WO2023044300A1 - Circuit de détection d'objet et détermination de position de véhicule - Google Patents

Circuit de détection d'objet et détermination de position de véhicule Download PDF

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Publication number
WO2023044300A1
WO2023044300A1 PCT/US2022/076345 US2022076345W WO2023044300A1 WO 2023044300 A1 WO2023044300 A1 WO 2023044300A1 US 2022076345 W US2022076345 W US 2022076345W WO 2023044300 A1 WO2023044300 A1 WO 2023044300A1
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WIPO (PCT)
Prior art keywords
sense
circuit
impedance
frequency
series
Prior art date
Application number
PCT/US2022/076345
Other languages
English (en)
Inventor
Hans Peter Widmer
José Pedro Castro Fonseca
Andreas Daetwyler
Lukas Frank Sieber
Original Assignee
Witricity Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US17/931,429 external-priority patent/US11914094B2/en
Application filed by Witricity Corporation filed Critical Witricity Corporation
Publication of WO2023044300A1 publication Critical patent/WO2023044300A1/fr

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J50/00—Circuit arrangements or systems for wireless supply or distribution of electric power
    • H02J50/10—Circuit arrangements or systems for wireless supply or distribution of electric power using inductive coupling
    • H02J50/12—Circuit arrangements or systems for wireless supply or distribution of electric power using inductive coupling of the resonant type
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
    • B60L53/00—Methods of charging batteries, specially adapted for electric vehicles; Charging stations or on-board charging equipment therefor; Exchange of energy storage elements in electric vehicles
    • B60L53/10—Methods of charging batteries, specially adapted for electric vehicles; Charging stations or on-board charging equipment therefor; Exchange of energy storage elements in electric vehicles characterised by the energy transfer between the charging station and the vehicle
    • B60L53/12—Inductive energy transfer
    • B60L53/124—Detection or removal of foreign bodies
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
    • B60L53/00—Methods of charging batteries, specially adapted for electric vehicles; Charging stations or on-board charging equipment therefor; Exchange of energy storage elements in electric vehicles
    • B60L53/30—Constructional details of charging stations
    • B60L53/35—Means for automatic or assisted adjustment of the relative position of charging devices and vehicles
    • B60L53/38—Means for automatic or assisted adjustment of the relative position of charging devices and vehicles specially adapted for charging by inductive energy transfer
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
    • G01V3/08—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices
    • G01V3/088—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices operating with electric fields
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
    • G01V3/08—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices
    • G01V3/10—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices using induction coils
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J50/00—Circuit arrangements or systems for wireless supply or distribution of electric power
    • H02J50/60—Circuit arrangements or systems for wireless supply or distribution of electric power responsive to the presence of foreign objects, e.g. detection of living beings
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J50/00—Circuit arrangements or systems for wireless supply or distribution of electric power
    • H02J50/90—Circuit arrangements or systems for wireless supply or distribution of electric power involving detection or optimisation of position, e.g. alignment
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2310/00—The network for supplying or distributing electric power characterised by its spatial reach or by the load
    • H02J2310/40—The network being an on-board power network, i.e. within a vehicle
    • H02J2310/48—The network being an on-board power network, i.e. within a vehicle for electric vehicles [EV] or hybrid vehicles [HEV]
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/02—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries for charging batteries from ac mains by converters
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/60—Other road transportation technologies with climate change mitigation effect
    • Y02T10/70—Energy storage systems for electromobility, e.g. batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/60—Other road transportation technologies with climate change mitigation effect
    • Y02T10/7072—Electromobility specific charging systems or methods for batteries, ultracapacitors, supercapacitors or double-layer capacitors
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T90/00—Enabling technologies or technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02T90/10—Technologies relating to charging of electric vehicles
    • Y02T90/14—Plug-in electric vehicles

Definitions

  • the present disclosure relates generally to object detection and vehicle position determination, for example, in an application for inductive wireless charging of electric vehicles.
  • the present disclosure is directed to a multi-purpose detection circuit configurable for detecting foreign metallic objects, living objects located near an inductive wireless power transmitter as well as for detecting a vehicle above the wireless power transmitter and for determining a position of the vehicle relative to the inductive wireless power transmitter.
  • WPT Inductive wireless power transfer
  • a primary power device transmits power wirelessly to a secondary power device (or wireless power receiver).
  • a secondary power device or wireless power receiver.
  • Each of the wireless power transmitter and wireless power receiver includes an inductive power transfer structure, typically a single or multi-coil arrangement of windings comprising electric current conveying materials (e.g., copper Litz wire).
  • An alternating current passing through the coil e.g., of a primary wireless power transfer structure produces an alternating magnetic field.
  • the alternating magnetic field induces an electromotive force (EMF) into the secondary wireless power transfer structure according to Faraday’s law, thereby wirelessly transferring power to the wireless power receiver if a resistive load is connected to the wireless power receiver.
  • EMF electromotive force
  • 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 forming a resonance substantially at a fundamental operating frequency of the inductive WPT system (e.g., in the range from 80 kHz to 90 kHz).
  • Inductive wireless power transfer to electrically chargeable vehicles at power levels of several kilowatts in both domestic and public parking zones may require special protective measures for safety of persons and equipment.
  • Such measures may include detection of foreign objects in an inductive power region of the inductive WPT system where electromagnetic field exposure levels exceed certain limits. This may be particularly true for systems where the inductive power region is open and accessible.
  • Such measures may include detection of electrically conducting (metallic) objects and living objects, (e.g., humans, extremities of humans, or animals) that may be present within or near the inductive power region.
  • inductive wireless power transfer system for electric vehicle charging operating at a fundamental frequency in the range from 80 kHz to 90 kHz, magnetic flux densities in the inductive power region (e.g., above a primary wireless power transfer structure) can reach relatively high levels (e.g., above 2 mT) to allow for sufficient power transfer (e.g., 3.3 kW, 7 kW, 11 kW, and the like). Therefore, metallic objects or other objects present in the magnetic field can experience undesirable induction heating.
  • foreign object detection may be implemented to detect metallic objects or other objects that are affected by the magnetic field generated by the primary and/or the secondary wireless power transfer structure of the inductive WPT system.
  • FOD foreign object detection
  • living object detection LOD may be implemented to detect living objects (e.g., human extremities, animals), or other objects that may be exposed to the magnetic field generated by the primary and/or the secondary wireless power transfer structure of the inductive WPT system.
  • inductive wireless charging of electric vehicles it may also be useful to be able to detect a vehicle or the type of vehicle that may be present above the wireless power transmitter (e.g., above the primary wireless power transfer structure). For this reason, vehicle detection (VD) may be implemented.
  • vehicle detection (VD) it may also be useful to be able to transmit data (e.g., a vehicle identifier or the like) from the vehicle-based secondary device to the ground-based primary device. For this reason, vehicle detection (VD) may be extended for receiving low rate signaling from the vehicle.
  • Efficiency of an inductive WPT system for electric vehicle charging depends at least in part on achieving sufficient alignment between the ground-based primary wireless power transfer structure and the secondary wireless power transfer structure. Therefore, in certain applications for inductive wireless charging of electric vehicles, it may be useful to be able to determine a position of the vehicle relative to the wireless power transmitter for purposes of guidance and alignment. More specifically, it may be useful to be able to determine a position of the vehicle- based wireless power transfer structure (e.g., the secondary wireless power transfer structure) relative to the ground-based wireless power transfer structure (e.g., the primary wireless power transfer structure). For this reason, position determination (PD) may be implemented.
  • PD position determination
  • an apparatus for determining at least one of a presence of a metallic object, living object, vehicle, type of vehicle, and a vehicle position is provided.
  • the apparatus includes a plurality of inductive sense circuits and a plurality of capacitive sense circuits.
  • Each of the plurality of inductive sense circuits includes at least one inductive sense element (e.g., a sense coil) and an associated capacitive element to compensate for the gross reactance as presented at the terminals of the at least one inductive sense element at an operating frequency herein referred to as the sense frequency.
  • Each of the plurality of capacitive sense circuits includes at least one capacitive sense element (e.g., a sense electrode) and an associated inductive element to compensate for the gross reactance as presented at the terminals of the at least one capacitive sense element at the sense frequency.
  • At least one of the plurality of inductive and capacitive sense circuits also includes an impedance matching element (e.g., a transformer) for transforming the impedance of the sense circuit to match with an operating impedance range of the apparatus.
  • the apparatus further includes a measurement circuit for selectively and sequentially measuring an electrical characteristic (e.g., an impedance) in each of the plurality of inductive and capacitive sense circuits according to a predetermined time multiplexing scheme.
  • the measurement circuit includes a driver circuit including multiplexing (input multiplexing) electrically connected to the plurality of inductive and capacitive sense circuits for selectively and sequentially driving each of the plurality of sense circuits with a drive signal (e.g., a current signal) at the sense frequency based on a driver input signal.
  • the measurement circuit further includes a measurement amplifier circuit including multiplexing (output multiplexing) electrically connected to the plurality of inductive and capacitive sense circuits for selectively and sequentially amplifying a measurement signal (e.g., a voltage signal) in each of the plurality of sense circuits and for providing a measurement amplifier output signal indicative of the measurement signal in each of the plurality of sense circuits.
  • the measurement circuit also includes a signal generator circuit electrically connected to the input of the driver circuit for generating the driver input signal.
  • the measurement circuit further includes a signal processing circuit electrically connected to the output of the measurement amplifier circuit for receiving and processing the measurement amplifier output signal and for determining the electrical characteristic in each of the plurality of inductive and capacitive sense circuits based on the driver input signal and the measurement amplifier output signal.
  • the apparatus further includes a control and evaluation circuit electrically connected to the measurement circuit for controlling the signal generator circuit, for controlling the input and output multiplexing according to the predetermined time multiplexing scheme, for evaluating the electrical characteristic as measured in each of the inductive and capacitive sense circuits, and for determining at least one of a presence of a metallic object, living object, vehicle, type of vehicle, and a vehicle position based on changes in the measured electrical characteristics.
  • a control and evaluation circuit electrically connected to the measurement circuit for controlling the signal generator circuit, for controlling the input and output multiplexing according to the predetermined time multiplexing scheme, for evaluating the electrical characteristic as measured in each of the inductive and capacitive sense circuits, and for determining at least one of a presence of a metallic object, living object, vehicle, type of vehicle, and a vehicle position based on changes in the measured electrical characteristics.
  • the method includes selectively and sequentially measuring, in a measurement circuit, an electrical characteristic (e.g., an impedance) in each of the plurality of inductive and capacitive sense circuits according to a predetermined time multiplexing scheme. More specifically, the method includes selectively and sequentially applying, from a driver circuit as part of the measurement circuit and including input multiplexing, a drive signal (e.g., a current signal) at a sense frequency to each of the plurality of inductive and capacitive sense circuits according to the predetermined time multiplexing scheme.
  • a driver circuit as part of the measurement circuit and including input multiplexing, a drive signal (e.g., a current signal) at a sense frequency to each of the plurality of inductive and capacitive sense circuits according to the predetermined time multiplexing scheme.
  • the method further includes selectively and sequentially amplifying, in a measurement amplifier circuit as part of the measurement circuit, and including output multiplexing, a measurement signal (e.g., a voltage signal) in each of the plurality of inductive and capacitive sense circuits according to the predetermined time multiplexing scheme, and providing a measurement amplifier output signal indicative for the measurement signal.
  • the method further includes applying, from a signal generator circuit as part of the measurement circuit, a driver input signal to the driver circuit.
  • the method further includes receiving and processing, in a signal processing circuit as part of the measurement circuit, the measurement amplifier output signal, and determining the electrical characteristic in each of the plurality of inductive and capacitive sense circuits based on the driver input signal and the measurement amplifier output signal.
  • the method further includes controlling, in a control and evaluation circuit, the signal generator circuit and the input and output multiplexing according to the time multiplexing scheme.
  • the method further includes evaluating the electrical characteristic as measured in each of the inductive and capacitive sense circuits and determining at least one of a presence of a metallic object, living object, vehicle, type of vehicle, and a vehicle position based on changes in the measured electrical characteristics.
  • FIG.1 is a schematic view illustrating an example implementation of a multi-purpose detection circuit including a plurality of inductive and capacitive sense circuits, a non-living (e.g., metallic) object, and a living object.
  • FIG.2 is a schematic view illustrating an example implementation of a wireless power transfer structure of a wireless power transmitter integrating a portion of the multi-purpose detection circuit shown in FIG.2, the non-living and the living object of FIG.1.
  • FIG.3 is a vertical cut view illustrating a portion of a WPT system including the vehicle- based wireless power transfer structure and the ground-based wireless power transfer structure integrating a portion of the multi-purpose detection circuit of FIG.
  • FIG.4 is a generic block diagram of an example implementation of the multi-purpose detection circuit o FIG.1.
  • FIG.5A is a schematic diagram of a circuit illustrating an example implementation of a portion of the multi-purpose detection circuit of FIG. 1 based on inductive sensing and an impedance measurement approach, and the non-living and the living object of FIG.1.
  • FIG.5B is a schematic diagram of a circuit illustrating another example implementation of a portion of the multi-purpose detection circuit of FIG. 1 based on inductive sensing and the impedance measurement approach of FIG.5A, and the non-living and the living object of FIG.1.
  • FIG.5C is a schematic diagram of a circuit illustrating an example implementation of a portion of the multi-purpose detection circuit of FIG. 1 based on inductive sensing and another impedance measurement approach, and the non-living and the living object of FIG.1.
  • FIG.5D is a schematic diagram of a circuit illustrating an example implementation of a portion of the multi-purpose detection circuit of FIG. 1 based on inductive sensing and a transimpedance measurement approach, and the non-living and the living object of FIG.1.
  • FIG.5E is a schematic diagram of a circuit illustrating another example implementation of a portion of the multi-purpose detection circuit of FIG. 1 based on inductive sensing and the transimpedance measurement approach of FIG.
  • FIG.5F illustrates an equivalent circuit model of the example implementation of FIG. 5A.
  • FIG.5G illustrates an equivalent circuit model of the example implementation of FIG. 5C.
  • FIG.5H illustrates an equivalent circuit model of a portion of the circuits of FIGs.5C, 7C, 7F, and 7H.
  • FIG.5I illustrates an equivalent circuit model of another portion of the circuits of FIGs. 5D and 5E.
  • FIG.5J illustrates another equivalent circuit model of the portion of the circuits of FIGs. 5D and 5E illustrated in FIG.5I.
  • FIG. 5F illustrates an equivalent circuit model of the example implementation of FIG. 5A.
  • FIG.5G illustrates an equivalent circuit model of the example implementation of FIG. 5C.
  • FIG.5H illustrates an equivalent circuit model of a portion of the circuits of FIGs.5C, 7C, 7F, and 7H.
  • FIG.5I illustrates an equivalent circuit model of another portion of the circuits of FIGs. 5D and 5E.
  • FIG.6 illustrates a complex impedance plane, different types of objects of FIG.1, and corresponding areas where changes of impedance may occur in presence of the object.
  • FIG.7A is a schematic diagram of a circuit illustrating an example implementation of a portion of the multi-purpose detection circuit of FIG. 1 based on capacitive sensing and the impedance measurement approach of FIG.5A, and the living and the non-living object of FIG.1.
  • FIG.7B is a schematic diagram of a circuit illustrating another example implementation of a portion of the multi-purpose detection circuit of FIG.
  • FIG. 7C is a schematic diagram of a circuit illustrating a further example implementation of a portion of the multi-purpose detection circuit of FIG. 1 based on capacitive sensing and the impedance measurement approach of FIG. 5A, and the living and the non-living object of FIG.1.
  • FIG. 7D is a schematic diagram of a circuit illustrating yet another example implementation of a portion of the multi-purpose detection circuit of FIG. 1 based on capacitive sensing and the impedance measurement approach of FIG. 5A, and the living and the non-living object of FIG.1.
  • FIG.7E is a schematic diagram of a circuit illustrating an example implementation of a portion of the multi-purpose detection circuit of FIG. 1 based on capacitive sensing and the impedance measurement approach of FIG.5C, and the living and the non-living object of FIG.1.
  • FIG.7F is a schematic diagram of a circuit illustrating another example implementation of a portion of the multi-purpose detection circuit of FIG. 1 based on capacitive sensing and the impedance measurement approach of FIG.5C, and the living and the non-living object of FIG.1.
  • FIG.7G is a schematic diagram of a circuit illustrating an example implementation of a portion of the multi-purpose detection circuit of FIG.
  • FIG.7H is a schematic diagram of a circuit illustrating another example implementation of a portion of the multi-purpose detection circuit of FIG. 1 based on capacitive sensing and the transimpedance measurement approach of FIG. 5D, and the living and the non-living object of FIG.1.
  • FIG.7I is a schematic diagram of a circuit illustrating a further example implementation of a portion of the multi-purpose detection circuit of FIG. 1 based on capacitive sensing and the transimpedance measurement approach of FIG. 5D, and the living and the non-living object of FIG.1.
  • FIG.7J illustrates an equivalent circuit model of the example implementation of FIG. 7A.
  • FIG.7K illustrates an equivalent circuit model of the example implementation of FIG. 7E.
  • FIG.7L illustrates an equivalent circuit model of a portion of the circuits of FIGs.7G, 7H, and 7I.
  • FIG.7M illustrates another equivalent circuit model of a portion of the circuits of FIGs. 7G, 7H, and 7I.
  • FIG. 7N shows a table of equations that may be relevant for the equivalent circuit models of FIG.7J and FIG.7K.
  • FIG.8A illustrates a complex admittance plane, different types of objects of FIG.1, and corresponding areas where changes of admittamce may occur in presence of the object.
  • FIG. 8B illustrates an equivalent circuit model applicable to an object of FIG. 1 proximate to the capacitive sense element of FIG.7A.
  • FIG. 8C shows a normalized admittance chart indicating lines of constant real permittivity and constant imaginary permittivity.
  • FIG. 8D shows the normalized admittance chart of FIG. 8C indicating measured admittance changes in presence of an object of FIG.1.
  • FIG.8E shows another normalized admittance chart indicating the angle of a portion of the measured admittance changes of FIG.8D.
  • FIG. 8F shows the normalized admittance chart of FIG. 8E indicating the angle of another portion of the measured admittance changes of FIG.8D.
  • FIG. 8G shows a diagram indicating a normalized effective conductivity and susceptibility as determined from the measured admittance changes of FIG.8D.
  • FIG. 8H illustrates a complex plane indicating an effective complex permittivity as determined from the measured admittance changes of FIG.8D.
  • FIG.9A is a schematic diagram of a circuit illustrating an example implementation of a portion of the multi-purpose detection circuit of FIG. 1 including a plurality of inductive and capacitive sense circuits.
  • FIG.9B is a schematic diagram illustrating an example implementation of a portion of the circuit of FIG.9A.
  • FIG. 9C is a schematic diagram illustrating an example implementation of another portion of the circuit of FIG.9A.
  • FIG. 9D is a schematic diagram illustrating an example implementation of a further portion of the circuit of FIG.9A.
  • FIG.9E is a schematic diagram illustrating an example implementation of yet another portion of the circuit of FIG.9A.
  • FIG.9F is a schematic diagram illustrating an example implementation of yet a further portion of the circuit of FIG.9A.
  • FIG.10 is a schematic diagram of a circuit illustrating another example implementation of a portion of the multi-purpose detection circuit of FIG.1 including a plurality of inductive and capacitive sense circuits.
  • FIG.11 is a schematic diagram of a circuit illustrating a further example implementation of a portion of the multi-purpose detection circuit of FIG.1 including a plurality of inductive and capacitive sense circuits.
  • FIG.12A is a schematic view illustrating an example implementation of the housing of the ground-based wireless power transfer structure integrating single-ended capacitive sense elements of the multi-purpose detection circuit of FIG.1.
  • FIG.12A is a schematic view illustrating an example implementation of the housing of the ground-based wireless power transfer structure integrating double-ended capacitive sense element of the multi-purpose detection circuit of FIG.1.
  • FIG. 13A is a schematic view illustrating an example printed circuit board implementation of a holohedral sense electrode.
  • FIG. 13B is schematic view illustrating an example printed circuit board implementation of a sense electrode having a finger structure.
  • FIGs. 14A to 14C illustrates an electric vehicle approaching a ground-based wireless power transfer structure installed in a parking space.
  • FIGs. 15A and 15B illustrates an example implementation of vehicle position determination (PD) based on pattern detection.
  • PD vehicle position determination
  • a FOD system may include a plurality of inductive sense circuits each including an inductive sense element (e.g., a sense coil) distributed across a predetermined area (e.g., a planar array of sense coils integrated into the ground-based wireless power transfer structure).
  • the predetermined region may be defined by the space where metal objects may be found and where the magnetic flux density exceeds certain limits (e.g., a threshold determined based on what levels of temperature a metal object might be heated up). This is generally a three-dimensional space above the plurality of indictive sense elements.
  • the number of the inductive sense elements may be proportional or related to the minimum size of objects that are desirable to be detected.
  • the number of sense elements may be relatively high (e.g., in the order of 100).
  • An example FOD system is described in U.S. Patent No.10,627,257, titled Systems, Methods, and Apparatus for Detection of Metal Objects in a Predetermined Space, the entire contents of which are hereby incorporated by reference.
  • LOD living object detection
  • a LOD system may include a plurality of capacitive sense circuits each including a capacitive sense element (e.g., a sense electrode) e.g., disposed along the periphery of a ground-based wireless power transfer structure of a WPT system.
  • the predetermined region may be defined by the space accessible for living objects and where living objects may be located and where the exposure magnetic field strength exceeds certain limits (e.g., as recommended by ICNIRP). This is generally a three-dimensional space.
  • the number of the capacitive sense elements may be proportional or related to the minimum size of living objects that are desirable to be detected.
  • the number of sense elements may be relatively low (e.g., in the order of 4).
  • An example LOD system is described in U.S. Patent No. 9,952,266, titled Object Detection for Wireless Energy Transfer Systems, the entire contents of which are hereby incorporated by reference.
  • a VD system may include a plurality of inductive sense circuits each including an inductive sense element (e.g., a sense coil) distributed across an area defined by the ground-based wireless power transfer structure (e.g., a planar array of sense coils) and a plurality of capacitive sense circuits each including a capacitive sense element (e.g., a sense electrode) disposed in an area defined by the ground-based wireless power transfer structure.
  • an inductive sense element e.g., a sense coil
  • the ground-based wireless power transfer structure e.g., a planar array of sense coils
  • capacitive sense circuits each including a capacitive sense element (e.g., a sense electrode) disposed in an area defined by the ground-based wireless power transfer structure.
  • Drive circuitry for applying drive signals to each of the inductive and capacitive sense circuits, each including an inductive and capacitive sense element, respectively and additional elements for conditioning, as well as corresponding measurement circuitry as needed for measuring an electrical characteristic in each of the plurality of capacitive sense circuits and for looking for changes in the electrical characteristics that may correspond to the presence of a vehicle.
  • a position (PD) of a vehicle e.g., the position of the vehicle-based wireless power transfer structure relative to the ground-based wireless power transfer structure of a WPT system
  • a PD system may include a plurality of inductive sense circuits each including an inductive sense element (e.g., a sense coil) distributed across an area defined by the ground-based wireless power transfer structure (e.g., a planar array of sense coils) and a plurality of capacitive sense circuits each including a capacitive sense element (e.g., a sense electrode) disposed in an area defined by the ground-based wireless power transfer structure.
  • the PD system is configured to support a passive beacon PD technique. Passive beacon PD uses at least one passive beacon transponder that may be integrated into the vehicle-based wireless power transfer structure or that may be mounted elsewhere at the vehicle underbody.
  • the passive beacon transponder When positioned above the inductive and capacitive sense element array of the multi-purpose detection circuit, the passive beacon transponder produces a distinct time- varying change (a modulated response) in the electrical characteristic of at least one of the plurality of inductive sense circuits and capacitive sense circuits.
  • This modulated response may be used for determining a position of the at least one passive beacon transponder relative to the array of sense elements, which is related to the position of the vehicle-based wireless power transfer structure relative to the ground-based wireless power transfer structure.
  • the at least one passive beacon transponder may also be used for determining presence of a vehicle (VD) or the type of vehicle e.g., by means of a modulation that is characteristic for the type of vehicle.
  • the at least one passive beacon transponder may be used to transmit data (e.g., at a low data rate) to the primary device by means of the passive modulation technique.
  • the at least one passive beacon transponder includes an inductive passive beacon transponder configured to mainly interact with the inductive sense circuits.
  • the at least one passive beacon transponder includes a capacitive passive beacon transponder configured to mainly interact with the capacitive sense circuits.
  • the at least one passive beacon transponder is configured to interact with both the inductive and capacitive sense circuits.
  • An example inductive passive beacon PD system is described in U.S.
  • Circuitry for applying drive signals to each of the plurality of inductive and/or capacitive sense circuits each including a sense element and additional elements for conditioning, as well as corresponding measurement, control and evaluation circuitry as needed for measuring an electrical characteristic in each of the plurality of inductive sense circuits and detecting changes in the electrical characteristics that may be indicative of one of the presence of a metal object, a living object, a vehicle, the type of vehicle, and a vehicle position may be complex and costly as the number of sense elements increases.
  • An electric vehicle is used herein to describe a remote system, an example of which is a vehicle that includes, as part of its locomotion capabilities, electrical power derived from a chargeable energy storage device (e.g., one or more rechargeable electrochemical cells or other type of battery).
  • a chargeable energy storage device e.g., one or more rechargeable electrochemical cells or other type of battery.
  • some electric vehicles may be hybrid electric vehicles that include, besides electric motors, a traditional combustion engine for direct locomotion or to charge the vehicle’s battery. Other electric vehicles may draw all locomotion ability from electrical power.
  • An electric vehicle is not limited to an automobile and may include motorcycles, carts, scooters, and the like.
  • a foreign object is used herein to describe an object that does not naturally belong to the WPT system.
  • a foreign object may include a metallic object, a non-living dielectric (substantially nonconductive) object, a living object (e.g., an animal, a human extremity), a vehicle, or a combination thereof. It may describe an object that needs to be detected for purposes of safety of equipment or persons, but it may also refer to an object of no harm that is potential to produce a false positive detection in a multi-purpose detection system.
  • FIG.1 illustrates an example implementation of a multi-purpose detection circuit 100 that includes a plurality of inductive sense circuits 106 and a plurality of capacitive sense circuits 108 illustrated in FIG. 1 by inductive sense circuits 106a, 106b, some dots, and 106n and by capacitive sense circuits 108a, 108b, some dots, and 108n.
  • the dots shall indicate that the number of inductive sense circuits 106 and/or the number of capacitive sense circuits 108 may be greater than three.
  • the plurality of inductive sense circuits 106 is also sometimes referred herein as the plurality of inductive sense circuits 106a, 106b, ..., 106n.
  • each of the inductive sense circuit of the plurality of sense circuits 106a, 106b, ..., 106n includes a corresponding inductive sense element (e.g., a sense coil) of a plurality of inductive sense elements 107a, 107b, ..., 107n, respectively.
  • a corresponding inductive sense element e.g., a sense coil
  • each of the capacitive sense circuits of the plurality of sense circuits 108a, 108b, ..., 108n includes a corresponding capacitive sense element (e.g., a pair of sense electrodes) of a plurality of capacitive sense elements 109a, 109b, ..., 109n, respectively.
  • FIG. 1 also illustrates foreign objects 110 and 112 as referred to herein as non-living objects and a living object 114.
  • the object 110 may represent a metallic (substantially electrically conductive object) that is potentially heated when exposed to the WPT magnetic field as previously discussed, while the object 112 may be representative for a dielectric or ferromagnetic object that is substantially electrically non-conductive and that does not heat to hazardous temperatures when exposed to the WPT magnetic field.
  • the living object 114 may stand for a human extremity (e.g., a hand as depicted in FIG.1) or an animal that is dielectric and substantially electrically non-conductive.
  • the inductive sense elements 107a, 107b, ..., 107n and capacitive sense elements 109a, 109b, ..., 109n are configured to sense at least one of a presence of a foreign object (e.g., object 110) in proximity to at least one of the plurality of inductive sense elements 107a, 107b, ..., 107n, a living object (e.g., object 114) in proximity to at least one of the plurality of capacitive sense elements 109a, 109b, ..., 10n, a vehicle or type of vehicle (not shown in FIG.1) positioned above the plurality of inductive and capacitive sense elements 107a-107n and 109a-109n, respectively, and for determining a vehicle position based on measuring one or more electrical characteristics (e.g., an impedance) in each of the plurality of inductive sense circuits 106a, 106b, ..., 106n and capacitive sense circuits 108a, 108b,
  • Each of the plurality of inductive sense circuits 106a, 106b, ..., 106n and capacitive sense circuits 108a, 108b, ..., 108n may also include additional conditioning circuitry (not shown in FIG. 1) e.g., configured to improve measurement of the one or more electrical characteristics and thus sensitivity and reliability of the multi-purpose detection circuit 100.
  • Each of the plurality of sense circuits also defines at least one measurement port (not shown in FIG.1) where the one or more electrical characteristics is measured and refers to.
  • Each of the plurality of inductive sense elements 107a, 107b, ..., 107n is shown in FIG. 1 as a “circular” coil for purposes of illustration.
  • the inductive sense elements 107a, 107b, ..., 107n may include a sense coil having another coil topology, e.g., a “figure-eight-like” topology.
  • the plurality of inductive sense elements 107a, 107b, ..., 107n may include sense coils of a mixed coil topology, e.g., “circular” and “figure-eight-like”.
  • the plurality of inductive sense elements 107a, 107b, ..., 107n may include sense coils (e.g., solenoid coils) with a ferrite core (not shown herein) that are physically smaller compared to “air” coils.
  • the plurality of sense elements 107a, 107b, ..., 107n may include other inductive devices that can be used for generating a magnetic field for detecting a foreign object (e.g., object 110), a vehicle, or for determining a vehicle position.
  • each of the plurality of inductive sense elements 107a, 107b, ..., 107n may include a double or even a triple sense coil arrangement that may be used in conjunction with a transimpedance or mutual impedance measurement technique.
  • the plurality of inductive sense elements 107a, 107b, ..., 107n is arranged in an array 107, such as a two-dimensional array 107 as shown in FIG.
  • the sense elements of the plurality of inductive sense elements 107a, 107b, ..., 107n are arranged in other configurations that do not conform to rows or columns (radial or interleaved), are at least partially overlapping or have irregular spacing, have different size, have different shapes (circular, hexagonal, etc.), or cover irregular detection areas, or any combination thereof.
  • array denotes a plurality of sense elements that are arranged over a predetermined area.
  • the number of sense elements of an array 107 and thus the number of sense circuits can vary widely based on the application including the total region in which a foreign object (e.g., object 110) is to be detected and the smallest size of an object the multi-purpose detection circuit 100 is configured to detect.
  • Example implementations of the inductive sense element (e.g., 107a) and arrangements of inductive sense elements are described in U.S. Patent No. 9,726,518, titled Systems, Methods, and Apparatus for Detection of Metal Objects in a Predetermined Space, in U.S. Patent application 16/358,534, titled Foreign Object Detection Circuit Using Mutual Impedance Sensing, in U.S. Patent No.
  • Each of the plurality of capacitive sense elements 109a, 109b, ..., 109n is shown in FIG. 1 as a pair of sense electrodes for purposes of illustration. However, in other implementations, the capacitive sense elements 109a, 109b, ..., 10n may include a single electrode providing a single terminal.
  • the capacitive sense elements 109a, 109b, ..., 109n may be driven and configured for measuring a transimpedance (a mutual capacitance).
  • the capacitive sense elements 109a, 109b, ..., 109n may include other capacitive devices that can be used for generating and detecting an electric field for detecting a foreign object (e.g., object 112), a living object (e.g., object 114), a vehicle (e.g., vehicle 330), or for determining a type of vehicle or a vehicle position.
  • a foreign object e.g., object 112
  • a living object e.g., object 114
  • a vehicle e.g., vehicle 330
  • the capacitive sense elements 109a, 109b, ..., 109n are shown arranged in an area around the array of inductive sense elements 107a, 107b, ..., 107n.
  • the capacitive sense elements of the plurality of capacitive sense elements 109a, 109b, ..., 109n are arranged in other configurations, e.g., distributed over the area of the array 107 of the inductive sense elements.
  • Example implementations of the capacitive sense element (e.g., 109a) and arrangements of capacitive sense elements are described in U.S. Patent No.9,952,266, titled Object Detection for Wireless Energy Transfer Systems, the entire contents of which are hereby incorporated by reference.
  • Each of the plurality of inductive sense circuits 106 and the plurality of capacitive sense circuits 108 including a corresponding sense element of the plurality of inductive sense elements 107a-107n and the plurality of capacitive sense elements 109a-109n are operably 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 characteristics in each of the plurality of inductive and capacitive sense circuits (106 and 108, respectively) and to provide outputs to the control and evaluation circuit 102.
  • the measurement circuit 104 is configured to cause each of the plurality of inductive sense elements (e.g., sense coils) 107a, 107b, ..., 107n to selectively and sequentially generate an alternating magnetic field at the sense frequency, e.g., by selectively and sequentially applying a sense signal (e.g., a current) to each of the plurality of inductive sense circuits 106a, 106b, ..., 106n. If a metallic object (e.g., object 110) is present in the alternating magnetic field, eddy currents will be generated in the object.
  • a metallic object e.g., object 110
  • the eddy currents in the object will generate another (secondary) magnetic field that interacts with the primary magnetic field as generated by the respective sense element, and a mutual coupling is developed.
  • This may cause a change in an electrical characteristic (e.g., an impedance) as measured by the measurement circuit 104 in the respective inductive sense circuit (e.g., inductive sense circuit 106a).
  • a change in a measured electrical characteristic may also be caused by a substantially non-conductive but ferromagnetic object (not shown in FIG.1) with a relative permeability ⁇ r > 1 that interacts with the alternating magnetic field as generated by the respective sense element.
  • Applying a sense signal to an inductive sense circuit may also cause the respective inductive sense element 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 the electrical characteristic as measured in the respective inductive sense circuit (capacitive sensing effect).
  • This alternating electric field may also interact with a metallic (substantially electrically conductive) object (e.g., object 110).
  • this effect may be orders of magnitude weaker than the magnetic field effect.
  • the measurement circuit 104 is further configured to cause each of the plurality of capacitive sense elements (e.g., sense electrodes) 109a, 109b, ..., 109n to selectively and sequentially generate an alternating electric field at the sense frequency, e.g., by selectively and sequentially applying a sense signal (e.g., a current) to each of the plurality of capacitive sense circuits 108a, 108b, ..., 108n. If a substantially non-conductive, dielectric object (e.g., living object 114 or non-living object 112) with a relative permittivity ⁇ r > 1 is present in the alternating electric field, it will interact with the electric field.
  • a substantially non-conductive, dielectric object e.g., living object 114 or non-living object 112 with a relative permittivity ⁇ r > 1 is present in the alternating electric field, it will interact with the electric field.
  • This may cause a change in an electrical characteristic (e.g., an impedance) as measured by the measurement circuit 104 in the respective capacitive sense circuit (e.g., capacitive sense circuit 108a).
  • a change in a measured electrical characteristic may also be caused by a metallic object (e.g., object 110) as it will also interact with the alternating electric field as generated by the respective capacitive sense element.
  • Applying a sense signal (e.g., current) to a capacitive sense circuit may also cause the respective capacitive sense element to generate an alternating magnetic field that may interact with a metallic object (e.g., object 110) causing a change in the electrical characteristic as measured in the respective capacitive sense circuit (inductive sensing effect).
  • a sense signal e.g., current
  • a capacitive sense circuit e.g., sense circuit 106a
  • the respective capacitive sense element may also cause the respective capacitive sense element to generate an alternating magnetic field that may interact with a metallic object (e.g., object 110) causing a change in the electrical characteristic as measured in the respective capacitive sense circuit (inductive sensing effect).
  • this effect may be orders of magnitude weaker than the electric field effect.
  • the control and evaluation circuit 102 is configured to control the measurement circuit 104 (e.g., the multiplexing) and to evaluate the outputs of the measurement circuit 104, to determine at least one of a presence of a foreign object (e.g., object 110), living object (e.g., object 114), a presence of a vehicle with reference to FIG. 3, a type of vehicle, and a vehicle position based on changes in the measured one or more electrical characteristics.
  • the control and evaluation circuit 102 may include the decision functions as needed for FOD, LOD, and VD as well as the position calculation functions needed for PD.
  • the vehicle position is determined in a unit external to the multi-purpose detection circuit 100 (not shown herein) based on outputs (e.g., raw data) from the control and evaluation circuit 102 and on outputs provided by other ground- or vehicle-based sensors (not shown herein).
  • outputs e.g., raw data
  • the evaluation is based on a time-differential detection scheme that is sensitive e.g., to a fast (e.g., abrupt) change in a sequence (time-series) of consecutive outputs of the measurement circuit 104 (e.g., the measured electrical characteristics), each associated to the same at least one sense circuit (e.g., sense circuit 106a) of the plurality of sense circuits 106 and 108.
  • the measured electrical characteristics e.g., an impedance
  • presence of an object is assumed, if at least one difference between a first measurement output associated to a sense circuit (e.g., sense circuit 106a) and at least one first time and a second measurement output associated to the same sense circuit and at least one second time exceeds a threshold.
  • a sense circuit e.g., sense circuit 106a
  • a second measurement output associated to the same sense circuit and at least one second time exceeds a threshold.
  • an object can be detected when it enters or leaves the proximity of the at least one sense element (e.g., sense element 107a) or generally when it moves in the proximity of the at least one sense element.
  • the evaluation is based on a sense circuit-differential detection scheme that is sensitive to differences between measurement outputs associated to different sense circuits of the plurality of sense circuits (e.g., 106).
  • This detection scheme may be also referred to as space-differential detection.
  • presence of an object e.g., object 110
  • a first measurement output associated to at least one first sense circuit e.g., sense circuit 106a
  • a second measurement output associated to at least one second sense circuit e.g., sense circuit 106b
  • the plurality of measurement outputs used to determine a difference refer to substantially the same time. It may be appreciated that in certain cases, space-differential detection may be less sensitive and reliable than time-differential detection because sense circuits of the plurality of sense circuits 104a, 104b, ..., 104n may be at least partially differently (individually) affected by temperature, mechanical impacts, and ageing. [0085] In some aspects, time-differential detection may be sensitive to movements of metallic structures in the environment of the sense element array (e.g., array 107). Such environmental effects may include movements of the metallic vehicle underbody structure when a vehicle is parked over the wireless power transfer structure.
  • This reference value may be e.g., a mean value, a median value (50th percentile), or any other percentile value that is derived from a histogram built upon the plurality of measurement outputs. It may be appreciated that this special detection scheme has the potential to discriminate environmental effects e.g., from a moving vehicle underbody that may produce changes in an electrical characteristic (e.g., an impedance) in a majority (cluster) of sense circuits.
  • This special scheme may be considered as a mechanism that automatically adapts the detection threshold used by the control and evaluation circuit 102 for determining presence of an object (e.g., object 110). More specifically, in some implementations or operations, the control and evaluation circuit 102 automatically adjusts the reference value as described above.
  • FIG.2 illustrates an example implementation of a wireless power transfer structure 200 that is a portion of a WPT system including a portion of the multi-purpose detection circuit 100 of FIG.1.
  • the wireless power transfer structure 200 may depict either a wireless power transmitter that generates a magnetic field (e.g., at an operating frequency in the range from 80 - 90 kHz) for transferring power or a wireless power receiver that can couple and receive power via a magnetic field. It may be more likely that when integrated with a multi-purpose detection circuit 100, the wireless power transfer structure 200 may be a wireless power transmitter as power may be generally transferred from the ground or other upward facing surface where foreign objects (e.g., object 110 or 112) will generally come to a rest. However other implementations are possible, e.g., the multi-purpose detection circuit 100 or a portion thereof may be also integrated into a wireless power receiver (e.g., a vehicle-based wireless power transfer structure).
  • a wireless power receiver e.g., a vehicle-based wireless power transfer structure
  • the wireless power transfer structure 200 may be configured to wirelessly transmit or receive power.
  • the wireless power transfer structure 200 includes a coil 202 (e.g., a Litz wire coil) also referred to as the WPT coil that is configured to generate an alternating magnetic field when driven with a current by a power conversion circuit (not shown herein).
  • the wireless power transfer structure 200 may further include a ferrite 204 structure configured to channel and/or provide a path for magnetic flux (e.g., may be arranged in one or more ferrite tiles).
  • the wireless power transfer structure 200 may also include a metal shield 206 (also sometimes referred to as a back plate).
  • the metal shield 206 is configured to prevent the magnetic field or associated electromagnetic emissions from extending far beyond a boundary determined by the shield 206 or at least to attenuate the magnetic field extending beyond that boundary.
  • the shield 206 may be formed from aluminum.
  • FIG.2 illustrates one example how the plurality of inductive sense elements (array 107) and the plurality of capacitive sense elements 109 of FIG. 1 may be integrated into the wireless power transfer structure 200.
  • FIG. 3 illustrates a vertical cut view of a portion 300 of a WPT system applicable to wireless electric vehicle charging. This portion 300 includes the ground-based (e.g., transmit) wireless power transfer structure 200 with reference to FIG.2 and the vehicle-based (e.g., receive) wireless power transfer structure 310.
  • the ground-based wireless power transfer structure 200 includes the shield (back plate) 206, a layer of ferrite 204, and a WPT coil 202 with reference to FIG.2. It also includes a housing 328 configured to house the WPT coil 202, the ferrite 204, and the shield 206.
  • the housing 328 is configured to house the plurality of inductive sense elements (array 107) and the plurality of capacitive sense elements (109) as part of the multi- purpose detection circuit 100 as illustrated in FIG. 2.
  • the shield 206 may form a portion of the housing 328 as illustrated in FIG.3. Further, the housing 328 may be inclined along its perimeter from its edge toward its interior to form a ramp over which a vehicle may drive.
