Foreign object detection and friendly metal

Abstract

This disclosure provides systems, methods, and devices for object detection by a power transmitter (PTx) that supports both induction heating and wireless power transfer. The object detection evaluation is based on measurements obtained while PTx transmits an object detection pulse (also referred to as an object detection signal). When the PTx determines that the power receiver (PRx) is present in the magnetic field of the PTx, the measurements may also be compared to various thresholds to determine whether foreign objects are also present in the magnetic field. The various thresholds include a PRx threshold range. In some implementations, the PRx threshold range may enable PTx to discriminate between foreign objects and PRx containing a friendly metal that would otherwise be detected as a foreign object. In some implementations, object detection evaluation may be combined with coupling factor measurements to simultaneously detect foreign objects and calculate coupling factors between PTx and PRx.

Description

Technical Field

[0001] The present disclosure relates generally to wireless power transfer and, in some instances, to foreign object detection techniques. Background Art

[0002] An electrical appliance, such as a kitchen stove or range, can support induction heating of objects, such as cooking utensils or appliances. For example, a stove may include several "burner" positions where a user can place the cooking utensils or appliances to be heated. In conventional stoves, an electric or gas heat source is used to heat the cooking utensils that are in contact with the heat source. Modern stoves that support induction heating can use an electromagnetic field (without a direct heat source) to heat the cooking utensils or appliances within it. The electromagnetic field can be generated by one or more coils (sometimes called induction coils). During induction heating, the electromagnetic field induces an electric current in the metal surface of the cooking utensils or appliances. The current induced in the surface of the cooking utensils or appliances then even induces other currents (sometimes called eddy currents) within the cooking utensils, thereby providing heat throughout the cooking utensils.

[0003] At the same time, in an independent technical field, technologies for enabling wireless power transmission have been developed. Wireless power transmission may be referred to as contactless power transmission or contactless power transmission. Wireless power may be transmitted using inductive coupling or resonant coupling between a power transmitter (sometimes also referred to as a "wireless power transmission device") and a power receiver (sometimes also referred to as a "wireless power receiving device"). For example, a power transmitter may include one or more coils (called primary coils) that generate an electromagnetic field. When the secondary coil is placed near the primary coil, the electromagnetic field may induce an electromotive force in the secondary coil of the power receiver. In this configuration, the electromagnetic field may transmit power wirelessly to the secondary coil. The power receiver may be included in various types of devices, such as mobile devices, small electronic devices, computers, tablets, gadgets, appliances (such as cordless blenders, kettles or mixers), and some types of larger electronic devices.

[0004] Because induction heating and wireless power transfer have some common components and applications in the kitchen, there is a desire to provide a multi-function stove that supports both induction heating mode and wireless power transfer mode. Depending on which type of object is present at a particular time, the multi-function stove can alternatively support induction heating of one type of object (e.g., cooking utensils or appliances) and wireless power transfer of another type of object (e.g., appliances with power receivers). The third type of object (e.g., keys, coins, metal cans, or aluminum foil, etc.) is referred to as a foreign metal object or foreign object. When a foreign object is present in an electromagnetic field, the foreign metal object may generate heat undesirably due to eddy currents. Therefore, the multi-function stove must accurately determine which type of object is present in the electromagnetic field, especially before the multi-function stove initiates induction heating or wireless power transfer. Summary of the Invention

[0005] The systems, methods, and devices of the present disclosure each have several innovative aspects, no single one of which is solely responsible for the desirable attributes disclosed herein.

[0006] One innovative aspect of the subject matter described in this disclosure can be implemented as a method for wireless power transfer by a power transmitter. The method includes receiving a communication from a power receiver present in a magnetic field of the power transmitter. The method includes obtaining a measurement based on an object detection evaluation. The method includes determining whether a foreign object is present in the magnetic field with the power receiver based on the measurement.

[0007] Another innovative aspect of the subject matter described in this disclosure can be implemented as a method for wireless power transmission. The method includes receiving a communication from a power receiver present in a magnetic field of a power transmitter. The method includes obtaining measurements of low-power transmissions from the power transmitter during an object detection evaluation. The method includes calculating a coupling factor between the power transmitter and the power receiver based on the measurements, wherein the coupling factor represents alignment of a primary coil of the power transmitter with a secondary coil of the power receiver.

[0008] Another innovative aspect of the subject matter described in this disclosure can be implemented as a device for wireless power transmission. The device includes a communication unit configured to receive communications from a power receiver present in a magnetic field of a power transmitter. The device includes a measurement unit configured to obtain a measurement value based on an object detection evaluation. The device includes a control unit configured to determine whether a foreign object is present in the magnetic field with the power receiver based on the measurement value.

[0009] Another innovative aspect of the subject matter described in this disclosure can be implemented as a device for wireless power transmission. The device includes a communication unit configured to receive communications from a power receiver present in a magnetic field of a power transmitter. The device includes a measurement unit configured to obtain measurements of low-power transmission from the power transmitter during object detection evaluation. The device includes a control unit configured to calculate a coupling factor between the power transmitter and the power receiver based on the measurements, wherein the coupling factor represents alignment of a primary coil of the power transmitter with a secondary coil of the power receiver. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the following description. Other features, aspects, and advantages will become apparent from the description, drawings, and claims. Note that the relative dimensions of the following figures may not be drawn to scale.

[0011] Figure 1 is a conceptual diagram illustrating an example multi-function stove and an example object.

[0012] Figure 2 A block diagram of an example wireless power transfer system is shown.

[0013] Figure 3 A flow chart illustrating an example process for object detection evaluation is shown.

[0014] Figure 4 is a simplified diagram conceptually illustrating various ranges and measurements for object detection.

[0015] Figure 5 is a simplified diagram conceptually illustrating the measurements and ranges of a power receiver (PRx) with a friendly metal.

[0016] Figure 6 is a timing diagram showing a baseline situation when PRx with friendly metal is repeatedly detected as a foreign object.

[0017] Figure 7 is a timing diagram illustrating an example situation in which a reference value of PRx with a friendly metal may be used for subsequent object detection evaluation.

[0018] Figure 8 is a timing diagram illustrating an example situation in which communication from a PRx with friendly metal can improve object detection evaluation results.

[0019] Figure 9 A block diagram of an example power transmitter (PTx) is shown.

[0020] Figure 10A block diagram of an example PRx with a switch that enables disconnection of the secondary coil during object detection evaluation with coupling factor measurement is shown.

[0021] Figure 11 A flowchart illustrating an example process according to some aspects of the present disclosure is shown.

[0022] Figure 12 A flowchart illustrating an example process according to some aspects of the present disclosure is shown.

[0023] Figure 13 A block diagram of an example apparatus for use in a multi-function cooking range is shown.

[0024] Like reference numbers and designations in the various drawings indicate like elements. DETAILED DESCRIPTION

[0025] A device (e.g., a multi-function stove) can support an induction heating mode (for use with some types of devices) and a wireless power transfer mode (for use with other types of devices). For example, in the induction heating mode, the device can support induction heating of an induction heating device (e.g., a cooking vessel or appliance). In the wireless power transfer (WPT) mode, the device can support wireless power transfer to a wireless power receiver (PRx). For simplicity, the present disclosure may refer to the device as a power transmitter (PTx) because it supports the wireless power transfer mode. In addition, although the multi-function stove may have multiple such PTx, the concepts of the present disclosure are described with respect to one PTx and can be extended to other PTx of the multi-function stove. The disclosed PTx differs from a conventional PTx in that, when an appropriate induction heating device is located near one or more coils of the disclosed PTx, the PTx is configured to also support the induction heating mode.

[0026] Because the PTx of the present disclosure supports both induction heating and wireless power transfer, it is desirable to detect different types of objects that may be located near one or more coils of the PTx. Examples of the first type of object may include pots, pans, woks, or any cooking vessel or utensil suitable for induction heating mode. Any of these objects may be referred to as an induction heating device. Examples of the second type of object may include mobile devices, small electronic devices, computers, tablets, gadgets, appliances (such as cordless blenders, kettles, or mixers), or any type of device including a PRx suitable for wireless power transfer mode. Another type of object that may inadvertently be located in the operating environment of the PTx may be referred to as a foreign object. Non-limiting examples of foreign objects include ferrous objects, metal cans, coins, metal spoons, keys, aluminum foil, or other conductive or ferrous objects that are not induction heating devices or PRx. When a foreign object (FO) is near the magnetic field of the PTx, the foreign object may interact with the magnetic field and become undesirably heated. Therefore, it is desirable to detect which type of object (induction heating device, PRx, or FO) is present in the operating environment of the PTx.

[0027] Typically, PTx will perform an object detection assessment before initiating induction heating or wireless power transfer. The object detection assessment can be used to detect whether the object is an induction heating (heading) device, PRx, or a foreign object. Therefore, the object detection assessment may also be referred to as a foreign object detection procedure, a pot detection procedure, a pan detection procedure, a PRx detection procedure, a foreign object detection procedure, or other terms. As part of the object detection assessment, the PTx may send pulses to the primary coil or one or more object detection coils. The PTx measures a measurement value associated with the magnetic field generated by the pulse or associated with a characteristic of the primary coil or one or more object detection coils. Examples of measurement values (sometimes also referred to as parameters) include voltage, current, impedance, quality factor, coupling factor, differential value (the difference between measurements at two coils, such as differential voltage, differential current, or differential impedance), or any other type of parameter associated with the power transfer circuit. The measurement value may also be referred to as an object detection measurement, a measurement parameter, or other similar terms. The object detection assessment includes comparing the measurement value to one or more thresholds to determine the type of object in the operating environment. Therefore, the object detection assessment can be used to detect the presence of an induction heating device, PRx, or a foreign object. The PTx is configured to perform an object detection assessment before transitioning to the power transfer phase to ensure that no foreign objects have been introduced into the operating environment.

