Patent Publication Number: US-2022239160-A1

Title: Wire-Wound Structures for Electromagnetic Sensing of Objects

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Patent Application Ser. No. 63/141,730, filed Jan. 26, 2021, the entire disclosure of which is hereby incorporated by reference. 
    
    
     FIELD 
     The present disclosure generally relates to foreign object detection, for example, in an application for inductive wireless charging of electric vehicles. In particular, the present disclosure is directed to wire-wound structures configured for electromagnetic sensing of foreign objects located near an inductive wireless power transfer system. 
     BACKGROUND 
     Inductive wireless power transfer (WPT) systems provide one example of wireless transfer of energy. In an inductive WPT system, a primary power device (or wireless power transmitter) transmits power wirelessly to a secondary power device (or wireless power receiver). Each of the wireless power transmitter and wireless power receiver includes a wireless 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. When a secondary wireless power transfer structure is placed in proximity to the primary wireless power transfer structure, the alternating magnetic field induces an electromotive force (EMF) into the coil of a secondary wireless power transfer structure according to Faraday&#39;s law, thereby wirelessly transferring power to the wireless power receiver if a resistive load is connected to the wireless power receiver. To improve a power transfer efficiency, some implementations use a wireless power transfer structure that is part of a resonant structure (resonator). The resonant structure may comprise a capacitively loaded inductor 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 WPT 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 that may be present within or near the inductive power region. 
     In certain applications for inductive wireless charging of electric vehicles, it may be useful to be able to detect foreign objects that may be present in the inductive power region and that could be susceptible to induction heating due to the high magnetic-field strength in that region. In an 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 millitesla (mT)) to allow for sufficient power transfer (e.g., 3.3 kilowatt (kW), 7 kW, 11 kW, and the like). Therefore, metallic objects or other objects present in the magnetic field can experience undesirable induction heating. For this reason, foreign object detection (FOD) 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. 
     In certain applications for inductive wireless charging of electric vehicles, it may also be useful to be able to detect living objects that may be present within or near an inductive power region where the level of electromagnetic field exposure exceeds certain limits (e.g., as defined by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) recommendation). For this reason, 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. 
     An example FOD system based on inductive sensing using a plurality (e.g., an array) of sense loops (e.g., multi-turn sense loops) integrated into a surface of a wireless power transfer structure is described in U.S. Pat. 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. In this example FOD system, an electrical characteristic (e.g., an impedance, a transimpedance, a Q-factor, a dampening factor, an induced voltage, a pulse response, a response to a swept frequency signal or a pseudorandom signal) is measured in each of a plurality of sense circuits each including at least one of the plurality of sense loop. Presence of the foreign object located near the wireless power transfer structure (e.g., in the predetermined space) is determined in response to a change in the measured electrical characteristics. 
     Another example FOD system based on joint inductive and thermal sensing (inductive thermal sensing) using a plurality of sense loops is described in U.S. patent application Ser. No. 14/279,112 titled Systems, Methods, and Apparatus for Foreign Object Detection Loop Based on Inductive Thermal Sensing, the entire contents of which are hereby incorporated by reference. In this example FOD system, a foreign object is detected based on a change of the object&#39;s temperature when exposed to the WPT magnetic field. Metallic objects of certain categories have at least one electrical property (e.g., electrical conductivity, magnetic permeability) that changes as a function of temperature. An object of these categories in proximity of a sense loop potentially changes an electrical characteristic of the sense loop in response to a change of the object&#39;s electrical property when the object is heated (e.g., by induction heating as discussed above). 
     A further example FOD system based on inductive and thermal sensing (heat sensing) using a plurality of sense loops is described in U.S. Pat. No. 10,444,394 titled Foreign Object Detection Using Heat Sensitive Material and Inductive Sensing, the entire contents of which are hereby incorporated by reference. In addition to inductive sensing using the plurality of sense loops, this example FOD system uses a heat-sensitive material having a property configured to change as a function of temperature. This material may be integrated into a surface of a wireless power transfer structure. 
     An example LOD system based on capacitive sensing using a plurality (e.g., an array) of sense electrodes integrated into a surface of a wireless power transfer structure is described in U.S. Pat. No. 9,952,266, titled Object Detection for Wireless Energy Transfer Systems, and U.S. patent application Ser. No. 17/077,124, titled Circuit for Object Detection and Vehicle Position Determination, the entire contents of which are hereby incorporated by reference. In this example system, an electrical characteristic (e.g., an impedance, a transimpedance, a capacitance, a resistance, an induced voltage, a pulse response, a response to an arbitrary waveform signal) is measured in each of a plurality of sense circuits each including at least one of the plurality of sense electrodes. Presence of a living object located near the wireless power transfer structure is determined in response to a change in the measured electrical characteristic. 
     In an example wireless power transfer system, at least one of the FOD and the LOD system is also configured to detect one or more of a presence, a type, and a position of a vehicle above the ground-based wireless power transfer structure e.g., using a passive beacon transponder technique as described in U.S. patent application Ser. No. 16/052,445, titled Hybrid Foreign-Object Detection and Positioning System, the entire contents of which are hereby incorporated by reference and in U.S. patent application Ser. No. 17/077,124 as previously referenced. 
     U.S. Pat. No. 10,627,257 describes various implementations of a substantially planar conductive structure (e.g., an array of loops or coils) configured for inductive sensing of foreign objects. In an example implementation, the conductive structure includes loops of one or more turns of thin enameled copper wire. In another implementation, the conductive structure includes loops of one or more turns and is printed on one or more layers of a circuit board. 
     U.S. Pat. No. 9,952,266 and U.S. patent application Ser. No. 17/077,124 describe various implementations of a conductive structure (e.g., an arrangement of electrodes) configured for capacitive sensing of living objects. In an example implementation, the conductive structure includes finger-structured electrodes printed on a single layer circuit board. In another implementation, the conductive structure includes electrodes printed on an inner surface of a plastic enclosure of the wireless power transfer structure (e.g., using a Molded Interconnect Device (MID) technology). In a further implementation, the conductive structure is made of thin metal sheet and is embedded in the plastic enclosure of the wireless power transfer structure. 
     Printed circuit board (PCB) implementations have conventionally been a common solution for the conductive structure. However, employing advanced manufacturing and assembling processes involving highly efficient robots, production costs for a wire-wound structure (e.g., wire-wound coil arrays) can be substantially lowered and may potentially fall below that of a PCB solution. This may be particularly true for inductive sense coil arrays covering an area larger than a quarter of a square meter. Moreover, coils made of copper wire may have electrical properties that are more favorable for the sensing of foreign objects in the inductive power region of a WPT system compared to corresponding PCB coils. 
