory. 
     When the removable accessory is both coupled to the device and placed on a wireless charging mat, the wireless charging mat may transfer wireless power through the removable accessory to the device. In this scenario, the switchable ferrimagnetic core may be operable in a second state where the switchable ferrimagnetic core is saturated by a magnetic field from a permanent magnet in the wireless charging mat. In the second state, the switchable ferrimagnetic core may have a lower magnetic permeability and higher magnetic reluctance than in the first state. The switchable ferrimagnetic core may have a saturation flux density that is selected such that the switchable ferrimagnetic core has different magnetic reluctances depending on the presence of the wireless power transmitting device and its permanent magnet. 
    
    
     
       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 wireless power transmitting and receiving circuitry in accordance with an embodiment. 
         FIG.  3    is a top view of an illustrative removable case having a front cover portion in accordance with an embodiment. 
         FIG.  4    is a cross-sectional side view of the illustrative removable case of  FIG.  3    in accordance with an embodiment. 
         FIG.  5    is a perspective view of an illustrative wireless charging system with a portable electronic device and a removable accessory on the charging surface of a wireless power transmitting device in accordance with an embodiment. 
         FIG.  6    is a cross-sectional side view of an illustrative wireless charging system with a portable electronic device on the charging surface of a wireless power transmitting device in accordance with an embodiment. 
         FIG.  7    is a cross-sectional side view of an illustrative wireless charging system with a portable electronic device coupled to a removable accessory in accordance with an embodiment. 
         FIG.  8    is a cross-sectional side view of an illustrative wireless charging system with a portable electronic device and a removable accessory on the charging surface of a wireless power transmitting device in accordance with an embodiment. 
         FIG.  9    is a top view of a rear portion of an illustrative removable accessory having a ring-shaped switchable ferrimagnetic core in accordance with an embodiment. 
         FIG.  10    is a top view of an illustrative portable electronic device with a transmitting coil having a central opening and a receiving coil within the central opening in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A wireless power system may include one or more electronic devices that transmit wireless power, one or more electronic devices that receive wireless power, and one or more electronic devices that both transmit and receive wireless power. The wireless power transmitting device may be a wireless charging mat or wireless charging puck, as examples. The wireless power receiving device may be a device such as a wrist watch, cellular telephone, tablet computer, laptop computer, or other electronic equipment, as examples. The wireless power transmitting and receiving device may be an electronic device case (e.g., a case for a cellular telephone) or other type of electronic device. The wireless power transmitting device may wirelessly transmit power to a wireless power receiving device. 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. 
     An illustrative wireless power system (wireless charging system) is shown in  FIG.  1   . As shown in  FIG.  1   , wireless power system  8  may include one or more wireless power transmitting devices such as wireless power transmitting device  12 , one or more wireless power receiving devices such as wireless power receiving device  24 , and one or more electronic devices capable of both transmitting and receiving wireless power such as wireless power transmitting and receiving device  18 . It should be understood that one or more of each type of device may be present in the wireless power system at any given time, with devices being added and removed from the system in a fluid manner. The function of power transmitting and receiving  18  may change depending upon the arrangement of the system at a given time. A power transmitting and receiving device may only transmit power in some scenarios, may only receive power in some scenarios, and may both transmit and receive power in some scenarios. A power transmitting device  12  may transmit power directly to a power receiving device  24  in some scenarios. In other scenarios, power transmitting device  12  may transmit power to a power transmitting and receiving device  18 , which then transmits the power to power receiving device  24 . The functionality of each device and inductive coupling between each device within the system may be updated as devices are added to and removed from the system. 
     Wireless power transmitting device  12  includes control circuitry  16 . Wireless power receiving device  24  includes control circuitry  30 . Wireless power transmitting and receiving device  18  includes control circuitry  78 . Control circuitry in system  8  such as control circuitry  16 , control circuitry  30 , and control circuitry  78  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 ,  18 , 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 ,  18 , 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 ,  30 , and/or  78 . 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 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 . For simplicity, an example is described herein of power transmitting device  12  transmitting wireless power to power receiving device  24 . However, it should be understood that a power transmitting and receiving device  18  may substitute for one or both of the power transmitting device and the power receiving device during wireless power transfer operations. 
     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 coil(s)  36 . These coil drive signals cause coil(s)  36  to transmit wireless power. Coils  36  may be arranged in a planar coil array or may be arranged to form a cluster of coils. 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 . In other words, one or more of coils  36  is inductively coupled to one or more of coils  48 . 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 (sometimes referred to as magnetic flux) are received by coil(s)  48  (e.g., when magnetic flux passes through coils  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  18  may optionally have one or more input-output devices  92  (e.g., input devices and/or output devices of the type described in connection with input-output devices  56 ). 