[0028] In some cases, an appliance may include a PRx as well as friendly metals. Friendly metals can include conductive materials in the device (e.g., knobs, metal shields, wires, microprocessors, or motors, etc.) that are intentionally included to support the functionality or construction of the device. Due to the presence of friendly metals, the PTx may perform an object detection evaluation that results in a foreign object detection (FOD) fault, even though the object is actually an appliance with a PRx and friendly metal. Typically, the user can clear the FOD fault through user action, such as removing the appliance from the operating environment and returning the appliance to the operating environment to clear the FOD fault.

[0029] There may be instances where the PRx remains in the operating environment, but occasionally transitions into and out of the power transfer phase. For example, the PRx may be in an appliance that is occasionally turned on or off by user action, or the PRx may be programmed to receive wireless power according to a schedule. The PTx may perform a new object detection evaluation before each transition to the power transfer phase. However, due to the presence of friendly metal at the PRx, the PTx may erroneously detect the PRx and the friendly metal as foreign objects and trigger a FOD fault before each transition to the power transfer phase. This can be frustrating for the end user, especially when the FOD fault is repeatedly triggered for the same PRx each time the PRx requests the PTx to transition to the power transfer phase and each FOD fault requires user interaction.

[0030] The present disclosure provides systems, methods, and devices for object detection that accommodate metal-friendly PRx. The present disclosure includes several aspects of object detection in which user interaction can be minimized or eliminated for object detection evaluations of the same metal-friendly PRx. In some aspects, the PTx can determine whether a foreign object is present in the magnetic field with the PRx based on a comparison of a measurement value to one or more threshold ranges. For example, the PRx threshold range may be based on a reference value for a metal-friendly PRx. Alternatively or additionally, the reference value or PRx threshold range may be based on a previous measurement value from a previous object detection evaluation in which the object was confirmed to be metal-friendly PRx. When the PTx determines that no foreign object is present in the magnetic field with the PTx, the PTx may store the previous measurement value as the reference value for the PRx or update the PRx threshold range. When the PTx moves, the measurement value may change. When the PTx detects that a new PRx measurement value is due to PRx movement rather than FO, the PTx may store the new measurement value as the reference value for the PRx.

[0031] In some aspects, the PRx may communicate a reference value or expected value range to the PTx during the pre-power transfer phase, wherein the reference value or expected value range is based on the results of an object detection evaluation in a test environment when the PRx is placed on a standard test PTx and no foreign objects are present. The PTx may determine the PRx threshold range based on the reference value. Alternatively or additionally, the PRx may communicate an indication (which may be referred to as a metal-friendly indication) to inform the PTx that the PRx is metal-friendly, thereby causing the PTx to adjust the PRx threshold range.

[0032] In some aspects, PRx may communicate an identification of PRx associated with a reference value, a range of expected measurement values, or a friendly metal indication. PTx may store an identification of PRx associated with a reference value, a range of expected measurement values, or a friendly metal indication of PRx.

[0033] In some aspects, object detection evaluation can be combined with coupling factor measurement. The coupling factor (which may be referred to as the K factor) refers to a metric that indicates the alignment of the PTx's primary coil and the PRx's secondary coil. The coupling factor is calculated based on the ratio of the voltage applied to the primary coil and the voltage measured at the secondary coil. In some aspects, the same pulse used for object detection evaluation (which may be referred to as the object detection pulse) can also be used for coupling factor measurement. In some implementations, the same measurement value (for a first parameter) can be used for object detection evaluation and coupling factor measurement. In some implementations, the PTX can obtain a first measurement value (for the first parameter) and a second measurement value (for the second parameter) during the same object detection evaluation. The PTx can use the first measurement value (e.g., voltage) to calculate the coupling factor, while the second measurement value (e.g., impedance or Q factor) can be used to detect foreign objects or the PRx. The object detection evaluation can include the PTx transmitting an energy pulse via the primary coil. The energy pulse can have a measured or configured voltage, referred to as a transmit voltage. In some cases, the PTx can measure the coil current or coil impedance of the primary coil during the object detection pulse. At the same time, during the pulse, the PRx can measure the voltage induced on the secondary coil of the PRx due to the pulse. For example, the PRx can measure the voltage (which can be referred to as the received voltage or the induced voltage) while the switch of the power receiving circuit is electrically opened to obtain accurate voltage measurement and / or protect other components of the PRx. After the pulse, the PRx can pass the received voltage value to the PTx. The PTx can calculate the coupling factor based at least in part on the ratio of the received voltage value and the transmitted voltage value of the pulse voltage on the PTx side. The PTx obtains the same measurement value for a first parameter (e.g., voltage) or a different measurement value for a second parameter (e.g., current, impedance, quality factor, or other parameter) during the pulse and uses the measurement value for object detection evaluation.

[0034] Specific implementations of the subject matter described in this disclosure can be implemented to achieve one or more of the following potential advantages. PTx can use the techniques of this disclosure to more accurately detect various types of objects, such as induction heating devices, appliances with PTx and friendly metals, or foreign objects. In some cases, PRx with friendly metals can use the techniques of this disclosure to help PTx detect PRx with little or no user interaction. PTx can use historical information from one or more previous object detection evaluations to reduce the occurrence of false positive FO detections, thereby increasing the usability and user satisfaction of PTx. In some instances, the combination of object detection evaluations and coupling factor measurements can improve the overall operation of the wireless power system.

[0035] Figure 1 1 is a conceptual diagram 100 illustrating an example multi-function stove 110 and an example object. The multi-function stove 110 may include several locations 104 for placing objects. At least one of the locations 104 may include a PTx 120 that supports inductive heating or wireless power transfer to the object when a suitable object is placed in the location associated with the PTx 120. Figure 1 A PTx 120 is depicted at one of the locations 104. It should be understood that a multi-function stove 110 may include a PTx at more than one (or even all) of the locations 104. In this case, each location 104 including a PTx may operate according to the implementation described herein with reference to the PTx 120. The multi-function stove 110 may include a first user interface 140 having an input (e.g., a knob, button, or touchscreen sensor) for receiving user input or presenting instructions to the user of the multi-function stove 110. In some implementations, the multi-function stove 110 may be referred to as a stove, cooktop, oven, or other terminology referring to a kitchen appliance. Furthermore, while the examples described in this disclosure relate to multi-function stoves, aspects of this disclosure may be used with other types of appliances that support both induction heating and wireless power transfer. In some implementations, the multi-function stove may be portable in nature and may include a single PTx. For example, a portable multi-function stove may include batteries or have the capability of supplying power to the PTx using an external power source. In some implementations, a portable multi-function stove (with one or more PTxs) may be suitable for camping.

[0036] The PTx 120 may include one or more primary coils. For simplicity, this disclosure refers to the one or more primary coils as primary coils 130—however, it should be understood that some implementations of the PTx 120 may include more than one primary coil 130. The primary coil 130 is configured to generate a magnetic field for transmitting wireless energy to an object within the magnetic field of the primary coil 130. In some implementations, the primary coil 130 may be a coil coupled to a driver that applies power to the primary coil 130 during an induction heating operation or a wireless power transfer operation.

[0037] The multi-function stovetop 110 may include at least one PTx 120 that supports either induction heating or wireless power transfer, depending on the type of object in proximity to the primary coil 130. The primary coil 130 may be referred to as an induction coil, particularly when the PTx 120 is used in induction heating mode. Additionally or alternatively, the primary coil 130 may be referred to as a power transfer coil, particularly when the PTx 120 is used in wireless power transfer mode. For simplicity, this disclosure may use the terms "device" and "PTx" interchangeably to collectively refer to devices that support both induction heating and wireless power transfer modes.

[0038] Figure 1 Also illustrated are examples 150 of various types of objects that may be placed in the magnetic field of the primary coil 130. In a first example 160, the object may be an induction heating device 165. In a second example 170, the object may be a wireless power receiver (PRx) 175. In a third example 180, the object may be a foreign object 190.

[0039] Referring to the first example 160, the induction heating device 165 can be a cooking vessel, a utensil, or any other device intended to be heated using induction heating. During induction heating, the primary coil 130 can generate a magnetic field to transmit energy that causes eddy currents to be conducted in the ferrous or semi-ferrous surfaces of the induction heating device 165. The eddy currents conducted in the ferrous or semi-ferrous components of the induction heating device 165 cause the induction heating device 165 to heat up, thereby heating food or other materials placed in the induction heating device 165.

[0040] Referring to the second example 170, a device may include a PRx 175 having one or more receiving coils (sometimes referred to as secondary coils). The PRx 175 may also have a rectifier to extract power from the magnetic field and use that power to operate various other components of the device in which the PRx 175 is located. The PRx 175 and the PTx 120 may operate according to technical standard specifications that define a communication protocol to control the amount of power transmitted by the magnetic field. When both the PTx 120 and the PRx 175 are present, they may form a wireless power transfer system.

[0041] It should be understood that induction heating is different from wireless power transfer. The purpose of induction heating is to transfer energy that generates eddy currents in the induction heating device 165, and such eddy currents are undesirable in the PRx 175. The purpose of wireless power transfer is to transfer energy that generates an electromagnetic potential in the secondary coil, which can be harvested to supply power to components of the device containing the PRx 175.

[0042] Referring to a third example 180, a foreign object 190 (sometimes referred to as a foreign metal object) may be in the operating environment of the primary coil 130. The FO 190 may be any object that is electrically conductive or has magnetic permeability and is not intended to be an inductive heating device 165 or PRx 175. When the FO 190 is in the operating environment of the primary coil 130 and the primary coil 130 is generating a magnetic field, the FO 190 may be undesirably heated. If the FO 190 is heated by inductive heating or wireless power transfer, there is a potential for fire, damage to the PTx 120, or injury to the user. Therefore, when the FO 190 is detected, the PTx 120 may stop generating the primary magnetic field or otherwise prevent the PTx 120 from transmitting sufficient energy in the FO 190 to cause the FO 190 to heat beyond a safe level.

