Foreign object detection using combined inductive and thermal sensing - Patents.com

Abstract

A method for detecting a metallic foreign object near an inductive wireless power transfer system is based on combined inductive sensing and thermal sensing. The sensing system senses the object based on an inductive effect or a thermal effect. The sensing system includes a sensing element having an electrical characteristic that changes in the presence of the object based on the inductive effect. The intermediate heat-sensitive material has a characteristic that varies with temperature and changes the electrical characteristic of the sensing element as the characteristic changes. When the foreign object is heated by a magnetic field generated by the wireless power transfer system, the intermediate heat-sensitive material is heated by the foreign object. A controller measures the electrical characteristic and determines the presence of the object based on the change in the measured electrical characteristic.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Application No. 63 / 267,532, filed February 3, 2022, the entire contents of which are incorporated herein by reference. This application is related to U.S. Patent Application No. 15 / 620,548, filed June 12, 2017, the entire contents of which are incorporated herein by reference.

[0002] The present application relates generally to wireless charging power transfer applications, and in particular to a method and apparatus for detecting foreign objects using combined inductive and thermal sensing. [Background technology]

[0003] An inductive wireless power transfer (WPT) system provides an example of wireless transfer of energy. In an inductive WPT system, a primary power device (i.e., a wireless power transmitter) wirelessly transmits power to a secondary power device (i.e., a wireless power receiver). Each of the wireless power transmitter and the wireless power receiver includes an inductive power transfer structure, a single coil arrangement or a multiple coil arrangement, typically a winding with a current carrying material (e.g., copper Litz wire). An alternating current passing through a coil (e.g., of the primary wireless power transfer structure) generates an alternating magnetic field. When the secondary wireless power transfer structure is placed in the vicinity of the primary wireless power transfer structure, the alternating magnetic field induces an electromotive force (EMF) in the secondary wireless power transfer structure according to Faraday's law, thereby wirelessly transferring power to the wireless power receiver when a resistive load is connected to the wireless power receiver. To improve power transfer efficiency, some implementations use a wireless power transfer structure that is part of a resonant structure (resonator). The resonant structure may comprise a capacitively loaded inductor that forms a resonance substantially at the fundamental operating frequency of the inductive WPT system (eg, in the range of 80 kHz to 90 kHz).

[0004] Inductive WPT to electrically chargeable vehicles at power levels of several kilowatts, both in domestic and public parking zones, may require special protective measures for the safety of people and equipment. Such measures may include detection of foreign objects within the inductive power field of the inductive WPT system, where the electromagnetic field exposure levels exceed some limits. This need for protective measures may apply especially to systems where the inductive power field is open and accessible. Such measures may include detection of conductive (metallic) objects and living objects (e.g., humans, human limbs, or animals) that may be present within or near the inductive power field.

[0005] In some applications for inductive wireless charging of electric vehicles, it may be useful to be able to detect foreign objects that may be present in the inductive power field and may be susceptible to inductive heating due to the high magnetic field strength in the field. In an inductive WPT system for electric vehicle charging that operates at a fundamental frequency in the range of 80 kHz to 90 kHz, the magnetic flux density in the inductive power field (e.g., above the primary wireless power transfer structure) may reach a relatively high level (e.g., greater than 2 millitesla (mT)) to enable sufficient power transfer (e.g., 3.3 kilowatts (kW), 7 kW, 11 kW, etc.). Thus, metal objects or other objects present in the magnetic field may experience undesirable inductive heating due to eddy current loss effects. In ferromagnetic metal objects, inductive heating may be even more intense due to additional current displacement (skin) and hysteresis loss effects. For this reason, foreign object detection (FOD) may be implemented to detect metal objects or other objects that are affected by the magnetic fields generated by the primary or secondary wireless power transfer structures of an inductive WPT system. When the presence of a foreign object is detected, the WPT system may reduce or turn off power and may issue an alert prompting the user to remove the foreign object. Upon removal of the foreign object, normal power transfer may be resumed, i.e., initiated, either manually by the user or automatically by the WPT system (e.g., based on object removal detection).

[0006] In some applications for inductive wireless charging of electric vehicles, it may also be useful to be able to detect living objects that may be present in or near the inductive power region where the level of electromagnetic field exposure exceeds some limit (e.g., as defined by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) recommendations). For this reason, living object detection (LOD) may be implemented to detect living objects (e.g., human limbs, animals) or other objects that may be exposed to the magnetic field generated by the primary or secondary wireless power transfer structures of the inductive WPT system. When the presence of a living object is detected, the WPT system may immediately turn off and automatically resume normal power transfer when the presence of the living object is no longer detected or after the expiration of a time period that begins when the presence of the living object is no longer detected. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] U.S. Patent No. 10,627,257 [Patent Document 2] U.S. Patent No. 9,952,266 [Patent Document 3] U.S. Patent Application Serial No. 17 / 931,429 [Patent Document 4] U.S. Patent No. 9,726,518 [Patent Document 5] U.S. Patent No. 11,002,874 [Patent Document 6] U.S. Patent No. 10,122,192 [Patent Document 7] U.S. Patent No. 10,124,687 [Patent Document 8] U.S. Patent No. 9,921,045 [Patent Document 9] U.S. Patent No. 10,295,693 [Patent Document 10] U.S. Patent No. 10,302,795 [Patent Document 11] U.S. Patent No. 10,298,049 [Patent Document 12] U.S. Patent No. 11,046,193 [Patent Document 13] U.S. Patent No. 10,855,117 Summary of the Invention [Means for solving the problem]

[0008] Various implementations of the systems, methods, and devices within the scope of the appended claims each have several aspects, no single aspect of which is solely responsible for the desirable attributes described herein. Without limiting the scope of the appended claims, some distinguishing features are described herein.

[0009] The details of one or more implementations of the subject matter described herein are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, drawings, and claims.

[0010] In general, in one aspect, a foreign object is detected in an inductive wireless power transfer system using a sensing system configured to sense the foreign object based on one or more of an inductive effect and a thermal effect. The sensing system includes a sensing element having an electrical characteristic, the sensing element configured to sense the foreign object based on an inductive effect related to a first alternating magnetic field, and an intermediary heat-sensitive material is coupled to the sensing element. The intermediary heat-sensitive material has a characteristic that varies depending on a temperature when heated by the foreign object exposed to a second alternating magnetic field generated by the inductive wireless power transfer system, and the intermediary heat-sensitive material changes an electrical characteristic of the sensing element depending on the characteristic. A controller coupled to the sensing system measures the electrical characteristic of the sensing element and determines the presence of the foreign object based on a change in the measured electrical characteristic caused by at least one of the inductive effect and the thermal effect through the intermediary heat-sensitive material.

[0011] The embodiment may include one or more of the following features in any order or combination: The property of the intermediate heat sensitive material may be one or more of resistivity, conductivity, impedance, capacitance, inductance, magnetic permeability, and electrical permittivity. The intermediate heat sensitive material may be configured to significantly change properties when the temperature of the intermediate heat sensitive material passes a threshold value higher than 373 Kelvin. The intermediate heat sensitive material may include one or more of a negative temperature coefficient (NTC) resistive material, a positive temperature coefficient (PTC) resistive material, a low Curie point dielectric material, and a low Curie point ferrite material. The sensing element may include one or more turns of an electrical conductor. The sensing element may be mounted on a printed circuit board. The sensing element may include an intermediate heat sensitive material. The sensing element may be embedded in a layer that also includes the intermediate heat sensitive material. The heat sensitive material may be in a different layer than the layer that includes the sensing element. The sensing system may include an array of sensing elements, and the mediator thermal sensitive material may be associated with at least one sensing element of the array. The electrical property measured by the controller may include one or more of impedance, transimpedance, direct current (DC) resistance, voltage, current, induced voltage, impulse response, and another waveform response.

[0012] The controller may be configured to determine the presence of a foreign object by correlating the measured electrical characteristic with a level of a second alternating magnetic field generated by the inductive wireless power transfer system. Correlating the measured electrical characteristic with a level of the second alternating magnetic field may include at least one of inductive thermal sensing (ITS), inductive ferromagnetic sensing (IFS), or inductive motion sensing (IMS). The heat resistant material may protect the sensing system against damage from heat from the foreign object. The heat resistant material may constitute at least a portion of an enclosure of the wireless power transfer system. The heat resistant material may be in a first layer exposed to an exterior of the device, and the heat sensitive material is in a second layer covered by the first layer. The heat resistant material may have a melting point greater than 473 Kelvin and be configured to withstand temperatures reached by foreign objects greater than 473 Kelvin without losing structural integrity. [Brief description of the drawings]

[0013] [Figure 1] 1A-1C are schematic diagrams illustrating example implementations of a detection circuit including an inductive sensing circuit and a capacitive sensing circuit, a non-living (e.g., metallic) object, and a living object. [Diagram 2] 2 is a schematic diagram illustrating an example implementation of a ground-based wireless power transfer structure integrating a portion of the detection circuit shown in FIG. 1, as well as the non-living and living objects of FIG. 1. [Diagram 3] A vertical cutaway view showing a portion of a WPT system including a vehicle-based wireless power transfer structure and the ground-based wireless power transfer structure of FIG. 2 that integrates a portion of the detection circuit of FIG. 1, as well as the non-living object and the livable object of FIG. 1. [Figure 4] 2 is a general block diagram of an example implementation of the detection circuit of FIG. 1. [Figure 5A] FIG. 1 illustrates a housing for a wireless power transfer structure. [Figure 5B]FIG. 1 illustrates a housing for a wireless power transfer structure. [Figure 5C] FIG. 1 illustrates a housing for a wireless power transfer structure. [Figure 5D] FIG. 1 illustrates a housing for a wireless power transfer structure. [Figure 5E] FIG. 1 illustrates a housing for a wireless power transfer structure. [Figure 5F] FIG. 1 illustrates a housing for a wireless power transfer structure. [Figure 6A] FIG. 1 illustrates a combined inductive and thermal sensing system. [Figure 6B] FIG. 1 illustrates a combined inductive and thermal sensing system. [Figure 6C] FIG. 1 illustrates a combined inductive and thermal sensing system. [Figure 6D] FIG. 1 illustrates a combined inductive and thermal sensing system. [Figure 7] 1 illustrates example operations for performing combined inductive and thermal sensing in a foreign object detection system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] As mentioned above, foreign object detection (FOD), particularly metal object detection, may be useful for a variety of applications. For detection within a predefined region, an FOD system may include multiple inductive sensing circuits, each including an inductive sensing element (e.g., a sensing coil) distributed over a predefined area (e.g., a planar array of sensing coils integrated into a ground-based wireless power transfer structure). The predefined region may be defined by a space in which a metal object may be found and where the magnetic flux density exceeds some limit (e.g., a threshold determined based on what temperature the metal object may be heated to). This space, referred to as the detection space, is generally a three-dimensional space above the inductive sensing elements that define the detection area. The number of inductive sensing elements may relate to the form factor of the detection space or detection area and the minimum size of the object desired to be detected. For a system configured to detect small objects (e.g., paper clips), the number of sensing elements may be relatively large (e.g., on the order of 100). The FOD system may further include control and measurement circuitry for applying drive signals to each of the inductive sensing circuits, each of which includes an inductive sensing element and additional elements for conditioning, and for measuring electrical properties in each of the capacitive sensing circuits, and for detecting changes in the electrical properties that may indicate the presence of a foreign object (e.g., made of metal). An exemplary FOD system is described in U.S. Patent No. 10,627,257, entitled "Systems, Methods, and Apparatus for Detection of Metal Objects in a Predetermined Space," the entire contents of which are incorporated herein by reference.