     Device  12 , device  18 , 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 (e.g., to device  18  or device  24 ) using an antenna. Wireless transceiver circuitry  40  may be used to wirelessly receive out-of-band signals from device  18  or  24  using the antenna. Device  24  may have wireless transceiver circuitry  46  that transmits out-of-band signals. Receiver circuitry in wireless transceiver  46  may use an antenna to receive out-of-band signals. Device  18  may have wireless transceiver circuitry  80  that transmits out-of-band signals. Receiver circuitry in wireless transceiver  80  may use an antenna to receive out-of-band signals. Wireless transceiver circuitry  40 ,  46 , and  80  may also be used for in-band transmissions between devices  12 ,  24 , and  18  using coils  36 ,  48 , and  90 . 
     Frequency-shift keying (FSK) and/or amplitude-shift keying (ASK) may be used to convey in-band data between devices  12 ,  18 , and  24 . Power may be conveyed wirelessly during these FSK and ASK transmissions. 
     It is desirable for power transmitting device  12 , power transmitting and receiving device  18 , 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, this process need not involve the transmission of personally identifiable information. 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 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 (sometimes referred to as magnetic alignment structures) that removably attach device  12  to device  24 , in the process aligning coil  48  with coil  36  for efficient 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  18  or  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 . 
     Power transmitting and receiving device  18  may be a wireless charging mat or puck that is coupled to a power adapter or other equipment by a cable, may be equipment that has been incorporated into furniture, a vehicle, or other system, may be a removable battery case, 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 and receiving device  18  is capable of both transmitting and receiving wireless power. Power transmitting and receiving device  18  therefore may include power transmitting components, similar to power transmitting device  12 . Power transmitting and receiving device  18  may also include power receiving components, similar to power receiving device  24 . 
     Power transmitting and receiving device  18  may have an alternating-current (AC) to direct-current (DC) power converter such as AC-DC power converter  96  for converting AC power from a wall outlet or other power source into DC power. DC power may be used to power control circuitry  78 . Control circuitry  78  includes wireless transceiver circuitry  80  for in-band communications (using coils  90 ) and out-of-band communications (using an antenna). Control circuitry  78  may also optionally include measurement circuitry  82  (e.g., measurement circuitry of the type described in connection with measurement circuitry  41 ). 
     Wireless power circuitry  84  in device  18  may include both an inverter  86  and a rectifier  88 . Inverter circuitry  86  (e.g., formed from transistors) may be turned on and off based on control signals provided by control circuitry  78  to create AC current signals through one or more coils such as coil(s)  90 . These coil drive signals cause coil(s)  90  to transmit wireless power. Coils  90  may be arranged in a planar coil array or may be arranged to form a cluster of coils. In some arrangements, device  18  may have only a single coil. In other arrangements, device  18  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  90 , 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 . In other words, one or more of coils  90  may be inductively coupled to one or more of coils  48 . 
     Power transmitting and receiving device  18  may also receive wireless power (e.g., from power transmitting device  12 ). Coil(s)  90  may receive alternating-current electromagnetic fields from transmitting coils  36 , resulting in corresponding alternating-current currents in coil(s)  90 . Rectifier circuitry such as rectifier circuitry  88 , 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  90  into DC voltage signals for powering device  18 . The DC voltage produced by rectifier circuitry  88  can be used in charging a battery such as battery  94  and can be used in powering other components in device  18 . 
     The depiction of alternating-electromagnetic fields between each type of device in  FIG.  1    is merely illustrative (to show the type of inductive coupling that is possible). In practice, alternating-electromagnetic fields will only be conveyed between select devices within the system. For example, transmitting device  12  may transmit power to device  24  and device  18  (while device  18  does not separately transmit power to device  18 ). In another example, transmitting device  12  transmits power to device  18 , which transmits power to device  24  (without direct exchange of power from device  12  to device  24 ). 
     In some applications, power transmitting and receiving device  18  only transmits wireless power (e.g., using inverter  86  and coil(s)  90 ). In some applications, power transmitting and receiving device  18  only receives wireless power (e.g., using rectifier  88  and coil(s)  90 ). In some applications, power transmitting and receiving device simultaneously receives and transmits wireless power. When simultaneously receiving and transmitting wireless power, device  18  may optionally perform both the power transmitting and power receiving operations associated with inverter  86  and rectifier  88  (e.g., device  18  uses the rectifier to charge the battery and operate the device and independently uses the inverter to transmit a desired amount of power). Alternatively, device  18  may relay received power signals without rectifying the power. Device  18  may include only one coil that is used for both wireless power transmission and wireless power reception. Alternatively, device  18  may have at least one dedicated wireless power transmitting coil and at least one dedicated wireless power receiving coil. Device  18  may have multiple coils that are all capable of both wireless power transmission and wireless power reception. Different coils in device  18  may optionally be shorted together in different modes of operation. 
       FIG.  2    is a circuit diagram of illustrative wireless charging circuitry for system  8 . Wireless charging circuitry of a power transmitting device  12  and a power receiving device  24  is shown. However, it should be understood that device  18  may have the corresponding components for both power transmission and power reception and may be used in place of either device  12  and/or device  24  if desired. As shown in  FIG.  2   , circuitry  52  may include inverter circuitry such as one or more inverters  61  or other drive circuitry that produces wireless power signals that are transmitted through an output circuit that includes one or more coils  36  and capacitors such as capacitor  71 . In some embodiments, device  12  may include multiple individually controlled inverters  61 , each of which supplies drive signals to a respective coil  36 . In other embodiments, an inverter  61  is shared between multiple coils  36  using switching circuitry. 