  • the power conversion circuit may be electrically connected to the WPT coil 202 or a portion or all may also be housed in the housing 328.
  • the capacitive sense elements e.g., the capacitive sense elements 109a, 109b, ..., 109n
  • the capacitive sense elements may be oriented to be nonparallel with a plane defined by the array 107 of inductive sense elements.
  • the capacitive sense elements may be oriented to be substantially parallel to the inclined top surface of the housing 328 along the housing’s perimeter.
  • the vehicle-based wireless power transfer structure 310 includes a WPT coil 312, a layer of ferrite 315, and a shield 316 made of an electrically conductive material.
  • the shield 316 may be formed from a portion of the apparatus that the ferrite 315 and the WPT coil 312 are affixed to the metallic underbody of a vehicle 330.
  • a housing 318 configured to house the WPT coil 312 and ferrite 315 is provided but that may not house the shield 316.
  • a conductive back plate is included in the housing 318.
  • a power conversion circuit (not shown herein) may be electrically connected to the WPT coil 312 or a portion or all may also be housed in the housing 318.
  • the vehicle-based wireless power transfer structure 310 may also integrate at least one of an inductive passive beacon transponder 313 and a capacitive beacon transponder 314 e.g., for purposes of PD and VD as previously discussed.
  • the inductive passive beacon transponder 313 may be configured to primarily interact with the inductive sense elements e.g., the inductive sense elements 107a, 107b, ..., 107n.
  • the inductive passive beacon transponder 313 includes a transponder coil, a capacitive element to compensate for the gross reactance of the coil at the operating (sense) frequency of the multi-purpose detection circuit 100, and a passive impedance modulation circuit (these elements not shown in herein).
  • the capacitive passive beacon transponder 314 may be configured to primarily interact with the capacitive sense elements e.g., the capacitive sense elements 109a, 109b, ..., 109n.
  • the capacitive passive beacon transponder 314 includes a transponder electrode, an inductive element to compensate for the gross reactance of the electrode at the operating (sense) frequency of the multi-purpose detection circuit 100, and a passive impedance modulation circuit (these elements not shown in herein).
  • the passive beacon transponder e.g., passive beacon transponder 313
  • the passive beacon transponder is configured to interact with both the inductive and capacitive sense elements of the multi-purpose detection circuit 100.
  • the ground-based (e.g., transmit) wireless power transfer structure 200 may be configured to generate a magnetic field 232.
  • the vehicle-based wireless power transfer structure 310 may be configured to inductively receive power via the magnetic field.
  • an object e.g., object 110 or 112 may come to rest at the top surface of the housing 328 as illustrated in FIG. 3. The object may thereby be potentially exposed to high levels of magnetic flux density if power is being transferred.
  • FIG 4 is a generic block diagram illustrating an example implementation or operation of a multi-purpose detection circuit 100.
  • the circuit 100 includes the plurality of inductive sense circuits 106a, 106b, ...,106n, including the inductive sense elements 107a, 107b, ..., 107n, respectively, the plurality of capacitive sense circuits 108a, 108b,...,108n, including the capacitive sense elements 109a, 109b, ..., 109n, respectively, the measurement circuit 104, and the control and evaluation circuit 102 with reference to FIG.1.
  • Each of the plurality of inductive sense circuits 106 may also include an associated capacitive element (not shown herein) to compensate for the gross reactance as presented at the terminals of the at least one inductive sense element at the sense frequency.
  • Each of the plurality of capacitive sense circuits 108 may also include an associated inductive element (not shown herein) to compensate for the gross reactance as presented at the terminals of the at least one capacitive sense element at the sense frequency.
  • At least one of the plurality of inductive and capacitive sense circuits also includes an impedance matching element (e.g., a transformer) for transforming the impedance of the sense circuit (e.g., sense circuit 108a) to match with an operating impedance range of the multi-purpose detection circuit 100.
  • an impedance matching element e.g., a transformer
  • each of the plurality of inductive sense circuits 106 is naturally matched with an operating impedance range without using an additional impedance matching element.
  • the measurement circuit 104 is electrically connected to the plurality of inductive and capacitive sense circuits and configured for selectively and sequentially measuring one or more electrical characteristics (e.g., an impedance) in each of the plurality of inductive and capacitive sense circuits according to a predetermined time multiplexing scheme.
  • the control and evaluation circuit 102 is electrically connected to the measurement circuit 104 and configured to control time multiplexing (input multiplexer (MUX) control and output MUX control in FIG. 4) according to the predetermined time multiplexing scheme, to evaluate the one or more electrical characteristics as measured in each of the inductive and capacitive sense circuits, and to determine at least one of a presence of a foreign object (e.g., object 110 or 112), a living object (e.g., object 114), a vehicle (e.g., vehicle 330), a type of vehicle, and a vehicle position based on changes in the measured one or more electrical characteristics.
  • a foreign object e.g., object 110 or 112
  • a living object e.g., object 114
  • vehicle e.g., vehicle 330
  • a type of vehicle e.g., vehicle position based on changes in the measured one or more electrical characteristics.
  • 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.
  • the driver circuit 402 including multiplexing (input multiplexing) is electrically connected to the plurality of inductive sense circuits 106 and the plurality of capacitive sense circuits 108 and configured to selectively and sequentially apply a drive signal (e.g., a current signal) at the sense frequency to each of the plurality of inductive sense circuits 106 and the plurality of capacitive sense circuits 108 based on a driver input signal generated by the signal generator circuit 406.
  • a drive signal e.g., a current signal
  • the measurement amplifier circuit 404 including multiplexing (output multiplexing) is electrically connected to the plurality of inductive sense circuits 106 and the plurality of capacitive sense circuits 108 and configured to selectively and sequentially amplify a measurement signal (e.g., a voltage signal) in each the plurality of inductive sense circuits 106 and the plurality of capacitive sense circuits 108 and to provide a measurement amplifier output signal indicative of the measurement signal in each of the plurality of sense circuits.
  • the signal generator circuit 406 electrically connected to the input of the driver circuit 402 is configured to generate the driver input signal.
  • the signal processing circuit 408 electrically connected to the output of the measurement amplifier circuit 404 is configured to receive and process the measurement amplifier output signal and to determine the one or more electrical characteristics in each of the plurality of inductive and capacitive sense circuits based on the driver input signal and the measurement amplifier output signal.
  • the dashed lines used in FIG.4 emphasize that the components and their configuration in the driver circuit 402 and the measurement amplifier circuit 404 are illustrative, and other implementations may have these or other components configured to selectively and sequentially drive the plurality of sense circuits 106 and 108 with a drive signal and to selectively and sequentially amplify a measurement signal in each of the plurality of sense circuits 106 and 108.
  • the sense signal is selectively and sequentially applied to each of the plurality of inductive sense circuits 106 and to each of the plurality of the capacitive sense circuits 108 according to a time division multiplexing scheme and in a round robin fashion.
  • the sense signal for driving an inductive sense circuit (e.g., inductive sense circuit 106a) is applied in a time interval (time slot) allocated to that sense circuit and has a maximum duration equal or shorter than the duration of the time slot.
  • the time frame corresponding to the sum of time slots allocated to the plurality of inductive sense circuits 106 and capacitive sense circuits 108 is also referred herein as to the scan cycle or to the repetition period.
  • a first sense signal is selectively and sequentially applied to each of a portion of the plurality of inductive sense circuits 106 and capacitive sense circuits 108 and a second sense signal is concurrently, selectively and sequentially applied to each of the remaining portions of inductive and capacitive sense circuits.
  • Concurrently applying two or more sense signals reduces the scan cycle and may result in a reduced detection latency with respect to FOD and LOD and in an increased position update rate with respect to PD (e.g., using the passive beaconing approach as previously described).
  • the first and the at least one concurrently applied second sense signal are sinusoidal signals of the same frequency.
  • the first and the at least one concurrently applied second sense signal are sinusoidal signals but differ in frequency.
  • each of the first and the at least one concurrent second sinusoidal sense signals as applied in time slots allocated to the same sense circuit start with the same phase (e.g., zero-phase).
  • starting sense signals in time slots allocated to the same sense circuit with the same phase may help to mitigate interference caused by intermodulation effects as described in U.S. Patent Application No.
  • time slots of a scan cycle are reallocated based on some conditions (e.g., whether WPT is active or inactive). In an aspect, it may be desirable to reduce the detection latency with respect to LOD when WPT is active. Therefore, in an example operation, two or more time slots of a scan cycle are allocated to each of the capacitive sense circuits 108 when WPT is active. Conversely, the LOD function may not be required when WPT is inactive.
  • time slots of a scan cycle are only allocated to inductive sense circuits (e.g., to the plurality of inductive sense circuits 106) when WPT is inactive.
  • two or more time slots of a scan cycle are allocated to each of the plurality of inductive sense circuits (e.g., inductive sense circuits 106) and one time slot is allocated to each of the plurality of capacitive sense circuits when WPT is inactive.
  • This mode of operation may allow maintaining a limited LOD function when WPT is inactive (e.g., for purposes of monitoring proper functioning of the multi-purpose detection circuit 100 with respect to LOD).
  • the time spacing between time slots allocated to the same sense circuit in any of the scanning modes described above is maximized.
  • FIGs. 5A to 5E illustrate example implementations of a portion of the multi-purpose detection circuit 100 of FIG. 1 based on inductive sensing by measuring at least one electrical characteristic (e.g., a complex impedance). These examples are to illustrate the principle of the sensing and measurement technique and do not show all the details of a multi-purpose detection circuit 100. Particularly, for illustrative purposes, they only show a single inductive sense circuit rather than the plurality of inductive sense circuits (e.g., the plurality of inductive sense circuits 106a, 106b, ..., 106n with reference to FIG.1).
  • circuits 500, 520, and 540 of FIGs.5A, 5B, and 5C, respectively are based on measuring a one-port impedance Z 11 , while the circuits 560 and 580 of FIGs.5D and 5E, respectively, employ a two-port transimpedance Z 21 measurement at the sense frequency e.g., using a sinusoidal sense signal.
  • the sense signal is a high frequency signal with a spectrum substantially in the megahertz (MHz) range (e.g., in a frequency range from 2.5 MHz to 3.5 MHz). In other implementations, the sense signal is constraint to the frequency range from 3.155 MHz to 3.400 MHz for frequency regulatory reasons.
  • MHz megahertz
  • this frequency range may permit higher emission levels e.g., a magnetic field strength H ⁇ 13.5 dB ⁇ A/m at 10 m from the radiating parts of the multi-purpose detection circuit 100 (e.g., from the inductive sense element array 107).
  • a magnetic field strength H ⁇ 13.5 dB ⁇ A/m at 10 m from the radiating parts of the multi-purpose detection circuit 100 (e.g., from the inductive sense element array 107).
  • the ground symbol shown in the schematic diagrams of FIGs. 5A to 5E indicate a network node on ground potential referred to as the “circuit ground”. However, this should not exclude non-ground-based implementations or implementations that use different grounds on different potentials.
  • the circuit 500 of FIG.5A illustrates an example implementation based on measuring a complex impedance Z 11 of a one-port inductive sense circuit 501 (shown in FIG.5A as the circuit on the right side of the dashed line). More specifically, the impedance Z 11 is measured at the measurement port 508 (indicated in FIG.5A by a terminal and a dashed line) by applying, from a current source 512 (sense circuit current source 512), a sinusoidal current I 0 at the sense frequency with a defined amplitude and phase and by measuring, using a voltage measurement circuit 510, the complex open-circuit voltage V (amplitude and phase) as indicated in FIG.5A.
  • a current source 512 sense circuit current source 512
  • V complex open-circuit voltage
  • the impedance Z 11 is then determined by dividing the measured voltage V by the defined (known) current I 0 .
  • This impedance measurement technique is also referred herein as to the current source voltage measurement technique.
  • the sense circuit 501 comprises a single-coil sense element (e.g., sense coil 502) having an inductance L and an equivalent series resistance R, a series capacitor 504 having a capacitance C s and an equivalent series resistance R Cs electrically connected in series to the sense coil 502, and a parallel inductor 506 having an inductance L p and an equivalent series resistance R Lp electrically connected to the capacitor 504 in parallel to the measurement port 508.
  • the circuit 500 further illustrates the sense signal current source 512 and the voltage measurement circuit 510 both electrically connected to the sense circuit 501 at the measurement port 508.
  • the equivalent series resistance R includes all electrical losses intrinsic to the sense coil 502 and extraneous losses as they may occur in its surrounding materials (e.g., the Litz wire of the WPT coil 202 and the ferrite of the wireless power transfer structure 200 where the sense coil 502 may be integrated). These materials may interact with the magnetic field as generated by the sense coil 502 causing losses.
  • the circuit 500 of FIG.5A also indicates parasitic capacitances (by dashed lines) such as the sense coil’s 502 self-capacitance (or intra winding capacitance) Ciw, the sense coil’s 502 ground capacitance C gnd , and the capacitance C wpt between the sense coil 502 and the WPT coil 202 with reference to FIG. 2 (abstracted in FIG. 5A by a line).
  • parasitic capacitances by dashed lines
  • the sense coil’s 502 ground capacitance C gnd the capacitance C wpt between the sense coil 502 and the WPT coil 202 with reference to FIG. 2 (abstracted in FIG. 5A by a line).
  • These capacitances and the associated electric stray fields may cause a certain sensitivity of the circuit 500 on substantially non-conductive, dielectric objects (e.g., object 112 or 114).
  • the sense circuit 501 may be configured to provide a local minimum in the impedance magnitude function
  • the minimum of the impedance magnitude is also referred to herein as the series resonance by definition and applies to the inductive sense circuits with reference to FIGs. 5A to 5E.
  • the sense circuit 501 may be configured to provide a local minimum in the admittance magnitude function
  • substantially at the nominal sense frequency, where Y 11,0 ( 1/Z 11,0 ) refers to the admittance as presented by the sense circuit 501 at the measurement port 508 in absence of a foreign object.
  • the minimum of the admittance magnitude is also referred to herein as the parallel resonance by definition and applies to the inductive sense circuits with reference to FIGs.5A to 5E.
  • the reactance of the series capacitor 504 substantially compensates for the reactance of the sense coil 502 at the nominal sense frequency providing an impedance Z 11,0 that is substantially real (resistive).
  • the inductance L p of the parallel inductor 506 may be similar or larger than the inductance L of the sense coil 502.
  • the impedance magnitude of the parallel inductor 506 may be substantially (e.g., 10 times) higher than the impedance magnitude
  • the parallel inductor 506 may exert a negligible impact on the impedance
  • the reactance of the series capacitor 504 overcompensates for the reactance of the sense coil 502 at the nominal sense frequency.
  • the residual capacitive susceptance of the series connection of the capacitor 504 and the sense coil 502 is substantially compensated for by the susceptance of the parallel inductor 506 providing an admittance Y 11,0 that is substantially real (resistive).
  • the inductance L p of the parallel inductor 506 may be smaller, similar, or larger than the inductance L of the sense coil 502.
  • the admittance magnitude of the parallel inductor 506 may be substantially (e.g., 20 times) higher than the admittance magnitude
  • the parallel inductor 506 exerts a significant impact on the admittance Y 11,0 at the nominal sense frequency.
  • the parallel inductor 506 together with the series capacitor 504 are used for purposes of resonance tuning and impedance transformation e.g., to transform the impedance Z 11 to match the sense circuit 501 with an operating impedance range as previously mentioned with reference to FIG.1.
  • the inductance ratio L/L p may be a parameter to control the impedance magnitude
  • Impedance transformation may be particularly effective, if the sense circuit 501 is configured for parallel resonance. More specifically, increasing the inductance ratio L/L p , while maintaining series resonance at the nominal sense frequency, may substantially increase the admittance magnitude
  • the sense circuit 501 in the parallel resonant configuration may be considered as an alternative to the sense circuit 521 illustrated in FIG.5B using a transformer.
  • Increasing the inductance ratio L/L p while maintaining resonance at the nominal sense frequency, may also somewhat decrease the impedance magnitude
  • impedance transformation may be limited and far less effective than that of the series resonant configuration.
  • the series capacitor 504 may include a variable capacitor whose capacitance C s can be electronically controlled (e.g., a direct current (DC) controlled capacitor) forming a variable capacitor 504.
  • DC direct current
  • a variable capacitor 504 is used to compensate for a temperature drift, an ageing, or a detuning of the sense circuit 701 caused by an external impact and to maintain its resonance substantially at the nominal sense frequency.
  • the parallel inductor 506 may include a variable inductor whose inductance L p can be electronically controlled (e.g., a DC controlled inductor) forming a variable inductor 506.
  • the variable capacitor 504 and variable inductor 506 in combination are used to vary the impedance
  • the series capacitor 504 in combination with the parallel inductor 506 form a 2 nd order high pass filter to attenuate a low frequency disturbance component in the voltage V emanating from the voltage inductively coupled into the sense coil 502 by the magnetic and electric field as generated during wireless power transfer.
  • This high pass filter may reduce dynamic range requirements of the voltage measurement circuit 510 and may also protect the voltage measurement circuit 510 and the current source 512 from being overloaded. Stated in other words, it may reduce non-linear distortion effects (e.g., signal clipping) in a voltage measurement circuit 510 with a limited dynamic range.
  • the sense circuit 501, the sense coil 502, the series capacitor 504, and the parallel inductor 506 may correspond e.g., to the inductive sense circuit 106a, the inductive sense element 107a, and the associated capacitive element, respectively.
  • the current source 512 may include the signal generator circuit 406 and the driver circuit 402, while the voltage measurement circuit 510 may include the measurement amplifier circuit 404 and the signal processing circuit 408 with reference to FIG.4.
  • a current source (e.g., current source 512) may be characterized by a quasi-ideal current source providing a source admittance magnitude
  • the voltage measurement circuit 510 may be characterized by a quasi-ideal voltage measurement circuit with an admittance magnitude
  • a measurement circuit (e.g., measurement circuit 104 of FIG.
  • a current source e.g., current source 512
  • a voltage measurement circuit e.g., voltage measurement circuit 510) configured to measure the admittance Y 11 of a one-port sense circuit (e.g., sense circuit 501)
  • a quasi-ideal measurement circuit providing a measurement circuit admittance magnitude
  • the quality of a measurement circuit e.g., measurement circuit 104 of FIG.
  • Equation (2) may be used to assess the quality of a measurement circuit (e.g., measurement circuit 104 of FIG.4) based on the current source voltage measurement approach.
  • a more general definition of the quality of a measurement circuit (e.g., measurement circuit 104 of FIG.4) based on the current source voltage measurement approach, also applicable to a two-port sense circuit (e.g., sense circuit 561 with reference to FIG.5D) may be given by: Q mc ⁇
  • characterizations of the current source 512, the voltage measurement circuit 510, and the measurement circuit 104 may be generalized to non-sinusoidal sense signals, where the notions of complex impedance and complex amplitude may not directly apply.
  • impedance measurement techniques may also be contemplated e.g., by applying a sinusoidal voltage, from a voltage source (e.g., voltage source 552 with reference to FIG. 5C) with a defined voltage V 0 (amplitude and phase) to the sense circuit 501 and by measuring the complex current I (amplitude and phase) at the measurement port 508 using a current measurement circuit (e.g., current measurement circuit 550 with reference to FIG.5C).
  • a voltage source e.g., voltage source 552 with reference to FIG. 5C
  • V 0 amplitude and phase
  • the voltage source 552 (sense signal voltage source 552) may be characterized by a quasi-ideal voltage source with a source impedance magnitude
  • the current measurement circuit 550 may be characterized by a quasi-ideal current measurement circuit with an impedance magnitude
  • a measurement circuit (e.g., measurement circuit 104 of FIG.
  • a voltage source e.g., voltage source 552
  • a current measurement circuit e.g., current measurement circuit 550
  • Z mc substantially (e.g., at least 10 times) lower than
  • the measurement circuit impedance may be defined, using above impedance definitions, as: Z mc ⁇ Z vs + Z cm (4) [0136]
  • the quality of a measurement circuit e.g., measurement circuit 104 of FIG.
  • Equation (5) may be used to assess the quality of a measurement circuit (e.g., measurement circuit 104 of FIG.4) based on the voltage source current measurement approach.
  • Other impedance measurement techniques may also include approaches where the sense circuit 501 is driven by a non-ideal source and the voltage V and the current I are measured e.g., using a quasi-ideal voltage measurement circuit and a quasi-ideal current measurement circuit, respectively.
  • measurement of the voltage V and thus of the impedance Z 11 may be affected by noise and other disturbance signals reducing a detection sensitivity of the multi-purpose detection circuit 100.
  • the noise may include circuit intrinsic noise as generated in active and passive components of the circuit 500 of FIG.5A. It may also include quantization noise e.g., generated in a digital implementation of the signal generator circuit 406 and the signal processing circuit 408 with reference to FIG. 4.
  • Other disturbance signals may emanate from sources external to the circuit 500 (e.g., from the WPT system during wireless power transfer, from a switched-mode power supply, from a digital processing unit, etc.).
  • the voltage measurement circuit 510 includes a filter to selectively filter the sense signal and to suppress noise and other disturbance signal components as discussed above and consequently to improve the detection sensitivity.
  • the filter may be matched to the sense signal and configured to maximize a signal-to-noise ratio (SNR) in presence of noise and other disturbance signals.
  • SNR signal-to-noise ratio
  • the voltage measurement circuit 510 may be frequency selective (narrowband) and tuned to the sense signal frequency.
  • the voltage measurement circuit 510 also includes a noise analyzer (e.g., included in the signal processing circuit 408 with reference to FIG.4) that is continuously analyzing the noise. Further, it includes a controller (e.g., the control and evaluation circuit 102 of FIG.
  • the voltage measurement circuit 510 includes a spectrum analyzer and a controller that is continuously looking for frequencies with a minimum disturbance (noise) level and adjusts the frequency of the sense signal (sense frequency) to a frequency with the minimum disturbance level, avoiding switching harmonics of the WPT system and remaining substantially at resonance of the sense circuit 501.
  • FIG.5A also illustrates objects 110, 112, and 114 proximate to the sense coil 502.
  • Presence of any one of these objects including vehicle 330 may cause a change in one or more electrical characteristics of the sense coil 502 and consequently of the sense circuit 501. As non-limiting examples, it may cause a change in at least one of the inductance L and the equivalent series resistance R and hence in the sense coil’s 502 impedance Z.
  • This change of impedance herein referred to as the reflected impedance ⁇ Z r of the object (e.g., object 110), results in an impedance change ⁇ Z with respect to the impedance Z 11,0 as presented at the measurement port 508 in absence of a foreign object.
  • the reflected impedance ⁇ Z r of the object e.g., object 110
  • the reflected impedance ⁇ Z r and the related impedance change ⁇ Z may be indicative of electrical properties of the object (e.g., object 110).
  • Presence of an object e.g., object 110
  • ⁇ Z satisfies certain criteria e.g., magnitude
  • a change ⁇ Z r in Z and thus ⁇ Z in the impedance Z 11 may also be caused by the underbody of a vehicle (e.g., vehicle 330), by the vehicle-based wireless power transfer structure (e.g., wireless power transfer structure 310 of FIG.
  • a change ⁇ Z may be also indicative of the presence of a vehicle or a type of vehicle above the sense coil 502.
  • an impedance change ⁇ Z may be caused by a substantially non- conductive, dielectric object (e.g., object 112 or 114) proximate to the sense coil 502 due to the capacitive sensing effect inherent to the sense coil 502 as previously mentioned. More specifically, the object 112 or 114 in proximity of the sense coil 502 may change one or more of its parasitic capacitances Ciw, Cgnd, and Cwpt as illustrated in FIG.5A.
  • presence of an object may cause a change ⁇ Y with respect to the admittance Y 11,0 as measured in absence of a foreign object.
  • presence of an object e.g., object 110
  • measuring the complex voltage V may be equivalent to measuring the complex impedance Z 11 .
  • the complex voltage V may be indicative of the complex impedance Z 11 and there may be no requirement for additionally measuring the current I 0 thus reducing complexity of the measurement circuit (e.g., measurement circuit 104 of FIG.1).
  • measuring the complex voltage V and determining the reciprocal value 1/V may be equivalent to measuring the complex admittance Y 11 .
  • Z defines the sense coil’s 502 impedance in presence of an object (e.g., object 110).
  • the normalized reflected impedance ⁇ Z r ’ or the normalized reflected admittance ⁇ Z r ’ determine the impact of an object (e.g., object 110) on the sense coil’s 502 impedance or admittance, respectively.
  • SNR signal-to-noise ratio
  • the normalized reflected impedance ⁇ Z r ’ of an object and thus the related fractional change ⁇ Z’ may be increased by optimizing the design of the sense coil 502 with respect to its geometry and its integration into the wireless power transfer structure (e.g., wireless power transfer structure 200 with reference to FIGs 2 and 3).
  • the fractional change ⁇ Z’ may be further increased by resonance tuning e.g., using the series capacitor 504, and by improving the Q-factor of the sense circuit 501. Improving the Q-factor may also increase the SNR, if the noise voltage V n is predominantly circuit intrinsic noise as discussed below with reference to FIG. 5F.
  • the sense coil’s inductance L and equivalent series resistance R, the series capacitor’s 504 capacitance, and the parallel inductor’s 506 inductance L p and equivalent series resistance R Lp may be subjected to thermal drift. Thermal drift effects may deteriorate the detection sensitivity of the multi-purpose detection circuit 100.
  • a test object e.g., object 110
  • the fractional change ⁇ Z ⁇ ’ may be considered the complex temperature coefficient of a sense circuit (e.g., sense circuit 501).
  • the temperature sensitivity S ⁇ may also be expressed in terms of the fractional admittance changes ⁇ Y ⁇ ’ and ⁇ Y’.
  • the reflected impedance ⁇ Z r and particularly the angle arg ⁇ Z r ⁇ may reflect electrical properties of the object 110, 112, 114, or vehicle 330. The same may be true for the reflected admittance ⁇ Y r .
  • the change ⁇ Z in the impedance Z 11 caused by an object is indicative of the reflected impedance ⁇ Z r .
  • the circuit 500 may be configured to determine the angle arg ⁇ Z ⁇ with the required accuracy.
  • measuring the angle arg ⁇ Z ⁇ may be subject to errors for various reasons.
  • One prominent error source of some implementations of the circuit 500 is an unknown (e.g., frequency dependent) phase offset of the output of the voltage measurement circuit 510 relative to the drive current I 0 as generated by the current source 512. In a mixed digital and analog implementation of the circuit 500, this phase offset may be attributed to the analog frontend portion of the circuit 500.
  • a multipurpose detection circuit 100 employs a phase calibration of the analog circuitry (e.g., the analog front end portion of the measurement circuit 104 with reference to FIG. 4).
  • This phase calibration may be a factory calibration or it may be performed at the time of installation and commissioning of the wireless power transfer structure 200 (integrating the multipurpose detection circuit 100).
  • this phase calibration is repeated periodically in fixed intervals (e.g., to mitigate ageing effects). In other operations, it is executed after the multipurpose detection circuit 100 is reactivated (powered on).
  • this calibration is initiated e.g., if the temperature as measured in the wireless power transfer structure 200 exceeds or falls below a threshold.
  • Reactance compensation (resonance tuning) in the sense circuit 501 produces a local extremum (minimum or maximum) in the impedance magnitude function
  • the sense frequency is adjusted to the local minimum of the voltage magnitude
  • the complex impedance Z 11,0 and hence the complex voltage V across the measurement port 508 may be substantially real. Otherwise stated, the angles arg ⁇ Z 11,0 ⁇ and arg ⁇ V ⁇ are substantially zero.
  • the voltage measurement circuit 510 is corrected by applying a phase shift such that the imaginary part of the complex voltage value as determined and output by the voltage measurement circuit 510 at this frequency vanishes.
  • the residual angle error of an example series resonant configuration of the circuit 500 and for an example object 110 is provided in TABLE 2.
  • the residual error described above is reduced by configuring the parallel inductor 506 with an inductance L p whose impedance Z Lp is substantially larger (e.g., 10 times larger) than the series resonant resistance of the sense circuit 501.
  • the residual error is reduced by measuring the impedance Z 11,0 at two or more substantially different frequencies and by determining the elements of an equivalent circuit model of the sense circuit 501 (e.g., the equivalent circuit model illustrated in FIG. 5F) based on the measured impedances Z 11,0 employing a best fit method.
  • these two or more frequencies include at least the frequency of the minimum and the maximum of
  • inductive sense circuits 106a, 106b, ..., 106n each including a respective inductive sense element (e.g., inductive sense element 107a, 107b, ..., 107n) of an array (e.g., array 107)
  • a further residual error may be caused by a parasitic resonance effect of sense circuits associated to adjacent inductive sense elements.
  • a residual error in a first sense circuit (e.g., inductive sense circuit 106a) including a first inductive sense element (e.g., inductive sense element 107a) may be caused by a parasitic resonance effect of at least one second inductive sense circuit (e.g., inductive sense circuit 106b) including a second inductive sense element (e.g., inductive sense element 107b) that is located adjacent to the first inductive sense element.
  • the measurement accuracy of the angle arg ⁇ Z ⁇ and thus of the angle arg ⁇ Z r ⁇ is increased by an optimized design of the sense coil 502 and by introducing some spacing between adjacent sense coils 502 of an array (e.g., array 107).
  • the circuit 500 may be configured to measure the admittance Y 11 and corresponding changes ⁇ Y of Y 11 as caused by the object 110, 112, 114, or vehicle 330. In this case, the admittance change ⁇ Y may be indicative of the reflected impedance ⁇ Z r as previously introduced.
  • the angle arg ⁇ Y ⁇ may be subjected to an error and therefore may require calibration to reduce an error in the measurement of the angle arg ⁇ Y ⁇ and thus of the angle arg ⁇ Z r ⁇ .
  • the circuit 500 may be calibrated analogously to the series resonant configuration using the local minimum of the admittance function
  • the sense frequency is adjusted to the local maximum of the voltage magnitude
  • the admittance Y 11,0 and hence the voltage V across the measurement port 508 may be substantially real. Otherwise stated, the angles arg ⁇ Y 11,0 ⁇ and arg ⁇ V ⁇ are substantially zero.
  • the voltage measurement circuit 510 is corrected by applying a phase shift (impedance plane rotation) as defined above by Equation (13). [0161] Applying the angle correction of Equation (13), an object (e.g., object 110) reflecting an impedance ⁇ Z r that is imaginary (reactive) may result in a measured voltage change ⁇ V cal that is substantially imaginary. A residual error may remain in the angle arg ⁇ V cal ⁇ due to the transformation of ⁇ Z r to ⁇ Y in the lossy sense circuit 501.
  • the residual angle error of an example parallel resonant configuration of the circuit 500 and for example reflected impedance ⁇ Z r is provided in TABLE 2.
  • the residual error due to the transformation of ⁇ Z r to ⁇ Y is reduced by measuring the admittance Y 11,0 at two or more substantially different frequencies, supposing absence of a foreign object, and by determining the elements of an equivalent circuit model (e.g., the equivalent circuit model of FIG. 5F) based on the measured admittances Y 11,0 employing a best fit method.
  • these two or more frequencies include at least the frequency of the minimum and the maximum of
  • the series and the parallel resonant configuration of the circuit 500 of FIG. 5A are further analyzed below with reference to FIG. 5F with respect to various characteristics such as the Q-factor, fractional change, and various definitions of SNR based on an equivalent circuit model.
  • the circuit 520 of FIG. 5B illustrates another example implementation based on measuring a complex impedance Z 11 of a one-port inductive sense circuit 521 (shown in FIG.5B as the circuit on the right side of the dashed line).
  • the sense circuit 521 comprises the single-coil inductive sense element (e.g., sense coil 502) having the inductance L with reference to FIG.5A and a capacitor 524 having a capacitance C s electrically connected in series to the sense coil 502.
  • the sense circuit 521 shows the parallel inductor 506 of FIG.5A replaced by a transformer 526.
  • the transformer 526 may include a primary winding and a galvanically insulated secondary winding wound on a common core as suggested by the transformer symbol in FIG. 5B.
  • FIG. 5B also indicates a transformation ratio nT:1, a main inductance L m , a leakage inductance L ⁇ , and equivalent series resistances R Lm and R w that may represent core and conductor losses, respectively.
  • nT:1 a transformation ratio
  • L m main inductance
  • L ⁇ leakage inductance
  • R Lm and R w equivalent series resistances
  • the circuit 5B shows its primary winding electrically connected in parallel to the measurement port 528, while its secondary winding is electrically connected to the series capacitor 524.
  • the circuit 520 further illustrates the sense signal current source 512 and the voltage measurement circuit 510 both electrically connected to the sense circuit 521 at the measurement port 528.
  • the series capacitor 524 and the sense coil 502 may also include the equivalent series resistance R Cs and the parasitic capacitances Ciw, Cgnd, and Cwpt, respectively, as shown in FIG.5A.
  • the sense circuit 521 may be configured to provide a local minimum in the impedance magnitude function
  • the reactance of the series capacitor 504 substantially compensates for the reactance of the sense coil 502 at the nominal sense frequency providing an impedance Z 11,0 at the measurement port 528 that is substantially real (resistive).
  • the reactance of the series capacitor 524 also compensates for the reactance of the transformer’s 526 secondary referred leakage inductance L ⁇ with reference to FIG.5H.
  • the transformer’s 526 secondary referred main inductance L m may be similar or larger than the inductance L of the sense coil 502.
  • the primary referred open-circuit impedance of the transformer 526 may be substantially (e.g., 10 times) higher than the impedance magnitude
  • the transformer 526 may exert a negligible impact on the impedance
  • the reactance of the series capacitor 524 overcompensates for the sum reactance of the sense coil 502 and the transformer’s 526 leakage inductance L ⁇ at the nominal sense frequency.
  • the residual capacitive susceptance of the series connection of the capacitor 524, the sense coil 502 and the transformer’s leakage inductance L ⁇ is substantially compensated for by the susceptance of the transformer’s 526 secondary referred inductance L m providing an admittance Y 11,0 that is substantially real (resistive).
  • the inductance L m may be smaller, similar, or larger than the inductance L of the sense coil 502.
  • the primary referred open-circuit admittance of the transformer 526 may be substantially (e.g., 20 times) higher than the admittance magnitude
  • the transformer 526 may serve for various purposes.
  • the transformer 526 is a n T :1 transformer with n T ⁇ 1 used at least for impedance transformation e.g., to match the impedance magnitude
  • the transformer 526 increases the impedance
  • it increases the admittance
  • it is a balancing (balun) transformer used to reduce a common mode disturbance voltage capacitively coupled to the sense coil 502 (e.g., via parasitic capacitance Cwpt).
  • the transformer 526 is also part of the resonance tuning as described above.
  • the inductance ratio L/L m may be an additional parameter to match the admittance magnitude
  • FIG. 5B also illustrates the objects 110, 112, and 114 (with reference to FIG. 1) proximate to the sense coil 502. As previously discussed with reference to FIG.1, presence of an object (e.g., object 110, 112, 114, or vehicle 330) may cause a change in one or more electrical characteristics of the sense coil 502 and consequently of the sense circuit 521.
  • an object e.g., object 110, 112, 114, or vehicle 330
  • the object may change the sense coil’s impedance Z referred to as the reflected impedance ⁇ Z r with reference to FIG.5A.
  • the losses of the transformer 526 and its leakage inductance L ⁇ may somewhat reduce the fractional change ⁇ Z (or ⁇ Y) of the sense circuit 521 if compared to the transformerless sense circuit 501 of FIG.5A. This is further analyzed and discussed below with reference to FIG.5F.
  • the circuit 540 of FIG. 5C illustrates another example implementation based on measuring a complex impedance Z 11 of a one-port inductive sense circuit 541 (shown in FIG.5C as the circuit on the right side of the dashed line).
  • the impedance Z 11 is measured at the measurement port 548 (indicated in FIG.5C by a terminal and a dashed line) by applying, from a voltage source 552, a sinusoidal voltage V 0 and by measuring, using a current measurement circuit 550, the complex short-circuit current I as previously mentioned with reference to FIG.5A (voltage source current measurement technique).
  • the circuit 540 may be considered an electrically dual circuit of the circuit 500 of FIG. 5A according to the principle of duality in electrical engineering.
  • the circuit 540 includes the sense circuit 541 comprising the sense coil 502 having an inductance L with reference to FIG.
  • the circuit 540 further illustrates the sense signal voltage source 552 and the current measurement circuit 550 both electrically connected to the sense circuit 541 at the measurement port 548.
  • the sense circuit 541 may also include a transformer (not shown herein) e.g., electrically connected between the measurement port 548 and the capacitor 546 e.g., for purposes of balancing.
  • the capacitive and inductive elements of the sense circuit 541 may also cause electrical losses that may be represented by a respective equivalent series resistance as previously discussed with reference to FIG. 5A.
  • the sense coil 502 may also include the parasitic capacitances Ciw, Cgnd, and Cwpt as indicated in FIG.5A by dashed lines.
  • the circuit 540 of FIG. 5C may be configured to provide a local minimum in the admittance magnitude function
  • the susceptance of the parallel capacitor 544 substantially compensates for the susceptance of the sense coil 502 at the nominal sense frequency providing an admittance Y 11,0 that is substantially real (resistive).
  • the capacitance C s of the series capacitor 546 may be similar or larger than the capacitance C p of the parallel capacitor 544.
  • the admittance magnitude of the series capacitor 546 may be substantially (e.g., 10 times) higher than the admittance magnitude
  • the susceptance of the parallel capacitor 544 undercompensates for the susceptance of the sense coil 502 at the nominal sense frequency. The residual inductive reactance of the parallel connection of the capacitor 544 and the sense coil 502 is substantially compensated for by the reactance of the series capacitor 546 providing an impedance Z 11,0 that is substantially real (resistive).
  • the capacitance C s of the series capacitor 546 may be smaller, similar, or larger than the capacitance C p of the parallel capacitor 544.
  • the impedance magnitude of the series capacitor 546 may be substantially (e.g., 20 times) higher than the impedance magnitude
  • the series capacitor 546 exerts a significant impact on the impedance Z 11,0 at the nominal sense frequency.
  • the series capacitor 546 together with the parallel capacitor 544 are used for purposes of resonance tuning and impedance transformation e.g., to transform the impedance Z 11 to match the sense circuit 541 with an operating impedance range as previously mentioned with reference to FIG. 1.
  • the capacitance ratio C p /C s may be a parameter to control the impedance magnitude
  • Impedance transformation may be particularly effective, if the sense circuit 541 is configured for series resonance. More specifically, increasing the capacitance ratio C p /C s , while maintaining series resonance at the nominal sense frequency, may substantially increase the impedance magnitude
  • the sense circuit 541 due to the series capacitor 546 in conjunction with the voltage source current measurement technique provides a high pass filter characteristic to attenuate a low frequency disturbance component in the current I emanating from the voltage inductively coupled into the sense coil 502 by the magnetic and electric field as generated during wireless power transfer.
  • This high pass filter may reduce dynamic range requirements of the current measurement circuit 550 and may also protect the current measurement circuit 550 and the voltage source 552 from being overloaded. Stated in other terms, it may reduce non-linear distortion effects (e.g., signal clipping) in a current measurement circuit 550 with a limited dynamic range.
  • the sense circuit 541, the sense coil 502, the parallel capacitor 544, and the series capacitor 546 may correspond e.g., to the inductive sense circuit 106a, the inductive sense element 107a, and the associated capacitive element, respectively.
  • the voltage source 552 may include the signal generator circuit 406 and the driver circuit 402, while the current measurement circuit 550 may include the measurement amplifier circuit 404 and the signal processing circuit 408 with reference to FIG.4.
  • the voltage source 552 may be characterized by a quasi-ideal voltage source providing a source impedance whose magnitude is substantially (e.g., 10 times) lower than the magnitude of the impedance
  • the current measurement circuit 550 may be characterized by a quasi- ideal current measurement circuit with an impedance magnitude substantially (e.g., 10 times) lower than the impedance magnitude
  • characterizations of the voltage source 552 and the current measurement circuit 550 may be generalized to non-sinusoidal sense signals as previously discussed with reference to FIG.5A.
  • Other impedance measurement techniques may also be contemplated e.g., by applying a sinusoidal current, from the current source 512, with a defined current I 0 (amplitude and phase) to the sense circuit 541 and by measuring the complex voltage V (amplitude and phase) at the measurement port 548 using the voltage measurement circuit 510 as previously discussed with reference to FIG.5A.
  • measurement of the current I and thus of the impedance Z 11 may be affected by noise and other disturbance signals reducing a detection sensitivity of the multi-purpose detection circuit 100 as previously discussed with reference to FIG. 5A. Therefore, in some implementations, the current measurement circuit 550 includes a filter to selectively filter the sense signal and to suppress noise and other disturbance signal components and consequently to improve the detection sensitivity as previously discussed. [0191] With reference to FIG. 1, FIG. 5C also illustrates the objects 110, 112, and 114 proximate to the sense coil 502.
  • Presence of the object 110, 112, 114, or vehicle 330 may cause a change in one or more electrical characteristics of the sense coil 502 and consequently of the sense circuit 541. As non-limiting examples, it may cause a change of the sense coil’s 502 admittance Y referred to as the reflected admittance ⁇ Y r with reference to FIG. 5A, a change ⁇ Y with respect to the admittance Y 11,0 as measured in absence of a foreign object.
  • Presence of an object e.g., object 110
  • a change ⁇ Y in the admittance Y 11 (e.g., due to presence of the object 110) manifests in a change ⁇ I in the current I while the voltage V 0 remains substantially unaffected. Therefore, measuring the complex current I may be equivalent to measuring the complex admittance Y 11 .