[0015] As also mentioned above, live object detection (LOD) (e.g., human limbs, animals) may be useful for various applications. For detection within a predetermined area, the LOD system may include a plurality of capacitive sensing circuits, each including a capacitive sensing element (e.g., sensing electrode), disposed, for example, along the perimeter of the ground-based wireless power transfer structure of the WPT system. The predetermined area may be defined by a space that is accessible to the live object and in which the live object may be located and the exposed magnetic field strength exceeds some limit (e.g., as recommended by ICNIRP). This space, called the detection space, is generally three-dimensional. The number of capacitive sensing elements may be related to the detection space and the minimum size of the live object desired to be detected. For a system configured to detect human limbs (e.g., hands) and animals (e.g., cats), the number of sensing elements may be relatively small (e.g., around four). The LOD system may further include control and measurement circuitry for applying drive signals to each of the capacitive sensing circuits, each of which includes a capacitive sensing element and additional elements for conditioning, and for measuring electrical properties in each of the capacitive sensing circuits and for detecting changes in the electrical properties that may indicate the presence of a living object. An exemplary LOD system is described in U.S. Patent No. 9,952,266, entitled "Object Detection for Wireless Energy Transfer Systems," the entire contents of which are incorporated herein by reference.

[0016] In terms of hardware complexity reduction and cost savings, it may be useful and desirable to share, as far as possible and perceptible, the use of hardware components of the detection circuit for FOD, LOD, vehicle detection (VD), and position detection (PD) functions. A multi-purpose detection circuit configurable for FOD, LOD, VD, and PD functions is described in U.S. patent application Ser. No. 17 / 931,429, entitled "Circuit for Object Detection and Vehicle Position Determination," the entire contents of which are incorporated herein by reference.

[0017] An "electric vehicle" refers to a remote system, an example of which is a vehicle that includes as part of its driving capabilities electrical power derived from a rechargeable energy storage device (e.g., one or more rechargeable electrochemical cells or another type of battery). As non-limiting examples, some electric vehicles may be hybrid electric vehicles that include a conventional internal combustion engine in addition to an electric motor for direct driving or to charge the vehicle's battery. Other electric vehicles may derive all driving capabilities from electrical power. Electric vehicles are not limited to automobiles, but may include motorcycles, carts, scooters, and the like.

[0018] "Foreign object" refers to an object that does not belong in the wireless power transfer (WPT) system by itself. A foreign object may include a metal object, a non-living dielectric (substantially non-conductive) object, a living object (e.g., an animal, a human limb), a vehicle, or a combination thereof. It may represent an object that needs to be detected for the safety of equipment or personnel, but may also refer to an object that is harmless (e.g., has the potential to cause a false positive detection in the detection system and therefore needs to be discriminated).

[0019] FIG. 1 illustrates an exemplary implementation of a detection circuit 100 including a plurality of inductive sensing circuits 106a, 106b, ... 106n and a plurality of capacitive sensing circuits 108a, 108b, ... 108n. The number of inductive sensing circuits 106a-106n and the number of capacitive sensing circuits 108a-108n may each be fewer or more than the three shown. In examples referring to any one of such numbered sensing circuits, they are referenced as 106i and 108i, respectively. As illustrated in FIG. 1, each of the sensing circuits 106a-106n includes a corresponding inductive sensing element (e.g., a sensing coil) of a plurality of inductive sensing elements 107a-107n, respectively. Similarly, each of the capacitive sensing circuits 108a-108n includes a corresponding capacitive sensing element (e.g., a pair of sensing electrodes) of a plurality of capacitive sensing elements 109a-109n, respectively. In the examples referring to any one of such numbered sensing elements, they are referenced as 107i and 109i, respectively.

[0020] 1 also shows foreign objects 110 and 112, which represent non-living objects, and a living object 114. Object 110 represents a metallic (substantially conductive) object that potentially heats up when exposed to a WPT magnetic field, and object 112 represents a dielectric or ferromagnetic object that is substantially non-conductive and does not heat up when exposed to a WPT magnetic field. Living object 114 may represent a human limb (e.g., a hand as shown in FIG. 1) or an animal that is dielectric and substantially non-conductive.

[0021] The inductive sensing elements 107a-107n and the capacitive sensing elements 109a-109n are configured to sense the presence of a foreign object (e.g., object 110) in the vicinity of at least one of the inductive sensing elements 107a-107n and a live object (e.g., object 114) in the vicinity of at least one of the capacitive sensing elements 109a-109n by measuring one or more electrical properties (e.g., impedance) in each of the inductive sensing circuits 106a-106n and the capacitive sensing circuits 108a-108n and by detecting changes in the measured electrical properties. The sensing elements may also detect the presence, identification, or location of a vehicle in a similar manner. Each of the inductive sensing circuits 106a-106n and the capacitive sensing circuits 108a-108n may also include additional conditioning circuitry (not shown in FIG. 1 ) configured to, for example, improve the measurement of one or more electrical properties and thus the detection sensitivity and reliability of the detection circuit 100. Each of the sensing circuits also defines at least one measurement port (not shown in FIG. 1) at which one or more electrical properties are measured and referenced.

[0022] Each of the inductive sensing elements 107a-107n is shown in FIG. 1 as a “circular” coil for illustrative purposes. However, in other implementations, the inductive sensing elements 107a-107n may include sensing coils with another coil topology (e.g., a “figure eight” topology). In still other implementations, the inductive sensing elements 107a-107n may include sensing coils of mixed coil topology (e.g., “circular” and “figure eight”). In still further implementations, the inductive sensing elements 107a-107n may include sensing coils with ferrite cores (e.g., solenoid coils, not shown herein) that are physically smaller compared to “air” coils. In still further implementations, the sensing elements 107a-107n may include other inductive devices that may be used to generate magnetic fields for detecting foreign objects (e.g., object 110) or vehicles or for determining vehicle position. In some implementations (not shown herein), each of the inductive sensing elements 107a-107n may include a dual or even triple sensing coil arrangement that may be used with transimpedance measurement techniques (e.g., based on mutual inductance or mutual impedance). In some implementations, the inductive sensing elements 107a-107n are arranged in an array 107, such as a two-dimensional array 107 as shown in FIG. 1. However, in other implementations, the inductive sensing elements 107a-107n are arranged in other configurations, including not following rows or columns (radial or interleaved), having at least partial overlap or irregular spacing, having different sizes, having different shapes (circular, hexagonal, etc.), covering an irregular detection area, or any combination thereof. Thus, as used herein, the term "array" refers to a plurality of sensing elements arranged over a given area. Furthermore, the number of inductive sensing elements in the array 107, and therefore the number of sensing circuits, can vary widely based on the application, including the total area within which foreign objects are to be detected and the minimum size of objects that the detection circuit 100 is configured to detect.Exemplary implementations of inductive sensing elements and arrangements of inductive sensing elements are described in U.S. Pat. No. 9,726,518, entitled "Systems, Methods, and Apparatus for Detection of Metal Objects in a Predetermined Space," U.S. Pat. No. 11,002,874, entitled "Foreign Object Detection Circuit Using Mutual Impedance Sensing," U.S. Pat. No. 10,122,192, entitled "Sense Coil Geometry with Improved Sensitivity for Metallic Object Detection in a Predetermined Space," and U.S. Pat. No. 10,124,687, entitled "Hybrid Foreign Object Detection (FOD) Loop Array Board," the contents of which are incorporated herein by reference in their entireties.

[0023] Each of the capacitive sensing elements 109a-109n is shown in FIG. 1 as a pair of sensing electrodes for illustrative purposes. However, in other implementations, the capacitive sensing elements 109a-109n may include a single electrode providing a single terminal. In further implementations, the capacitive sensing elements 109a-109n may be configured and driven to measure transimpedance (e.g., based on mutual capacitance or mutual impedance). In still further implementations, the capacitive sensing elements 109a-109n may include other capacitive devices that may be used to generate and detect electric fields to detect foreign objects (e.g., object 112), living objects (e.g., object 114), or vehicles (e.g., vehicle 340, FIG. 3), or to determine a vehicle type or vehicle location. In FIG. 1, the capacitive sensing elements 109a-109n are illustrated disposed within an area surrounding an array of inductive sensing elements 107a-107n. However, in other implementations, the capacitive sensing elements 109a-109n are arranged in other configurations (e.g., distributed across the area of ​​the array of inductive sensing elements 107). Exemplary implementations of capacitive sensing elements (e.g., capacitive sensing element 109a) and arrangements of capacitive sensing elements are described in U.S. Pat. No. 9,952,266, entitled "Object Detection for Wireless Energy Transfer Systems," the entire contents of which are incorporated herein by reference.

[0024] Continuing with the example of FIG. 1, each of the inductive sensing circuits 106a-106n and capacitive sensing circuits 108a-108n, including corresponding sensing elements 107a-107n and 109a-109n, are operatively connected to a measurement circuit 104. The measurement circuit 104, including multiplexing (not shown in FIG. 1), is configured to selectively and sequentially measure one or more electrical properties in each of the inductive sensing circuits 106a-106n and capacitive sensing circuits 108a-108n and provide outputs to the control and evaluation circuit 102.

[0025] The measurement circuit 104 is configured to selectively and sequentially cause each of the inductive sensing elements 107a-107n to generate an alternating magnetic field at a sense frequency (e.g., by selectively and sequentially applying a sense signal (e.g., current) to each of the inductive sensing circuits 106a-106n). When a metal object (e.g., object 110) is present in the alternating magnetic field, eddy currents are generated in the object. According to Lenz's law, the eddy currents in the object generate another (secondary) magnetic field that interacts with the primary magnetic field as generated by the respective sensing element, and mutual coupling is manifested. This may cause a change in an electrical property (e.g., impedance) of each inductive sensing circuit 106i as measured by the measurement circuit 104. The change in the measured electrical property may also be a function of the relative permeability μ of the magnetic field interacting with the alternating magnetic field as generated by the respective inductive sensing element. r The sensing signal may be caused by a substantially non-conductive but ferromagnetic object (e.g., object 112) with a capacitance >1. Applying a sensing signal to the inductive sensing circuit 106i may also cause the respective inductive sensing element 107i to generate an alternating electric field that may interact with a substantially non-conductive dielectric object (e.g., non-living object 112 or living object 114), causing a change in electrical properties (capacitive sensing effect) as measured in the respective inductive sensing circuit. This alternating electric field may also interact with a metallic (substantially conductive) object (e.g., object 110). However, this effect is expected to be orders of magnitude weaker than the magnetic field effect.

[0026] The measurement circuit 104 is further configured to selectively and sequentially cause each of the capacitive sensing elements (e.g., sensing electrodes) 109a-109n to generate an alternating electric field at a sensing frequency (e.g., by selectively and sequentially applying a sensing signal (e.g., current) to each of the capacitive sensing circuits 108a-108n). rA substantially non-conductive dielectric object (e.g., living object 114 or non-living object 112) having a .DELTA..times ...