     SUMMARY 
     In certain aspects of this disclosure, an apparatus for detecting a presence of an object in a predetermined area of an inductive wireless power transfer system is provided. The apparatus comprises a first electrically conductive wire-wound structure configured for electromagnetic sensing of the object in a predetermined area and a substantially planar coil-former. The coil-former has a first surface and a second surface opposite to the first surface and is configured to form, carry, and hold in place the first wire-wound structure on the first surface and a second electrically conductive wire-wound structure on the second surface. The second wire-wound structure is configured to transfer power inductively. The apparatus further comprises a detection circuit coupled to the first wire-wound structure and configured to measure an electrical characteristic of the first wire-wound structure and to determine presence of the object in response to a change in the electrical characteristic. 
     In certain aspects of this disclosure, the first electrically conductive wire-wound structure comprises at least one piece of wire (e.g., an enameled copper wire) configured to form a double-wire lead line and a wire loop of one or more turns configured to sense the object inductively by means of an alternating magnetic field. Each wire end is further configured to provide a terminal to electrically connect the piece of wire to the detection circuit. 
     In certain aspects of this disclosure, the first electrically conductive wire-wound structure comprises at least one piece of wire (e.g., an enameled copper wire) configured to form a single-wire lead line and a substantially two-dimensional wire-wound structure configured to sense the object capacitively by means of an alternating electric field. One wire end is further configured to provide a terminal to electrically connect the piece of wire to the detection circuit. 
     In certain aspects of this disclosure, the coil-former is substantially formed of an electrically insulating material. It is configured to form and accommodate the first and second wire-wound structure and for automated robot winding of the first and second wire-wound structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the figures, the third and fourth digit of a reference number identify the figure in which the reference number first appears. The use of the same reference numbers in different instances in the description or the figures indicates like elements. 
         FIG. 1  is a schematic view illustrating an example implementation of an object detection system including a detection circuit, a plurality of inductive and capacitive sense elements, and 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 an inductive wireless power transfer system integrating the plurality of inductive and capacitive sense elements of  FIG. 1 , as well as the non-living and the living object of  FIG. 1 . 
         FIG. 3  is a vertical cut view illustrating a portion of an inductive wireless power transfer system including the vehicle-based wireless power transfer structure and the ground-based wireless power transfer structure including a wireless power transfer coil and the inductive and capacitive sense elements of  FIG. 1 , and the non-living and the living object of  FIG. 1 . 
         FIG. 4A  is a schematic top-down view illustrating an example implementation of a coil assembly including a coil-former, a first electrically conductive wire-wound structure configured for inductive sensing and capacitive sensing, and a second electrically conductive wire-wound structure configured for inductive wireless power transfer. 
         FIG. 4B  is a schematic vertical cut view illustrating an example implementation of the coil assembly of  FIG. 4A  including the coil-former of  FIG. 4A  configured with a protrusive structure to form, carry, and hold in place the first and second wire-wound structures of  FIG. 4A . 
         FIG. 4C  is a schematic vertical cut view illustrating another example implementation of a coil assembly of  FIG. 4A  with the coil-former configured with a recessed (groove) structure to form, carry, and hold in place the first and second wire-wound structures of  FIG. 4A . 
         FIG. 4D  is a schematic vertical cut view illustrating a further example implementation of the coil assembly of  FIG. 4A  including the coil-former of  FIG. 4C  modified with slanted edge areas. 
         FIG. 4E  is a schematic vertical cut view illustrating the ground-based wireless power transfer structure of  FIG. 3  integrating the coil assembly of  FIG. 4D . 
         FIG. 5  is a schematic top-down view illustrating another example implementation of the coil assembly of  FIG. 4A . 
         FIG. 6  is a top-down view of a detail of an example implementation of the coil-former of  FIG. 4C  and a portion of the first wire-wound structure of  FIG. 4A  configured for inductive sensing. 
         FIG. 7A  is a vertical cut view illustrating a protrusive rectangular profile configured to form, carry, and hold in place the first and second wire-wound structure of  FIG. 4A . 
         FIG. 7B  is a vertical cut view illustrating a recessed rectangular profile configured to form, carry, and hold in place the first and second wire-wound structure of  FIG. 4A . 
         FIG. 7C  is a vertical cut view illustrating a protrusive “L”-shaped coil profile configured to form, carry, and hold in place the first and second wire-wound structure of  FIG. 4A . 
         FIG. 7D  is a vertical cut view illustrating a recessed “L”-shaped profile configured to form, carry, and hold in place the first and second wire-wound structure of  FIG. 4A . 
         FIG. 7E  is a vertical cut view illustrating a protrusive “T”-shaped profile configured to form, carry, and hold in place the first and second wire-wound structure of  FIG. 4A . 
         FIG. 7F  is a vertical cut view illustrating a recessed “T”-shaped profile configured to form, carry, and hold in place the first and second wire-wound structure of  FIG. 4A . 
         FIG. 7G  is a vertical cut view illustrating a protrusive right-angled trapezoidal profile configured to form, carry, and hold in place the first and second wire-wound structure of  FIG. 4A . 
         FIG. 7H  is a vertical cut view illustrating a recessed right-angled trapezoidal profile configured to form, carry, and hold in place the first and second wire-wound structure of  FIG. 4A . 
         FIG. 7I  is a vertical cut view illustrating a protrusive trapezoidal profile configured to form, carry, and hold in place the first and second wire-wound structure of  FIG. 4A . 
         FIG. 7J  is a vertical cut view illustrating a recessed trapezoidal profile configured to form, carry, and hold in place the first and second wire-wound structure of  FIG. 4A . 
         FIG. 7K  is a vertical cut view illustrating the recessed rectangular profile of  FIG. 7B  filled with a filling material. 
         FIG. 8A  is a schematic cut view of a detail illustrating an example implementation of a “pin header” connector configured for soldering of a terminal of the first wire-wound structure of  FIG. 4A . 
         FIG. 8B  is a schematic cut view of the detail of  FIG. 8A , illustrating another example implementation of the “pin header” connector of  FIG. 8A  configured for wire wrapping of a terminal of the first wire-wound structure of  FIG. 4A . 
         FIG. 8C  is a schematic cut view of the detail of  FIG. 8A , illustrating a further example implementation of the “pin header” connector of  FIG. 8A  as an integral part of the coil-former of  FIG. 4A . 
     
    
    
     DETAILED DESCRIPTION 
     The detailed description set forth below in connection with the appended drawings is intended as a description of example implementations and is not intended to represent the only implementations in which the techniques described herein may be practiced. The term “example” used throughout this description means “serving as an example, instance, or illustration” and should not necessarily be construed as preferred or advantageous over other example implementations. The detailed description includes specific details for the purpose of providing a thorough understanding of the example implementations. In some instances, some devices are shown in block diagram form. Drawing elements that are common among the following figures may be identified using the same reference numerals. 
     As mentioned above, foreign object detection (FOD) (and particularly metal object detection) may be valuable for a variety of applications. For detection in a predetermined area, a FOD system may include a plurality of inductive sense elements (e.g., a sense coil) distributed across the predetermined area (e.g., a planar array of sense coils integrated into the ground-based wireless power transfer structure). The predetermined area 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 inductive sense elements. The number of the inductive sense elements may be related to the minimum size of objects that are desirable to be detected. For a system that is configured to detect small objects (e.g., a paper clip), the number of sense elements may be relatively high (e.g.,  64 ). 
