Device, system and method for detecting foreign matter

Abstract

A detection device (100) includes a detection pad (102) having a plurality of detection coils (106) and at least one pair of detection coil groups (106), wherein the pair of detection coil groups (106) includes a first detection coil group (106) and a second detection coil group (106). The first detection coil group (106) and the second detection coil group (106) include a first impedance value and a second impedance value. The detection device (100) includes one or more drive subsystems (112) and a comparison subsystem (112). The drive subsystem (112) is operably coupled to the detection pad (102) and is configured to excite at least one pair of detection coil groups (106). The comparison subsystem (114) is operably coupled to the detection pad (102) and is configured to receive a differential current signal from the pair of detection coil groups (106), and the comparison subsystem (114) is configured to generate a control signal based on the differential current signal.

Description

Technical Field

[0001] Embodiments of the present specification relate to a detection device, and more particularly, embodiments of the present specification relate to a detection device for detecting foreign matter in an operating environment of a system. Background Art

[0002] Conventional wireless power transfer (WPT) systems are based on the principle of inductive power transfer, which wirelessly transfers electrical energy from one device to another. Typically, in a WPT system, a master power device (e.g., a transmitter) wirelessly transfers power to a slave power device called a receiver. The transmitter and receiver include corresponding coils that are set in the vicinity of the operation during the operation of the WPT system. When current passes through the transmitter coil, the generated magnetic field induces an electromotive force in the receiver coil, thereby wirelessly transferring power from the transmitter to the receiver.

[0003] In such a WPT system, if there is any metal object, for example, a metal can or aluminum foil, between the transmitter and receiver coils during wireless power transmission, the metal object may be heated undesirably due to eddy currents. This may cause safety hazards, for example, fire safety hazards. In addition, the efficiency of the wireless power transmission process may be inadvertently affected, or the entire process may be completely interrupted.

[0004] There are various different methods to detect foreign objects in WPT systems. These include detecting the presence of foreign objects through changes in the frequency of the current in the primary coil, detecting unbalanced differences in current and voltage in the primary coil based on measurements of the power drawn from the primary coil, etc. In addition, in some detection methods, there may be some delay in detecting foreign objects after the wireless power transfer is initiated. During this period, the foreign object continues to draw power, which results in power waste. Summary of the invention

[0005] In one embodiment, the detection device includes a detection pad having a plurality of detection coils and at least one pair of detection coil groups, wherein the pair of detection coil groups includes a first detection coil group and a second detection coil group. The first detection coil group includes a first impedance value, and the second detection coil group includes a second impedance value. In addition, the detection device includes one or more drive subsystems and a comparison subsystem. The drive subsystem is operably coupled to the detection pad and configured to excite the at least one pair of detection coil groups. The comparison subsystem is operably coupled to the detection pad and configured to receive a differential current signal from the at least one pair of detection coil groups, wherein the comparison subsystem is configured to generate a control signal based on the differential current signal.

[0006] In another embodiment, a detection system includes a detection device and a wireless power transmission (WPT) system. The detection device includes a detection pad having a plurality of detection coils and at least one pair of detection coil groups, wherein the pair of detection coil groups includes a first detection coil group and a second detection coil group. The first detection coil group includes a first impedance value, and the second detection coil group includes a second impedance value. In addition, the detection device includes one or more drive subsystems and a comparison subsystem. The drive subsystem is operably coupled to the detection pad and configured to excite at least one pair of detection coil groups. The comparison subsystem is operably coupled to the detection pad and configured to receive a differential current signal from at least one pair of detection coil groups, wherein the comparison subsystem is configured to generate a control signal based on the differential current signal. The WPT system includes a main power supply configured to supply power in the form of an alternating current (AC) voltage signal. The WPT system also includes a transmitter unit having at least one transmitter coil, wherein the transmitter unit is configured to receive an AC voltage signal from the main power supply. In addition, the transmitter unit is configured to generate a main magnetic field in response to the received AC voltage signal, and wherein the detection pad is operably coupled to the transmitter unit. The WPT system further comprises a receiver unit comprising at least one receiver coil and configured to receive at least a portion of the main magnetic field generated by the transmitter unit. In addition, the WPT system comprises a control unit operatively coupled to the detection device and configured to receive a control signal from the detection device and control power supply to the transmitter unit based on the control signal.

[0007] In yet another embodiment, a method includes utilizing a detection device including a detection pad having a plurality of detection coils and at least one pair of detection coil groups, wherein the pair of detection coil groups includes a first detection coil group and a second detection coil group. The first detection coil group includes a first impedance value, and the second detection coil group includes a second impedance value. The method also includes exciting the at least one pair of detection coil groups and determining a differential current signal from the at least one pair of detection coil groups. In addition, the method includes generating a control signal based on the differential current signal and transmitting the control signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] These and other features and aspects of embodiments of the present invention will be better understood when the following detailed description is read with reference to the accompanying drawings, in which like characters represent like parts throughout the drawings, and in which:

[0009] Figure 1 is a schematic diagram of an example detection device for detecting the presence of foreign matter according to aspects of the present specification;

[0010] FIG. 2A to FIG. 2B is a diagrammatic representation of an example pair of detection coil sets according to aspects of the present specification;

[0011] FIG. 3A to FIG. 3Bis a diagrammatic representation of a portion of a detection device including a pair of detection coil sets coupled to a drive subsystem according to aspects of the present specification;

[0012] FIG. 3C to FIG. 3E is a schematic representation of a portion of a detection device having one or more drive subsystems coupled to several pairs of detection coil sets according to aspects of the present specification;

[0013] Figure 4 is a diagrammatic representation of an example detection system having a detection device for detecting the presence of a foreign object in an operating environment of a WPT system according to aspects of the present specification;

[0014] Figure 5 is a diagrammatic representation of an example comparison subsystem of a detection device according to aspects of the present specification;

[0015] Figure 6 to Figure 7 is an example method for detecting the presence of a foreign object in an operating environment of a WPT system according to aspects of the present specification; and

[0016] Figure 8 is a cross-sectional view of a detection pad according to various aspects of the present description. DETAILED DESCRIPTION

[0017] Embodiments of the present specification relate to detection devices, detection systems, and methods for detecting foreign objects. In certain embodiments, the detection device can be used to detect foreign objects in a wireless power transfer (WPT) system. As used herein, the term "foreign object" refers to objects that are conductive or have detectable magnetic permeability that are not part of the system but are inadvertently present in the operating environment of the system. Non-limiting examples of foreign objects can include ferrous objects, tin cans, or other conductive or ferrous objects. In one example, a can or a bunch of keys are considered foreign objects in the operating environment of the WPT system.

