Patent Publication Number: US-2023163640-A1

Title: Wireless power transfer system, methods or devices

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. Pat. Application No. 16/836,643, filed Mar. 31, 2020; and claims priority to and benefit of U.S. Provisional Application No. 62/865,873, filed Jun. 24, 2019, both entitled “WIRELESS POWER TRANSFER SYSTEM, METHODS AOR DEVICES,” which are incorporated herein by reference in their entirety for all purposes. 
    
    
     FIELD 
     This relates to a wireless power transfer system, related methods or devices. 
     BACKGROUND 
     In wireless power transfer systems, a wireless power transmitter wirelessly transmits power to a wireless power receiver. The wireless power receiver receives the wirelessly transmitted power and provides power to an associated load, such as to an internal battery of an associated device for charging the battery. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG.  1    is a schematic diagram of an illustrative wireless power system in accordance with some embodiments. 
         FIG.  2    is a flow chart of a wireless power transfer protocol which may be used by the wireless power transfer system of  FIG.  1    in some embodiments. 
         FIG.  3    is a flow chart of a further wireless power transfer protocol which may be used by the wireless power transfer system of  FIG.  1    in some embodiments. 
         FIGS.  4  to  12    are graphs showing a timing of communications in the wireless power transfer system of  FIG.  1    according to various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     A wireless power system has a wireless power transmitting device (which may also be referred to in some instances as a wireless power transmitter or an inductive power transmitter) that transmits power wirelessly to a wireless power receiving device (which may also be referred to in some instances as a wireless power receiver or an inductive power receiver). The wireless power transmitting device is a device such as a wireless charging mat, wireless charging puck, wireless charging stand, wireless charging table, or other wireless power transmitting equipment. The wireless power transmitting device may be a stand-alone device or built into other electronic devices such as a laptop or tablet computer, cellular telephone or other electronic device. The wireless power transmitting device has one or more coils that are used in transmitting wireless power to one or more wireless power receiving coils in the wireless power receiving device. The wireless power receiving device is a device such as a cellular telephone, watch, media player, tablet computer, pair of earbuds, remote control, laptop computer, electronic pencil or stylus, other portable electronic device, or other wireless power receiving equipment. 
     During operation, the wireless power transmitting device supplies alternating-current signals to one or more wireless power transmitting coils. This causes the coils to generate an alternating magnetic field and to transmit alternating-current electromagnetic signals (sometimes referred to as wireless power signals) to one or more corresponding coils in the wireless power receiving device. Rectifier circuitry in the wireless power receiving device converts received wireless power signals into direct-current (DC) power for powering the wireless power receiving device. 
     The term “coil” may include an electrically conductive structure where an electrical current generates a magnetic field. For example, inductive “coils” may be electrically conductive wire in three dimensional shapes or two dimensional planar shapes, electrically conductive material fabricated using printed circuit board (PCB) techniques into three dimensional shapes over plural PCB “layers”, and other coil-like shapes. Other configurations may be used depending on the application. The use of the term “coil”, in either singular or plural, is not meant to be restrictive in this sense. 
     An illustrative wireless power system is shown in  FIG.  1   . As shown in  FIG.  1   , a wireless power system  8  includes a wireless power transmitting device  12  (which may also be referred to in some instances as an inductive power transmitter) and one or more wireless power receiving devices such as wireless power receiving device  10  (which may also be referred to in some instances as an inductive power receiver). Device  12  may be a stand-alone device such as a wireless charging mat, may be built into a laptop or tablet computer, cellular telephone or other electronic device, furniture, or may be other wireless charging equipment. Device  10  is a portable electronic device such as a wristwatch, a cellular telephone, a laptop or tablet computer, an electronic pencil or stylus, or other electronic equipment. Illustrative configurations in which device  12  is a tablet computer or similar electronic device and in which device  10  is an electronic accessory that couples with the tablet computer or similar electronic device during wireless power transfer operations may sometimes be described herein as examples. For example, in one example electronic device  12  is a tablet computer and electronic device  10  is a stylus configured to attach to electronic device  12  (tablet) and be wirelessly (e.g., inductively) charged by electronic device  12  (tablet). Illustrative configurations in which device  12  is a mat or other equipment that forms a wireless charging surface and in which device  10  is a portable electronic device or electronic accessory that rests on the wireless charging surface during wireless power transfer operations may also sometimes be described herein as examples. 