[0043] Figure 2 A block diagram of an example wireless power transfer system 200 is shown. Figure 1 As described above, a wireless power transmission system may include a PTx 120 and a PRx 175. The PTx 120 may include one or more primary coils 130 configured to transmit wireless energy (as wireless power signals) to one or more corresponding secondary coils 220 in the PRx 175. A primary coil is a source of wireless energy (e.g., inductive or magnetic resonance energy that generates an electromagnetic field) in a power transmitter. The primary coil 130 may be associated with a power driver 206. The primary coil 130 may be a coil of wire that transmits wireless power (which may also be referred to as wireless energy or a wireless power signal). The power driver and the primary coil may together generate a primary magnetic field during wireless power transmission. The power driver 206 may include components (not shown) that provide power to the primary coil 130, thereby causing the primary coil 130 to generate a wireless power signal. For example, the power driver 206 may include one or more switches, drivers, series capacitors, rectifiers, or other components. The PTx 120 may also include a transmission controller 208 (sometimes referred to as a PTX controller or simply a controller) that controls the components of the power driver 206. For example, transmit controller 208 may determine an operating point (eg, voltage or current) and control power driver 206 according to the operating point.

[0044] In some implementations, the power driver 206, the transmit controller 208, and other components (not shown) may be collectively referred to as a power transmitter circuit. Some or all of the power transmitter circuit may be embodied as an integrated circuit (IC) implementing features of the present disclosure for controlling and transmitting wireless power to one or more power receivers. The transmit controller 208 may be implemented as a microcontroller, a dedicated processor, an integrated circuit, an application-specific integrated circuit (ASIC), or any other suitable electronic device.

[0045] The power source 212 can provide power to the power transmitter circuit in the PTx 120. The power source 212 can convert alternating current (AC) power into direct current (DC) power. For example, the power source 212 can include a converter that receives AC power from an external power supply (e.g., a supply mains) and converts the AC power into DC power used by the power driver 206.

[0046] In some implementations, the first communication unit 242 can be coupled to components of the power driver 206 or the primary coil 130 to send or receive communications via wireless power signals. The first communication unit 242 may include logic for controlling one or more switches and other components that cause the transmission and reception of wireless signals via the wireless power signals. For example, the first communication unit 242 may include a modulator or demodulator that converts information into a modulated signal that is added to the wireless power signal. In one example, the first communication unit 242 may convert data from the transmit controller 208 into a frequency shift keying (FSK) modulated signal that is combined with the wireless power signal for communication from the PTx 120 to the PRx 175. In another example, the first communication unit 242 may sense a load-modulated amplitude shift keying (ASK) signal from the power driver 206 or the primary coil 130 and demodulate the ASK signal to obtain data that the first communication unit 242 provides to the transmit controller 208.

[0047] In some implementations, the PTx 120 may include a wireless communication interface 214. The wireless communication interface 214 may be connected to a first communication coil 216 (which may be a coil or loop antenna). The wireless communication interface 214 may include logic for controlling one or more switches and other components that cause the transmission and reception of wireless communication signals via the first communication coil 216. In some implementations, the wireless communication interface 214 may support short-range radio frequency communications (e.g., Bluetooth TM ) or Near Field Communication (NFC). NFC is a technology through which data transmission is performed on a 13.56 MHz carrier frequency. The wireless communication unit 214 may also support any suitable communication protocol.

[0048] The transmit controller 208 can use various techniques to detect the presence or proximity of the PRx 175. In some implementations, the presence or proximity of the PRx 175 can be detected based on a load change in response to a periodic low-power signal generated by the power driver 206 and the primary coil 130. In some implementations, the presence or proximity of the PRx 175 can occur during a periodic pinging process of the wireless communication interface 214 in the PTx 120. When the PRx 175 is placed on the interface surface of the PTx 120, the ping of the wireless communication interface 214 via the first communication coil 216 can be responded to by a reply communication from the PRx 175. The ping and reply communication can form part of a handshake process that includes bidirectional communication between the PTx 120 and the PRx 175. Based on a successful handshake, the transmit controller 208 can determine that the PRx 175 is detected. As described herein, the PTx 120 can perform an object detection assessment that can detect the presence of an induction heating device (not shown), the PRx 175, or the FO 190. The PTx 120 may perform object detection evaluations at various times that may precede and / or follow the periodic low power signal or periodic pinging procedures of conventional wireless power systems.

[0049] The transmit controller 208 can control the characteristics of the wireless power provided by the PTx 120 to the PRx 175. After detecting the PRx 175, the transmit controller 208 can receive information from the PRx 175. For example, the transmit controller 208 can receive information during a handshake process with the PRx 175. This information can include information about the PRx 175 (e.g., power rating, load status, manufacturer, model, or receiver parameters when operating on a standard transmitter). The transmit controller 208 can use this information to determine at least one operational control parameter (e.g., frequency, duty cycle, voltage, etc.) of the wireless power it provides to the PRx 175. To configure the wireless power, the transmit controller 208 can modify the frequency, duty cycle, voltage, or any other suitable characteristic of the power driver 206.

[0050] PRx 175 may include a secondary coil 220, a rectifier 226, and a receiver controller 228. Secondary coil 220 may receive wireless energy via an electromagnetic field. When secondary coil 220 is aligned with primary coil 130, secondary coil 220 may generate an induced voltage based on the wireless power signal received from primary coil 130. A capacitor (not shown) and a switch (not shown) may be connected in series between secondary coil 220 and rectifier 226. Rectifier 226 may rectify the induced voltage and provide the induced voltage to load 230. In some implementations, load 230 may be external to PRx 175 and coupled via wires from rectifier 226. In some implementations, rectifier 226 may not be present, and the induced voltage in secondary coil 220 may be fed to an element connected in series with secondary coil 220 and load 230.

[0051] The receiver controller 228 can be connected to the rectifier 226 and the second communication unit 252. The second communication unit 252 can be coupled to the secondary coil 220 or components of the rectifier 226 to transmit or receive communications via wireless power signals. The second communication unit 252 may include logic for controlling one or more switches and other components that cause the transmission and reception of communication signals via the wireless power signals. For example, the second communication unit 252 may include a modulator or demodulator that converts information into an ASK or FSK modulated signal. In one example, the second communication unit 252 may convert data from the receiver controller 228 into an ASK modulated signal, which is used to load modulate the wireless power signal communicated from the PRx 175 to the PTx 120. In another example, the second communication unit 252 may sense an FSK signal in the wireless power signal at the secondary coil 220 or rectifier 226 and demodulate the FSK signal to obtain data that the second communication unit 252 provides to the receiver controller 228.

[0052] In some implementations, the PRx 175 may include a wireless communication interface 232. The wireless communication interface 232 may include modulation and demodulation circuitry to enable wireless communication via a second communication coil 234 (which may be a coil or loop antenna). Thus, the receiver controller 228 may wirelessly communicate with the transmit controller 208 via the wireless communication interface 232 and the wireless communication interface 214 using NFC communication or Bluetooth.

[0053] The interface surface 280 (sometimes also referred to as an "interface space") can demarcate the space between the power transmitter and the power receiver. For example, the interface surface can include a surface of the power transmitter on which the power receiver can be placed. The distance between the primary coil 130 and the secondary coil 220 can include the thickness of the surface in the interface surface. During wireless power transfer, the primary coil 130 can induce a magnetic field (referred to as a primary magnetic field) through the interface surface and into the operating environment in which the secondary coil is located. Therefore, the "operating environment" is defined by the primary magnetic field in the system, where the primary magnetic field of the primary coil 130 is detectably present and can detectably interact with the secondary coil or a foreign object 190 (shown as FO 190).

[0054] When a foreign object 190 is present in the operating environment of the WPT system, the foreign object 190 may experience an increase in temperature due to interaction with the magnetic field. Therefore, when a foreign object is detected, the PTx 120 stops generating the primary magnetic field or otherwise prevents the PTx 120 from transmitting an amount of energy in the foreign object 190 that would cause the foreign object 190 to heat up beyond a safe level.

[0055] The PTx 120 may also include an object detection unit 290. In some implementations, the object detection unit 290 may be referred to as a pot / pan detection unit, a PRx detection unit, or a FO detection unit. In some implementations, the object detection unit 290 may be integrated into the conveyor controller 208. For example, the object detection unit 290 may be collocated or implemented within the conveyor controller 208 as software. Alternatively or additionally, the object detection unit 290 may be implemented as a standalone system of the PTx 120 or a multi-function cooktop including the PTx 120. For example, the multi-function cooktop may include an object detection pad configured to detect foreign objects at the induction heating device, the PRx, or any of a plurality of PTx locations.

[0056] The object detection unit 290 can be configured to detect objects in the operating environment of the PTx 120 based on measurements obtained in conjunction with object detection pulses. The object detection pulses can be generated by the power driver 206 or a different driver (not shown). As part of the object detection evaluation, the object detection unit 290 can cause the object detection pulses to be transmitted via the primary coil 120 or one or more object detection coils (not shown). The object detection unit 290 can obtain the measurements while transmitting the pulses. The object detection unit 290 can provide the measurements to the transmit controller 208 so that the transmit controller 208 can compare the measurements with one or more thresholds to detect various types of objects. Alternatively, the object detection unit 290 can perform a comparison of the measurements with the one or more thresholds and provide the results of the object detection evaluation to the transmit controller 208.

[0057] Figure 3 1 is a flow chart showing an example process 300 for object detection evaluation. The operations of process 300 may be performed by a controller or object detection unit of a PTx (e.g., referring to FIG. Figure 2 In some implementations, process 300 may be implemented by a controller included in or as part of a processor of a multi-function stove.

[0058] In some implementations, the steps of process 300 may begin after the PTx has detected or received an indication that a PRx or induction heating device is in proximity to the PTx. For example, the PTx may receive wireless communications or read an NFC tag, either of which may indicate the presence of the PRx or induction heating device. Alternatively, the controller may periodically execute process 300 to detect an object and determine its type. In such a case, not all steps of 300 may be implemented.

[0059] At block 310 , the controller causes a power driver or other component to generate an object detection pulse. The object detection pulse may be a relatively low power signal transmitted by the primary coil or one or more detection coils.