[0027] 2 shows an example implementation of a wireless power transfer structure 200 that is part of a WPT system. The wireless power transfer structure 200 includes a coil 202 (e.g., a Litz wire coil), also called a WPT coil, configured to generate an alternating magnetic field when driven with a current by a power conversion circuit (not shown). The wireless power transfer structure 200 also includes a ferrite structure 204 that may be made of one or more ferrite tiles and configured to channel or provide a low reluctance path for magnetic flux. The wireless power transfer structure 200 further includes a backplate 206. In some implementations, the backplate 206 is made of metal and acts as a shield configured to guide the magnetic flux and prevent magnetic and electric fields from extending far beyond a boundary determined by the backplate 206, or at least attenuate fields that extend beyond the boundary. As an example, the backplate 206 may be formed from aluminum. 2 further illustrates an example of how the inductive sensing element array 107 and the capacitive sensing element array 109 of FIG. 1 can be integrated into a wireless power transfer structure 200. In some implementations, the wireless power transfer structure 200 also includes a tuning and matching network (not shown) for tuning the wireless power transfer structure 200 to a resonance substantially at the WPT operating frequency and for matching impedance to a power conversion circuit (not shown). FIG. 2 also illustrates foreign objects such as a metal object 110, a non-metallic object 112, and a living object 114 as in FIG. 1.

[0028] FIG. 2 shows a ground-based wireless power transfer structure, sometimes called a "ground assembly (GA)", a GA pad, a "base pad", or a GA resonator when integrating a tuning and matching network. The ground-based wireless power transfer structure 200 is typically configured to transmit power to a corresponding receiver on a vehicle (not shown in FIG. 2) and may be an integral part of a grid-side assembly of a WPT system, including a power converter and a tuning and matching network. In some implementations, the ground-based wireless power transfer structure 200 is configured to transmit or receive power to or from a vehicle depending on the operation mode of the WPT system. In the transmit mode, power is transferred from the GA to the vehicle, while in the receive mode, power is transferred from the vehicle to the GA in a mode called "V2G" as needed (e.g., to transfer power from the vehicle to the grid). When excited by a current, the WPT coil 202 generates a magnetic field (e.g., at a WPT operating frequency in the range of 80 kHz to 90 kHz) to transfer power from the GA to the vehicle. Furthermore, when the ground-based wireless power transfer structure 200 may be placed on the ground or on another upper facing surface, a foreign object may come to rest on the upper surface of the housing of the ground-based wireless power transfer structure 200. The object may be exposed to a high level of magnetic flux density when power is being transferred. As previously described, a metal object or other object present in this magnetic field may experience undesirable induction heating due to eddy current loss effects or hysteresis loss effects. Metal object 110 in particular may experience induction heating. Moreover, a human limb (e.g., a hand), as illustrated by object 114, may be exposed to the magnetic field when approaching the wireless power transfer structure 200. Thus, exposure of both types of objects may require protection mechanisms as described herein.

[0029] 3 shows a vertical cutaway view of a portion 300 of a WPT system applicable to wireless electric vehicle charging. The portion 300 includes the ground-based wireless power transfer structure 200 with respect to FIG. 2 and a vehicle-based wireless power transfer structure 320, also referred to as a "vehicle assembly (VA)," attached to the bottom of a vehicle 340. The vehicle-based wireless power transfer structure 320 may be an integral part of a vehicle-side WPT system, including power converters and tuning and matching networks.

[0030] The ground-based wireless power transfer structure 200 includes a WPT coil 202, a ferrite structure 204, and a backplate 206, as well as inductive sensing elements 107a-107n (array 107) and capacitive sensing elements 109a-109n (array 109) as part of the detection circuit 100 shown in Figures 1 and 2.

[0031] FIG. 3 further illustrates a housing 310 that houses other components of the ground-based wireless power transfer structure 200, such as the WPT coil 202, the ferrite structure 204, and the sense element arrays 107 and 109. The housing 310 includes a cover shell 312 and the backplate 206 from FIG. 2. In some implementations, the housing 310 may also house the tuning and impedance matching network as described above, as well as the measurement circuit 104 and the control and evaluation circuit 102 as part of the detection circuit 100 of FIG. 1. In another implementation, the housing 310 additionally houses some or all of the power conversion circuit (not shown). The housing 310 may be tilted along its perimeter from its edge toward its interior to form a slope over which a vehicle may travel. The capacitive sense elements 109a-109n may be tilted (non-parallel) with respect to a plane defined by the inductive sense element array 107. For example, the capacitive sensing elements may be oriented along the perimeter of the housing so as to be substantially parallel to the sloped surface of the housing 310. Figure 3 also shows the non-living objects 110 and 112 and the livable object 114 from Figure 1.

[0032] The vehicle-based wireless power transfer structure 320 includes a WPT coil 322, a ferrite structure 324, and a shield 334 made of a conductive material. In some implementations, the shield 334 may be formed from a portion of a structure to which the ferrite structure 324 and the WPT coil 322 are attached at the bottom of the vehicle 340. In this case, the housing 330 that houses the WPT coil 322 and the ferrite structure 324 may not house the shield 334. Other implementations are possible in which the housing 330 includes a cover shell 332 and a conductive back plate (not shown) similar to the housing 310 of the wireless power transfer structure 200. A power conversion circuit (not shown) may be electrically connected to the WPT coil 322, and a portion or all of the power conversion circuit may also be housed within the housing 330.

[0033] As explained above, the ground-based wireless power transfer structure 200 generates a magnetic field, while the vehicle-based wireless power transfer structure 320 inductively receives power via the magnetic field. In implementations that support V2G, the vehicle-based wireless power transfer structure 320 may also generate a magnetic field, and the ground-based wireless power transfer structure 200 may receive power via the magnetic field generated by the vehicle-based wireless power transfer structure.

[0034] The vehicle-based wireless power transfer structure 320 may also integrate at least one of an inductive passive beacon transponder 326 and a capacitive passive beacon transponder 328 (e.g., for PD and VD). The inductive passive beacon transponder 326 may be configured to interact primarily with inductive sensing elements (e.g., inductive sensing elements 107a-107n). In some implementations, the inductive passive beacon transponder 326 includes a transponder coil, a capacitive element for compensating the total reactance of the coil at the operating (sensing) frequency of the detection circuit 100, and a passive impedance modulation circuit (these elements are not illustrated herein). The capacitive passive beacon transponder 328 may be configured to interact primarily with capacitive sensing elements (e.g., capacitive sensing elements 109a-109n). In some implementations, the capacitive passive beacon transponder 328 includes a transponder electrode, an inductive element to compensate for the total reactance of the electrode at the operating (sensing) frequency of the detection circuit 100, and a passive impedance modulation circuit (these elements are not shown herein). In a further implementation (not shown herein), a passive beacon transponder (e.g., passive beacon transponder 326) is configured to interact with both the inductive and capacitive sensing elements of the detection circuit 100.

[0035] In some implementations (not shown), the vehicle-based wireless power transfer structure 320 also includes one or more inductive and capacitive sensing elements configured to detect non-living and living objects (e.g., metal objects 110 and living objects 114) in the same manner as described for the detection circuit 100.

[0036] 4 is a general block diagram illustrating an example implementation or operation of detection circuit 100. Detection circuit 100 includes inductive sensing circuits 106a-106n including inductive sensing elements 107a-107n, capacitive sensing circuits 108a-108n including capacitive sensing elements 109a-109n, measurement circuit 104, and control and evaluation circuit 102 with respect to FIG.

[0037] Each of the inductive sensing circuits 106a-106n may also include an associated capacitive element (not shown) to compensate for the total reactance as presented at the terminals of the inductive sensing element at the sensing frequency. Each of the capacitive sensing circuits 108a-108n may also include an associated inductive element (not shown) to compensate for the total reactance as presented at the terminals of the capacitive sensing element at the sensing frequency. At least one of the inductive and capacitive sensing circuits also includes an impedance matching element (e.g., a transformer) to transform the impedance of the sensing circuit to match the operating impedance range of the multi-purpose object detection circuit 100. In one exemplary implementation, each of the inductive sensing circuits 106a-106n is naturally matched to the operating impedance range without the use of an additional impedance matching element. However, the capacitive sensing circuits 108a-108n are not naturally matched, and therefore an additional impedance matching element (e.g., a transformer) is used. In another exemplary implementation, the opposite is true. In a further example implementation, both the inductive sensing circuits 106a-106n and the capacitive sensing circuits 108a-108n include additional impedance matching elements.

[0038] The measurement circuit 104 is electrically connected to the inductive and capacitive sensing circuits and configured to selectively and sequentially measure one or more electrical properties (e.g., impedance) in each of the inductive and capacitive sensing circuits according to a predetermined time-multiplexing scheme. The output of the measurement circuit 104, also referred to as the measurement output, as shown in FIG. 4, is indicative of the one or more electrical properties being measured. The measurement circuit 104 further includes a driver circuit 402, a measurement amplifier circuit 404, a signal generator circuit 406, and a signal processing circuit 408.

[0039] A driver circuit 402 including an input multiplexer (input MUX) circuit is electrically connected to the inductive sensing circuits 106a-106n and the capacitive sensing circuits 108a-108n and configured to selectively and sequentially apply drive signals (e.g., current signals) at a sensing frequency to each of the inductive sensing circuits 106a-106n and the capacitive sensing circuits 108a-108n based on a driver input signal generated by a signal generator circuit 406.

[0040] A measurement amplifier circuit 404, which includes an output multiplexer (OUTPUT MUX) circuit, is electrically connected to the inductive sensing circuits 106a-106n and the capacitive sensing circuits 108a-108n and is configured to selectively and sequentially amplify the measurement signals (e.g., voltage signals) in each of the inductive sensing circuits 106a-106n and the capacitive sensing circuits 108a-108n and provide measurement amplifier output signals indicative of the measurement signals in each of the sensing circuits.

[0041] A signal generator circuit 406 electrically connected to an input of the driver circuit 402 is configured to generate a driver input signal.

[0042] A signal processing circuit 408 electrically connected to an output of the measurement amplifier circuit 404 is configured to receive and process the measurement amplifier output signal and determine one or more electrical characteristics in each of the inductive and capacitive sensing circuits based on the driver input signal and the measurement amplifier output signal. Processing the measurement amplifier output signal may include filtering, combining, averaging, etc. Filtering may include reducing disturbance (e.g., noise) components superimposed on the sensing signal as received by the signal processing circuit 408 to improve a signal-to-noise ratio (SNR) at the measurement output of the signal processing circuit 408.

[0043] The control and evaluation circuit 102 is electrically connected to the measurement circuit 104 and configured to control the input MUX circuit and the output MUX circuit of the driver circuit 402 and the measurement amplifier circuit 404 via the input MUX control and the output MUX control, respectively, as shown in FIG. 4. The input and output MUX circuit controls evaluate one or more electrical properties (measurement outputs) as measured in each of the inductive and capacitive sensing circuits according to a predetermined time multiplexing scheme, and determine at least one of the presence of a foreign object, a live object, or a vehicle, the type of the vehicle, and the vehicle location based on changes in the one or more electrical properties measured. The control and evaluation circuit 102 may provide various outputs as shown in FIG. 4. In the detection circuit 100 configured for FOD, LOD, VD, and PD, the control and evaluation circuit 102 provides corresponding FOD output, LOD output, VD output, and PD output.

