US20200300622A1

US20200300622A1 - Automatic laser distance calibration kit for wireless charging test system

Info

Publication number: US20200300622A1
Application number: US16/896,525
Authority: US
Inventors: Tun LI; Siming PAN; Dawei He; Yi Liu; Jingdong Sun
Original assignee: Sichuan Energy Internet Research Institute EIRI Tsinghua University
Current assignee: Sichuan Energy Internet Research Institute EIRI Tsinghua University
Priority date: 2017-12-13
Filing date: 2020-06-09
Publication date: 2020-09-24
Also published as: CN109917194A; US20200326371A1; WO2019114168A1; US11293753B2

Abstract

An automated laser calibration kit for calibrating a distance between a testing device and a device-under-test (DUT) of a wireless charging system is disclosed. The calibration kit may be positioned on a wireless charging testing system. The testing system may comprise a testing plane to hold the DUT and a clamp arm to hold the testing device. The calibration kit may comprise a laser pointer configured to emit a laser beam; a reflection mirror positioned on the clamp arm and configured to reflect the laser beam to form a light point on the testing plane; and a camera configured to monitor a position of the light point.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This present application is a continuation of International Patent Application No. PCT/CN2018/083640, filed on Apr. 19, 2018, titled “Automatic Laser Distance Calibration Kit for Wireless Charging Test System”, which claims the benefit of and priority to Chinese Patent Application No. 201711324032.7, filed on Dec. 13, 2017. The above-referenced applications are herein incorporated by reference in their entirety.

TECHNICAL FIELD

The disclosure relates generally to a wireless charging system, particularly, to a method and an automated laser calibration kit for calibrating a distance between magnetic coils in a wireless charging testing system.

BACKGROUND

Wireless charging is an evolving technology that may bring a new level of convenience of charging electronic devices. In a wireless charging system, particularly an inductive wireless charging system, energy is transferred from one or more power transmitter (TX) coils to one or more power receiver (RX) coils through a coupling of a magnetic field.
A magnetic coil can generate a magnetic field, and the coupling of the magnetic field between TX and RX coils is influenced by the relative position and distance between the coils, which may further affect a charging efficiency of a charging system. To improve a user experience and guarantee a reliability of the wireless charging, a wireless charging system should be thoroughly tested. In order to characterize the coupling between the TX and RX coils in a wireless charging system, a calibration of the distance between the coils is needed to ensure reliable and consistent results.
This disclosure provides an automated laser calibration kit for a wireless charging testing system. This kit can be easily integrated into a wireless charging testing system or similar measurement equipment. It can calibrate the distance between TX and RX coils precisely and automatically.

SUMMARY

One aspect of the present disclosure is directed to an automated laser calibration kit for calibrating a distance between a testing device and a device-under-test (DUT) of a wireless charging system. The calibration kit may be positioned on a wireless charging testing system. The testing system may comprise a testing plane to hold the DUT and a clamp arm to hold the testing device. The calibration kit may comprise a laser pointer configured to emit a laser beam; a reflection mirror positioned on the clamp arm and configured to reflect the laser beam to form a light point on the testing plane; and a camera configured to monitor a position of the light point.
Another aspect of the present disclosure is directed to a wireless charging testing system for testing a wireless charging system. The testing system may include a clamp arm configured to hold a testing device; a testing plane configured to hold a DUT; and an automated laser calibration kit for calibrating a distance between the testing device and the DUT.
Another aspect of the present disclosure is directed to a method for calibrating a distance between a testing device and a DUT of a wireless charging system by using an automated laser calibration kit installed on a wireless charging testing system. The testing system may include a testing plane to hold the DUT and a clamp arm to hold the testing device. The calibration kit may include a laser pointer configured to emit a laser beam; a reflection mirror positioned on the clamp arm and configured to reflect the laser beam to form a light point on the testing plane; and a camera configured to monitor a position of the light point. The method may include setting a reference position for the light point; setting an initial distance between the DUT and the testing device; changing the distance between the DUT and the testing device and monitoring the position of the light point; and stopping changing the distance between the DUT and the testing device when the position of the light point overlaps with the reference position.
A further aspect of the present disclosure is directed to a method for calibrating a distance between a testing device and a DUT of a wireless charging system by using an automated laser calibration kit installed on a wireless charging testing system. The testing system may include a testing plane to hold the DUT, a clamp arm to hold the testing device, and a laser pointer mounted on the clamp arm and configured to form a light point on the testing plane. The method may include setting a reference position for the light point on the testing plane, and moving the clamp arm relative to the testing plane until the light point coincide with the reference position on the testing plane.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which constitute a part of this disclosure, illustrate several non-limiting embodiments and, together with the description, serve to explain the disclosed principles.