  • the complex current I may be indicative of the complex admittance Y 11 and there may be no requirement for additionally measuring the voltage V 0 thus reducing complexity of the measurement circuit (e.g., measurement circuit 104 of FIG.1)
  • the fractional change ⁇ Y’ (or ⁇ Z’) as defined by Equations (8) and (9) and with respect to a defined test object (e.g., object 110) placed at a defined position relative to the sense coil 502 may relate to the detection sensitivity of an object detection circuit (e.g., the multi-purpose detection circuit 100 of FIG.1) based on the sense circuit 541.
  • SNR signal-to-noise ratio
  • the fractional change may reduce dynamic range requirements of the current measurement circuit 550.
  • the fractional change may be increased by optimizing the design of the sense coil 502 with respect to its geometry and its integration into the wireless power transfer structure (e.g., wireless power transfer structure 200 with reference to FIGs.2 and 3), by resonance tuning e.g., using the parallel capacitor 544, and by improving the Q-factor of the sense circuit 541.
  • Improving the Q-factor may increase the SNR, if the noise current In is predominantly circuit intrinsic noise as discussed below with reference to FIG.5G.
  • the change ⁇ Y in the admittance Y 11 caused by an object is indicative of the reflected admittance ⁇ Y r .
  • the circuit 540 may be configured to determine the angle arg ⁇ Y ⁇ and thus the angle arg ⁇ Z r ⁇ with the required accuracy.
  • measuring the admittance Y 11 including the change ⁇ Y may be subject to errors for various reasons as previously discussed with reference to the circuit 500 of FIG.5A.
  • at the measurement port 548 provides a mean to calibrate the current measurement circuit 550 and hence the admittance measurement with respect to the angle arg ⁇ Y ⁇ .
  • the sense frequency is adjusted to the local minimum of the current magnitude
  • the admittance Y 11,0 and hence the current I at the measurement port 548 may be substantially real. Otherwise stated, the angles arg ⁇ Y 11,0 ⁇ and arg ⁇ I ⁇ are substantially zero.
  • the current measurement circuit 550 is corrected by applying a phase shift such that the imaginary part of the complex current value as determined and output by the current measurement circuit 550 at this frequency vanishes.
  • the residual error may remain in the angle arg ⁇ I cal ⁇ due to the impact of the series capacitor 546 and the electrical losses in the sense circuit 541.
  • the residual angle error of an example parallel resonant configuration of the circuit 540 and for an example object 110 is provided in TABLE 2.
  • the residual error is reduced by configuring the series capacitor 546 with a capacitance C s whose admittance Y Cs is substantially larger (e.g., 10 times larger) than the parallel resonant conductance of the sense circuit 541.
  • the residual error is reduced by computing the error in the measured angle arg ⁇ Y ⁇ by estimating parameters of the sense circuit 541 (e.g., the Q-factor) at the actual sense frequency.
  • the residual error is reduced by measuring the admittance Y 11,0 at two or more substantially different frequencies and by determining the elements of an equivalent circuit model of the sense circuit 541 (e.g., the equivalent circuit model illustrated in FIG. 5G) based on the measured admittances Y 11,0 employing a best fit method.
  • these two or more frequencies include at least the frequency of the minimum and the maximum of
  • the circuit 540 may be configured to measure the impedance Z 11 and corresponding changes ⁇ Z of Z 11 as caused by the object 110, 112, 114, or vehicle 330.
  • the impedance change ⁇ Z may be indicative of the reflected admittance ⁇ Z r as previously introduced.
  • the angle arg ⁇ Z ⁇ may be subjected to an error and therefore may require calibration to reduce an error in the measurement of the angle arg ⁇ Z ⁇ and thus of the angle arg ⁇ Y r ⁇ .
  • the circuit 540 may be calibrated analogously to the parallel resonant configuration however using the local minimum of the impedance function
  • the sense frequency is adjusted to the local maximum of the current magnitude
  • the impedance Z 11,0 and hence the current I at the measurement port 548 may be substantially real. Otherwise stated, the angles arg ⁇ Z 11,0 ⁇ and arg ⁇ I ⁇ are substantially zero.
  • the current measurement circuit 550 is corrected by applying a phase shift (impedance plane rotation) as given above by Equation (15).
  • an object e.g., object 110 reflecting an admittance ⁇ Z r that is imaginary (reactive) may result in a measured current change ⁇ I cal that is substantially imaginary. Nevertheless, a residual error may remain in the angle arg ⁇ I cal ⁇ due to the transformation of ⁇ Z r to ⁇ Z in the lossy sense circuit 541.
  • the residual angle error of an example series resonant configuration of the circuit 540 and for an example object 110 is provided in TABLE 2.
  • the residual error due to the transformation of ⁇ Y r to ⁇ Z is reduced by measuring the impedance Z 11,0 at two or more substantially different frequencies, supposing absence of a foreign object, and by determining the elements of an equivalent circuit model (e.g., the equivalent circuit model of FIG. 5G) based on the measured impedances Z 11,0 employing a best fit method.
  • these two or more frequencies include at least the frequency of the minimum and the maximum of
  • the circuit 560 of FIG. 5D illustrates a further example implementation based on measuring a complex transimpedance Z 21 of a two-port inductive sense circuit (e.g., sense circuit 561, shown in FIG.5D as the circuit between the left and right dashed lines).
  • a complex transimpedance Z 21 of a two-port inductive sense circuit e.g., sense circuit 561, shown in FIG.5D as the circuit between the left and right dashed lines.
  • the transimpedance Z 21 is measured by applying, from a current source 512, a sinusoidal current I 0,1 at the sense frequency with a defined amplitude and phase to the measurement port 568 (indicated in FIG.5D by a terminal and a dashed line) and by measuring, using a voltage measurement circuit 510, the complex open-circuit voltage V 2 (amplitude and phase) at the measurement port 569 (indicated in FIG.5D by a terminal and a dashed line). The transimpedance Z 21 is then determined by dividing the measured voltage V 2 by the defined (known) current I 0,1 .
  • the sense circuit 561 of FIG.5D comprises a double-coil inductive sense element 562 composed of a first (primary) sense coil 562a having an inductance L 1 and an equivalent series resistance R 1 and a second (secondary) sense coil 562b having an inductance L 2 and an equivalent series resistance R 2 .
  • FIG. 5D also indicates a mutual inductance LM and an equivalent mutual resistance R M between the first sense coil 562a and the second sense coil 562b.
  • the equivalent resistances R 1 , R 2 , and RM include a variety of sense element intrinsic and extraneous electrical losses as previously discussed with reference to FIG.5A.
  • the sense circuit 561 further comprises a first series capacitor 564 having a capacitance C s ,1 electrically connected in series to the first sense coil 562a, a second series capacitor 565 having a capacitance C s,2 electrically connected in series to the second sense coil 562b.
  • the sense circuit 561 further comprises a first parallel inductor 566 having an inductance L p,1 electrically connected to the first capacitor 564 and in parallel to the measurement port 568 and a second parallel inductor 567 having an inductance L p,2 electrically connected to the second capacitor 565 and in parallel to the measurement port 569.
  • an inductive coupling factor: k L L M (L 1 L 2 ) -1 ⁇ 2 (16) may be defined for the two-port inductive sense element 562. Further, a two-port inductive sense element (e.g., inductive sense element 562 of FIG. 5D) may be modeled by a “T”-equivalent circuit based on inductances L 1 , L 2 , L M as illustrated in FIG.5I.
  • the reactance of C s,1 substantially compensates for the reactance of L 1 providing a local impedance minimum
  • the reactance of C s,2 substantially compensates for the reactance of L 2 providing a local impedance minimum
  • the sense circuit 561 is configured to provide a local minimum of the admittance magnitude functions
  • the sense circuit 561 is configured to provide a local minimum of the admittance magnitude function
  • the sense circuit 561 is configured to provide a local minimum of the impedance magnitude function
  • the reactance of the parallel inductors 566 and 567 is substantially higher than the impedance magnitudes
  • at least one of the series capacitors 564 and 565 is omitted and the sense circuit 561 is operated as a non-resonant or partially resonant circuit.
  • the first series capacitor 564 in combination with the first parallel inductor 566 form a 2 nd order high pass filter to attenuate a low frequency disturbance component in the voltage V 1 .
  • the second series capacitor 565 in combination with the second parallel inductor 567 form a 2 nd order high pass filter to attenuate a low frequency disturbance component in the voltage V 2 for purposes as previously discussed in connection with FIG.5A.
  • the sense circuit 561, the sense coils 562a and 562b, and the respective capacitors 564, 565 and the respective inductors 566, 567 may correspond e.g., to the inductive sense circuit 106a, the inductive sense element 107a (double sense coil), and the respective associated capacitive elements, respectively.
  • the circuit 560 of FIG.5D may also include parasitic capacitances (not shown in FIG.5D) such as the self-capacitances (intra winding capacitances C iw and intercoil capacitance), the ground capacitances Cgnd, and the capacitances Cwpt between each of the sense coils 562a and 562b and the WPT coil (e.g., WPT coil 202 of FIG. 2). These capacitances and the associated electric stray fields may cause a certain sensitivity of the circuit 560 on substantially non-conductive, dielectric objects (e.g., object 112).
  • parasitic capacitances such as the self-capacitances (intra winding capacitances C iw and intercoil capacitance), the ground capacitances Cgnd, and the capacitances Cwpt between each of the sense coils 562a and 562b and the WPT coil (e.g., WPT coil 202 of FIG. 2).
  • transimpedance measurement techniques such as the voltage source current measurement technique or any other combination may apply (e.g., a current source current measurement technique).
  • at least one of the impedances Z 11 and Z 22 of the sense circuit 561 is additionally measured to the transimpedance Z 21 (e.g., using one or more of the techniques as previously discussed with reference to FIG. 5A).
  • presence of an object e.g., object 110 is determined based on a change in at least one of an impedance Z 11 , Z 22 , and Z 21 .
  • At least one of an impedance transformation and balancing may apply to at least one of the primary-side and secondary-side of the sense circuit 561 (not shown herein). More specifically, with reference to the circuit 521 of FIG. 5B, a transformer (e.g., transformer 526) may be used instead of the parallel inductors 566 and 567. Alternatively, with reference to the sense circuit 541 of FIG. 5C, a series capacitor and a parallel capacitor (e.g., capacitors 546 and 544, respectively) may apply at least on the primary side.
  • FIG. 5D also illustrates the objects 110, 112, and 114 proximate to the inductive sense element 562.
  • presence of the object 110, 112, 114, or vehicle 330 may cause a change in one or more electrical characteristics of the sense circuit 561. As non-limiting examples, it may change the self- inductances L 1 and L 2 , the equivalent series resistances R 1 and R 2 , the mutual inductance L M , and the mutual equivalent series resistance RM generally resulting in a change ⁇ Z with respect to the transimpedance Z 21,0 as measured in absence of a foreign object. Presence of an object (e.g., object 110) may be determined if ⁇ Z satisfies certain criteria (e.g., the magnitude of ⁇ Z exceeds a detection threshold).
  • certain criteria e.g., the magnitude of ⁇ Z exceeds a detection threshold
  • a change ⁇ Z in the measured impedance Z 21 may also be caused by a vehicle (e.g., vehicle 330, not shown in FIG. 5D), which may indicate presence of a vehicle above the inductive sense element 562.
  • an impedance change ⁇ Z may also be caused by a substantially non-conductive, dielectric object (e.g., object 112 or 114) proximate to at least one of the sense coils 562a and 562b as previously discussed with reference to FIG.1.
  • a dielectric object e.g., object 112 or 114 proximate to at least one of the sense coils 562a and 562b may change one or more of the parasitic capacitances as mentioned above.
  • measuring the complex voltage V 2 may be equivalent to measuring the complex transimpedance Z 21 .
  • the complex voltage V 2 may be indicative of the complex transimpedance Z 21 and there may be no requirement for additionally measuring the current I 0,1 thus reducing complexity of the measurement circuit (e.g., measurement circuit 104 of FIG.1)
  • it may be useful to define the normalized transimpedance change of a two- port sense circuit (e.g., sense circuit 561 of FIG.5D) as: ⁇ Z’ (Z 21 - Z 21,0 )/
  • ⁇ Z/
  • (19) and, correspondingly, the normalized transadmittance change as: ⁇ Y’ (Y 21 -Y 21,0 )/
  • ⁇ Y/
  • the fractional change ⁇ Z’ (or ⁇ Y’) caused by a defined test object (e.g., object 110) placed at a defined position relative to the inductive sense element 562 may relate to the detection sensitivity of an object detection circuit (e.g., the multi-purpose detection circuit 100 of FIG. 1) based on a two-port inductive sense circuit (e.g., sense circuit 561). Increasing the fractional change ⁇ Z’ (or ⁇ Y’) may increase a detection sensitivity of the circuit 560.
  • the fractional change may be increased by optimizing the design and arrangement of the sense coils 562a and 562b, their integration into the wireless power transfer structure (e.g., wireless power transfer structure 200 with reference to FIGs.2 and 3), by resonance tuning e.g., using the series capacitors 564 and 565 as previously described, and by improving a Q-factor of the sense circuit 561.
  • SNR signal-to- noise ratio
  • the fractional change ⁇ Z’ (or ⁇ Y’) is substantially increased by configuring and arranging the sense coils 562a and 562b such that the mutual inductance LM substantially vanishes in absence of a foreign object, resulting in a transimpedance
  • Example implementations of double sense coil arrangements providing a substantially zero mutual inductance LM are described in U.S. Patent application 16/358,534, titled Foreign Object Detection Circuit Using Mutual Impedance Sensing, the entire contents of which are hereby incorporated by reference.
  • FIG. 5E illustrates yet a further example implementation based on measuring a complex transimpedance Z 21 of a two-port inductive sense circuit 581 (shown in FIG. 5E as the circuit between the left and the right dashed line).
  • the transimpedance Z 21 is measured by applying, from a current source 512, a sinusoidal current I 0,1 at the sense frequency with a defined amplitude and phase to the measurement port 588 (indicated in FIG.5E by a terminal and a dashed line) and by measuring, using a voltage measurement circuit 510, the complex open- circuit voltage V 2 (amplitude and phase) at the measurement port 589 (indicated in FIG. 5E by a terminal and a dashed line).
  • the transimpedance Z 21 is then determined by dividing the measured voltage V 2 by the defined (known) current I 0,1 .
  • the sense circuit 581 of FIG. 5E comprises a double-coil inductive sense element 562 with reference to FIG. 5D composed of the first sense coil 562a having an inductance L 1 and an equivalent series resistance R 1 and a second sense coil 562b having an inductance L 2 and an equivalent series resistance R 2 .
  • FIG. 5E also indicates the mutual inductance LM and the equivalent mutual resistance R M .
  • the equivalent resistances R 1 , R 2 , and R M include a variety of sense element intrinsic and extraneous electrical losses as previously discussed with reference to FIG.5A.
  • the sense circuit 561 further comprises a series capacitor 584 having a capacitance C s electrically connected to the second terminal of the sense coils 562a and 562b, a first parallel inductor 586 having an inductance L p,1 electrically connected to the first terminal of the sense coil 562a and in parallel to the measurement port 588 and a second parallel inductor 587 having an inductance L p,2 electrically connected to the first terminal of the sense coil 562b and in parallel to the measurement port 589.
  • the circuit 580 further illustrates the sense signal current source 512 and the voltage measurement circuit 510 electrically connected to the measurement ports 588 and 589, respectively. [0230] Though not indicated in FIG.
  • the series capacitor 584 and the parallel inductors 586, 587 may cause electrical losses that may be represented by respective equivalent series resistances.
  • the sense coils 562a and 562b are tightly coupled resulting in an inductive coupling factor kL as defined by Equation (16) that is near unity (kL ⁇ 1).
  • Example implementations of double-coil inductive sense elements 562 providing an inductive coupling factor kL near unity are described in U.S. Patent application 16/358,534, titled Foreign Object Detection Circuit Using Mutual Impedance Sensing, the entire contents of which are hereby incorporated by reference.
  • the sense circuit 581 may be configured to provide a local minimum in the transimpedance magnitude function
  • the sense circuit 581 may be configured to provide a local minimum in the transadmittance magnitude function
  • the reactance of the series capacitor 584 substantially compensates for the reactance of the mutual inductance L M providing a local minimum in the transimpedance magnitude function
  • FIG.5I illustrating a “T” equivalent circuit model 562-1 of the two-port inductive sense element 562 and by considering the capacitance C s of the capacitor 584 inserted in series to the mutual inductance LM.
  • C s the capacitance of the capacitor 584 inserted in series to the mutual inductance LM.
  • both the series inductances L 1 - LM and L 2 - LM become substantially zero.
  • the inductance L p,1 and L p,2 of the parallel inductor 586 and 587, respectively may be similar or larger than the inductance L 1 and L 2 of the sense coils 562a and 562b, respectively.
  • the impedance magnitude of the parallel inductor 586 and 587 may be substantially higher than the impedance magnitude
  • the parallel inductors 586 and 587 may exert a negligible impact on the impedances and transimpedance
  • the reactance of the series capacitor 584 overcompensates for the reactance of the mutual inductance L M at the nominal sense frequency.
  • the residual capacitive susceptance of the series connection of the capacitor 584 and the mutual inductance LM is substantially compensated for by the susceptance of the parallel inductors 586 and 587 providing a transadmittance Y 21,0 that is substantially real (resistive).
  • the inductances L p,1 and L p,2 of the parallel inductors 586 and 587, respectively may be smaller, similar, or larger than the inductance L 1 and L 2 of the sense coils 562a and 562b, respectively.
  • the admittance magnitude of each of the parallel inductors 586 and 587 may be substantially (e.g., 20 times) higher than the admittance magnitudes
  • the parallel inductors 586 and 587 exert a significant impact on the admittance and transadmittance magnitudes
  • the parallel inductors 586 and 587 together with the series capacitor 584 are used for purposes of resonance tuning and transimpedance transformation, e.g., to transform the transimpedance Z 21 to match the sense circuit 581 with an operating transimpedance range as previously mentioned with reference to FIG. 1.
  • the inductance ratios L 1 /L p,1 and L 2 /L p,2 may be parameters to control the impedance magnitudes
  • Impedance and transimpedance transformation may be particularly effective, if the sense circuit 581 is configured for parallel resonance.
  • increasing the inductance ratios L 1 /L p,1 and L 2 /L p,2 while maintaining parallel resonance at the nominal sense frequency, may substantially increase the admittance magnitudes
  • increasing the inductance ratios L 1 /L p,1 and L 2 /L p,2 while maintaining resonance at the nominal sense frequency, may also somewhat decrease the impedance magnitudes
  • the series capacitor 584 in combination with the first parallel inductor 586 form a 2 nd order high pass filter to attenuate a low frequency disturbance component in the voltage V 1 .
  • the second series capacitor 584 in combination with the second parallel inductor 587 form a 2 nd order high pass filter to attenuate a low frequency disturbance component in the voltage V 2 for purposes as previously discussed in connection with FIG.5A.
  • the sense circuit 581, the sense coils 562a and 562b, and the capacitor 584 may correspond e.g., to the inductive sense circuit 106a, the inductive sense element 107a (double sense coil), and the respective associated capacitive element, respectively.
  • FIG. 5E also illustrates the objects 110, 112, and 114 proximate to the inductive sense element 562. As previously discussed with reference to FIG.1, presence of the object 110, 112, 114, or vehicle 330 may cause a change in one or more electrical characteristics of the sense circuit 561 as previously discussed with reference to FIG.5D.
  • the change ⁇ Z may be primarily related to a change in the mutual inductance LM and the equivalent mutual resistance RM.
  • the fractional change ⁇ Z’ (or ⁇ Y’) caused by a defined test object may relate to the detection sensitivity of the sense circuit 581.
  • an inductive sense element 562 with k L ⁇ 1 reduces the impact of the equivalent series resistances R 1 and R 2 on the fractional change, if compared e.g., to the circuit 500 of FIG.5A.
  • the fractional change of the sense circuit 581 with k L ⁇ 1 is governed by the Q-factor: Q M ⁇ ⁇ L M /R M (22) of the inductive sense element 562 with respect to L M and R M .
  • the impedance change ⁇ Z may reflect electrical properties of the object 110, 112, or 114 as discussed with reference to the circuit 500 of FIG.5A.
  • FIGs. 5F and 5G illustrate an equivalent circuit model 500-1 and 540-1, respectively, used below for purposes of a theoretical analysis and performance comparison. More specifically, the equivalent circuit model 500-1 is used to analyze the circuit 500 of FIG. 5A and the circuit 520 of FIG. 5B (using the transformer 526), while the equivalent circuit model 540-1 serves for the analysis of the circuit 540 of FIG. 5C.
  • Each of the circuits 500, 520, and 540 are analyzed with respect to its series and parallel resonant configuration and with respect to various characteristics such as the impedance and the Q-factor of the sense circuit at resonance, the fractional change, and various SNRs as defined below.
  • an identical sense coil 502 an equal sense coil current level
  • the equivalent circuit model 500-1 as illustrated in FIG.5F comprises the sense coil’s 502 inductance L and its equivalent series resistance R, the series capacitor’s 504 capacitance C s the parallel inductor’s 506 inductance L p and its equivalent series resistance R Lp , an ideal sense signal current source 512 and an ideal voltage measurement circuit 510. It may be appreciated that in practical implementations, losses in capacitors are generally substantially lower than losses in inductors. Therefore, the equivalent series resistance of series capacitor 504 is neglected (not shown) in the equivalent circuit model 500-1 of FIG. 5F.
  • the equivalent circuit model 500-1 includes an impedance ⁇ Z r in series to the inductance L representing the reflected impedance of the object 110, 112, or 114 proximate to the sense coil 502. (The reflected impedance ⁇ Z r may be regarded as the object 110, 112, or 114 as illustrated in FIG.5A abstracted away).
  • the equivalent circuit model 500-1 also includes a noise voltage source V sn in series to the inductance L representing the noise voltage inductively and capacitively coupled into sense coil 502 by the magnetic and electric field as generated when WPT is active.
  • the noise voltage V sn may include any low frequency component (e.g., at the fundamental of the WPT operating frequency and harmonics thereof) as well as any high frequency component (e.g., switching noise at the sense frequency).
  • the impedance Z 11 at the measurement port 508 of the circuit 500 of FIG.5F in presence of an object may be expressed as: Z 11 ⁇ R + (j ⁇ C s ) -1 + j ⁇ L + ⁇ Z r (27)
  • occurs substantially at an angular frequency ⁇ satisfying: (j ⁇ C s ) -1 + j ⁇ L ⁇ 0 (28) yielding the series resonant angular frequency: ⁇ s ⁇ (L C s ) -1/2 (29)
  • Equation (3) the fractional change ⁇ Z’ for the series resonant configuration of the circuit 500 of FIG.5F becomes approximately: ⁇ Z’ ⁇ ⁇ Z r /R s ⁇ ⁇ Z r /R (32)
  • Equation (6) the definition of Equation (6) of the normalized reflected impedance ⁇ Z r ‘ at ⁇ s and defining a Q-factor of the series resonant configuration of the circuit 500 of FIG.5F: Q s ⁇ ⁇ s L/R s (33) which approximately equals the Q-factor of the sense coil 502 at the series resonant frequency:
  • Q ⁇ s L/R ⁇ Q s (34)
  • the fractional change may also be written in terms of ⁇ Z r ‘ and Q s as: ⁇ Z’ ⁇ Q s ⁇ Z r ‘ (35) Equation (35) shows that reactance compensation in the series resonant configuration of the circuit 500 of FIG.
  • the admittance Y 11,0 of Equation (42) at ⁇ p may be expressed as: Y 11,0 ⁇ G p ⁇ n L ((Q/Q Lp ) + n L )/(Q ⁇ p L) (48)
  • the parallel resonant conductance G p becomes approximately: G p ⁇ n L 2 /(Q ⁇ p L) (49)
  • the parallel resonant configuration of the circuit 500 of FIG.5A is employed as an alternative to using a transformer (e.g., transformer 526 of FIG. 5B) for transforming the admittance Y 11 to be within a suitable operating range as previously discussed with reference to FIG.5B.
  • a transformer e.g., transformer 526 of FIG. 5B
  • the angle arg ⁇ Y ⁇ of the measured admittance change ⁇ Y is indicative of the angle arg ⁇ Z r ⁇ .
  • the accuracy of the measured angle may be improved by applying calibration.
  • Qp ⁇ p (L p + L)/(R + R Lp ) ⁇ n L (1 + n L )/(G p ⁇ p L) (51) which may be also expressed in terms of the Q-factors Q and Q Lp as:
  • Q p Q (1 + n L )/((Q/Q Lp ) + n L ) (52) using the definition of Equation (6) of the normalized reflected impedance at ⁇ p , and applying Equations (51) and (47) to Equation (50), the fractional admittance change ⁇ Y’ may also be written as: ⁇ Y’ ⁇ Qp
  • of the parallel resonant configuration is approximately 1/2 of the fractional change
  • amounts to about 4/5 of
  • the drive current level I 0 , the resulting voltage V at the measurement port 508, and the drive power level P are considered. In some implementations based on the circuit 500 of FIG.
  • the current level I 0 of the current source 512 is adjusted to achieve a specified current level
  • the current level I 0 approximately equals
  • Equations (42), (47), and (51) for the parallel resonant configuration of the circuit 500 of FIG.5F, it can be shown that the current
  • the SNR may determine the sensitivity of the multi- purpose detection circuit 100. It may be distinguished between the intrinsic SNR (the sense signal- to-circuit intrinsic noise ratio) and the extrinsic SNR (the sense signal-to-circuit extrinsic noise ratio).
  • circuit intrinsic noise may include contributions from the noise current I 0,n caused by the current source 512 and from noise inherent to the voltage measurement circuit 510. Further, it may include a contribution from thermal noise of the loss resistances R and R Lp inherent to the sense circuit 501.
  • Circuit extrinsic noise may include any disturbance signal component inductively and capacitively coupled into the sense coil 502 (e.g., via the magnetic and electric field as caused by the WPT system when active).
  • circuit extrinsic noise may prevail when WPT is active, while circuit intrinsic noise may determine the SNR when WPT is inactive.
  • the multi-purpose detection circuit 100 is also used when WPT is inactive (e.g., for determining presence of a foreign object, a vehicle, a type of vehicle, or the position of a vehicle).
  • It may be further distinguished between a narrowband SNR resulting at the nominal sense frequency in the bandwidth of the voltage measurement circuit 510 and a broadband SNR defined in a larger bandwidth e.g., also covering the WPT operating frequency.
  • the former mainly relates to the sensitivity of a multi-purpose detection circuit 100, while the latter may determine the dynamic range and filtering requirements of the voltage measurement circuit 510.
  • denotes the magnitude of the change in the measured voltage V due to the presence of an object (e.g., object 110) and Vn the additive noise voltage component as indicated in the circuit 500 of FIG. 5F.
  • may refer to the r.m.s. voltage and V n to the r.m.s.
  • This noise voltage V n may include circuit intrinsic and extrinsic noise components as discussed above.
  • the SNR as given by Equation (10) is referred herein as to the differential narrowband SNR.
  • SNR W
  • the differential narrowband extrinsic SNR for the series resonant configuration of the circuit 500 of FIG.5F may be expressed as: ⁇ SNR ex,s ⁇
  • /V sn
  • the noise current I 0,n as indicated in FIG. 5F may cause the predominant contribution in V n when WPT is inactive.
  • the noise voltage V n for the series resonant configuration is approximately: Vn ⁇ R I 0,n (65) while the voltage change
  • (66) Applying Equations (35), (65), and (66) to Equation (10), the differential narrowband intrinsic SNR with respect to the noise current I 0,n for the series resonant configuration of the circuit 500 of FIG.5F may be expressed as: ⁇ SNR int,s ⁇ (
  • the differential narrowband intrinsic SNR with respect to the noise current I 0,n for the parallel resonant configuration of the circuit 500 of FIG.5F may be expressed as: ⁇ SNR int,p ⁇ (
  • a thermal noise voltage is generated by the series equivalent loss resistances R Lp and R.
  • Equation (66) and (74) provides for the differential narrowband intrinsic SNR with respect to thermal noise for the series resonant configuration of the circuit 500 of FIG.5F: ⁇ SNR int,s ⁇
  • /Vn ⁇
  • the thermal noise voltage Vn as resulting at parallel resonance may be considered as the thermal noise generated by the parallel resonant conductance G p as defined by Equation (42).
  • the disturbance signal voltage V sn may relate to the WPT coil current I WPT as follows: V sn ⁇ V sW ⁇ ⁇ W L sW I WPT (80) where L s W denotes the mutual inductance between the sense coil 502 and the WPT coil (e.g., WPT coil 202 with reference to FIGs.2 and 3).
  • the factor ( ⁇ W / ⁇ s ) 2 /n L may be considered as the attenuation of the low frequency induced voltage V sW by the high pass filter effect of the sense circuit 501.
  • the broadband extrinsic SNR for the series resonant configuration of the circuit 500 of FIG.5F may be expressed in terms of the Q-factor Q s and the inductance ratio n L as: SNRW,s ⁇ (
  • V n V W ⁇ V sW ⁇ W C s ⁇ W L p ⁇ V sW ( ⁇ W / ⁇ p ) 2 /(1 + n L ) (86)
  • the factor ( ⁇ W / ⁇ p ) 2 /(1 + n L ) may be considered as the attenuation of the low frequency induced voltage V sW by the high pass filter effect of the sense circuit 501.
  • the broadband extrinsic SNR with respect to the WPT fundamental disturbance voltage component V sW for the parallel resonant configuration of the circuit 500 of FIG.5F may be expressed as: SNR W,p ⁇ (
  • the temperature sensitivity as defined by Equations (11) and (12) for the real and imaginary part of Z 11 , respectively, is considered.
  • Equation (89) shows that the real part temperature sensitivity reduces as the Q-factor Q s of the sense circuit 501 increases.
  • the imaginary part temperature sensitivity may not improve and may only reduce by lowering a temperature coefficient associated with the inductive and capacitive elements of the sense circuit 501.
  • components and materials with a low temperature coefficient e.g., NP0-type capacitors are used.
  • temperature sensitivity is reduced e.g., using a combination of components or materials with a positive temperature coefficient and components or materials with a negative temperature coefficient in a manner such that the overall thermal drift is cancelled out.
  • Equations (8) to (89) may also apply to the circuit 520 of FIG.
  • L ⁇ denotes the transformer’s 526 secondary referred leakage inductance
  • Rw its secondary referred equivalent series resistance with respect to the conductor losses
  • L m its secondary referred main inductance
  • R m its secondary referred equivalent series resistance with respect to the core losses with reference to FIG. 5H.
  • L ⁇ is a substantial portion of L + L ⁇
  • the normalized reflected impedance ⁇ Z r ‘ can be replaced by ⁇ Z r ‘ L/(L + L ⁇ ).
  • the correction factor L/(L + L ⁇ ) can be applied to the normalized reflected admittance ⁇ Y r ‘.
  • the ratio nT:1 refers to the transformation ratio of the ideal transformer as used in the transformer’s 526 equivalent circuit model with reference to FIG. 5H.
  • the factor ⁇ determines the impact of the transformer’s main inductance L m on the measured impedance Z 11,0 and hence on the angle arg ⁇ Z ⁇ as relevant for purposes of object discrimination as previously discussed with reference to FIG. 5A.
  • the factor ⁇ is referred herein as to the transformer impact factor.
  • Equation (95) may also be written as:
  • ⁇ R s ⁇ n T 2 (R + R w ) ⁇ n T 2 (( ⁇ s L/Q) + ( ⁇ s L m /Q w )) ⁇ n T 2 ⁇ s L m / ⁇ (95) yielding for the inductance ratio n L for satisfying Equation (92): n L L/L m ⁇ (Q/ ⁇ ) - (Q/Qw) > 0 (96) Equation (95) may also be written as:
  • the transformer impact factor ⁇ represents a trade-off between an error in the measured impedance change ⁇ Z (e.g., with respect to the angle arg ⁇ Z r ⁇ as previously discussed with reference to FIG. 5A) and a degradation of the fractional change
  • Equation (104) the Q-factor for the parallel resonant configuration of the sense circuit 521 may be expressed as: Qp ⁇ ⁇ p (L + L m )/(R + RW + R Lm ) ⁇ Q (1 + n L )/(n L + (Q/Qw) + (Q/Q Lm )) (106) and the fractional change using Equation (53): ⁇ Y’ ⁇ Q p ⁇ Z r ‘ n L /(1 + n L ) ⁇ Q ⁇ Z r ‘ n L /(n L + (Q/Q w ) + (Q/Q Lm )) (107) As n L increases, the factor Q p n L /(1 +
  • this factor may be Q/3.
  • the fractional change ⁇ Y‘ may equal ⁇ Z‘ of the series resonant configuration of the circuit 520 of FIG. 5B as given by Equation (100).
  • a transformer e.g., transformer 526) is indispensable e.g., for purposes of balancing as previously discussed with reference to FIG. 5B, decreasing the inductance ratio n L rather than nT may result in a larger fractional change.
  • the equivalent circuit model 540-1 as illustrated in FIG.5G comprises the sense coil’s 502 inductance L and its equivalent parallel conductance G, the parallel capacitor’s 544 capacitance C p , and the series capacitor’s 546 capacitance C s , an ideal sense signal voltage source 552, and an ideal current measurement circuit 550. It may be appreciated that in practical implementations, losses in the capacitors are generally substantially lower than losses in inductors. Therefore, the equivalent series resistance of the capacitors 544 and 546 are neglected (not shown) in the equivalent circuit model 540-1 of FIG. 5G.
  • the equivalent circuit model 540-1 includes an admittance ⁇ Y r in parallel to the inductance L representing the reflected admittance of the object 110, 112, or 114 proximate to the sense coil 502. (The reflected admittance ⁇ Z r may be regarded as the object 110, 112, or 114 as illustrated in FIG. 5C abstracted away).
  • the equivalent circuit model 540-1 also includes a noise current source Isn in parallel to the inductance L representing the noise current inductively and capacitively coupled into the sense coil 502 by the magnetic and electric field, respectively, as generated when WPT is active.
  • the noise current I sn may include any low frequency component (e.g., the fundamental of the WPT operating frequency and harmonics thereof) as well as any high frequency component (e.g., switching noise at the sense frequency).
  • ⁇ Z r ’ ⁇ Z r ’ (108) G ⁇ R/( ⁇ L) 2 (109) ⁇ Z r ⁇ ⁇ Z r /( ⁇ L) 2 (110) Isn ⁇ V sn /( ⁇ L) (111) with ⁇ Y r ’, ⁇ Z r ’, ⁇ Z r , R, and V sn referring to the normalized reflected admittance, the normalized reflected impedance, the reflected impedance of the object 110 in the sense coil 502, the equivalent series resistance of the sense coil 502, and the disturbance voltage V sn with reference to the circuit 500 of FIG.5F, respectively.
  • the admittance Y 11 at the measurement port 548 of the circuit 540 of FIG.5G in presence of an object may be expressed as: Y 11 ⁇ G + (j ⁇ L) -1 + j ⁇ C p + ⁇ Y r (115)
  • occurs substantially at an angular frequency ⁇ satisfying: (j ⁇ L) -1 + j ⁇ C p ⁇ 0 (116) yielding the parallel resonant angular frequency: ⁇ p ⁇ (L C p ) -1/2 (117)
  • Equation (126) may be approximated as: Z 11 ⁇ (j ⁇ C s ) -1 + (j ⁇ C p + (j ⁇ L) -1 ) -1 + (G + ⁇ Y r ) ( ⁇ C p + ( ⁇ L) -1 ) -2 (127)
  • occurs substantially at an angular frequency ⁇ satisfying: (j ⁇ L) -1 + j ⁇ (C p + C s ) ⁇ 0 (128) yielding for the series resonant angular frequency: ⁇ s ⁇ (L (C p +
  • a transformer e.g., transformer 526 of FIG. 5B
  • the voltage level V 0 of the voltage source 542 is adjusted to achieve a specified current level
  • the voltage level V 0 approximately equals the voltage across the sense coil 502 providing the relation: V 0 ⁇ ⁇ p L
  • the current I at the measurement port 548 may be expressed approximately as: I ⁇
  • ⁇ p L G
  • /Q (141) and the drive power level: P ⁇ V 0 I
  • across the sense coil 502 is approximately:
  • ⁇ s C s ⁇ s 2 L
  • C s /(C s + C p )
  • may refer to the r.m.s. current and I n to the r.m.s. noise current as measured at the nominal sense frequency in the bandwidth B m of the current measurement circuit 550.
  • This noise current I n may include circuit intrinsic and extrinsic noise components as discussed above.
  • the SNR as given by Equation (14) is referred herein as to the differential narrowband SNR.
  • SNR W
  • denotes the magnitude of the sense signal current and IW the disturbance current at the fundamental WPT operating frequency, which may be a prominent component in In when WPT is active. More specifically, the current
  • the differential narrowband extrinsic SNR of the parallel resonant configuration of the circuit 540 of FIG.5G may be expressed as: ⁇ SNR ex,p ⁇
  • /Isn
  • /I sn (148) with I sn the noise current as illustrated in FIG.5G.
  • Equation (148) also applies to the series resonant configuration, meaning that: ⁇ SNR ex,s ⁇ ⁇ SNR ex,p (149)
  • the noise current I n in the parallel resonant configuration of the circuit 540 is approximately: In ⁇ G p V 0,n (150) and the current change in presence of an object (e.g., object 110) is:
  • the differential narrowband intrinsic SNR with respect to the noise voltage V 0,n for the parallel resonant configuration of the circuit 540 of FIG.5G may be expressed as: ⁇ SNR int,p ⁇ (
  • Equation (14) the differential narrowband intrinsic SNR with respect to the noise voltage V 0,n for the series resonant configuration of the circuit 540 of FIG.5G may be expressed as: ⁇ SNR int,s ⁇ (
  • a thermal noise current is generated by the equivalent parallel conductance G of the sense coil 502.
  • the differential narrowband intrinsic SNR with respect to thermal noise of the parallel resonant configuration of the circuit 540 may be expressed as: ⁇ SNR int,p ⁇
  • I sn I sW (165) 1/( ⁇ W C p ) >> ⁇ W L (166) and using Equation (117), the disturbance current component IW in the current I for the parallel resonant configuration of the circuit 540 of FIG.5G becomes approximately:
  • I n I W ⁇ I sW ⁇ W L ⁇ W C s ⁇ I sW ( ⁇ W / ⁇ p ) 2 /n C (167)
  • the factor ( ⁇ W / ⁇ p ) 2 /n C may be considered as the attenuation of the low frequency induced current I sW by the high pass filter effect of the sense circuit 541.
  • the broadband extrinsic SNR of the parallel resonant configuration of the circuit 540 of FIG.5G may be expressed as: SNR W,p ⁇ (
  • Equation (169) may also be written as: SNR W,p ⁇ (
  • Equation (174) may also be written as: SNRW,s ⁇ (
  • Values for the induced disturbance voltage V sW , the noise voltage V sn , and their equivalent respective currents I sW and I sn of the circuit 540 may be considered typical for the multi-purpose detection circuit 100 integrated into a wireless power transfer structure (e.g., wireless power transfer structure 200 with reference to FIG.2).
  • the normalized reflected impedance of the object 110 as given in TABLE 1 may be typical for a paperclip placed on the surface of the wireless power transfer structure 200 at a worst case position 3 mm above the sense coil 502 (e.g., inductive sense element 107a) with a form factor of 60 x 80 mm.
  • may be within a constraint given by an electromagnetic emission limit of an established electromagnetic compatibility (EMC) standard (e.g., EN 300330).
  • EMC electromagnetic compatibility
  • /V 0,n for the circuit 500 and 540, respectively, may be typical for a digital implementation of a sense signal source (e.g., sense signal current source 512 and sense signal voltage source 552), respectively, as previously described with reference to FIG.4.
  • TABLE 1 [0307] Numerical results as obtained from a circuit analysis using the numerical assumptions of TABLE 1 are listed in TABLE 2. While the SNR values are obtained using the corresponding approximate equations as defined above with reference to FIGs.
  • TABLE 2 also includes numerical results for the angle error in the measured impedance change ⁇ Z e.g., in presence of the object 110.
  • a multipurpose detection circuit 100 employing an angle calibration procedure as previously described with reference to FIGs. 5A. For the series resonant configuration of the circuit 500 of FIG.
  • the angle error is defined as: ⁇ ⁇ arg ⁇ Z exp(-j arg ⁇ Z 11,0 ⁇ ) ⁇ - arg ⁇ Z r ’ ⁇ (178) where ⁇ Z exp(-j arg ⁇ Z 11,0 ⁇ ) denotes the impedance change with the angle correction applied.
  • TABLE 2 includes the drive current level I 0 , the drive power level P required to drive the sense coil 502 of the sense circuit 501 with the sense current
  • the drive voltage level V 0 the drive power level P required to drive the sense coil 502 of the sense circuit 541 with the sense current
  • TABLE 2 [0308] Based on the numerical results of TABLE 2, the following conclusions may be drawn.
  • n C 1
  • the results in TABLE 2 show circuits and configurations equivalent in terms of the differential narrowband extrinsic SNR (WPT switching noise).
  • the numbers for the differential narrowband intrinsic SNR show the parallel resonant configuration of the circuit 500 slightly inferior to the other circuits and configurations.
  • the high numbers obtained for the differential narrowband intrinsic SNR show that thermal noise is negligible, even when WPT is inactive.
  • the numbers resulting for the broadband extrinsic SNR show a substantial difference (> 60 dB) between the parallel resonant configuration of the circuit 500 and 540.
  • the series resonant configuration of the circuit 500 and 540 are almost equivalent and the SNRs are slightly above 6 dB, which may be a minimum requirement in a practical implementation.
  • TABLE 2 further shows a negligible angle error
  • FIG. 5H illustrates an “L” equivalent circuit model 526-1 applicable to the non-ideal transformer 526 and 726 with reference to the circuit 520 of FIG.5B and the circuit 720 of FIG. 7C, respectively.
  • the “L” equivalent circuit comprises an ideal transformer (indicated by the infinity symbol) with transformation ratio nT:1, a secondary referred main inductance L m , and a secondary referred series (leakage) inductance L ⁇ .