[0044] The dashed lines used in FIG. 4 emphasize that the components and their configurations in the measurement circuit 104, and particularly in the driver circuit 402 and the measurement amplifier circuit 404, are exemplary, and that other implementations may have these or other components configured to drive the sense circuits 106a-106n and 108a-108n with drive signals and amplify the measurement signals in each of the sense circuits 106a-106n and 108a-108n. Additionally, while some circuit elements are described as being connected between other elements, it should be appreciated that there may be other circuit elements in various implementations that may also be intermediate two elements (e.g., other intervening elements) that are described as being electrically connected. In an exemplary alternative implementation of the measurement circuit 104 (not shown herein), there is only one MUX circuit common to both the driver circuit 402 and the measurement amplifier circuit 404.

[0045] No. 9,726,518 entitled "Systems, Methods, and Apparatus for Detection of Metal Objects in a Predetermined Space," U.S. Patent No. 9,921,045 entitled "Systems, Methods, and Apparatus for Increased Foreign Object Detection Loop Array Sensitivity," U.S. Patent No. 10,295,693 entitled "Systems, Methods, and Apparatus for Foreign Object Detection Loop Based on Inductive Thermal Sensing," U.S. Patent No. 10,302,795 entitled "Systems, Methods, and Apparatus for Detecting Ferromagnetic Objects in a Predetermined Space," U.S. Patent No. 10,298,049 entitled "Systems, Methods, and Apparatus for Detecting Metallic Objects in a Predetermined Space via Inductive Kinematic Sensing," the entire contents of which are incorporated herein by reference. Exemplary implementations of the detection circuit 100 are described in U.S. Pat. No. 11,046,193, entitled "Foreign Object Detection Signal Processing," U.S. Pat. No. 10,855,117, entitled "Extended Foreign Object Detection Signal Processing," and U.S. Pat. No. 11,002,874, entitled "Foreign Object Detection Circuit Using Mutual Impedance Sensing."

[0046] In an exemplary operation of the detection circuit 100, a sense signal is selectively and sequentially applied to each of the inductive sensing circuits 106a-106n and each of the capacitive sensing circuits 108a-108n according to a time division multiplexing scheme and in a round robin manner. A sense signal for driving an inductive sensing circuit is applied during a time interval (time slot) allocated to that sensing circuit and has a maximum duration equal to or less than the duration of the time slot. A time frame corresponding to the sum of the time slots allocated to the inductive sensing circuits 106a-106n and the capacitive sensing circuits 108a-108n is also referred to herein as a scan cycle or repetition period.

[0047] In one embodiment, to reduce the duration of a scan cycle, a first sense signal is selectively and sequentially applied to each of a portion of the inductive sensing circuits 106a-106n and the capacitive sensing circuits 108a-108n, and a second sense signal is selectively and sequentially applied in parallel to each of the remaining portions of the inductive and capacitive sensing circuits. Applying two or more sense signals in parallel may reduce the scan cycle and result in reduced detection latency for FOD and LOD, and increased location update rates for PDs (e.g., using passive beaconing techniques as previously described).

[0048] In an exemplary implementation or operation of the detection circuit 100, the sense signals applied in parallel are sinusoidal signals of the same frequency. In another example, the sense signals applied in parallel are sinusoidal signals but of different frequencies.

[0049] In a further example, each of the parallel sinusoidal sense signals applied in a time slot allocated to the same sense circuit starts with the same phase (e.g., 0 phase). In some implementations using three or more current sense signals, starting the sense signals with the same phase in a time slot allocated to the same sense circuit may help mitigate interference caused by intermodulation effects as described in the aforementioned U.S. Patent No. 10,855,117.

[0050] In some implementations, the time slots of the scan cycle are reallocated based on some conditions (e.g., whether the WPT is active or inactive). For example, it may be desirable to reduce the detection latency for LOD when the WPT is active. Thus, in an exemplary operation, when the WPT is active, two or more time slots of the scan cycle are allocated to each of the capacitive sensing circuits 108a-108n. Conversely, when the WPT is inactive, the LOD function may not be required, and thus, when the WPT is inactive, the time slots of the scan cycle are allocated only to the inductive sensing circuit. In another example, when the WPT is inactive, two or more time slots of the scan cycle are allocated to each of the inductive sensing circuits and one time slot is allocated to each of the capacitive sensing circuits. This mode of operation may maintain limited LOD functionality when the WPT is inactive (e.g., to monitor the correct functioning of the detection circuit 100 for LOD). Moreover, the time separation between time slots allocated to the same sensing circuit in any of the scanning modes described above is maximized.

[0051] The control and evaluation circuit 102 is configured to control the measurement circuit 104 (e.g., multiplexed), evaluate an output (measurement output) of the measurement circuit 104 indicative of one or more measured electrical characteristics, and determine at least one of the presence of a foreign object, live object, or vehicle, the type of vehicle, and the vehicle location based on changes in the measurement output.

[0052] In some implementations, the control and evaluation circuit 102 may include the determination functions required for FOD, LOD, and VD, as well as the position calculation functions required for PD. In other implementations, the vehicle position is determined in a unit (not shown) external to the detection circuit 100 based on the output (e.g., raw data) from the control and evaluation circuit 102 as well as outputs provided by other ground or vehicle-based sensors (not shown).

[0053] In an exemplary implementation or operation of the control and evaluation circuit 102, the evaluation is based on a time-differential detection (TDD) scheme that is sensitive (e.g., to relatively fast changes in a sequence (time series) of successive measurement outputs, each associated with at least one same sensing circuit of the plurality of sensing circuits 106a-106n and 108a-108n). A relatively fast change may be defined as a change that is significantly faster than the drift of the measured electrical characteristic due to the varying ambient temperature of the sensing circuit.

[0054] In some implementations or operations based on a TDD scheme, the presence of an object is assumed if at least one difference between a first measurement output associated with a sensing circuit at a first time and a second measurement output associated with the same sensing circuit at a second time exceeds a threshold value. Using TDD, an object may be detected as it enters or leaves the vicinity of a sensing element, or in general as it moves within the vicinity of a sensing element.

[0055] In a further exemplary implementation or operation of the detection circuit 100, the evaluation is based on a sensing circuit differential detection scheme that is sensitive to differences between outputs of the measurement circuit 104 associated with different sensing circuits of the plurality of sensing circuits. This detection scheme may be referred to as space-differential detection (SDD). In some implementations or operations based on SDD, the presence of an object is assumed if at least one difference between a first measurement output associated with at least one first sensing circuit and a second measurement output associated with at least one second sensing circuit exceeds a threshold value. In some implementations or operations of a true SDD scheme, the multiple measurement outputs used to determine the difference refer to substantially the same time. It may be appreciated that in some cases, SDD may be less sensitive and reliable than TDD because individual sensing circuits of the plurality of sensing circuits may be affected at least in part differently by ambient temperature, mechanical shock, and aging.

[0056] In some aspects, TDD may be sensitive to movement of metallic structures in the environment of the sensing element array. Such environmental effects may include movement of the metallic bottom structure of a vehicle when the vehicle is parked above the wireless power transfer structure. These movements may cause false detections in some implementations of detection circuits based solely on the TDD approach. Thus, in some aspects, it may be desirable to mitigate such disturbance effects.

[0057] Combining a TDD with an SDD is one approach to effectively discriminate such disturbance effects. In some implementations or operations of the combined TDD and SDD, the presence of an object is determined by evaluating at least one difference between a TDD output associated with at least one sensing circuit and a reference value determined based on a plurality of TDD outputs, each associated with one of the sensing circuits. The reference value may be, for example, an average, a median (50th percentile), or any other statistical value derived from the measurement output. It can be appreciated that this special detection scheme has potential for discriminating environmental effects (e.g., from a moving vehicle underside) that may result in changes in electrical characteristics (e.g., impedance) in a large portion (cluster) of the sensing circuits. This special scheme may be considered as a mechanism for automatically adapting the detection threshold used in the control and evaluation circuit 102 to determine the presence of an object. More specifically, in some implementations or operations, the control and evaluation circuit 102 automatically adjusts the reference value as described above. When the vehicle underside is moving, the reference value (detection threshold) may be larger. Increasing the reference value reduces the false positive rate, but also reduces the detection sensitivity to some extent. Thus, a somewhat lower sensitivity may be acceptable for objects entering a given space while the vehicle is moving. As soon as the vehicle bottom becomes stationary, the reference value may automatically stabilize and the detection circuit 100 may return to its normal detection sensitivity that maintains the specified false positive rate.

[0058] Inductive Thermal Sensing (ITS), described in U.S. Patent No. 10,295,693 (incorporated herein), is a specialized detection scheme for detecting a category of metallic objects characterized by at least one electrical property (e.g., conductivity, permeability) that can be inductively sensed at FOD sensing frequencies and that is a function of the object's temperature and changes at a rate significantly faster than the inherent thermal drift of the system in the absence of the object when the object is heated. This category of object can potentially be detected by exposing it to a sufficiently strong alternating magnetic field to cause inductive heating, as previously described. In some implementations, this magnetic field is a low-frequency magnetic field, such as that generated by a wireless power transfer system.

[0059] Non-limiting examples of objects detectable by an ITS may be cigarette packets containing metallized foil, aluminum covers (lids) on yogurt cups, chewing gum wrappers, cigarette lighters with metallized lighter heads, and paper clips. These objects may be characterized by rapid heating (e.g., on the order of seconds) and by at least one electrical property that changes significantly with temperature when exposed to an alternating magnetic field having a flux density greater than 1 mT at a frequency of 85 kHz.

[0060] It may be appreciated that this category of object may also change the electrical characteristics (e.g., impedance) of the inductive sensing element (i.e., one or more of the sensing elements 107a-107n) in proximity to the object when heated. This results in a change in the electrical characteristics as measured in the corresponding inductive sensing circuit (e.g., sensing circuit 106a-106n) by the measurement circuit 104 at the FOD sensing frequency, and thus a change in the measurement output. Exposing the object to a heating magnetic field may be considered to stimulate the object to make it detectable, either absolutely, without the need for precise calibration and long-term stability of the circuitry, or by the TDD method as described above.

[0061] In some implementations or operations of the ITS, the potential metal object is stimulated by intermittently applying magnetic field exposure in such a manner that the temperature of the object clearly tracks the ON and OFF cycles of exposure but does not exceed a critical level. When an object of the above-mentioned category is in close proximity to at least one inductive sensing element, the associated measurement output also tracks the ON and OFF cycles of exposure. In alternative implementations or operations of the ITS, the potential metal object is stimulated by varying the magnetic field exposure between higher and lower levels rather than by applying ON / OFF cycling.

[0062] In some implementations of the detection circuit 100 using an ITS, the presence of an object is determined by the control and evaluation circuit 102 based on a correlation between a sequence of measurement outputs indicative of an electrical characteristic of the inductive sensing circuit as determined at the FOD sensing frequency and a signal indicative of a level of magnetic field exposure used for heating (stimulation). The magnetic field exposure level may be sensed using at least one of the inductive sensing elements 107a-107n and with a measurement amplifier circuit 404 and a signal processing circuit 408 also configured to measure a voltage induced in the at least one inductive sensing element.

[0063] In some example implementations or operations of the detection circuit 100, the ITS is combined with an SDD scheme. If at least one difference between a level of correlation between a measurement output and magnetic field exposure associated with at least one first sensing circuit (e.g., the inductive sensing circuit 106a) and a level of correlation associated with at least one second sensing circuit (e.g., the inductive sensing circuit 106b) exceeds a threshold, the presence of an object is assumed.

