# US 12,184,087 B2 · Foreign object detection using combined inductive and thermal sensing > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,184,087 B2 - Document ID: US12184087B2 - Status: Granted - Kind: B2 - Application number: 18/161,396 - Filed: 2023-01-30 - Published: 2023-08-03 - Granted: 2024-12-31 - Earliest claimed: 2022-02-03 - Assignees: WiTricity Corporation - Applicants: WiTricity Corporation - Inventors: Hans Peter Widmer; Marcel Fischer; Ning Liu - Web page: https://patentgrep.com/patent/US12184087B2 ## CPC - H02J 50/60: responsive to the presence of foreign objects, e.g. detection of living beings - B60L 53/124: Detection or removal of foreign bodies - G01K 7/16: using resistive elements - G01V 3/10: using induction coils - H02J 50/10: using inductive coupling - H02J 50/402: {the two or more transmitting or the two or more receiving devices being integrated in the same unit, e.g. power mats with several coils or antennas with several sub-antennas} - B60L 53/12: Inductive energy transfer - Y02T 10/70: Energy storage systems for electromobility, e.g. batteries - Y02T 10/7072: Electromobility specific charging systems or methods for batteries, ultracapacitors, supercapacitors or double-layer capacitors - Y02T 90/14: Plug-in electric vehicles - H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY - B60L: PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES (arrangements or mounting of electrical propulsion units or of plural diverse prime-movers for mutual or common propulsion in vehicles B60K1/00, B60K6/20; arrangements or mounting of electrical gearing in vehicles B60K17/12, B60K17/14; preventing wheel slip by reducing power in rail vehicles B61C15/08; dynamo-electric machines H02K; control or regulation of electric motors H02P); SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES (electric coupling devices combined with mechanical couplings of vehicles B60D1/64; electric heating for vehicles B60H1/00); ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL (control or regulation of electric motors H02P); MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES - G01K: MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR (radiation pyrometry G01J5/00) - G01V: GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS (means for indicating the location of accidentally buried, e.g. snow-buried, persons A63B29/02) - Y02T: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION ## Abstract A method for detecting a foreign metal object near an inductive wireless power transfer system is based on combined inductive sensing and thermal sensing. A sensing system senses the object based on an inductive or thermal effect. The sensing system includes a sense element which has an electrical characteristic that changes in a presence of the object based on the inductive effect. A mediating heat-sensitive material has a property that varies as a function of temperature and changes the electrical characteristic of the sense element as the property changes. The mediating heat-sensitive material is heated by the foreign object when the foreign object is heated by a magnetic field generated by the wireless power transfer system. A controller measures the electrical characteristic and determines a presence of the object based on the change in the measured electrical characteristics. ## Claims ### Claim 1 An apparatus for detecting a presence of a foreign object in an inductive wireless power transfer system, the apparatus comprising: 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 including: a sense element having an electrical characteristic, the sense element being configured to sense the foreign object based on the inductive effect related to a first alternating magnetic field; and a mediating heat-sensitive material coupled to, but electrically separate from, the sense element, wherein the mediating heat-sensitive material has a property that varies as a function of temperature when heated by the foreign object exposed to a second alternating magnetic field generated by the inductive wireless power transfer system, wherein the mediating heat-sensitive material changes the electrical characteristic of the sense element as a function of the property; and a controller coupled to the sensing system, the controller configured to: measure the electrical characteristic of the sense element; and determine the presence of the foreign object based on the change in the measured electrical characteristic caused by at least one of the inductive effect and the thermal effect through the mediating heat-sensitive material. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein the property of the mediating heat-sensitive material comprises one or more of a resistivity, a conductivity, an impedance, a capacitance, an inductance, a magnetic permeability, and an electric permittivity. ### Claim 3 (depends on 1) The apparatus of claim 1, wherein the mediating heat-sensitive material is configured to substantially change the property as the temperature of the mediating heat-sensitive material passes a threshold that is higher than 373 Kelvin. ### Claim 4 (depends on 3) The apparatus of claim 3, wherein the mediating heat-sensitive material includes one or more of a negative temperature coefficient (NTC) resistance material, a positive temperature coefficient (PTC) resistance material, a dielectric material with a low Curie point, and a ferrite material with a low Curie point. ### Claim 5 (depends on 1) The apparatus of claim 1, wherein the sense element comprises one or more turns of an electrical conductor. ### Claim 6 (depends on 5) The apparatus of claim 5, wherein the sense element is implemented on a printed circuit board. ### Claim 7 (depends on 1) The apparatus of claim 1, wherein the sense element is embedded in a layer also comprising the mediating heat-sensitive material. ### Claim 8 (depends on 1) The apparatus of claim 1, wherein the heat-sensitive material is in a first layer different from a second layer comprising the sense element. ### Claim 9 (depends on 1) The apparatus of claim 1, wherein the sensing system comprises an array of sense elements, and the mediating heat-sensitive material is associated with at least one sense element of the array. ### Claim 10 (depends on 1) The apparatus of claim 1, wherein the electrical characteristic measured by the controller comprises one or more of an impedance, a transimpedance, a direct current (DC) resistance, a voltage, a current, an induced voltage, an impulse response, and a response of another waveform. ### Claim 11 (depends on 1) 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. ### Claim 12 (depends on 11) The apparatus of claim 11, wherein correlating the measured electrical characteristic 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). ### Claim 13 (depends on 1) 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. ### Claim 14 (depends on 13) The apparatus of claim 13, wherein the heat-resistant material constitutes at least a portion of an enclosure of the wireless power transfer system. ### Claim 15 (depends on 13) The apparatus of claim 13, wherein the heat-resistant material is in a first layer exposed to an exterior of the apparatus, and the heat-sensitive material is in a second layer covered by the first layer. ### Claim 16 (depends on 13) The apparatus of claim 13, wherein the heat-resistant material is configured to have a melting point higher than 473 Kelvin and to withstand a temperature reached by the foreign object higher than 473 Kelvin without losing structural integrity. ### Claim 17 A method of detecting a 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, the method comprising: measuring an electrical characteristic of a sense element sensitive to the presence of the foreign object based on an inductive effect related to a first alternating magnetic field; and while a second alternating magnetic field is being generated by the inductive wireless power transfer system: measuring the electrical characteristic of the sense element; determining that the electrical characteristic has changed due to the thermal effect when the electrical characteristic has changed in a manner that indicates that the change was due to a property of a mediating heat-sensitive material coupled to, but electrically separate from, the sense element, the property varying as a function of temperature when the mediating 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 characteristic caused by at least one of the inductive effect or the thermal effect through the mediating heat-sensitive material. ### Claim 18 (depends on 17) The method of claim 17, wherein measuring the electrical characteristic of the sense element includes measuring one or more of an impedance, a transimpedance, a direct current (DC) resistance, a voltage, a current, an induced voltage, an impulse response, and a response of another waveform. ### Claim 19 (depends on 17) The method of claim 17, wherein determining the presence of the foreign object includes correlating the measured electrical characteristic with a level of the second alternating magnetic field generated by the inductive wireless power transfer system. ### Claim 20 (depends on 19) The method of claim 19, wherein correlating the measured electrical characteristic 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).