     During operation, control signals for inverter(s)  61  are provided by control circuitry  16  at control input  74 . A single inverter  61  and single coil  36  is shown in the example of  FIG.  2   , but multiple inverters  61  and multiple coils  36  may be used, if desired. In a multiple coil configuration, switching circuitry (e.g., multiplexer circuitry) can be used to couple a single inverter  61  to multiple coils  36  and/or each coil  36  may be coupled to a respective inverter  61 . During wireless power transmission operations, transistors in one or more selected inverters  61  are driven by AC control signals from control circuitry  16 . The relative phase between the inverters can be adjusted dynamically. For example, a pair of inverters  61  may produce output signals in phase or out of phase (e.g., 180 degrees out of phase). 
     The application of drive signals using inverter(s)  61  (e.g., transistors or other switches in circuitry  52 ) causes the output circuits formed from selected coils  36  and capacitors  71  to produce alternating-current electromagnetic fields (signals  44 ) that are received by wireless power receiving circuitry  54  using a wireless power receiving circuit formed from one or more coils  48  and one or more capacitors  72  in device  24 . 
     If desired, the relative phase between driven coils  36  (e.g., the phase of one of coils  36  that is being driven relative to another adjacent one of coils  36  that is being driven) may be adjusted by control circuitry  16  to help enhance wireless power transfer between device  12  and device  24 . Rectifier circuitry  50  is coupled to one or more coils  48  and converts received power from AC to DC and supplies a corresponding direct current output voltage Vrect across rectifier output terminals  76  for powering load circuitry in device  24  (e.g., for charging battery  58 , for powering a display and/or other input-output devices  56 , and/or for powering other components). A single coil  48  or multiple coils  48  may be included in device  24 . 
     As previously mentioned, in-band transmissions using coils  36  and  48  may be used to convey (e.g., transmit and receive) information between devices  12  and  24 . With one illustrative configuration, frequency-shift keying (FSK) is used to transmit in-band data from device  12  to device  24  and amplitude-shift keying (ASK) is used to transmit in-band data from device  24  to device  12 . In other words, a device transmitting wireless power may use FSK to transmit in-band data to a device receiving wireless power (regardless of whether either device is a dedicated power transmitting/receiving device  12 / 24  or a power receiving and transmitting device  18 ). A device receiving wireless power may use ASK to transmit in-band data to a device transmitting wireless power (regardless of whether either device is a dedicated power transmitting/receiving device  12 / 24  or a power receiving and transmitting device  18 ). 
     Power may be conveyed wirelessly from device  12  to device  24  during these FSK and ASK transmissions. While power transmitting circuitry  52  is driving AC signals into one or more of coils  36  to produce signals  44  at the power transmission frequency, wireless transceiver circuitry  40  may use FSK modulation to modulate the power transmission frequency of the driving AC signals and thereby modulate the frequency of signals  44 . In device  24 , coil  48  is used to receive signals  44 . Power receiving circuitry  54  uses the received signals on coil  48  and rectifier  50  to produce DC power. At the same time, wireless transceiver circuitry  46  monitors the frequency of the AC signal passing through coil(s)  48  and uses FSK demodulation to extract the transmitted in-band data from signals  44 . This approach allows FSK data (e.g., FSK data packets) to be transmitted in-band from device  12  to device  24  with coils  36  and  48  while power is simultaneously being wirelessly conveyed from device  12  to device  24  using coils  36  and  48 . 
     In-band communications between device  24  and device  12  may use ASK modulation and demodulation techniques. Wireless transceiver circuitry  46  transmits in-band data to device  12  by using a switch (e.g., one or more transistors in transceiver  46  that are coupled coil  48 ) to modulate the impedance of power receiving circuitry  54  (e.g., coil  48 ). This, in turn, modulates the amplitude of signal  44  and the amplitude of the AC signal passing through coil(s)  36 . Wireless transceiver circuitry  40  monitors the amplitude of the AC signal passing through coil(s)  36  and, using ASK demodulation, extracts the transmitted in-band data from these signals that was transmitted by wireless transceiver circuitry  46 . The use of ASK communications allows ASK data bits (e.g., ASK data packets) to be transmitted in-band from device  24  to device  12  with coils  48  and  36  while power is simultaneously being wirelessly conveyed from device  12  to device  24  using coils  36  and  48 . 
     The example of FSK modulation being used to convey in-band data from power transmitting device  12  to power receiving device  24  and ASK modulation being used to convey in-band data from power receiving device  24  to power transmitting device  12  is merely illustrative. In general, any desired communication techniques may be used to convey information from power transmitting device  12  to power receiving device  24  and from power receiving device  24  to power transmitting device  12 . 