[0064] In some implementations, system-specific thermal effects may occur due to one or more properties (e.g., resistivity, dielectric constant) of the conductive and insulating materials contained in the inductive sensing element, which are also functions of temperature. When exposed to a low-frequency WPT magnetic field, the one or more properties may change, causing the electrical properties of the inductive sensing element to change (e.g., drift). In the presence of a metal object, the system-specific thermal effects superimpose on the system-external thermal effects produced by the object, thus altering or even dominating the desired system-external effects. Thus, in some implementations, the detection circuit 100 employs a process of calibration (or learning) by determining the change (e.g., drift) of the electrical properties as produced by the system-specific thermal effects in the absence of any foreign object. During normal operation, the control and evaluation circuit 102 may compensate (e.g., subtract) the system-specific effects, resulting in improved sensitivity for detecting metal objects based on ITS.

[0065] In a further implementation, the inherent thermal effects of the system are reduced by using special materials or components configured to reduce the thermal coefficient of one or more properties.

[0066] Inductive ferromagnetic sensing (IFS), described in U.S. Pat. No. 10,302,795 (incorporated herein), is another specialized detection scheme for detecting a category of metallic ferromagnetic objects that can be inductively sensed at the FOD sensing frequency and are characterized by at least one electrical property (e.g., conductivity, permeability) that is a function of the instantaneous amplitude of the bias field in a manner that can be significantly varied (modulated) by applying a low-frequency bias field (e.g., a WPT field of 85 kHz). For ferromagnetic objects, this function is generally nonlinear, meaning that negative and positive field amplitudes change the electrical property equally, resulting in a rectified modulation. This rectified modulation produces a DC component, a fundamental frequency component at twice the frequency of the bias field (e.g., 170 kHz), and higher harmonics depending on the degree of saturation. The modulation function may also include memory (hysteresis) effects and thermal effects (e.g., the Curie temperature effect).

[0067] Non-limiting examples of objects detectable by IFS are objects made of ferromagnetic steel, such as paperclips, pieces of wire, tacks, pins, screws, nuts, washers, etc. These objects, when exposed to an alternating magnetic field having a flux density greater than 1 mT at a frequency of about 85 kHz, may be characterized by a significant magnetic bias effect and by at least one electrical property that varies significantly as a function of the flux density of exposure.

[0068] It can be appreciated that this category of object may also modulate the electrical characteristics (e.g., impedance) of an inductive sensing element (e.g., one of sensing elements 107a-107n) proximate to the object when exposed to a low frequency magnetic field. This results in a modulation of the electrical characteristics as measured in a corresponding inductive sensing circuit (e.g., one of sensing circuits 106a-106n) at the FOD sensing frequency by measurement circuit 104. Exposing the object to the magnetic field induces a magnetic bias that may be considered as stimulating the object to be detectable absolutely without the need for precise calibration and long term stability of the circuit or by a TDD method as described above.

[0069] In the frequency domain, modulation by the bias low frequency magnetic field can be manifested in a change in a spectral peak at the FOD sensing frequency (corresponding to the DC component of the modulation), but also in the occurrence of modulation sidebands to the left and right of the FOD sensing frequency. The modulation sidebands may include one or more spectral peaks in both the lower and higher sidebands corresponding to a fundamental and higher harmonics offset from the FOD sensing frequency by n times the fundamental modulation frequency (e.g., 2×85 kHz), where n is an even integer including 2, 4, 6, etc. In some implementations, the signal processing circuit 408 extracts the component at the FOD sensing frequency (the DC component of the rectified modulation), and the measurement output indicates the DC component. In other implementations, the signal processing circuit 408 extracts one or more of the fundamental and harmonic components of the modulation spectrum, and the measurement output indicates one or more of the fundamental and harmonic components.

[0070] In some implementations or operations of the IFS, the potential metal object is stimulated by applying a low frequency magnetic field (e.g., having a frequency of 85 kHz) in a manner that modulates the electrical properties of the object during the exposure ON cycle, but with a level and duration that does not cause the object to exceed a critical temperature. The exposure ON cycle may be considered as a substantially rectangular pulse relative to the envelope of the low frequency magnetic field. When an object of the above-mentioned category is in close proximity to at least one inductive sensing element, the associated measurement output also changes over the duration of the exposure ON cycle (e.g., pulse duration). In an alternative implementation or operation of the IFS, the potential metal object is stimulated by varying the magnetic field exposure between higher and lower levels rather than applying an ON / OFF cycle.

[0071] In some implementations of the detection circuit 100 using the IFS, the presence of an object is determined by the control and evaluation circuit 102 based on a correlation between a sequence of measurement outputs indicative of the electrical characteristics of the inductive sensing circuit as determined at one or more of the FOD sensing frequency and modulation sidebands and a signal indicative of the level of magnetic field exposure used for modulation (stimulation). The magnetic field exposure level may be sensed using at least one of the inductive sensing elements 107a-107n in a manner as described above with respect to the ITS.

[0072] In some implementations of the control and evaluation circuit 102, the presence of an object is determined based on the correlation as described above, but using the ITS and IFS together. This may improve detection of small ferromagnetic objects (e.g., paperclips) that exhibit both thermal and magnetic bias effects.

[0073] In some implementations, a magnetic bias effect may also occur in the ferrite material used in the wireless power transfer structure (e.g., in the ferrite structure 204 of the wireless power transfer structure 200 of FIG. 2 and FIG. 3), causing a change in the electrical properties (e.g., impedance) of the inductive sensing element when a low-frequency WPT magnetic field is applied. In the presence of a ferromagnetic object, this system-specific magnetic bias effect superimposes on the system-external magnetic bias effect produced by the object, thus corrupting or even dominating the desired system-external effect. Thus, in some implementations, the detection circuit 100 employs a process of calibration (or learning) by determining the change in electrical properties as produced by the system-specific bias effect in the absence of any foreign object. During normal operation, the control and evaluation circuit 102 may compensate (e.g., subtract) the system-specific effect, resulting in improved sensitivity for detecting ferromagnetic objects based on the IFS.

[0074] In a further implementation, the inherent magnetic bias effect of the system is reduced by using a ferrite structure that includes a ferrite material configured to reduce the magnetic bias effect when exposed to a low frequency magnetic field.

[0075] Inductive motion sensing (IMS), as described in U.S. Patent No. 10,298,049 (incorporated herein), is a more specialized detection scheme for detecting an object by its relative motion (e.g., when the object is mechanically moved relative to a sensing element). Relative motion of an object in the vicinity of a sensing element can produce a change in the electrical characteristics (e.g., impedance) of the corresponding inductive sensing circuit and, therefore, the measurement output of the measurement circuit 104.

[0076] In an exemplary implementation or operation of an IMS, an object is mechanically moved back and forth relative to the sensing element array 107. This may be accomplished by moving the top surface of the housing 310 of FIG. 3, where the object may come to rest, a portion of the wireless power transfer structure 200, or both. In some implementations or operations of an IMS, the object is moved relative to the sensing elements at low frequencies (e.g., 3 Hz) with amplitudes in the centimeter range. In other implementations or operations, the object is moved (vibrated) at higher frequencies (e.g., 100 Hz) with amplitudes in the millimeter range or even sub-millimeter range.

[0077] In another implementation or operation of IMS, a metal object is moved by applying a time-varying magnetic field that exerts an electrodynamic force on the object (e.g., due to eddy currents induced in the object), as described in U.S. Patent No. 9,726,518 (incorporated herein). In this implementation or operation, the object may be a low-mass object (e.g., a thin metal foil), and the applied alternating magnetic field may be a WPT low-frequency magnetic field (e.g., 85 kHz). In a further implementation or operation of IMS, a ferromagnetic metal object (e.g., object 110) is moved by applying a magnetic field that exerts a magnetic force on the object.

[0078] In yet another implementation or operation of the IMS, an object (e.g., object 110) is moved by gravity or a deformation force. An example may be a composite object that includes a metal portion and a plastic portion (e.g., a plastic yogurt cup with an aluminum lid). The metal portion, when inductively heated, may partially melt or deform the plastic, thus causing the metal portion to move slightly.

[0079] In some implementations or operations of an IMS, the presence of an object is determined based on a correlation between a measurement output indicative of a measured electrical characteristic (e.g., impedance) and a signal indicative of mechanical movement. In other implementations or operations of an IMS, the presence of an object is determined based on a correlation between a measurement output indicative of a measured electrical characteristic and a signal indicative of a level of magnetic field exposure that causes the object to move.

[0080] In some implementations or operations of the detection circuit 100, one or more power correlation-based detection schemes (e.g., ITS, IFS, IMS) are employed during a pre-charging phase (e.g., before the normal charging process begins) when a vehicle is parked over a ground-based wireless power transfer structure where the wireless power transfer structure cannot be easily accessed by humans or animals. In such conditions, a relatively large current (e.g., >30A rms The use of ITS, IFS, and IMS, which require the WPT coil to be excited by a power supply, may be considered safe and access for live objects may be more easily protected by LOD. This procedure, which uses a correlation-based detection scheme, is to verify that the ground-based wireless power transfer structure is clear for WPT (e.g., charging). This procedure is sometimes called a "clean pad check" and may last several minutes.

[0081] In other implementations or operations, and if supported by the WPT system and the vehicle battery's management system, the detection circuit 100 employs one or more of the power correlation-based detection schemes (e.g., ITS, IFS, IMS) during normal power transfer. The use of correlation-based detection schemes may require the WPT system to frequently and rapidly ramp up and down power.

[0082] Object detection using thermal mediator materials The potential for induction heating of some categories of metallic objects may not be detectable by any of the power correlation methods mentioned above (e.g., ITS, IFS, IMS) when the sensing frequency is in the MHz range. This category of objects may not exhibit significant thermal or magnetic bias effects or movement when exposed to the WPT magnetic field. This category includes copper or nickel coated objects (e.g., some coins) with a ferromagnetic steel core. Undetectable objects resting on the top surface of the housing 310 of the wireless power transfer structure 200 as shown in FIG. 3 may heat up when exposed to the WPT magnetic field and melt into the housing 310, potentially causing irreparable damage if the cover shell 312 of the housing 310 is made from standard low-cost plastic.

[0083] Thus, methods and apparatus for protecting a wireless power transfer structure from such objects are desirable. In some aspects, the wireless power transfer structure includes one or more portions of an intermediary heat-sensitive material. The foreign object may be detected based on a change in a property of the intermediary heat-sensitive material rather than a change in a property of the object itself. The portion of heat-sensitive material may advantageously be part of a system configured to detect a foreign object in the vicinity of the wireless power transfer structure based on a thermal effect. In some aspects, the heat-sensitive material may be a material that changes electrical resistance based on the temperature of the material. More generally, the heat-sensitive material may be a material that changes impedance as measured at an operating frequency (e.g., FOD sensing frequency) as a function of the temperature of the material. More specifically, the heat-sensitive impedance material may change one or more of resistivity, conductivity, capacitance, inductance, electrical permittivity, magnetic permeability, and another electrical property based on the temperature of the material.