[0018] As used herein, the term "main magnetic field" refers to the magnetic field induced by a transmitter unit (e.g., a transmitter unit of a WPT system). The term "operating environment" is defined by the main magnetic field in the system, wherein the main magnetic field of the transmitter unit is detectably present and detectably interacts with foreign matter. For example, foreign matter present in the operating environment of the WPT system may experience a temperature increase due to interaction with the main magnetic field.

[0019] As used herein, the term "detection coil set" refers to a single detection coil or two or more coils, wherein each individual set of detection coils are electrically coupled to each other. Furthermore, the term "a pair of detection coil sets" refers to two such detection coil sets.

[0020] Some electric vehicles (EVs) and hybrid vehicles use WPT systems for charging via wireless power transfer or inductive power transfer. A WPT system consists mainly of two parts, namely, a transmitter as part of a charging station and a receiver set in an electric vehicle (EV). The transmitter unit of the charging station is inductively coupled to the receiver unit of the EV. Typically, power transfer begins between the coils of the transmitter and receiver units when the receiver coil of the EV is introduced into the operating environment of the transmitter coil and power is started to be supplied to the transmitter unit.

[0021] When a foreign object made of a conductive material or a ferrous material is inadvertently placed in the operating environment of a WPT, the foreign object may interact with the magnetic field generated by the transmitter unit. As a result, the foreign object may inadvertently intercept the magnetic field and draw power from the transmitter unit via the magnetic field. Therefore, the power drawn by the foreign object results in power waste and undesired heating of the foreign object. If not handled promptly, or if not noticed, the temperature of the foreign object may increase to a value that may make the foreign object unsafe to handle and may also cause safety risks. Therefore, it is desirable to detect the presence of foreign objects to prevent power waste and avoid the risk of an unsafe environment.

[0022] Figure 1 A detection device 100 is shown having a detection pad 102 having a plurality of detection coils 106 and at least one pair ( Figure 1 ) detection coil set 106. The at least one pair of detection coil sets 106 includes a first detection coil set 106 and a second detection coil set 106, wherein the first detection coil set 106 has a first impedance value and the second detection coil set 106 has a second impedance value. The detection device 100 also includes one or more drive subsystems 112, which are operably coupled to the detection pad 102 and configured to excite the at least one pair of detection coil sets 106. In addition, the detection device 100 includes a comparison subsystem 114, which is operably coupled to the detection pad 102 and configured to receive a differential current signal from the at least one pair of detection coil sets 106. The comparison subsystem 114 is configured to generate a control signal based on the differential current signal.

[0023] In some embodiments, the detection device 100 is configured to detect a wireless power transmission (WPT) system ( Figure 1 The presence of foreign matter in the operating environment of the WPT system may cause a change in the impedance value of one or more detection coils 106. This change in the impedance value of the detection coil 106 is used to determine the presence of foreign matter. FIG. 2A to FIG. 2B and FIG. 3A to FIG. 3B The detection coil set 106 is explained in more detail.

[0024] In addition, the detection pad 102 may include several geometric locations, also referred to as "detection zones" 104. The detection zones 104 define discrete areas of the detection pad 102, wherein each detection zone 104 includes one or more detection coil sets 106. It may be noted that the detection zones 104 may not be physically separated or insulated from each other, and the detection zones 104 may be electrically insulated from each other. In addition, the detection zones 104 may have geometric or non-geometric shapes.

[0025] The detection pad 102 can be a flexible pad, a conformable pad, a rigid pad or a plug-and-play pad, a stand-alone pad or a combination thereof. It can be noted that the surface area of ​​the detection pad 102 can be greater than or equal to the surface area of ​​the transmitter unit on which the detection pad 102 is disposed. The substrate of the detection pad 102 can be made of an electrically insulating material. The detection pad 102 can also include a mechanically wear-resistant material to withstand the movement of an electric vehicle thereon. The detection pad 102 can be further designed for outdoor applications and designed to withstand temperature, humidity, and water ingress.

[0026] In some embodiments, for user safety and aesthetics, the detection coil 106 can be disposed on the substrate of the detection pad 102, or can be embedded in the substrate of the detection pad 102. In some other embodiments, the detection coil 106 can be printed, molded, woven, or otherwise manufactured on the substrate of the detection pad 102.

[0027] The detection coil 106 is an electromagnetic coil. Figure 1 In the illustrated embodiment, the detection coils 106 are used for representative purposes, and it can be noted that each detection coil 106 can include a spiral or other coil topology. In addition, each detection zone 104 can have one or more detection coils 106. In some embodiments, the detection coil group 106 can include various coil topologies, shapes, and geometric arrangements of the detection coils 106. Non-limiting examples of the shapes of the detection coils 106 can include spiral coils, spiral coils, non-circular coils, etc. Different detection coils 106 or detection coil groups 106 present on the detection pad 102 can have the same or different impedance values.

[0028] Each pair of detection coil groups 106 includes two groups arranged at the same or different geometric positions on the detection pad 102 to form the pair of detection coil groups 106. For example, the two groups in the pair can be arranged in the same detection area 104, or can be arranged in two different detection areas 104. In a non-limiting example, each detection coil group 106 may include concentric coils, coils arranged adjacently, and coils arranged side by side. In addition, one or more detection coil groups 106 can be arranged in a single plane or in two or more layers. The detection coils 106 in a detection coil group 106 can be connected in series, in parallel, or in a combination of series and parallel connections.

[0029] In some embodiments, a pair of detection coil assemblies 106 includes concentric coils. In a non-limiting example, the inductance value of one of the two concentric coils is different from the inductance value of the other concentric coil. For example, while the inductance value of one of the pair of concentric coils can be represented by L, the inductance value of the other concentric coil in the pair of concentric coils can be represented by nL.

[0030] The drive subsystem 112 includes one or more drive units and a drive controller. The drive subsystem 112 is operably coupled to the detection pad 102 and is configured to excite one or more pairs of detection coil groups 106. The drive subsystem 112 can be configured to intermittently or periodically excite a determined detection coil group 106 of the detection device 100, wherein the determined detection coil group forms one or more pairs of detection coil groups 106. The drive subsystem 112 can be configured to excite pairs of detection coil groups 106 belonging to the same or different detection zones 104. In some embodiments, the drive subsystem 112 can be configured to excite a main magnetic field relative to the WPT system ( Figure 1 A detection coil set 106 (not shown) is symmetrically positioned.