FIG. 1 is a graphical representation illustrating a wireless charging testing system installed with an automated laser distance calibration kit, consistent with exemplary embodiments of the present disclosure.

FIG. 2 is a graphical representation illustrating working mechanism of an automated laser distance calibration kit, consistent with exemplary embodiments of the present disclosure.

FIG. 3(a) is a flow diagram illustrating a method for calibrating a distance between a device-under-test and a testing device by an automated laser distance calibration kit; FIG. 3(b) is a diagram illustrating a geometrical relationship an automated laser distance calibration kit of consistent with exemplary embodiments of the present disclosure.

FIG. 4(a) is graphical representation illustrating a structure of a spatial filter; FIG. 4(b) is a photo of exemplary spatial filters; FIG. 4(c) is a photo of exemplary components of a spatial filter; FIG. 4(d) is a diagram illustrating dimensions of exemplary components of a spatial filter, consistent with exemplary embodiments of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings in which the same numbers in different drawings represent the same or similar elements unless otherwise represented. The implementations set forth in the following description of exemplary embodiments consistent with the present invention do not represent all implementations consistent with the invention. Instead, they are merely examples of systems and methods consistent with aspects related to the invention.
In this disclosure, we propose an automated laser distance calibration kit. A structure of this calibration kit and calibration method are introduced. This calibration kit may measure the actual position of RX coils by monitoring the position of a light point generated by a laser pointer, thus can eliminate any significant error introduced during measurement processes. In addition, the calibration kit can be easily mounted and integrated in a wireless charging testing system, a near field scanning instrument or other similar testing equipment.
FIG. 1 shows a wireless charging testing system 100 installed with an automated laser distance calibration kit, consistent with exemplary embodiments of the present disclosure. The system 100 and the calibration kit may comprise a number of components, some of which may be optional. In some embodiments, the system 100 and the calibration kit may include many more components than those shown in FIG. 1. However, it is not necessary that all of these components be shown in order to disclose an illustrative embodiment.
As shown in FIG. 1, an automated laser distance calibration kit may include a laser pointer 110, a reflection mirror 120 and a camera 130. The kit may be mounted on a wireless charging testing system 100. The system 100 may include a testing plane 101, and a clamp arm 102. In some embodiments, the laser pointer 110 and the reflection mirror 120 may be mounted on the clamp arm 102.
In some embodiments, the testing plane 101 may be a flat plane that is horizontally positioned with the surface of the plane parallel to the ground, and is also parallel to the x-y plane. A device-under-test (DUT) can be secured on the testing plane 101 for measurement. In some embodiments, the DUT may be a TX coil or a TX related electronic product. The clamp arm 102 is movable along the z-direction. It may be configured to hold and move a measurement probe, a DUT clamp, a RX related electronic product, the automated laser distance calibration kit, etc. A testing device can be secured on the DUT clamp, and is movable along the z-direction, together with the reflection mirror 120 by the clamp arm 102. In some embodiments, the testing device may be a RX coil, a measurement probe, or a RX related electronic product. A distance between the DUT on the testing plane 101 and testing device on the clamp arm 102 (e.g., TX and RX coils) in the z-direction can be controlled by the clamp arm 102. Some of the description uses TX coil as an exemplary DUT and RX coil as an exemplary testing device.
Positions of the testing device and the device-under-test may be interchangeable. In one embodiment, the testing device may be secured on the clamp arm 102, and the device-under-test may be secured on the testing plane 101. In another embodiment, the testing device may be secured on the testing plane 101, and the device-under-test may be secured on the clamp arm 102.
In some embodiments, the testing plane 101 is also movable along the z-direction, and by adjusting the position of the testing plane 101, the distance between the DUT and testing device (e.g., TX and RX coils) can also be changed.