[0060] At block 320, the controller obtains a measurement associated with the object detection pulse. For example, the controller may obtain the measurement from a voltage sensor, current sensor, impedance sensor, or other measurement unit connected to the primary coil or one or more detection coils. In some implementations, the measurement may be a measured parameter at the output of the primary coil or power driver (e.g., coil impedance, coil current, or coil voltage). Alternatively, the measurement may be a difference between the measured parameters at two or more detection coils such that the measurement represents a differential impedance, a differential current, or a differential voltage. Figure 3In an example, the measurement indicates that an object is present in the magnetic field of the PTx. For example, an object may be detected based on a measurement that is different from a steady-state measurement in which the object is not present.

[0061] At block 330, the controller compares the measured value to the threshold ranges. In some implementations, one or more of the threshold ranges may be predefined or preconfigured in a memory of the controller. Figure 3 In the example of FIG, the first range represents a range of measurement values expected for the induction heating device, the second range represents a range of measurement values expected for PRx, and the third range represents a range of measurement values expected for foreign objects. If the measurement value is within the first range, the flowchart continues to block 340. If the measurement value is within the second range, the flowchart continues to block 350. If the measurement value is within the third range, the flowchart continues to block 360. If the measurement value is not within any of the first, second, or third ranges, the controller may default to block 360 or may restart the object detection evaluation.

[0062] At block 340 , when the measured value is within the first range, the controller may determine that the object is an induction heating device, such as a pot or pan. The controller may continue the induction heating mode of operation.

[0063] At block 350 , when the measured value is within the second range, the controller may determine that the object is an electrical appliance including PRx. The controller may continue the wireless power transfer mode of operation.

[0064] At block 360 , when the measured value is within the third range, the controller may determine that the object is a foreign object. The controller may indicate a foreign object detection (FOD) fault, for example, via a user interface associated with the PTx.

[0065] refer to Figure 3 The described operation enables PTx to detect various types of objects using object detection pulses. Figure 4 and Figure 5 As described, the various ranges of measured values may, without the techniques of the present disclosure, lead to unpredictable or inaccurate results.

[0066] In some implementations, PTx may perform blocks 310, 320, 330, 340, and 360 as part of the pot detection evaluation. PTx may use alternative techniques (e.g., communication from PRx) to detect the presence of PRx. For example, at block 345, PTx may detect PRx using a communication handshake that includes a ping using the NFC coil and a response from PRx. In this case, when the communication handshake is achieved, PTx may skip the pot detection evaluation and proceed directly to block 350 to continue wireless power transfer mode. In wireless power transfer mode, PTx may use an object detection evaluation (this time referred to as a foreign object detection evaluation) to determine whether a foreign object is present with PRx. The foreign object detection evaluation includes an object detection pulse (similar to block 310), obtaining a measurement (similar to block 320), and comparing the measurement to the second range and / or third range (similar to block 330). In some implementations, the measurement in the foreign object detection evaluation may be based on a coupling factor measurement. Foreign object detection evaluation typically occurs during the connection phase of the power transfer protocol performed by the PTx and PRx, during which the secondary coil of the PRx is disconnected from the rest of the PRx circuit and load using a series switch.

[0067] Figure 4 4 is a simplified diagram 400 conceptually illustrating various ranges and measurements for object detection. A scale 440 may represent various measurements that may be obtained during an object detection evaluation. A first range 410 may be associated with an induction heating device. A second range 420 may be associated with a foreign object and may be referred to as a FO threshold range. A third range 430 may be associated with a wireless power receiver and may be referred to as a PRx threshold range. Depending on the measurement's position within scale 440, the measurement may be within the first range 410, the second range 420, or the third range. For example, a first measurement 412 obtained when the induction heating device is present is within the first range 410. A second measurement 414 obtained when a foreign object is present is within the second range 420. A third measurement 416 obtained when the wireless power receiver (or an appliance incorporating PRx) is present is within the third range 430.

[0068] As described herein, there may be instances where a PRx (or an appliance containing a PRx) has a friendly metal. The friendly metal may shift the range of expected measurements closer to or overlap with the second range 420 associated with foreign objects.

[0069] Figure 5 is a diagram 500 conceptually illustrating the measured values and ranges of PRx with friendly metals. Figure 5 , the first range 410 and the second range 420 are shown on the scale 440, as shown in FIG. Figure 4However, the third range 530 shows the range of measurement values that may be expected for PRx with friendly metals. Figure 5 As shown in , there may be overlapping ranges of values 550 that fall within the second range 420 and the third range 530. In addition, the measurement 518 may be for a foreign object or a PRx. Using the techniques of this disclosure, the PTx (or controller) can determine whether the measurement 518 is a PRx with friendly metal or a foreign object.

[0070] Figure 6 is a timing diagram 600 illustrating a baseline situation when a PRx with friendly metal is repeatedly detected as a foreign object. As mentioned earlier, object detection pulses can also be used for FOD in the presence of a valid PRx identified using a communication handshake. The timing diagram 600 shows a communication 601 from the PRx to the PTx as part of the communication handshake. The timing diagram 600 shows the PTx 120 performing a first object detection evaluation 610 (which may be referred to as a foreign object detection evaluation) where the PRx 175 is present. The first object detection evaluation 610 may occur before the PTx 120 continues in the wireless power transfer mode. Alternatively or additionally, the first object detection evaluation 610 may occur in the connection phase before the PTx 120 transitions to the power transfer phase.

[0071] exist Figure 6 In the example of , PRx 175 has friendly metal, which may cause PRx 175 to be falsely detected as a foreign object. For example, the measurement value of the first object detection evaluation 610 may be in the reference Figure 5 Detection evaluation 610 may be performed by a user interface operative to detect the object being detected by the PTx 120. The user interface operative to detect the object being detected by the PTx 120 may be performed by a user interface operative to detect the object being detected by the PTx 120. The user interface operative to detect the object being detected by the PTx 120 may be performed by a user interface operative to detect the object being detected by the PTx 120. The user interface operative to detect the object being detected by the PTx 120 may be performed by a user interface operative to detect the object being detected by the PTx 120.

[0072] Later, the PRx 175 may request the PTx 120 to transition to the connection mode and remain in that phase until the next power transfer phase. In some cases, the PRx 175 may periodically request transitions to the power transfer phase or the connection phase - thereby causing multiple subsequent object detection evaluations to detect the presence of FO. For simplicity, Figure 6Only one subsequent object detection evaluation (second object detection evaluation 620) is shown. In the baseline case, the second object detection evaluation 620 results in another FOD failure, thereby requiring a second FOD failure process 622. The second FOD failure process 622 may also include user interaction. Due to repeated FOD failures, the operator of the PRx 175 may be required to perform multiple user interactions, resulting in frustration or dissatisfaction.

[0073] Figure 7 is a timing diagram 700 illustrating an example situation in which a reference value of PRx with a friendly metal can be used for subsequent object detection evaluation. Figure 6 Likewise, the timing diagram 700 shows a communication 701 from PRx to PTx as part of a communication handshake. The timing diagram 700 also shows the PTx 120 performing a first (foreign) object detection evaluation 610 in which the PRx 175 is present. However, Figure 7 and Figure 6 The difference is that after the first FOD fault processing 612, the PTx 120 may store a reference value for the PRx 175 (as shown at block 714). For example, the reference value may be a measurement value of the first object detection evaluation 610. In some implementations, the reference value may be stored in association with an identification (ID) of the PRx 175 (e.g., an ID in a communication (not shown) from the PRx 175 to the PTx 120).

[0074] continue Figure 7 , PTx 120 may perform a subsequent object detection evaluation (second foreign object detection evaluation 720). PTx 120 may compare the measurement value of second object detection evaluation 720 to reference value 714. If the measurement of second object detection evaluation 720 is within a threshold range of reference value 714, PTx 120 may determine that the detected object is the previously detected PRx 175.

[0075] In some implementations, the measurement value may change when the PRx 175 moves in the operating environment of the PTx 120. Similarly, the measurement value may change due to temperature drift or other discernible changes (where the measurement value is affected without the introduction of a foreign object). The PTx 120 can determine that the change in the measurement value is due to movement, temperature drift, or other discernible changes related to the PRx 175, rather than the introduction of a foreign object. For example, a change in the alignment of the receiver can be determined based on a change in the measurement value from the power receiver, which is for a foreign object detection pulse applied at the power transmitter. When the PTx 120 determines that the measurement value has changed and no FO has been introduced, the PTx 120 can store the changed measurement value as an updated reference value for the PRx 175 and use the updated measurement value for subsequent object detection evaluations (not shown).

[0076] Figure 8 is a timing diagram 800 illustrating an example situation in which communication from a PRx with a friendly metal can improve object detection evaluation results. Figure 6 and Figure 7 Likewise, timing diagram 800 illustrates operations associated with PTx 120 and PRx 175. PTx 120 detects PRx 175 via communication 801 from PRx to PTx as part of a communication handshake. Figure 8 and Figure 6 and Figure 7 175 is configured to pass communication 802 to PTx 120. Communications 801 and 802 can be short-range radio frequency communications (e.g., using NFC). Communications 801 and 802 can be active or passive transmissions. Passive transmissions can include an NFC tag integrated or attached to the PRx 175 and readable by the NFC interface of the PTx 120. Communication 802 can be an NFC Data Exchange Format (NDEF) message. Communication 802 can include a reference measurement value, a range of expected measurements, or a friendly metal indication.

[0077] In one example, communication 802 includes a reference measurement value obtained by performing a test object detection evaluation with a standard power transmitter, in which the PRx 175 is not present with a foreign object. At block 805, the PTx 120 can store the reference measurement value as a reference value for the PRx 175. During each of the object detection evaluations 810 and 820, when the measurement value is within the PRx threshold range of the reference value (stored in block 805), the PTx 120 can determine that the detected object is the PRx 175 without the foreign object. Thus, the PTx 120 can avoid triggering a FOD fault and prevent the need for FOD fault processing.