     During operation of system  8 , a user places one or more devices  10  on or near the charging region of device  12 . Power transmitting device  12  is coupled to a source of alternating-current voltage such as alternating-current power source  50  (e.g., a wall outlet that supplies line power or other source of mains electricity), has a battery such as battery  38  for supplying power, and/or is coupled to another source of power. A power converter such as AC-DC power converter  40  can be included to convert power from a mains power source or other alternating current (AC) power source into DC power that is used to power control circuitry  42  and other circuitry in device  12 . During operation, control circuitry  42  uses wireless power transmitting circuitry  34  and one or more coils  36  coupled to circuitry  34  to generate an alternating magnetic field and to transmit alternating-current wireless power signals  48  to device  10  and thereby convey wireless power to wireless power receiving circuitry  46  of device  10 . 
     Power transmitting circuitry  34  has switching circuitry (e.g., transistors in an inverter circuit) that are turned on and off based on control signals provided by control circuitry  42  to create AC current signals through one or more coils  36 . As the AC currents pass through a coil  36  that is being driven by the switching circuitry, a time-varying magnetic field (wireless power signals  48 ) or “flux” is generated, that is received by one or more corresponding coils  14  electrically connected to wireless power receiving circuitry  46  in receiving device  10 . If the time-varying magnetic field is magnetically coupled to coil  14 , an AC voltage is induced and a corresponding AC currents flows in coil  14 . Rectifier circuitry in circuitry  46  can convert the induced AC voltage in the one or more coils  14  into a DC voltage signals for powering device  10 . The DC voltages are used in powering components in device  10  such as display  52 , touch sensor components and other sensors  54  (e.g., accelerometers, force sensors, temperature sensors, light sensors, pressure sensors, gas sensors, moisture sensors, magnetic sensors, etc.), wireless communications circuitry  56  for communicating wirelessly with control circuitry  42  of device  12  and/or other equipment, audio components, and other components (e.g., input-output devices  22  and/or control circuitry  20 ) and/or are used in charging an internal battery in device  10  such as battery  18 , or to charge subsequent devices, either wired or wirelessly. 
     Devices  12  and  10  include control circuitry  42  and  20 . Control circuitry  42  and  20  may include storage and processing circuitry such as analogue circuitry, microprocessors, power management units, baseband processors, digital signal processors, field-programmable gate arrays, microcontrollers, application-specific integrated circuits with processing circuits and/or any combination thereof. Control circuitry  42  and  20  is configured to execute instructions for implementing desired control and communications features in system  8 . For example, control circuitry  42  and/or  20  may be used in selecting a cloaking mode, negotiating a communications data stream during cloaking, initiating a hot start from cloaking, sensing for foreign or other nonreceiver objects (e.g.: metallic objects such as coins or RFID tags within electronic devices), determining power transmission levels, processing sensor data, processing user input, processing other information such as information on wireless coupling efficiency from transmitting circuitry  34 , processing information from receiving circuitry  46 , using information from circuitry  34  and/or  46  such as signal measurements on output circuitry in circuitry  34  and other information from circuitry  34  and/or  46  to determine when to start and stop wireless charging operations, adjusting charging parameters such as charging frequencies, coil assignments in a multi-coil array, and wireless power transmission levels, and performing other control functions. Control circuitry  42  and/or  20  may be configured to perform these operations using hardware (e.g., dedicated hardware or circuitry) and/or software (e.g., code that runs on the hardware of system  8 ). Software code for performing these operations is stored on non-transitory computer readable storage media (e.g., tangible computer readable storage media). The software code may sometimes be referred to as software, data, program instructions, instructions, or code. The non-transitory computer readable storage media may include non-volatile memory such as non-volatile random-access memory (NVRAM), one or more hard drives (e.g., magnetic drives or solid state drives), one or more removable flash drives or other removable media, other computer readable media, or combinations of these computer readable media or other storage. Such media may sometimes be referred to herein as electronic memory. Software stored on the non-transitory computer readable storage media may be executed on the processing circuitry of control circuitry  42  and/or  20 . The processing circuitry may include application-specific integrated circuits with processing circuitry, one or more microprocessors, or other processing circuitry. 