The laser pointer 110 in the automated laser distance calibration kit may emit a narrow laser beam along the z-direction which then is reflected by the reflection mirror 120, and forms a light point on the testing plane 101. The reflection mirror 120 may be fixed on the clamp arm 102 with a certain angle, and is configured to reflect the laser beam emitted by the laser pointer 110. The angle of the reflection mirror 120 with respect to the testing plane 101 may be designed by a user's request. For example, it can be 30°, 45°, or 60° depending on a specific requirement. The camera 130 is configured to monitor the position of the light point on the testing plane 101 through an image processing technique. The camera 130 also transfers the information of the position of the light point to a controller computer, which can control the distance between the TX and RX coils by changing the position of the clamp arm (or the testing plane). The controller computer may include a linear actuator which can adjust the position of the clamp arm (or the testing plane). The linear actuator, may, controlled by the controller computer, move the clamp arm (or the testing plane) at different speeds. For example, the controller computer moves the clamp arm faster when the distance between the TX and RX coils is largely different from the target distance, and moves the clamp arm slower when the distance is close to the target distance. The controller computer may comprise a non-transitory computer-readable medium that stores program code to control the calibration process, measure and analyze the distance between the TX and RX coils.
FIG. 2 is a graphical representation illustrating the working mechanism of an automated laser distance calibration kit, consistent with exemplary embodiments of the present disclosure.
As shown in FIG. 2, a wireless charging testing system may include a testing plane 201, a clamp arm 202, and a DUT clamp 203 fixed on the clamp arm 202. A DUT 204 is placed on the testing plane 201. In some embodiments, the DUT 204 may be a wireless charging pad, and may include one or more TX coils. A testing device 205 (e.g., a RX coil) may be secured on the DUT clamp 203. An automated laser distance calibration kit is mounted on the clamp arm 202. The calibration kit moves along with the testing device 205 by the clamp arm 202. The calibration kit may include a laser point 210 and a reflection mirror 220. In some embodiments, the laser pointer 210 and the reflection mirror 220 may be mounted on the clamp arm 202. The laser pointer 210 generates a laser beam along the z-direction. The laser beam is reflected by the reflection mirror 220 and forms a light point on the testing plane 201. The reflection mirror 220 may be positioned with an angle relative to the testing plane 201. A change in the position of the light point on the testing plane 201 is proportionally to a change in the distance between the DUT and the testing device. The calibration kit may further include a camera (not shown in FIG. 2) for capturing the position of the light point on the testing plane 201.
In some embodiments, a distance between the DUT 204 and the testing device 205 in the z-direction may be changed by moving the position of the clamp arm 202. In some embodiments, the distance may be changed by moving the position of the testing plane 201. To better illustrate the working mechanism, the position of the DUT 204 is selected as a reference in FIG. 2. The position of the light point can be determined by the angle of the reflection mirror 220 and the distance between the DUT 204 and the testing device 205. At Position 1, the distance between the DUT 204 and the testing device 205 in the z-direction is denoted as h₁, and a distance between the light point and the DUT 204 on the testing plane is denoted as d₁. At Position 2, the distance between the DUT 204 and the testing device 205 in the z-direction is denoted as h₂, and the distance between the light point and the DUT 204 on the testing plane is denoted as d₂. The changes in the distances are proportional, that is, Δh∝Δd, where Δh=|h₁−h₂|, and Δd=|d₁−d₂|. In other words, the change of the position of the light point Δd can be measured, and the change in the distance between the DUT 204 and the testing device 205 in the z-direction can be determined accordingly. As the position of the light point is monitored and reported to the controller computer, the distance between the DUT 204 and the testing device 205 in the z-direction can be determined and calibrated.
The laser beam may not be limited to forming a light point on a testing plane of a wireless charging testing system. In some embodiments, the laser beam reflected by the reflection mirror, can form a light point on any flat surface, as long as the change of the position of the light point on the surface is proportional to the change in the distance between the DUT and the testing device in the z-direction.
FIG. 3(a) is a flow diagram illustrating a method 300 for calibrating a distance between a DUT and a testing device by an automated laser distance calibration kit, consistent with exemplary embodiments of the present disclosure. In some embodiments, the DUT may be a TX coil, and the testing device may be a RX coil. As discussed previously, the TX coil can be mounted on a testing plane of a wireless charging testing system, and the RX coil can be secured on the DUT clamp on a clamp arm of the testing system. The system is installed with an automated laser distance calibration kit to calibrate the distance between the TX and RX coils.