[0078] In another example, communication 802 includes a range of expected measurement values for PRx 175. For example, the range of expected measurement values may indicate a threshold value of acceptable measurement values for an object detection evaluation that should result in detection of PRx 175 rather than a foreign object. At block 805, PTx 120 may store the range of expected measurement values and determine a PRx threshold range based on the range of expected measurement values. During each of object detection evaluations 810 and 820, when the measurement value is within the range of expected measurement values (stored in block 805), PTx 120 may determine that the detected object is PRx 175. Alternatively, at block 805, PTx 120 may calculate a reference value based on the range of expected measurement values and store the reference value.

[0079] The range can be in any format including offset, minimum, maximum, minimum and maximum, or scale factor. Figure 3-Figure 5 , the range of expected measurement values may be the third range 430 or 530. If the range of expected measurement values overlaps with the second range 420, the PTx 120 may override the second range 420 for the overlapping range 550 and consider any measurement values in the overlapping range 500 to be within the third range 530 (the range of expected measurement values) and detect the object as a PRx rather than a foreign object.

[0080] In yet another example, communication 802 includes a friendly metal indication. For example, the friendly metal indication can be a value or bit that notifies PTx 120 that PRx 175 is metal-friendly. At block 805, PTx 120 can store the friendly metal indication. During each of object detection evaluations 810 and 820, upon receiving the friendly metal indication from PRx 175 in communication 802, PTx 120 can determine that the detected object is PRx 175. For example, PTx 120 can ignore measurements that would otherwise be associated with a foreign object.

[0081] In another example method, when a PRx 175 is first placed on a PTx 120, the PRx may indicate the presence of a friendly metal 802. The PTx stores information 805. During the initial object assessment (object detection assessment 810), the PTx 120 stores the measurement value along with the PRx ID in its non-volatile memory. During subsequent object detection assessments (e.g., object detection assessment 820), either during the first placement of a PRx 175 on a PTx 120 or during subsequent placements of a PRx 175 on a PTx 120, the PTx 120 checks whether the measurement value is within the PRx threshold range corresponding to the stored measurement value for that PRx 175. If the measurement value is outside the PRx threshold range, the PTx 120 triggers a FOD action. The FOD action may prompt a user action to confirm the absence of a FOD. If the user action confirms the absence of a FOD, the PTx 120 updates the stored measurement value corresponding to the PRx 175 in its non-volatile memory. The value can be replaced, or the range of values can be updated.

[0082] Figure 9 FIGURE 1 shows a block diagram of an example PTx 120. The PTx 120 may include a Figure 2 The power source 212, power driver 206, transmit controller 208, primary coil 130, wireless communication interface 214, and first communication coil 216 are depicted. The power driver 206 is illustrated with a half-bridge circuit to convert DC power from the power source 212 into an AC signal applied to the primary coil 130. Figure 8 Although not shown in the figure, the power source 212 may include a conversion unit that converts the AC mains power into DC power for the power source 212. In addition, the power driver 206 may be any type of power conversion circuit capable of providing an AC signal to the primary coil 130. For example, Figure 8 As shown in , the power driver 206 may include a half-bridge circuit with parallel capacitors. Alternatively, the power driver 206 may include a full-bridge circuit.

[0083] The transmit controller 208 can cause the PTx 120 to transmit an object detection pulse via the primary coil 130. In some implementations, the object detection pulse may also be referred to as a ping or "pan detection" signal. When an induction heating device is placed near the primary coil 130, the PTx 120 (or an object detection unit therein) can measure a change in a measurement value (e.g., impedance) to detect whether the induction heating device is located above the primary coil 130. If the measurement value falls within a predetermined range (e.g., a tolerance), the PTx 120 changes operation from a ping mode to an induction-based heating mode, in which the PTx 120 uses induction to transfer energy. Thus, the induction heating device can be detected based on the impedance presented by the pan / appliance. In the case of a power receiver (such as those described herein), one or more switches may cause the impedance of the secondary coil to be outside the tolerance. For example, a series switch may cause the impedance measured by the PTx 120 to be above the tolerance.

[0084] In some implementations, once a power receiver is detected (e.g., through a communication handshake), an object detection pulse can be used simultaneously to detect the presence of the FO and the power receiver and to determine the coupling factor of the power receiver. The coupling factor (sometimes referred to as the k-factor) can be an indication of how well the secondary coil and the primary coil are able to transmit wireless power. For example, the k-factor can be a measure of the potential flux linkage for wireless power transfer between the primary coil and the secondary coil. In some implementations, the k-factor can depend on the number of turns in the primary coil (n1), the number of turns in the secondary coil (n2), the voltage transmitted by the primary coil (v1), and the voltage induced in the secondary coil during the measurement period (v2), among other things. The voltage v1 can also be referred to as the transmitted voltage, and the voltage v2 can also be referred to as the received voltage. The k-factor can be calculated as follows (Equation 1): In some implementations, it is desirable to disconnect the secondary coil from other components of the power receiver during the measurement period used to determine the k-factor. Therefore, in some implementations, when object detection evaluation is combined with k-factor measurement, the power receiver can use one or more switches to disconnect the secondary coil from one or more other components (e.g., a rectifier, a load, or both) during the object detection evaluation.

[0085] Figure 10 A block diagram of an example PRx 175 is shown with a switch that enables disconnection of the secondary coil during object detection evaluation with coupling factor measurement. Components of the PRx 175 may include reference Figure 2 The PRx 175 is described with similarly numbered components. Figure 10 The switch 1050 is shown as a series switch on one leg of the secondary coil 220. However, in some implementations, the switch 1050 can be any type of switch that prevents or minimizes current flow through the secondary coil 220 when the switch 1050 is in the first position. Figure 10 10. In the embodiment of the present invention, the first position of the switch 1050 is an open position, so that the circuit including the secondary coil 220 does not conduct current. The PRx 175 may also include a voltage sensor 1020 coupled to the secondary coil 220. During the object detection evaluation, the receiver controller 228 may cause the switch 1050 to disconnect the secondary coil 220 from the power receiving circuit (e.g., the rectifier 226 and the load 230). During the power transfer phase, the receiver controller 228 may cause the switch 1050 to connect the secondary coil 220 to the power receiving circuit.

[0086] When performing object detection evaluation, the switch 1050 can also be used to disconnect the secondary coil 220 from the power receiving circuit (e.g., the rectifier 226, the load 230, or both). The object detection evaluation can include any of the operations described herein, such as with reference to Figure 3-Figure 8 Object detection evaluation as described. Object detection evaluation may be performed during a foreign object detection (FOD) period, a k-factor measurement period, or both.

[0087] exist Figure 10In this embodiment, object detection evaluation (performed as a foreign object detection evaluation) is combined with coupling factor measurement. As part of the foreign object detection evaluation with an active PRx receiver during the connection phase, a PTx (not shown) may transmit an object detection pulse. In some implementations, the object detection pulse may be transmitted using a known or predetermined voltage (v1) and frequency (fp). The PTx may determine the presence of FO based on the measured values (voltage, current, impedance, or quality factor) used to detect FO. Simultaneously, the voltage sensor 1020 may allow the receiver controller 228 to measure the received voltage (v2) of the secondary coil 220 induced by the object detection pulse. The receiver controller 228 may transmit a message to the PTx via the wireless communication interface 232. The message may include a received voltage value based on the measured v2. The PTx may use the received voltage value to determine a coupling factor (k factor). The k factor may be used by the PTx to determine the operating point of the wireless power signal transmitted by the PTx during the power transfer phase. For example, the operating point may be based on a calculation that takes into account the ratio between v1 and v2. Thus, the same object detection pulse is used to measure the coupling factor and detect the presence of FO.

[0088] Figure 11 1100 according to some aspects of the present disclosure. Figure 11 One or more process blocks of may be performed by a PTx (e.g., PTx 120 described herein). Alternatively, Figure 11 One or more process blocks of may be performed by a controller or object detection unit of the PTx. For simplicity, the process blocks are described as being performed by the PTx.

[0089] At block 1110, the PTx receives a communication from a power receiver present in the magnetic field of the power transmitter. The communication may be part of a communication handshake indicating the presence of the power receiver. At block 1120, the PTx obtains a measurement value based on the object detection evaluation. At block 1130, the PTx determines whether a foreign object is present in the magnetic field with the power receiver based on the measurement value. For example, when the measurement value is outside a foreign object (FO) threshold range for foreign objects, the PTx may determine that the foreign object is not present. Alternatively or additionally, when the measurement value is within a PRx threshold range based on a reference measurement value of the power receiver (PRx), the PTx may determine that the foreign object is not present. In some implementations, the FO threshold range may be similar to the reference measurement value. Figure 3-Figure 4 In some implementations, the PRx threshold range can be similar to the reference Figure 3-Figure 4 In some implementations, the PRx threshold range can be based on the reference Figure 7-Figure 8 The previous object detection evaluation or communication from the power receiver.

[0090] although Figure 11 Example blocks of process 1100 are shown, but in some implementations, process 1100 may include more Figure 11 The blocks of process 1100 may be more blocks, fewer blocks, different blocks, or blocks arranged differently than those depicted in the flowchart. Additionally or alternatively, two or more of the blocks of process 1100 may be executed in parallel.

[0091] Figure 12 1200 according to some aspects of the present disclosure. Figure 12 One or more process blocks of may be performed by a PTx (e.g., PTx 120 described herein). Alternatively, Figure 12 One or more process blocks of may be performed by a controller or object detection unit of the PTx. For simplicity, the process blocks are described as being performed by the PTx.

[0092] At block 1210, the PTx receives communications from a power receiver present in the magnetic field of the power transmitter. At block 1220, the PTx obtains measurements of low-power transmissions from the PTx during object detection evaluation. At block 1230, the PTx calculates a coupling factor between the PTx and the PRx based on the measurements, where the coupling factor represents the alignment of the PTx's primary coil with the PRx's secondary coil.

[0093] although Figure 12 Example blocks of process 1200 are shown, but in some implementations, process 1200 may include more Figure 12 More blocks, fewer blocks, different blocks, or a different arrangement of blocks than those depicted in process 1200. Additionally or alternatively, two or more of the blocks of process 1200 can be executed in parallel.