  • FIG. 5H illustrates an “L” equivalent circuit model 526-1 applicable to the non-ideal transformer 526 and 726 with reference to the circuit 520 of FIG.5B and the circuit 720 of FIG. 7C, respectively.
  • the “L” equivalent circuit comprises an ideal transformer (indicated by the infinity symbol) with transformation ratio nT:1, a secondary referred main inductance L m , and a secondary referred series (leakage) inductance L ⁇ .
  • FIG. 5I illustrates a “T”-equivalent circuit model 562-1 applicable to the double-coil inductive sense elements 562 used in the circuit 560 of FIG. 5D and the circuit 580 of FIG. 5E.
  • the circuit model 562-1 comprises three inductances connected in a “T”-topology and related to the inductance L 1 , L 2 , and the mutual inductance LM as indicated in FIGs.5D and 5E.
  • FIG.5J illustrates another equivalent circuit model 562-2 applicable to the double-coil inductive sense element used in the circuit 560 of FIG. 5D and the circuit 580 of FIG. 5E.
  • the circuit model 562-2 comprises the inductances L 1 and L 2 in series to the respective current- controlled voltage sources Vind,1 and Vind,2 representing the voltage induced into the first and second sense coil, respectively.
  • FIG.5K shows a table of a summary of selected equations with respect to the resonant frequency, the Q-factor of the sense circuit, the impedance/admittance of the sense circuit, the fractional change, and the various SNRs for the series and parallel resonant configurations of the circuit 500 of FIG. 5F and the circuit 540 of FIG. 5G. As previously noted, these equations are valid for the assumptions made with reference to FIGs.5F and 5G.
  • FIG.5K shows a table of a summary of selected equations with respect to the resonant frequency, the Q-factor of the sense circuit, the impedance/admittance of the sense circuit, the fractional change, and the various SNRs for the series and parallel resonant configurations of the circuit 500 of FIG. 5F and the circuit
  • FIG. 6 illustrates a complex plane 600 or more precisely a complex half plane comprising quadrant 1 and 4 where the reflected impedances ⁇ Z r of different types (categories) of objects (e.g., object 110a – 110d, 112, 113, 114, or vehicle 330) may occur if proximate to a sense coil (e.g., sense coil 502 with reference to FIG.5A). More specifically, FIG.6 shows shaded areas (e.g., angle ranges 602 to 610) where the reflected impedances ⁇ Z r of different types (categories) of objects (e.g., object 110a – 110d, 112, 114) may be measured at a sense frequency (e.g., in the MHz range).
  • a sense coil e.g., sense coil 502 with reference to FIG.5A
  • FIG.6 shows shaded areas (e.g., angle ranges 602 to 610) where the reflected impedances ⁇ Z r of different types (
  • the angle ranges 602 to 610 indicated in FIG. 6 may be not drawn to scale and should be considered qualitative rather than quantitative.
  • the actual angle ranges may also depend on the particular sense frequency, certain characteristics of the inductive sense element (e.g., sense coil 502), the capacitive sensing effect of the inductive sense element as previously discussed with reference to FIG.1, the position and orientation of an object relative to the inductive sense element.
  • the complex plane 600 and the shaded areas (e.g., angle ranges 602 to 610) may also apply to the reflected admittance ⁇ Y r by simply relabeling the real and imaginary axis by Re ⁇ Y r ⁇ and j Im ⁇ Z r ⁇ , respectively (not shown in FIG.6).
  • FIG.6 illustrates different types of metallic objects 110 such as a 1 € cent coin (object 110a), a metal foil (object 110b), a steel nut (object 110c), a steel nail, a fixing pin, and steel wire pieces (objects 110d).
  • metallic objects 110 such as a 1 € cent coin (object 110a), a metal foil (object 110b), a steel nut (object 110c), a steel nail, a fixing pin, and steel wire pieces (objects 110d).
  • non-living, substantially non-conductive or weakly conductive objects such as a ferrite core (object 113), a plastic bottle filled with water (object 112), and a living object 114 representing a hand (symbolizing a human extremity).
  • the angle range 602 (e.g., close to -90°) in quadrant 4 may be characteristic for an object (e.g., object 110a) exhibiting a relatively high electric conductivity (e.g., ⁇ > 50 MS/m) and that is substantially non ferromagnetic (relative permeability ⁇ r ⁇ 1) at the sense frequency.
  • a relatively high electric conductivity e.g., ⁇ > 50 MS/m
  • ⁇ r ⁇ 1 relative ferromagnetic
  • the angle range 604 (e.g., around -80°) in quadrant 4 may be characteristic for an object (e.g., 110) exhibiting a substantially lower equivalent conductivity (e.g., ⁇ > 5 MS/m) and substantially no ferromagnetic effect (relative permeability ⁇ r ⁇ 1) at the sense frequency.
  • a piece of thin foil or metallized paper (e.g., aluminum coated paper) as illustrated in FIG. 6 by object 110b (e.g., with a thickness of the metal layer smaller than the skin depth ⁇ at the sense frequency) may reflect an impedance ⁇ Z r in the angle range 604 for a sense frequency in the MHz range.
  • the angle range 606 (around 0°) in quadrant 4 and 1 may be characteristic for an object (e.g., object 110c) exhibiting a relatively high conductivity (e.g., ⁇ > 10 MS/m) and a substantial ferromagnetic effect (e.g., ⁇ r > 50) at the sense frequency.
  • An object made of ferromagnetic steel may reflect an impedance ⁇ Z r in the angle range 606 for a sense frequency in the MHz range.
  • Ferromagnetism ( ⁇ r > 1) in the metallic object 110c generally reflects an impedance ⁇ Z r with an imaginary part Im ⁇ ⁇ Z r ⁇ > 0.
  • the electrical conductivity of the metallic object 110d generally reflects an impedance ⁇ Z r with Im ⁇ Z r ⁇ ⁇ 0 and Re ⁇ Z r ⁇ > 0. Superimposing the two opposing effects may result in a net reflected impedance ⁇ Z r e.g., in the angle range 606.
  • the angle range 608 e.g., around 45°
  • the angle range 608 may be characteristic for an object (e.g., object 110d) exhibiting a relatively high conductivity (e.g., ⁇ > 10 MS/m) and a substantial ferromagnetic effect (e.g., ⁇ r > 50) at the sense frequency and with a length substantially larger than a thickness.
  • An object made of ferromagnetic steel and with such geometry may reflect an impedance ⁇ Z r in the angle range 606 for a sense frequency in the MHz range.
  • Ferromagnetism ( ⁇ r > 1) in the metallic object 110d generally reflects an impedance ⁇ Z r with a positive imaginary part that prevails the conductivity effect acting in the opposite direction as described above with reference to the object 110c.
  • Superimposing the two effects results is a net reflected impedance ⁇ Z r with a positive imaginary part (Im ⁇ Z r ⁇ > 0) substantially equal to the real part Re ⁇ Z r ⁇ corresponding to the angle range 608.
  • a reflected impedance ⁇ Z r in this angle range may also be observed from a paper clip made of ferromagnetic steel (not shown in FIG.6).
  • the angle range 610 (e.g., close to 90°) in the quadrant 1 may be characteristic for a substantially non-conductive object (e.g., object 112, object 114) that exhibits a dielectric effect ( ⁇ r > 1) at the sense frequency.
  • a dielectric object (e.g., object 112) may reflect an impedance ⁇ Z r in the angle range 610.
  • a living object e.g., object 114) may also reflect an impedance ⁇ Z r in the angle range 610.
  • dielectric objects may interact with the sense coil (e.g., sense coil 502 of FIG.5A) via the electric stray field generated by the sense coil’s parasitic capacitances (e.g., C iw , Cgnd, and Cwpt) as illustrated in FIG. 5A.
  • the angle range 610 e.g., close to 90°
  • the angle range 610 may be characteristic for a substantially non-conductive object (e.g., object 113) that exhibits a ferromagnetic effect ( ⁇ r > 1) at the sense frequency.
  • An object made of ferrite material e.g., object 113) may reflect an impedance ⁇ Z r in the angle range 610.
  • objects 110 e.g., object 110a, 110b, 110c, 110d
  • objects 110b reflecting an impedance ⁇ Z r in the respective angle ranges 602, 604, 606, and 608 or anywhere between these ranges
  • induction heating if exposed to the strong WPT magnetic field.
  • objects 110b may be subject of induction heating if exposed to the strong WPT magnetic field.
  • objects 110c and 110d may be particularly true for thin foils (e.g., object 110b) and objects that are both substantially electrically conductive and ferromagnetic (e.g., objects 110c and 110d).
  • Ferromagnetism in a metallic object e.g., object 110c
  • this object category may be characterized by the highest loss power density (e.g., in Watt per unit surface area) and thus highest heating temperatures. Therefore, it may be desirable to selectively increase a sensitivity of a multi-purpose detection circuit 100 to objects (e.g., objects 110) of this category as disclosed in U.S.
  • the inductive sense circuit (e.g., inductive sense circuit 501 of FIG. 5A using sense coil 502) may be used for capacitive sensing of living objects (e.g., a human hand, a cat, or any other animal) that are predominantly dielectric and that may be located in proximity of the sense coil.
  • living objects e.g., a human hand, a cat, or any other animal
  • the multi-purpose detection circuit 100 may be able to discriminate dielectric objects (e.g., object 112b or 114) from metallic objects (e.g., object 110) considering different measures may apply upon detection of a dielectric object (e.g., object 112 or 114) than for a metallic object (e.g., object 110b).
  • detection of a metallic object e.g., object 110b
  • the 6 may refer to the complex output of a time-differential detector.
  • An object e.g., object 110a
  • brought into proximity of the sense coil 502 may cause the time- differential detector to produce a complex output ⁇ Z/ ⁇ t whose angle arg ⁇ Z/ ⁇ t ⁇ is indicative of the angle of the reflected impedance ⁇ Z r of the object.
  • this object may cause the time-differential detector to temporarily produce an output - ⁇ Z/ ⁇ t whose angle is indicative of the angle of - ⁇ Z r (the sign inverted reflected impedance).
  • outputs of a time-differential detector may fall in all four quadrants of the complex plane 600, depending on the reflected impedance ⁇ Z r of the object and whether it is brought into or removed from the proximity of the sense coil 502.
  • discriminating objects e.g., object 112 from object 110a
  • ⁇ Z r close to the imaginary axis angle ranges 610 and 602, respectively
  • angle of complex outputs of a time-differential detector may require accurate measurement of the angle arg ⁇ Z r ⁇ .
  • an error in the measured angle of a few degrees may cause the output of the time-differential detector to infringe into the angle range 602, when the object 112 is removed from the proximity of the sense coil 502 as explained above.
  • Such event may pretend a metal object (e.g., object 110 a) brought into the proximity of sense coil 502 and a cause for a false detection.
  • a reliable discrimination between the object 112 and the object 110a based on the angle of complex outputs of a time-differential detector can hardly be achieved.
  • a wireless power transfer structure e.g., housing 328 of the wireless power transfer structure 200 with reference to FIG. 2.
  • Such water accumulation may be caused by rain, condensation, melting of snow or ice, or splashing from passing vehicles. Due to the cohesiveness of water (surface tension) and a hydrophobic plastic surface of the housing 328, water accumulation may form puddles that may be considered as a dielectric object 112.
  • a water object e.g., a water bubble, object 112 moving (flowing) on the surface of the housing 328 into the proximity of a sense coil 502 may first cause an output of the time-differential detector in the angle range 610.
  • a sense coil 502 when leaving the proximity of a sense coil 502, it may cause a complex output in the angle range 602 (due to the angle error) potentially triggering a false positive detection of a metal object (e.g., metal object 110a).
  • a metal object e.g., metal object 110a
  • the magnitude of the complex output ⁇ Z/ ⁇ t of the time-differential detector increases with the speed of movement (first time derivative) of the water object, the probability of a false positive detection of a metal object (e.g., metal object 110a) increases with the speed of the water flow.
  • some implementations of the multi-purpose detection circuit 100 employ a water flow detector configured for detecting formation and flow of water puddles.
  • Outputs of the water flow detector are used to discriminate a water object (e.g., object 112, water bubble) from a metal object (e.g., object 110a) and thus to prevent a false positive detection.
  • the water flow detector is based on a pattern recognition approach using a plurality of time series of complex outputs of a time-differential detector. Each time series is associated to a sense element of the plurality of sense elements 107a, 107b, ..., 107n in the array 107.
  • a spatial pattern is created by mapping quasi-concurrent outputs of the time- differential detector onto a two-dimensional matrix consisting of a plurality of elements arranged in lines and columns. The position of each matrix element corresponds to the position of the associated sense element in the two-dimensional array 107.
  • a temporal and spatial pattern refers to a three-dimensional matrix consisting of a plurality of elements arranged in lines, first columns, and second columns where the elements of a second column are consecutively received outputs of the time-differential detector associated to a sense coil (e.g., sense element 107a with reference to FIG.1).
  • the water flow detector is based on a pattern recognition approach using at least in part a plurality of time series of complex detector outputs indicative of the impedance Z 11 with reference to FIGs.5A to 5C.
  • the water flow detector is based on a pattern recognition approach using at least in part a plurality of time series of complex detector outputs indicative of the impedance Z 21 with reference to FIGs.
  • the water flow detector is based on a pattern recognition approach using at least in part a plurality of time series of detector outputs indicative of another electrical characteristic of a sense coil (e.g., sense element 107a) or the sense circuit (e.g., sense circuit 106a).
  • FIGs. 7A to 7I illustrate example implementations of another portion of the multi- purpose detection circuit 100 of FIG. 1 based on capacitive sensing by measuring at least one electrical characteristic (e.g., a complex impedance). These examples are to illustrate the principle of the sensing and measurement technique and do not show all the details of a multi-purpose detection circuit 100.
  • the circuits 760, 770, and 780 of FIGs. 7F to 7I, respectively, are based on measuring a one-port impedance Z 11 , while the circuits 760, 770, and 780 of FIGs. 7F to 7I, respectively, employ a two-port transimpedance Z 21 measurement at the sense frequency e.g., using a sinusoidal sense signal.
  • the sense signal is a high frequency signal with a spectrum substantially in the MHz range (e.g., in a range from 2.5 MHz to 3.5 MHz).
  • the sense signal is constraint to the range from 3.155 MHz to 3.400 MHz for frequency regulatory reasons as previously mentioned in connection with FIGs.5A to 5F. In some geographic regions or countries, this frequency range may permit higher magnetic field strength level H in the specified distance from the plurality of capacitive sense elements (e.g., the plurality of capacitive sense elements 109 of the multi-purpose detection circuit 100).
  • the ground symbol shown in the schematic diagrams of FIGs. 7A to 7I indicate a network node on ground potential referred to as the “circuit ground”. However, this should not exclude non-ground-based implementations or implementations that use different grounds on different potentials.
  • the circuit 700 of FIG.7A illustrates an example implementation based on measuring a complex impedance Z 11 of a one-port capacitive sense circuit 701 (shown in FIG. 7A as the circuit on the right side of the dashed line). More specifically, the impedance Z 11 is measured at the measurement port 708 (indicated in FIG. 7A by a terminal and a dashed line) by applying, from the current source 512, a sinusoidal current I 0 at the sense frequency (e.g., in the MHz range) with a defined amplitude and phase and by measuring, using a voltage measurement circuit 510, the complex open-circuit voltage V (amplitude and phase) as previously described with reference to FIG.5A.
  • the sense circuit 701 comprises a single-electrode capacitive sense element 702 (single- ended sense electrode 702) having a signal terminal 703, a capacitance C and an equivalent series resistance R, a series inductor 704 having an inductance L s and an equivalent series resistance R Ls electrically connected in series to the sense electrode 702 at the signal terminal 703, and a parallel inductor 706 having an inductance L p and an equivalent series resistance R Lp electrically connected to the series inductor 704 and in parallel to the measurement port 708.
  • electrical losses in the series inductor 704 and in the parallel inductor 706 are the most prominent losses in the capacitive sense circuit 701.
  • the sense electrode 702 capacitance C may include various capacitances as indicated in FIG. 7A by dashed lines. Particularly, it may include capacitance Ceg of the sense electrode 702 towards ground and a capacitance C ew towards the WPT coil 202 with reference to FIG. 2.
  • the circuit 700 further illustrates the sense signal current source 512 and the voltage measurement circuit 510 both electrically connected to the sense circuit 701 at the measurement port 708.
  • the sense electrode 702 may also include a self-inductance (not indicated in FIG.7A).
  • the associated magnetic fields may interact with a metallic object (e.g., object 110). However, this effect may be insignificant compared to that of the electric field that also interacts with a metallic object (e.g., object 110).
  • the sense circuit 701 may be configured to provide a local minimum in the impedance magnitude
  • the sense circuit 701 may be configured to provide a local minimum of the admittance magnitude function
  • (parallel resonance) substantially at the nominal sense frequency, where Y 11,0 ( 1/Z 11,0 ) refers to the admittance as presented by the sense circuit 701 at the measurement port 508 in absence of a foreign object.
  • the reactance of the series inductor 704 substantially compensates for the reactance of the sense electrode 702 at the nominal sense frequency providing an impedance Z 11,0 that is substantially real (resistive).
  • the inductance L p of the parallel inductor 706 may be similar or larger than the inductance L s of the series inductor 704.
  • the impedance magnitude of the parallel inductor 706 may be substantially (e.g., 10 times) higher than the impedance magnitude
  • the parallel inductor 706 may exert a negligible impact on the impedance
  • the reactance of the series inductor 704 undercompensates for the reactance of the sense electrode 702 at the nominal sense frequency.
  • the residual capacitive susceptance of the series connection of the inductor 704 and the sense electrode 702 is substantially compensated for by the susceptance of the parallel inductor 706 providing an admittance Y 11,0 that is substantially real (resistive).
  • the inductance L p of the parallel inductor 706 may be smaller, similar, or larger than the inductance L s of the series inductor 704.
  • the admittance magnitude of the parallel inductor 706 may be substantially (e.g., 20 times) higher than the admittance magnitude
  • the parallel inductor 706 together with the series inductor 704 are used for purposes of resonance tuning and impedance transformation, e.g., to transform the impedance Z 11 to match the sense circuit 701 with an operating impedance range as previously mentioned with reference to FIG.1.
  • the inductance ratio L s /L p may be a parameter to control the impedance magnitude
  • Impedance transformation may be particularly effective, if the sense circuit 701 is configured for parallel resonance. More specifically, increasing the inductance ratio L s /L p , while maintaining parallel resonance at the nominal sense frequency, may substantially increase the admittance
  • At least one of the series inductor 704 and the parallel inductor 706 include a variable inductor as previously discussed with reference to FIG. 5A.
  • at least one of the variable inductors 704 and 706 is used to compensate for a temperature drift, an ageing, or a detuning of the sense circuit 701 caused by an external impact and to maintain its resonance substantially at the nominal sense frequency.
  • the variable inductor 704 in combination with the variable inductor 706 are used to vary the impedance
  • the sense electrode’s 702 capacitance C in combination with the parallel inductor 706 form a 2 nd order high pass filter to attenuate a low frequency disturbance component in the voltage V for purposes as previously discussed with reference to FIG.5A.
  • This low frequency disturbance component may emanate from a disturbance current capacitively coupled into the sense electrode 702 (e.g., via capacitance C ew ) during wireless power transfer.
  • the sense circuit 701, the sense electrode 702, and the series inductor 704 may correspond e.g., to the capacitive sense circuit 108a, the capacitive sense element 109a (comprising a double-ended sense electrode that may be electrically connected in parallel to form a single-ended sense electrode), and the associated inductive element, respectively.
  • the current source 512 may include the signal generator circuit 406 and the driver circuit 402, while the voltage measurement circuit 510 may include the measurement amplifier circuit 404 and the signal processing circuit 408 with reference to FIG.4. [0349] In some implementations, the current source 512 may be characterized by a quasi-ideal current source and the voltage measurement circuit 510 by a quasi-ideal voltage measurement circuit as previously defined with reference to FIG.5A.
  • measurement of the voltage V and thus of the impedance Z 11 may be affected by noise and other disturbance signals reducing a detection sensitivity of the multi-purpose detection circuit 100.
  • the noise may include circuit intrinsic noise as generated in active and passive components of the circuit 700 of FIG.7A. It may also include quantization noise e.g., generated in a digital implementation of the signal generator circuit 406 and the signal processing circuit 408 with reference to FIG. 4.
  • Other disturbance signals may emanate from sources external to the circuit 700 (e.g., from the WPT system during wireless power transfer, from a switched-mode power supply, from a digital processing unit, etc.). These circuit extrinsic disturbance signals may be capacitively coupled (e.g., via capacitance C ew ) to the sense electrode 702 and may include the fundamental and harmonics of the WPT operating frequency and other switching noise components as generated by the WPT system.
  • sources external to the circuit 700 e.g., from the WPT system during wireless power transfer, from a switched-mode power supply, from a digital processing unit, etc.
  • These circuit extrinsic disturbance signals may be capacitively coupled (e.g., via capacitance C ew ) to the sense electrode 702 and may include the fundamental and harmonics of the WPT operating frequency and other switching noise components as generated by the WPT system.
  • the voltage measurement circuit 510 includes a filter to selectively filter the sense signal and to suppress noise and other disturbance signal components as previously discussed with reference to FIG.5A [0352] Moreover, in implementations employing a selective voltage measurement circuit 510 as discussed above, the sense signal waveform as generated by the current source 512 and the corresponding filter of the voltage measurement circuit 510 are adapted e.g., to improve the SNR and consequently to improve the detection sensitivity as previously discussed with reference to FIG.5A. [0353] With reference to FIG. 1, FIG. 7A also illustrates the non-living objects 110 and 112 and the living object 114 proximate to the sense electrode 702.
  • Presence of the object 110, 112, 114, or vehicle 330 may cause a change in one or more electrical characteristics of the sense circuit 701. As non-limiting examples, it may cause a change in the capacitance C and in the equivalent series resistance R resulting in an impedance change ⁇ Z with respect to the impedance Z 11,0 as measured in absence of a foreign object with reference to FIG. 3.
  • Presence of an object e.g., object 114 may be determined if ⁇ Z satisfies certain criteria (e.g., the magnitude of ⁇ Z exceeds a detection threshold).
  • a change ⁇ Z in the measured impedance Z 11 may also be caused by the underbody of a vehicle or by the vehicle-based wireless power transfer structure (e.g., vehicle 330 and vehicle-based wireless power transfer structure 310 with reference to FIG. 3), which may indicate presence of a vehicle above the sense electrode 702.
  • an impedance change ⁇ Z may also be caused by a substantially conductive (metallic) object (e.g., object 110) proximate to the sense electrode 702 since it also interacts with the electric field as generated by the sense electrode 702.
  • a metal object proximate to the sense electrode 702 may change one or more the capacitances Ceg and CeW as illustrated in FIG.7A as well as the self-inductance as previously mentioned.
  • presence of the object 110, 112, 114, or vehicle 330 may cause a change ⁇ Y with respect to the admittance Y 11,0 as measured in absence of a foreign object.
  • presence of an object e.g., object 110
  • may be determined if ⁇ Y satisfies certain criteria e.g., the magnitude of ⁇ Y exceeds a detection threshold).
  • a change ⁇ Z in the impedance Z 11 manifests in a change ⁇ V in the voltage V that is proportional to ⁇ Z while the current I 0 remains substantially unaffected.
  • measuring the complex voltage V may be equivalent to measuring the complex impedance Z 11 and there may be no requirement for additionally measuring the current I thus reducing complexity of the measurement circuit (e.g., measurement circuit 104 of FIG.1)
  • the fractional change ⁇ Z’ (or ⁇ Y’) caused by a defined test object (e.g., object 112) placed at a defined position relative to the sense electrode 702 may relate to the detection sensitivity of an object detection circuit (e.g., the multi-purpose detection circuit 100 of FIG. 1) based on the one-port capacitive sense circuit 701. More specifically, increasing the fractional change ⁇ Z’ (or ⁇ Y’) may increase the SNR as defined by Equation (10).
  • the fractional change ⁇ Z’ (or ⁇ Y’) may be increased by optimizing the design of the sense electrode 702 with respect to its geometry and its integration into the wireless power transfer structure (e.g., wireless power transfer structure 200 with reference to FIGs. 2 and 3), by resonance tuning e.g., using the series inductor 704, and by improving the Q-factor of the sense circuit 701. Improving the Q-factor may increase the SNR, if the noise voltage Vn is predominantly circuit intrinsic noise as discussed below with reference to FIG.7J. [0357] As further analyzed and discussed below with reference to FIG.
  • this may be accomplished based on characteristics of the change of the sense electrode’s 702 impedance as produced by any of the objects 110, 112, 114, or vehicle 330, also referred to herein as the reflected impedance ⁇ Z r .
  • the reflected impedance ⁇ Z r and particularly the angle arg ⁇ Z r ⁇ may reflect electrical properties of the object 110, 112, 114, or vehicle 330. The same is true for the reflected admittance ⁇ Z r .
  • the circuit 700 may be configured to determine the angle arg ⁇ Z ⁇ with the required accuracy.
  • measuring the angle arg ⁇ Z ⁇ may be subject to errors for various reasons as previously discussed with reference to FIG.5A.
  • some implementations of a multipurpose detection circuit 100 employ a phase calibration of the analog circuitry (e.g., the analog front end portion of the measurement circuit 104 with reference to FIG. 4) as previously described with reference to FIG.5A.
  • Reactance compensation (resonance tuning) in the sense circuit 701 produces a local extremum (minimum or maximum) in the impedance magnitude function
  • the sense frequency is adjusted to the local minimum of the voltage magnitude
  • the complex impedance Z 11,0 and hence the complex voltage V across the measurement port 708 may be substantially real. Otherwise stated, the angles arg ⁇ Z 11,0 ⁇ and arg ⁇ V ⁇ are substantially zero.
  • the voltage measurement circuit 510 is corrected by applying a phase shift (impedance plane rotation) as previously described with reference to FIG.5A and defined by Equation (13). [0363] Applying the angle correction of Equation (13), an object (e.g., object 114) reflecting an impedance ⁇ Z r that is imaginary (reactive) may cause a measured voltage change ⁇ V cal that is substantially imaginary.
  • the residual angle error of an example series resonant configuration of the circuit 700 and for an example object 114 is provided in TABLE 4.
  • the residual error described above is reduced by configuring the parallel inductor 706 with an inductance L p whose impedance Z Lp is substantially larger (e.g., 10 times larger) than the series resonant resistance of the sense circuit 701.
  • the residual error is reduced by measuring the impedance Z 11,0 at two or more substantially different frequencies and by determining the elements of an equivalent circuit model of the sense circuit 701 (e.g., the equivalent circuit model illustrated in FIG. 7J) based on the measured impedances Z 11,0 employing a best fit method.
  • these two or more frequencies include at least the frequency of the minimum and the maximum of
  • a residual error may be caused by a parasitic resonance effect of sense circuits associated to adjacent capacitive sense elements of an arrangement of sense electrodes.
  • a residual error in a first sense circuit (e.g., capacitive sense circuit 108a) including a first capacitive sense element (e.g., capacitive sense element 109a) may be caused by a parasitic resonance effect of at least one second capacitive sense circuit (e.g., capacitive sense circuit 108b) including a second capacitive sense element (e.g., capacitive sense element 109b) that is located adjacent to the first capacitive sense element.
  • the measurement accuracy of the angle arg ⁇ Z ⁇ and thus of the angle arg ⁇ Z r ⁇ is increased by an optimized design of the sense electrode 702 and by introducing some spacing between adjacent sense electrodes 702 in an arrangement of sense electrodes.
  • the circuit 700 may be configured to measure the admittance Y 11 and corresponding changes ⁇ Y of Y 11 as caused by the object 110, 112, 114, or vehicle 330. In this case, the admittance change ⁇ Y may be indicative of the reflected impedance ⁇ Z r as previously introduced.
  • the angle arg ⁇ Y ⁇ may be subjected to an error and therefore may require calibration to reduce an error in the measurement of the angle arg ⁇ Y ⁇ and thus of the angle arg ⁇ Z r ⁇ .
  • the circuit 700 may be calibrated analogously to the series resonant configuration however using the local minimum of the admittance function
  • the sense frequency is adjusted to the local maximum of the voltage magnitude
  • the admittance Y 11,0 and hence the voltage V across the measurement port 708 may be substantially real. Otherwise stated, the angles arg ⁇ Y 11,0 ⁇ and arg ⁇ V ⁇ are substantially zero.
  • the voltage measurement circuit 510 is corrected by applying a phase shift (impedance plane rotation) as defined above by Equation (13). [0370] Applying the angle correction of Equation (13), an object (e.g., object 114) reflecting an impedance ⁇ Z r that is imaginary (reactive) produces a measured voltage change ⁇ V cal that is substantially imaginary.
  • a residual error may remain in the angle arg ⁇ V cal ⁇ due to the transformation of ⁇ Z r to ⁇ Y in the lossy sense circuit (e.g., sense circuit 701).
  • the residual angle error of an example parallel resonant configuration of the circuit 700 and for an example reflected impedance ⁇ Z r is provided in TABLE 4.
  • the residual error due to the transformation of ⁇ Z r to ⁇ Y is reduced by measuring the admittance Y 11,0 at two or more substantially different frequencies, supposing absence of a foreign object, and by determining the elements of an equivalent circuit model (e.g., the equivalent circuit model of FIG. 7J) based on the measured admittances Y 11,0 employing a best fit method.
  • these two or more frequencies include at least the frequency of the minimum and the maximum of
  • the series and the parallel resonant configuration of the circuit 700 of FIG. 7A are analyzed below with reference to FIG. 7J with respect to various characteristics such as the Q- factor, fractional change, and various definitions of SNR based on an equivalent circuit model.
  • the circuit 710 of FIG. 7B illustrates another example implementation based on measuring a complex impedance Z 11 of a one-port capacitive sense circuit 711 (shown in FIG.7B as the circuit on the right side of the dashed line).
  • the impedance Z 11 is measured at the measurement port 718 (indicated in FIG.7B by a terminal and a dashed line) by applying, from the current source 512, a sinusoidal current I 0 and by measuring, using the voltage measurement circuit 510, the complex open-circuit voltage V as previously described with reference to FIG.5A.
  • the sense circuit 701 of FIG.7A the sense circuit 711 comprises the single-electrode capacitive sense element 702 (single-ended sense electrode 702) having the signal terminal 703 and the capacitance C with reference to FIG.
  • the capacitance C may include the capacitances C eg and C ew (not shown in FIG.7B) as previously discussed with reference to FIG.7A.
  • the sense circuit 711 further includes a parallel capacitor 715 having a capacitance C p .
  • the circuit 710 further illustrates the sense signal current source 512 and the voltage measurement circuit 510 electrically connected to the measurement port 718.
  • the inductive and capacitive elements of the sense circuit 711 may also cause electrical losses that may be represented by a respective equivalent series resistance.
  • the sense circuit 711 may be configured to provide a local minimum in the impedance magnitude function
  • the sense circuit 711 may be configured to provide a local minimum of the admittance magnitude function
  • the reactance of the series inductor 714 substantially compensates for the reactance of the sense electrode 702 in parallel to the capacitor 715 at the nominal sense frequency providing an impedance Z 11,0 that is substantially real (resistive).
  • the inductance L p of the parallel inductor 706 may be similar or larger than the inductance L s of the series inductor 714.
  • the impedance magnitude of the parallel inductor 716 may be substantially (e.g., 10 times) higher than the impedance magnitude
  • the parallel inductor 716 may exert a negligible impact on the impedance
  • the reactance of the series inductor 714 undercompensates for the reactance of the sense electrode 702 in parallel to the capacitor 715 at the nominal sense frequency.
  • the residual capacitive susceptance of the series connection of the inductor 704 and the parallel connection of the sense electrode 702 and capacitor 715 is substantially compensated for by the susceptance of the parallel inductor 716 providing an admittance Y 11,0 that is substantially real (resistive).
  • the inductance L p of the parallel inductor 706 may be smaller, similar, or larger than the inductance L s of the series inductor 714.
  • the admittance magnitude of the parallel inductor 716 may be substantially (e.g., 20 times) higher than the admittance magnitude
  • the parallel inductor 716 together with the series inductor 714 and the parallel capacitor 715 are used for purposes of resonance tuning and impedance transformation, e.g., to transform the impedance Z 11 to match the sense circuit 711 with an operating impedance range as previously mentioned with reference to FIG. 1.
  • the inductance ratio L s /L p and the capacitance ratio C/C p may be parameters to control the impedance magnitude
  • may be decreased mainly by decreasing the capacitance ratio C/C p .
  • may be increased mainly by increasing the inductance ratio L s /L p .
  • the parallel capacitor 715 may include a variable capacitor whose capacitance C s can be electronically controlled (e.g., a DC controlled capacitor) forming a variable capacitor 715.
  • a variable capacitor 715 is used to compensate for a temperature drift, an ageing, or a detuning of the sense circuit 701 caused by an external impact and to maintain its resonance substantially at the nominal sense frequency.
  • variable capacitor 714 in combination with a variable inductor 714 are used to vary the impedance
  • the sense electrode’s 702 capacitance C in combination with the parallel inductor 716 form a 2 nd order high pass filter to attenuate a low frequency disturbance component in the voltage V for purposes as previously discussed with reference to FIGs.5A.
  • FIG. 7B also illustrates the objects 110, 112, and 114 proximate to the capacitive sense element 702. As previously discussed with reference to FIG.
  • the circuit 720 of FIG. 7C illustrates a further example implementation based on measuring a complex impedance Z 11 of a one-port capacitive sense circuit 721 (shown in FIG.7C as the circuit on the right side of the dashed line). More specifically, the impedance Z 11 is measured at the measurement port 728 (indicated in FIG.7C by a terminal and a dashed line) by applying, from the current source 512, a sinusoidal current I 0 and by measuring, using the voltage measurement circuit 510, the complex open-circuit voltage V as previously described with reference to FIG.7A.
  • the sense circuit 721 comprises the single-electrode capacitive sense element 702 (also referred to herein as a single-ended sense electrode) having the capacitance C with reference to FIG.7A, a series inductor 724 having an inductance L s electrically connected in series to the single-ended sense electrode 702.
  • the sense circuit 721 shows the parallel inductor 706 replaced by a transformer 726 with a transformation ratio nT:1 as indicated in FIG. 7C.
  • the transformer may include a primary winding and a galvanically insulated secondary winding wound on a common core as suggested by the transformer symbol in FIG. 7C.
  • FIG. 7C also indicates the main inductance L m , the series (leakage) inductance L ⁇ , and the equivalent series resistances R Lm and Rw referring to the equivalent circuit model of a non-ideal transformer illustrated in FIG.5H.
  • FIG.7C shows its primary winding electrically connected in parallel to the measurement port 728, while its secondary winding is electrically connected to the series inductor 724.
  • the circuit 720 further illustrates the sense signal current source 512 and the voltage measurement circuit 510 both electrically connected to the sense circuit 721 at the measurement port 728.
  • the sense circuit 721 may be configured to provide a local minimum in the impedance magnitude function
  • the reactance of the series inductor 724 together with the transformer’s 726 secondary referred leakage inductance L ⁇ substantially compensates for the reactance of the sense electrode 702 at the nominal sense frequency providing an impedance Z 11,0 at the measurement port 728 that is substantially real (resistive).
  • the transformer’s 726 secondary referred main inductance L m may be similar or larger than the inductance L s of the series inductor 724.
  • the primary referred open-circuit impedance of the transformer 726 may be substantially (e.g., 10 times) higher than the impedance magnitude
  • the transformer 726 may exert a negligible impact on the impedance
  • the reactance of the series inductor 724 together with the transformer’s 726 secondary referred leakage inductance L ⁇ undercompensates for the reactance of the sense electrode 702 at the nominal sense frequency.
  • the residual capacitive susceptance of the series connection of the inductor 724, the transformer’s 726 leakage inductance L ⁇ , and the sense electrode 702 is substantially compensated for by the susceptance of the transformer’s 726 secondary referred inductance L m providing an admittance Y 11,0 that is substantially real (resistive).
  • the inductance L m may be smaller, similar, or larger than the inductance L s of the series inductor 724.
  • the primary referred open-circuit admittance of the transformer 726 may be substantially (e.g., 20 times) higher than the admittance magnitude
  • the transformer 726 exerts a significant impact on the admittance Y 11,0 at the nominal sense frequency.
  • the transformer 726 may serve for various purposes.
  • the transformer 726 is a nT:1 transformer with nT ⁇ 1 used at least for impedance transformation e.g., to match the impedance magnitude
  • the transformer 726 increases the impedance
  • it increases the admittance
  • it is a balancing transformer used to reduce a leakage current e.g., on the feeder cable of the wireless power transfer structure (e.g., wireless power transfer structure 200 of FIGs. 2 and 3) where the sense electrode 702 is integrated. Reducing this leakage current may reduce an unwanted sensitivity of other WPT system parts to a living object (e.g., living object 114).
  • the transformer 726 is also part of the resonance tuning using its main inductance L p in a manner similar to the parallel inductor 506 with reference to FIG.5A.
  • the inductance ratio L s /L m may be an additional parameter to match the admittance magnitude
  • the sense electrode’s 702 capacitance C in combination with the transformer’s 726 main inductance L m form a 2 nd order high pass filter to attenuate a low frequency disturbance component in the voltage V for purposes as previously discussed in connection with FIG.5A.
  • FIG. 7C also illustrates the objects 110, 112, and 114 proximate to the sense electrode 702.
  • the circuit 730 of FIG. 7D illustrates yet another example implementation based on measuring a complex impedance Z 11 of a one-port capacitive sense circuit 731 (shown in FIG.7D as the circuit on the right side of the dashed line).
  • the impedance Z 11 is measured at the measurement port 738 (indicated in FIG.7D by a terminal and a dashed line) by applying, from the current source 512, a sinusoidal current I 0 and by measuring, using the voltage measurement circuit 510, the complex open-circuit voltage V as previously described with reference to FIG.5A.
  • the sense circuit 731 is operated in a differential mode and uses a substantially symmetric double-electrode capacitive sense element (e.g., double-ended sense electrode 732) composed of electrodes 732a and 732b (also referred to herein as a double-ended sense electrode) providing a differential-mode capacitance C.
  • a substantially symmetric double-electrode capacitive sense element e.g., double-ended sense electrode 732
  • electrodes 732a and 732b also referred to herein as a double-ended sense electrode
  • the sense circuit 731 may be split into a first branch and a second branch with an equal topology.
  • the sense circuit 731 may be substantially symmetric (balanced) with respect to its capacitances and inductances.
  • the sense circuit 731 comprises a differential-mode series inductor 734 having an inductance L s /2 in each branch and that is electrically connected to the double-ended sense electrode 732.
  • the sense circuit 731 comprises a transformer 736 with a transformation ratio nT:1 and secondary referred main inductance L m with reference to FIG. 5H. Its primary winding is electrically connected in parallel to the measurement port 738, while its secondary winding is electrically connected to the differential-mode series inductor 734.
  • the circuit 730 further illustrates the sense signal current source 512 and the voltage measurement circuit 510 both electrically connected to the sense circuit 731 at the measurement port 738.
  • the double-ended sense electrode 732 provides a differential-mode capacitance C that may include various capacitances as indicated in FIG. 7D by dashed lines. In particular, it may include an interelectrode capacitance C ee between electrodes 732a and 732b, a capacitance C eg,a and C eg,b towards ground and a capacitance C ew ,a and C ew ,b towards the WPT coil 202 for the respective electrode 732a and 732b. [0397] Though not indicated in FIG.
  • the capacitive and inductive elements of the sense circuit 731 may cause electrical losses that may be represented by a respective equivalent series resistance as previously discussed with reference to FIG.7A.
  • the sense circuit 731 may be configured to provide a local minimum in the impedance magnitude function
  • the reactance of the differential-mode series inductor 734 together with the transformer’s 736 secondary-referred leakage inductance L ⁇ substantially compensates for the reactance of the double-ended sense electrode 732 at the nominal sense frequency providing an impedance Z 11,0 at the measurement port 738 that is substantially real (resistive).
  • the transformer’s 736 secondary referred main inductance L m may be similar or larger than the inductance L s of the differential- mode series inductor 734.
  • the primary referred open-circuit impedance of the transformer 736 may be substantially (e.g., 10 times) higher than the impedance magnitude
  • the reactance of the differential-mode series inductor 734 together with the transformer’s 736 secondary referred leakage inductance L ⁇ undercompensates for the reactance of the double-ended sense electrode 732 at the nominal sense frequency.
  • the residual capacitive susceptance of the series connection of the differential-mode series inductor 734, the transformer’s 736 leakage inductance L ⁇ , and the double-ended sense electrode 732 is substantially compensated for by the susceptance of the transformer’s 736 secondary referred inductance L m providing an admittance Y 11,0 that is substantially real (resistive).
  • the inductance L m may be smaller, similar, or larger than the inductance L s of the differential-mode series inductor 734.
  • the primary referred open-circuit admittance of the transformer 736 may be substantially (e.g., 20 times) higher than the admittance magnitude
  • the transformer 736 exerts a significant impact on the admittance Y 11,0 at the nominal sense frequency.
  • the double-ended sense electrode’s 732 capacitance C in combination with the transformer’s 736 main inductance L m form a 2 nd order high pass filter to attenuate a low frequency disturbance component in the voltage V for purposes as previously discussed with reference to FIGs.5A.
  • the differential-mode series inductor 734 is configured to also provide a common mode inductance e.g., to attenuate a disturbance signal component in the voltage V emanating from a common mode current capacitively and inductively coupled into the double-ended sense electrode 732 (e.g., via capacitances C ew ,a and C ew ,b) during wireless power transfer.
  • the transformer 736 may serve for various purposes. In some implementations, the transformer 736 is used to match the impedance Z 11 of the sense circuit 731 with an operating impedance range as previously discussed with reference to FIG.5B.