     As mentioned above, a FOD system including supplementary heat sensing of hot metal objects heated by the WPT magnetic field may be valuable for a variety of applications and for enhancing FOD e.g., with respect to reliability and foreign object handling as disclosed in U.S. Pat. No. 10,444,394. For detection in a predetermined area, a FOD system may include heat sensing elements using heat-sensitive materials having a property configured to change as a function of a temperature at the location of the heat sensing element. 
     As mentioned above living object detection (LOD) (e.g., human extremities, animals) may be valuable for a variety of applications. For detection in a predetermined area, a LOD system may include a plurality of capacitive sense elements (e.g., a sense electrode) e.g., disposed along the periphery (edge area) of a ground-based wireless power transfer structure of a WPT system. The predetermined area may be defined by the space accessible for living objects 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 related to the minimum size of living objects that are desirable to be detected. For a system that is configured to detect human extremities (e.g., a hand) and animals (e.g., a cat), the number of capacitive sense elements may be relatively low (e.g., in the order of 4). 
     As mentioned above, vehicle detection (VD), the detection of the type of vehicle, or determination of a position of the vehicle (PD) relative to the ground-based wireless power transfer structure, may be valuable for a variety of applications. For detection of a vehicle, the type or position of the vehicle, a VD or PD system may include a plurality of inductive sense elements (e.g., sense coils) 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. 
     A FOD and LOD system may include detection circuitry for applying drive signals to each of the plurality of inductive, capacitive, and heat sensing elements, and for measuring an electrical characteristic in each of the plurality of sense elements and for looking for changes in the electrical characteristics that may correspond to the presence of an object, a hot object, a living object, or a vehicle. 
     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). As non-limiting examples, 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&#39;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 non-conductive) 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. 
       FIG. 1  illustrates an example implementation of an object detection system  100  that includes a detection circuit  102  and a plurality of inductive sense elements  104  and a plurality of capacitive sense elements  108  illustrated in  FIG. 1  by inductive sense elements  104   a ,  104   b , . . . , and  104   n ; and by capacitive sense elements  108   a ,  108   b , some dots, and  108   n . The dots shall indicate that the number of inductive sense elements  104  and/or the number of capacitive sense elements  108  may be greater than three. The plurality of inductive sense elements  104  is also sometimes referred to herein as the plurality of inductive sense elements  104   a ,  104   b , . . . ,  104   n . Likewise, the plurality of capacitive sense elements  108  is also sometimes referred to herein as the plurality of capacitive sense elements  108   a ,  108   b , . . . ,  108   n.    
       FIG. 1  also illustrates foreign objects  110  and  112  as referred to herein as the non-living object and the living object, respectively. The non-living object  110  may represent a metallic (substantially electrically conductive object) that is potentially heated when exposed to the WPT magnetic field as previously discussed. But the object may also be representative of a dielectric or ferromagnetic object that is substantially electrically non-conductive and that does not heat to critical (e.g., hazardous) temperatures when exposed to the WPT magnetic field. The living object  112  may stand for a human extremity (e.g., a hand as depicted in  FIG. 1 ) or an animal. 
     The inductive sense elements  104  and capacitive sense elements  108  are configured to sense at least one of a presence of a foreign object (e.g., non-living object  110 ) in proximity to at least one of the plurality of inductive sense elements  104 , a living object (e.g., living object  112 ) in proximity to at least one of the plurality of capacitive sense elements  108 , a vehicle or type of vehicle (not shown in  FIG. 1 ) positioned above the plurality of inductive and capacitive sense elements  104  and  108 , respectively, and for determining a vehicle position. Inductive and capacitive sensing is based on measuring one or more electrical characteristics (e.g., an impedance, a transimpedance, a voltage, a current, a pulse response) in each of the plurality of inductive sense elements  104  and capacitive sense elements  108  and further based on detecting changes in the measured one or more electrical characteristics. 
     The object detection system  100  may also include detection of hot foreign objects (e.g., non-living object  110 ) based on heat sensing as mentioned above. In some implementations, heat sensing is accomplished using supplementary (dedicated) sense elements (not shown in  FIG. 1 ) configured to have an electrical characteristic that changes as a function of a temperature. In other implementations, heat sensing is performed using the plurality of inductive sense elements  104 , each configured to have an electrical characteristic that also changes as a function of temperature. A heat-sensitive inductive sense element (e.g., inductive sense element  104   a ) includes a heat-sensitive material having a property configured to change as a function of temperature. In some implementations, the conductive structures configured for inductive sensing include a heat-sensitive material e.g., configured to have a heat-sensitive electrical resistance. In other implementations, a heat-sensitive material is included in an insulating material e.g., configured to have an electrical property (e.g., insulation resistance, impedance, magnetic permeability, electric permittivity) configured to change as a function of temperature. In further implementations, the insulating structure (not shown in  FIG. 1 ) that carries the plurality of inductive sense elements  104  (e.g., array  106 ) includes the heat-sensitive material as described above. In yet other implementations, heat sensing is also included in the plurality of capacitive sense elements  108 , each configured to have an electrical characteristic that also changes as a function of temperature. 
     Each of the plurality of inductive sense elements  104  is shown in  FIG. 1  as a “circular” coil for purposes of illustration. However, in other implementations, the inductive sense elements  104  may include a sense coil (e.g., a multi-turn loop) having another coil topology, e.g., a “figure-eight-like” topology. In yet other implementations, the plurality of inductive sense elements  104 , may include sense coils of a mixed coil topology, e.g., “circular” and “figure-eight-like,” In further implementations, the plurality of inductive sense elements  104  may include sense coils (e.g., solenoid coils) with a ferrite core (not shown herein) that are physically smaller compared to “air” coils. In some implementations (not shown herein), each of the plurality of inductive sense elements  104  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 or using another two-port electrical characteristic between sense coils. 
     In some implementations, the plurality of inductive sense elements  104   a ,  104   b ,  104   n  is arranged in an array  106 , such as a two-dimensional array  106 , as shown in  FIG. 1 . However, in other implementations, the sense elements of the plurality of inductive sense elements  104   a ,  104   b , . . . ,  104   n  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.), cover irregular detection areas, or any combination thereof. As such the term “array” as used herein denotes a plurality of sense elements that are arranged over a predetermined area. Furthermore, the number of sense elements of an array  106  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., non-living object  110 ) is to be detected and the smallest size of the object detection system  100  is configured to detect. Example implementations of the inductive sense element (e.g.,  104   a ) and arrangements of inductive sense elements are described in U.S. Pat. No. 9,726,518, titled Systems, Methods, and Apparatus for Detection of Metal Objects in a Predetermined Space, in U.S. patent application Ser. No. 16/358,534, titled Foreign Object Detection Circuit Using Mutual Impedance Sensing, in U.S. Pat. No. 10,122,192, titled Sense Coil Geometries with Improved Sensitivity for Metallic Object Detection in a Predetermined Space, in U.S. Pat. No. 10,124,687, titled Hybrid Foreign Object Detection (FOD) Loop Array Board, the entire contents of which are hereby incorporated by reference. 