     The power transmission frequency used for transmission of wireless power may be, for example, a predetermined frequency of about 125 kHz, at least 80 kHz, at least 100 kHz, between 100 kHz and 205 kHz, less than 500 kHz, less than 300 kHz, or other suitable wireless power frequency. In some configurations, the power transmission frequency may be negotiated in communications between devices  12  and  24 . In other configurations, the power transmission frequency may be fixed. 
     It has been described that power may be simultaneously conveyed between devices while using in-band communication for data transmission between the devices. In other words, in some examples in-band communications may rely on modulation of the power transmission signal (e.g., modulating the power transmission frequency or modulating amplitude of a signal at the power transmission frequency). However, other communication techniques may be used that do not rely on modulation of the power transmission signals. For example, signals (sometimes referred to as in-band signals) may be conveyed between coils in the system at a frequency that is different than the power transmission frequency. Signals (at the same frequency or a different frequency than the power transmission frequency) that are conveyed using the coils (e.g., coils  36 ,  48 , and  90 ) may be considered in-band signals. 
     Moreover, it should be noted that in-band communication may occur between devices before the devices agree upon a power transfer rate, power transmission frequency, etc. After initial detection and inductive coupling, devices may go through a handshake process to determine compatibility, negotiate power transfer frequency, negotiate power transfer rate, etc. During this process, in-band communication may involve FSK and/or ASK modulation of signals transmitted using the coils. Therefore, wireless power is transmitted during this process. This is advantageous as it allows the devices to complete the handshake process even if the power receiving device has little or no remaining battery power. This transmission of wireless power during in-band communications may occur during the handshake process even if, ultimately, the negotiations between the devices result in no sustained transmission of wireless power. 
     A device in wireless charging system  8  may optionally be coupled to a removable accessory such as a case. The case may optionally have wireless charging functionality (e.g., the case may be capable of receiving and/or transmitting wireless power).  FIG.  3    is a top view of an accessory such as a removable cover. 
     Removable accessory  102  (sometimes referred to as a removable case or removable cover) may have any suitable shape that allows cover  102  to mate with another device. Accessory  102  and the device to which it is coupled may each serve as a power transmitting device, a power receiving device, or a power transmitting and receiving device. The device held by accessory  102  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. 
     In the example of  FIG.  3   , cover  102  has a folio shape (sometimes referred to as a folio cover) with a rear portion  102 R and front portion  102 F. Rear portion  102 R may have a rectangular recess with a rear wall surrounded by peripheral sidewalls  102 W and/or other suitable coupling structures (straps, clips, a sleeve, corner pockets, etc.) that allow cover  102  to receive and couple to the additional device. 
     The portion of cover  102  that extends along fold axis  122  between rear portion  102 R and front portion  102 F may have hinge structures (e.g., flexible cover material that serves as a hinge or other hinge structures that couple portions  102 F and  102 R while allowing these portions to rotate relative to each other). In some configurations, additional bendable portions may be provided. For example, front portion  102 F may have one or more flexible strips. Each flexible strip allows additional folds to be formed in cover  102  (e.g., to manipulate the cover into one or more stand configurations and prop the additional device at a desired angle while cover  102  is coupled to the additional device). Each flexible strip may extend parallel to fold axis  122  from one side of the front portion  102 F to another side of front portion  102 F. 
     When it is desired to protect the additional device in cover  102 , the device (e.g., a housing of the device) may be press fit into a recess formed by the sidewalls  102 W and/or rear wall of cover  102 , coupled to cover  102  using magnets, clips, or straps, or otherwise coupled to cover  102 . Cover  102  may be formed from fabric, leather, polymer, other materials, and/or combinations of these materials. 
     As previously mentioned, cover  102  may in some embodiments include a coil that transmits and/or receives wireless power. For example, cover  102  may be a wireless power receiving device (e.g., device  24  in  FIG.  1   ) with a receiving coil  48  in region  178  on a rear portion  102 R of the cover. The receiving coil  48  in region  178  may be aligned with a transmitting coil in the device coupled to accessory  102 . When accessory  102  is coupled to the additional device, the additional device may transmit wireless power to the receiving coil in region  178  of cover  102 . 
     Incorporating a wireless power receiving coil in the cover may allow for the cover to charge an internal battery, power components within the cover (e.g. input-output components such as a keyboard), and/or provide wireless power to additional accessories. For example, cover  102  may be configured to charge an electronic stylus (e.g., that may be used to provide input on a display in the additional device). In this type of arrangement, cover  102  may be a power transmitting and receiving device (e.g., device  18  in  FIG.  1   ). Cover  102  may include a wireless power receiving coil in region  178  and a separate wireless power transmitting coil. The separate wireless power transmitting coil may optionally be positioned in a different portion of the cover than region  178  (e.g., in a region along fold axis  122 , in one of sidewalls  102 W, or another desired location within the cover). 
       FIG.  4    is a cross-sectional side view showing device  100  held in removable cover  102 . Device  100  may have a housing  164 . Housing  164  may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of any two or more of these materials. In one illustrative example, device  100  is a power transmitting and receiving device (e.g., device  18  in  FIG.  1   ). Device  102  may be a power receiving device (e.g., device  24  in  FIG.  1   ) that receives wireless power from device  100 . Alternatively, device  102  may also be a power transmitting and receiving device that receives wireless power from device  100  and transmits wireless power to an additional accessory device such as a stylus. In yet another possible configuration, device  102  may be capable of transmitting wireless power to device  100 . 