  • it is a 1:1 balancing (balun) transformer used to reduce a common mode disturbance current capacitively coupled to the double-ended sense electrode 732 (e.g., via capacitance C ew,a and C ew,b ).
  • it is a nT:1 transformer with nT ⁇ 1 and serves for both impedance transformation and balancing.
  • the inductance ratio L s /L m may be an additional parameter to match the admittance magnitude
  • the sense circuit 731, the double-ended sense electrode 732, and the differential-mode series inductor 734 may correspond e.g., to the capacitive sense circuit 108a, the capacitive sense element 109a (comprising a double-ended sense electrode), and the associated inductive element, respectively.
  • FIG. 7D also illustrates the objects 110, 112, and 114 proximate to the electrodes 732a and 732b. As previously discussed with reference to FIG. 7A, presence of the object 110, 112, 114, or vehicle 330 may cause a change in one or more electrical characteristics of the sense circuit 731.
  • the use of a double-ended sense electrode may reduce a disturbance voltage component in the voltage V e.g., emanating from the voltage capacitively coupled into the sense electrode by the electric field as generated during wireless power transfer. Due to its symmetry, the double-ended sense electrode 732 integrated into a wireless power transfer structure (e.g., wireless power transfer structure 200 of FIG.1) may pick-up substantially less disturbance voltage as compared to an equivalent single-ended sense electrode (sense electrode 702 of FIG.7A) formed by connecting the electrodes 732a and 732b in parallel.
  • a wireless power transfer structure e.g., wireless power transfer structure 200 of FIG.
  • the fractional change defined by Equation (8) and (9) of a sense circuit (e.g., sense circuit 731) using the double-ended sense electrode 732 may be substantially smaller than that of a sense circuit (e.g., sense circuit 701) using an equivalent single-ended sense electrode 702 formed by connecting the electrodes 732a and 732b in parallel. Therefore, the resulting SNR (e.g., defined by Equation (10)) as obtained for the sense circuits 731 and 701 when driven with the same current I 0 may not differ that much.
  • the sense circuit 731 using the double-ended sense electrode 732 is less sensitive for detecting an object (e.g., living object 114) than the sense circuit 701 using an equivalent single-ended sense electrode 702.
  • the electromagnetic emissions produced by the double-ended sense electrode 732 when driving the sense circuit 731 with a current I 0 may be substantially lower than that of the equivalent single-ended sense electrode 702 when driving the sense circuit 701 with the same current I 0 .
  • the circuit 740 of FIG. 7E illustrates another example implementation based on measuring a complex impedance Z 11 of a one-port inductive sense circuit (e.g., sense circuit 741, shown in FIG. 7E as the circuit on the right side of the dashed line). More specifically, the impedance Z 11 is measured at the measurement port 748 (indicated in FIG.
  • the circuit 740 may be considered as electrically dual to the circuit 700 of FIG. 7A.
  • the circuit 740 includes the sense circuit 741 comprising the single-ended sense electrode 702 having a capacitance C and an equivalent series resistance R with reference to FIG.7A, a parallel inductor 744 having an inductance L p and an equivalent series resistance R Lp , a series capacitor 746 having a capacitance C s electrically connected in series to the parallel connection of the sense electrode 702 and the parallel inductor 744.
  • the circuit 740 further illustrates the sense signal voltage source 552 electrically connected to the sense circuit 741 at the measurement port 748 via the current measurement circuit 550.
  • FIG.7E illustrates the current source (e.g., the current measurement circuit 550) as non-ground-based (floating).
  • the non-ground-based current source is accomplished by using a ground-based current source with an output transformer providing galvanic isolation.
  • the circuit 740 of FIG.7E may be configured to be operated at parallel resonance substantially at the nominal sense frequency. Alternatively, it may be configured for series resonance substantially at the nominal sense frequency.
  • the susceptance of the parallel inductor 744 substantially compensates for the susceptance of the sense electrode 702 at the nominal sense frequency providing an admittance Y 11,0 that is substantially real (resistive).
  • the capacitance C s of the series capacitor 746 may be similar or larger than the capacitance C of the sense electrode 702. Stated otherwise, the admittance magnitude of the series capacitor 746 may be substantially (e.g., 10 times) higher than the admittance magnitude
  • the susceptance of the parallel inductor 744 overcompensates for the susceptance of the sense electrode 702 at the nominal sense frequency.
  • the residual inductive reactance of the parallel connection of the parallel inductor 744 and the sense electrode 702 is substantially compensated for by the reactance of the series capacitor 746 providing an impedance Z 11,0 that is substantially real (resistive).
  • the capacitance C s of the series capacitor 746 may be smaller, similar, or larger than the capacitance C of the sense electrode 702.
  • the impedance magnitude of the series capacitor 746 may be substantially (e.g., 20 times) higher than the impedance magnitude
  • the series capacitor 746 exerts a significant impact on the impedance Z 11,0 at the nominal sense frequency.
  • the series capacitor 746 together with the parallel inductor 744 are used for purposes of resonance tuning and impedance transformation e.g., to transform the impedance Z 11 to match the sense circuit 741 with an operating impedance range as previously mentioned with reference to FIG.1.
  • the capacitance ratio C/C s may be a parameter to control the impedance magnitude
  • Impedance transformation may be particularly effective, if the sense circuit 741 is configured for series resonance. More specifically, increasing the capacitance ratio C/C s , while maintaining series resonance at the nominal sense frequency, may substantially increase the impedance magnitude
  • the sense circuit 741 in the series resonant configuration may be considered as an alternative to the sense circuit 711 of FIG.7B using the parallel capacitor 715 or to the sense circuit 721 of FIG.7C using the transformer 726.
  • Increasing the capacitance ratio C/C s while maintaining resonance at the nominal sense frequency, may also somewhat decrease the admittance magnitude
  • impedance transformation may be limited and far less effective than that of the series resonant configuration.
  • FIG. 7E also illustrates the objects 110, 112, and 114 proximate to the sense electrode 702.
  • presence of the object 110, 112, 114, or vehicle 330 may cause a change in one or more electrical characteristics of the sense circuit 751.
  • they may cause a change in the capacitance C and in an equivalent series resistance R that is considered included in R Ls .
  • the fractional change ⁇ Y’ (or ⁇ Z’) as defined by Equations (8) and (9) and with respect to a defined test object (e.g., object 112) placed at a defined position relative to the sense electrode 702 may relate to the detection sensitivity of an object detection circuit (e.g., the multi-purpose detection circuit 100 of FIG.1) based on the sense circuit 741. More specifically, increasing the fractional change ⁇ Y’ (or ⁇ Z’) may increase a signal-to-noise ratio (SNR) e.g., as defined by Equation (14).
  • SNR signal-to-noise ratio
  • the fractional change may be increased by optimizing the design of the sense electrode 702 with respect to its geometry and its integration into the wireless power transfer structure (e.g., wireless power transfer structure 200 with reference to FIGs.2 and 3), by resonance tuning e.g., using the parallel inductor 744, and by improving the Q-factor of the sense circuit 741. Improving the Q-factor may increase the SNR, if the noise current I n is predominantly circuit intrinsic noise as discussed above with reference to FIG.5G.
  • the circuit 740 of FIG.7E may be configured to determine the angle arg ⁇ Y ⁇ and thus the angle arg ⁇ Y r ⁇ with the required accuracy.
  • measuring the admittance Y 11 including the change ⁇ Y may be subject to errors for various reasons as previously discussed with reference to the circuit 700 of FIG.7A.
  • at the measurement port 748 provides a mean to calibrate the current measurement circuit 550 and hence the admittance measurement with respect to the angle arg ⁇ Y ⁇ .
  • the sense frequency is adjusted to the local minimum of the current magnitude
  • the admittance Y 11,0 and hence the current I at the measurement port 748 may be substantially real. Otherwise stated, the angles arg ⁇ Y 11,0 ⁇ and arg ⁇ I ⁇ are substantially zero.
  • the current measurement circuit 550 is corrected by applying a phase shift such that the imaginary part of the complex current value as determined and output by the current measurement circuit 550 at this frequency vanishes.
  • the residual angle error of an example parallel resonant configuration of the circuit 740 and for an example object 110 is provided in TABLE 4.
  • the residual error is reduced by configuring the series capacitor 746 with a capacitance C s whose admittance Y Cs is substantially larger (e.g., 10 times larger) than the parallel resonant conductance of the sense circuit 741.
  • the residual error is reduced by measuring the admittance Y 11,0 at two or more substantially different frequencies and by determining the elements of an equivalent circuit model of the sense circuit 741 (e.g., the equivalent circuit model illustrated in FIG. 7K) based on the measured admittances Y 11,0 employing a best fit method.
  • these two or more frequencies include at least the frequency of the minimum and the maximum of
  • the circuit 540 may be configured to measure the impedance Z 11 and corresponding changes ⁇ Z of Z 11 as caused by the object 110, 112, 114, or vehicle 330.
  • the impedance change ⁇ Z may be indicative of the reflected admittance ⁇ Y r as previously introduced.
  • the angle arg ⁇ Z ⁇ may be subjected to an error and therefore may require calibration to reduce an error in the measurement of the angle arg ⁇ Z ⁇ and thus of the angle arg ⁇ Z r ⁇ .
  • the circuit 740 may be calibrated analogously to the parallel resonant configuration however using the local minimum of the impedance function
  • the sense frequency is adjusted to the local maximum of the current magnitude
  • the impedance Z 11,0 and hence the current I at the measurement port 748 may be substantially real. Otherwise stated, the angles arg ⁇ Z 11,0 ⁇ and arg ⁇ I ⁇ are substantially zero.
  • the current measurement circuit 550 is corrected by applying a phase shift (impedance plane rotation) as given above by Equation (15).
  • an object e.g., object 114 reflecting an admittance ⁇ Y r that is imaginary (reactive) may result in a measured current change ⁇ I cal that is substantially imaginary. Nevertheless, a residual error may remain in the angle arg ⁇ I cal ⁇ due to the transformation of ⁇ Y r to ⁇ Z in the lossy sense circuit (e.g., sense circuit 741).
  • the residual angle error of an example series resonant configuration of the circuit 540 and for an example object 110 is provided in TABLE 4.
  • the residual error due to the transformation of ⁇ Y r to ⁇ Z is reduced by measuring the impedance Z 11,0 at two or more substantially different frequencies, supposing absence of a foreign object, and by determining the elements of an equivalent circuit model (e.g., the equivalent circuit model of FIG. 7K) based on the measured impedances Z 11,0 employing a best fit method.
  • these two or more frequencies include at least the frequency of the minimum and the maximum of
  • the change ⁇ Y in the admittance Y 11 if correctly measured at the measurement port 748, directly relates to the reflected admittance ⁇ Z r as previously defined.
  • the circuit 740 may be configured to determine the angle arg ⁇ Y ⁇ and thus the angle arg ⁇ Z r ⁇ with sufficient accuracy.
  • measuring the admittance Y 11 including the change ⁇ Y may be subject to errors for various reasons.
  • susceptance compensation (resonance tuning) of the sense circuit 741 may provide a mean to calibrate the admittance measurement and hence improve its accuracy e.g., with respect to the angle arg ⁇ Y 11 ⁇ .
  • the circuit 740 is calibrated according to the procedure as previously described with reference to the circuit 540 of FIG.5C. Nevertheless, a residual error may remain in the angle arg ⁇ Y ⁇ due to the impact of the series capacitor 746. In some implementations, the error in the angle arg ⁇ Y ⁇ or in the angle arg ⁇ Y r ⁇ is reduced analogously to the procedures as previously discussed with reference to FIG.5A.
  • the circuit 740 may be configured to measure the impedance Z 11 and corresponding changes ⁇ Z of Z 11 as caused by the object 110, 112, 114, or vehicle 330.
  • the angle arg ⁇ Z ⁇ may disagree with the angle arg ⁇ Z r ⁇ of the reflected impedance as previously defined with reference to FIG. 7A.
  • calibration is performed by measuring the impedance Z 11,0 at substantially different frequencies, supposing absence of a foreign object, and by determining the elements of an equivalent circuit model (e.g., the equivalent circuit model of FIG. 7K) based on the measured impedances Z 11,0 employing a best fit method. In some implementations, at least the frequency of the minimum and the maximum of
  • a ground- based current measurement circuit 550 and a non-ground-based (floating) voltage source 552 is used.
  • both the voltage source 552 and the current measurement circuit 550 are ground-based and a transformer is used for purposes of galvanic separation.
  • the transformer may be considered inserted between the measurement port 748 and the series capacitor 746.
  • the circuit 750 of FIG. 7F illustrates yet another example implementation based on measuring a complex impedance Z 11 of a one-port inductive sense circuit 751 (shown in FIG.7F as the circuit on the right side of the dashed line). More specifically, the impedance Z 11 is measured at the measurement port 758 (indicated in FIG.
  • the circuit 750 is a modification of the circuit 740 of FIG. 7E to operate with the double-ended sense electrode 732 of FIG. 7D.
  • the circuit 750 includes the sense circuit 751 comprising the double-ended sense electrode 732 having a differential-mode capacitance C, a parallel inductor 754 having an inductance L p , a series capacitor 756 having a capacitance C s electrically connected in series to the parallel connection of the inductor 754 and the double-ended sense electrode 732.
  • the series capacitor 756 is split into two capacitors, each with a capacitance 2C s , providing a symmetric topology.
  • the sense circuit 751 includes a transformer 757 having a transformation ratio nT:1 and a secondary referred main inductance L m .
  • the circuit 750 further illustrates the sense signal voltage source 552 and the current measurement circuit 550 both electrically connected to the sense circuit 751 at the measurement port 758.
  • the current measurement circuit 550 of the circuit 740 is ground-based.
  • the capacitive and inductive elements of the sense circuit 751 may cause electrical losses that may be represented by a respective equivalent series resistance as previously discussed with reference to FIG. 7A and 7E.
  • the circuit 750 of FIG.7F may be configured to be operated at parallel resonance substantially at the nominal sense frequency. Alternatively, it may be configured for series resonance substantially at the nominal sense frequency.
  • the transformer’s 757 main inductance L m , the series capacitor 756, and the parallel inductor 754 are used for purposes of resonance tuning and impedance transformation, e.g., to transform the impedance Z 11 to match the sense circuit 711 with an operating impedance range as previously mentioned with reference to FIG. 1.
  • the inductance ratio L m /L p and the capacitance ratio C/C s may be parameters to control the impedance magnitude
  • the transformer 757 is a 1:1 transformer and serves for balancing. In other implementations, it is a nT:1 transformer (nT ⁇ 1 ) and is also used for impedance transformation.
  • the double-ended sense electrode’s 732 capacitance C in combination with the parallel inductor 754, the series capacitor 756, and the transformer’s 757 main inductance L m form a higher order high pass filter to attenuate a low frequency disturbance component in the current I for purposes as previously discussed in connection with FIG.5A.
  • FIG. 7F also illustrates the objects 110 , 112, and 114 proximate to the double-ended sense electrode 732.
  • presence of the object 110, 112, 114, or vehicle 330 may cause a change in one or more electrical characteristics of the sense circuit 751. As non-limiting examples, it may a change the capacitance C and an equivalent series resistance (not shown in FIG.7F) resulting in an impedance change ⁇ Z with respect to the impedance Z 11,0 as measured in absence of a foreign object with reference to FIG.3.
  • the series capacitor 756 may be composed of a single capacitor 756 having capacitance C s directly connecting to the terminal of the measurement port 758 and to the transformer’s 757 primary winding.
  • the circuit 760 of FIG.7G illustrates an example implementation based on measuring a complex transimpedance Z 21 of a two-port capacitive sense circuit 761 (shown in FIG.7G as the circuit between the left and the right dashed line). More specifically, the transimpedance Z 21 is measured by applying, from the current source 512, a sinusoidal current I 0,1 at the sense frequency with a defined amplitude and phase to the measurement port 768 (indicated in FIG.
  • the sense circuit 761 comprises a double-electrode capacitive sense element 762 comprising a first single-ended sense electrode 762a having a single terminal 763a and a second single-ended-sense electrode 762b having a single terminal 763b.
  • the sense circuit 761 further comprises a first series inductor 764 having an inductance L s,1 electrically connected in series to the first sense electrode 762a at the terminal 763a and a second series inductor 765 having an inductance L s,2 electrically connected in series to the second sense electrode 762b at the terminal 763b.
  • the sense circuit 761 further comprises a first parallel inductor 766 having an inductance L p,1 electrically connected to the first series inductor 764 and in parallel to the measurement port 768 and a second parallel inductor 767 having an inductance L p,2 electrically connected to the second series inductor 765 and in parallel to the measurement port 769.
  • the circuit 760 further illustrates the sense signal current source 512 connected to the measurement port 768 and the voltage measurement circuit 510 connected to the measurement port 769.
  • the inductors 764, 765, 766, and 767 may also cause electrical losses that may be represented by a respective equivalent series resistance as indicated in FIG.7A.
  • FIG.7G indicates, in dashed lines, a capacitance C ag between the first sense electrode 762a and ground, a capacitance C ab between the first sense electrode 762a and the second sense electrode 762b, and a capacitance Cbg between the second sense electrode 762b and ground.
  • the capacitances C ag , and C bg may include other capacitances as discussed with reference to FIG.7A.
  • a two-port inductive sense element e.g., inductive sense element 562 of FIG.5D comprising the sense coils 562a and 562b
  • a first self-capacitance C 1 , a second self-capacitance C 2 , and a mutual capacitance C M as indicated in FIG. 7G may be attributed to the two-port capacitive sense element 762.
  • the self-capacitance C 1 may be defined as the capacitance as measured between the terminal 763a of the first sense electrode 762a and ground with the terminal 763b shortened to ground.
  • the self-capacitance C 2 may be defined as the capacitance as measured between the terminal 763b of the second sense electrode 762b and ground with the terminal 763a shortened to ground.
  • FIG. 7G also indicates corresponding equivalent series resistance R 1 , R 2 , and R M representing electrical losses in the capacitive sense element 762.
  • a two-port capacitive sense element (e.g., capacitive sense element 762) may be modeled by a “ ⁇ ”-equivalent circuit based on capacitances C 1 , C 2 , C M as illustrated in FIG. 7L.
  • the equivalent circuit model 762-1 of FIG. 7M is electrically dual to the equivalent circuit model 562-2 of FIG.5J.
  • the reactance of L s ,1 substantially compensates for the reactance of C 1 providing a local impedance minimum
  • the reactance of L s ,2 substantially compensates for the reactance of C 2 L 2 providing a local impedance minimum
  • the sense circuit 761 is configured to provide a local minimum of the admittance magnitude functions
  • the sense circuit 761 is configured to provide a local minimum of the admittance magnitude function
  • the sense circuit 761 is configured to provide a local minimum of the impedance magnitude function
  • the reactance of the parallel inductors 766 and 767 is substantially higher than the impedance magnitudes
  • the sense circuit 761 is operated as a non-resonant or partially resonant circuit.
  • the capacitance C 1 of the first sense electrode 762a in combination with the first parallel inductor 766 form a 2 nd order high pass filter to attenuate a low frequency disturbance component in the voltage V 1 .
  • the capacitance C 2 of the second sense electrode 762b form a 2 nd order high pass filter to attenuate a low frequency disturbance component in the voltage V 2 for purposes as previously discussed in connection with FIGs.5A.
  • the sense circuit 761, the capacitive sense element 762 (including sense electrodes 762a and 762b), and the respective series inductors 764 and 765 may correspond e.g., to the capacitive sense circuit 108a, the capacitive sense element 109a (including a double-ended sense electrode), and the respective associated capacitive elements.
  • other transimpedance measurement techniques such as the voltage source current measurement technique or any other combination may apply (e.g., a voltage source voltage measurement technique).
  • At least one of the impedances Z 11 and Z 22 of the sense circuit 781 is additionally measured to the transimpedance Z 21 (e.g., using one or more of the techniques as previously discussed with reference to FIG. 5A).
  • presence of an object e.g., object 114 is determined based on a change in at least one of an impedance Z 11 , Z 22 , and Z 21 .
  • at least one of an impedance transformation and balancing may apply to at least one of the primary-side and secondary-side of the sense circuit 761 (not shown herein). More specifically, with reference to the sense circuit 721 of FIG.
  • FIG. 7G also illustrates the objects 110, 112, and 114 proximate to the capacitive sense element 762. As previously discussed with reference to FIG.1, presence of the object 110, 112, 114, or vehicle 330 may cause a change in one or more electrical characteristics of the sense circuit 761.
  • it may change at least one of the self-capacitances C 1 , C 2 , the equivalent series resistances R 1 , R 2 , the mutual capacitance C M and the mutual equivalent series resistance R M generally resulting in a change ⁇ Z of the transimpedance Z 21,0 as measured in absence of a foreign object.
  • Presence of an object e.g., object 114
  • measuring the complex voltage V 2 may be equivalent to measuring the complex transimpedance Z 21 .
  • the complex voltage V 2 may be indicative of the complex transimpedance Z 21 and there may be no requirement for additionally measuring the current I 0,1 thus reducing complexity of the measurement circuit (e.g., measurement circuit 104 of FIG.1)
  • the fractional change ⁇ Z’ (or ⁇ Y’) caused by a defined test object (e.g., object 112) placed at a defined position relative to the capacitive sense element 762 may relate to the detection sensitivity of an object detection circuit (e.g., the multi- purpose detection circuit 100 of FIG. 1) based on a two-port capacitive sense circuit 761.
  • Increasing the fractional change ⁇ Z’ may increase a detection sensitivity of the circuit 760. More specifically, it may increase a signal-to-noise ratio (SNR) e.g., as defined by Equation (21)
  • SNR signal-to-noise ratio
  • the fractional change ⁇ Z’ (or ⁇ Y’) may be increased by optimizing the design and the arrangement of the sense electrodes 762a and 762b, their integration into the wireless power transfer structure (e.g., wireless power transfer structure 200 with reference to FIGs.2 and 3), by resonance tuning using series inductors 764 and 765 as previously described, and by improving a Q-factor of the sense circuit 761.
  • FIG. 7H illustrates another example implementation based on measuring a complex transimpedance Z 21 of a two-port capacitive sense circuit 771 (shown in FIG. 7H as the circuit between the left and the right dashed line). More specifically, the transimpedance Z 21 is measured by applying, from the current source 512, a sinusoidal current I 0,1 at the sense frequency with a defined amplitude and phase to the measurement port 778 (indicated in FIG. 7H by a terminal and a dashed line) and by measuring, using the voltage measurement circuit 510, the complex open-circuit voltage V 2 (amplitude and phase) at the measurement port 779 (indicated in FIG.7H by a terminal and a dashed line) as previously described with reference to FIG.5D.
  • the sense circuit 771 is operated in a differential mode. It may be split into a first branch and a second branch with an equal topology.
  • the sense circuit 771 may be substantially symmetric (balanced) with respect to its capacitances and inductances.
  • the sense circuit 771 includes a quad-electrode capacitive sense element 772 comprising a first double-ended sense electrode composed of sense electrodes 772a and 772b having respective terminals 773a and 773b and a second double-ended sense electrode composed of sense electrodes 772c and 772d having respective terminals 773c and 773d.
  • the first double- ended sense electrode 772a/b is electrically connected to a differential-mode inductor 774 providing an inductance L s ,1/2 in each branch.
  • the second double-ended sense electrode 772c/d is electrically connected to a differential-mode inductor 775 providing an inductance L s , 2 /2 in each branch.
  • the sense circuit 771 also includes a transformer 776 with a transformation ratio n1:1 and a secondary referred main inductance L m,1 . Its primary winding is electrically connected in parallel to the measurement port 778, while its secondary winding is electrically connected to the differential-mode inductor 774.
  • the sense circuit 771 includes a transformer 777 with a transformation ratio 1:n2 and a primary referred main inductance L m,2 . Its primary winding is electrically connected to the differential-mode inductor 775, while its secondary winding is electrically connected in parallel to the measurement port 779.
  • the circuit 770 further illustrates the sense signal current source 512 electrically connected to the measurement port 778 and the voltage measurement circuit 510 electrically connected to the measurement port 779.
  • the sense circuit 771 may cause electrical losses in the inductive and capacitive elements that may be represented by a respective equivalent series resistance as previously described with reference to FIGs.7A and 7G.
  • FIG. 7H indicates, in dashed lines, a plurality of capacitances comprising a capacitance C ab between electrodes 772a and 772b, a capacitance C ac between electrodes 772a and 772c, a capacitance C ad between electrodes 772a and 772d, a capacitance C bc between electrodes 772b and 772c, a capacitance C bd between electrodes 772b and 772d, and a capacitance C c d between electrodes 772c and 772d.
  • capacitances may refer to capacitances as measured between respective terminals 773a, 773b, 773c, and 773d with the differential-mode inductors 774 and 775 disconnected from the respective sense electrodes.
  • the capacitances C ab and C cd may further include various capacitances as previously illustrated with reference to FIG.7A.
  • a first self-capacitance C 1 As with the capacitive sense element 762 of FIG. 7G, a first self-capacitance C 1 , a second self-capacitance C 2 , and a mutual capacitance C M as indicated in FIG.7H may be attributed to the capacitive sense element 772.
  • the sense circuit 771 is operated in a differential mode, these capacitances may be considered as differential-mode capacitances.
  • the quad-electrode capacitive sense element e.g., capacitive sense element 762
  • the quad-electrode capacitive sense element may be modeled by the “ ⁇ ”-equivalent circuit model based on capacitances C 1 , C 2 , C M as illustrated in FIG.7L.
  • the ground-based “ ⁇ ” circuit may be replaced by an equivalent ground-symmetric network having a mutual capacitance C M /2 in each branch (not shown herein).
  • C 1 C ab +((C ac + C ad ) (C bc + C bd )/ ⁇ C) (189)
  • C 2 C cd + ((C ac + C bc ) (C ad + C bd )/ ⁇ C) (190)
  • the sense circuit 771 is configured to provide a local minimum of the admittance magnitude functions
  • the sense circuit 771 is configured to provide a local minimum of the impedance magnitude function
  • the reactance of the transformer’s 776 primary referred main inductance and the transformer’s 776 secondary referred main inductance is substantially higher than the impedance magnitudes
  • the circuit 771 is operated as a non-resonant or partially resonant circuit.
  • the capacitance C 1 of the first double-ended sense electrode 772a/b in combination with the first transformer’s 776 main inductance L m,1 form a 2 nd order high pass filter to attenuate a low frequency disturbance component in the voltage V1.
  • the capacitance C 2 of the second double-ended sense electrode 772c/d in combination with the second transformer’s 777 main inductance L m,2 form a 2 nd order high pass filter to attenuate a low frequency disturbance component in the voltage V 2 for purposes as previously discussed in connection with FIGs.5A.
  • the sense circuit 771, the capacitive sense element 772 (including electrodes 772a, 772b, 772c, and 772d), and the respective differential-mode inductors 774 and 775 may correspond e.g., to the capacitive sense circuit 108a, the capacitive sense element 109a (including a pair of double-ended sense electrodes, not shown in FIG.1), and the respective associated capacitive elements.
  • FIG. 7H also illustrates the objects 110, 112, and 114 proximate to the capacitive sense element 772. As previously discussed with reference to FIG.
  • presence of the object 110, 112, 114, or vehicle 330 may cause a change in one or more electrical characteristics of the sense circuit 771. As non-limiting examples, it may change at least one of the capacitances C 1 , C 2 , C M and the equivalent series resistances R 1 , R 2 , R M generally resulting in a change ⁇ Z of the transimpedance Z 21,0 as measured in absence of a foreign object. Presence of an object (e.g., object 114) may be determined as previously discussed with reference to FIG.7A.
  • the fractional change ⁇ Z’ (or ⁇ Y’) caused by a defined test object (e.g., object 112) placed at a defined position relative to the capacitive sense element 772 may relate to the detection sensitivity of an object detection circuit (e.g., the multi- purpose detection circuit 100 of FIG. 1) based on a two-port capacitive sense circuit 771.
  • an object detection circuit e.g., the multi- purpose detection circuit 100 of FIG. 1
  • Increasing the fractional change ⁇ Z’ (or ⁇ Y’) may increase a detection sensitivity of the circuit 770 as previously discussed with reference to FIG.7G.
  • the fractional change ⁇ Z’ may be increased by optimizing the design and the arrangement of the double-ended sense electrodes 772a/b and 772c/d, their integration into the wireless power transfer structure (e.g., wireless power transfer structure 200 with reference to FIGs. 2 and 3), by resonance tuning using series inductors (e.g., differential-mode inductors 774 and 775) as previously described, and by improving a Q-factor of the sense circuit 761.
  • series inductors e.g., differential-mode inductors 774 and 775
  • the capacitive sense element 772 is configured for the mutual capacitance C M to vanish in absence of a foreign object, resulting in a transimpedance
  • FIG 12A An example implementation of a capacitive sense element 772 using an arrangement of four single-ended sense electrodes that may provide a substantially zero mutual capacitance (C M ⁇ 0) is illustrated in FIG 12A.
  • the circuit 780 of FIG. 7I illustrates yet another example implementation based on measuring a complex transimpedance Z 21 of a two-port capacitive sense circuit 781 (shown in FIG. 7I as the circuit between the left and the right dashed line). More specifically, the transimpedance Z 21 is measured by applying, from the voltage source 552, a sinusoidal voltage V 0,1 at the sense frequency with a defined amplitude and phase to the measurement port 788 (indicated in FIG. 7I by a terminal and a dashed line) and by measuring, using the current measurement circuit 550, the complex short-circuit current I 2 (amplitude and phase) at the measurement port 789 (indicated in FIG. 7I by a terminal and a dashed line).
  • the circuit 780 of FIG.7I may be considered as electrically dual to the circuit 580 of FIG.5E.
  • the sense circuit 781 includes the double-electrode capacitive sense element 762 with reference to FIG. 7G composed of the first single-ended sense electrode 762a and the second single-ended sense electrode 762b with reference to FIG.7G.
  • FIG.7I also indicates capacitances C ag , C ab , C bg and the related capacitances C 1 , C 2 , C M as previously discussed with reference to FIG. 7G.
  • the first electrode 762a is electrically connected to the first terminal of a parallel inductor 784 having an inductance L p and the second electrode 762b is electrically connected to the second terminal of the parallel inductor 784. Further, the first electrode 762a and the second electrode 762b is electrically connected to the first terminal of a first series capacitor 786 and to the first terminal of a second series capacitor 787, respectively, while the second terminal of the series capacitor 786 and 787 is electrically connected to the measurement ports 788 and 789, respectively. [0490] Though not indicated in FIG. 7I for purposes of illustration, the sense circuit 781 may cause electrical losses in the inductive and capacitive elements that may be represented by a respective equivalent series resistance as previously described with reference to FIGs.7A and 7G.
  • the capacitive sense element 762 may include the equivalent series resistances R 1 , R 2 , and R M .
  • the basic topology of the circuit 780 of FIG. 7I equals the topology of the circuit 760 of FIG.7F if the transformer 757 is omitted. Therefore, some implementations or configurations of the circuit 780 measuring a transimpedance Z 21 may be considered equivalent to the circuit 760 measuring an impedance Z 11 .
  • the sense electrodes 762a and 762b are tightly coupled resulting in a capacitive coupling factor k C as defined by Equation (186) that is near unity (k C ⁇ 1).
  • the sense circuit 781 may be configured to provide a local minimum in the transimpedance magnitude function
  • the sense circuit 581 may be configured to provide a local minimum in the transadmittance magnitude function
  • the susceptance of the parallel inductor 784 substantially compensates for the susceptance of the mutual capacitance C M providing a local minimum in the transadmittance magnitude function
  • FIG. 7L illustrating the “ ⁇ ”-equivalent circuit model 762-1 of the two-port capacitive sense element 762 and by considering the inductance L p of the parallel inductor 784 inserted in parallel to the mutual capacitance C M .
  • L p the parallel capacitances C 1 – C M and C 2 – C M become substantially zero.
  • the capacitances C s,1 and C s,2 of the series capacitor 786 and 787, respectively may be similar or larger than the capacitance C 1 and C 2 of the sense electrodes 762a and 762b, respectively.
  • the admittance magnitude of the series capacitor 786 and 787 may be substantially higher than the admittance magnitude
  • the series capacitor 786 and 787 may exert a negligible impact on the admittances and transadmittance
  • the susceptance of the parallel inductor 784 overcompensates for the susceptance of the mutual capacitance C M at the nominal sense frequency.
  • the capacitances C s ,1 and C s ,2 of the series capacitors 786 and 787, respectively may be smaller, similar, or larger than the capacitances C 1 and C 2 of the sense electrodes 762a and 762b, respectively.
  • the impedance magnitude of each of the series capacitors 786 and 787 may be substantially (e.g., 20 times) higher than the impedance magnitudes
  • the series capacitors 786 and 787 exert a significant impact on the impedance and transimpedance magnitudes
  • the capacitance C 1 of the first sense electrode 762a in combination with the first series capacitor 786 form a high pass filter to attenuate a low frequency disturbance component in the current I1.
  • the capacitance C 2 of the second sense electrode 762b in combination with the second series capacitor 787 form a high pass filter to attenuate a low frequency disturbance component in the current I2 for purposes as previously discussed in connection with FIG.5A.
  • the capacitance C M of the capacitive sense element 762 in combination with the parallel inductor 784 form a 2 nd order high pass filter to attenuate a differential low frequency disturbance voltage between the sense electrodes 762a and 762b.
  • the sense circuit 781, the capacitive sense element 762 (including sense electrodes 762a and 762b), and the parallel inductor 784 may correspond e.g., to the capacitive sense circuit 108a, the capacitive sense element 109a (including a double-ended sense electrode), and the respective associated inductive element, respectively.
  • other transimpedance and impedance measurement techniques may apply as previously mentioned with reference to FIG.7G.
  • at least one of an impedance transformation and balancing may apply to at least one of a primary-side and secondary side of the sense circuit 781 (not shown herein).
  • FIG.7I also illustrates the objects 110, 112, and 114 proximate to the capacitive sense element 762.
  • presence of the object 110, 112, 114, or vehicle 330 may cause a change in one or more electrical characteristics of the sense circuit 781 as previously discussed with reference to FIG. 7D.
  • a change in the mutual capacitance C M , and the equivalent mutual resistance RM generally results in a change ⁇ Z with respect to the transimpedance Z 21,0 as measured in absence of a foreign object.
  • the fractional change ⁇ Z’ (or ⁇ Y’) caused by a defined test object may relate to the detection sensitivity of the sense circuit 781.
  • the fractional change ⁇ Z’ (or ⁇ Y’) may be increased by optimizing the design and the arrangement of the sense electrodes 762a and 762b, their integration into the wireless power transfer structure (e.g., wireless power transfer structure 200 with reference to FIGs.2 and 3), by resonance tuning using the parallel inductor 784 as previously described, and by improving a Q-factor of the sense circuit 781.
  • the sense circuit 781 configured for a capacitive coupling factor k C ⁇ 1 reduces the impact of the equivalent series resistances R 1 and R 2 on the fractional change, if compared e.g., to the circuit 700 of FIG.7A.
  • the impedance change ⁇ Z may reflect electrical properties of an object (e.g., object 110) as discussed with reference to the circuit 700 of FIG. 7A. It may further allow calibration and correction of the angle arg ⁇ Z ⁇ in a procedure as previously described with reference to FIG.5A.
  • FIGs.7J and 7K illustrate equivalent circuit models 700-1 and 740-1, respectively, used below for purposes of a theoretical analysis and performance comparison.
  • the equivalent circuit model 700-1 is used to analyze the circuit 700 of FIG. 7A, the circuit 710 of FIG.7B (using the parallel capacitor 715), and the circuit 720 of FIG.7C (using the transformer 726) , while the equivalent circuit model 740-1 serves for the analysis of the circuit 740 of FIG. 7E (the electrically dual of the circuit 700).
  • Each of the circuits 700, 710, 720, and 740 are analyzed with respect to its series and parallel resonant configuration and with respect to various characteristics such as the impedance and the Q-factor of the sense circuit at resonance, the fractional change, and the various SNRs as previously defined with reference to FIGs.5F and 5G.
  • is assumed for both configurations of the circuits 700, 710, 720, and 740, though practical implementations configured for parallel resonance may prefer a sense electrode 702 with a higher capacitance C. Comparing SNRs at the same sense electrode current level
  • FIG.7J comprises the sense electrode’s 702 capacitance C, the series inductor’s 704 inductance L s and its equivalent series resistance R Ls , the parallel inductor’s 706 inductance L p and its equivalent series resistance R Lp , an ideal sense signal current source 512 and an ideal voltage measurement circuit 510.
  • FIG.7J also includes the capacitance C p of the parallel capacitor 715 (as optional in dashed lines) with reference to the circuit 710 of FIG.7B. It may be appreciated that in practical implementations losses in capacitors (including the sense electrode 702) are generally substantially lower than losses in inductors.
  • the equivalent circuit model 700-1 further includes an impedance ⁇ Z r in series to the capacitance C representing the reflected impedance of the object 110, 112, or 114 proximate to the sense electrode 702 as previously discussed with reference to FIG. 7A.
  • the reflected impedance ⁇ Z r may be regarded as the object 110, 112, or 114 as illustrated in FIG.7A abstracted away).
  • the equivalent circuit model 700-1 also includes a noise voltage source V sn in series to the capacitance C representing the noise voltage induced into the sense electrode 702 primarily by the electric field as generated when WPT is active.
  • the noise voltage V sn may include any low frequency component (e.g., at the fundamental of the WPT operating frequency and harmonics thereof) as well as any high frequency component (e.g., switching noise at the sense frequency).
  • the impedance Z 11 at the measurement port 708 of the circuit 700 of FIG.7J in presence of an object may be expressed as: Z 11 ⁇ R Ls + j ⁇ L s + (j ⁇ C) -1 + ⁇ Z r (205)
  • occurs substantially at an angular frequency ⁇ satisfying: (j ⁇ L s ) -1 + j ⁇ C ⁇ 0 (206) yielding the series resonant angular frequency: ⁇ s ⁇ (C L s ) -1/2 (207)
  • Y 11 (R Lp + j ⁇ L p ) -1 + (R Ls + j ⁇ L s + (j ⁇ C) -1 + ⁇ Z r ) -1 (216) and using Equation (38) approximated as: Y 11 ⁇ (j ⁇ L p ) -1 – R Lp (j ⁇ L p ) -2 + (j ⁇ L s + (j ⁇ C) -1 ) -1 – (R Ls + ⁇ Z r ) ( ⁇ L s + ( ⁇ (217) C) -1 ) -2
  • (parallel resonance) occurs substantially at an angular frequency ⁇ satisfying: (j ⁇ C) -1 + j ⁇ (L s + L p ) (218) yielding for the parallel resonant angular frequency: ⁇
  • the admittance Y 11 at ⁇ p of Equations (221) may also be expressed as: Y 11 ⁇ G p + ⁇ Y ⁇ G p + (1 + n L ) 2 ( ⁇ p C) 2 (227) [0514]
  • the parallel resonant configuration of the circuit 700 of FIG.7A is employed as an alternative to using a transformer (e.g., transformer 726) for transforming the admittance Y 11 to be within a suitable operating admittance range as previously discussed with reference to FIGs. 7B and 7C.
  • a transformer e.g., transformer 726
  • the angle arg ⁇ Y ⁇ of the measured admittance change ⁇ Y is indicative of the angle arg ⁇ Z r ⁇ .
  • the accuracy of the measured angle is improved by applying the angle correction based on the calibration procedure as previously described with reference to the circuit 500 of FIG. 5A.
  • the impedance Z 11 at measurement port 708 in presence of an object for the series resonant configuration becomes: Z 11 ⁇ R Ls + j ⁇ L s + (j ⁇ C p + ((j ⁇ C) -1 + ⁇ Z r ) -1 ) -1 (233)
  • the impedance Z 11 may be approximated as: Z 11 ⁇ R Ls + j ⁇ L s + (j ⁇ (C + C p )) -1 + ⁇ Z r C 2 /(C + C p ) 2 (234)
  • Series resonance in absence of a foreign object occurs approximately at an angular frequency satisfying: (j ⁇ (C + C p )) -1 + j ⁇ L s ⁇ 0 (235) yielding the series resonant angular frequency: ⁇ s ⁇ (L s (C + C p )
  • the series resonant resistance R s amounts to 1/3 of that of the sense circuit 501 of FIG. 5F. Therefore, in some implementations, the series resonant configuration of the circuit 710 of FIG. 7B using the parallel capacitor is employed as an alternative to using a transformer (e.g., transformer 726 of FIG. 7C) for transforming the impedance Z 11 to be within a suitable operating admittance range as discussed with reference to FIG.7C.
  • a transformer e.g., transformer 726 of FIG. 7C
  • the impedance change ⁇ Z resulting at the measurement port 718 of the sense circuit 711 of FIG.7B becomes approximately: ⁇ Z ⁇ (n C /(1 + n C )) 2 ⁇ Z r (241)
  • the fractional change ⁇ Z’ may be expressed as: ⁇ Z’ ⁇ ⁇ Z/R s ⁇ n C /(1 + n C ) Q s ⁇ Z r ’ (243)
  • adding a parallel capacitor 715 as shown in FIG.
  • the current level I 0 of the current source 512 is adjusted to match a specified current
  • the current level I 0 approximately equals
  • of the current through the sense electrode 702 is approximately Q p times higher than the drive current level I 0 providing: I 0 ⁇
  • the voltage across the measurement port 708 becomes approximately: V ⁇ I 0 /
  • the differential narrowband extrinsic SNR ⁇ SNR ex,s may also be expressed in terms of the normalized reflected impedance
  • to be delivered by the current source 512 may increase by the factor (1 + n C )/n C , hence increasing the losses in the equivalent series resistances R Ls of the inductor 704 by the factor ((1 + n C )/n C ) 2 .