[0031] In one example, the drive subsystem 112 can be configured to excite a group in a pair of detection coil groups 106 simultaneously or sequentially. Additionally or alternatively, the drive subsystem 112 can be configured to excite two or more pairs of detection coil groups 106 of the detection pad 102 simultaneously or sequentially. In one example, the drive subsystem 112 can be configured to scan the detection pad 102 for the presence of foreign matter. The detection of the presence of foreign matter can be completed before starting the wireless power transmission of the device (e.g., EV). In addition, the detection of the presence of foreign matter can also be performed periodically or intermittently during the wireless power transmission of the device (e.g., EV).

[0032] If you will refer to FIG. 3A to FIG. 3E As described in detail, in one example, each pair of detection coil assemblies 106 may be coupled to a corresponding drive subsystem, and in another example, two or more pairs of detection coil assemblies 106 may be coupled to different drive units that share a common drive controller.

[0033] In some embodiments, the drive unit of the drive subsystem 112 is configured to provide a voltage signal to one or more detection coil groups 106, and the drive controller is configured to control the operation of the drive unit. To this end, the drive controller turns on the drive subsystem 112 to excite one or more detection coil groups 106, and turns off the drive subsystem 112 when the detection coil group 106 is not required to be excited. In some embodiments, the drive subsystem 112 includes one or more of an inverter, a converter, a linear amplifier, an electronic switch, or a combination thereof. The switching of the drive subsystem 112 can be performed by an electronic switch, for example, a bidirectional switch, a semiconductor switch, a mechanical switch, for example, a relay, a contractor, or a combination thereof. In some embodiments, the drive subsystem 112 can draw power from a main power supply configured to power a transmitter unit of the WPT system. Optionally, the drive subsystem 112 can have a separate power supply, such as but not limited to a battery.

[0034] It may be noted that, in operation, if present on the detection pad 102, foreign matter may be inductively coupled to one or more detection coils 106, thereby affecting the composite impedance value of those particular groups of detection coils 106. Furthermore, it may be noted that, in the absence of foreign matter, the inherent impedance values ​​of different detection coil groups 106 of the detection device 100 may be the same or different. Furthermore, in the absence of foreign matter, the inherent impedance values ​​of the two groups of a pair of detection coil groups 106 may be the same or different. In some of these embodiments, the detection pad 102 further includes a compensator element ( Figure 1 106 ), the compensator element is operably coupled to at least one of the pair of detection coil assemblies 106 to provide similar synthetic impedance values ​​from each of the two groups of the pair of detection coil assemblies 106 in the absence of foreign matter. In some other embodiments, the drive controller can be used to provide voltage compensation for one of the pair of detection coil assemblies 106. For example, the drive controller of the drive subsystem 112 provides different voltage signals to the two groups of the pair of detection coil assemblies 106, so that in the absence of foreign matter, the two groups of the pair of detection coil assemblies 106 are driven by the same current with similar amplitude and phase.

[0035] The comparison subsystem 114 is operably coupled to the detection pad 102 and is configured to receive one or more differential current signals from the detection pad 102. The comparison subsystem 114 is configured to determine the detection voltage signal based on the differential current signal. It can be noted that the value of the differential current signal may be very small and undetectable in the absence of foreign matter. In addition, due to the inductive coupling between the foreign matter and the one or more detection coils 106, the value of the differential current signal may be a detectable non-zero value in the presence of foreign matter.

[0036] The detection device 100 may be a stand-alone device that can be used to detect the presence of foreign matter in a system, such as but not limited to a WPT system. To this end, the detection device 100 may be used with an existing WPT system to detect the presence of foreign matter before and / or during wireless power transmission. In addition to the detection pad 102, the drive subsystem 112, and the comparison subsystem 114, the detection device 100 may also include a communication unit ( Figure 1 The communication unit enables the detection device 100 to communicate with the system using it. For example, the communication unit can enable the detection device 100 to communicate with the WPT system according to the Society of Automotive Engineers (SAE) standard. The communication unit can be used to transmit the detection voltage signal to the control unit of the WPT system to evaluate whether to continue to supply power to the transmitter unit of the WPT system.

[0037] Advantageously, the detection apparatus 100 of the present technology is configured to detect the presence of even relatively small foreign objects in the operating environment of a WPT system. In one example, the foreign object may have a surface area of ​​2 square centimeters or more.

[0038] Reference now FIG. 2A to FIG. 2B In some embodiments, one or more pairs of detection coils of the detection device can be energized to determine a differential current signal from the detection pad, wherein the differential current signal is used to determine the presence or absence of a foreign object. It can be noted that each of the two separate groups of the pair of detection coils can include one or more detection coils.

[0039] In some embodiments, the first group and the second group of the paired detection coil groups are symmetrically arranged relative to the main magnetic field. In addition, the first group and the second group of the paired detection coil groups are arranged in the same geometric area on the detection pad. In some embodiments, the first group and the second group of the paired detection coil groups include a similar structural arrangement of the detection coils. In addition, in some embodiments, in the absence of foreign matter in the operating environment of the WPT system, the first impedance value and the second impedance value of the groups in the paired detection coil groups are similar. As used herein, similar impedance values ​​refer to impedance values ​​that vary less than or equal to 0.5% from each other. For example, the impedance value of the first group may be within -0.5% of the impedance value of the second group, wherein the first group and the second group form a pair of detection coil groups.

[0040] In some other embodiments, in the absence of foreign matter, the first impedance value and the second impedance value are different. In some of these embodiments, the detection pad may include a compensator element operably coupled to one of the first and second detection coil groups in the pair to compensate for the difference in impedance values ​​of the first and second detection coil groups 106. In some embodiments, in the absence of foreign matter, the first impedance value and the second impedance value are different, and wherein the one or more drive subsystems further include a drive controller configured to provide different voltage signals to the first and second detection coil groups, so that in the absence of foreign matter, the first and second groups in the pair of detection coil groups are driven by the same current with similar amplitude and phase.