     Each capacitive sense element (e.g., capacitive sense element  108   a ), as shown in  FIG. 1 , includes a single electrode providing a single terminal. In other implementations, the capacitive sense elements  108  may be double-ended electrodes configured e.g., for differential mode sensing. As with the inductive sense elements  104 , the capacitive sense elements may be driven and configured for measuring one or more of an impedance, a transimpedance (e.g., a mutual impedance), and another two-port electrical characteristic as defined between electrodes. In  FIG. 1 , the capacitive sense elements  108  are shown arranged in a peripheral area around the array of inductive sense elements  104 . However, in other implementations, the capacitive sense elements of the plurality of capacitive sense elements  108  are arranged in other configurations, e.g., distributed over the area of the array of inductive sense elements  104 . Example implementations of the capacitive sense element (e.g.,  108   a ) and arrangements of capacitive sense elements are described in U.S. Pat. No. 9,952,266 as previously referenced. 
     Each of the plurality of inductive sense elements  104  and the plurality of capacitive sense elements  108  are operably coupled to a detection circuit  102 . The detection circuit  102  may be configured to selectively and sequentially measure one or more electrical characteristics in each of the plurality of inductive sense elements  104  and capacitive sense elements  108  and to provide outputs indicative of the presence of an object (e.g., non-living object  110 ). 
     The detection circuit  102  is configured to cause each of the plurality of inductive sense elements (e.g., sense coils)  104   a ,  104   b , . . . ,  104   n  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 elements  104 . If a metallic object (e.g., non-living object  110 ) is present in the alternating magnetic field, eddy currents will be generated in the object. According to Lenz&#39;s law, the eddy currents in the object will generate another (e.g., opposing) magnetic field that interacts with the primary magnetic field as generated by the respective sense element, and a mutual coupling between object and sense element is developed. This may cause a change in an electrical characteristic (e.g., an impedance) as measured by the detection circuit  1042  in the respective inductive sense elements (e.g., inductive sense element  104   a ). A change in a measured electrical characteristic may also be caused by a substantially non-conductive but ferromagnetic object with a relative permeability μ r &gt;1 that interacts with the alternating magnetic field as generated by the respective sense element. Applying a sense signal to an inductive sense element (e.g., inductive sense element  104   a ) 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., living object  112 ), causing a change in the electrical characteristic as measured in the respective inductive sense element (capacitive sensing effect). 
     The detection circuit  102  is further configured to cause each of the plurality of capacitive sense elements (e.g., sense electrodes)  108   a ,  108   b , . . . ,  108   n  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 voltage) to each of the plurality of capacitive sense elements  108 . If a substantially non-conductive, dielectric object (e.g., living object  112  or non-living object  110 ) with a relative permittivity ε r &gt;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 detection circuit  102  in the respective capacitive sense circuit (e.g., capacitive sense element  108   a ). A change in a measured electrical characteristic may also be caused by a metallic object (e.g., non-living object  110 ) as it will also interact with an alternating magnetic field as generated by the respective capacitive sense element. 
     The detection circuit  102  is configured to determine at least one of a presence of a foreign object (e.g., non-living object  110 ), a living object (e.g., living object  112 ), 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. In some implementations, the detection circuit  102  may include the decision functions as needed for FOD, LOD, and VD, as well as the position calculation functions needed for PD. In other implementations, the vehicle position is determined in a unit external to the object detection system  100  (not shown herein) based on outputs (e.g., raw data) from the detection circuit  102  and on outputs provided by other ground- or vehicle-based sensors (not shown herein). 
       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 object detection system  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 an object detection system  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 a foreign object (e.g., non-living object  110 ) will generally come to a rest. However other implementations are possible, e.g., the object detection system  100  or a portion thereof may also be integrated into a wireless power receiver (e.g., a vehicle-based wireless power transfer structure). The wireless power transfer structure  200  (also sometimes referred to as a “ground assembly” or “base bad”) 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 herein as the wireless power transfer 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 structure  204  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. As an example, the shield  206  may be formed from aluminum. 
       FIG. 2  illustrates one example of how the plurality of inductive sense elements (array  106 ) and the plurality of capacitive sense elements  108  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 , the ferrite structure  204 , and a wireless power transfer coil  202  with reference to  FIG. 2 . It also includes a housing  328  configured to house the wireless power transfer coil  202 , the ferrite structure  204 , and the shield  206 . In addition, the housing  328  is configured to house the plurality of inductive sense elements (array  106 ) and the plurality of capacitive sense elements ( 108 ) as part of the object detection system  100  as illustrated in  FIG. 2 . In some implementations, 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 (not shown herein) may be electrically connected to the wireless power transfer coil  202 , a portion or all of which may also be housed in the housing  328 . In an aspect, the capacitive sense elements (e.g., the capacitive sense elements  109   a ,  109   b , . . . ,  109   n ) may be oriented to be nonparallel with a plane defined by the array  106  of inductive sense elements. For example, the capacitive sense elements may be slanted e.g., oriented to be substantially parallel to the inclined top surface of the housing  328  along the housing&#39;s perimeter. 
     The vehicle-based wireless power transfer structure  310  includes a wireless power transfer coil  312 , a layer of ferrite  315 , and a shield  316  made of an electrically conductive material. In some implementations, the shield  316  may be formed from a portion of the apparatus that the ferrite  315  and the wireless power transfer coil  312  are affixed to, which may be the metallic underbody of a vehicle  330 . In this case, a housing  318  configured to house the wireless power transfer coil  312  and ferrite  315  is provided, though the housing  318  may not house the shield  316 . Other implementations are possible, however, where a conductive back plate is included in the housing  318 . A power-conversion circuit (not shown herein) may be electrically connected to the wireless power transfer coil  312  or a portion or all may also be housed in the housing  318 . 