  • the noise voltage Vn for the series resonant configuration is approximately: Vn ⁇ R Ls I 0,n (252) while the voltage change
  • the differential narrowband intrinsic SNR with respect to the drive current noise I 0,n for the series resonant configuration of the circuit 700 of FIG.7J may be expressed as: ⁇ SNR int,s ⁇ (
  • /R Ls (
  • the broadband extrinsic SNR as defined by Equation (62) with respect to the induced voltage component V sW at the fundamental WPT operating angular frequency ⁇ W is considered.
  • the disturbance signal voltage V sn may relate to the WPT coil voltage V WPT as follows: V sn ⁇ V sW ⁇ (C s W/C) V W PT (259) where C s W denotes the mutual capacitance between the sense electrode 702 and the WPT coil (e.g., WPT coil 202 with reference to FIGs.2 and 3).
  • V W in the voltage V for the series resonant configuration of the circuit 700 of FIG.7J becomes approximately: V W ⁇ V sW ⁇ W C ⁇ W L p ⁇ V sW ( ⁇ W / ⁇ s ) 2 /n L (262)
  • the factor ( ⁇ W / ⁇ s ) 2 /n L may be considered as the attenuation of the low frequency induced voltage V sW by the high pass filter effect of the sense circuit 701.
  • the broadband extrinsic SNR with respect to the fundamental WPT fundamental disturbance component V sW for the series resonant configuration of the circuit 700 of FIG.7J may be expressed as: SNR W,s ⁇ (
  • the broadband extrinsic SNR for the series resonant configuration of the circuit 700 of FIG.7J is proportional to the inductance ratio n L , the square of the frequency ratio ⁇ s / ⁇ W , but inverse proportional to the Q-factor Q s of the sense circuit 701.
  • the factor ( ⁇ W / ⁇ p ) 2 /(1 + n L ) may be considered as the attenuation of the low frequency induced voltage V sW by the high pass filter effect of the sense circuit 701.
  • the broadband extrinsic SNR with respect to the WPT fundamental disturbance voltage component V sW for the parallel resonant configuration of the circuit 700 of FIG.7J may be expressed as: SNR W,p ⁇ (
  • the broadband extrinsic SNR for the parallel resonant configuration of the circuit 700 of FIG.7J is proportional to the square of the frequency ratio ⁇ p / ⁇ W , but no function of Qp and n L .
  • Equation 268 the broadband extrinsic SNRs of the series and parallel resonant configurations of the circuit 700 of FIG. 7G as given by Equations (264) and (267), respectively: SNRW,p ⁇ SNRW,s Q s /n L (268) where Q s refers to the Q-factor of the series resonant configuration of the circuit 700. From Equation (268), it can be seen that the broadband extrinsic SNR for the parallel resonant configuration of the circuit 700 of FIG. 7J may be substantially higher than that of the series resonant configuration.
  • the broadband extrinsic SNR of the parallel resonant configuration may be 36 dB higher.
  • may be expressed for the series resonant configuration of the circuit 700 of FIG.7J including the capacitor 715 as:
  • Equations (201) to (268) may also apply to the circuit 720 of FIG.7C with some minor modifications e.g., by replacing the inductance L s by L s + L ⁇ , the series resistance R Ls by R Ls + R w , the inductance L p by L m , and the series resistance R Lp by Rm, where L ⁇ denotes the transformer’s 726 secondary referred leakage inductance, R w its secondary referred equivalent series resistance with respect to the conductor losses, L m its secondary referred main inductance, and Rm its secondary referred equivalent series resistance with respect to the core losses with reference to FIG. 5H.
  • the equivalent circuit model 740-1 as illustrated in FIG. 7K comprises the sense electrode’s 702 capacitance C, the parallel inductor’s 744 inductance LP and its equivalent parallel conductance G Lp , the series capacitor’s 746 capacitance C s , an ideal sense signal voltage source 552, and an ideal current measurement circuit 550.
  • the equivalent circuit model 740-1 includes an admittance ⁇ Z r in parallel to the capacitance C representing the reflected admittance of the object 110, 112, or 114 proximate to the sense electrode 702. (The reflected admittance ⁇ Y r may be regarded as the object 110, 112, or 114 as illustrated in FIG. 7E abstracted away).
  • the equivalent circuit model 740-1 also includes a noise current source I sn in parallel to the capacitance C representing the noise current induced into sense electrode 702 by the electric field as generated when WPT is active.
  • the noise current Isn may include any low frequency component (e.g., the fundamental of the WPT operating frequency and harmonics thereof) as well as any high frequency component (e.g., switching noise at the sense frequency).
  • ⁇ Y r ’ ⁇ Z r ‘ (273) ⁇ Z r ⁇ ⁇ Z r ( ⁇ C) 2 (274) Isn ⁇ V sn ⁇ C (275) ⁇ Y r ’, ⁇ Z r ’, ⁇ Z r , and V sn referring to the normalized reflected admittance, the normalized reflected impedance, the reflected impedance of the object 110 in the sense electrode 702, and the disturbance voltage V sn with reference to the circuit 700 of FIG.7J, respectively.
  • the admittance Y 11 at the measurement port 748 of the circuit 740 of FIG.7K in presence of an object may be expressed as: Y 11 ⁇ G Lp + (j ⁇ L p ) -1 + j ⁇ C + ⁇ Z r (279)
  • occurs substantially at an angular frequency ⁇ satisfying: (j ⁇ L p ) -1 + j ⁇ C ⁇ 0 (280) yielding the parallel resonant angular frequency: ⁇ p ⁇ (L p C) -1/2 (281)
  • the impedance Z 11 may be approximated as: Z 11 ⁇ (j ⁇ C s ) -1 + (j ⁇ C + (j ⁇ L p ) -1 ) -1 + (G Lp + ⁇ Z r )/( ⁇ C - ( ⁇ L p ) -1 ) 2 (291)
  • occurs substantially at an angular frequency ⁇ satisfying: (j ⁇ L p ) -1 + j ⁇ (C + C s ) ⁇ 0 (292) yielding for the series resonant angular frequency: ⁇
  • the series resonant configuration of the circuit 740 of FIG. 7K is employed as an alternative to using a transformer (e.g., transformer 726 of FIG. 7C) for transforming the impedance Z 11 to be within a suitable operating impedance range as previously discussed with reference to FIG.7C.
  • a transformer e.g., transformer 726 of FIG. 7C
  • Equation (302) may also be expressed in terms of the series resonant resistance R s , the electrode 702 capacitance C, and the capacitance ratio n C as: Q s ⁇ n C (1 + n C )/(R s ⁇ s C) (303)
  • the fractional impedance change ⁇ Z’ may also be written in terms of Q s and ⁇ Z r ‘ as: ⁇ Z’ ⁇ Q s ⁇ Y r ‘ n C /(1 + n C ) (305) [0544]
  • Equation (302) may also be expressed in terms of the series resonant resistance R s , the electrode 702 capacitance C, and the capacitance ratio n C as: Q s ⁇ n C (1 + n C )/(R s ⁇ s C) (303)
  • the voltage level V 0 of the voltage source 542 is adjusted to match a specified current
  • the voltage level V 0 approximately equals the voltage across the sense electrode 702 providing the relation: V 0 ⁇
  • the current I at the measurement port 748 becomes approximately: I ⁇
  • 2 G Lp /( ⁇ p C) 2
  • across the sense electrode 702 is approximately:
  • the narrowband SNR at the measurement port 748 of the circuit 740 of FIG.7K may be meaningful to define the narrowband SNR at the measurement port 748 of the circuit 740 of FIG.7K as given by Equation (14), where
  • the SNR as given by Equation (14) is referred herein as to the differential narrowband SNR.
  • denotes the magnitude of the sense signal current and I W the disturbance current at the fundamental WPT operating frequency, which may be a prominent component in In when WPT is active. More specifically, the current
  • the differential narrowband extrinsic SNR of the parallel resonant configuration of the circuit 740 of FIG.7K may be expressed as: ⁇ SNR ex,p ⁇ (
  • / ⁇ p C) (
  • Equation (311) also applies to the series resonant configuration, meaning that: ⁇ SNR ex,s ⁇ ⁇ SNR ex,p (312) [0550]
  • the noise current In for the parallel resonant configuration of the circuit 740 is approximately: In ⁇ G p V 0,n (313) while the current change in presence of an object (e.g., object 112) is:
  • Equation (315) may also be written as: ⁇ SNR int,p ⁇ (
  • 7K may be expressed as: SNRW,p ⁇ (
  • Equation (326) may also be written in terms of the Q-factor Qp and the inductance ratio n C as: SNR W,p ⁇ (
  • the disturbance current I W in the current I for the series resonant configuration of the circuit 740 of FIG.7K becomes approximately: I W ⁇ I sW ⁇ W L ⁇ W C s ⁇ I sW ( ⁇ W / ⁇ s ) 2 /(1 + n C ) (329)
  • the factor ( ⁇ W / ⁇ p ) 2 /(1 +n C ) may be considered as the attenuation of the low frequency induced current I sW by the high pass filter effect of the sense circuit 741.
  • TABLE 3 provides example parameter values as used for a numerical analysis of the series and parallel resonant configuration of the circuit 700 of FIG.7J and the circuit 740 of FIG. 7K. Values for the induced disturbance voltage V sW , the noise voltage V sn , and the equivalent respective currents IsW and Isn of the circuit 740 may be considered typical for the multi-purpose detection circuit 100 integrated into a wireless power transfer structure (e.g., wireless power transfer structure 200 with reference to FIG.2).
  • a wireless power transfer structure e.g., wireless power transfer structure 200 with reference to FIG.2
  • the normalized reflected impedance of the object 114 as given in TABLE 1 may be typical for a human extremity (e.g., a hand) in a distance of 150 mm from a single-ended sense electrode 702 (e.g., capacitive sense element 109a) composed of two sections (as illustrated in FIG.1) each with a form factor of about 350 x 45 mm and electrically connected in parallel.
  • may be within a constraint given by an electromagnetic emission limit of an established EMC standard (e.g., EN 300330).
  • /V 0,n may be typical for a digital implementation of a sense signal source (e.g., sense signal current source 512 and sense signal voltage source 552), respectively, as previously described with reference to FIGs.4 and 5F.
  • TABLE 3 [0558] Numerical results as obtained based on the numerical assumptions of TABLE 3 using the relevant equations as defined above with reference to FIGs.7J and 7K are listed in TABLE 6. TABLE 6 additionally includes numerical results for the angle error arg ⁇ Z’ ⁇ as noted in connection with FIG.7A.
  • the results in TABLE 4 show the circuits and configurations equivalent in terms of the differential narrowband extrinsic SNR ( ⁇ SNR ex ) e.g., with respect to WPT switching noise.
  • the numbers for the differential narrowband intrinsic SNR with respect to thermal (resistance) noise show the circuits and configurations equivalent. They also indicate that thermal noise may have a negligible impact on the overall noise, even when WPT is inactive.
  • the numbers resulting for the broadband extrinsic SNR with respect to the WPT fundamental disturbance voltage (V sW ) show a substantial difference (> 60 dB) between the series resonant configuration of the circuit 700 and 740.
  • the parallel resonant configuration of the circuit 700 and 740 are almost equivalent and the broadband extrinsic SNRs of the circuits and configurations are above 6 dB, which may be a minimum requirement in a practical implementation.
  • TABLE 4 further shows a negligible angle error
  • may be within suitable ranges of low power electronics for the other circuits and configurations as theoretically analyzed herein.
  • the voltage as required to drive the circuit 740 in the parallel resonant configuration may exceed a constraint as given by electronic circuitry and may require transformation e.g., using the transformer 726.
  • FIG. 7L illustrates a “ ⁇ ”-equivalent circuit model applicable to the capacitive sense elements used in the 760, 770, and 780 of FIGs.7G, 7H, and 7I, respectively.
  • the circuit model 762-1 comprises three capacitances connected in a “ ⁇ ”-topology and related to the capacitances C 1 , C 2 , and the mutual capacitance C M as indicated in FIGs.7G, 7H, and 7I.
  • FIG.7M illustrates another equivalent circuit model 762-2 applicable to the capacitive sense elements used in the circuits 760, 770, and 780 of FIGs.7G, 7H, and 7I, respectively.
  • the circuit model 762-2 comprises the capacitances C 1 and C 2 in parallel to the respective voltage-controlled current sources I ind,1 and I ind,2 representing the current induced into the primary and secondary sense electrode, respectively.
  • the equivalent circuit model 762-2 of FIG. 7M is electrically dual to the equivalent circuit model 562-2 of FIG.5J.
  • FIG.7N shows a table of a summary of selected equations with respect to the resonant frequency, the Q-factor and the impedance or admittance of the sense circuit, fractional change, and the various SNRs for the series and parallel resonant configurations of the circuit 700 of FIG. 7J and the circuit 740 of FIG.
  • FIG. 8A illustrates a complex plane 800 or more precisely a portion of the complex plane comprising quadrant 1 where the reflected admittance ⁇ Z r of different types (categories) of objects (e.g., object 110, 112, 114, or vehicle 330) may occur if proximate to a capacitive sense element (e.g., sense electrode 702 with reference to FIG.7A).
  • a capacitive sense element e.g., sense electrode 702 with reference to FIG.7A.
  • FIG.8A shows shaded areas (angle ranges 802 and 804) where the reflected admittance ⁇ Y r of different types (categories) of objects (e.g., object 110, 112, 114) may be measured at a sense frequency (e.g., in the MHz range).
  • a sense frequency e.g., in the MHz range.
  • the angle ranges 802 to 804 indicated in FIG. 8A may be not drawn to scale and should be considered qualitative rather than quantitative.
  • angle ranges may also depend on the particular sense frequency, certain characteristics of the capacitive sense element (e.g., sense element 702), the inductive sensing effect of the capacitive sense element as previously discussed with reference to FIG.1, the size, position, and orientation of an object relative to the capacitive sense element.
  • the complex plane 800 and the shaded areas may also apply to the reflected impedance ⁇ Z r by simply relabeling the real and imaginary axis by Re ⁇ Z r ⁇ and jIm ⁇ Z r ⁇ , respectively (not shown in FIG.8A).
  • FIG.8A illustrates a metallic object 110 represented by a 1 € cent coin (object 110a), two different types of non-living dielectric objects 112 such as a piece of plastic (object 112c) and water drops (object 112d). Moreover, it illustrates a living object 114 representing a hand (symbolizing a human extremity).
  • FIG. 8A shows the metallic object 110a, the dielectric object 112c, and the living object 114 associated with the angle range 802. Further, FIG. 8A shows water drops (object 112d) associated with the angle range 804.
  • water dripping from a wet underbody of a vehicle (e.g., vehicle 330) onto the housing of a wireless power transfer structure (e.g., housing 328 of wireless power transfer structure 200 of FIG. 3) integrating a capacitive sense element (e.g., capacitive sense element 109a) may cause a false positive detection. Therefore, it may be desirable to discriminate water drops (object 112d) based on the angle arg ⁇ Z r ⁇ to prevent a false positive detection due to the water drops.
  • the equivalent circuit model 810 comprises a primary parallel capacitance C ⁇ - C M , a secondary parallel capacitance C ob – C M , a parallel conductance G ob , and a mutual capacitance C M .
  • the capacitance C ob – C M together with conductance Gob represents an abstract model of the object (e.g., object 110, 112, 114, or vehicle 330) indicated in FIG. 8B by a dashed box.
  • the capacitance C ⁇ refers to the sense electrode’s 702 capacitance to ground as it may be measured at the signal terminal 703 in presence of an object (e.g., object 110, 112, or 114) that is modelled by at least one of an infinite capacitance C ob and infinite conductance Gob (secondary-side short circuit).
  • the capacitance C ob refers to the equivalent capacitance of the object in presence of the sense electrode 702 shortened to ground at its signal terminal 703 (primary-side short circuit).
  • the mutual capacitance C M stands for the capacitive coupling between the sense electrode 702 and the object.
  • Both capacitances C ob and C M may relate to the object’s size, geometry, position, and orientation relative to the sense electrode 702 and ground, but also to electrical properties of the materials the object is composed of. It may be appreciated that the equivalent circuit model also applies to any other capacitive sense element such as e.g., 732, 762, and 772 illustrated in FIGs.7F to 7I.
  • any real heterogenous object e.g., object 110, 112, or 114
  • ⁇ r refers to the relative real permittivity
  • ⁇ r’ to the relative imaginary permittivity related to the electrical losses of the material.
  • the relative imaginary permittivity may comprise a dielectric loss coefficient ⁇ d,r ’’ attributed to bound charge and dipole relaxation phenomena of the material and another loss coefficient attributed to the material’s electrical conductivity ⁇ .
  • the complex relative permittivity of the equivalent material may also depend on the size, geometry, position, and orientation of the real object relative to the capacitive sense element (e.g., sense electrode 702).
  • the dielectric loss coefficient ⁇ d,r ’’ is normally negligible meaning that electrically insulating materials with virtually zero conductivity ( ⁇ ⁇ 0) exhibit a loss angle close to zero ( ⁇ ⁇ 0).
  • the imaginary relative permittivity of distilled water is ⁇ r’’ ⁇ 0, while for water with some ion content, ⁇ r’’ is governed by its conductivity ⁇ .
  • tan ⁇ may approach infinity ( ⁇ ⁇ 90°).
  • the object e.g., object 110, 112, 114, or vehicle 330
  • Y ob G ob + j ⁇ C ob .
  • the factor a is indicative of how easily a dielectric object (e.g., object 112) can be polarized by an externally applied electric field and herein referred to as polarizability.
  • the polarizability a generally depends on the size, geometry, position, and orientation of the object relative to the sense electrode 702 and the ground. For objects made of an ordinary dielectric material, the polarizability must be in a range 1 ⁇ a ⁇ ⁇ .
  • exposing a dielectric object e.g., object 112 to an electric field polarizes its material in turn starting to generate its own (secondary) electric field referred to as a polarization field.
  • This polarization field counteracts the applied field in the object’s material until an equilibrium state is reached.
  • This mechanism is also known as depolarization.
  • Depolarization is commonly quantified by the depolarization factor in analogy to the magnetic depolarization in ferromagnetic bodies.
  • the depolarization factor may be defined as the reciprocal 1/a of the polarization factor. For small a (e.g., 1 ⁇ a ⁇ ⁇ r ⁇ ), the internal electric field (in the material) may be substantially reduced (e.g., virtually cancelled out) by the polarization field. In contrast, a dielectric object with high a (e.g., a >> ⁇ r ⁇ ) experiences little depolarization, resulting in an internal field substantially equal to the applied field.
  • Polarizability of a thin dielectric sheet may be close to one (a ⁇ 1) with respect to an electric field perpendicular to the sheet.
  • a ⁇ 1 For an oblate dielectric sphere subjected to a uniform electric field parallel to its short (minor) axis, the polarizability can be found in the range 1 ⁇ a ⁇ 3.
  • the polarizability a is higher in any other axis and is thus anisotropic.
  • polarizability is again anisotropic and highest in its major axis (a > 3).
  • the major axis is sometimes also referred to as the “easy” axis.
  • the polarization field neutralizes a portion of the internal field, it contributes to the external field. It may be appreciated that an increase of the external field also causes an increase of the capacitance and thus an increase of the susceptance (imaginary admittance) as measured at terminal 703 when the object is introduced.
  • depolarization may prevent generating losses resulting in a reflected admittance (susceptance) that is substantially imaginary (e.g., with arg ⁇ Z r ⁇ in the angle range 802 of FIG. 8A).
  • a reflected admittance susceptance
  • the losses may become more prominent, reflecting an admittance whose angle arg ⁇ Z r ⁇ tends to the complementary loss angle 90° - ⁇ (e.g., in the angle range 804 of FIG.8A).
  • the effective relative permittivity ⁇ r,eff corresponds to the ratio of the applied field strength to the internal field strength.
  • this ratio approaches the material’s relative permittivity ( ⁇ r,eff ⁇ ⁇ r).
  • the coupling factor approaches zero (k C ⁇ 0) while for the thin dielectric needle (a ⁇ ⁇ ), it approaches unity (k C ⁇ 1).
  • the shape (form factor) of an object e.g., object 112 is responsible for its polarizability in a substantially uniform electric field. Exposing an object (e.g., object 112) to a substantially uniform field requires the object to be small compared to its distance to the sense electrode 702. Referring to FIG.
  • a comparatively large object closely proximate to the sense electrode 702 may be subjected to a substantially non- uniform field.
  • Such a scenario may be characterized by a relatively high mutual capacitance C M (e.g., higher than the object’s equivalent capacitance C ob ) and consequently a coupling factor near or even close to one (k C ⁇ 1) (a strongly coupled regime).
  • ⁇ ⁇ 1 it may be appreciated that only a high factor a (e.g., a ⁇ ⁇ ) can satisfy Equation (347) for k C ⁇ 1 and it may be concluded that an object (e.g., object 112) exposed to an electric field in a strongly coupled regime experiences enforced polarization regardless of its shape.
  • Enforced polarization may be illustrated by the example of a cube-shaped dielectric body (e.g., object 112) filling the air space between the plates of a parallel plate capacitor whose first and second plate may be considered as the sense electrode 702 and the ground, respectively.
  • the dielectric body may have an unfavorable formfactor with respect to polarizability in a uniform field.
  • Equation (348) corresponds to the admittance increase when inserting dielectric material with ⁇ r into the parallel plate capacitor.
  • Equation (348) demonstrates that the angle arg ⁇ Z r ⁇ directly reflects the complementary loss angle 90° - ⁇ of a dielectric fill material with ⁇ r ⁇ >> 1 similarly to a dielectric object (e.g., object 112) with a formfactor favorable for high polarization if subjected to a substantially uniform electric field as previously discussed. It may be argued that the field as produced by the parallel plate capacitor is also uniform. However, this is only true for the space between the capacitor’s plates (in the dielectric fill material) but false if the space outside is considered too.
  • the parallel plate capacitor shows an example of a highly non-uniform field.
  • the angle arg ⁇ Y r ⁇ is indicative of the complementary loss angle 90° - ⁇ of a dielectric object (e.g., object 112) if the object’s formfactor is favorable for polarization (a >> ⁇ r ⁇ ) or if the object is in a strongly coupled regime.
  • An object with low polarizability in a weakly coupled regime may reflect an angle arg ⁇ Z r ⁇ close to 90° regardless of its loss angle ⁇ .
  • Equation (352) it may be appreciated that an object (e.g., object 112) with low polarizability (e.g., 1 ⁇ a ⁇
  • FIG.8C illustrates quadrant 1 of another complex plane 820 of the normalized reflected admittance ⁇ Z r /
  • FIG.8C also shows that objects with a high effective relative permittivity (e.g., ⁇ r,eff ⁇ >> 1) reflect a normalized admittance ⁇ Y r /
  • This may include objects characterized by a predominant real part ⁇ r,eff ‘ >> 1 (e.g., dielectric object 112 or living object 114) as well as objects characterized by a high conductivity ⁇ >> 1 (e.g., metal object 110 or vehicle 330).
  • a dielectric object with a low effective relative permittivity may reflect an admittance with an angle arg ⁇ Y r ⁇ similar to the complementary loss angle 90° - ⁇ (e.g., in the angle range 804).
  • various living and non-living objects e.g., objects 110, 112, and 114 were tested with respect to the reflected admittance ⁇ Z r at a sense frequency of 3 MHz when brought into proximity of a capacitive sense element (e.g., sense electrode 702, which may correspond to the capacitive sense element 109a of FIG.
  • the reflected admittance ⁇ Z r was determined by measuring the change ⁇ Z of the impedance Z 11 at the measurement port 728 of a sense circuit 721 of FIG. 7C using a properly calibrated impedance measurement circuit (e.g., circuit 104 of FIG.4).
  • living objects e.g., a human body extremity of an adult, of an infant, a cat, etc.
  • TABLE 5 lists the real and imaginary part of the complex permittivity ⁇ r and the related conductivity ⁇ of various human tissue types at 3 MHz as they may be found in scientific publications. These tissue types together may constitute a substantial portion of a human body extremity.
  • the numbers in TABLE 5 suggest a relative permittivity generally in a range ⁇ r’ > 30 and ⁇ r ’’ > 36 for a living object (e.g., object 114).
  • Electromagnetic field exposure regulations may require a living object to be detected already at a distance from the capacitive sense element (e.g., sense electrode 702 of FIG.7A) in a weakly coupled regime.
  • a living object in a weakly coupled regime typically exhibits a low polarizability (e.g., a in the order of 3) thus reflecting an admittance ⁇ Z r that is substantially imaginary (e.g., in the angle range 802 of FIG. 8A) as previously discussed and also experimentally observed.
  • a reflected admittance ⁇ Y r virtually at the imaginary axis was also measured for metallic objects (e.g., object 110) made of a material with a conductivity e.g., ⁇ > 10 MS/m as expected from Equation (349).
  • nonliving dielectric objects e.g., object 112
  • a piece of plastic with ⁇ r‘ ⁇ 3 e.g., a polyethylene terephthalate (PET) plastic bottle filled with distilled water ( ⁇ ⁇ 0), filled with tap water ( ⁇ ⁇ 0.5 mS/m), filled with salt water ( ⁇ ⁇ 40 mS/m), potting soil, wet foliage, snow, and ice.
  • All test objects reflected an admittance ⁇ Y r virtually at the imaginary axis (e.g., in the angle range 802 of FIG. 8A).
  • TABLE 6 lists ⁇ r‘, ⁇ r‘’, and the loss tangent tan ⁇ of solid and liquid dielectric materials.
  • Equation (352) an object (e.g., object 112) of any of these materials may cause a substantially imaginary reflected admittance (e.g., in the angle range 802).
  • a substantially imaginary reflected admittance e.g., in the angle range 802
  • water filled in a plastic bottle and disposed in a weakly coupled regime may reflect an admittance ⁇ Y r close to the imaginary axis due to its high relative permittivity ⁇ r‘ ⁇ 78 and low polarizability (e.g., a in the order of 3) as expected from Equations (339) and (352).
  • Tests were also performed with water dripping on the plastic housing of a wireless power transfer structure (e.g., housing 328 of the wireless power transfer structure 200 with reference to FIG.3) integrating a capacitive sense element (e.g., capacitive sense element 109a of FIG. 3). These tests may be representative for rain water, melt water, or condensation dripping from the vehicle’s underbody (e.g., vehicle 330) onto a sensitive area above the capacitive sense element when the vehicle is parked over the wireless power transfer structure.
  • a wireless power transfer structure e.g., housing 328 of the wireless power transfer structure 200 with reference to FIG.3
  • capacitive sense element e.g., capacitive sense element 109a of FIG. 3
  • tap water droplets after their impact on the surface of the housing above the capacitive sense element, may reflect an admittance with an angle arg ⁇ Y r ⁇ substantially lower than measured using the same water contained in a plastic bottle as mentioned above.
  • Angles arg ⁇ Z r ⁇ as low as 25° were observed after the impact of a water droplet.
  • a low angle arg ⁇ Z r ⁇ implies an effective relative permittivity
  • the flattening at impact may cause a substantial increase of its polarizability with respect to a major axis (e.g., from a ⁇ 3 to a >> 3) and consequently, the angle arg ⁇ Z r ⁇ to shift from about 90° (e.g., in angle range 802) towards a lower value (e.g., in the angle range 804) as shown by the theory above.
  • This is particularly true at positions where the incident electric field has a substantial component in the major axis of the flattened water object e.g., when the droplet hits a point near the upper edge of a sense electrode (e.g., sense electrode 109a) or is gliding down the ramp of housing 328 and reaches the lower edge of the sense electrode.
  • the electric field in these edge zones is oblique relative to the surface (ramp) of housing 328 thus has a component in an axis of increased polarizability.
  • Specific lab experiments were carried out to further investigate this phenomenon using a test set up with water contained in a plastic hose disposed proximate to a capacitive sense element (e.g., capacitive sense element 109a).
  • the plastic hose was connected to a water reservoir allowing the water level in the hose to be accurately adjusted. More specifically, in a first experiment, the reflected admittance ⁇ Y r was measured for a change of water level by 60 mm in a first plastic hose with a diameter of 2 mm.
  • a spherical water droplet of 4 mm diameter provides a volume-to-surface area of 0.66 mm.
  • the first and second experiments were performed with commercially off-the-shelf distilled water, tap water with about 0.03% of calcium and magnesium ions, and with water of different salinity using a NaCl solution. Starting with distilled water, the NaCl concentration was successively increased (doubled) in a series of measurements.
  • FIG.8D displays the normalized reflected admittances ⁇ Z r /
  • the limit reflected admittance ⁇ Z r , ⁇ was determined by extrapolating the series of measured data points ( ⁇ Y r ) towards a fictitious water sample with an infinite conductivity ⁇ . Further, it illustrates objects 112 referring here to the cylindrically shaped water samples that are added to the existing water column in the first and second experiment as described above.
  • the reflected admittance ⁇ Z r as determined in the first and second experiment refers to the admittance change as produced by increasing the water level in the hose by 60 mm and 15 mm, respectively. It is also noted that a different admittance change may result if the water samples (object 112) are introduced in absence of the hose (e.g., in a thin plastic capsule with 2 x 60 mm fill volume).
  • the circular and rectangular marks refer to the normalized reflected admittance as determined for the 2 x 60 mm and for the 4 x 15 mm water sample, respectively, using distilled water, tap water, and the NaCl solution at concentrations as indicated in percentage (%).
  • the table on the right also indicates the mass percentage of NaCl dissolved in water, the corresponding molarity (in moles per liter), and the conductivity ⁇ in mS/m as predicted by theory.
  • the data points displayed in FIG.8D suggest that the effective relative permittivity ⁇ r,eff ’ of water with a low NaCl concentration (e.g., ⁇ 0.1%) substantially reduces as the volume-to-surface area ratio decreases (e.g., below 1 mm), but steadily increases as the NaCl concentration increases.
  • FIG. 8D To illustrate the variation of the angle arg ⁇ Y r ⁇ over the range of tested ion concentrations in the 2 x 60 mm water sample, FIG.
  • FIG. 8E displays the unity reflected admittance ⁇ Y r /
  • FIG. 8E shows the angle of the reflected admittance ⁇ Z r extremely sensitive on the ion concentration.
  • a very low NaCl concentration e.g., ⁇ 0.01%
  • the angle initially decreases as the NaCl concentration increases reaching a minimum of 28.6° at about 0.04% NaCl.
  • the angle arg ⁇ Y r ⁇ turns around and reaches 86.5° at 20.5%.
  • the tap water sample reflected an admittance with an angle close to the minimum angle.
  • tests performed with water collected from a vehicle’s underbody provide evidence that rain or melt water on the road splashing to the vehicle’s underbody already contains enough dissolved minerals to produce an angle substantially different from 90° (e.g., ⁇ 60°).
  • FIG.8F displays the unity reflected admittance ⁇ Y r /
  • the data suggests that the angle variation ratio reduces as the volume-to-area ratio of the water sample increases, which may be explained by the theory of capacitive sensing of dielectric objects as provided herein.
  • FIG.8G displays the ratios ⁇ e,eff/ ⁇ e vs.
  • ⁇ eff / ⁇ in a log-log diagram 860, where ⁇ e and ⁇ denote the electric susceptibility and the conductivity, respectively, of water as predicted by theory for the NaCl concentrations as indicated in FIG.8G, for 3 MHz, and for a water temperature of 25°C.
  • the diagram 860 of FIG.8G reveals that the ratio ⁇ e,eff / ⁇ e increases with increasing NaCl concentration while the ratio ⁇ eff / ⁇ decreases. However, both ratios converge to a limit value for a vanishing NaCl concentration (e.g., ⁇ 0.02%).
  • the diagram 880 shows the real part ⁇ r,eff ‘ of the effective relative permittivity of the 2 x 60 mm water sample close to one at ⁇ 0% NaCl (distilled water) and increasing as the NaCl concentration increases reaching a value of ⁇ 1.8 at 20.5% NaCl, while the absolute value of the imaginary part (representing the electrical loss) ⁇ r,eff ‘’ varies between ⁇ 0 and ⁇ 4.8.
  • the effective relative permittivity ⁇ r,eff ‘ starts at ⁇ 1.2 for ⁇ 0% NaCl (distilled water) and reaches ⁇ 3.1 at 20.5% NaCl, while ⁇ r,eff ‘’ varies between ⁇ 0 and ⁇ 10.5.
  • discriminating water (e.g., object 112) dripping from the vehicle’s (e.g., vehicle 330) underbody may also be accomplished based on other electrical characteristics as they may be measured in some implementations of the multi-purpose detection circuit 100 and as mentioned in any of the US patent applications herein incorporated by reference.
  • water (e.g., object 112) dripping from the vehicle’s (e.g., vehicle 330) underbody may also cause a change in an electrical characteristic different from a change produced by other objects (e.g., object 110 and 114).
  • FIG.9A is a circuit diagram of a circuit 900 illustrating an example implementation of a portion of a multi-purpose detection circuit 100.
  • the circuit 900 of FIG.9A illustrates an analog front-end circuit portion of the multi-purpose detection circuit 100 with reference to FIGs. 1 and 4.
  • FIG.9A excludes various other signal generation, processing, control, and evaluation circuits (e.g., as shown in FIG. 4) that may be needed in some implementations of a multi-purpose detection circuit 100.
  • the circuit 900 implements inductive and capacitive sensing measuring an impedance based on the current source voltage measurement approach as previously described in connection with FIGs.5A and 7A, respectively.
  • the circuit 900 may be subdivided into a driver circuit 402, a plurality of inductive sense circuits 106, a plurality of capacitive sense circuits 108, and a measurement amplifier circuit 404 with reference to the generic block diagram of FIG. 4.
  • the driver circuit 402 and the measurement amplifier circuit 404 constitute a portion of the measurement circuit 104 with reference to FIGs. 1 and 4.
  • the plurality of inductive sense circuits 106 includes sense circuits 106a, 106b, ..., 106n (106n not shown in FIG. 9A for purposes of illustration).
  • the plurality of capacitive sense circuits 108 includes sense circuits 108a, 108b, ..., 108n, (108a and 108b not shown in FIG.9A for purposes of illustration).
  • each of the plurality of inductive sense circuits 106 have an identical circuit topology.
  • each of the plurality of capacitive sense circuits 108 have an identical circuit topology. Therefore, descriptions given below for the inductive sense circuit 106a also apply to the other inductive sense circuits (e.g., 106b) and descriptions given below for the capacitive sense circuit 108n also apply to the other capacitive sense circuits (e.g., 108a).
  • Each of the plurality of inductive sense circuits 106 provides a first measurement port 936 (indicated in FIG.9A by a terminal) for driving the inductive sense circuit (e.g., sense circuit 106) with an electrical current I1 (as indicated in FIG. 9A) and a second measurement port 937 (indicated in FIG. 9A by a terminal) for measuring an electrical voltage V 2 (as indicated in FIG. 9A) e.g., in response to the current I1. Therefore, the sense circuits 106 may be considered as two- port circuits.
  • each of the plurality of capacitive sense circuits 108 provides a first measurement port 938 (indicated in FIG.9A by a terminal) for driving the capacitive sense circuit (e.g., sense circuit 108n) with the current I 1 (as indicated in FIG.9A) and a second measurement port 939 (indicated in FIG. 9A by a terminal) for measuring the voltage V 2 (as indicated in FIG. 9A) e.g., in response to the current I 1 . Therefore, the sense circuits 108 may be considered as two- port circuits.
  • the driver circuit 402 includes an input multiplexer circuit 910 to selectively (e.g., sequentially) drive each of the plurality of sense circuits 106 and 108 with the current I1.
  • the measurement amplifier circuit 404 includes an output multiplexer circuit 940 configured to selectively (e.g., sequentially) measure the voltage V 2 in each of the plurality of sense circuits 106 and 108. More specifically, but not indicated in FIG.9A for purposes of illustration, the current I1 driving the sense circuit 106a may be denoted by I1a, the current I1 driving the sense circuit 106b may be denoted as I 1b , etc.
  • the circuit 900 may be configured and operated in a mode to selectively (e.g., sequentially) measure an intra-sense circuit transimpedance Z 21 e.g., between the measurement ports 936 and 937 of each of the plurality of the sense circuits 106.
  • This intra-sense circuit transimpedance Z 21 may be defined for the sense circuit 106a as: Z2a1a ⁇ V 2 a / I1a (352)
  • the two-port transimpedance Z 21 substantially equals the one-port impedance Z 11 as it may be measured at the first measurement port (e.g., measurement port 936) with the second measurement port (e.g., measurement port 937) open-circuited.
  • the circuit 900 may also be configured and operated in a mode to selectively (e.g., sequentially) measure an inter-sense circuit transimpedance Z 21 e.g., between each of a plurality of pairs of sense circuits associated with neighboring sense elements (e.g., inductive sense element 107a and 107b) providing sufficient cross-coupling.
  • an inter-sense circuit transimpedance Z 21 e.g., between each of a plurality of pairs of sense circuits associated with neighboring sense elements (e.g., inductive sense element 107a and 107b) providing sufficient cross-coupling.
  • inter-sense circuit transimpedance Z 21 as measured between the measurement port 936 of sense circuit 106a and the measurement port 937 of sense circuit 106b may be defined as: Z 2a1b ⁇ V 2b / I1a (353) [0602] In some implementations or operations, inter-sense circuit transimpedance Z 21 measurements are performed between pairs of inductive sense circuits (e.g., inductive sense circuits 106a and 106b) and between pairs of capacitive sense circuits (e.g., capacitive sense circuits 108a and 108b).
  • the intra-sense circuit transimpedance Z 21 herein is often referred to as the impedance Z 11 and the inter-sense circuit transimpedance Z 21 as the transimpedance Z 21 .
  • both Z 11 and Z 21 may represent a transimpedance.
  • an object e.g., object 110
  • the neighboring sense elements e.g., 107a and 107b
  • the inductive sense circuit 106a includes an inductive sense element 107a including a sense coil (e.g., sense coil 502 of FIG.5A) with an inductance L, a first capacitor (e.g., capacitor 504 of FIG. 5A) with capacitance C s , an inductor (e.g., inductor 506 of FIG.
  • a sense coil e.g., sense coil 502 of FIG.5A
  • a first capacitor e.g., capacitor 504 of FIG. 5A
  • C s capacitance C s
  • an inductor e.g., inductor 506 of FIG.
  • the first capacitor 504 is electrically connected in series to the inductive sense element 107a that also connects to ground.
  • the inductor 506 is electrically connected in parallel to the series circuit of capacitor 504 and inductive sense element 107a.
  • the second capacitor 928 capacitively couples the series circuit capacitor 504 and inductive sense element 107a to the measurement port 936, while the third capacitor 929 capacitively couples to the measurement port 937.
  • each of the plurality of inductive sense circuits 106 is configured (tuned) to provide a minimum of the impedance
  • at least the capacitor 504 is of a type with a low temperature coefficient providing high thermal stability (e.g., a NP0-type capacitor) reducing thermal drift of an electrical characteristic (e.g., an impedance Z 11 ) as measured at each of the plurality of inductive sense circuits 106a, 106b, ..., 106n.
  • the capacitor 504 is a temperature compensation capacitor configured to compensate at least a portion of a temperature drift of the inductive sense element 107a.
  • the inductor 506 may use a ferrite core or may be an air coil e.g., for purposes of a higher linearity.
  • the plurality of inductors 506 is arranged to reduce a magnetic field coupling between neighboring inductors 506, e.g., by an alternating orientation.
  • the inductor 506 is electromagnetically shielded to reduce at least one of a magnetic field coupling between neighboring inductors 506 and a disturbance voltage induced into the inductor 506 e.g., by the magnetic field as generated by the wireless power transfer structure (e.g., wireless power transfer structure 200 with reference to FIGs 2 and 3).
  • the wireless power transfer structure e.g., wireless power transfer structure 200 with reference to FIGs 2 and 3.
  • the first capacitor 504 together with the parallel inductor 506 form a 2 nd order high pass filter to attenuate a low frequency disturbance component (e.g., at the WPT frequency) in the voltage V as previously discussed with reference to FIG. 5A.
  • the capacitor 504 together with the parallel inductor 506 may be configured to attenuate this low frequency disturbance component to a level e.g., significantly below the level of the voltage V 2 in response to the respective current I 1 at the sense frequency. Therefore, this high pass filter may substantially reduce dynamic range requirements in the measurement amplifier circuit 404 and in a further processing (e.g., in the signal processing circuit 408 with reference to FIG.4). It may also reduce any cross-modulation effects between any low frequency signals at the WPT operating frequency (fundamental and harmonics thereof) and the sense signal at the sense frequency. Cross-modulation may be produced e.g., by non-linear distortion effects in the measurement amplifier circuit 404.
  • this high pass filter may exert a minor impact on the voltage V 2 and thus on the measured impedance Z 11 and which may be corrected in a further processing (e.g., in the signal processing circuit 408 of FIG. 4). Any phase shift caused by this high pass filter may be determined e.g., by performing a calibration as previously discussed with reference to FIG.5A.
  • the second capacitor 928 may be needed in some implementations to block any DC flow at the output of the driver circuit 402. In an aspect, the capacitor 928 may also help to attenuate any residual low frequency voltage component (e.g., at the WPT operating frequency) at the output of the driver circuit 402.
  • the third capacitor 929 may be needed in some implementations to block any DC flow at the input of the measurement amplifier circuit 404. In some aspect, the capacitor 929 may also help to attenuate any residual low frequency current component (e.g., at the WPT operating frequency) at the input of the measurement amplifier circuit 404.
  • the intra-sense circuit transimpedance Z 21 substantially equals the impedance Z 11 as discussed above.
  • of the inductive sense circuit 106a at series resonance is assumed in the suitable measuring range of the measurement circuit (e.g., measurement circuit 104 with reference to FIG. 4). Therefore, the inductive sense circuits 106 as illustrated in FIG.