     Device  12  and/or device  10  may communicate wirelessly. Devices  10  and  12  may, for example, have wireless transceiver circuitry in control circuitry  42  and  20  (and/or wireless communications circuitry such as circuitry  56  of  FIG.  1   ) that allows wireless transmission of signals between devices  10  and  12  (e.g., using antennas that are separate from coils  36  and  14  to transmit and receive unidirectional or bidirectional wireless signals, using coils  36  and  14  to transmit and receive unidirectional or bidirectional wireless signals, etc.). For example, device  12  and/or device  10  may communicate using in-band communications injected or combined into the wireless power signals  48  such as proposed in the Wireless Power Consortium Qi specification 1.2.3, which is incorporated herein by reference. Alternatively, a separate Bluetooth, RFID, NFC, Zigbee, WiFi, RF or other communication system may be employed. A wireless transmission signal may include a “message” from one device to the other. A wireless communication message can comprise data that can be read by control circuitry  42  or  20  of devices  10  or  12 . Sending and receiving a “message” is to be interpreted as sending and receiving a wireless communication signal comprising the message. 
     Wireless Power Transfer Process 
     Referring to  FIG.  2   , in some embodiments, transmitting and receiving devices  12  and  10  are configured to operate in accordance with a wireless power transfer protocol  200  for initiating and controlling wireless power transfer. The power transfer protocol  200  comprises an initiation phase  201 , a handshake phase  202  and a wireless power transfer phase  203 . The process may also comprise an optional calibration phase (not shown in  FIG.  2   ), but briefly described below. The phases of the process  200  may be sequential in that a previous phase must be terminated before a current phase is initiated, or in some embodiments, one or more phases may be combined or be allowed to operate simultaneously. One or both of transmitting or receiving devices  12  or  10  may be configured to act as “initiator” of a phase and/or as “terminator” of a phase. Typically the receiving device  10  acts as the “master”. 
     During initiation phase  201 , transmitting device  12  establishes wireless communication with a receiving device  10  when receiving device  10  is within communication range of transmitting device  12 . Transmitting device  12  can confirm the presence of receiving device  10  by sending interrogation signal(s) and listening for a response signal from receiving device  10 , for example. Control circuitry  42  of transmitting device  12  can be configured to continuously or periodically generate and send (via wireless power transmitting circuitry  34  or other wireless communications circuitry), interrogation signal(s), or ping signals, during a selection or ping phase of the initiation phase  201 . Control circuitry  20  of receiving device  10  can be configured to listen for interrogation signal(s) from nearby transmitting device(s)  12  and to generate and send, in response, one or more response message(s) (via wireless communications circuitry  56 , for example). The response message(s) may include data indicative of a received signal strength. Receiving device  10  may send further messages including identification data associated with receiving device  10  during an identification &amp; configuration phase of the initiation phase  201 . The message(s) may also include configuration data indicative of a desired or required configuration settings for transmitting device  12 . Control circuitry  42  of transmitting device  12  can be configured to receive the response message(s) from receiving device  10  and determine from the messages(s) an appropriate connection for wireless power transfer. For example, control circuitry  42  may be configured to confirm the suitability of a connection using one or more variables associated with the response message(s), such as signal strength, receiver identification and/or configuration settings. Control circuitry  42  may also update or adjust one or more configuration parameters associated with wireless power transfer using configuration data from the response message(s). 