[0084] In one aspect, the thermally sensitive material may be a material that changes its electrical conductivity as a function of temperature. An exemplary thermally sensitive material may have an electrical conductivity with a pronounced negative temperature coefficient (NTC) characteristic, such that its electrical conductivity increases significantly as the temperature increases and decreases as the temperature decreases. When the temperature exceeds a threshold value (e.g., 100 degrees Celsius (°C), 373 Kelvin (K)), the electrical conductivity of the thermally sensitive material may increase rapidly and significantly. In one implementation, the thermally sensitive material is a doped polymer (e.g., CoolPoly® thermally conductive plastic from Celanese Corporation) with NTC characteristics, with electrical conductivity increasing significantly as the temperature increases above 100°C (373K). In another example, the thermally sensitive material acts substantially as an insulator at temperatures below a threshold value and becomes conductive when the temperature exceeds the threshold value. In some implementations, the thermally sensitive material is a type of ceramic or crystalline material with a pronounced NTC characteristic (e.g., due to a phase change in the crystal structure when the temperature increases).

[0085] In another aspect, the thermally sensitive material may have a resistance with a pronounced positive temperature coefficient (PTC) characteristic, such that its resistance increases significantly as the temperature increases and decreases as the temperature decreases. In one implementation, the thermally sensitive material is a PTC screen printable ink (e.g., Loctite® PTC ink from Henkel Corporation) that has a defined temperature threshold whose sheet resistance (Ω / square) increases rapidly as the temperature increases above the threshold.

[0086] In a further aspect, the thermally sensitive material may change its electrical permittivity (e.g., dielectric constant) as a function of temperature. One example of such a material has a dielectric constant that changes rapidly when the temperature exceeds a threshold value (e.g., 100° C., 373 K). This threshold value may be the Curie temperature of the dielectric material. In one implementation, the thermally sensitive material includes barium titanate (BaTiO3) or a similar chemical compound that has a low Curie point (e.g., around 100° C., 373 K).

[0087] In yet another aspect, the thermally sensitive material may change its magnetic permeability as a function of temperature. One example of such a material is a ferrite powder plastic compound that has a magnetic permeability that changes rapidly when the temperature exceeds a threshold value. This threshold value may be the Curie temperature of the ferrite material. In one implementation, the ferrite material is at least one of iron oxide (Fe2O3) or zinc oxide (ZnO), which exhibits a chemical composition of manganese zinc (MnZn) and a relatively low Curie point (e.g., about 100°C, 373K) that can be controlled by its oxide component.

[0088] In one aspect of the IFS, the use of a material with thermal permeability may increase the system's inherent magnetic bias effect as previously described with respect to FIG. 4. Thus, in some implementations, the thermally sensitive material is also configured to reduce the material's inherent magnetic bias effect. In other implementations, the thermally sensitive material is also configured to reduce the overall inherent magnetic bias effect caused by the thermally sensitive material (e.g., together with the ferrite structure 204). In some implementations, the inherent magnetic bias effect is controlled by one of the particle size of the ferrite powder, the blending ratio of different particle sizes, and the chemical composition of the ferrite powder.

[0089] In still further embodiments, the thermally sensitive material may change another physical (non-electrical) property as a function of temperature, such as by changing shape. This deformation may cause the metal object to move slightly, making it detectable using IMS as described above, due to a change in the measured electrical property (e.g., impedance) of the inductive sensing element.

[0090] Further, some embodiments combine inductive sensing with a thermal sensing material to detect metal objects using a sensing system that combines a plurality of sensing elements with a mediating thermal sensing material, each sensing element comprising a conductive structure. At least a portion of the plurality of sensing elements are configured as inductive sensing elements having electrical properties that change based on an inductive effect in the presence of a metal object. The mediating thermal sensing material has properties that vary with temperature as described above when heated by a metal object resting on a top surface of the housing (e.g., housing 310 in FIG. 3) and exposed to an alternating magnetic field generated by the wireless power transfer structure. The mediating thermal sensing material changes electrical properties of at least a portion of the plurality of sensing elements as the properties change, thereby mediating sensing of the object based on a thermal effect. The electrical properties of each of the sensing elements may be measured periodically by the measurement circuit 104 in a time-multiplexed manner as described with respect to FIG. 4. The measurement output of the measurement circuit 104 is evaluated and monitored by a control and evaluation circuit 102 configured to make a determination whether a change in the measured electrical property of the sensing element indicates the presence of a metallic object through normal inductive effects, or an object being heated by a magnetic field through thermal effects. Although several aspects are described herein with respect to detecting a foreign object resting on the top surface of the wireless power transfer structure 200, similar techniques may be used for foreign object detection in other implementations.

[0091] Moreover, some embodiments combine capacitive sensing with thermal sensing to detect metal objects using a sensing system comprising a plurality of sensing elements and an intermediate thermal sensitive material, each sensing element comprising a conductive structure. At least a portion of the plurality of sensing elements are configured as capacitive sensing elements and to have electrical properties that change based on a capacitive effect in the presence of a metal object. The intermediate thermal sensitive material has properties as described above, and changes the electrical properties of at least a portion of the plurality of sensing elements as the properties change, mediating the sensing of the object based on a thermal effect. The electrical properties of each of the sensing elements may be measured periodically by the measurement circuit 104 in a time multiplexed manner as described with respect to FIG. 4. The measurement output of the measurement circuit 104 is evaluated and monitored by the control and evaluation circuit 102, which is configured to make a determination whether the change in the measured electrical properties of the sensing elements indicates the presence of a metal object through a capacitive effect, or an object being heated by a magnetic field through a thermal effect.

[0092] In one embodiment of combined inductive and thermal sensing or combined capacitive and thermal sensing using an intermediate thermal sensitive material, the detection circuit 100 may employ an ITS scheme as previously described to detect some metal objects based on correlation with the level of magnetic field exposure as previously described. An ITS based on an intermediate thermal sensitive material may be referred to as an indirect ITS (ID-ITS), where an object is detected based on a change in the properties of the intermediate thermal sensitive material rather than a change in the properties of the object itself.

[0093] In some aspects herein, the housing of a ground-based wireless power transfer structure is constructed, at least in part, from a thermally sensitive material that changes at least one of its electrical or non-electrical properties based on the temperature of the material, allowing an inductive or capacitive sensor inside the structure to detect foreign objects based on thermal effects in the thermally sensitive material of the housing.

[0094] In another embodiment, the housing may at least partially comprise a heat resistant material capable of withstanding temperatures that a foreign object may reach before the system detects the foreign object, which may be as high as or greater than 200° C. (473 K). The heat resistant material may have, for example, a melting point greater than 200° C. (473 K). In another embodiment, the heat resistant material may be flame retardant. In a further embodiment, the material may have a high autoignition temperature. For example, the heat resistant material may include one or more of plastics, such as nylon resins (e.g., Minlon® or Zytel® resins from Dupont), perfluoroelastomers (e.g., Kalrez® products from Dupont), polymerized siloxanes (e.g., silicone rubber), glass or carbon fiber reinforced plastics, structural composites (e.g., PyroSic®, PyroKarb™ composites from Pyromeral Systems), sintered high temperature polymers (e.g., polyimides (PI) such as TECASINT™ from Ensinger), or ceramic matrix composites (CMCs) (e.g., glass ceramics).

[0095] On the mechanical side, the housing may include a material that is resistant to mechanical shock, bending, or compressive stress. Such mechanical resistance may protect the wireless power transfer structure from physical damage. Additionally, the material may be elastic so as not to be brittle, thereby allowing the material to flex or bend under pressure without breaking (e.g., from a vehicle driving over the wireless power transfer structure). Furthermore, the material may have a low thermal expansion to avoid bulging or deformation due to heat (e.g., from solar irradiation or foreign objects). Moreover, the material may provide good machinability or be suitable for injection molding.

[0096] In terms of mass (weight) and other aspects discussed herein, the housing may include engineering plastics with relatively low mass density (specific gravity), such as polyamide (e.g., Durethan® plastic from LANXESS), polybutylene terephthalate (PBT) (e.g., Pocan® plastic from LANXESS), and fiber reinforced plastic composites (e.g., Tepex® composite from LANXESS).

[0097] On the thermal side, the housing may include a material with high thermal conductivity to dissipate heat (e.g., heat generated by foreign objects). The thermal conductivity may be significantly greater than that of prevalent plastic materials. Alternatively, the housing may include a material with low thermal conductivity (e.g., silica, carbon-carbon composites, fiberglass, etc.). The housing may also include a material that is resistant to long-term ultraviolet (UV) radiation exposure and chemicals (e.g., lubricating oils and diesel fuels, gasoline, brake fluid, coolants, solvents, etc.).

[0098] On the electrical side, the housing may comprise a material that is non-conductive so as not to generate significant eddy currents and that exhibits low dielectric polarization losses so as not to generate significant displacement currents when exposed to wireless power electromagnetic fields. Additionally, the material may be non-magnetic or only weakly magnetic so as not to significantly affect the wireless power magnetic field or magnetic fields such as those generated to sense foreign objects.

[0099] In a commercial aspect, the housing may include conventional low-cost materials that may not provide the properties of heat-sensitive or heat-resistant materials as defined above. Such materials may include one or more of polyethylene (PE), acrylonitrile butadiene styrene (ABS), polyoxymethylene (POM), and fiber-reinforced epoxy materials. The housing may combine materials that provide heat sensitivity, heat resistance, or both with any of the other aspects described above.

[0100] 5A-5F show examples of respective housings 310A-310F for a wireless power transfer structure (e.g., wireless power transfer structure 200 of FIG. 3). Each of the housings 310A-310F includes a cover shell 312 and a backplate 206 of FIG. 2 and may be suitable structures for a ground-mounted wireless power transfer structure. However, they should not be construed as being limited to this application. Some concepts disclosed in FIG. 5A-5F along with some adaptations may also be used in a recessed or ground-embedded wireless power transfer structure (not shown herein).

[0101] As previously described with reference to FIG. 2 and FIG. 3, the housings 310A-310F house the WPT coil 202, the ferrite structure 204, the sensing element arrays 107 and 109, and other components. The cover shell 312 is placed over a portion of the wireless power transfer structure that faces the vehicle-based wireless power transfer structure to wirelessly transfer power. For example, the cover shell 312 may be disposed over a portion of the wireless power transfer structure that faces away from the ground (e.g., above the ground) when the wireless power transfer structure is placed on the ground. The backplate 206 is placed under a portion of the wireless power transfer structure that faces the vehicle-based wireless power transfer structure 320 to wirelessly transfer power. For example, the backplate 206 may be disposed over a portion of the wireless power transfer structure that faces toward the ground when the wireless power transfer pad is placed on the ground. The backplate 206 may be made of metal (e.g., aluminum), may be made of plastic, or may be made of the same material as the cover shell 312. The cover shell 312 may have a size and shape to cover the wireless power transfer structure. As will be appreciated, the cover shell 312 or the backplate 206 may have any suitable size or shape.

[0102] In some implementations, the interior of the housing is potted using injection molding resin or any other suitable material to fill the voids. In such implementations, the cover shell 312 may no longer be a separable part after the potting process that makes it blend in with other plastic support structures within the interior of the housing. In other implementations (e.g., optimized for a special injection molding process), the cover shell 312 may act as a thermal insulation and protective material surrounding the electrical components of the wireless power transfer structure, such as the sense element arrays 107 and 109, the WPT coil 202, and the ferrite structure 204 as shown in FIG.

[0103] The material used for the cover shell 312 may combine electrical, mechanical, chemical, thermal, and radiation exposure properties as previously described. The cover shell 312 may be resistant to mechanical shock, heat, bending, or compressive stress. Such mechanical strength or heat resistance may protect the wireless power transfer structure from physical damage. In addition, the cover shell 312 may be resilient so as not to be brittle, thereby allowing the cover shell 312 to flex or bend under pressure without breaking (e.g., from a vehicle running over the cover shell 312). Thermal conductivity may also, in some aspects, prevent foreign objects from becoming excessively hot, as the thermally conductive material absorbs and dissipates heat from hot foreign objects. Thus, the use of a thermally conductive material for the cover shell 312 may prevent the development of localized hot spots on the top surface of the cover shell 312 and the resulting damage to portions of the wireless power transfer structure.