     In  FIG.  4   , the front portion  102 F of cover  102  is folded over and covers the front face of device  100 . Accordingly, front portion  102 F of cover  102  covers a display in device  100 . This may protect the display from damage. As previously mentioned, cover  102  may include a wireless power receiving coil in rear portion  102 R that is configured to receive wireless power from device  100 . In other arrangements, device  100  may need to transmit and/or receive wireless charging signals through cover  102 . For example, device  100  may be coupled to cover  102  and placed on a wireless charging mat. The wireless charging mat may transfer wireless power signals to the device  100  through cover  102 . In this type of situation, it is desirable for the cover to not interfere with the wireless power transfer operations through the cover. 
     The example in  FIGS.  3  and  4    of removable case  102  being a removable cover having a cover portion ( 102 F) configured to fold over and cover the display of device  100  is merely illustrative. In some arrangements, the front cover portion  102 F may be omitted from the removable case. 
     As an example, the removable case may include only a rear portion (e.g., configured to cover a rear housing wall of device  100 , sometimes referred to as rear wall) and sidewalls (e.g., four peripheral sidewalls that extend from the rear wall). The sidewalls (e.g., sidewalls  102 W in  FIG.  3   ) may extend perpendicular to the rear portion of the removable case. The sidewalls may form a recess that is configured to receive and secure device  100  within the removable case. When it is desired to protect device  100  in the removable case, device  100  (e.g., housing  164  of device  100 ) may be press fit into a recess formed by the sidewalls of the removable case, coupled to the removable case using magnets, clips, or straps, or otherwise coupled to the removable case. The removable case (that does not include a front cover portion) may be formed from fabric, leather, polymer, metal other materials, and/or combinations of these materials. 
     In general, wireless power signals may be conveyed to or from various portions of case  102 . Wireless power signals may also be conveyed through case  102  at any desired locations. In one example, case  102  may be a power transmitting and receiving device that includes a power receiving coil in a rear wall. Case  102  may also include a power transmitting coil in another desired region (e.g., a peripheral sidewall). This example is merely illustrative, and other arrangements for conveying wireless power to, from, or through case  102  may be used if desired. 
     The wireless power circuitry in each device in the wireless charging system may be designed to accommodate a number of different charging scenarios. In one scenario, shown in  FIG.  4   , an electronic device such as a tablet computer or cellular telephone (e.g., device  100 ) is coupled to a removable accessory. The electronic device may transmit wireless power to the removable accessory in this scenario (e.g., so that the removable accessory can in turn provide power to a stylus, power internal components, etc.). 
     In another scenario, device  100  may be placed on a power transmitting device (without the removable accessory being present). In yet another scenario, shown in  FIG.  5   , device  100  may be both coupled to removable accessory  102  and placed on a power transmitting device. In this scenario, power transmitting device  104  may transmit wireless power to device  100  through accessory  102  and/or to accessory  102  itself. 
     Similar to as discussed in connection with  FIG.  1   , the power transmitting device  104  may be a wireless charging mat, wireless charging puck, a battery case (e.g., a dedicated wireless power transmitting device), or another electronic device (e.g., a wireless power transmitting and receiving device). An example is described herein where the power transmitting device  104  is a wireless charging mat. The wireless charging mat  104  may be coupled to a wall outlet (e.g., an alternating current power source). Using power from this power source, the wireless charging mat  104  may transmit wireless power to one or more devices. 
       FIGS.  6 - 8    are cross-sectional side views showing the wireless charging system in some of these scenarios.  FIG.  6    is a cross-sectional side view of a portable electronic device  100  (e.g., a wrist watch, a cellular telephone, a laptop computer, a tablet computer, an accessory such as an earbud, or other electronic equipment) on the surface of a wireless charging mat  104 . Device  100  may be a wireless power transmitting and receiving device (e.g., device  18  in  FIG.  1   ) whereas device  104  is a wireless power transmitting device (e.g., device  12  in  FIG.  1   ). 
     As shown, a power transmitting assembly  202  (e.g., part of power transmitting circuitry  52 ) is included within wireless power transmitting device  104 . The power transmitting assembly (sometimes referred to as an inductive power transmitting assembly) includes a magnetic core  203  having a base  204 , a first limb  206 , and a second limb  208 . A coil  212  is positioned on the magnetic core (e.g., between limbs  208  and  206 ). Limb  206  may have a ring-shape that is concentric with coil  212 , as one example. Coil  212  may be coupled to inverter circuitry (e.g., inverter  61  in  FIG.  1   ). The inverter circuitry can drive the coil  212  to generate magnetic flux. Coil  212  may be wound from a single-strand conductor, a multiple strand conductor having multiple wires connected in parallel, braided wire, Litz wire, a conductive ink or conductive trace such as multilayer tracks on a printed circuit board, or other conductive elements suitable for forming coils. 