     As mentioned above and as illustrated in  FIG. 3 , 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 VD and PD 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  104  as described in more detail e.g., in U.S. patent application Ser. No. 16/052,445 as previously referenced. Analogously, the capacitive passive beacon transponder  314  may be configured to primarily interact with the capacitive sense elements, for example, the capacitive sense elements  108 , (e.g., as described in U.S. patent application Ser. No. 17/077,124 as previously referenced). In further implementations, the passive beacon transponder (e.g., passive beacon transponder  313 ) is configured to interact with both the inductive and capacitive sense elements of the object detection system  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. Furthermore, as the ground-based wireless power transfer structure  200  may be positioned on a ground or other top facing surface, a foreign object (e.g., non-living object  110 ) 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. 4A  is a top-down schematic view illustrating an example implementation of a portion of the object detection system  100  of  FIG. 1  including a coil-former  420  and a first wire-wound structure  402  configured for inductive and capacitive sensing of the object (e.g., non-living object  110  and  112 ). The portion is also referred to herein as a coil assembly  400 . The coil-former  420  is a substantially planar structure providing a top surface and a bottom surface. The first wire-wound structure  402  is attached to the top surface and configured to form inductive sense elements (e.g., sense coils)  104   a ,  104   b , and  104   n  and single-ended capacitive sense elements (e.g., sense electrodes)  108   a  and  108   b , e.g., with reference to  FIGS. 1 and 2 . Though the plurality of sense elements  104  and  108  may comprise a larger number of sense elements, only three inductive and two capacitive sense elements are shown in  FIG. 4A  for purposes of illustration. The capacitive sense elements  108   a  and  108   b  are disposed in edge areas of the coil-former  420 , which may be more favorable with respect to capacitive sensing of living objects (e.g., living object  112 ) approaching the wireless power transfer structure  200 .  FIG. 4A  also illustrates a second electrically conductive wire-wound structure  414  (dashed line) attached to the bottom surface of the coil-former  420 . The second wire-wound structure  414  may be the wireless power transfer coil  202  of the wireless power transfer structure  200  with reference to  FIG. 2 . 
     Each inductive sense element (e.g., inductive sense element  104   a ) of the first wire-wound structure  402  is created by winding a piece of wire and provides a pair of terminals  408  (wire ends) electrically connected to a connector  440  (e.g., a multi-pin connector as illustrated in  FIG. 4A ). Each capacitive sense element (e.g., capacitive sense element  108   a ) of the first wire-wound structure  402  is also created by winding a piece of wire and provides a single terminal  416  (wire end) electrically connected to the connector  440 . 
     In some implementations, different wire materials are used to wind the first wire-wound structure  402  and the second wire-wound structure  414  configured for the inductive power transfer. In an example coil assembly  400 , a first wire material (e.g., a single enameled copper wire with a diameter less than 1 mm) is used to wind the inductive sense elements  104  and a second wire material (e.g., a high-frequency Litz wire composed of a plurality of enabled copper wires with an overall diameter larger than 4 mm) is used to create the wire-wound structure  414 . In another example coil assembly  400 , a first wire material with a diameter smaller than 1 mm is used to wind the plurality of inductive sense elements  104 , while a second wire material with a diameter larger than 2 mm is used to create the plurality of capacitive sense elements  108 , e.g., for purposes of increasing a capacitance of the capacitive sense element  108  (e.g., sense electrode). In a further example coil assembly  400 , the first wire-wound structure  402  or portions thereof is wound with a wire of at least one of aluminum, an alloy (e.g., copper alloy), and a material with a relatively high electrical resistance (e.g., higher than that of copper). 
     In an aspect of connecting the wire ends (e.g., wire terminal  416 ) to the connector  440 , the wire-wound structure  402  may be wound using one or more of a non-insulated copper wire, a directly solderable enameled copper wire (e.g., with an enamel that melts away at a soldering temperature above 400° C.), a magnetic wire for wire-wrapping based on magnetics, a wire configured for wire-wrapping based on cold welding a tin plated copper wire. 
     In an aspect of electrical properties, the wire-wound structure  402  may be wound using one or more of a high-frequency Litz wire, a twisted multi-filar wire, a wire bundle, a low electrical-resistance wire, a high electrical-resistance wire, a temperature-compensated electrical resistance wire, a heat-sensitive resistance wire as previously discussed with reference to  FIG. 1 . 
     In an aspect of heat resistance, the wire-wound structure  402  may be wound using a wire with a heat-resistant insulation, e.g., to prevent the wire from insulation damage due to a hot object (e.g., non-living object  110 ) resting on the top surface of the ground-based wireless power transfer structure  200 . 
     In some implementations including heat sensing as previously described e.g., with reference to  FIG. 1 , the first wire-wound structure  402  includes a heat-sensitive wire material having an electrical property (e.g., resistance, insulation resistance) configured to change as a function of temperature. In an example implementation, the first wire-wound structure  402  includes supplementary (dedicated) wire-wound structures configured for heat sensing (not shown in  FIG. 4A ). In another example implementation, at least a portion of the first wire-wound structure  402  is also configured for heat sensing, e.g., using a wire material having an electrical property that change as a function of temperature. Heat sensitive materials potentially applicable to the wire-wound structure  402  are mentioned in U.S. Pat. No. 10,444,394. 
     In some implementations, the connector  440  is configured to electrically connect or disconnect the coil assembly  400  to or from the detection circuit  102  of the object detection system  100 . In certain implementations, the connector  440  provides a soldered (fixed) connection, while in other implementations, the connector  440  is a plug-in connector, e.g., to ease a process of assembly or disassembly of the wireless power transfer structure  200 . 
     In the example implementation illustrated in  FIG. 4A , each wire piece of the plurality of inductive sense elements  104  is wound to form a multi-turn wire loop  404  and a double-wire lead line  406 . Each multi-turn wire loop  404  constitutes a sense coil configured to sense an object (e.g., non-living object  110 ) inductively. Analogously, each wire piece of the plurality of capacitive sense elements  108  is wound to form a substantially two-dimensional (2D) wire-wound structure  410  and a single-wire lead line  412 . Each 2D wire-wound structure  410  constitutes a sense electrode used to sense an object (e.g., living object  112 ) capacitively. In aspects, a predetermined area for sensing the object inductively differs from a predetermined area for sensing the object capacitively. 
     In some implementations, the 2D wire-wound structure  410  is one of a folded wire-wound structure, a spiral wire-wound structure, a serpentine wire-wound structure, and a meander wire-wound structure. 
     Further, in some implementations, the double-wire lead line  406  is configured to have an inductance substantially smaller than the inductance of the entire inductive sense element (e.g., inductive sense element  104   a ), where the inductance refers to the inductance as measured at the corresponding terminals  408  and at a wavelength substantially longer than the length of the wire piece and where the inductance of the double-wire lead line  406  refers to the short circuit inductance. Likewise, the single-wire lead line  412  may be configured to have a capacitance substantially smaller than the capacitance of the entire capacitive sense element (e.g., capacitive sense element  108   a ), where the capacitance refers to the capacitance as measured at the corresponding terminal  416  and at a wavelength substantially longer than the length of the wire piece and where the capacitance of the single-wire lead line  412  refers to the open-circuit capacitance. More specifically, the capacitance may refer to the capacitance as measured between terminal  416  and a ground reference (e.g., the shield  206  of the wireless power transfer structure  200  with reference to  FIG. 2 ). Alternatively, the capacitance may refer to the capacitance as measured between terminal  416  of a first capacitive sense element (e.g., capacitive element  108   a ) and terminal  416  of a second capacitive sense element (e.g., capacitive sense element  108   b ). 
     The coil-former  420  is substantially from an electrically non-conductive (insulating) material and configured to form, carry, and hold in place the first wire-wound structure  402  and the second wire-wound structure  414 . In some implementations, the coil-former  420  includes one or more of a plastic material, a composite material, and a carbon material. 