[0104] 5A shows an exemplary implementation of an enclosure 310A for a wireless power transfer structure. In this implementation, the entire cover shell 312 is made from a heat-sensitive material configured to detect the presence of a foreign object above the top surface of the cover shell 312 as described above and therefore protect the wireless power transfer structure. The heat-sensitive material may combine properties such as electrical properties that are significantly temperature-dependent along with one or more of mechanical, chemical, thermal, and radiation exposure properties as described above. In particular, the heat-sensitive material may combine electrical properties that are significantly temperature-dependent along with heat resistance.

[0105] 5B-5F, the cover shell 312 includes one or more inlays. The inlays may include at least one of a heat-sensitive material, a heat-resistant material, and a heat-blocking material. In some implementations, the inlays may be separate parts that are assembled with the cover shell 312 during the manufacturing process. In other implementations, the inlays may be defined areas of the cover shell 312 that are created by specific and localized treatment of the cover shell's substrate (e.g., plastic). In further implementations, the areas are created by locally adding one or more materials (e.g., heat-sensitive ferrite powder) having desired properties to the substrate during formation (e.g., during an injection molding process).

[0106] In the example of FIG. 5B, the housing 310B is similar to the housing 310A, except that the cover shell 312 is not entirely formed of a thermally sensitive material. Instead, as shown, the cover shell 312 includes an inlay 512 on the top surface of the cover shell 312. The inlay 512 may be made of a thermally sensitive material (thermal inlay). The remaining portion of the cover shell may be made of a non-thermal sensitive material. By reducing the amount of thermally sensitive material used for the cover shell 312, the cost of the housing 310B may be reduced without compromising FOD performance. The thermal inlay 512 may cover only a portion of the top surface of the cover shell 312, or may cover the entire top surface as shown. The material used for the thermal inlay 512 may combine properties such as electrical properties that are significantly temperature dependent, along with one or more of the mechanical, chemical, thermal, and radiation exposure properties as previously described. In particular, such materials may combine electrical properties that are significantly temperature dependent along with heat resistance.

[0107] 5C illustrates a further example of a housing 310C. The housing 310C is similar to the housing 310B in that it includes a heat sensitive inlay 512, but the heat sensitive inlay 512 is embedded within the cover shell 312 instead of being on the top surface of the cover shell 312.

[0108] FIG. 5D illustrates yet another example of a housing 310D for a wireless power transfer structure. The housing 310D is similar to the housings 310B and 310C in that it includes a heat-sensitive inlay 512, but the cover shell 312 further includes a heat-resistant inlay 513. As shown in FIG. 5D, the heat-resistant inlay 513 is on the top surface of the cover shell 312, but the heat-sensitive inlay 512 is disposed below the heat-resistant inlay 513. In some implementations, the heat-sensitive inlay 512 and the heat-resistant inlay 513 may be adjacent (in physical contact), as shown in FIG. 5D. The material used for the heat-resistant inlay 513 may combine properties such as heat resistance with one or more of the mechanical, chemical, thermal, and radiation exposure properties as previously described.

[0109] The heat-resistant inlay 513 may include multiple layers, such as a first layer including a first material (e.g., plastic) that has some heat resistance (e.g., greater than 200° C., 473 K) and a high ignition temperature (e.g., greater than 600° C., 873 K), and a second layer including a highly heat-resistant mesh structure or tissue of a second material that maintains its structure at high temperatures (e.g., greater than 600° C. (873 K)). The inclusion of such multiple layers prevents objects from sinking into the cover shell 312 if the first material begins to melt. The second material may be glass or carbon. In another example, the heat-resistant inlay 513 is made from a compound including a first and a second material that prevents objects from sinking into the cover shell 312 if the first material begins to melt. In a further example, the heat-sensitive inlay 512 is omitted and the entire remaining portion of the cover shell 312 is made from a heat-sensitive material. In yet another example, the heat resistant inlay 513 is omitted and the entire remainder of the cover shell 312 is made from a heat resistant material.

[0110] In the example of FIG. 5E, the housing 310E is similar to the housing 310D in that it includes a heat resistant inlay 513 on the top surface as shown, but the cover shell 312 further includes a thermal insulation layer in the form of a thermal insulation inlay 514. The thermal insulation inlay 514 may be made from a material having a low thermal conductivity as previously described. The thermal insulation inlay 514 may protect the wireless transfer structure from heat (e.g., generated by a foreign object) and resulting damage. For example, the thermal insulation inlay 513 may prevent a hot object from physically contacting exposed components of the wireless power transfer structure housed within the housing 310E, but in some aspects, heat may still pass through the thermal insulation inlay 513 to those components of the wireless power transfer structure and cause damage. Thus, the thermal insulation inlay 514 may prevent or mitigate heat generated by a foreign object from reaching exposed components within the interior of the housing 310E of the wireless power transfer structure. As shown in FIG. 5E, a thermal insulating inlay 514 may be disposed adjacent to (eg, below) the heat resistant inlay 513.

[0111] In another example, the heat resistant inlay 513 is omitted and the entire remainder of the cover shell 312 is made from a heat resistant material, and the insulating inlay 514 is embedded within the cover shell 312 .

[0112] The use of the heat resistant inlay 513 in combination with the insulating inlay 514 may sufficiently protect the cover shell 312 from damage caused by a hot object resting on its upper surface for an extended period of time (e.g., several hours), and thus heat sensing (e.g., using a heat sensitive material) may not be required.

[0113] In the example of FIG. 5F, the housing 310F is similar to any of the housings 310A-310E and may include a heat sensitive inlay, a heat resistant inlay, or a thermal insulating inlay (not shown). The cover shell 312 further includes an arrangement 516 of one or more sensing elements configured to detect a foreign object. In some implementations, the arrangement 516 includes at least one sensing element array, such as one or both of the sensing element arrays 107 and 109 of FIG. 1. The arrangement 516 may be electrically coupled to a measurement circuit or some circuit configured to detect a foreign object near the cover shell 312, such as by detecting a change in an electrical characteristic of the one or more sensing elements.

[0114] 6A-6D are schematic diagrams illustrating example implementations of sensing systems 600A-600D, respectively, each configured for combined inductive and thermal sensing. Each of the example sensing systems 600A-600D includes a sensing element 610 and a planar thermal sensitive structure 602 (e.g., a sheet) made from an intermediate thermal sensitive material and disposed in contact with or in close proximity to the sensing element 610. For illustrative purposes, FIGS. 6A-6D show only a single sensing element 610 and cutaway view of the thermal sensitive structure 602. In some implementations, the sensing element 610, or a portion thereof, may correspond to an inductive sensing element (e.g., one of the inductive sensing elements 107a-107n) with respect to FIG. 1, and the thermal sensitive structure 602 may correspond to the cover shell 312 or the inlay 512 with respect to FIGS. 5A-5D. Each sensing element 610 includes a conductive planar structure consisting of a pair of sensing coils 611 and 612, which provide terminals 1a, 1b and 2a, 2b, respectively, for interfacing to additional elements of a sensing circuit (e.g., one of the sensing circuits 106a-106n) as previously described with respect to FIG. 1. In some concepts or implementations, the terminals 1a, 1b and 2a, 2b define a reference plane to which the electrical characteristics of the sensing element 610 are referenced. However, in other concepts or implementations, the electrical characteristics include the entire sensing circuit and are measured at the terminals of the sensing circuit (e.g., by a measurement circuit 104 as shown in FIG. 4). FIGS. 6A-6D also show a cross-section (perpendicular cut to the drawing plane) of a small portion of the planar thermal sensitive structure 602, as well as a cross-section of one cut of the coils 611 and 612, at the top right.

[0115] FIG. 6A shows an exemplary implementation of a sensing system 600A, where both sensing coils 611 and 612 are disposed on the bottom surface of the heat-sensitive structure 602 and galvanically contact the heat-sensitive structure 602. The galvanic contact may extend over the entire conductor length of the coil winding. FIG. 6B shows an exemplary implementation of a sensing system 600B, where the sensing coils 611 and 612 are disposed opposite each other on different sides of the heat-sensitive structure 602 and galvanically contact the heat-sensitive structure 602. FIG. 6C shows an exemplary implementation of a sensing system 600C, where the sensing coils 611 and 612 are embedded in the heat-sensitive structure 602 and galvanically contact the heat-sensitive structure 602. FIG. 6D shows an example implementation of a sensing system 600D, in which sensing coils 611 and 612 are disposed below the heat sensitive structure 602 but are physically separated (galvanically isolated) from the heat sensitive structure 602.

[0116] In the general example with reference to FIGS. 6A-6D, multiple electrical characteristics may be defined and measured between the terminals of the sensing element 610, as known from a 4-pole network. More specifically, one-port self-electrical characteristics may be defined between terminals 1a and 1b and between terminals 2a and 2b for the sensing coils 611 and 612, respectively. Furthermore, one-port mutual electrical characteristics may be defined between various pairs of terminals 1a and 2a, 1b and 2b, 1a and 2b, and 1b and 2a. Moreover, two-port mutual electrical characteristics may be defined between terminals 1a, 1b and terminals 2a, 2b. In some implementations, the basic electrical characteristics measured are one or more of impedance as measured at the operating frequency (e.g., the sensing frequency) of the detection circuit 100, resistance as measured at DC, impulse response in current as measured when applying a voltage pulse, and current or voltage response of another voltage or current waveform, respectively. These basic characteristics may apply primarily to both the self-electrical characteristics and the mutual electrical characteristics.

[0117] A change in one or more of the measured electrical properties (e.g., self-impedance, mutual impedance) may indicate an object. The change may be defined as a difference to a reference value as determined in the absence of any object, and may be used to determine the presence of a foreign object. More specifically, the change in one or more of the measured electrical properties may be produced by the presence of an object based on one or more of inductive and thermal effects. In particular, a metal object in thermal contact with the heat-sensitive structure 602 and inductively heated by a strong alternating magnetic field (e.g., as generated by the wireless power transfer structure 200) may change the properties of the heat-sensitive structure 602. This change, in turn, may cause a change in one or more of the measured electrical properties of the sensing element 610 disposed adjacent or proximate to the heat-sensitive structure 602, which acts as a mediator material.

[0118] In the exemplary implementation with reference to FIGS. 6A-6C, the thermally sensitive structure 602 is configured to have a DC resistance (e.g., sheet DC resistance in Ω / square) that varies with temperature (example described above). In this implementation, a local change in DC resistance caused by a heated object is expected to also cause a change in the DC resistance as measured (e.g., between terminals 1a and 2a) based on thermal effects. Meanwhile, a metal object in close proximity to the sensing element 610 may cause a change in the self-impedance and mutual impedance as measured between terminals 1a, 1b, 2a, and 2b due to inductive effects. However, an increase in the DC resistance of the thermally sensitive structure 602 may also be evident in a change in the self-impedance and mutual impedance as measured at a sensing frequency (e.g., high frequency) between terminals 1a, 1b, 2a, and 2b of the sensing element 610.