     During or prior to initiation phase  201 , transmitting device  12  may be configured to determine the presence of a foreign object such as bankcards, coins or other metals, in the field of magnetic flux. Control circuitry  42  of transmitting device  12  may only enable progression of process  200  into the handshake phase  202 , or any other succeeding stages, if the absence of a foreign object with adverse effects is first confirmed. Foreign object detection may be carried out using a number of methods according to the application requirements. For example, impedance or Q factor measurements, which may be measured at one or more predetermined frequencies, over one or more ranges of frequencies, power loss accounting, or known characteristics of foreign objects may be monitored for. 
     Upon establishing a connection, connected transmitting and receiving devices  12  and  10  can proceed into a handshake or negotiation phase  202 . During handshake phase  202 , transmitting and receiving devices  12  and  10  communicate to establish a power transfer contract, governing one or more conditions of power transfer for the power transfer phase  203 . The power transfer condition(s) of the power transfer contract may comprise, for example, a maximum power transfer limit, guaranteed power, received power packet (RP) format, FSK polarity and modulation depth. The power transfer condition(s) can be stored in memory associated with control circuitry  42  of transmitting device  12  and used to control wireless power transmitting circuitry  34  during the power transfer phase  203  accordingly. In some embodiments, one or more of the power transfer condition(s) may be pre-established and pre-stored in memory associated with control circuitry  42  of the transmitting device  12 . In some embodiments, one or more of the power transfer condition(s) may be communicated by the receiving device  10  to the transmitting device  12  during handshake phase  202 . In some embodiments, one or more of the power transfer condition(s) may be determined by the transmitting device  12  or receiving device  10  using on one or more operational variables of receiving device  10 . For example, a maximum power transfer limit condition may be determined by receiving device  10  using a state of charge of a battery  18  associated with receiving device  10 . The determined maximum power transfer limit condition can be communicated by receiving device  10  to transmitting device  12  during the handshake phase  202 . Control circuity  42  of transmitting device  12  is configured to drive wireless power transmitting circuitry  34  to transmit wireless power in accordance with the power transfer contract established in phase  202 , during the power transfer phase  203 . 
     In some embodiments, transmitting and receiving devices  10  and  12  may be configured to perform a pre-power-transfer calibration (not shown in  FIG.  2   ). In pre-power-transfer calibration, transmitting device  12  can be configured to subject receiving device to multiple varying calibration power levels, and to receive received power message(s) in response indicative of a level of wireless power received by receiving device  10 . Two or more varying calibration power levels may be transmitted to receiving device  10  in this phase. Control circuitry  42  can determine the calibration power levels using one or more operational variables associated with a load. For example, each calibration power level may be determined based on a different percentage of a maximum power consumable by the load, e.g., 10% and 100%. Other calibration load levels within this range may be transmitted in this phase. Control circuitry  42  can use the received power message(s) and associated the calibration power levels to generate a model of expected load behavior. For example, the model may be generated using a linear regression technique. The model can be stored in electronic memory associated with control circuitry  42 . During power transfer phase  203 , control circuitry  42  can use received power message(s) sent by receiving device  10  and the pre-stored model to determine the potential presence of a foreign object. Control circuitry  42  may compare a level of received power against an expected level of received power obtained from the model for a current transmission power level, and determine from the level of deviation a value indicative of the presence of a foreign object. Control circuitry  42  may adjust operation of wireless power transmitting circuitry  34  and/or send message(s) to receiving device  10  upon detection of a foreign object as previously described. 
     During power transfer phase  203 , transmitting device  12  transfers wireless power to the receiving device  10  for supply to a load of the receiving device  10 , such as battery  18 . Wireless power transfer is substantially continuous in phase  203 . Received wireless power may also be used by receiving device  10  to power other devices or circuitry in the receiving device  10 , such as wireless power receiving circuitry  46 , input-output devices  22  and control circuitry  20 . In phase  203 , control circuitry  42  can be configured to generate a drive signal for wireless power transmitting circuitry  34  to transfer wireless power from transmitting device  12  to receiving device  10  in accordance with the condition(s) of the power transfer contract established during handshake phase  202 . 