[0094] Figure 13 A block diagram of an example device 1300 for use in a multi-function stove is shown. In some implementations, the device 1300 may be part of a PTx (e.g., any of the PTx described herein). In some implementations, the device 1300 may be implemented as part of a multi-function stove that includes one or more PTx capable of operating in an induction heating mode and a wireless power transfer mode. The device 1300 may include a processor 1302 (which may include multiple processors, multiple cores, multiple nodes, or implement multi-threading, etc.). The device 1300 may also include a memory 1306. The memory 1306 may be system memory or any one or more of the possible implementations of a computer-readable medium described herein. The device 1300 may also include a bus 1311 (e.g., PCI, ISA, PCI-Express, AHB, AXI, etc.).

[0095] Device 1300 may include one or more controllers (e.g., controller 1362) configured to manage object detection evaluation. Object detection evaluation may be performed by an object detection unit (not shown). Alternatively, controller 1362 may implement the object detection unit. In some implementations, controller 1362 may be distributed across processor 1302, memory 1306, and bus 1311. Controller 1362 may perform some or all of the operations described herein.

[0096] The memory 1306 may include executable instructions executed by the processor 1302 to implement the reference Figures 1-12 Any of these functionalities may be implemented partially (or entirely) in hardware or on the processor 1302. For example, the functionality may be implemented in a dedicated integrated circuit, in logic implemented in the processor 1302, in a coprocessor on a peripheral device or card, etc. In addition, the implementation may include Figure 13 The processor 1302, memory 1306, and controller 1362 may be coupled to a bus 1311. Although illustrated as being coupled to the bus 1311, the memory 1306 may be coupled to the processor 1302.

[0097] The figures, operations, and components described herein are examples intended to aid in understanding example implementations and should not be used to limit potential implementations or to limit the scope of the claims. Some implementations may perform additional operations, fewer operations, operations in parallel or in a different order, and perform some operations differently.

[0098] The foregoing disclosure provides illustrations and descriptions, but is not intended to be exhaustive or to limit the aspects to the exact form disclosed. Modifications and changes may be made in light of the above disclosure, or modifications and changes may be obtained from the practice of the aspects. Although the aspects of the present disclosure have been described according to various examples, any combination of aspects from any of the examples is also within the scope of the present disclosure. The examples in this disclosure are provided for teaching purposes. Alternatively, or in addition to other examples described herein, the examples include any combination of the following implementation options (listed as clauses for clarity). Terms

[0099] Clause 1. A method for wireless power transfer via a power transmitter, comprising: receiving a communication from a power receiver present in a magnetic field of the power transmitter; obtaining a measurement based on an object detection evaluation; and determining whether a foreign object is present in the magnetic field with the power receiver based on the measurement.

[0100] Clause 2. A method according to Clause 1, wherein determining whether the foreign object exists includes at least one of the following: determining that the foreign object does not exist when the measurement value is outside a foreign object (FO) threshold range for foreign objects, or determining that the foreign object does not exist when the measurement value is within a PRx threshold range based on a reference measurement value of a power receiver (PRx).

[0101] Clause 3. The method according to Clause 2, wherein determining whether the foreign object exists further includes at least one of the following: determining that the foreign object exists when the measurement value is outside the PRx threshold range, or determining that the foreign object exists when the measurement value is within the FO threshold range.

[0102] Clause 4. The method of any one of clauses 2-3, wherein the PRx threshold range and the FO threshold range overlap each other, and wherein the measurement value is compared to the PRx threshold range before the measurement value is compared to the FO threshold range.

[0103] Clause 5. The method of any of clauses 2-4, further comprising determining the PRx threshold range based on a fixed offset of a reference value of the power receiver.

[0104] Clause 6. The method of any one of clauses 2-5, further comprising: determining the PRx threshold range based on previous measurement values of a previous object detection evaluation, in which the power transmitter confirmed that the foreign object was not present in the magnetic field together with the power receiver.

[0105] Clause 7. The method according to Clause 6 further includes: when the previous object detection evaluation is within the FO threshold range, detecting a user action after the previous object detection evaluation, wherein the user action indicates that no foreign object is present in the magnetic field; storing the previous measurement value as a reference value for the power receiver; and updating the PRx threshold range based on the reference value.

[0106] Clause 8. The method of clause 6, further comprising: receiving a communication from the power receiver after the previous object detection evaluation when the previous object detection evaluation is within the FO threshold range, wherein the communication indicates that no foreign objects are present in the magnetic field; storing the previous measurement value as the reference value of the power receiver; and updating the PRx threshold range based on the reference value.

[0107] Clause 9. The method of any one of clauses 2-8, further comprising: receiving a communication from the power receiver, the communication indicating the PRx threshold range of the power receiver, the PRx threshold range having been measured in a test environment when the power receiver was placed on a standard power transmitter in the absence of foreign objects.

[0108] Clause 10. The method of any of clauses 2-9, further comprising: receiving a communication from the power receiver, the communication indicating a reference value for the power receiver; and determining the PRx threshold range based on the reference value.

[0109] Clause 11. The method of clause 10, wherein the reference value comprises a reference measurement value that has been measured in a test environment when the power receiver is placed on a standard power transmitter.

[0110] Clause 12. The method of any of clauses 2-11, further comprising: receiving a communication from the power receiver indicating that the power receiver contains a friendly metal; and determining the PRx threshold range based on predetermined measurements of power receivers containing friendly metals.

[0111] Clause 13. The method of any of clauses 2-12, further comprising: receiving a communication from the power receiver, the communication indicating a range of expected measurement values for the power receiver; and determining the PRx threshold range based on the range of expected measurement values.

[0112] Clause 14. The method of any of clauses 2-13, further comprising obtaining the PRx threshold range, or a reference value indicative of the PRx threshold range, or both, from a data field in out-of-band communication received by the power transmitter from the power receiver.

[0113] Clause 15. The method of clause 14, wherein the out-of-band communication is a Near Field Communication (NFC) Data Exchange Format (NDEF) message.

[0114] Clause 16. The method according to any one of clauses 1-11, further comprising: enabling a wireless power transfer mode of the power transmitter if the foreign object is not present with the power receiver; and disabling the wireless power transfer mode of the power transmitter if the foreign object is present with the power receiver.

[0115] Clause 17. The method according to any one of clauses 2-16, further comprising: calculating a coupling factor between the power transmitter and the power receiver based on the measurement value, wherein the coupling factor represents an alignment of a primary coil of the power transmitter and a secondary coil of the power receiver.

[0116] Clause 18. A method according to any one of clauses 1-17, wherein the measured value is at least one value selected from the group consisting of: a coil voltage or a differential voltage of two or more detection coils of a coil pair; a coil current or a differential current of the two or more detection coils of the coil pair; a coil impedance or a differential impedance of the two or more detection coils of the coil pair; a quality factor calculated as part of the object detection evaluation; and energy losses of low power transmission of the primary coil of the power transmitter.

[0117] Clause 19. A method for wireless power transfer, comprising: receiving a communication from a power receiver present in a magnetic field of a power transmitter; obtaining a first measurement of a first parameter of a low power transfer from the power transmitter during an object detection evaluation; and calculating a coupling factor between the power transmitter and the power receiver based on the first measurement, wherein the coupling factor represents an alignment of a primary coil of the power transmitter with a secondary coil of the power receiver.

[0118] Clause 20. The method of clause 19, further comprising determining whether a foreign object is present in the magnetic field with the power receiver based on at least one of: the first measurement, or a second measurement of a second parameter obtained during the object detection evaluation.

[0119] Clause 21. A method according to Clause 20, wherein determining whether the foreign object exists includes at least one of the following: determining that the foreign object does not exist when the first measurement value or the second measurement value is outside a foreign object (FO) threshold range for foreign objects, or determining that the foreign object does not exist when the first measurement value or the second measurement value is within a PRx threshold range based on a reference measurement value of a power receiver (PRx).

[0120] Clause 22. A method according to any one of clauses 19-21, wherein obtaining the measurement value includes: transmitting the low power signal when a power receiving circuit of the power receiver is disabled, the low power signal having a first voltage at the primary coil; receiving a communication from the power receiver indicating a second voltage at the power receiving circuit caused by the low power signal; and calculating the coupling factor based at least in part on a ratio of the second voltage to the first voltage.

[0121] Clause 23. A device for wireless power transmission, comprising: a communication unit configured to receive communications from a power receiver present in a magnetic field of the power transmitter; a measurement unit configured to obtain a measurement value based on an object detection evaluation; and a control unit configured to determine whether a foreign object is present in the magnetic field together with the power receiver based on the measurement value.

[0122] Clause 24. An apparatus according to clause 23, wherein the control unit is configured to: determine that the foreign object does not exist when the measurement value is outside a foreign object (FO) threshold range for foreign objects, or determine that the foreign object does not exist when the measurement value is within a PRx threshold range based on a reference measurement value of a power receiver (PRx).

[0123] Clause 25. The apparatus of clause 24, wherein the control unit is configured to determine that the foreign object exists when the measurement value is outside the PRx threshold range, or to determine that the foreign object exists when the measurement value is within the FO threshold range.

[0124] Clause 26. An apparatus according to any one of clauses 24-25, wherein the PRx threshold range and the FO threshold range overlap each other, and wherein the control unit is configured to compare the measurement value with the PRx threshold range before comparing the measurement value with the FO threshold range.

[0125] Clause 27. The apparatus of any of clauses 24-26, wherein the control unit is configured to determine the PRx threshold range based on a fixed offset of a reference value of the power receiver.

[0126] Clause 28. An apparatus according to any one of clauses 24-27, wherein the control unit is configured to: determine the PRx threshold range based on previous measurement values of a previous object detection evaluation, in which the power transmitter confirmed that the foreign object was not present in the magnetic field together with the power receiver.

[0127] Clause 29. An apparatus according to clause 28, wherein the control unit is configured to: detect a user action after the previous object detection evaluation when the previous object detection evaluation is within the FO threshold range, wherein the user action indicates that no foreign object is present in the magnetic field; store the previous measurement value as a reference value for the power receiver; and update the PRx threshold range based on the reference value.