     A power receiving assembly  222  is included within device  100 . As previously mentioned, device  100  may be a power transmitting and receiving device  18  as in  FIG.  1    (and power receiving assembly  222  may be part of wireless power circuitry  84  in  FIG.  1   ). The power receiving assembly (sometimes referred to as an inductive power receiving assembly) includes a magnetic core  224 . A coil  226  is formed on the magnetic core. Coil  226  may be coupled to rectifier circuitry (e.g., rectifier  88  in  FIG.  1   ). The rectifier circuitry converts received AC signals from coil  226  into DC voltage signals for powering device  100 . Coil  226  may be wound from a single-strand conductor, a multiple strand conductor having multiple wires connected in parallel, braided wire, Litz wire, a conductive ink or conductive trace such as multilayer tracks on a printed circuit board, or other conductive elements suitable for forming coils. 
     Alignment structures such as magnetic alignment structures  214  and  254  may optionally be included in the system. As shown in  FIG.  6   , wireless power transmitting device  104  may have magnetic alignment structures  214 . Wireless power transmitting and receiving device  100  may have magnetic alignment structures  254 . Each magnetic alignment structure  214  in the transmitting device may magnetically couple with a corresponding magnetic alignment structure  254  in the receiving device. When the alignment structures  214  in device  104  are coupled to the alignment structures  254  in device  100 , the transmitting coil  212  may be aligned with the receiving coil  226 . Therefore, the magnetic alignment structures ensure proper alignment of the receiving coil relative to the transmitting coil. Magnetic alignment structures  214  and  254  may be permanent magnets (e.g., formed from hard magnetic materials that retain their magnetism over time). 
     Device  100  may also include a power transmitting assembly  242 . The power transmitting assembly (sometimes referred to as an inductive power transmitting assembly) includes a magnetic core  244 . A coil  246  is formed on the magnetic core. Coil  246  may be coupled to inverter circuitry (e.g., inverter  86  in  FIG.  1   ). The inverter circuitry can drive the coil  246  to generate magnetic flux. Coils  246  and  226  may be coplanar and/or magnetic cores  244  and  224  may be coplanar. Coil  246  may be wound from a single-strand conductor, a multiple strand conductor having multiple wires connected in parallel, braided wire, Litz wire, a conductive ink or conductive trace such as multilayer tracks on a printed circuit board, or other conductive elements suitable for forming coils. 
     When device  100  is placed on charging mat  104  in the absence of removable accessory  102 , transmitting assembly  242  may be disabled (e.g., wireless power is not transmitted using coil  246  and device  100  only receives wireless power using coil  226 ). However, when device  100  is coupled to accessory  102  in the absence of charging mat  104 , receiving assembly  222  may be disabled (e.g., wireless power is not received using coil  226  and device  100  only transmits wireless power using coil  246 ). 
     The magnetic cores in  FIG.  6    (e.g.,  203 ,  224 , and  244 ) may be formed from a soft magnetic material such as ferrite. The magnetic cores may have a high magnetic permeability, allowing them to guide the magnetic fields in the system. The example of using ferrite cores is merely illustrative. Other ferromagnetic and/or ferrimagnetic materials such as iron, mild steel, mu-metal (a nickel-iron alloy), a nanocrystalline magnetic material, rare earth metals, or other magnetic materials having a sufficiently high magnetic permeability to guide magnetic fields in the system may be used for one or more of the cores if desired. The magnetic cores may sometimes be referred to as ferrimagnetic cores. Magnetic cores  203 ,  224 , and  244 , may be a single piece or made from separate pieces. The cores may be molded, sintered, formed from laminations, formed from particles (e.g., ceramic particles) distributed in a polymer, or manufactured by other processes. 
     Magnetic cores  203  and  224  may improve coupling between coils  212  and  226  (compared to an arrangement where cores  203  and  224  are omitted). Magnetic core  224  in  FIG.  6    may redirect received magnetic flux to coil  226 . Magnetic core  224  may have a disc shape or other desired shape. 
     Each core may be optimized for its particular function and position within the wireless charging system. Different devices may have different space constraints that result in the cores being formed from different materials and/or having different geometries. In one illustrative example, coil  226  may be operable at a higher maximum power level than coil  246 . In other words, coil  226  may be configured to receive wireless power at a first maximum power level. Coil  246  is configured to transmit wireless power at a second maximum power level that is lower than the first maximum power level. In one example, the maximum power level for coil  226  may be 10 Watts or greater whereas the maximum power level for coil  246  may be less than 10 Watts. In one example, coil  226  can receive at up to 15 Watts and coil  246  can transmit at up to 5 Watts. These magnitudes for the maximum power levels are merely illustrative. In general, each coil may operate any desired power level. 
     Due to the different associated geometries and power levels, magnetic core  244  may have one or more properties that are different than the properties of magnetic core  224 . For example, core  244  may be formed from a different material than core  224  (e.g., a material having a different magnetic permeability). Cores  244  and  224  may have different thicknesses. As shown, core  244  has a thickness  250  whereas core  224  has a thickness  252 . Thickness  250  may be greater than thickness  252 , in one example. Cores  244  and  224  may have different magnetic permeabilities, different magnetic reluctances, or other desired different properties. Cores  244  and  224  may also have different saturation flux densities. 