     Wireless power is transferred from transmitting device  12  to receiving device  10  according to the power requirements of the receiver’s load, such as the charging requirements of a battery  18 . Receiving device  10  can be configured to generate feedback message(s) indicative of a level of deviation between received power and a desired power requirement of the load. The feedback message(s) such as control error (CE) packets may be communicated to transmitting device  12  for adjusting a level of transferred wireless power accordingly, if necessary. Control circuitry  42  of transmitting device  12  can be configured to receive feedback message(s) and to adjust a driving signal (in amplitude, duty cycle, phase or frequency) for wireless power transmitting circuitry  34  using the feedback message(s) to reduce the level of deviation towards zero. The feedback message(s) may be generated periodically by control circuitry  20  during power transfer phase  203 . 
     Control circuitry  20  of receiving device  10  is also configured to generate received power message(s) using the receiving circuitry  46 , and to send the received power message(s) to transmitting device  12  using wireless communication circuitry  56 . The received power P PR  (RP) message(s) can indicate of a level of power received by coil(s)  14 , including associated power loss. This may be determined empirically using a test setup and may take into account the power P out  provided at the receiver output and adding any power P PRloss  that is lost inside the receiver device. This power P PRloss  may include, for example: the power loss in the rectifier, the power loss in the receiver coil, the power loss in the resonance capacitor, the power loss in the shielding of the receiver assembly, and the power loss in any metal parts of the receiver). The received power message(s) may be sent periodically during calibration or power transfer phase  203 . Control circuitry  42  of transmitting device  12 , can be configured to receive the received power message(s) and to determine, using the received power message(s), the potential presence of a foreign object. For example, control circuitry  42  may compare the level of received power to a predetermined expected level of received power stored in associated memory to determine the presence of an unwanted foreign object. Upon detection of a foreign object, control circuitry  42  may reduce transmitted power to a safe level or terminate wireless power transfer by driving wireless power transmitting circuitry  34  accordingly. 
     In some embodiments, transmitting and receiving devices  12  and  10  may be configured to terminate a power transfer phase  203  and to return to a handshake phase  202  to establish a new power transfer contract, if prompted by one of the devices  12  or  10 . In some embodiments, either one of transmitting or receiving device  12  or  10  may be configured to terminate power transfer phase  203  and reinitiate handshake phase  202 . In other embodiments, only one of transmitting or receiving device  12  or  10  may be configured to terminate power transfer phase  203  and reinitiate handshake phase  202 . For example, receiving device  10  may be configured to terminate a power transfer phase  203  and re-initiate a handshake phase  202  when a desired power requirement of an associated load, such as battery  18 , is outside a threshold value or range of a current power transfer contract. 
     Referring to  FIG.  3    a further example protocol  300  is shown for initiating and controlling power transfer. Initially if an object is detected  301  the transmitter sends a ping  302  using the power transmitting coil. The ping is typically an analogue signal that wakes a receiver if that is the adjacent object. This is followed by a digital ping from the transmitter, and a compatible receiver then replies with a signal strength packet. If the signal strength packet is valid, the power transmitter proceeds to the next phase. The receiver then replies  304  with a configuration packet, and identification packet. The configuration packet includes a number of flag bits for various scenarios. If the “negotiation” bit is false  306 , the transmitter begins power transfer  328  under the basic power profile (BPP)  308 . 
     If the “negotiation” bit is true  310 , the transmitter and receiver enter a negotiation phase  312 , with the transmitter responding with a FSK response pattern. If the negotiation is successful  314 , then the transmitter enters a power calibration phase  316 . If the calibration is successful  318 , the transmitter begins power transfer  328  under the extended power profile (EPP)  320 . 