  • the capacitive sense circuit 108n includes a capacitive sense element 109n including a sense electrode (e.g., sense electrode 702 of FIG. 7C illustrating a single-ended sense electrode) having a capacitance C, a series inductor 724 (e.g., series inductor 724 of FIG. 7C) having an inductance L s , and a transformer 726 (e.g., transformer 726 of FIG. 7C) providing a primary and secondary port, a secondary-referred main inductance L m and a voltage transformation ratio 1:nVT.
  • a sense electrode e.g., sense electrode 702 of FIG. 7C illustrating a single-ended sense electrode
  • a series inductor 724 e.g., series inductor 724 of FIG. 7C
  • L s inductance L s
  • transformer 726 e.g., transformer 726 of FIG. 7C
  • first capacitor 930 with a capacitance C b3 and a second capacitor 931 with a capacitance Cb4 e.g., for purposes as previously discussed with reference to the inductive sense circuits 106 of FIG. 9A.
  • the inductor 724 is electrically connected in series to the capacitive sense element 109n.
  • the series circuit of inductor 724 and capacitive sense element 109n is electrically connected to the transformer’s 726 secondary port that also connects to ground.
  • the transformer’s 726 primary port is capacitively coupled to the measurement ports 938 and 939 via capacitors 930 and 931, respectively, and also electrically connects to ground.
  • the transformer 726 comprises a primary winding and a galvanically isolated secondary winding, both windings wound on a common ferrite core as indicated in FIG. 10.
  • An example transformer 726 configured for a nominal sense frequency in the MHz-range uses a two-hole ferrite core.
  • each of the plurality of capacitive sense circuits 108 is configured (tuned) to provide a minimum of the impedance magnitude
  • the inductor 704 may be of a type with a low temperature coefficient providing higher thermal stability reducing thermal drift of the impedance Z 11 as measured at each of the plurality of the capacitive sense circuits 108.
  • the inductor 704 is a temperature compensation inductor configured to compensate at least a portion of a temperature drift of the capacitive sense element 109n.
  • a supplementary temperature compensation capacitor is electrically connected in parallel to the capacitive sense element 109n (e.g., as illustrated by capacitor 715 in FIG.7B) configured to compensate at least a portion of the total temperature drift of the inductor 704 and the capacitive sense element 109n.
  • the inductor 724 may uses a ferrite core or is an air coil providing higher linearity.
  • the plurality of inductors 724 is arranged to reduce a magnetic field coupling between neighboring inductors 724 and a neighboring inductor 506 of an inductive sense circuit (e.g., inductive sense circuit 106a), e.g., by an alternating orientation.
  • At least one of the inductor 724 and the transformer 726 is electromagnetically shielded to reduce at least one of a magnetic field coupling between neighboring inductors 724, 506, and a disturbance voltage induced e.g., by the magnetic field as generated by the wireless power transfer structure (e.g., wireless power transfer structure 200 with reference to FIGs 2 and 3).
  • the wireless power transfer structure e.g., wireless power transfer structure 200 with reference to FIGs 2 and 3.
  • at least a portion of the required inductance L s is realized by a leakage inductance of the transformer 726 as previously mentioned with reference to the circuit 720 of FIG.7C.
  • the secondary-referred main inductance L m of the transformer 726 together with capacitance C of the capacitive sense element 109n form a 2 nd order high pass filter to attenuate a low frequency disturbance component in the voltage V 2 as previously discussed with reference to FIGs.7A, 7C, and the inductive sense circuits 106 of FIG.9A.
  • the transformer 726 may be configured to attenuate this low frequency disturbance component to a level e.g., significantly below the level of the voltage V 2 in response to the respective current I 1 at the sense frequency.
  • this high pass filter may exert a minor impact on the voltage V 2 and thus on the measurement of the impedance Z 11 and which may be corrected in a further processing (e.g., in the signal processing circuit 408 of FIG.4). Any phase shift caused by this high pass filter may be determined e.g., by performing a calibration as previously discussed with reference to FIG.7A.
  • the transformer 726 may be employed to transform the impedance Z 11 of the sense circuit 108n as presented at the series resonance into the suitable measuring range of the measurement circuit (e.g., measurement circuit 104 of FIG. 4) by adjusting the transformation ratio 1:nVT accordingly.
  • the driver circuit 402 includes a driver amplifier circuit 902, an input multiplexer circuit 910 illustrated in FIG. 9A as a plurality of switches 911a, 911b, ..., 911n, and a plurality of series resistors 914 and 915.
  • the series resistors 914 connected to the inductive sense circuits 106 have a resistance R ser1
  • the series resistors 915 connected to the capacitive sense circuits have a resistance R ser3 that generally differs from R ser1 .
  • Each of the outputs of the input multiplexer circuit 910 connects to the respective sense circuit of the plurality of sense circuits 106 and 108 via the respective series resistors 914 and 915.
  • the driver circuit 402 is configured to operate as a current source (e.g., current source 512 as described in connection with FIG. 5A) and to selectively (e.g., sequentially) apply a drive current signal I1 at the sense frequency to each of the plurality of inductive sense circuits 106 and to each of the plurality of the capacitive sense circuits 108.
  • the drive current signal I1 (e.g., a sinusoidal signal) is based on a driver input signal which may be an output of the signal generator circuit 406 with reference to FIG.4.
  • the driver amplifier circuit 902 as illustrated in FIG.9A by example includes an amplifier 904 and external resistance circuitry comprising a first (feedback) resistor 906 and a second resistor 908 for adjusting a gain.
  • the amplifier is at least one of a low noise operational amplifier and an operational amplifier providing high linearity.
  • the driver amplifier circuit 902 is configured to receive the driver input signal and to provide a corresponding output with an accurate and stable voltage (a voltage source output).
  • a DC voltage may be present at any of the plurality of outputs of the driver circuit 402 caused e.g., by a DC offset in the amplifier’s 904 output voltage or by certain types of analog switches (e.g., switch 911a) of the input multiplexer circuit 910.
  • the driver amplifier circuit 902 together with series resistors (e.g., series resistor 914) mimic a current source characteristic at each of the plurality of outputs of the driver circuit 402.
  • the series resistor e.g., series resistor 914 with a resistance (e.g., R ser1 ) substantially larger (e.g., 10 times larger) than the impedance magnitude
  • Increasing the series resistance e.g., R ser1
  • the drive current level may impact a SNR as previously defined with reference to FIG. 5F.
  • the series resistances R ser1 and R ser3 may represent a trade-off between a current source characteristic and a SNR.
  • the current source characteristic is realized using a resistor (e.g., series resistor 914) with a lower resistance (e.g., R ser1 ) instead using the DC block capacitor (e.g., capacitor 928) with a higher reactance, together providing an impedance substantially larger (e.g., 10 times larger) than the impedance as presented at the primary port of the transformer 726 at series resonance.
  • the resistor e.g., series resistor 914
  • the high impedance is realized by the DC block capacitor (e.g., capacitor 928).
  • the high series impedance as required to mimic a current source characteristic is realized at least in part by using at least one of an inductor (not shown in FIG.9A) and a leakage inductance of a transformer.
  • the current source characteristic is realized using a driver amplifier circuit 902 configured as a regulated current source. An example current source circuit using an operational amplifier is illustrated in FIG. 9B.
  • the current source characteristic as apparent at each of the plurality of outputs of the of the driver circuit 402 may be significantly impaired by the parasitic capacitances of the switch (e.g., switch 911a) as previously described. Therefore, this implementation variant (not shown herein), may incorporate the input multiplexer circuit 910 into the driver amplifier circuit 902 also employing an additional (third) multiplexer circuit in a feedback path. This implementation variant may provide a regulated (stable) current source characteristic at each of the plurality of outputs of the driver circuit 402 substantially eliminating the effect of the switch’ parasitic capacitances. [0623] In another implementation variant (not shown herein), the driver amplifier circuit 902 additionally includes an output transformer e.g., for purposes of transforming an output voltage.
  • an output transformer e.g., for purposes of transforming an output voltage.
  • the input multiplexer circuit 910 includes a plurality of switches 911a, 911b, ..., 911n and is configured to selectively connect each of the plurality of inductive sense circuits 106 and each of the plurality of capacitive sense circuits 108 via the respective series resistor 914 and 915 to the driver circuit 402 to selectively (e.g., sequentially) drive each of the plurality of inductive sense circuits 106 and each of the plurality of capacitive sense circuits 108 with the current I 1 at the sense frequency.
  • each of the plurality of switches 911a, 911b, ..., 911n is electrically connected to the driver amplifier circuit’s 902 output that is also referred to as the common input node.
  • the input multiplexer circuit 910 is further configured to receive an input MUX control signal from a control circuit (e.g., from the control and evaluation circuit 102 of FIG.4) that controls the input multiplexer circuit 910.
  • Each of the plurality of switches 911a, 911b, ..., 911n may be one of a semiconductor analog switch (e.g., a single field effect transistor (FET) switch, a complementary FET switch composed of a p-channel and a n-channel type FET), a micro-mechanical systems (MEMS) switch or any other type of switch providing a sufficiently low series resistance, when the switch is closed (closed-state) and a sufficiently high current signal attenuation, when the switch is open (open- state).
  • FET field effect transistor
  • MEMS micro-mechanical systems
  • the switches may be characterized by a closed-state series resistance, an equivalent open-state series capacitance, and an equivalent parallel capacitance at each side of the switch. It may be appreciated that the closed-state resistance of the switch (e.g., switch 911a) is non-critical as it merges with the resistance (e.g., R ser1 ) of the series resistor (e.g., series resistor 914). It may also be appreciated that the total capacitive load produced by the plurality of parallel capacitances at the common input node may be non-critical since it is in parallel to the voltage source output of the driver amplifier circuit 902.
  • the switch (e.g., switch 911a) of an example input multiplexer circuit 910 may use complementary FET switches with a closed-state resistance of 5 ⁇ , an equivalent open-state series capacitance of 3 pF (corresponding to a series reactance of 17.7 k ⁇ at a sense frequency of 3 MHz), and an equivalent parallel capacitance of 12 pF on each side of the switch.
  • the closed-state resistance of a semiconductor analog switch e.g., switch 911a
  • the impact of the input multiplexer circuit 910 switch is reduced by using a resistor (e.g., series resistor 914) whose resistance (e.g., R ser1 ) is substantially larger than the closed-state resistance of the switch. Therefore, in some implementations, the series resistances R ser1 and R ser3 may also represent a trade-off between a temperature stability and a SNR as discussed above.
  • the order of the series resistor (e.g., series resistor 914) and the switch (e.g., switch 911a) is reversed, meaning that the plurality of series resistors 914 and 915 are electrically connected to the output of the driver amplifier circuit 902 (common input node) and the input multiplexer circuit 910 is inserted between the plurality of series resistors 914 and 915 and the plurality of sense circuits 106 and 108. Reversing the order may be advantageous for the design of the switch (e.g., switch 911a) as the voltage V 2 across the sense circuit may be substantially lower than the voltage at the output of the driver amplifier circuit 902.
  • a low frequency disturbance voltage (e.g., at WPT frequency) may be present at the driver circuit 402 output and at the measurement amplifier circuit 404 input e.g., due to the voltage induced into the sense element (e.g., sense element 107a) by the WPT magnetic field.
  • a switch e.g., switch 911b
  • a substantial low frequency voltage may also be present across the switch. This may be particularly true during active WPT operation. If too large, the open-switch voltage may affect any of the switch’ open-state electrical characteristic or cause damage to the switch.
  • the open-switch voltage is limited by configuring the inductive and capacitive sense circuits (e.g., sense circuit 106a and sense circuit 108) accordingly, trading-off the open-switch voltage vs. other impacts.
  • the measurement amplifier circuit 404 is configured to operate as the analog front-end part of a voltage measurement circuit (e.g., voltage measurement circuit 510 as described in connection with FIG. 5A). It is configured to selectively (e.g., sequentially) buffer and amplify the voltage V 2 in each of the plurality of inductive sense circuits 106 and in each of the plurality of capacitive sense circuits 108 and to provide a measurement amplifier output voltage signal V out (as indicated in FIG.
  • the measurement amplifier circuit 404 mainly serves for impedance buffering and is configured for unity gain. In further implementations, the output voltage Vout is even smaller than V 2 .
  • a DC flow at any of the plurality of inputs of the measurement amplifier circuit 404 may be present e.g., caused by a DC offset at the amplifier’s 954 input or by certain types of analog switches (e.g., switch 941a).
  • the measurement amplifier circuit 404 includes a transimpedance amplifier circuit 952, an output multiplexer circuit 940 illustrated in FIG.9A as a plurality of switches 941a, 941b, ..., 941n, and a plurality of resistors 944 and 945 (series resistors) connected in series to the respective output of the output multiplexer circuit 940.
  • the series resistors 944 connected to the inductive sense circuits 106 have a resistance R ser2 that may differ from the series resistance R ser1
  • the series resistors 945 connected to the capacitive sense circuits 108 have a resistance R ser4 that may differ from R ser3 and R ser2 . Further, it includes.
  • the plurality of switches 941a, 941b, ..., 941n are electrically connected to the transimpedance amplifier circuit’s 952 input that is also referred to herein as the common output node of the output multiplexer circuit 940.
  • the example transimpedance amplifier circuit 952 as illustrated in FIG.9A includes an amplifier 954, a feedback resistor 956 having a resistance Rf, and a feedback capacitor 958 having a capacitance C f .
  • the amplifier 954 is at least one of a low noise operational amplifier and an amplifier providing high linearity.
  • the positive input (+) of the amplifier 954 connects to ground.
  • Both the feedback resistor 956 and the feedback capacitor 958 are electrically connected between the output (Vout) and the negative input (-) of the amplifier 954. Further, the transimpedance amplifier circuit 952 is configured to receive an input current I in , which is the output current at the common output node of the output multiplexer circuit 940 and to convert the input current I in into a proportional output voltage V out .
  • the conversion gain (transimpedance) is determined by the impedance of the parallel connection of the feedback resistor 956 and the feedback capacitor 958. Since the voltage at the negative input (-) of the amplifier 954 is virtually zero (virtual ground), the transimpedance amplifier circuit 952 presents a virtually zero input impedance at its negative input (-).
  • the transimpedance amplifier circuit 952 together with the series resistor mimic a voltage measurement circuit characteristic at each of the plurality of inputs of the measurement amplifier circuit 404.
  • the series resistor e.g., resistor 944 with a resistance (e.g., R ser2 ) substantially larger (e.g., 10 times larger) than the impedance magnitude
  • increasing the resistance (e.g., R ser2 ) of the series resistor may improve a voltage measurement circuit characteristic but reduce the input current level Iin.
  • the input current level Iin may impact a SNR as previously defined with reference to FIG.5F.
  • increasing the resistance (e.g., R ser2 ) may reduce an impact of the output multiplexer circuit 940 switch (e.g., switch 941a) (e.g., a temperature drift) as discussed above in connection with the input multiplexer circuit 910.
  • the resistances R ser2 and R s er4 may represent a trade-off between a voltage measurement circuit characteristic, a temperature stability, and a SNR.
  • an impact of the output multiplexer circuit 940 switch e.g., switch 941a
  • a temperature drift is reduced by omitting the output multiplexer circuit 940, instead using a plurality (bank) of measurement amplifiers (not shown herein), whose inputs are electrically connected to the respective measurement port (e.g., measurement port 937) of the respective sense circuit (e.g., sense circuit 106a) and whose outputs are electrically connected to a common output (Vout).
  • Each measurement amplifier circuit 404 is configured to provide a high input impedance and includes an operational amplifier (e.g., amplifier 954) providing a mute control input to apply a logic signal indicative for the output MUX control signal as indicted in FIG.9A.
  • the operational amplifier is further configured to provide a virtually zero gain and a high output impedance when muted.
  • An example circuit using a bank of operational amplifiers is disclosed in U.S. Patent application 16/226,156, titled Foreign Object Detection Circuit Using Current Measurement, the entire contents of which are hereby incorporated by reference.
  • the voltage measurement circuit characteristic is realized using a resistor (e.g., resistor 944) with a lower resistance (e.g., R ser2 ) instead using the DC block capacitor (e.g., capacitor 929 of sense circuit 106a) with a higher reactance, together providing a series impedance substantially larger (e.g., 10 times larger) than the impedance of the series circuit e.g., of the sense element 107a and the capacitor 504 at series resonance.
  • the series resistor e.g., resistor 944
  • the voltage measurement circuit characteristic is realized using the DC block capacitor (e.g., capacitor 929) configured to provide a high enough series impedance.
  • the high series impedance as required to mimic a current source characteristic is realized at least in part by using at least one of an inductor (not shown in FIG.9A) and a leakage inductance of a transformer.
  • the feedback capacitor 958 provides the transimpedance amplifier circuit 952 with a first order low pass filter characteristic to attenuate disturbance signal components at frequencies higher than the sense frequency (e.g., high order WPT harmonics).
  • the capacitance Cf may be a trade-off between a reduction in gain at the sense frequency and an attenuation of the high frequency signal components.
  • the feedback capacitor 958 may reduce a risk for signal clipping or non-linear distortion in the amplifier 954 or in the further processing (e.g., the signal processing circuit 408 with reference to FIG. 4) e.g., during WPT operation. In other words, it may reduce the dynamic range requirements for the measurement amplifier circuit 404 and in the further processing.
  • the transimpedance amplifier circuit 952 is further enhanced by a supplementary feedback inductor electrically connected in parallel to the feedback capacitor 958 providing the transimpedance amplifier circuit 952 with a bandpass characteristic tuned to the sense frequency. This inductor may help to further suppress low frequency disturbance signal components (e.g., the WPT fundamental and low frequency harmonics thereof).
  • the feedback capacitor 958 may be a temperature compensation capacitor to compensate for at least a portion of the feedback inductor’s temperature drift.
  • the measurement amplifier circuit 404 is configured as an active filter providing a bandpass characteristic similar to the implementation variant described above using a parallel feedback inductor. This circuit may not use any inductors.
  • An example implementation of a measurement amplifier circuit 404 using an active filter is illustrated in FIG.9C.
  • the output multiplexer circuit 940 including the plurality of switches 941a, 941b, ..., 941n is configured to selectively connect each of the plurality of inductive sense circuits 106 and each of the plurality of capacitive sense circuits 108 via the respective series resistors 944 and 945 to the transimpedance amplifier circuit 952 to selectively (e.g., sequentially) buffer and amplify the voltage V 2 at each of the plurality of sense circuits 106 and 108 in response to a current I 0 at the sense frequency. Therefore, each of the plurality of switches 941a, 941b, ..., 941n is electrically connected to the common output node that is electrically connected to the negative input of the transimpedance amplifier circuit 952.
  • each of the plurality of switches 941a, 941b, ..., 1041n may be one of a semiconductor analog switch (e.g., a single FET switch, a complementary FET switch composed of a p-channel and a n-channel type FET), a micro- mechanical systems (MEMS) switch or any other type of switch providing a sufficiently high current signal attenuation in the open-state.
  • a semiconductor analog switch e.g., a single FET switch, a complementary FET switch composed of a p-channel and a n-channel type FET
  • MEMS micro- mechanical systems
  • each of the plurality of switches 941a, 941b, ..., 941n may exhibit a closed-state series resistance, an equivalent open-state series capacitance, and an equivalent parallel capacitance on each side of the switch. It may be appreciated that the closed-state series resistance (e.g., of switch 941a) may be non-critical for the functioning of the measurement amplifier circuit 404 since it merges into an overall series resistance R ser2 or R ser4 .
  • An example output multiplexer circuit 940 for a sense frequency of 3 MHz may use complementary FET switches with the same characteristics as those used for the example input multiplexer circuit 910 as specified above.
  • a low frequency voltage e.g., at WPT frequency
  • the switch e.g., switch 941a
  • this open-switch voltage may affect any of the switch’s open-state electrical characteristics or cause damage to the switch.
  • the open-switch voltage is limited as previously discussed for the input multiplexer circuit 910.
  • the order of the series resistor (e.g., resistor 944) and the switch (e.g., switch 941a) is reversed, meaning that the series resistor (e.g., resistor 944) is electrically connected to the input of the transimpedance amplifier circuit 952 (common output node) and the output multiplexer circuit 940 is inserted between the plurality of sense circuits 106 and 108 and the plurality of resistors 944 and 945.
  • a further implementation variant of the circuit 900 omits the output multiplexer circuit 940 e.g., for reasons of complexity and cost reduction.
  • the input multiplexer circuit 910 may be enough to selectively (e.g., sequentially) drive a sense circuit (e.g., sense circuit 106a) with the current I1 and to selectively measure the voltage V 2 at its measurement port 937 in response to the current I 1 .
  • the measurement amplifier circuit 404 is configured as a voltage summation amplifier, its output voltage Vout is indicative of the sum of the voltages at each of the plurality of measurement ports 937.
  • the output voltage Vout is indicative of the voltage V 2 of the active sense circuit (e.g., sense circuit 106a) driven by the current I 1 .
  • disturbance voltages e.g., inductively or capacitively coupled into the sense element (e.g., inductive sense element 107b) may also sum up resulting in a lower SNR as compared to a circuit 900 using the output multiplexer circuit 940.
  • a circuit 900 omitting the output multiplexer circuit 940 may not support supplementary inter-sense circuit transimpedance Z 12 measurements as described above.
  • the inter-sense circuit transimpedance Z12 between the measurement port 936 of sense circuit 106a and the measurement port 937 of sense circuit 106b may be measured by setting the switches 911a and 941b to the close-state and the other switches of the plurality of switches 911a, 911b, ..., 911n to the open-state.
  • a WPT operating frequency fWPT 85 kHz is assumed.
  • TABLE 7 also includes a system Q-factor defined as the ratio Q s:ys ⁇
  • inductive sense element e.g., inductive sense element 107a
  • a capacitive sense element e.g., capacitive sense element 109n
  • TABLE 7 includes a quality of the measurement circuit 104 defined as the ratio: Q mc ⁇
  • TABLE 7 includes a degradation of the fractional change in the measurement amplifier circuit’s 404 output voltage V out defined as: ⁇ Vout ⁇ 1 – (
  • This degradation may be the result of imperfections in the driver circuit 402 and the measurement amplifier circuit 404 and in other circuit elements as needed in a practical implementation.
  • FIG.9C is a circuit diagram illustrating an example implementation of a measurement amplifier circuit 404 using an active filter providing a bandpass characteristic as previously mentioned with reference to FIG. 9A.
  • the measurement amplifier circuit 404 is configured to selectively (e.g., sequentially) buffer and amplify the voltage V 2 in each of the plurality of inductive sense circuits 106 and in each of the plurality of capacitive sense circuits 108 and to provide an output voltage V out based on the respective voltage V 2 at a level suitable for further processing e.g., in the signal processing circuit 408 with reference to FIG. 4.
  • the bandpass filter characteristic of the active filter substantially equals the bandpass pass characteristics of the measurement amplifier circuit 404 based on a transimpedance amplifier circuit 952 including a feedback network comprising a resistor, a capacitor, and an inductor as previously described in connection with FIG.9A.
  • the example measurement amplifier circuit 404 of FIG.9C includes a transimpedance amplifier circuit 952, an output multiplexer circuit 940 including a plurality of switches 941a, 941b, ..., 941n, and a plurality of capacitors (series capacitors 946 and 947) connected in series to the respective switch.
  • the resistors 944 and 945 with reference to FIG.
  • the transimpedance amplifier circuit includes an amplifier 954 (e.g., at least one of a low noise operational amplifier and an operational amplifier providing high linearity).
  • the amplifier s 954 positive input (+) is electrically connected to ground.
  • a feedback capacitor 958 with capacitance C 1 is electrically connected between the output (V out ) and the negative input (-) of the amplifier 954.
  • a feedback resistor 956 with resistance R 1 is electrically connected between the output (V out ) and the input (I in ) of the transimpedance amplifier circuit 952.
  • a resistor 959 with resistance R 2 is electrically connected between the input (Iin) of the transimpedance amplifier circuit 952 and the negative input (-) of the amplifier 954.
  • a capacitor 960 with capacitance C 2 is electrically connected between the input (Iin) of the transimpedance amplifier circuit 952 and ground.
  • each of the capacitors 946 having a capacitance C 3 capacitively couples a respective switch (e.g., switch 941a) to the respective inductive sense circuit (e.g., inductive sense circuit 106a), while each of the capacitors 947 having a capacitance C 4 capacitively couples a respective switch (e.g., switch 941n) to the respective capacitive sense circuit (e.g., capacitive sense circuit 108a).
  • FIG.9D is a circuit diagram illustrating an example implementation of an analog switch (e.g., 941a) as used in an example implementation of the output multiplexer circuit 940.
  • the analog switch uses a single field-effect transistor (FET) 942 (e.g., a n-channel metal–oxide– semiconductor field-effect transistor (MOSFET)).
  • FET field-effect transistor
  • the analog switch is controlled by a switch control signal applied to the gate (G) of the FET 942.
  • the Drain (D) of the FET 942 is DC biased with a positive voltage +VB via a resistor having a resistance RB1 (e.g., in the k ⁇ range).
  • the positive DC voltage +V B ensures that the voltage across the FET channel remains positive at any time when in open-state and in presence of a superimposed alternating voltage across the FET channel (e.g., during WPT operation as previously discussed with reference to FIG. 9).
  • FIG.9E is a circuit diagram illustrating an alternative example implementation of the inductive sense circuit 106a of the plurality of inductive sense circuits 106 of the circuit 900 of FIG.9A.
  • This alternative example implementation illustrated in FIG.9E additionally includes a parallel capacitor 507 having a capacitance C p1 and applies to any of the plurality of inductive sense circuits 106.
  • the parallel inductor 506 and the parallel capacitor 507 are configured to provide a parallel resonance substantially at the nominal sense frequency.
  • the sense element 107a having inductance L in combination with the parallel capacitor 507 having capacitance C p1 form a 2 nd order low pass filter to attenuate a disturbance component in the voltage V 2 at a frequency substantially higher than the nominal sense frequency.
  • this disturbance component emanates from a voltage inductively or capacitively coupled into the sense element 107a by the magnetic or electric field, respectively, as generated during wireless power transfer.
  • FIG.9F is a circuit diagram illustrating an alternative example implementation of the capacitive sense circuit 108n of the plurality of capacitive sense circuits 108 of the circuit 900 of FIG.9A.
  • This alternative example implementation additionally includes a parallel capacitor 727 having a capacitance C p 2 and applies to any of the plurality of capacitive sense circuits 108.
  • the transformer 726 having the secondary-referred main inductance L m (with reference to the equivalent circuit of FIG. 5H) and the parallel capacitor 507 having capacitance C p2 are configured to provide a parallel resonance substantially at the nominal sense frequency.
  • the series inductor 724 having inductance L s in combination with the parallel capacitor 727 having capacitance C p 2 form a 2 nd order low pass filter to attenuate a disturbance component in the voltage V 2 at a frequency substantially higher than the nominal sense frequency.
  • this disturbance component emanates from a voltage coupled into the sense electrode (e.g., capacitive sense element 109n) e.g., by the electric field as generated during wireless power transfer.
  • each of the parallel capacitors 507 and 727 as part of a 2 nd order low pass filter reduces dynamic range requirements of the measurement amplifier circuit 404 and may also protect the driver circuit 402 including the input multiplexer circuit 910 and the measurement amplifier circuit 404 including the output multiplexer circuit 940 from being overloaded. Stated more generally, it may reduce non-linear distortion effects (e.g., signal clipping) in the circuit 900 of FIG.9A.
  • FIG. 10 is a circuit diagram of a circuit 1000 illustrating another example implementation of a portion of a multi-purpose detection circuit 100.
  • the circuit 1000 of FIG.10 illustrates an analog front-end circuit portion of the multi-purpose detection circuit 100 with reference to FIGs.1 and 4.
  • FIG.10 excludes various other signal generation, processing, control and evaluation circuits (e.g., as shown in FIG.4) that may be needed in some implementations of a multi-purpose detection circuit 100.
  • the circuit 1000 implements inductive and capacitive sensing by measuring an impedance based on the current source voltage measurement approach as previously described in connection with FIG.5C. [0660] As with the circuit 900 of FIG.
  • the circuit 1000 may be subdivided into a driver circuit 402, a plurality of inductive sense circuits 106 including sense circuits 106a, 106b, ..., 106n (106n not shown in FIG. 10 for purposes of illustration), a plurality of capacitive sense circuits 108 including sense circuits 108a, 108b, ..., 108n (108a and 108b not shown in FIG. 10 for purposes of illustration), and a measurement amplifier circuit 404 with reference to the generic block diagram of FIG. 4.
  • each of the plurality of inductive sense circuits 106a, 106b, ..., 106n is based on the sense circuit 541 of FIG.
  • each of the plurality of capacitive sense circuits 108a, 108b, ..., 108n is based on the sense circuit 721 of FIG.7C.
  • the dots indicated in FIG. 10 shall indicate that the number of inductive sense circuits 106 and/or the number of capacitive sense circuits 108 may be greater than three as previously noted with reference to FIG. 1.
  • each of the plurality of inductive sense circuits 106 have an identical circuit topology.
  • each of the plurality of capacitive sense circuits 108 have an identical circuit topology.
  • Each of the plurality of inductive sense circuits 106 provides a first measurement port 936 (indicated in FIG.10 by a terminal) for applying an electrical voltage V1 (as indicated in FIG. 10) and a second measurement port 937 (indicated in FIG. 10 by a terminal) for measuring an electrical current I2 (as indicated in FIG.10) e.g., in response to the voltage V1.
  • each of the plurality of capacitive sense circuits 108 provides a first measurement port 938 (indicated in FIG. 10 by a terminal) for applying the voltage V1 (as indicated in FIG. 10) and a second measurement port 939 (indicated in FIG. 10 by a terminal) for measuring the current I 2 (as indicated in FIG. 10) e.g., in response to the current V1.
  • the sense circuits 106 and 108 as illustrated in FIG. 10 may be considered as one-port circuits as further discussed below.
  • the driver circuit 402 includes an input multiplexer circuit 910 to selectively (e.g., sequentially) apply the voltage V1 to each of the plurality of sense circuits 106 and 108.
  • the measurement amplifier circuit 404 includes an output multiplexer circuit 940 configured to selectively (e.g., sequentially) measure the current I2 in each of the plurality of sense circuits 106 and 108. More specifically, but not indicated in FIG.10 for purposes of illustration, the voltage V1 applied to the sense circuit 106a may be denoted by V1a, the voltage V1 applied to the sense circuit 106b may be denoted as V 1b , etc. Likewise, the currents I 2 in the sense circuits 106a and 106b may be denoted by I2a and I2b, respectively.
  • the circuit 1000 may be configured and operated in a mode to selectively (e.g., sequentially) measure the intra-sense circuit transimpedance Z 21 e.g., between the measurement ports 936 and 937 of each of the plurality of the sense circuits 106 defined as: Z 2a1a ⁇ V 1a / I 2a (357) As mentioned above and further discussed below, the two-port transimpedance Z 21 substantially equals the one-port impedance Z 11 as it may be measured at the first measurement port (e.g., measurement port 936) with the second measurement port (e.g., measurement port 937) short- circuited. [0665] However, as opposed to the circuit 900 of FIG. 9A, the circuit 1000 as illustrated in FIG.
  • the inductive sense circuit 106a includes an inductive sense element 107a including a sense coil (e.g., sense coil 502 of FIG.5A) with an inductance L, a first capacitor (e.g., capacitor 544 of FIG. 5C) with capacitance C p , a second capacitor (e.g., capacitor 546 of FIG. 5C) with a capacitance C s .
  • a sense coil e.g., sense coil 502 of FIG.5A
  • a first capacitor e.g., capacitor 544 of FIG. 5C
  • C p capacitance C p
  • a second capacitor e.g., capacitor 546 of FIG. 5C
  • the sense circuits 106 of the circuit 1000 may not require an inductor (e.g., inductor 506) other than the inductive sense element (e.g., inductive sense element 107a) since the capacitor 546 may suffice to provide the required high pass filter characteristic.
  • the first capacitor (parallel capacitor 544) is electrically connected in parallel to the inductive sense element 107a.
  • the parallel circuit of capacitor 544 and inductive sense element 107a is capacitively coupled to the measurement port 936 via capacitor 546 and also electrically connected to the measurement port 936. None of the components of the sense circuit 106a is ground-connected, meaning that there is ideally no current flow towards ground when the voltage V1 is applied at the measurement port 936.
  • each of the plurality of inductive sense circuits 106 is configured to provide a minimum of the impedance magnitude
  • the capacitors 544 and 546 may be configured to provide an impedance magnitude
  • at the sense frequency in a suitable range for the measurement circuit (e.g., measurement circuit 104 of FIG.4) by adjusting the capacitance ratio n C C p /C s accordingly as previously discussed with reference to FIG.5G.
  • may be increased to a level substantially higher than that of the inductive sense circuit 106a of the circuit 900 of FIG. 9A.
  • may be a requirement of the voltage source current measurement technique e.g., for selectively applying the voltage V 1 to each of the plurality of sense circuits 106 by the driver circuit 402 without exceeding an output current limit. It may also be a requirement for selectively measuring a current in each of the plurality of sense circuits 106 by the measurement amplifier circuit 404 without exceeding an input current limit. Further, it may be a requirement to reduce an impact of the input multiplexer circuit 910 and the output multiplexer circuit 940 as further discussed below.
  • the capacitors 544 and 546 are of a type with a low temperature coefficient providing high thermal stability (e.g., a NP0-type capacitor) reducing thermal drift of an electrical characteristic (e.g., an impedance) as measured at each of the plurality of inductive sense circuits 106a, 106b, ..., 106n.
  • an electrical characteristic e.g., an impedance
  • the inductive sense circuit 106a in conjunction with the voltage source current measurement technique creates a high pass filter characteristic to attenuate a low frequency disturbance component in the current I2 for purposes as previously discussed with reference to FIG. 9A.
  • the series capacitor 546 together with the parallel capacitor 544 may be configured to attenuate this low frequency disturbance component to a level e.g., below the level of the current I 2 in response to the respective sense voltage V1 at the sense frequency, while maintaining series resonance at the sense frequency as previously discussed with reference to FIG. 5G.
  • this high pass filter characteristic may exert a minor impact on the current I2 and thus on the measurement of the impedance Z 11 and which may be corrected in a further processing (e.g., in the signal processing circuit 408 of FIG.4) as previously discussed with reference to the circuit 900 of FIG.9A.
  • the inductive sense circuits 106 may not need any supplementary capacitors (e.g., capacitors 928 and 929 ) for purposes of DC blocking as previously discussed with reference to the circuit 900 of FIG. 9A, as the series capacitor 546 already blocks any DC. Therefore, the passive component count of the plurality of inductive sense circuit 106a of FIG.10 may be lower as compared to the circuit 900 of FIG.9A.
  • the capacitive sense circuit 108n includes a capacitive sense element 109n including a sense electrode (e.g., sense electrode 702 of FIG.
  • FIG. 7C illustrating a single-ended sense electrode) with a capacitance C
  • a series inductor 724 e.g., series inductor 724 of FIG. 7C
  • an inductance L s e.g., L s
  • a transformer 726 e.g., transformer 726 of FIG. 7C
  • it includes a capacitor 930 with a capacitance Cb e.g., for purposes as previously discussed with reference to the sense circuits 106 and 108 of FIG. 9A.
  • the inductor 724 is electrically connected in series to the capacitive sense element 109n.
  • the series circuit of inductor 724 and capacitive sense element 109n is electrically connected to the transformer’s 726 secondary port that also connects to ground. Further, the transformer’s 726 primary port is capacitively coupled to the measurement port 938 via capacitor 930 and also electrically connects to the measurement port 939. Though the transformer’s 726 secondary port electrically connects to ground, the sense circuit 108n ideally may not be ground-related. In an implementation using a transformer 726 composed of a primary winding and a galvanically isolated secondary winding as previously described with reference to FIG. 9A, there is ideally no current flow towards ground when the voltage V1 is applied at the measurement port 938.
  • the capacitive sense circuits 108n may be considered a one-port rather than a two-port circuit. In practice however, some residual ground current flow may exist due to a parasitic interwinding capacitance of the transformer 726.
  • the sense circuits 108 may not need a transformer (e.g., transformer 726) for purposes of ground-decoupling.
  • each of the plurality of capacitive sense circuits 108 is based on the sense circuit 781 as illustrated in FIG.7I.
  • each of the plurality of capacitive sense circuits 108 is configured to provide a minimum of the impedance magnitude
  • the transformer 726 may be configured to provide an impedance
  • may be a requirement of the voltage source current measurement technique as previously discussed.
  • the secondary-referred main inductance L m of the transformer 726 together with the capacitance C of the capacitive sense element 109n form a 2 nd order high pass filter to attenuate a low frequency disturbance component in the current I 2 as previously discussed with reference to FIG. 7C.
  • the transformer 726 may be configured to attenuate this low frequency disturbance component to a level e.g., significantly below the level of the current I 2 in response to the respective voltage V1 at the sense frequency.
  • the driver circuit 402 includes a driver amplifier circuit 902, an input multiplexer circuit 910 illustrated in FIG.10 as a plurality of switches 911a, 911b, ..., 911n, and a plurality of resistors 1014 and 1015 (parallel resistors) connected in parallel to the respective output of the input multiplexer circuit 910 for purposes as described below.
  • the parallel resistors 1014 connected to the inductive sense circuits 106 have a resistance R par1
  • the parallel resistors 1015 connected to the capacitive sense circuits 108 have a resistance Rpar3 that may generally differ from R par1 .
  • the driver circuit 402 is configured to operate as a voltage source (e.g., voltage source 552 as described in connection with FIG. 5C) and to selectively (e.g., sequentially) apply a voltage signal V1 at the sense frequency to each of the plurality of inductive sense circuits 106 and to each of the plurality of the capacitive sense circuits 108.
  • the voltage signal V 1 (e.g., a sinusoidal sense signal) is based on a driver input signal which may be an output of the signal generator circuit 406 with reference to FIG. 4.
  • the driver amplifier circuit 902 as illustrated in FIG.10 by example includes an amplifier 904 and external resistance circuitry comprising a first (feedback) resistor 906 and a second resistor 908 for adjusting a gain.
  • the amplifier 904 is at least one of a low noise operational amplifier and an operational amplifier providing high linearity.
  • the driver amplifier circuit 902 is configured to receive the driver input signal and to provide a corresponding output with an accurate and stable voltage (a voltage source output).
  • the input multiplexer circuit 910 includes a plurality of switches 911a, 911b, ..., 911n and is configured to selectively connect each of the plurality of inductive sense circuits 106 and each of the plurality of capacitive sense circuits 108 to the driver circuit 402 to selectively (e.g., sequentially) apply the voltage V1 at the sense frequency to each of the plurality of inductive sense circuits 106 and to each of the plurality of capacitive sense circuits 108. Therefore, each of the plurality of switches 911a, 911b, ..., 911n is electrically connected to the driver amplifier circuit’s 902 output that is also referred to as the common input node.
  • the input multiplexer circuit 910 is further configured to receive an input MUX control signal from a control circuit (e.g., from the control and evaluation circuit 102 of FIG.4) that controls the input multiplexer circuit 910.
  • a control circuit e.g., from the control and evaluation circuit 102 of FIG.4
  • Each of the plurality of switches 911a, 911b, ..., 911n may be one of a type as previously mentioned with reference to the circuit 900 of FIG.9A. It may be appreciated that the closed-state resistance of the switch (e.g., switch 911a) may be less critical if the impedance magnitude
  • may also reduce an impact of the switch’ (e.g., switch 911a) temperature dependent closed-state resistance and thus improve a temperature stability of the driver circuit 402 as previously discussed with reference to the circuit 900 of FIG. 9A. It may also be appreciated that the total capacitive load produced by the plurality of parallel capacitances at the common input node may be non-critical since it is in parallel to the voltage source output of the driver amplifier circuit 902.
  • the switch (e.g., switch 911a) of an example input multiplexer circuit 910 may use complementary FET switches with a closed-state resistance of 5 ⁇ , an equivalent open-state series capacitance of 3 pF (corresponding to a series reactance of 17.7 k ⁇ at a sense frequency of 3 MHz), and an equivalent parallel capacitance of 12 pF on each side of the switch.
  • the resistances Rpar1 and Rpar3 are a trade-off between a driver amplifier circuit 902 output load, temperature stability, and the open- switch voltage.
  • the parallel resistor e.g., parallel 1014 provides a resistance (e.g., R par1 ) in the order of the impedance
  • the input multiplexer circuit 910 is incorporated into the driver amplifier circuit 902 also employing an additional (third) multiplexer circuit in a feedback path.
  • This implementation variant may provide a regulated (stable) voltage source characteristic at each of the plurality of outputs of the driver circuit 402 substantially eliminating the effect of the switch’ temperature dependent closed-state resistance.
  • An example circuit of the driver circuit 402, which is voltage regulated, is disclosed in U.S. Patent application 16/226,156, titled Foreign Object Detection Circuit Using Current Measurement.
  • the measurement amplifier circuit 404 is configured to operate as the analog front-end part of a current measurement circuit (e.g., current measurement circuit 550 as described in connection with FIG. 5C).
  • It is configured to selectively (e.g., sequentially) buffer and convert the current I 2 in each of the plurality of inductive sense circuits 106 and in each of the plurality of capacitive sense circuits 108 and to provide an output voltage signal Vout (as indicated in FIG.9A) based on the respective current I 2 at a level suitable for further processing e.g., in the signal processing circuit 408 with reference to FIG.4.
  • the measurement amplifier circuit 404 includes a transimpedance amplifier circuit 952, an output multiplexer circuit 940 illustrated in FIG.10 as a plurality of switches 941a, 941b, ..., 941n, and a plurality of resistors 1044 and 1055 (parallel resistors) connected in parallel to the respective input of the output multiplexer circuit 940.
  • the parallel resistors 1044 connected to the inductive sense circuits 106 have a resistance Rpar2 that generally differs from the parallel resistance R par1
  • the parallel resistors 1045 connected to the capacitive sense circuits 108 have a resistance Rpar4 that generally differs from Rpar3 and Rpar2.