     In an aspect of heat sensing as previously described, e.g., with reference to  FIG. 1 , the coil-former  420  includes a heat-sensitive material having a property (e.g., insulation resistance, impedance, magnetic permeability, electric permittivity) configured to change as a function of temperature. In an example implementation, the heat-sensitive materials include at least one of a heat-sensitive metal and a heat-sensitive plastic embedded in the coil-former  420 . In another example implementation, the coil-former  420  is from a heat-sensitive compound. Heat-sensitive materials potentially applicable to the coil-former  420  are mentioned in U.S. Pat. No. 10,444,394 as previously referenced. 
     In an aspect of capacitive sensing, the coil-former  420  is substantially from a material having a low electric permittivity (e.g., a relative permittivity below 3). 
     In an aspect of heat resistance, the coil-former  420  is substantially from a heat resistant material to prevent damage due to a hot object (e.g., non-living object  110 ) resting on the top surface of the ground-based wireless power transfer structure  200 . In some implementations, the coil-former is substantially from one or more of an epoxy material, a glass fiber reinforced material, and a ceramic material. Further, heat resistant materials potentially suitable for the coil-former  420  are mentioned in U.S. Pat. No. 10,444,394. 
     In an aspect of mechanical strength, the coil-former  420  is substantially from one or more of an epoxy material and a glass-fiber-reinforced material. 
     In the example implementation shown by  FIG. 4A , the coil-former  420  also integrates the connector  440 . In some implementations, the coil-former  420  integrates more than one multi-pin connector  440  disposed at different locations of the coil-former  420 . In an aspect of integration into the wireless power transfer structure (e.g., wireless power transfer structure  200 ), the one or more multi-pin connectors  440  are disposed in a peripheral area of the coil-former  420  as shown in  FIG. 4A  by example. 
     In an aspect of manufacturing, the coil-former  420  is configured for fabrication using one or more of a machining technique, an injection molding technique, a casting technique, a pouring technique, a thermoforming technique, and a compression-forming technique. 
       FIG. 4B  is a schematic vertical cut view of an example implementation of the coil assembly  400  with reference to  FIG. 4A .  FIG. 4B  illustrates the substantially planar coil-former  420 , the first wire-wound structure  402  attached to the top surface, and the second wire-wound structure  414  attached to the bottom surface of the coil-former  420 . In the implementation shown in  FIG. 4B , the coil-former  420  provides protrusive structures  422  (e.g., braces, railings) to form, carry, and hold in place the first and second wire-wound structure  402  and  414 , respectively. A coil-former  420  may be considered protrusively structured if the structured area of the coil-former&#39;s  420  surface is smaller than the non-structured area. Further,  FIG. 4B  indicates portions of the first wire-wound structure  402  configured as inductive sense elements  104   a ,  104   b , and  104   n  and portions configured as capacitive sense elements  108   a  and  108   b . In some implementations, the protrusively structured coil-former  420  of  FIG. 4B  is configured to separate the first wire-wound structure  402  from the second wire-wound structure  414  by at least 5 mm. 
       FIG. 4C  is a schematic vertical cut view illustrating another example implementation of the coil assembly  400  with reference to  FIG. 4A . The coil assembly  400  includes the substantially planar coil-former  420 , the first wire-wound structure  402  attached to the top surface of the coil-former  420 , and the wire-wound structure  414  attached to its bottom surface. The coil-former  420  provides recessed structures  424  (e.g., grooves, channels) configured to form, carry, and hold in place the first and second wire-wound structure  402  and  414 , respectively. For example, at least a portion of the first and second wire-wound structures  402  and  414 , respectively, may be placed inside a groove. A coil-former  420  may be considered recessed structured if the structured area of the coil-former&#39;s  420  surface is smaller than the non-structured area. Further,  FIG. 4C  indicates portions of the first wire-wound structure  402  configured as inductive sense elements  104   a ,  104   b , and  104   n  and portions configured as capacitive sense elements  108   a  and  108   b . In some implementations, the recessed structured coil-former  420  of  FIG. 4B  is configured to separate the first wire-wound structure  402  from the second wire-wound structure  414  by at least 5 mm. 
     In some implementation variants (not shown herein), the coil-former  420  is a combination of the coil-former  420  of  FIG. 4B  and the coil-former  420  of  FIG. 4C . In an example variant, the first wire-wound structure  402  is formed, carried, and held in place by protrusive structures  422  and the second wire-wound structure  414  is formed, carried, and held in place by recessed structures  424 . In another example variant, it is vice versa. 
     In another example variant, at least one of the wire-wound structures  402  and  414  is formed, carried, and held in place by protrusive structures  422  that are disposed along portions of the respective wire-wound structure (e.g., wire-wound structure  402 ). 
     In a further example variant, at least one of the wire-wound structures  402  and  414  is formed, carried, and held in place by recessed structures  424  that are disposed along the respective wire-wound structure (e.g., wire-wound structure  402 ). 
     In yet another example variant, at least one of the wire-wound structure  402  and  414  is formed, carried, and held in place by recessed structures  424  that are disposed along portions of the respective wire-wound structure (e.g., wire-wound structure  402 ) and by protrusive structures  422  disposed along other (e.g., remaining) portions of the respective wire-wound structure. 
       FIG. 4D  is a schematic vertical cut view illustrating another example implementation based on a modification of the coil assembly  400  as illustrated in  FIG. 4C . This modification includes a substantially planar coil-former  420  providing slanted edge areas configured to form, carry, and hold in place the capacitive sense elements  108   a  and  108   b  by recessed structures  424 . In some implementations, the top surface of the coil-former  420  including the slanted edge areas conform with the shape of the housing of a wireless power transfer structure (e.g., housing  328  of the wireless power transfer structure  200  illustrated in  FIG. 3 ). For example, the slanted edge areas may be a peripheral area of the coil-former  420  having a slant angle substantially equal to the angle of the inclined portions of the housing  328  as previously discussed with reference to  FIG. 3 . 
       FIG. 4E  illustrates a schematic vertical cut view illustrating a wireless power transfer structure  200  integrating the coil assembly  400  of  FIG. 4D . The coil-former  420  is shaped to conform with the inner surface of the housing  328  as discussed above with reference to  FIG. 4D . The substantially planar bottom surface of the coil-former  420  may mechanically contact the ferrite structure  204  with reference to  FIG. 3 . In some implementations, an additional thin insulation layer (not shown in  FIG. 4E ) is disposed between the coil-former  420  and the ferrite structure  204 , for example, to prevent partial discharge at the second wire-wound structure  414  during WPT operation. 