       FIG.  7    is a cross-sectional side view of a portable electronic device  100  coupled to removable accessory  102  (e.g., device  100  may be pressed into accessory  102  as shown in  FIG.  3   ). Accessory  102  may include a power receiving assembly  270  that includes a coil  274  for receiving wireless power from device  100  and switchable magnetic core  272 . Power receiving assembly  270  in accessory  102  may be optimized for different charging scenarios. When accessory  102  is coupled to device  100  in the absence of power transmitter  104  (as in  FIG.  7   ), it is desirable for device  100  to efficiently transfer wireless power to cover  102 . However, when accessory is coupled to device  100  and placed on power transmitter  104  (as in  FIG.  8   ), it is desirable for accessory  102  to not disrupt the power transfer from device  104  to device  100 . 
     To ensure satisfactory operation of the wireless charging system in both of these charging scenarios, accessory  102  may include a switchable magnetic core. In the absence of the transmitting device  104 , the switchable magnetic core may have a high magnetic permeability and therefore low magnetic reluctance. In the presence of the transmitting device  104 , the switchable magnetic core may have a low magnetic permeability and therefore high magnetic reluctance. This may be achieved by selecting a material for magnetic core  272  with a low saturation flux density. 
     When transmitting device  104  is not present, as shown in  FIG.  7   , switchable magnetic core  272  (sometimes referred to as switchable ferrimagnetic core  272 ) is not exposed to a significant external magnetic field. Therefore, switchable core  272  does not reach its saturation flux density and maintains a high magnetic permeability and low magnetic reluctance. In this state, switchable core  272  serves as a magnetic core that guides the magnetic fields in the system. In other words, in  FIG.  7    coil  274  is inductively coupled to coil  246  and magnetic core  272  redirect received magnetic flux to coil  274 . 
     When transmitting device  104  is present, as shown in  FIG.  8   , switchable magnetic core  272  is exposed to the external magnetic field of magnetic alignment structures  214  (which may include one or more permanent magnets). The magnetic field from the magnetic alignment structures  214  may be sufficiently high to saturate switchable magnetic core  272 . Once saturated, the magnetic permeability of switchable core  272  declines and the magnetic reluctance of the switchable core increases. Due to the drop in magnetic permeability and increase in magnetic reluctance, the magnetic core does not guide the magnetic fields in the system. Effectively, saturating the switchable magnetic core  272  using permanent magnet  214  turns ‘off’ magnetic core  272 . This prevents switchable core  272  from undesirably redirecting magnetic flux passing through the accessory between coil  212  and coil  226 . 
     In  FIG.  8   , when accessory  102  is interposed between device  104  and device  100 , device  104  may transfer wireless power through cover  102  to device  100 . Similar to as when cover  102  is not present, coils  226  and  212  are inductively coupled. Magnetic core  224  in device  100  redirects received magnetic flux to coil  226 . 
     When accessory  102  is interposed between device  104  and device  100  as in  FIG.  8   , the transmitting assembly in device  100  may be disabled. In other words, coils  246  and  274  are not inductively coupled in  FIG.  8   . Because coils  246  and  274  are not inductively coupled, switchable core  272  being saturated does not adversely affects the charging efficiency between coils  246  and  274 . Additionally, switchable core  272  being saturated ensures that the inductive coupling between coils  212  and  226  is uninterrupted by the switchable core. Coils  212  and  226  may operate at a higher maximum power level than coil  274 . Therefore, efficient power transfer between these coils is prioritized by saturating magnetic core  272  when transmitting device  104  is present. 
     When removable accessory  102  is placed on charging mat  104  (as in  FIG.  8   ), coil  274  may also be inductively coupled to coil  212  in device  104 . Power transfer levels between coils  212  and  274  may be lower than between coils  212  and  226 . This example is merely illustrative. In another possible embodiment, coils  274  may not be inductively coupled to coil  212  in an arrangement of the type shown in  FIG.  8   . 
     Coil  274  may be wound from a single-strand conductor, a multiple strand conductor having multiple wires connected in parallel, braided wire, Litz wire, a conductive ink or conductive trace such as multilayer tracks on a printed circuit board, or other conductive elements suitable for forming coils. 
     Switchable magnetic core  272  in  FIGS.  7  and  8    may be formed from a soft magnetic material such as ferrite. The example of using a ferrite core is merely illustrative. Other ferromagnetic and/or ferrimagnetic materials such as iron, mild steel, mu-metal (a nickel-iron alloy), a nanocrystalline magnetic material, rare earth metals, or other magnetic materials having a sufficiently high magnetic permeability to guide magnetic fields in the system may be used for the core. The magnetic core may sometimes be referred to as a switchable ferrimagnetic core. Magnetic core  272  may be a single piece or made from separate pieces. The core may be molded, sintered, formed from laminations, formed from particles (e.g., ceramic particles) distributed in a polymer, or manufactured by other processes. 