[0041] If you will refer to Figure 2A As described above, the detection coils of a particular pair of detection coil sets are arranged symmetrically with respect to the main magnetic field, and thus experience a main magnetic field of similar strength. Figure 2B As described, the groups in a pair of detection coil groups can be arranged in the same geometric area of ​​the detection pad, so that these groups can be subjected to the main magnetic field of similar strength. In some embodiments, each group in the pair of detection coil groups includes the same impedance value in the absence of foreign matter in the operating environment of the WPT system. In some other embodiments, the two groups in the pair of detection coil groups have different impedance values. In these embodiments, the two groups of a pair of detection coils can provide a negligible and undetectable differential current amount in association with a compensator element or with the help of a drive controller, however, in the presence of foreign matter, when one or more detection coils belonging to one group of the pair of detection coil groups are electrically coupled with foreign matter, and the net impedance of the group of detection coils is changed, which results in a difference in the current drawn by the two groups in the pair of detection coil groups. Therefore, the differential current reaches a detectable value, which is the difference between the input current of one of the two groups and the input current of the other group in the pair of detection coil groups.

[0042] Figure 2AAn exemplary detection pad 200 is shown having a plurality of detection zones 202, the detection zones 202 having groups 204 of detection coils 205. In the non-limiting illustrated embodiment, the detection pad 200 is shown as having a 4×4 array of detection zones 202, and each detection zone 202 is shown as having 4 groups 204 of detection coils 205, however, it is noted that the number of detection zones 202 in the detection pad 200 and the number of groups 204 in each detection zone 202 may vary and are for illustrative purposes only. Furthermore, although the detection pad 200 is shown as having 16 detection zones 202 in the illustrated example, it is noted that the number of detection zones 202 in a detection pad (e.g., detection pad 200) may be one or more. Furthermore, each group 204 may include one or more detection coils 205. Furthermore, the spiral shape of the detection coils 205 of the group 204 is for illustrative purposes, and the detection coils 205 may be various shapes, such as, but not limited to, circular, non-circular, spiral, helical, or combinations thereof. The detection pad 200 may be disposed on a transmitter unit ( Figure 2A In addition, the dotted circle 206 represents the transmitter coil of the transmitter unit disposed under the detection pad 200.

[0043] Any two groups 204 of detection coils are likely to be subjected to a main magnetic field of similar strength and may be paired to form a pair of detection coil groups for detecting the presence of foreign objects. Several plausible pairs of groups 204 of detection coils 205 are represented by n-n'. For example, the group 204 represented by reference numeral 208 is symmetrically arranged with respect to the main magnetic field of the transmitter coil 206 or the transmitter unit and forms a pair 212 of detection coil groups 208. Similarly, the group 210 is symmetrically arranged with respect to the main magnetic field of the transmitter unit and forms another pair 214 of detection coil groups 210. It may be noted that in addition to 212, 214, n-n', other pairs of groups 204 of detection coils 205 are possible.

[0044] In some embodiments, when the detection pad 200 is disposed on the transmitter unit, in order to detect the WPT system ( Figure 2A The presence of a foreign object in an operating environment (not shown) may excite the group 204 of one or more pairs of detection coils 205. For example, one of the two pairs 212 or 214 may be excited by the drive subsystem. In addition, in the case where the impedance values ​​of the two groups in a pair of groups are different, the compensator element 218 may be operably coupled to at least one group 204 of the group 204 of a pair of detection coils 205 to provide a similar synthetic impedance value from each of the two groups 204 of the pair of detection coils 205 in the absence of a foreign object.

[0045] Figure 2B220 having a plurality of detection zones 224, wherein the detection zones 224 have two or more detection coils 222. The detection device 220 may be disposed in a transmitter unit ( Figure 2B In the illustrated embodiment, the dotted circle 225 represents a transmitter coil of a transmitter unit disposed below the detection device 220. In addition, each region 224 includes a plurality of groups of concentric detection coils 222 disposed in each detection zone 224. It can be noted that within the scope of the present application, it is conceivable that each region 224 has a greater number of detection coils 222 or detection coils 222 with different shapes and geometries, and Figure 2B The illustrated embodiment is a representative embodiment presented for illustration purposes only. A pair 226 of groups 228 and 230 of detection coils 222 are formed in the manner shown. Each group 228 and group 230 are arranged in the same geometric area so that the detection coils 222 of the group 228 and group 230 experience a main magnetic field of similar strength.

[0046] Figure 3A A portion 300 of a detection device of the present specification is shown. The portion 300 includes a pair 302 of detection coils 308 of a group 304 and a group 306 disposed on a detection pad of the detection device. In the currently contemplated embodiment, both groups 304 and 306 of detection coils 308 are excited by a single drive subsystem 310. The drive subsystem 310 includes a drive unit 311 and a drive controller 314. In addition, a single drive unit 311 of the drive subsystem 310 is used to excite the groups 304 and 306 of detection coils 308. The drive unit 311 includes an inverter / converter 312, capacitors 309 and 311, and one or more compensator elements 315 and 317. It can be noted that the capacitance values ​​of the capacitors 309 and 311 can be fixed or variable. The drive controller 314 of the drive subsystem 310 is configured to control the excitation voltage of the two groups 304 and 306 of detection coils 308. As shown, the detection coils 308 within each group 304 and 306 can be coupled to each other by being connected in series, in parallel, or both. Capacitors 309 and 311 are coupled to the groups 304 and 306 and form a resonant circuit with the detection coils 308 of the groups 304 and 306. Capacitors 309 and 311 help to adjust the current driven in the detection coils 308 and thus change the magnetic field strength used to detect foreign objects on the detection pad of the detection device.

[0047] One or more detection coils 308 present in the vicinity of a foreign object may be electromagnetically coupled to the foreign object, and this inductive coupling may result in a change in the value of the current drawn by the detection coil 308. In one embodiment, in the absence of a foreign object, the two groups 304 and 306 of a pair 302 of detection coils 308 may have detectably similar impedance values. To detect the presence of a foreign object, based on the return current signal I of the group 304, the detection coils 308 may be coupled to the foreign object.1 318 and the ongoing current signal I of group 306 2 320 to calculate the differential current signal for pair 302 and vice versa. In another embodiment, where the two groups 304 and 306 have detectably different impedances in the absence of foreign matter, one or more compensator elements 315 and 317 are used to ensure that the currents drawn by the two groups are similar in the absence of foreign matter. Non-limiting examples of compensator elements 315 and 317 may include inductors, resistors, capacitors in series or parallel, or both.