     A Boolean true signal can be a signal that represents a binary of “one”, a voltage signal exceeding a threshold, a pattern of specific binary bit values, or other values representative of true depending on the requirements of the application. Conversely a Boolean false signal can be a signal that represents a binary of “zero”, a voltage signal below a threshold, a pattern of specific binary bit values, or other values representative of false depending on the requirements of the application. 
     For a power receiver that supports performing the calibration phase  316  it begins sending message packets (RP) containing the received power with a mode such as binary “001” denoting a light load power level until the power transmitter acknowledges that it has finished calibration in this mode with a light load power. Subsequently the power receiver begins sending RP packets containing the received power with a mode such as binary “010” denoting a connected load until the power transmitter acknowledges that it has finished calibration in this mode with a connected load. If the second (e.g. binary “010”) mode is successfully completed and acknowledged to the power receiver by the power transmitter, the power receiver will proceed with power transfer where message packets containing received power with a mode such as “000” are used. 
     If the configuration, negotiation, calibration, or power transfer phases return an error condition, then the process resets  330  and begins from the start. 
     Cloaking During Power Transfer Phase 
     Referring to  FIG.  4   , in some embodiments, control circuitry  20  of receiving device  10  is configured to temporarily disable power transfer during power transfer phase  203 , to “cloak” the receiver. In this manner, during the cloak state  400 , the receiving device  10  sends an End Power Transfer message  402  (as defined in the table below) to the transmitter device  12 , to start the period where the transmitter device enters a low power or non-transmitting state  404 . This may occur when the wireless power receiving device has reached temperature threshold limit, and it would be desirable for the transmitting device, the receiving device  10 , or both, to appear as if charging is still occurring. After cooling down during the cloak state  400 , wireless power transmission can resume. 
     Qi 1.2.3 provides for a number of different end power transfer packet codes. For example currently 0x0C to 0xFF are reserved for future functionality. The receiving device  10  may send a Re-ping after End of Power Transfer (EPT/rep) packet using reserved EPT code 0x0C. This will include a value for a negotiated period t reping , that the transmitting device  12  will deactivate, or enter a low power state  404 , before sending a new digital ping  406 . It may be desirable for the amount of heat generated by the transmitting device  12  to be reduced during the low power state  404 . After each digital ping  406  the receiving device  10  waits t wake  for the voltage to stabilize, before sending a message. This may be EPT/rep if it wants to stay cloaked, or a number of other message types  408 , as described below, if it wants to exit cloaking  410 . 
     Referring to  FIG.  5    the transmitting device  12  may wish to initiate a communication channel with the receiving device  10  during the cloaking state. It can be useful for the transmitting and receiving devices to perform some communication even though the receiving device is temporarily not needing wireless power. 
     For example, the transmitting and receiving devices may communicate and agree on a coordinated user interface experience. Consider the situation in which both the transmitting and receiving devices are capable of displaying charge-in-progress indicators using an LED and a touchscreen, respectively. If EPT/re-ping packets are being communicated on the order of milliseconds, it would improve the user’s experience if the two devices can agree on avoiding repeated updates of the charge-in-progress indicators at the milliseconds frequency, and instead to provide coordinated updates at a more user perceptible rate, (e.g., after seconds repeatedly, to provide a longer duration of cloaking, it may be the cloaking period on the order of milliseconds). 
     In a further example, the transmitting device  12  may wish to inform the receiving device  10  that the transmitting device  12  has started a terminal shutdown event, perhaps because of impending loss of input power (e.g. unplugged). In this scenario the receiving device  10  might not deduce this for up to 12.6 sec (when it expects to be re-pinged by the transmitting device  12 ), but by being informed early by means of the communication channel, prompt and intuitive change of state can be provided in the user interface on the receiving device  10 . Other events could include detection of a foreign object that will now inhibit continued charging (in which case prompt, intuitive change of state can be provided to the user interface instead of waiting to deduce that the transmitting device fails to resume on schedule in up to 12.6 sec). 