[0128] Clause 30. An apparatus according to clause 28, wherein the control unit is configured to receive a communication from the power receiver after the previous object detection evaluation when the previous object detection evaluation is within the FO threshold range, wherein the communication indicates that no foreign objects are present in the magnetic field; and wherein the control unit is configured to: store the previous measurement value as the reference value of the power receiver; and update the PRx threshold range based on the reference value.

[0129] Clause 31. An apparatus according to any of clauses 24-30, wherein the control unit is configured to receive a communication from the power receiver, the communication indicating the PRx threshold range of the power receiver, the PRx threshold range having been measured in a test environment when the power receiver was placed on a standard power transmitter in the absence of foreign objects.

[0130] Clause 32. An apparatus according to any one of clauses 24-31, wherein the control unit is configured to receive a communication from the power receiver, the communication indicating a reference value of the power receiver; and wherein the control unit is configured to determine the PRx threshold range based on the reference value.

[0131] Clause 33. The apparatus of clause 31, wherein the reference value comprises a reference measurement value that has been measured in a test environment when the power receiver is placed on a standard power transmitter.

[0132] Clause 34. An apparatus according to any one of clauses 24-33, wherein the control unit is configured to receive a communication from the power receiver indicating that the power receiver contains a friendly metal; and wherein the control unit is configured to determine the PRx threshold range based on a predetermined measurement value of the power receiver containing the friendly metal.

[0133] Clause 35. An apparatus according to any one of clauses 24-34, wherein the control unit is configured to receive a communication from the power receiver, the communication indicating a range of expected measurement values for the power receiver; and wherein the control unit is configured to determine the PRx threshold range based on the range of expected measurement values.

[0134] Clause 36. An apparatus according to any one of clauses 24-35, wherein the control unit is configured to obtain the PRx threshold range, or a reference value indicative of the PRx threshold range, or both, from a data field in an out-of-band communication received by the power transmitter from the power receiver.

[0135] Clause 37. The device of clause 36, wherein the out-of-band communication is a Near Field Communication (NFC) Data Exchange Format (NDEF) message.

[0136] Clause 38. An apparatus according to any one of clauses 23-33, wherein the control unit is configured to: enable the wireless power transmission mode of the power transmitter if the foreign object is not present with the power receiver; and disable the wireless power transmission mode of the power transmitter if the foreign object is present with the power receiver.

[0137] Clause 39. The apparatus of any one of clauses 24-38, wherein the control unit is configured to calculate a coupling factor between the power transmitter and the power receiver based on the measurement value, wherein the coupling factor represents an alignment of a primary coil of the power transmitter with a secondary coil of the power receiver.

[0138] Clause 40. An apparatus according to any of clauses 23-39, wherein the measured value is at least one value selected from the group consisting of: a coil voltage or a differential voltage of two or more detection coils of a coil pair; a coil current or a differential current of the two or more detection coils of the coil pair; a coil impedance or a differential impedance of the two or more detection coils of the coil pair; a quality factor calculated as part of the object detection evaluation; and energy loss for low power transmission of the primary coil of the power transmitter.

[0139] Item 41. A device for wireless power transmission, comprising: a communication unit configured to receive communications from a power receiver present in a magnetic field of a power transmitter; a measurement unit configured to obtain a first measurement value of a first parameter of a low power transmission from the power transmitter during an object detection evaluation; and a control unit configured to calculate a coupling factor between the power transmitter and the power receiver based on the first measurement value, wherein the coupling factor represents an alignment of a primary coil of the power transmitter with a secondary coil of the power receiver.

[0140] Clause 42. An apparatus according to clause 41, wherein the control unit is configured to: determine whether a foreign object is present in the magnetic field together with the power receiver based on at least one of the following: the first measurement value, or a second measurement value of a second parameter obtained during the object detection evaluation.

[0141] Clause 43. An apparatus according to clause 42, wherein the control unit is configured to: determine that the foreign object does not exist when the first measurement value or the second measurement value is outside a foreign object (FO) threshold range for foreign objects, or determine that the foreign object does not exist when the first measurement value or the second measurement value is within a PRx threshold range based on a reference measurement value of a power receiver (PRx).

[0142] Clause 44. An apparatus according to any one of clauses 41-43, wherein the control unit is configured to transmit the low power signal when the power receiving circuit of the power receiver is disabled, the low power signal having a first voltage at the primary coil; wherein the control unit is configured to receive a communication from the power receiver indicating a second voltage at the power receiving circuit caused by the low power signal; and wherein the control unit is configured to calculate the coupling factor based at least in part on a ratio of the second voltage to the first voltage.

[0143] Another innovative aspect of the subject matter described in this disclosure can be implemented as a device. The device may include a modem and at least one processor communicatively coupled to the at least one modem. The processor, together with the modem, may be configured to perform any of the above-mentioned methods or features described herein.

[0144] Another innovative aspect of the subject matter described in this disclosure can be implemented as a computer-readable medium having instructions stored therein that, when executed by a processor, cause the processor to perform any of the above-mentioned methods or features described herein.

[0145] Another innovative aspect of the subject matter described in this disclosure can be implemented as a system having components for implementing any of the above-mentioned methods or features described herein.

[0146] As used herein, a phrase referring to "at least one of" or "one or more of" a list of items refers to any combination of those items, including individual members. For example, "at least one of: a, b, or c" is intended to encompass the following possibilities: only a, only b, only c, a combination of a and b, a combination of a and c, a combination of b and c, and a combination of a, b, and c.

[0147] The various illustrative components, logic, logic blocks, modules, circuits, operations, and algorithmic processes described in connection with the implementations disclosed herein may be implemented as electronic hardware, firmware, software, or a combination of hardware, firmware, or software, including the structures disclosed in this specification and their structural equivalents. The interchangeability of hardware, firmware, and software has been generally described in terms of functionality and illustrated in the various illustrative components, blocks, modules, circuits, and processes described above. Whether such functionality is implemented in hardware, firmware, or software depends on the specific application and the design constraints imposed on the overall system.

[0148] The hardware and data processing equipment for implementing the various illustrative components, logic, logic blocks, modules and circuits described in conjunction with the aspects disclosed herein can be implemented or performed with a general-purpose single-chip or multi-chip processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic device (PLD), discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor can be a microprocessor, or any conventional processor, controller, microcontroller or state machine. A processor can also be implemented as a combination of computing devices, such as a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in combination with a DSP core, or any other such configuration. In some implementations, specific processes, operations and methods can be performed by circuits specific to a given function.

[0149] As described above, some aspects of the subject matter described in this specification can be implemented as software. For example, the various functions of the components disclosed herein or the various blocks or steps of the methods, operations, processes or algorithms disclosed herein can be implemented as one or more modules of one or more computer programs. Such a computer program may include non-transitory processor-executable or computer-executable instructions encoded on one or more tangible processor-readable or computer-readable storage media, which are used to be executed or control the operation thereof by a data processing device including a component of the device described herein. As an example and not a limitation, such a storage medium may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage devices, magnetic disk storage devices or other magnetic storage devices, or any other medium that can be used to store program codes in the form of instructions or data structures. The above combination should also be included in the scope of the storage medium.

[0150] Various modifications to the implementations described in this disclosure may be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other implementations without departing from the scope of this disclosure. Therefore, the claims are not intended to be limited to the implementations shown herein, but are to be accorded the widest scope consistent with this disclosure, the principles, and the novel features disclosed herein.

[0151] Furthermore, various features described in this specification in the context of separate implementations may also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation may also be implemented separately in multiple implementations or in any suitable subcombination. As such, although features may be described above as functioning in a particular combination and even initially claimed as such, one or more features from a claimed combination may in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variations of the subcombination.

[0152] Similarly, although operations are depicted in a particular order in the accompanying drawings, this should not be understood as requiring that such operations be performed in the particular order shown or in a continuous order, or that all illustrated operations be performed to achieve the desired result. In addition, the accompanying drawings may schematically depict one or more example processes in the form of a flow chart or a simplified flow chart. However, other operations that are not depicted may be incorporated into the example processes that are schematically illustrated. For example, one or more additional operations may be performed before, after, simultaneously, or between any of the operations described. In some cases, multitasking and parallel processing may be advantageous. In addition, the separation of the various system components in the implementation described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems may generally be integrated together in a single software product or packaged into multiple software products.

Claims

1. A method for wireless power transmission by a power transmitter, comprising: receiving communications from a power receiver present in the magnetic field of the power transmitter; Obtaining measurements based on object detection evaluation; as well as A determination is made based on the measurement whether a foreign object is present in the magnetic field together with the power receiver.

2. The method according to claim 1, wherein Determining whether the foreign object exists includes at least one of the following: When the measurement value is outside a foreign object (FO) threshold range for a foreign object, it is determined that the foreign object does not exist, or When the measurement value is within a PRx threshold range based on a reference measurement value of a power receiver (PRx), it is determined that the foreign object is not present.

3. The method according to claim 2, wherein: Determining whether the foreign object exists further includes at least one of the following: When the measured value is outside the PRx threshold range, it is determined that the foreign object exists, or When the measurement value is within the FO threshold range, it is determined that the foreign object exists.

4. The method according to any one of claims 2 to 3, wherein The PRx threshold range and the FO threshold range overlap each other, and wherein the measurement value is compared with the PRx threshold range before the measurement value is compared with the FO threshold range.

5. The method according to any one of claims 2 to 4, further comprising: The PRx threshold range is determined based on a fixed offset of a reference value of the power receiver.

6. The method according to any one of claims 2 to 5, further comprising: The PRx threshold range is determined based on previous measurements of a previous object detection evaluation in which the power transmitter confirmed that the foreign object was not present in the magnetic field with the power receiver.

7. The method according to claim 6, further comprising: detecting a user action subsequent to the previous object detection assessment when the previous object detection assessment is within the FO threshold range, wherein the user action indicates that no foreign objects are present in the magnetic field; storing the previous measurement value as a reference value for the power receiver; and The PRx threshold range is updated based on the reference value.