[0048] Figure 3B Another embodiment is shown, in which a portion 330 of the detection device of the present specification includes a pair 332 of first 334 and second 336 detection coils 338 disposed on a detection pad of the detection device. The two groups 334 and 336 are coupled to a drive subsystem 340. The drive subsystem 340 includes two drive units 342 and 344, which are configured to excite the first group 334 and the second group 336, respectively. The two drive units 342 and 344 include inverters 348 and 350, DC / DC converters 352 and 354, and capacitors 333 and 335. Although not shown, one or both of the drive units 342 and 244 may also include one or more compensator elements. The capacitors 333 and 335 coupled to the groups 334 and 336 form a resonant circuit with the detection coils 338 of the groups 334 and 336 and help regulate the current driven in the coils, thereby regulating the magnetic field strength in the detection pad. Inverters 348 and 350 receive inputs from two DC / DC converters 352 and 354 that drive two groups 334 and 336, which may have similar or different impedance values ​​in the absence of foreign matter.

[0049] The drive subsystem 340 also includes a drive controller 346, which can be configured to compensate for any difference in current values ​​of the first group 334 and the second group 336, regardless of the difference in impedance values ​​of the first group 334 and the second group 336. In embodiments where the groups 334 and 336 have different impedance values, the drive controller 346 can be configured to adjust the current used to drive the two groups 334 and 336 by one or more methods. In one embodiment, the drive controller 346 can be configured to change the voltage signal V of the inverters 348 and 350 by controlling the DC / DC stage converters 352 and 354. 1 and V 2In another embodiment, the duty cycle of the inverters 348 and 350 can be changed without changing the operating frequency of the inverters 348 and 350, so that in the absence of foreign matter, the first group 334 and the second group 336 of detection coils 338 can be driven by the same current with similar amplitude and phase. 1 356 and the ongoing current signal I of the second group 336 2 358 is used to calculate the differential current signal of 332, and vice versa.

[0050] Now turn to FIG. 3C to FIG. 3E , FIG. 3C to FIG. 3E Represents an implementation of the operational coupling between the drive subsystem and the detection coil group. During detection, the detection coil group is coupled to one or more drive subsystems of the detection system, and draws current from one or more drive units of the drive subsystem. When the impedance values ​​of the two groups of a pair of groups are similar, the current drawn by the two groups of the pair of detection coil groups is such that the value of the differential current can be ignored in the absence of foreign matter. However, in the case where the impedances of the two groups in a pair of detection coil groups are different, the drive controller provides compensation for one or both groups of a pair of detection coils to ensure that the two groups are driven by similar current signals in the absence of foreign matter. The drive controller also controls the excitation voltage, frequency, and excitation duration of the detection coil. The drive controller turns on the drive unit to excite the detection coil group and turns off the drive unit when the detection coil group does not need to be excited. The drive controller can use an electronic circuit to control the drive unit. Non-limiting examples of electronic circuits include microcontrollers, field programmable gate arrays (FPGAs), semiconductor devices, logic gates, device drivers, oscillators, and timers, or combinations thereof.

[0051] Figure 3C A detection device having a drive subsystem 362 is shown ( Figure 3C The drive subsystem 362 is coupled to a plurality 364 of detection coil sets 366 disposed on the detection pad. The drive subsystem 362 includes a plurality of drive units 368, wherein each drive unit 368 is coupled to a corresponding detection coil set 366. The drive subsystem 362 also includes a drive controller 370 that controls the operation of the drive units 368.

[0052] Figure 3D A detection device having a drive subsystem 382 is shown ( Figure 3D380 of the detection coil assembly 386 disposed on the detection pad. The drive subsystem 382 is coupled to a plurality 384 of detection coil assemblies 386 disposed on the detection pad. The drive subsystem 382 includes a plurality of drive units 387. The drive subsystem 382 also includes a drive controller 389 that controls the operation of the drive units 387. Several pairs 388 of the detection coil assemblies are coupled to the drive subsystem 382 such that each pair 388 is coupled to a corresponding single drive unit 387.

[0053] Figure 3E The detection device ( Figure 3E 390) of the detection device, wherein the detection device uses two drive subsystems 391 and 392 coupled to a plurality of 393 detection coil groups 394. The detection coils are arranged on the detection pad. The pairs 395 and 397 of the detection coil groups 394 are coupled to the drive subsystems 391 and 392, respectively. The drive subsystem 391 includes a drive unit 399 and a drive controller 401, and the drive subsystem 392 includes a drive unit 403 and a drive controller 405.

[0054] Figure 4 An exemplary detection system 400 is shown for detecting the presence of foreign objects in an operating environment 402 of a WPT system 404. The system 400 includes a detection device 406 and the WPT system 404. The detection device 406 includes a detection mat 408 having a plurality of detection coils and at least one pair of detection coil sets for detecting the presence of foreign objects in the operating environment 402 of the WPT system 404.

[0055] The detection device 406 also includes a drive subsystem 410. The drive subsystem 410 includes a drive unit 411 and a drive controller 412. Although not shown, the detection system 400 may include two or more drive subsystems 410. In addition, the drive subsystem 410 may include multiple drive units 411 or multiple drive controllers 412 or both. The drive subsystem 410 is operably coupled to the detection pad 408 and is configured to excite two or more detection coil groups of the detection pad 408. The detection device 406 also includes a comparison subsystem 414, which is operably coupled to the detection pad 408 and is configured to receive a differential current signal from the detection pad. In addition, the comparison subsystem 414 is configured to provide a control signal based on the differential current signal.

[0056] The WPT system 404 of the detection system 400 includes a main power supply 418, which is configured to supply power to a transmitter unit 420 of the WPT system 404 in the form of an alternating current (AC) voltage signal. The transmitter unit 420 includes at least one transmitter coil ( Figure 4 4. The transmitter unit 420 is configured to receive an AC voltage signal from the primary power source 418 and to generate a primary magnetic field or operating environment 402 in response to the received AC voltage signal.

[0057] The detection pad 408 is operably coupled to the transmitter unit 420. In particular, the detection pad 408 is disposed on the transmitter unit 420. In some embodiments, the detection pad 408 is disposed directly on the surface 422 of the transmitter unit 420. In some other embodiments, the detection pad 408 is located above the transmitter unit 408, so that the detection pad 408 is disposed in the operating environment of the WPT system 404. The detection pad 408 can be disposed and aligned relative to the transmitter coil of the transmitter unit 420. The detection pad 408 can be disposed so that the transmitter coil is geometrically symmetrically positioned relative to the detection pad 408. In addition, the detection pad 408 can be a stand-alone pad 408, a plug-and-play pad, and can have one or more of a flexible, conformable, and rigid structure.