[0119] In another exemplary implementation, referring to Figures 6A-6C, the thermally sensitive structure 602 is substantially an electrical insulator (example described above) configured to have a DC conductivity (e.g., sheet DC conductivity in siemens / m / square) that increases significantly when the temperature exceeds a threshold value. In this implementation, the local increase in conductivity caused by the heated object is also expected to cause a decrease in the DC insulation resistance value as measured (e.g., between terminals 1a and 2a) based on thermal effects. However, the increase in DC conductivity of the thermally sensitive structure 602 may also be evident in a change in self-impedance and mutual impedance as measured at a sensing frequency (e.g., high frequency) between terminals 1a, 1b, 2a, and 2b of the sensing element 610.

[0120] In a further exemplary implementation with reference to any of Figures 6A-6D, the thermally sensitive structure 602 is configured to have an impedance (e.g., sheet impedance or surface impedance in Ω / square) with a real (resistive) and imaginary (reactive) part that varies with temperature. This may be a material that varies its sheet inductance or sheet capacitance (e.g., due to a magnetic permeability or electric permittivity that varies with temperature (examples discussed above). In this implementation, a local change in the sheet impedance caused by a heated object may also cause a change in impedance as measured between any pair of terminals 1a, 2a, 1b, and 2b based on thermal effects and in addition to inductive effects. It may be appreciated that in the implementation of Figure 6D using a thermally sensitive structure 602 that is not in physical contact with the sensing element 610, a change in impedance based on both thermal and inductive effects would be expected. This may be true for a thermally sensitive material configured to vary either its sheet resistance or sheet impedance with temperature.

[0121] In yet another exemplary implementation referring to Figures 6A to 6D, the sensing element 610 includes only one sensing coil (e.g., sensing coil 611), and impedance is measured between terminals 1a and 1b to determine the presence of an object (e.g., object 110) based on one or more of inductive and thermal effects.

[0122] In an exemplary implementation of a sensing system based on one or more of the capacitive and thermal effects (not shown in this specification), the sensing element 610 is replaced by a capacitive sensing element (e.g., one of the capacitive sensing elements 109a-109n) having two electrodes each providing a terminal, and an impedance is measured between a terminal of the first electrode and a terminal of the second electrode to determine the presence of an object based on one or more of the inductive and thermal effects.

[0123] The implementations as shown in Figures 6A-6D should be construed as exemplary and non-limiting. They do not necessarily represent the only implementations of combined inductive sensing and thermal sensing FOD. For example, the thermal sensitive structure 602 may be omitted. Instead, the conductive structure of the sensing element 610 may include a thermally sensitive material (e.g., a thermally sensitive electrical conductor). The thermally sensitive electrical conductor may be configured to significantly increase its resistance when the temperature rises above a threshold value (e.g., 100°C, 373K) as previously described. The sensing element may be embedded in the cover shell 312 of Figure 3 (e.g., a few millimeters below its top surface) to maximize the thermal resistance of heat flow from the object to the sensing element.

[0124] As described above with reference to FIG. 4, the sensing system may be coupled to a controller (e.g., a controller including the measurement circuit 104 and the control and evaluation circuit 102 of FIG. 4). The controller may be configured to measure the electrical characteristics of the sensing element and control the wireless power transfer of the WPT system (e.g., via the control output shown in FIG. 4). For example, in some embodiments, if a change in the measured electrical characteristic meets a threshold or another defined criterion indicating the presence of a foreign object by either an inductive effect or a thermal effect mediated by a mediated heat-sensing structure, the controller determines that a foreign object is present and takes appropriate action.

[0125] In some embodiments, when the presence of a foreign object is detected, either by inductive or thermal effects as described above, the controller or WPT system may take one or more actions. For example, the system may enter a low power mode, reduce power, turn off, or issue an alert prompting the user to remove the object.

[0126] Further, in some embodiments, detection of a foreign object (e.g., object 110) based on thermal effects may be made more reliable by correlating changes in the measured characteristics of the sensing element 610, as described above for the ITS approach with respect to FIG. 4, with the level of an alternating magnetic field, as generated by one or more of the ground-based and vehicle-based wireless power transfer structures (e.g., 200 and 320 in FIG. 3).

[0127] In some other embodiments, detection of a foreign object may be made more reliable by correlating changes in the measured electrical characteristics of the sensing element 610 with the output of another foreign object detector (e.g., based on microwave radar sensing, infrared sensing, visible light sensing, etc., using an under-vehicle mounted camera or a ground-based camera).

[0128] In a further aspect, Figure 7 illustrates example operations for performing combined inductive and thermal sensing to detect a foreign object. In some aspects, the operations 700 may be performed by a controller.

[0129] The operation 700 begins at operation 702, where an alternating magnetic field is generated in a wireless power transfer system comprising a sensing system comprising one or more sensing elements and a mediating heat-sensitive material configured to detect a foreign object based on one or more of an inductive effect and a thermal effect. At 704, an electrical characteristic of the one or more sensing elements is measured. At 706, a change in the measured electrical characteristic of the one or more sensing elements is detected, where the change is caused by one or more of an inductive effect and a thermal effect mediated by a mediating heat-sensitive material configured to vary the characteristic in response to temperature when heated by a foreign object exposed to the alternating magnetic field, thereby changing the electrical characteristic of the one or more sensing elements. Finally, at 708, the presence of a foreign object is determined based on the detected change in the measured electrical characteristic.

[0130] As used herein, the term "determining" encompasses a wide variety of actions. For example, "determining" may include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, database, or another data structure), ascertaining, and the like. Also, "determining" may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory), and the like. Also, "determining" may include resolving, selecting, choosing, establishing, and the like.

[0131] The various example operations, logic blocks, modules, and circuits described in connection with this disclosure may be implemented or performed using a general purpose 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 may be a microprocessor, but alternatively, the processor may be any commercially available processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration).

[0132] It is to be understood that the claims are not limited to the precise configuration and components illustrated above. Various modifications, changes and variations may be made in the arrangement, operation and details of the methods and apparatus described above without departing from the scope of the claims. [Explanation of symbols]

[0133] 100 Detection circuit 102 Control and evaluation circuit 104 Measurement circuit 106 Inductive sensing circuit 107 Inductive sensing element, inductive sensing element array 108 Capacitive Sensing Circuit 109 Capacitive sensing element, capacitive sensing element array 110 Object, metal object, foreign object 112 Object, non-living object, foreign object 114 Object, living object 200 Wireless power transmission structure 202 WPT coil 204 Ferrite structure 206 Backplate Part of the 300 WPT system 310 Case 312 Cover Shell 320 Vehicle-based wireless power transfer structure 322 WPT coil 324 Ferrite structure 326 Inductive Passive Beacon Transponder 328 Capacitive Passive Beacon Transponder 330 Case 332 Cover Shell 334 Shield 340 vehicles 402 Driver circuit 404 Measuring Amplifier Circuit 406 Signal Generator Circuit 408 Signal Processing Circuit 512 Thermal Inlay 513 Heat-resistant inlay 514 Insulation Inlay 516 Placement 600 Sensing System 602 Heat-sensitive structure 610 Sensing element 611 Sensing coil 612 Sensing coil

Claims

1. 1. An apparatus for detecting the presence of a foreign object in an inductive wireless power transfer system, comprising: a sensing system configured to sense the foreign object based on one or more of an inductive effect and a thermal effect, a sensing element having electrical properties and configured to sense the foreign object based on the inductive effect associated with a first alternating magnetic field; and an intermediate heat-sensitive material coupled to the sensing element, the intermediate heat-sensitive material having a characteristic that varies with temperature when heated by the foreign object exposed to a second alternating magnetic field generated by the inductive wireless power transfer system, the intermediate heat-sensitive material changing the electrical characteristic of the sensing element in response to the characteristic. A sensing system comprising: a controller coupled to the sensing system, measuring the electrical characteristic of the sensing element; and determining the presence of the foreign object based on the change in the measured electrical property caused by at least one of the inductive effect and the thermal effect through the intermediary heat sensitive material. A controller and An apparatus comprising:

2. The apparatus of claim 1 , wherein the properties of the intermediate thermal sensitive material comprise one or more of resistivity, conductivity, impedance, capacitance, inductance, magnetic permeability, and electrical permittivity.

3. The apparatus of claim 1 , wherein the intermediate heat sensitive material is configured to significantly change the characteristic when the temperature of the intermediate heat sensitive material passes a threshold value greater than 373 Kelvin.

4. 4. The apparatus of claim 3, wherein the intermediary thermal sensitive material comprises one or more of a negative temperature coefficient (NTC) resistive material, a positive temperature coefficient (PTC) resistive material, a low Curie point dielectric material, and a low Curie point ferrite material.

5. The device of claim 1 , wherein the sensing element comprises one or more turns of an electrical conductor.

6. The apparatus of claim 5 , wherein the sensing element is mounted on a printed circuit board.

7. The device of claim 1 , wherein the sensing element comprises the intermediate heat sensitive material.

8. The device of claim 1 , wherein the sensing element is embedded in a layer that also comprises the intermediate heat-sensitive material.

9. The device of claim 1 , wherein the thermally sensitive material is in a first layer that is distinct from a second layer that comprises the sensing element.

10. The apparatus of claim 1 , wherein the sensing system comprises an array of sensing elements, and the intermediate heat sensitive material is associated with at least one sensing element of the array.

11. 10. The apparatus of claim 1, wherein the electrical characteristic measured by the controller comprises one or more of impedance, transimpedance, direct current (DC) resistance, voltage, current, induced voltage, impulse response, and a response of another waveform.

12. 2. The apparatus of claim 1, wherein the controller is configured to determine the presence of the foreign object by correlating the measured electrical characteristic with a level of the second alternating magnetic field generated by the inductive wireless power transfer system.

13. 13. The apparatus of claim 12, wherein correlating the measured electrical property with the level of the second alternating magnetic field comprises at least one of inductive thermal sensing (ITS), inductive ferromagnetic sensing (IFS), or inductive motion sensing (IMS).

14. The apparatus of claim 1 , further comprising a heat resistant material configured to protect the sensing system against damage from heat from the foreign object.

15. The apparatus of claim 14 , wherein the heat resistant material comprises at least a portion of a housing of the wireless power transfer system.

16. 15. The device of claim 14, wherein the heat resistant material is in a first layer exposed to an exterior of the device, and the heat sensitive material is in a second layer covered by the first layer.

17. 15. The apparatus of claim 14, wherein the heat resistant material has a melting point greater than 473 Kelvin and is configured to withstand temperatures reached by the foreign object greater than 473 Kelvin without losing structural integrity.

18. 1. A method for detecting the presence of a foreign object in an inductive wireless power transfer system based on one or more of an inductive effect and a thermal effect, comprising: measuring an electrical characteristic of a sensing element sensitive to the presence of the foreign object based on an induced effect associated with a first alternating magnetic field; While a second alternating magnetic field is being generated by the inductive wireless power transfer system, measuring the electrical characteristic of the sensing element; determining that the electrical characteristic has changed due to the thermal effect when the electrical characteristic has changed in a manner indicative of the change being due to a characteristic of an intermediate heat-sensitive material coupled to the sensing element, the characteristic varying with temperature when the intermediate heat-sensitive material is heated by the foreign object exposed to the second alternating magnetic field; and determining the presence of the foreign object based on the change in the measured electrical property caused by at least one of the inductive effect or the thermal effect through the intermediary heat sensitive material; A method comprising:

Images