At step 301, a reference position is set on the testing plane, indicated as an open circle in FIG. 3(a). The reference position can be viewed as a target position for the light point created by the laser beam. As the position of the light point is associated with the distance between the TX and RX coils, the reference position can set the distance between the TX and RX coils as a known value. In other words, once the light point overlaps the reference position, the distance between the TX and RX coils is a known value which is predetermined by a user. Therefore, the distance can be calibrated.
At step 302, an initial distance between the TX and RX coils is set by lifting the clamp arm up (or lowering the testing plane down). The laser pointer emits a laser beam which gets reflected by the reflection mirror and forms a light point on the testing plane. The initial distance can be any distance allowed by the testing system. For example, a user may set an initial distance wherein the light point is as close as possible by looking at the light point and the reference position with the user's eyes. Or, the initial distance can be the distance with the testing plane and the clamp arm left in positions of last measurement. In that case, step 302 can be omitted. The position of the light point, shown as a solid circle in FIG. 3(a), initially may be away from the reference position, and the distance between the TX and RX coils is different than the predetermined value.
At step 303, the distance between the TX and RX coils is gradually decreased by lowering the clamp arm to the testing plane (or moving the testing plane up to the clamp arm, or both). Accordingly, the position of the light point is gradually getting closer to the reference position, and the distance between the TX and RX coils is gradually getting closer to the predetermined value. The position of the light point is monitored by the camera and reported to a controller computer. In another situation, the initial positions of the TX and RX coils may be too close, and the distance is gradually increased by lifting the clamp arm and/or lowering testing plane, until the light point coincides with the reference position.
At step 304, stop changing the position of the clamp arm (or the testing plane) when the light point reaches the reference position, i.e., the light point completely overlaps with the reference position. Once the light point overlaps with the reference position, the distance between the TX and RX coils can be viewed as the same as the predetermined value, and the distance is calibrated. As discussed above, the testing system may include one or more linear actuator and the movement of the clamp arm and/or the testing plane may be actuated and controlled by the linear actuator.
FIG. 3(b) is a diagram illustrating a geometrical relationship of the automated laser distance calibration kit, consistent with exemplary embodiments of the present disclosure. The geometrical relationship illustrates how a reference position can be calculated by the controller computer. As shown in FIG. 3(b), the reference position may be determined by (1) an initial zero position, (2) a distance in the z-direction (d), and (3) an angle of the reflection mirror (a).
The initial zero position may refer to a position of the light point on the testing plane when a distance between a testing device and a DUT is minimum, i.e., the clamp arm is not able to move down further, or the testing plane is not able to move up further. In some embodiments, the initial zero position can be obtained by gradually moving the clamp arm down until a lower end of the testing device slightly contact with the DUT. At this point, a position of the light point can be recorded as the initial zero position.
The distance in the z-direction d is a target distance between the testing device and the DUT. For example, if a testing requires the distance between the testing device and the DUT is 5 mm, then the distance in the z-direction can be set as 5 mm.
The angle of the reflection mirror a is an angle of the reflection mirror relative to the testing plane. It can be tuned to different values, for example, 30°, 45°, or 60°. Once the angle of the reflection mirror is adjusted, the value of the angle should be updated to the controller computer.
Based on the direction in the z-direction d and the angle of the reflection mirror a, a moving distance of the light point (y) with respect to the initial zero position can be calculated. In other words, when the distance between the testing device and the DUT is d, the light point moves a distance of y away from the initial zero position, and reaches a new position. This new position of the light point is the reference position of the light point. The moving distance y can be calculated by the following formula:
$y = \frac{d}{\tan (2 α - 9 0^{\circ})}$
During a testing, when the light point overlaps with the reference position, the distance between the testing device and the DUT is calibrated to the target value (d).
In another embodiment, to calibrate a distance between a DUT and a testing device by an automated laser distance calibration kit, at a first step, the distance gradually decreases to zero. In other words, a surface of the testing device and a surface of the DUT slightly contact with each other. At this point, the distance between the DUT and the testing device is calibrated to zero, i.e., the testing system is calibrated. Turning on the automated laser distance calibration kit, the laser pointer emits a laser beam which gets reflected by the reflection mirror and forms a light point on the testing plane at Position O, which can be considered as an initial zero position of the light point. Any position change of the light point is measured from Position O.