[0058] The WPT system 404 also includes a receiver unit 424 having at least one receiver coil configured to receive at least a portion of the main magnetic field 402 generated by the transmitter unit 420. The receiver unit 424 can be disposed on the underside 426 of the device to be charged. In the illustrated embodiment, the receiver unit 424 is disposed on the underside 426 of an electric vehicle (EV) 416 to be charged using the WPT system 404. The EV 416 may include an external power source, such as a battery 417. The WPT system 404 also includes a control unit 426 that controls the operation of the main power source 418 and is also operably coupled to the detection device 406. The control unit 426 receives a control signal from the detection device 406. In addition, the control unit 426 controls the supply of power from the main power source 418 to the transmitter unit 420 based on the control signal.

[0059] In some embodiments, the detection device 406 includes a communication unit 428, which is operably coupled to the comparison subsystem 414 and is configured to receive a control signal from the comparison subsystem 414. In addition, the communication unit 428 is configured to communicate with the control unit 426 of the WPT system 404. In some embodiments, the communication unit 428 can send a control signal to a user of the EV 416 or an operator of a corresponding EV charging station, such as by using a mobile phone network, to convey the presence and / or absence of a foreign object.

[0060] The differential current signal received by the comparison subsystem 414 from the detection coil of the detection pad 408 is converted into a voltage signal, referred to as a detection voltage signal. In some embodiments, the detection voltage signal is compared with a threshold or threshold voltage signal. The threshold or threshold value can be defined, for example, by a user based on the parameters and design of the detection device 406. If the value of the detection voltage signal is greater than the value of the threshold voltage signal, it indicates that the currents drawn by the two groups of the pair of detection coil groups are different, which indicates that there is a foreign object in the operating environment of the WPT system 404. Optionally, if the value of the voltage signal is less than or equal to the value of the threshold voltage signal, it indicates that the currents drawn by the two groups of the pair of detection coil groups are appropriately similar, which indicates that there is no foreign object in the operating environment of the WPT system 404 or there is a very small foreign object (e.g., coil, etc.) that may not adversely affect the WPT operation.

[0061] In addition, in the case where the value of the detection voltage signal is greater than the value of the threshold voltage signal, a control signal may be transmitted by the detection device 406 to the WPT system 404 to interrupt the power supply to the transmitter unit 420. In some embodiments, the communication unit 428 communicates with the control unit 426, which in turn interrupts the power supply from the main power supply 418 to the transmitter unit 420. In another embodiment, in the case where the transmitter unit 420 is composed of a coil array, the control signal transmitted by the detection device 406 to the control unit 426 will cause the control unit 426 to excite only a subset of the coil array in the transmitter unit 420, thereby avoiding the area where the foreign object is detected.

[0062] Figure 5 An exemplary comparison subsystem 500 is shown of a pair 502 of detection coil sets 504 and 506 operably coupled to a detection pad. Figure 5 The example shown is a non-limiting example of measuring differential current, and it is noted that other methods for measuring differential current may also be employed in the present specification, wherein other methods may include sensing individual currents and using electronic devices (such as but not limited to differential amplifiers) to find the difference between the individual currents. The differential current signal from pair 502 may be determined by using the ongoing current signal to one group and the return current signal from the other group in the pair. In the illustrated embodiment, the return current signal I from group 504 is 1 508 and the ongoing current signal I from group 506 2 510 is used to derive the differential current signal of the pair 502 of groups 504 and 506 .

[0063] When the two current signals 508 and 510 pass through the magnetic core 512, the difference in the current signals 508 and 510 generates a flux linkage in the magnetic core and induces a corresponding sense voltage signal in an electrical winding 514 wound around the magnetic core 512, which is generally represented by the reference numeral 516. Under the condition that the magnetic core is not magnetically saturated, the sense voltage is proportional to the difference between the current signals 508 and 510 and represents a measurement of the differential current between the two groups 504 and 506 of the pair 502.

[0064] The comparison subsystem 500 also includes a rectifier 518 that receives and rectifies the detection voltage signal. An optional filter 520 filters the voltage signal before sending it to a comparator 522. In one example, the filter 520 is configured to filter out high frequency components from the measurement. The comparator 522 compares the filtered voltage signal to a threshold voltage signal and thus transmits a control signal to the WPT system, e.g. Figure 4 WPT system 404.

[0065] Figure 6 600 is an example method flow chart for detecting the presence of a foreign object in a system operating environment. In one example, the system can be a WPT system. In box 602, a detection device is utilized by placing a detection pad of the detection device on a transmitter unit of the WPT system. The detection pad can be placed directly on the transmitter unit, or the detection pad can be placed above the transmitter unit so that it is not in physical contact with the transmitter unit. The detection pad includes a plurality of detection coils and at least one pair of detection coil groups, wherein the at least one pair of detection coil groups includes a first detection coil group and a second detection coil group, and wherein the first detection coil group includes a first impedance value and the second detection coil group includes a second impedance value.

[0066] At block 604, at least one pair of detection coil groups is energized. In some embodiments, the groups of the pair may be symmetrically arranged relative to the main magnetic field. In some other embodiments, the groups of the pair are arranged at the same geometric position. In certain embodiments, the groups of the pair may be arranged in two different detection zones, and the detection zones may be selected so that two detection zones in the pair of detection zones are symmetrically placed relative to the magnetic field of the transmitter unit.

[0067] In some embodiments, more than one pair of detection coil groups can be excited. In one example, multiple pairs of detection coil groups can be excited simultaneously to detect the presence of foreign matter. In one embodiment, different pairs of detection coil groups can be selected so that the entire surface of the detection pad is excited to detect the presence of foreign matter. In some embodiments, different pairs can be excited at different times. In another embodiment, two or more pairs can be excited simultaneously. In one embodiment, different pairs of groups can be excited in a time sequence.

[0068] In addition, the paired groups can be excited before starting the wireless power transmission operation of the WPT system for the receiver unit and during the wireless power transmission operation of the WPT system. The paired groups can be excited intermittently or at periodic intervals. In addition, the detection coils corresponding to different detection zone pairs are excited at different times. In addition, different voltage signals are provided to the detection coils in the pair of detection coils having different impedance values, so that in the absence of foreign matter, the detection coils in the pair of detection coils are driven by the same current signal with similar amplitude and phase.