     After t response  from the EPT/rep, the transmitting device  12  sends and acknowledgement (ACK), indicating it wants to initiate a communication channel. If the receiving device  10  is able to proceed with communication, it will send a data stream request (DSR) packet to confirm this. In the case of a basic power profile (BPP) one way ASK comms from device  10  to device  12  is possible. In the case of an extended power profile (EPP) two way amplitude-shift key/frequency-shift key (ASK/FSK) comms between device  10  and device  12  is possible. Once the data stream is established, the transmitting device  12  may request for the receiving device  10  user interface (UI) to inhibit or disable the chime, prevent changing the charging light, or prevent changing any icons on the screen, that would normally occur when power transfer ends. 
     If the receiving device  10  wishes to initiate a communication channel with the transmitting device  12  during the cloaking state, it may come out of cloaking to communicate with the transmitting device  12 , by sending a Specific Request (GSR) packet (such as using reserved bit 0x05) which may include a request for the transmitting device  12  UI to inhibit or disable the charging light changing, that would normally occur when power transfer ends. 
     If instead, where the transmitting device  12  wishes to initiate a communication channel, the receiving device  10  may deny this as shown in  FIG.  6   . This may occur, where the receiving device  10  is in a critical temperature state and cannot permit any further heating at all. After t response  the transmitting device  12  sends ACK, indicating it wants to initiate a communication channel, and the receiving device  10  sends a deny communications end of power transfer packet (EPT/dny) using reserved bit 0x0E to deny the request. The transmitting device  12  will deactivate, or enter a low power state for t reping , before sending a new digital ping. 
     In the event that the initial ACK is not received from the transmitting device  12  within t terminate  and that the digital ping signal is still present (indicating that the transmitting device is still attempting to communicate), the receiving device  10  resends the EPT/rep, as shown in  FIG.  7   . If the subsequent ACK is received, the protocol proceeds as per  FIG.  6   . 
     Similarly if the initial EPT/rep is not received from the receiving device  10 , and as a result not response is received from the transmitting device  12  within t terminate  + t EPT , and that the digital ping signal is still present (indicating that the transmitting device is still attempting to communicate), the receiving device  10  resends the EPT/rep, as shown in  FIG.  8   . If the subsequent ACK is received, the protocol proceeds as per  FIG.  6   . 
     Referring to  FIG.  9    if the receiving device  10  wishes to initiate an immediate resumption of power transfer using the previously agreed power contract with the transmitting device  12 , it may use a hot start protocol. In order to ensure that receiving device  10  or transmitting device  12  have not changed, e.g.: if a new receiving device  10  is introduced or if a receiving device  10  is swapped between transmitting devices  12 , it may be necessary to interchange identity details to verify that neither party has changed. After the digital ping  406 , the receiving device  10  waits t wake  for the voltage to stabilize, before sending a RxID packet. The ID value may be the pseudo unique Basic Device Identifier from the ID packet. After t response  the transmitting device  12  sends ACK if it is able to proceed with hot start, then the receiving device  10  sends a general request packet requesting the transmitter identity (GRQ/id). After t response  the transmitting device  12  sends a Power Transmitter Identification Packet (TxID) (0x30) including the “Basic Device Identifier” in bytes B3,..,B6; defined in the same way for the power receiver’s Identification packet (a  32  bit arbitrary number/string, of which at least 20 bits must be unique to the unit i.e. random serial number). Alternatively a new unit identification (serial) number packet could be defined e.g., new packet type 0x32 “Unit Number” to contain a 32/24/16 bit (4/3/2 byte) serial number. If this is completed successfully the transmitting device  12  will resume power transfer  900  using the previously agreed power contract. 
     Similarly as shown in  FIG.  10    if the initial RxID packet is not received by the transmitting device  12 , and the receiving device  10  does not receive a response, the receiving device  10  will resend the RxID packet after waiting t start . In that case, if the subsequent RxID packet is received by the transmitting device  12 , the protocol proceeds as per  FIG.  9   . 