  • the plurality of switches 941a, 941b, ..., 941n are electrically connected to the transimpedance amplifier circuit’s 952 input that is also referred to herein as the common output node.
  • decreasing the resistance (e.g., R par2 ) of the parallel resistor 1044 will reduce the open-switch voltage (e.g., at WPT frequency) across the output multiplexer circuit 940 switch (e.g., switch 941a).
  • decreasing the resistance of the parallel resistor 1044 may be less critical since the voltage across the parallel resistor 1044 is low when the switch (e.g., switch 941a) is in closed-state.
  • the example transimpedance amplifier circuit 952 as illustrated in FIG.10 includes an amplifier 954, a feedback resistor 956 having a resistance Rf, and a feedback capacitor 958 having a capacitance C f .
  • the amplifier 954 is at least one of a low noise operational amplifier and an amplifier providing high linearity. The positive input (+) of the amplifier 954 connects to ground. Both the feedback resistor 956 and the feedback capacitor 958 are electrically connected between the output (Vout) and the negative input (-) of the amplifier 954.
  • the transimpedance amplifier circuit 952 is configured to receive an input current I in , which is the output current at the common output node of the output multiplexer circuit 940 and to convert the input current Iin into a proportional output voltage Vout.
  • the conversion gain (transimpedance) is determined by the impedance of the parallel connection of the feedback resistor 956 and the feedback capacitor 958. Since the voltage at the negative input (-) of the amplifier 954 is virtually zero (virtual ground), the transimpedance amplifier circuit 952 presents a virtually zero input impedance at its negative input (-).
  • the feedback capacitor 958 provides the transimpedance amplifier circuit 952 with a first order low pass filter characteristic to attenuate disturbance signal components at frequencies higher than the sense frequency (e.g., high order WPT harmonics) as previously discussed with reference to FIG.9A.
  • the filtering of the transimpedance amplifier circuit 952 is further enhanced in similar ways as previously described with reference to FIG.9A.
  • the transimpedance amplifier circuit 952 additionally includes an input transformer e.g., for purposes of transforming an input current I in .
  • the transformer may be used e.g., to reduce the current I in to a level not exceeding an input current constraint of the amplifier 954 and hence allowing the drive current I1 and eventually the sense currents I L and I C in the respective sense elements 107a, 107b, ..., 107n and 109a, 109b, ..., 109n to be increased.
  • An example transimpedance amplifier circuit 952 using an input transformer is disclosed in U.S. Patent application 16/226,156, titled Foreign Object Detection Circuit Using Current Measurement.
  • the output multiplexer circuit 940 including the plurality of switches 941a, 941b, ..., 941n is configured to selectively connect each of the plurality of inductive sense circuits 106 and each of the plurality of capacitive sense circuits 108 to the transimpedance amplifier circuit 952 to selectively (e.g., sequentially) buffer and convert the current I2 at each of the plurality of sense circuits 106 and 108 in response to the voltage V 1 at the sense frequency. Therefore, each of the plurality of switches 941a, 941b, ..., 941n is electrically connected to the common output node that is electrically connected to the negative input of the transimpedance amplifier circuit 952.
  • the output multiplexer circuit 940 is further configured to receive an output MUX control signal from a control circuit (e.g., from the control and evaluation circuit 102 of FIG.4) that controls the output multiplexer circuit 940.
  • a control circuit e.g., from the control and evaluation circuit 102 of FIG.4
  • each of the plurality of switches 941a, 941b, ..., 1041n may be one of a type of switch as previously specified with reference to the output multiplexer circuit 940 of the circuit 900 of FIG. 9A.
  • the closed-state series resistance (e.g., of switch 941a) may be non-critical for the functioning of the measurement amplifier circuit 404 if the impedance
  • An example output multiplexer circuit 940 for a sense frequency of 3 MHz may use complementary FET switches with the same characteristics as those used for the example input multiplexer circuit 910 as specified above.
  • the circuit 1000 as illustrated in FIG. 10 may not support measuring the inter-sense circuit transimpedance Z 12 as described with reference to FIG. 9A.
  • the circuit 1000 is equipped with an input multiplexer circuit 910 including a plurality of tri-state switches.
  • An example tri-state switch may be controlled to one of a first state that is an open state, a second state that is a closed state to connect a sense circuit (e.g., sense circuit 106a) e.g., to the output of the driver amplifier circuit 902, and a third state that is also a closed-state to shorten the sense circuit at the measurement port (e.g., measurement port 936) to ground.
  • a sense circuit e.g., sense circuit 106a
  • the measurement port e.g., measurement port 936
  • the transimpedance Z 12 between the measurement port 936 of sense circuits 106a and measurement port 937 of sense circuit 106b may be measured by setting the tri-state switches 911a and 911b to the second state, the tri-state switch 911b to third state, and all other tri-state switches of the plurality of tri-state switches 911a, 911b, ..., 911n and 941a, 941b, ..., 941n to the first state.
  • a tri-state switch may be equivalent to adding a third multiplexer circuit.
  • a further implementation variant of the circuit 1000 (not shown herein) omits the output multiplexer circuit 940 e.g., for reasons of complexity and cost reduction.
  • the input multiplexer circuit 910 may be enough to selectively (e.g., sequentially) apply the voltage V1 to a sense circuit (e.g., sense circuit 106a) and to selectively measure the current I 2 at its measurement port 937 in response to the voltage V1.
  • the measurement amplifier circuit 404 is configured as a current summation amplifier, its output voltage V out is indicative of the sum of the currents at each of the plurality of measurement ports 937.
  • the output voltage Vout is indicative of the current I2 of the active sense circuit (e.g., sense circuit 106a) where the voltage V 1 is applied.
  • disturbance currents e.g., capacitively coupling into the sense element (e.g., inductive sense element 107b) when WPT is active may also sum up resulting in a lower SNR as compared to a circuit 1000 using the output multiplexer circuit 940.
  • a WPT operating frequency fWPT 85 kHz is assumed.
  • TABLE 9 also includes the system Q-factor Q sys as defined above by Equation (354), the quality of the measurement circuit 104 defined as the ration: Qmc ⁇
  • a WPT operating frequency f WPT 85 kHz is assumed.
  • TABLE 10 also includes the system Q-factor Q s ys as defined above by Equation (354), the quality of the measurement circuit 104 as defined by Equation (358), and the degradation of the fractional change in the measurement amplifier circuit’s 404 output voltage Vout as defined by Equation (356).
  • Cross-coupling may degrade the Q-factor of a sense circuit (e.g., sense circuit 106a or 108n) due to energy absorption and may also distort its impedance function Z 11 ( ⁇ ) eventually compromising performance and the impedance angle measurement accuracy of the multipurpose detection circuit 100.
  • a circuit e.g., circuit 1000
  • a plurality of sense circuits 106 or 108 which, when inactive (e.g., deselected by the input and output multiplexer circuits 910 and 940, respectively), exhibit a parasitic parallel resonance as given by Equation (117) close to the sense frequency.
  • the parasitic parallel resonance may be at 1.3 MHz, while for the example implementation of the circuit 1000 specified in TABLE 9, it may occur close to the sense frequency at 3.29 MHz. Therefore, the impact of cross-coupling in the circuit 1000 may be more significant than in the circuit 900.
  • a cross-coupling effect between inductive sense circuits is reduced by configuring (tuning) the inductive sense circuits associated with neighboring sense elements (e.g., sense element 107a and 107b) to a different resonant frequency e.g., following a frequency reuse scheme.
  • this approach may cause a conflict in a multipurpose detection circuit 100 used to detect a passive beacon transponder (e.g., passive beacon transponder 313 of FIG.
  • detection of a passive beacon transponder requires each of the plurality of inductive sense circuits 106 to be configured (tuned) to a substantially equal resonant frequency.
  • a gap is introduced between adjacent sense coils (e.g., between elements coil 107a and 107b) to reduce a cross-coupling effect.
  • the sense coil e.g., sense element 107a
  • the capacitor 544 of the associated sense circuit e.g., sense circuit 106a
  • a long lead line This may apply to an implementation of the circuit 1000 where the array of sense coils (e.g., array 107) is carried on a separate printed circuit board (PCB) excluding any other components of the circuit 1000.
  • a long lead line may cause substantial electrical losses degrading the Q-factor of a sense circuit (e.g., sense circuit 106a) and hence the performance of the multipurpose detection circuit 100.
  • lead line losses are reduced by placing at least the parallel capacitor 544 at a position close to the terminals of the sense coil (e.g., sense element 107a).
  • the lead line of the sense circuit 106a may be between the series capacitor 546 and the parallel circuit of capacitor 544 and the sense element 107a. Since the capacitors 544 and 546 transform the impedance, the driver circuit 402 output current and thus the lead line current as required in the circuit 1000 to generate a specified sense coil current I L may be substantially lower than the corresponding currents in the circuit 900.
  • FIG. 11 is a circuit diagram of a circuit 1100 illustrating another example implementation of a portion of a multi-purpose detection circuit 100.
  • the circuit 1100 of FIG.11 illustrates an analog front-end circuit portion of the multi-purpose detection circuit 100 with reference to FIGs.1 and 4.
  • FIG.11 excludes various other signal generation, processing, control and evaluation circuits (e.g., as shown in FIG.4) that may be needed in some implementations of a multi-purpose detection circuit 100.
  • the circuit 1100 implements inductive and capacitive sensing by measuring an impedance based on the current source voltage measurement approach as previously described in connection with FIG.5C.
  • the circuit 1100 may be subdivided into an analog front-end part of the measurement circuit 104 and a plurality of inductive and capacitive sense circuits 106 and 108 as previously described with reference to the generic block diagram of FIG.4.
  • the analog-front end part of the measurement circuit 104 merges the driver circuit 402 and the measurement amplifier circuit 404 with reference to FIGs.
  • the plurality of inductive sense circuits 106 includes sense circuits 106a, 106b, ..., 106n (106n not shown in FIG. 11 for purposes of illustration).
  • the plurality of capacitive sense circuits 108 includes sense circuits 108a, 108b, ..., 108n, (108a and 108b not shown in FIG. 11 for purposes of illustration). The dots indicated in FIG.
  • each of the plurality of inductive sense circuits 106 have an identical circuit topology.
  • each of the plurality of capacitive sense circuits 108 have an identical circuit topology. Therefore, descriptions given below for the inductive sense circuit 106a also apply to the other inductive sense circuits (e.g., 106b) and descriptions given below for the capacitive sense circuit 108n also apply to the other capacitive sense circuits (e.g., 108a).
  • Each of the plurality of inductive sense circuits 106 provides a measurement port 936 (indicated in FIG.11 by a terminal) for applying an electrical voltage V1 (as indicated in FIG.11) and for measuring an electrical current I 1 (as indicated in FIG.11) in response to the voltage V 1 .
  • each of the plurality of capacitive sense circuits 108 provides a measurement port 938 (indicated in FIG. 11 by a terminal) for applying the voltage V 1 (as indicated in FIG.11) and for measuring the current I1 (as indicated in FIG.11) in response to the current V1.
  • the sense circuits 106 and 108 as illustrated in FIG.11 may be considered as one-port circuits.
  • the measurement circuit 104 of the circuit 1100 includes a single input multiplexer circuit 910 to selectively (e.g., sequentially) apply the voltage V 1 to each of the plurality of sense circuits 106 and 108 and to selectively (e.g., sequentially) measure a current I1 in response to the applied voltage V1. More specifically, but not indicated in FIG. 10 for purposes of illustration, the voltage V 1 applied to the sense circuit 106a may be denoted by V1a, the voltage V1 applied to the sense circuit 106b may be denoted as V 1b , etc.
  • the currents I 1 in the sense circuits 106a and 106b may be denoted by I 1a and I1b, respectively.
  • the circuit 1100 may be configured and operated in a mode to selectively (e.g., sequentially) measure the impedance Z 11 e.g., at the measurement port 936 of each of the plurality of the sense circuits 106 defined as: Z 11 ⁇ V 1a / I 1a (359) [0710]
  • the circuit 1100 as illustrated in FIG.11 may be less versatile. It may not support measuring the inter-sense circuit transimpedance Z12 as described with reference to FIG.9A.
  • the inductive sense circuit 106a includes an inductive sense element 107a including a sense coil (e.g., sense coil 502 of FIG.5A) with an inductance L, a first capacitor (e.g., capacitor 544 of FIG.5C) having a capacitance C p , and a second capacitor (e.g., capacitor 546 of FIG.5C) with a capacitance C s .
  • the first capacitor e.g., parallel capacitor 544
  • the parallel circuit of capacitor 544 and inductive sense element 107a electrically connects to ground and is also capacitively coupled to the measurement port 936 via the series capacitor 546.
  • each of the plurality of inductive sense circuits 106 is configured to provide a minimum of the impedance magnitude
  • the capacitors 544 and 546 may be configured to provide an impedance magnitude
  • at the sense frequency in a suitable range for the measurement circuit (e.g., measurement circuit 104 of FIG.4) by adjusting the capacitance ratio n C C p /C s accordingly as previously discussed with reference to FIG.5G.
  • may be increased to a level substantially (e.g., 10 times) higher than that of the inductive sense circuit 106a of the circuit 900 of FIG. 9A.
  • may be a requirement of the voltage source current measurement technique.
  • the capacitors 544 and 546 are of a type with a low temperature coefficient providing high thermal stability (e.g., a NP0-type capacitor) reducing thermal drift of an electrical characteristic (e.g., an impedance) as measured at each of the plurality of inductive sense circuits 106a, 106b, ..., 106n.
  • an electrical characteristic e.g., an impedance
  • the inductive sense circuit 106a in conjunction with the voltage source current measurement technique provides a high pass filter characteristic to attenuate a low frequency disturbance component in the current I1.
  • the series capacitor 546 together with the parallel capacitor 544 may be configured to attenuate this low frequency disturbance component to a level e.g., below the level of the current I1 in response to a respective sense voltage V1 at the sense frequency, while maintaining series resonance at the sense frequency as previously discussed with reference to FIG.5G.
  • this high pass filter characteristic may exert a minor impact on the current I1 and thus on the measurement of the impedance Z 11 and which may be corrected in a further processing (e.g., in the signal processing circuit 408 of FIG.4) as previously discussed with reference to the circuit 900 of FIG.9A.
  • the inductive sense circuits 106 may not need any supplementary capacitor (e.g., capacitor 928) for purposes of DC blocking as previously discussed with reference to the circuit 900 of FIG.9A, as the series capacitor 546 already blocks any DC.
  • the capacitive sense circuit 108n includes a capacitive sense element 109n including a sense electrode (e.g., sense electrode 702 of FIG. 7C illustrating a single-ended sense electrode) with a capacitance C, a series inductor 724 (e.g., series inductor 724 of FIG. 7C) with an inductance L s , a transformer 726 (e.g., transformer 726 of FIG.
  • the 7C providing a primary and secondary port, a secondary-referred main inductance L m and a voltage transformation ratio 1:n VT . Further, it includes a capacitor 930 with a capacitance Cb e.g., for purposes as previously discussed with reference to the sense circuits 106 and 108 of FIG.9A. As opposed to the sense circuit 108n of FIG. 10, the sense circuit 108n of FIG. 11 provides only one measurement port 938 for measuring the impedance Z 11 .
  • the inductor 724 is electrically connected in series to the capacitive sense element 109n.
  • the series circuit of inductor 724 and capacitive sense element 109n is electrically connected to the transformer’s 726 secondary port that also electrically connects to ground.
  • each of the plurality of capacitive sense circuits 108 is configured to provide a minimum of the impedance magnitude
  • the transformer 726 may be configured to provide an impedance magnitude
  • the transformer 726 may be configured to attenuate this low frequency disturbance component to a level e.g., significantly below the level of the current I 1 in response to a respective sense voltage V 1 at the sense frequency.
  • this high pass filter may exert a minor impact on the current I and thus on the measurement of the impedance Z 11 and which may be corrected in a further processing (e.g., in the signal processing circuit 408 of FIG.
  • the measurement circuit 104 includes a driver amplifier circuit 902, a transimpedance amplifier circuit (e.g., amplifier 904), a transformer 1102, an input multiplexer circuit 910 illustrated in FIG. 11 as a plurality of switches 911a, 911b, ..., 911n, and a plurality of resistors 1014 and 1015 (parallel resistors).
  • the parallel resistors 1014 and 1015 are electrically connected in parallel to the respective terminal of the input multiplexer circuit 910 whose terminals are electrically connected to the respective measurement port (e.g., measurement port 936) of the sense circuits 106 and 108.
  • the parallel resistors 1014 connected in parallel to the measurement ports 936 have a resistance Rpar1
  • the parallel resistors 1015 connected in parallel to the measurement ports 938 have a resistance R par2 that may generally differ from R par1 .
  • the measurement circuit 104 is configured to operate as a voltage source (e.g., voltage source 552 as described in connection with FIG.5C) and to selectively (e.g., sequentially) apply the voltage signal V 1 at the sense frequency to each of the plurality of inductive sense circuits 106 and to each of the plurality of the capacitive sense circuits 108.
  • the voltage signal V1 (e.g., a sinusoidal sense signal) is based on a driver input signal which may be an output of the signal generator circuit 406 with reference to FIG. 4.
  • the driver amplifier circuit 902 as illustrated in FIG.11 by example includes an amplifier 904 and external resistance circuitry comprising a first (feedback) resistor 906 and a second resistor 908 for adjusting a gain.
  • the amplifier 904 is one of a low noise operational amplifier and an amplifier providing high linearity.
  • the driver amplifier circuit 902 is configured to receive the driver input signal and to provide a corresponding output with an accurate and stable voltage (a voltage source output).
  • the measurement circuit 104 is also configured to operate as the analog front-end part of a current measurement circuit (e.g., current measurement circuit 550 as described in connection with FIG.5C). It is configured to selectively (e.g., sequentially) buffer and convert an electrical current I 1 in each of the plurality of inductive sense circuits 106 and in each of the plurality of capacitive sense circuits 108 and to provide an output voltage signal Vout (as indicated in FIG.11) based on the respective electrical current I 1 at a level suitable for further processing e.g., in the signal processing circuit 408 with reference to FIG. 4.
  • the example transimpedance amplifier circuit 952 as illustrated in FIG.
  • the 10 includes an amplifier 954, a feedback resistor 956 having a resistance Rf, and a feedback capacitor 958 having a capacitance Cf.
  • the amplifier 954 is at least one of a low noise operational amplifier and an amplifier providing high linearity.
  • the positive input (+) of the amplifier 954 connects to ground.
  • Both the feedback resistor 958 and the feedback capacitor 958 are electrically connected between the output (V out ) and the negative input (-) of the amplifier 954.
  • the transimpedance amplifier circuit 952 is configured to receive an input current I in that is a secondary current of the transformer 1102 and to convert the input current Iin into a proportional output voltage Vout.
  • the conversion gain is determined by the impedance of the parallel connection of the feedback resistor 956 and the feedback capacitor 958. Since the voltage at the negative input (-) of the amplifier 954 is virtually zero (virtual ground), the transimpedance amplifier circuit 952 presents a virtually zero input impedance at its negative input (-).
  • the feedback capacitor 958 provides the transimpedance amplifier circuit 952 with a first order low pass filter characteristic to attenuate disturbance signal components at frequencies higher than the sense frequency (e.g., high order WPT harmonics) as previously discussed with reference to FIG.9A. [0724]
  • the filtering of the transimpedance amplifier circuit 952 is further enhanced by a supplementary feedback inductor (not shown in FIG.
  • the transformer 1102 includes a primary winding and a galvanically insulated secondary winding wound on a common core as indicated in FIG. 11. A first terminal of the transformer’s 1102 primary winding electrically connects to the output of the driver amplifier circuit 902, while its second terminal is electrically connected to a common node of the input multiplexer circuit 910.
  • the transformer 1102 is configured as a current transformer providing a current transformation ratio 1:n C T.
  • the transformer’s primary current corresponding to the driver amplifier circuit’s 902 output current I may be indicative for the current I 1 in response to the applied voltage V1.
  • the transformer 1102 is supplanted by a parallel inductor (e.g., parallel inductor 716 with reference to the circuit 710 of FIG.7B. In further implementations, neither a transformer 1102 nor a parallel inductor is used.
  • the input multiplexer circuit 910 includes a plurality of switches 911a, 911b, ..., 911n and is configured to selectively connect each of the plurality of inductive sense circuits 106 and each of the plurality of capacitive sense circuits 108 to the driver amplifier circuit 902 and the transimpedance amplifier circuit 952 to selectively (e.g., sequentially) apply the voltage V1 at the sense frequency to each of the plurality of sense circuits 106 and 108 and to selectively (e.g., sequentially) measure the current I1 in response to the applied voltage V1.
  • the input multiplexer circuit 910 is further configured to receive a MUX control signal from a control circuit (e.g., from the control and evaluation circuit 102 of FIG.4) that controls the input multiplexer circuit 910.
  • a control circuit e.g., from the control and evaluation circuit 102 of FIG.4
  • Each of the plurality of switches 911a, 911b, ..., 911n may be one of a type as previously mentioned with reference to the circuit 900 of FIG.9A. It may be appreciated that the closed-state resistance of the switch (e.g., switch 911a) may be non-critical if the impedance magnitude
  • may also reduce an impact of the switch (e.g., switch 911a) and thus improve a temperature stability of the measurement circuit 104 as previously discussed with reference to FIG. 9A.
  • the impedance at the transformer’s 1102 primary port is small enough, the total capacitive load produced by the plurality of parallel capacitances at the common input/output node may be non-critical given the voltage source output of the driver amplifier circuit 902.
  • the parallel resistors 1014 and 1015 are used to limit the open-switch voltage (e.g., at WPT frequency) across the input multiplexer circuit 910 switch (e.g., switch 911a) when WPT is active as previously discussed with reference to FIG.
  • the impedance as measured by the measurement circuit 104 may differ from the impedance
  • the fractional change as measured in the measurement circuit 104 may be smaller than the fractional change
  • the input multiplexer circuit 910 switches are configured to sustain an open-switch voltage that is substantially (e.g., 5 times) higher than that of the switches used in the circuit 1000 and the resistances R par1 and R par2 are substantially (e.g., 5 times) higher than
  • Using an analog switch rated for a higher open-switch voltage may require other electrical characteristics (e.g., closed-state resistance, parasitic capacitances, etc.) of the switch to be compromised.
  • TABLE 10 also includes the system Q-factor Q sys as defined above by Equation (354), the quality of the measurement circuit 104 as defined by Equation (358), and the degradation of the fractional change in the measurement amplifier circuit’s 404 output voltage Vout as defined by Equation (356).
  • TABLE 10 also includes the system Q-factor Q sys as defined above by Equation (354), the quality of the measurement circuit 104 as defined by Equation (358), and the degradation of the fractional change in the measurement amplifier circuit’s 404 output voltage V out as defined by Equation (356).
  • TABLE 12 p [0732] The numerical values as shown in TABLEs 11 and 12 for the circuit 1100 are similar to those obtained for the circuit 1000 listed in TABLEs 9 and 10, respectively. The degradation of the fractional change in the circuit 1100 is larger. However, this drawback may be acceptable considering the potential for circuit complexity reduction in the circuit 1100.
  • FIGs.12A and 12B illustrate example implementations of capacitive sense elements 109a, 109b, ..., 109n integrated into the housing 328 (e.g., a plastic enclosure) of a wireless power transfer structure (e.g., wireless power transfer structure 200) with reference to FIGs. 2 and 3.
  • FIGs. 12A and 12B show top views of the example implementations, which, for simplicity of discussion, include only a portion of the housing 328.
  • FIG. 12A shows an arrangement 1200 of four single-ended capacitive sense elements each composed of an electrode pair electrically connected in parallel and providing a single terminal 1208 in the corner of the housing 328.
  • Each electrode is further subdivided into smaller elements 1202 tailored to fit into compartments 1204 of the housing 328.
  • the plurality of elements 1202 belonging to the same electrode are electrically connected e.g., using wires or similar electrical conductors that may pass through slots in the walls dividing the compartments 1204.
  • the compartments 1204 are located along a perimeter of the housing 328. In some aspects, the top surface of the compartments 1204 is inclined toward the interior of the housing 328 to form ramps over which a vehicle may drive.
  • FIG.12B shows an arrangement 1210 of four double-ended capacitive sense elements each composed of an electrode pair providing a terminal pair 1212 in the corner of the housing 328.
  • FIGs. 13A and 13B illustrate example implementations of an electrode element (e.g., element 1202) with reference to FIGs.12A and 12B, respectively.
  • FIG.13A illustrates holohedral sense electrode (e.g., element 1202) made of a holohedral conductive sheet 1304 (e.g., copper sheet) on a non-conductive substrate 1302.
  • a holohedral conductive sheet 1304 e.g., copper sheet
  • FIG. 13B shows an alternative implementation of an element 1202 configured to increase a surface impedance with respect to the holohedral conductive sheet 1204.
  • the element 1202 is shaped as a finger structure comprising a number of conductive strips electrically connected at only one end.
  • This finger structure may increase a surface impedance and thus reduce eddy current flow on the element’s 1202 surface and consequent heating.
  • Using a finger structure may also reduce the capacitance C of the capacitive sense element (e.g., capacitive sense element 109a).
  • the capacitive coupling to the object e.g., object 114) e.g., as defined by Equation (342), may not change substantially.
  • the element 1202 is made of a weakly conductive material providing a sufficiently high surface impedance.
  • the material may represent a trade-off between eddy current heating and an equivalent resistance (e.g., equivalent resistance R as indicated in FIG.7A) of the capacitive sense element (e.g., capacitive sense element 109a).
  • equivalent resistance R e.g., equivalent resistance R as indicated in FIG.7A
  • other suitable structures or materials are used to increase the surface impedance of the element 1202 trading-off eddy current heating and an equivalent resistance R of the capacitive sense element (e.g., capacitive sense element 109a) at the sense frequency as previously discussed with reference to FIG.7A.
  • the element 1202 is made as a printed circuit board (PCB).
  • the plurality of elements 1202 is a flex print that also includes the inter- element connections as mentioned above with reference to FIG.12A.
  • the electrodes of the capacitive sense elements e.g., capacitive sense element 109a
  • the electrodes of the capacitive sense elements are directly printed onto the non-conductive inner surface of the housing 328 e.g., using a 3D inkjet printer (conductive ink) or other manufacturing technologies such as Molded Interconnect Device (MID) and Laser Direct Structuring (LDS).
  • MID Molded Interconnect Device
  • LDS Laser Direct Structuring
  • electrodes are fully or partially embedded in the plastic material of the housing 328 e.g., using an injection molding process where electrodes are inlaid into the mold prior injection.
  • FIGs. 14A to 14C illustrate the electric vehicle 330 driving into a parking place 1404 (e.g., for purposes of charging) at three different positions.
  • the vehicle 330 provides the (secondary) wireless power transfer structure 310 mounted at its underbody at a location as illustrated in FIGs.14A to 14C and in FIG.3.
  • the parking place 1404 is equipped with the (primary) wireless power transfer structure 200 with reference to FIGs.2 and 3 e.g., to wirelessly deliver power to the vehicle 330 as previously described with reference to FIGs 2 and 3.
  • the wireless power transfer structure 200 integrates the multi-purpose detection circuit 100 including the array 107 of inductive sense elements 107a, 107b, ... 107n and the arrangement of capacitive sense elements 109a, 109b, ... 109n as illustrated in FIGs.2 and 3.
  • the array 107 of inductive elements is assumed to essentially cover the top surface of the wireless power transfer structure 200 as illustrated by FIGs.2 and 3.
  • FIG.14A shows the vehicle 330 approaching the ground-based wireless power transfer structure 200.
  • the vehicle’s 330 front partially overlaps the wireless power transfer structure 200, while FIG.
  • FIG. 14C represents the vehicle 330 close before its final parking position where the vehicle-mounted wireless power transfer structure 310 will be in sufficient alignment with the ground-based wireless power transfer structure 200 as previously mentioned in the introduction.
  • the sequence of images 1500 to 1580 of FIG.15A and 15B illustrate the electric vehicle 330 advancing towards the final parking position as described above with reference to FIG.14C.
  • FIGs. 15A and 15B display corresponding 8 x 8 pixel grayscale patterns 1502 to 1592.
  • Each of the patterns 1502 to 1592 may refer to a pattern produced by mapping the plurality of detection output values of the multi-purpose detection circuit 100 using an 8 x 8 array 107 of inductive sense elements 107a, 107b, .., 107n onto respective elements of an 8 x 8 matrix at the respective vehicle position. More specifically, in some implementations, these detection outputs may refer to outputs of the measurement circuit 104 with reference to FIG. 4. In other implementations, detection outputs may be outputs of a function (not shown herein) that is part of the evaluation & control circuit 102.
  • the pixel grayscale may be indicative of at least one of a magnitude and a phase of an impedance change (e.g., ⁇ Z ) in an inductive sense circuit (e.g., inductive sense circuit 106a) as caused by the presence of the vehicle 330. In some implementations, it may be indicative of another electrical characteristics as output by the multi- purpose detection circuit 100. “Dark gray” indicates zero change (e.g.,
  • Pattern 1502 (all pixels dark gray) refers to the absence of the vehicle 330 or to a vehicle 330 position as shown by image 1500 where the vehicle’s 330 impact on the detection outputs of the multi-purpose detection circuit 100 is below the detection threshold.
  • Pattern 1512 refers to a vehicle 330 position as shown by image 1510 where the front (leading edge) of the vehicle 330 starts to cause a minority of detection outputs to exceed the detection threshold resulting in brighter gray pixels in the 1 st and 2 nd column of the pattern 1512.
  • Pattern 1522 refers to a vehicle 330 position as shown by image 1520 where the leading edge of the vehicle 330 causes more detection outputs to exceed the detection threshold or even the saturation level resulting in white pixels in the 1 st and 2 nd column and brighter gray pixels in the 3 rd and 4 th column of the pattern 1522.
  • Pattern 1532 refers to a vehicle 330 position as shown by image 1530 where the leading edge of the vehicle 330 is further advanced and substantially overlapping the surface of the wireless power transfer structure 200, thus causing a majority of detection outputs to exceed the detection threshold and a higher number thereof to exceed the saturation level resulting in white pixels in the first four columns and brighter gray pixels in the 5 th and 6 th column of the pattern 1532.
  • Pattern 1542 refers to a vehicle 330 position as shown by image 1540 where the leading edge of the vehicle 330 is almost fully overlapping the wireless power transfer structure 200, thus causing all detection outputs to exceed the detection threshold and a majority thereof to exceed the saturation level resulting in white pixels in the first 6 columns and brighter gray pixels in the 7 th and 8 th column of the pattern 1542.
  • the pattern 1542 also shows a gray area in the first two columns caused by an inhomogeneous structure of the vehicle’s 330 underbody (e.g., by a different material or a cavity in the underbody).
  • Pattern 1552 refers to a vehicle 330 position as shown by image 1550 where the leading edge of the vehicle 330 entirely overlaps the wireless power transfer structure 200, thus causing detection outputs to exceed the detection threshold in all columns.
  • the gray area caused by the inhomogeneous underbody and that has become visible in the pattern 1542 has now moved to the 4 th and 6 th column of the pattern 1552.
  • Pattern 1562 refers to a vehicle 330 position as shown by image 1560 where the vehicle-based wireless power transfer structure 310 has reached the edge of the ground-based wireless power transfer structure 200 that starts now to also impact the pattern 1562.
  • the wireless power transfer structure 310 includes different materials (e.g., Litz wire made of copper, ferrite, aluminum, and other conductive and non-conductive materials, its impact on the individual inductive sense elements of the array 107 may be highly variable. While ferrite materials tend to produce a positive reactance change, highly conductive materials such as copper and aluminum tend to cause a negative reactance change. Depending on the actual relative position of the wireless power transfer structure 310, the impact of some portions of the wireless power transfer structure 310 on some inductive sense elements (e.g., inductive sense element 107a) may cancel out producing the dark gray area in column 1 of the pattern 1562.
  • inductive sense element 107a may cancel out producing the dark gray area in column 1 of the pattern 1562.
  • Pattern 1572 refers to a vehicle 330 position as shown by image 1570 where the center of the vehicle-based wireless power transfer structure 310 has just surpassed the edge of the ground-based wireless power transfer structure 200 producing a unique pattern of different gray levels in the first three columns. The gray area caused by the underbody inhomogeneity has now proceeded to the last two columns of the pattern 1572.
  • Pattern 1582 refers to a vehicle 330 position as shown by image 1580 where the vehicle-based wireless power transfer structure 310 now fully overlaps with the top surface of the ground-based wireless power transfer structure 200.
  • Pattern 1592 refers to a vehicle 330 position as shown by image 1590 where the vehicle-based wireless power transfer structure 310 is now well aligned with the ground-based wireless power transfer structure 200 displaying the grayscale pattern centered in the 8 x 8 pattern 1592.
  • the patterns 1502 to 1592 as used in FIGs. 15A and 15B may be considered example and simplified for purposes of illustration.
  • Patterns may also be produced from detection outputs of the multi- purpose detection circuit 100 associated to the plurality of capacitive sense elements 109a, 109b, ... 109n as illustrated in FIGs 2 and 3. More specifically, in some implementations, these detection outputs may refer to outputs of the measurement circuit 104 with reference to FIG. 4. In other implementations, detection outputs may be outputs of a function (not shown herein) that is part of the evaluation & control circuit 102.
  • gray levels in these patterns may be indicative of impedance changes as measured in the plurality of capacitive sense circuits 108a, 108b, ... 108n. Though with a lower image resolution, these patterns may also reflect structures of the vehicle’s 330 underbody (e.g., the vehicle-based wireless power transfer structure 310). [0758] Therefore, in some implementations, the patterns 1502 to 1592 may also refer to a pattern produced by mapping detection output values of the multi-purpose detection circuit 100 associated with at least one of the plurality of inductive sense elements 107a, 107b, .., 107n and the plurality of capacitive sense elements 109a, 109b, ..., 109c.
  • patterns as produced by detection outputs associated with at least one of the plurality of inductive sense circuits 106 and the plurality of capacitive sense circuits as previously described with reference to FIGs.15A and 15B are used to discriminate the vehicle 330 from an object (e.g., object 110). More specifically, in some implementations, detection outputs associated with at least one inductive sense circuit (e.g., inductive sense circuit 106a) are used to discriminate between the impact of the vehicle 330 and the impact of an object (e.g., object 112) in detection outputs associated with at least one capacitive sense circuit (e.g., capacitive sense circuit 108a).
  • inductive sense circuit e.g., inductive sense circuit 106a
  • detection outputs associated with at least one capacitive sense circuit are used to discriminate between the impact of the vehicle 330 and the impact of an object (e.g., object 110) in detection outputs associated with at least one inductive sense circuit (e.g., inductive sense circuit 106a).
  • detection outputs associated with at least one inductive sense circuit are used to reduce a false positive detection probability of LOD.
  • detection outputs associated with at least one capacitive sense circuit are used to reduce a false positive detection probability of FOD.
  • detection outputs associated with at least one inductive sense circuit e.g., inductive sense circuit 106a
  • at least one capacitive sense circuit e.g., capacitive sense circuit 108a
  • the detection threshold refers to at least one of FOD and LOD. Dynamically adjusting a detection threshold is described in U.S. Patent application 16/392,464, titled Extended Foreign Object Detection Signal Processing.
  • patterns as produced by detection outputs associated with at least one of the plurality of inductive sense circuits 106 and the plurality of capacitive sense circuits as previously described with reference to FIGs.15A and 15B are used to detect or identify a type of vehicle 330 or a type of vehicle-based wireless power transfer structures 310.
  • patterns as produced by detection outputs associated with at least one of the plurality of inductive sense circuits 106 and the plurality of capacitive sense circuits as previously described with reference to FIGs.15A and 15B are used to determine a position of the vehicle 330 (or the vehicle-based wireless power transfer structures 310) relative to the ground-based wireless power transfer structure 200.
  • the relative position is at least in part determined by using an image correlation technique (e.g., a similar technique as employed in the computer mouse using a laser sensor for surface structure detection).
  • the relative position is determined by tracking a “front-wave” in successively obtained patterns as produced by detection outputs associated with at least one of the plurality of inductive sense circuits 106 and the plurality of capacitive sense circuits and as illustrated by the patterns 1512 to 1542 of FIGs.15A.
  • This “front-wave” visible in patterns 1512 to 1542 as a transition of dark grey to white may be produced by the leading edge of the vehicle 330.
  • patterns as produced by detection outputs associated with at least one of the plurality of inductive sense circuits 106 and the plurality of capacitive sense circuits as previously described with reference to FIGs.15A and 15B are used to activate or prime another positioning system.
  • patterns as produced by detection outputs associated with at least one of the plurality of inductive sense circuits 106 and the plurality of capacitive sense circuits as previously described with reference to FIGs.15A and 15B are used to extend the range of another positioning system.
  • patterns as produced by detection outputs associated with at least one of the plurality of inductive sense circuits 106 and the plurality of capacitive sense circuits as previously described with reference to FIGs.15A and 15B are used to enhance the accuracy or reliability of another positioning system.
  • patterns as produced by detection outputs associated with at least one of the plurality of inductive sense circuits 106 and the plurality of capacitive sense circuits as previously described with reference to FIGs.15A and 15B are used to adjust or calibrate another positioning system.
  • Other positioning systems may include systems based on using at least one of an inductive and capacitive passive beacon transponder as previously discussed e.g., with reference to FIG. 3, sensing of at least one of a magnetic and electric field generated by an active beacon transmitter (e.g., active beacon as described in U.S. Patent Application No. 16/284,959 titled Extended-Range Positioning System Based on Foreign Object Detection, magnetic vectoring as described in U.S. Patent Application No. 15/003,521 titled Integration of Solenoid Positioning Antennas in Wireless Inductive Charging Power Applications, U.S.
  • an active beacon transmitter e.g., active beacon as described in U.S. Patent Application No. 16/284,959 titled Extended-Range Positioning System Based on Foreign Object Detection, magnetic vectoring as described in U.S. Patent Application No. 15/003,521 titled Integration of Solenoid Positioning Antennas in Wireless Inductive Charging Power Applications, U.S.
  • Patent No.10,340,752 titled System, Methods and Apparatuses for Guidance and Alignment in Electric Vehicles Wireless Inductive Charging Systems
  • U.S. Patent No. 10,566,839 titled Systems, Methods and Apparatus for Guidance and Alignment Between Electric Vehicles and Wireless Charging Systems, the entire contents of which are hereby incorporated by reference).
  • They may also include positioning systems based on optical sensors (cameras), LIDAR technologies, ultrasound sensors, inertial sensors.
  • the various operations of methods described above may be performed by any suitable means capable of performing the corresponding functions.
  • the means may include various hardware and/or software component(s) and/or module(s), including, but not limited to a circuit, an application-specific integrated circuit (ASIC), or processor.
  • ASIC application-specific integrated circuit
  • 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, a 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.
  • determining may include resolving, selecting, choosing, establishing, and the like.
  • a phrase referring to “at least one of” a list of items refers to any combination of those items, including single members.
  • “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c, as well as any combination with multiples of the same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b, b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c).
  • DSP digital signal processor
  • ASIC application specific integrated circuit
  • FPGA field programmable gate array
  • PLD programmable logic device
  • a processor may be a microprocessor, but in the alternative, 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, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.
  • the methods disclosed herein comprise one or more steps or actions for achieving the described method.
  • the method steps and/or actions may be interchanged with one another without departing from the scope of the claims. In other words, unless a specific order of steps or actions is specified, the order and/or use of specific steps and/or actions may be modified without departing from the scope of the claims.
  • the functions described may be implemented in hardware, software, firmware, or any combination thereof.
  • an example hardware configuration may comprise a processing system in a wireless node.
  • the processing system may be implemented with a bus architecture.
  • the bus may include any number of interconnecting buses and bridges depending on the specific application of the processing system and the overall design constraints.
  • the bus may link together various circuits including a processor, machine-readable media, and a bus interface.
  • the bus interface may be used to connect a network adapter, among other things, to the processing system via the bus.
  • the bus may also link various other circuits such as timing sources, peripherals, voltage regulators, power management circuits, and the like.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Remote Sensing (AREA)
  • Physics & Mathematics (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Electromagnetism (AREA)
  • Mechanical Engineering (AREA)
  • Transportation (AREA)
  • Environmental & Geological Engineering (AREA)
  • Geology (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Geophysics (AREA)
  • Geophysics And Detection Of Objects (AREA)

Abstract

L'invention concerne un circuit de détection polyvalent destiné à la détection d'objet et la détermination de la position d'un véhicule. Par exemple, le circuit peut être configuré pour détecter des corps étrangers métalliques, des objets vivants, et un véhicule ou un type de véhicule au-dessus d'un émetteur de puissance sans fil inductif. Le circuit peut également être configuré pour déterminer la position du véhicule par rapport à l'émetteur de puissance sans fil inductif. Un appareil donné à titre d'exemple comprend un circuit de mesure comprenant un multiplexeur, électriquement connecté à une pluralité de circuits de détection inductifs et capacitifs, servant à mesurer une ou plusieurs caractéristiques électriques dans chacun des circuits de détection inductifs et capacitifs selon un schéma de multiplexage temporel prédéfini. L'appareil comprend en outre un circuit de commande et d'évaluation destiné à évaluer les caractéristiques électriques mesurées et à déterminer une présence d'un objet métallique, d'un objet vivant, d'un véhicule ou d'un type de véhicule, et/ou une position de véhicule sur la base de changements des caractéristiques électriques mesurées.
PCT/US2022/076345 2021-09-14 2022-09-13 Circuit de détection d'objet et détermination de position de véhicule WO2023044300A1 (fr)

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US202163244165P 2021-09-14 2021-09-14
US63/244,165 2021-09-14
US17/931,429 US11914094B2 (en) 2019-10-25 2022-09-12 Circuit for object detection and vehicle position determination
US17/931,429 2022-09-12

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