[0069] At block 606, a differential current signal is determined for the energized detection coils. In one embodiment, the differential current signal is determined using the ongoing current signal of one of the pair of detection coil sets and the return current signal of the other of the pair of detection coil sets. In embodiments where two or more pairs are energized simultaneously, corresponding separate differential current signals may be determined to detect the presence of foreign matter. Based on the differential current signal, it is determined whether a foreign matter is present in the operating environment of the WPT system.

[0070] Subsequently, at block 608, a control signal is generated based on the differential current signal. At block 610, the generated control signal is transmitted. In one example, the control signal is transmitted to a control unit of the WPT system. In some embodiments, based on the control signal received by the control unit of the WPT system, power supply to the transmitter unit of the WPT system is continued, adjusted, or interrupted.

[0071] Figure 7 700 is a method flow chart of a method for controlling a power supply of a transmitter unit based on a control signal. At block 702, a detection voltage signal proportional to a differential current signal is generated using, for example, an electrical winding and a magnetic core of a comparison subsystem. At block 704, the detection voltage signal is compared to a threshold. In some embodiments, the threshold may be a threshold value or a threshold voltage signal. The threshold voltage signal may be a predetermined voltage signal based on characteristics of the WPT system.

[0072] At decision block 706, if the detected voltage signal is found to be greater than the threshold voltage signal, a control signal is transmitted to the WPT system to not start, adjust or interrupt the power supply to the transmitter unit (block 708). Alternatively, at decision block 706, if the detected voltage signal is lower than the threshold voltage signal, no communication is performed to the WPT system, or a control signal instructing the WPT system to continue or start the power supply to the transmitter unit may be transmitted to the WPT system (block 710).

[0073] The detection can be performed in real time or near real time. Near real time detection can be performed so that the control signal is generated and transmitted within a time period of a few microseconds to a few milliseconds from the start of detection. In some embodiments, the detection pad can be scanned for any foreign matter at a determined rate at periodic intervals, for example, once per second. Once a foreign matter is detected, a communication signal is sent to the transmitter unit.

[0074] Figure 8 is a cross-sectional view of a detection pad 800 according to aspects of the present specification. In some embodiments, the detection pad 800 can be a separate structure that can be detachably coupled to a transmitter unit, for example, Figure 4 The transmitter unit 420 of the present invention. In one example, the detection pad 800 can be a plug-and-play structure. The detection pad 800 includes a substrate 802 having one or more printed circuit boards (PCBs) 804. The substrate 802 can include an electrically insulating material. In some embodiments, the substrate 802 itself can be a printed circuit board (PCB).

[0075] In addition, a group 806 of detection coils 808 can be disposed on the substrate 802. In one embodiment, the group 806 of detection coils 808 can be disposed on a corresponding PCB 804. In some embodiments, for user safety and aesthetics, the detection coils 808 can be disposed on the substrate 802 or can be embedded in the substrate 802. The detection coils 808 can also be printed on a flexible or regular printed circuit board. In some embodiments, the detection coils 808 can be printed, molded, woven, or otherwise manufactured on the substrate 808 or the PCB 804. It can be noted that each detection coil 808 can be compact and wrapped in a thin gauge wire.

[0076] The cover layer 810 can be disposed on the detection coil 808. The cover layer 810 has a first side 812 and a second side 814. In some embodiments, the detection coil 808 can be disposed directly on the second side 814 of the cover layer 810. In some of these embodiments, the detection coil 808 may not be disposed on the PCB 804. In addition, suitable electronics 816 can be provided to the substrate 802 to enable the detection pad 800 to be operably coupled with the drive subsystem and the comparison subsystem of the detection device.

[0077] The substrate 802 and the cover layer 810 may include a flexible material, a hard material, or a combination thereof. The cover layer 810 includes a thermally conductive and electrically insulating (TCEI) material. In one embodiment, the thermally conductive and electrically insulating (TCEI) material may include an elastomer or thermoplastic with a wear-resistant filler. In one embodiment, the elastomer may be silicone rubber. The filler may be a TCEI filler, for example, aluminum oxide, aluminum nitride, beryllium oxide, boron nitride, graphene oxide, silicon carbide, and silicon nitride. Similarly, the thermoplastic may be a polyolefin, polycarbonate, poly(methyl methacrylate) (PMMA), and polyester. In addition, in some embodiments, the substrate 802 and the cover layer 810 may be folded together with the detection coil 808. In one embodiment, the detection pad 800 may be a conforming structure. To this end, when the detection pad 800 is disposed on the transmitter unit, the detection pad 800 may be configured to substantially conform to the gradient and curve of the surface of the transmitter unit. In some embodiments, the cover layer 810 can form a housing around the substrate 802 , the detection coil 808 , and can surround the electronics 816 .

[0078] In one embodiment, the detection pad 800 can be integrated with a standard SAE transmitter system. In some embodiments, the size of the detection pad 800 can be in a range from about 0.5m to about 2.2m. The detection pad 800 can be appropriately large to cover the surface area of ​​the transmitter coil. In some examples, the detection pad 800 can have a length in a range from about 0.5m to about 2.2m and a width in a range from about 0.5m to about 2.2m. In addition, the detection pad 800 can have a thickness in a range from about 1mm to about 20mm. In one embodiment, the detection pad 800 can be a unitary structure. In another embodiment, the detection pad 800 can be formed by integrating separate independent pieces.

[0079] Advantageously, the devices, systems, and methods of the present technology are simple in construction and do not require any complex assembly. In addition, the present technology is very sensitive and is able to detect the presence of foreign objects shortly after the wireless power transmission is started. This helps to minimize power waste. The embodiments of the present specification provide a highly sensitive, simple, and accurate system to detect foreign objects placed in the operating environment of the WPT system. In addition, the detection device of the present specification can be deployed in an existing WPT system, and only minimal changes or adjustments are required in the existing WPT system, or no changes or adjustments are required. Advantageously, the devices, systems, and methods of the present specification achieve a safe operating environment during wireless power transmission of an electric vehicle (EV), but stop the wireless transmission of the EV when a foreign object is detected, or sound an alarm when the presence of a foreign object is detected in the operating environment of the WPT system.

[0080] Although only certain features of the invention have been shown and described herein, many modifications and changes will occur to those skilled in the art. It is therefore to be understood that the appended claims are intended to cover all such modifications and changes as fall within the scope of the invention.