       FIG. 5  is a schematic top-down view illustrating a further example implementation of the coil assembly  400  with reference to  FIG. 4A  including the coil-former  420 , the first wire-wound structure  402  configured for inductive and capacitive sensing, and the second conductive structure  414  (not shown in  FIG. 5  for purposes of illustration). Differently from  FIG. 4A , the first wire-wound structure  402  is configured to form eight single-ended capacitive sense elements  108   a ,  108   b , . . . ,  108   n . Each capacitive sense element (e.g., capacitive sense element  108   a ) is created by winding a piece of wire and comprises a substantially 2D wire-wound structure  410  (illustrated in  FIG. 5  by a folded wire-wound structure) and a single-wire lead line  412  providing a single terminal  416  to electrically connect the capacitive sense element to a connector  440  (e.g., a multi-pin connector). The 2D wire-wound structure  410  constitutes a sense electrode configured to sense an object (e.g., living object  112 ) capacitively. In the example implementation of  FIG. 5 , the 2D wire-wound structures  410  are substantially equidistantly placed along the perimeter of the coil-former  420 . Further, each inductive sense element (e.g., inductive sense element  104   a ) is created by winding a piece of wire and comprises a multi-turn wire loop  404  and a double-wire lead line  406  providing a pair of terminals  408  to electrically connect the inductive sense element to the connector  440 . The multi-turn wire loop  404  constitutes a sense coil configured to sense an object (e.g., non-living object  110 ) inductively. In aspects, the wire loop  404  is a densely wound multi-turn loop maximizing the inductance of the wire loop  404 . Further, the wire loop  404  may be a planar spiral coil with a spacing between windings that is substantially larger than a diameter of the piece of the wire. As indicated in  FIG. 5  by dashed lines, the peripheral area of the coil-former  420  may be slanted on each of the four edges. 
     In an aspect of increasing a capacitance, a capacitive sense element (e.g., capacitive sense element  108   a ) may be created by winding of more than one wire piece, each forming a substantially 2D wire-wound structure  410  (single-ended electrode) and a corresponding single-wire lead line  412  as previously described. More specifically, the capacitive element  108   a  may include at least two 2D wire-wound structures  410  (e.g., single-ended electrodes) and a corresponding single-wire lead line  412  providing a terminal  416  electrically connected to the same pin of connector  440 . In some implementations, each capacitive sense element (e.g., capacitive element  108   a ) is created from at least two substantially congruent two-dimensional wire-wound structures disposed at substantially the same location. Such a capacitive sense element may be considered as a multi-filar wire-wound structure. In another implementation, one or more neighboring (e.g., adjacent) 2D wire-wound structures  410  are connected to a common pin of connector  440  via the corresponding single-wire lead line  412  and operated in parallel (common mode). In a further implementation, pairs of 2D wire-wound structure  410  (e.g., wire-wound single-ended electrodes) are configured as double-ended electrodes to be operated in a differential mode. In yet another implementation, pairs of wire-wound single or double-ended electrodes are used to sense an object (e.g., living object  112 ) capacitively by measuring a 2-port electrical characteristic (e.g., a transimpedance) at the corresponding pair of terminals  416 . 
       FIG. 6  is a top-down view illustrating an example implementation of a coil-former  420  providing recessed structures (grooves) configured to form, carry, and hold in place the first wire-wound structure  402 . More precisely,  FIG. 6  shows a portion (cutout) of the coil-former&#39;s  420  top surface configured to accommodate the plurality of wire-wound inductive sense elements  104 . Shaded areas  606  indicate examples of non-recessed areas of the coil-former&#39;s  420  top surface. The coil-former  420  may be referred to as a recessed structured coil-former  420  with reference to  FIG. 4C  due to the total non-structured area (e.g., shaded area  606 ) exceeding the total structured (recessed) area as apparent from  FIG. 6 . 
       FIG. 6  also illustrates a portion of the first wire-wound structure  402  configured for inductive sensing. More specifically, it shows a portion of the inductive sense element  104   n  from  FIG. 1 , including a multi-turn wire loop  404  (sense coil) and a portion of the double-wire lead line  406  electrically connecting the sense coil to a connector (e.g., connector  440 , not shown in  FIG. 6 ). The spread winding of the sense coil as illustrated in  FIG. 6  may reduce a variation of an object detection sensitivity over the predetermined area of the object detection system  100  with reference to  FIG. 1 . The object detection sensitivity may refer to an object (e.g., non-living object  110 ) substantially smaller than a size of the sense coil. In the example coil-former  420  shown in  FIG. 6 , the sense coils are regularly arranged in rows and columns and provide a substantially uniform (equidistant) spacing between windings of the same sense coil and between the outer windings of adjacent sense coils. 
     The recessed structures  424  (from  FIG. 4D ) on the coil-former&#39;s  420  top surface may include grooves  602  configured to accommodate the windings of the sense coil and grooves  604  configured to accommodate the plurality of double-wire lead lines  406  belonging to the subset of sense coils disposed in the same column of the array  106 . Therefore, in some implementations, at least one of a width and a depth of the groove  604  may be larger than a respective one of a width and depth of the groove  602  as also apparent from  FIG. 6 . 
     In an aspect, a portion of the grooves has a first depth, another portion of the grooves is deeper than the first depth, and wherein the first depth is less than three millimeters. 
       FIG. 6  also shows rounded corners at certain locations in groove junctions (e.g., crossing of a groove  602  and a groove  604 ) where the wire will be bent by an angle of 90°. Rounded corners may be required in a winding process applying mechanical tension (e.g., using a wire tensioner), e.g., with respect to a minimum wire bend radius as it may be specified to prevent a wire breaking or insulation damage. 
       FIGS. 7A to 7K  are vertical cut views illustrating various protrusive and corresponding recessed structures (profiles)  422  and  424 , respectively, that may be used to form, carry, and hold in place at least one of the wire-wound structures  402  and  414 . These profiles may apply to the structured areas of a coil-former&#39;s  420  surface. 
       FIGS. 7A and 7B  illustrate a protrusive rectangular profile  422 - 1  (e.g., a brace, railing) and a corresponding recessed profile  424 - 1  (e.g., a groove) to form, carry, and hold in place the first wire-wound structure  402  by lateral forces and stiction if the wire-wound structure  402  is wound under tension (e.g., using a wire tensioner). 
       FIGS. 7C and 7D  illustrate a protrusive “L”-shaped profile  422 - 2  and a corresponding recessed “L”-shaped profile  424 - 2  to form, carry, and hold in place the first wire-wound structure  402  if the wire-wound structure  402  is wound under tension. An “L”-shaped profile may apply to additionally secure a wire-wound structure (e.g., wire-wound structure  402 ) in the coil-former  420 . 
       FIGS. 7E and 7F  illustrate a protrusive “T”-shaped profile  422 - 3  and a corresponding recessed “T”-shaped profile  424 - 3 , respectively. As with the “L”-shaped profile, the “T”-shaped profile may serve to additionally secure a wire-wound structure (e.g., wire-wound structure  402 ) in the coil-former  420 . 