8. The method according to claim 6, further comprising: receiving a communication from the power receiver subsequent to the previous object detection assessment when the previous object detection assessment is within the FO threshold range, wherein the communication indicates that no foreign objects are present in the magnetic field; storing the previous measurement value as the reference value for the power receiver; and The PRx threshold range is updated based on the reference value.

9. The method according to any one of claims 2 to 8, further comprising: A communication is received from the power receiver, the communication indicating the PRx threshold range for the power receiver, the PRx threshold range having been measured in a test environment when the power receiver was placed on a standard power transmitter in the absence of foreign objects.

10. The method according to any one of claims 2 to 9, further comprising: receiving a communication from the power receiver, the communication indicating a reference value for the power receiver; as well as The PRx threshold range is determined based on the reference value.

11. The method according to claim 10, wherein: The reference values include reference measurement values that have been measured in a test environment when the power receiver is placed on a standard power transmitter.

12. The method according to any one of claims 2 to 11, further comprising: receiving a communication from the power receiver, the communication indicating that the power receiver contains a friendly metal; as well as The PRx threshold range is determined based on predetermined measurements of a power receiver containing a friendly metal.

13. The method according to any one of claims 2 to 12, further comprising: receiving a communication from the power receiver, the communication indicating a range of expected measurement values for the power receiver; as well as The PRx threshold range is determined based on the range of expected measurement values.

14. The method according to any one of claims 2 to 13, further comprising: The PRx threshold range, or a reference value indicative of the PRx threshold range, or both are obtained from a data field in out-of-band communication received by the power transmitter from the power receiver.

15. The method according to claim 14, wherein The out-of-band communication is a Near Field Communication (NFC) Data Exchange Format (NDEF) message.

16. The method according to any one of claims 1 to 11, further comprising: if the foreign object is not present with the power receiver, enabling a wireless power transfer mode of the power transmitter; as well as If the foreign object is present together with the power receiver, the wireless power transfer mode of the power transmitter is disabled.

17. The method according to any one of claims 2 to 16, further comprising: A coupling factor between the power transmitter and the power receiver is calculated based on the measurement values, wherein the coupling factor represents an alignment of a primary coil of the power transmitter and a secondary coil of the power receiver.

18. The method according to any one of claims 1 to 17, wherein The measured value is at least one value selected from the group consisting of: the coil voltage or differential voltage of two or more detection coils of a coil pair; coil currents or differential currents of the two or more detection coils of the coil pair; coil impedance or differential impedance of the two or more detection coils of the coil pair; a quality factor calculated as part of said object detection evaluation; as well as Energy loss in low power transmission of the primary coil of the power transmitter.

19. A method for wireless power transmission, comprising: receiving communications from a power receiver present in the magnetic field of the power transmitter; obtaining a first measurement of a first parameter of a low power transmission from the power transmitter during an object detection evaluation; as well as A coupling factor between the power transmitter and the power receiver is calculated based on the first measurement value, wherein the coupling factor represents an alignment of a primary coil of the power transmitter and a secondary coil of the power receiver.

20. The method of claim 19, further comprising: Determining whether a foreign object is present in the magnetic field together with the power receiver is based on at least one of: the first measurement value, or A second measurement of a second parameter is obtained during the object detection evaluation.

21. The method according to claim 20, wherein Determining whether the foreign object exists includes at least one of the following: When the first measurement value or the second measurement value is outside a foreign object (FO) threshold range for a foreign object, determining that the foreign object is not present, or When the first measurement value or the second measurement value is within a PRx threshold range based on a reference measurement value of a power receiver (PRx), it is determined that the foreign object does not exist.

22. The method according to any one of claims 19 to 21, wherein: Obtaining the measured value includes: transmitting the low power signal while a power receiving circuit of the power receiver is disabled, the low power signal having a first voltage at the primary coil; receiving a communication from a power receiver indicating a second voltage at the power receiving circuit caused by the low power signal; and The coupling factor is calculated based at least in part on a ratio of a second voltage to the first voltage.

23. A device for wireless power transmission, comprising: a communication unit configured to receive communications from a power receiver present in the magnetic field of the power transmitter; a measurement unit configured to obtain a measurement value based on the object detection evaluation; as well as A control unit is configured to determine, based on the measurement values, whether a foreign object is present in the magnetic field together with the power receiver.

24. The apparatus according to claim 23, wherein The control unit is configured to: When the measurement value is outside a foreign object (FO) threshold range for a foreign object, it is determined that the foreign object does not exist, or When the measurement value is within a PRx threshold range based on a reference measurement value of a power receiver (PRx), it is determined that the foreign object is not present.

25. The apparatus of claim 24, wherein: The control unit is configured to: When the measured value is outside the PRx threshold range, it is determined that the foreign object exists, or When the measurement value is within the FO threshold range, it is determined that the foreign object exists.

26. The apparatus according to any one of claims 24-25, wherein The PRx threshold range and the FO threshold range overlap each other, and wherein the control unit is configured to compare the measurement value with the PRx threshold range before comparing the measurement value with the FO threshold range.

27. The apparatus according to any one of claims 24 to 26, wherein: The control unit is configured to: The PRx threshold range is determined based on a fixed offset of a reference value of the power receiver.

28. The apparatus according to any one of claims 24 to 27, wherein The control unit is configured to: The PRx threshold range is determined based on previous measurements of a previous object detection evaluation in which the power transmitter confirmed that the foreign object was not present in the magnetic field with the power receiver.

29. The apparatus of claim 28, wherein The control unit is configured to: detecting a user action subsequent to the previous object detection assessment when the previous object detection assessment is within the FO threshold range, wherein the user action indicates that no foreign objects are present in the magnetic field; storing the previous measurement value as a reference value for the power receiver; and The PRx threshold range is updated based on the reference value.

30. The apparatus according to claim 28, in, the control unit being configured to receive a communication from the power receiver subsequent to the previous object detection evaluation when the previous object detection evaluation is within the FO threshold range, wherein the communication indicates that no foreign objects are present in the magnetic field; and Wherein, the control unit is configured to: storing the previous measurement value as the reference value for the power receiver; and The PRx threshold range is updated based on the reference value.

31. The apparatus according to any one of claims 24 to 30, in, The control unit is configured to receive a communication from the power receiver, the communication indicating the PRx threshold range of the power receiver, the PRx threshold range having been measured in a test environment when the power receiver was placed on a standard power transmitter in the absence of foreign objects.

32. The apparatus according to any one of claims 24 to 31, in, the control unit being configured to receive a communication from the power receiver, the communication indicating a reference value for the power receiver; as well as The control unit is configured to determine the PRx threshold range based on the reference value.

33. The apparatus of claim 31 , wherein: The reference values include reference measurement values that have been measured in a test environment when the power receiver is placed on a standard power transmitter.

34. The apparatus according to any one of claims 24 to 33, in, The control unit is configured to receive a communication from the power receiver, the communication indicating that the power receiver contains a friendly metal; as well as The control unit is configured to determine the PRx threshold range based on predetermined measurement values of a power receiver containing a friendly metal.

35. The apparatus according to any one of claims 24 to 34, in, The control unit is configured to receive a communication from the power receiver, the communication indicating a range of expected measurement values for the power receiver; and Wherein, the control unit is configured to determine the PRx threshold range based on the range of expected measurement values.

36. The apparatus according to any one of claims 24 to 35, wherein The control unit is configured to obtain the PRx threshold range, or a reference value indicating the PRx threshold range, or both, from a data field in out-of-band communication received by the power transmitter from the power receiver.

37. The apparatus of claim 36, wherein: The out-of-band communication is a Near Field Communication (NFC) Data Exchange Format (NDEF) message.

38. The apparatus according to any one of claims 23 to 33, wherein: The control unit is configured to: If the foreign object is not present with the power receiver, enabling a wireless power transfer mode of the power transmitter; and If the foreign object is present together with the power receiver, the wireless power transfer mode of the power transmitter is disabled.

39. The apparatus according to any one of claims 24 to 38, wherein The control unit is configured to: A coupling factor between the power transmitter and the power receiver is calculated based on the measurement values, wherein the coupling factor represents an alignment of a primary coil of the power transmitter and a secondary coil of the power receiver.

40. The apparatus according to any one of claims 23 to 39, wherein The measured value is at least one value selected from the group consisting of: the coil voltage or differential voltage of two or more detection coils of a coil pair; coil currents or differential currents of the two or more detection coils of the coil pair; coil impedance or differential impedance of the two or more detection coils of the coil pair; a quality factor calculated as part of said object detection evaluation; as well as Energy loss in low power transmission of the primary coil of the power transmitter.

41. A device for wireless power transmission, comprising: a communication unit configured to receive communications from a power receiver present in the magnetic field of the power transmitter; a measurement unit configured to obtain a first measurement value of a first parameter of a low power transmission from the power transmitter during an object detection evaluation; as well as A control unit is configured to calculate a coupling factor between the power transmitter and the power receiver based on the first measurement value, wherein the coupling factor represents an alignment of a primary coil of the power transmitter and a secondary coil of the power receiver.

42. The apparatus of claim 41, wherein The control unit is configured to: Determining whether a foreign object is present in the magnetic field together with the power receiver is based on at least one of: the first measurement value, or A second measurement of a second parameter is obtained during the object detection evaluation.

43. The apparatus of claim 42, wherein: The control unit is configured to: When the first measurement value or the second measurement value is outside a foreign object (FO) threshold range for a foreign object, determining that the foreign object is not present, or When the first measurement value or the second measurement value is within a PRx threshold range based on a reference measurement value of a power receiver (PRx), it is determined that the foreign object does not exist.

44. The apparatus according to any one of claims 41 to 43, in, the control unit being configured to transmit the low power signal while a power receiving circuit of the power receiver is disabled, the low power signal having a first voltage at the primary coil; wherein the control unit is configured to receive a communication from a power receiver indicating a second voltage at the power receiving circuit caused by the low power signal; and The control unit is configured to calculate the coupling factor based at least in part on a ratio of the second voltage to the first voltage.

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