Claims

1. A detection device (100), comprising: A detection pad (102) having a plurality of detection coils (106) and at least one pair of detection coil groups (106), wherein the at least one pair of detection coil groups (106) comprises a first detection coil group (106) and a second detection coil group (106), and wherein the first detection coil group (106) comprises a first impedance value, and the second detection coil group (106) comprises a second impedance value; One or more drive subsystems (112) operably coupled to the detection pad (102) and configured to energize at least one pair of detection coil sets (106); and A comparison subsystem (114) is operably coupled to the detection pad (102) and is configured to receive a differential current signal from the at least one pair of detection coil sets (106), wherein the differential current is determined using an ongoing current signal of one of the pair of detection coil sets and a return current signal of the other of the pair of detection coil sets, and wherein the comparison subsystem (114) is configured to generate a control signal based on the differential current signal.

2. The detection device (100) according to claim 1, wherein: The first detection coil group (106) and the second detection coil group (106) are symmetrically arranged relative to the main magnetic field of the wireless power transmission system, and wherein the detection device (100) is configured to detect the presence of foreign matter in the operating environment of the wireless power transmission system based on the differential current signal.

3. The detection device (100) according to claim 1, wherein: The first detection coil set (106) and the second detection coil set (106) include a similarly structured arrangement of detection coils (106).

4. The detection device (100) according to claim 1, wherein: The first detection coil group (106) and the second detection coil group (106) are arranged in the same geometric area on the detection pad (102).

5. The detection device (100) according to claim 1, wherein: The first impedance value and the second impedance value are similar to each other.

6. The detection device (100) according to claim 1, wherein: The first impedance value and the second impedance value are different from each other, and wherein the detection pad (102) further includes a compensator element, which is operably coupled to one of the first detection coil group (106) and the second detection coil group (106) to compensate for the difference in impedance values ​​of the first detection coil group (106) and the second detection coil group (106).

7. The detection device (100) according to claim 1, wherein: The first impedance value and the second impedance value are different from each other, and wherein the one or more driving subsystems (112) further include a driving controller, which is configured to provide different voltage signals to the first detection coil group (106) and the second detection coil group (106), so that the first detection coil group (106) and the second detection coil group (106) are driven by the same current with similar amplitude and phase.

8. The detection device (100) according to claim 1, wherein: The one or more driving subsystems (112) include two driving units respectively coupled to the first detection coil group (106) and the second detection coil group (106) and at least one driving controller, and wherein the driving controller is coupled to the driving units.

9. The detection device (100) according to claim 1, wherein: The plurality of detection coils (106) include a plurality of detection zones, wherein each detection zone of the plurality of detection zones includes one or more detection coil groups (106).

10. The detection device (100) according to claim 9, wherein: At least a portion of the one or more drive subsystems (112) is configured to be coupled to two or more detection zones of the plurality of detection zones.

11. The detection device (100) according to claim 10, wherein: The detection zones in the plurality of detection zones corresponding to a pair of detection zones include a structurally identical arrangement of detection coils (106).

12. The detection device (100) according to claim 1, wherein: The detection pad (102) is a flexible pad, a conformable pad, a rigid pad or a plug-and-play pad.

13. The detection device (100) according to claim 1, wherein: The detection coils (106) in a detection coil group (106) are coupled in a series connection, a parallel connection, or a combination of series and parallel connection, and wherein the plurality of detection coils (106) include concentric coils, adjacently arranged coils, and side-by-side arranged coils, and wherein the plurality of detection coils (106) are arranged in one or more layers.

14. The detection device (100) according to claim 1, wherein: The comparison subsystem (114) includes: An electrical winding and a magnetic core configured to receive the differential current signal from the first detection coil set (106) and the second detection coil set (106), and to generate a detection voltage signal based on the differential current signal; and The comparator is configured to compare the detection voltage signal with a threshold voltage signal to generate the control signal.

15. A detection system (400), comprising: The detection device (406) according to claim 1; as well as A wireless power transmission system, comprising: a main power source configured to supply power in the form of an alternating voltage signal; a transmitter unit comprising at least one transmitter coil, wherein the transmitter unit is configured to receive the AC voltage signal from the main power source, wherein the transmitter unit is configured to generate a main magnetic field in response to the received AC voltage signal, and wherein the detection pad (102) is operably coupled to the transmitter unit; a receiver unit comprising at least one receiver coil and configured to receive at least a portion of said main magnetic field generated by said transmitter unit; A control unit is operably coupled to the detection device and is configured to: receiving the control signal from the detection device; and Power supply to the transmitter unit is controlled based on the control signal.

16. The detection system (400) according to claim 15, wherein: The driving subsystem is configured to intermittently or periodically excite the detection device.

17. The detection system (400) according to claim 15, wherein: The one or more drive subsystems further include a communication unit configured to transmit the control signal to the control unit.

18. A detection method (600), comprising: Using (602) a detection device, the detection device comprising a detection pad having a plurality of detection coils and at least one pair of detection coil groups, wherein the at least one pair of detection coil groups comprises a first detection coil group and a second detection coil group, and wherein the first detection coil group comprises a first impedance value and the second detection coil group comprises a second impedance value; energizing (604) at least one pair of detection coil sets; determining (606) a differential current signal from the at least one pair of detection coil sets, using an ongoing current signal from one of the pair of detection coil sets and a return current signal from the other of the pair of detection coil sets to determine the differential current; and generating (608) a control signal based on the differential current signal; and The control signal is transmitted (610).

19. The method (600) of claim 18, further comprising controlling (700) a power supply of a transmitter unit based on the control signal.

20. The method (600) of claim 19, further comprising: generating (702) a detection voltage signal based on the differential current signal; and The detection voltage signal is compared with a threshold voltage signal ( 704 ) to generate the control signal.

21. The method (600) of claim 18, wherein: Exciting (604) the at least one pair of detection coil sets includes exciting the at least one pair of detection coil sets intermittently or at periodic intervals.

22. The method (600) of claim 18, wherein: Exciting (604) the at least one pair of detection coil groups includes exciting detection coil groups corresponding to different pairs of detection coil groups at different times.

23. The method (600) of claim 18, wherein: Exciting (604) the at least one pair of detection coil sets includes providing different voltage signals to detection coil sets in a pair of detection coil sets having dissimilar impedance values ​​such that sets in the pair of detection coil sets are driven by the same current signal having similar amplitude and phase.

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