     Further profiles suitable to secure a wire-wound structure (e.g., wire-wound structure  402 ) in the coil-former  420  are shown in  FIGS. 7G to 7J . For example,  FIGS. 7G and 7H  illustrate a protrusive right-angled trapezoidal-shaped profile  422 - 4  and a corresponding recessed right-angled trapezoidal-shaped profile  424 - 4 , respectively.  FIGS. 71 and 7J  illustrate a protrusive trapezoidal-shaped (dovetail-shaped) profile  422 - 5  and a corresponding recessed trapezoidal-shaped (dovetail-shaped) profile  424 - 5 , respectively. 
     In some implementations, different profiles apply to the top and bottom surface of the coil-former  420 . In an example coil-former  420 , the top surface is structured using a “T”-shaped profile (e.g., recessed “T”-shaped profile  424 - 3  of  FIG. 7F ) while the bottom surface is structured based on a rectangular profile (e.g., recessed rectangular profile  424 - 1  of  FIG. 7B ). 
     In other implementations, at least one of the top and bottom surfaces of the coil-former  420  is heterogeneously structured. In an example implementation, a majority of the coil-former&#39;s  420  top surface structure is rectangular shaped (e.g., recessed rectangular profile  424 - 1  of  FIG. 7B ) while an “L” or a “T”-shaped profile (e.g., recessed “T”-shaped profile  424 - 3  of  FIG. 7F ) applies only in certain areas, e.g., for purposes as mentioned above. 
     A rectangular-shaped profile (e.g., protrusive rectangular profile  422 - 1  of  FIG. 7A ) may be implemented more easily considering the manufacturing of a plastic coil-former (e.g., coil-former  420 ) using an injection molding process. It may be appreciated that overhanging profiles such as the “L”-, “T”- and trapezoidal-shaped profiles of  FIGS. 7C to 7J  may not allow the molded part (e.g., the coil-former  420 ) to be easily separated from the mold (molding tool). Therefore, in some manufacturing processes, overhanging structures are produced in a multi-step process including injection molding and one or more of a machining and thermoforming process. For example, a coil-former  420  structured with a protrusive “T”-shaped profile (e.g., profile  422 - 3  of  FIG. 7E ) may be manufactured by employing, in a first step, an injection molding process producing a coil-former  420  with an initially protrusive rectangular profile with a height larger than a target height. In a second step process employing thermoforming, the top of the protrusive rectangular profile is compressed to the target height, which will also broaden the top creating a profile similar to a “T”-shape. In some manufacturing processes, thermoforming applies directly after the coil winding (e.g., robot winding) process, e.g., to additionally secure a wire-wound structure (e.g., wire-wound structure  402 ). A person skilled in the art will appreciate that thermoforming is not limited to the manufacturing of “T”-shaped protrusive structures but may also apply to produce recessed overhanging profiles (e.g., a profile similar to a recessed “T”-shaped profile  424 - 3  of  FIG. 7F ). 
       FIG. 7K  illustrates an alternative approach to secure a wire-wound structure (e.g., wire-wound structure  402 ) formed, carried, and held in place by the recessed rectangular-shaped structure  424 - 1  (groove) of  FIG. 7B . In this approach, the groove is filled with a filling compound  720 , as shown in  FIG. 7K  directly after coil winding (e.g., robot winding). In some implementations, only portions of the grooves (e.g., grooves  602  and  604  of  FIG. 6 ) of a coil-former  420  are filled. The filling compound  720  may include any suitable filling compound, including a plastic compound, a resin, a rubber, a gum, an adhesive, a cement, or a combination of one or more such compounds. 
     In other implementations based on one or more protrusive and recessed structures, the wire-wound structure (e.g., wire-wound structure  402 ) is secured (fixed) at specific points, e.g., using an adhesive (e.g., a fast-setting glue, cement, gum, paste, etc.). These specific points may include the non-connected (open) wire ends of the wire-wound structure  402  forming the plurality of capacitive sense elements (e.g., capacitive sense elements  108   a ,  108   b , . . . ,  108   n ). 
     In further implementations, the open wire ends of the wire-wound structure  402  are secured (fixed) using a wire clamp disposed at positions as foreseen for the wire ends. 
       FIGS. 8A to 8C  are vertical cut views illustrating example implementations of a male “pin header” connector (e.g., a multi-pin connector). More precisely,  FIGS. 8A to 8C  show a detail (cutout) of the coil assembly  400 , including a portion of the coil-former  420 , the male pin header connector  440 , and a portion of the single-wire lead line  412  with reference to  FIG. 4A  accommodated in a recessed structure (groove)  424  configured to guide the wire to the connector  440  (e.g., groove  604  with reference to  FIG. 6 ). 
     In the example implementation illustrated in  FIG. 8A , the connector  440  comprises at least one connector pin  802 , an electrically insulating carrier (e.g., an insert  804 ), and a contacting element  806  (e.g., a printed circuit board) affixed to the connector pin  802 , e.g., using a solder joint as illustrated in  FIG. 8A  to provide a soldering pin. The contacting element  806  provides at least one soldering pad to electrically connect the wire terminal  416  with the connector pin  802 . Further, the connector pin  802  is solderable, the insert is configured for a press-fit mounting with respect to both the connector pin  802  in the connector  440  and the connector  440  in the coil-former  420 . 
     In the example implementation illustrated in  FIG. 8B , the connector  440  comprises at least one connector pin  802  and an electrically insulating carrier (e.g., the insert  804 ). The connector pin  802  is configured for a wire wrap connection by means of cold welding to provide a wire wrap pin. In an implementation variant, the wire wrap connection is additionally soldered to provide a long-term stable electrical connection of a wire that is not particularly suitable for wire wrapping by means of cold welding. As with the implementation of  FIG. 8A , the insert  804  is configured for a press-fit mounting of the connector pin  802  in the insert  804  and for a press-fit mounting of the connector  440  in the coil-former  420 . 
     In the example implementation illustrated in  FIG. 8C , the connector  440  comprises at least one connector pin  802  configured for a cold-welded or soldered wire-wrap connection. Both the connector pin  802  and the coil-former  420  are configured for a press-fit mount directly in the coil-former  420  without the need for an insert  804  with reference to  FIGS. 8A and 8B . (The insert  804  may be considered merged with the coil-former  420 .) In an implementation variant, the at least one connector pin  802  is inserted into the coil-former  420  as part of the injection molding process. 
     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 a processor. 
     As used herein, the term “determining” encompasses a wide variety of actions. For example, “determining” may include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database, or another data structure), ascertaining, and the like. “Determining” may also include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory), and the like. Further, “determining” may include resolving, selecting, choosing, establishing, and the like. 
     As used herein, a phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “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). 
     The various illustrative logical blocks, modules, and circuits described in connection with the present disclosure may be implemented or performed with a general-purpose processor, a digital signal processor (DSP), an ASIC, a field-programmable gate array (FPGA), or other programmable logic device (PLD), discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A 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. If implemented in hardware, 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. 
     It is to be understood that the claims are not limited to the precise configuration and components illustrated above. Various modifications, changes, and variations may be made in the arrangement, operation and details of the methods and apparatus described above without departing from the scope of the claims.