     In the event that the initial RxID packet is not received by the transmitting device  12 , and at least one further (for example two further) RxID packet is not received by the transmitting device  12 , then after t cloaktimeout  the transmitting device  12  will deactivate as per  FIG.  11   . 
     As described above, one aspect of the present technology relates to data communications between a wireless power transmitter and a wireless power receiver. In some instances, this data communication can include a Basic Device Identifier and Power Transmitter Identification Packet. 
     The use of such device identification data in the present technology can be used to the benefit of users. For example, it can be helpful for a wireless power transmitter to understand whether back-to-back data packets are being sent by the same wireless power receiver device, or if wireless power receiver devices have been swapped. The present disclosure recognizes that the communication of identification information, even if the identification information is not globally unique, may be perceived as the obtaining of personal information data. 
     It is thus recommended that entities responsible for the collection, analysis, disclosure, transfer, storage, or other use of such information data comply with well-established privacy policies and/or privacy practices. In particular, such entities should implement and consistently use privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining personal information data private and secure. Such policies should be easily accessible by users and should be updated as the collection and/or use of data changes. Personal information from users should be collected for legitimate and reasonable uses of the entity and not shared or sold outside of those legitimate uses. Further, such collection/sharing should occur after receiving the informed consent of the users. Additionally, such entities should consider taking any needed steps for safeguarding and securing access to such personal information data and ensuring that others with access to the personal information data adhere to their privacy policies and procedures. Further, such entities can subject themselves to evaluation by third parties to certify their adherence to widely accepted privacy policies and practices. In addition, policies and practices should be adapted for the particular types of personal information data being collected and/or accessed and adapted to applicable laws and standards, including jurisdiction-specific considerations. For instance, in the US, collection of or access to certain health data may be governed by federal and/or state laws, such as the Health Insurance Portability and Accountability Act (HIPAA); whereas health data in other countries may be subject to other regulations and policies and should be handled accordingly. Hence different privacy practices should be maintained for different data types in each country. 
     Despite the foregoing, the present disclosure also contemplates embodiments in which users selectively block the use of, or access to, information data such as those described above with respect to  FIGS.  9  to  11   . That is, the present disclosure contemplates that hardware and/or software elements can be provided to prevent or block access to such personal information data. For example, the present technology can be configured to allow users to select to “opt in” or “opt out” of participation in the collection of personal information data during registration for services or anytime thereafter. In another example, users can select the specific services and functions that personal information data will be used for. In yet another example, users can select to limit the length of time that personal data is stored or used for specific services and functions. In addition to providing “opt in” and “opt out” options, the present disclosure contemplates providing notifications relating to the access or use of personal information. For instance, a user may be notified upon downloading an app that their personal information data will be accessed and then reminded again just before personal information data is accessed by the app. 
     Moreover, it is the intent of the present disclosure that identification information data should be managed and handled in a way to minimize risks of unintentional or unauthorized access or use. Risk can be minimized by limiting the collection of data and deleting data once it is no longer needed. In addition, and when applicable, including in certain health related applications, data de-identification can be used to protect a user’s privacy. De-identification may be facilitated, when appropriate, by removing specific identifiers and controlling the amount or specificity of data stored (e.g., removing some bits out of a larger identification string and not using globally unique identification codes), controlling how data is stored (e.g., aggregating data across users), and/or other methods. 
     Referring to  FIG.  12    if a cloaked receiving device is replaced by an uncloaked receiving device which was in power transfer phase, the transmitting device  12  will deactivate or terminate. For example after t reping  and t wake , if the expected SSI, RxID or EPT/rep is not received, and instead a CE, RP or other unexpected packet is received, the transmitting device  12  will deactivate. Similarly if the first CE, RP or other unexpected packet is not received by the transmitting device  12 , and if the subsequent CE or RP packet is received by the transmitting device  12 , the transmitting device  12  will or revert / reset to a default / first time operating state or initialize as per  FIG.  12   . 
     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, and elements from one embodiment may be combined with others.