     Magnetic core  272  may reach saturation at less than 2 teslas (T), less than 1.5 T, less than 1.0 T, less than 0.8 T, less than 0.5 T, less than 0.3 T, less than 0.2 T, less than 0.1 T, etc. Magnetic cores  224 ,  203 , and/or  244  may reach saturation at a greater point than core  272 . 
     Magnetic alignment structures  214  and  254  may be magnetically coupled even when accessory  102  is present between devices  100  and  104 . 
       FIG.  9    is a top view of the rear portion  102 R of an illustrative removable accessory. As shown, the power receiving assembly  270  in  FIG.  9    includes a ring-shaped switchable magnetic core  272 . One or more coils  274  are formed over the magnetic core  272 . The ring-shaped switchable magnetic core  272  and coil  274  may be embedded in a dielectric material for the accessory such as dielectric material  276  (also shown in  FIGS.  7  and  8   ). Coil  274  and core  272  may be entirely surrounded by and in direct contact with dielectric material  276  (e.g., fabric, leather, polymer, and/or other materials). This example is merely illustrative. In an alternate arrangement, core  272  and coil  274  may be laterally surrounded by dielectric material  276  and may have one or more exposed surfaces on the upper/lower surfaces of rear portion  102 R. The core  272  and coil  274  may be concentric rings. 
     Power received using power receiving assembly  270  may be used to charge a battery in case  102 , power additional components in case  102  (e.g., additional input-output components), and/or provide wireless power to an additional accessory. As previously discussed, case  102  may optionally include a power transmitting assembly elsewhere within the accessory (e.g., in a sidewall) that transmits wireless power to an accessory such as an electronic stylus. In embodiments where accessory  102  includes a front portion  102 F that is coupled to rear portion  102 R, the optional additional power transmitting assembly may be formed at the flexible hinge structures between the front portion  102 F and the rear portion  102 R. 
       FIG.  10    is a top view of an illustrative portable electronic device having a power receiving assembly and power transmitting assembly such as device  100  in  FIGS.  6 - 8   . As shown, device  100  includes one or more coils  226  that overlap magnetic core  224 . Magnetic core  224  has a circular shape and may be referred to as disc-shaped or circular. Magnetic core  224  and coil  226  are used to form a power receiving assembly  222  as shown in  FIGS.  6 - 8   . Device  100  also includes a power transmitting assembly with one or more coils  246  overlapping magnetic core  244 . Coil  246  and core  244  may be ring-shaped. The ring-shaped coil  246  and core  244  have a central opening, with core  224  and coil  226  formed in the central opening. 
     A ring-shaped magnetic alignment structure  254  (e.g., permanent magnet) may laterally surround core  244 . Alignment structure  254  may have a central opening, with core  224 , coil  226 , core  244 , and coil  246  formed in the central opening. In  FIG.  10   , therefore, coil  226 , coil  246 , magnetic core  244 , and alignment structure  254  are concentric rings. This example is merely illustrative. Other arrangements may be used if desired (e.g., alignment structure  254  may be formed as two discrete permanent magnets on opposing sides of core  244 ). 
     The example of power transmitting assemblies and power receiving assemblies shown in  FIGS.  6 - 10    are merely illustrative. In general, the power transmitting assembly and power receiving assembly may have any desired design. In one possible arrangement, the magnetic core of the power transmitting assembly and/or power receiving assembly may have a pot-core design (e.g., an enclosure with a ring-shaped hollow portion that receives the coil). In yet another possible arrangement, the power transmitting assembly and/or power receiving assembly may include a winding on a bar-shaped ferrite. Any desired magnetic core and coil design may be used (e.g., a U-shaped core, a C-shaped core, an E-shaped core, a toroidal core, etc.). 
     In general, each transmitting/receiving assembly may have only one coil, two coils, three coils, more than three coils, etc. Each coil may have any desired number of windings. Each assembly may optionally include a transverse coil (e.g., a coil extending along the magnetic core base between two magnetic core limbs). The precise geometry of the coils and magnetic cores in devices  100 ,  102 , and  104  may be tailored to the specific design. Device  100  may be designed to cooperate specifically with wireless power transmitting device  104 . This is, however, merely illustrative. Device  100  may, in comes cases, not be specifically designed to cooperate with power transmitting device  104 . In general, each device may have different coil arrangements, different (or no) magnetic elements (e.g., magnetic cores), different coil and magnetic element sizes, different coil and magnetic element shapes, and other different characteristics. 
     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: 20210219
Publication Date: 20240618
Grant Date: 20240618
Priority Date: 20200619
Inventors: MOUSSAOUI, ZAKI
XU, Zelin
CHABALKO, MATTHEW J.
LIU, NAN
Assignee: APPLE INC
CPC Classifications: [{"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/90", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F2003/106", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F2003/103", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F3/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/366", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/90", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/24", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/90", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F2003/103", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F2003/106", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F3/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/366", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/24", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/005", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01F27/24", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/90", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 79023847