At a second step, the testing device and the DUT move away from each other by lifting the clamp arm up (or lowering the testing plane down, or both).
At a third step, a target distance between the DUT and the testing device can be set, for example, h=2 cm. Alternatively, the target distance can pre-set by a user. Since the testing system has been calibrated, to reach the h=2 cm position, the change in distance between the DUT and the testing device from its zero position is Δh=2 cm. As previously discussed, Δh∝Δd, a change of the position of the light point can be calculated. For example, if the reflection mirror is fixed with an angle of 22.5°, then Δh:Δd=1:1. Thus, when Δh=2 cm, we can have Δd=2 cm. In other words, in this case, when the distance between the DUT and the testing device is 2 cm, the light point changes 2 cm away from Position O. Then a reference position of the light point can be set as Position R, where the distance between Position O and Position R is 2 cm.
At a fourth step, the distance between the DUT and the testing device is gradually decreased by lowering the clamp arm to the testing plane (or moving the testing plane up to the clamp arm, or both). Alternatively, the distance can be gradually increased depending on the initial positions of the DUT and the testing device. Accordingly, the position of the light point is gradually getting closer to the reference position (Position R), and the distance between the DUT and the testing device is gradually getting closer to the target distance. The position of the light point is monitored by the camera and reported to a controller computer.
At a fifth step, stop changing the position of the clamp arm (or the testing plane) when the light point reaches the reference position, i.e., the light point completely overlaps Position R.
The above-discussed process can be controlled by the controller computer. The controller computer may receive the information of the position of the light point from the camera and compared it with the reference position by an image processing technique. When the position of the light point is not the same as the reference position, the controller computer can automatically change the distance between the TX and RX coils by changing the position of the clamp arm (and/or the testing plane). When the position of the light point is the same as the reference position, the controller computer can automatically stop changing the distance between the TX and RX coils, and set the distance as the predetermined value, thus finish the calibration of the distance. In addition, the controller computer may adjust the speed of the motion of the clamp arm (or the testing plane). For example, the controller computer moves the clamp arm faster when the distance between the TX and RX coils is largely different from the target distance, and moves the clamp arm slower when the distance is close to the target distance. The controller computer may comprise a non-transitory computer-readable medium that stores program code to control the calibration process, measure and analyze the position between the TX and RX coils.
In some embodiments, in order to improve the precision of the calibration, a small light point is of desire, and a spatial filter is designed in the laser pointer to eliminate haze of the laser beam. FIG. 4(a) is graphical representation illustrating a structure of a spatial filter 400, consistent with exemplary embodiments of the present disclosure.
The spatial filter 400 may include a convex lens 401, a concave lens 402 and a shielding box 403. The convex lens 401 is configured to converge an input laser beam to a point on the other side of the lens. The concave lens 402 can diverge the light rays. By using a pair of convex and concave lens, the output laser beam will be more focused than the input laser beam. The shielding box 403 is used to block the unwanted haze from of the output laser beam. The output from the shielding box 403 is a narrow laser beam without haze. FIG. 4(b) shows photos of exemplary spatial filters.
A distance between the convex lens 401 and concave lens 402 can be adjusted by two cylindrical-shaped components, Component 1 and Component 2. FIG. 4(c) is a photo of exemplary Component 1 and Component 2. The lens may be assembled at the end of these components. Dimensions of the two exemplary components are labeled in FIG. 4(d) and listed in Table 1. The distance between the convex lens and concave lens can be adjusted between H₃(55.4 mm) to H₃+H₁(83.4 mm).

TABLE 1

Label	H₁	H₂	H₃	D₁	D₂	D₃	D₄	D₅	D₆

Length (mm)	28	30	55.4	22.2	16.42	11.66	6.14	5.92	4.29

Note that one or more of the functions described above can be performed by software or firmware stored in memory and executed by a processor, or stored in program storage and executed by a processor. The software or firmware can also be stored and/or transported within any non-transitory computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “computer-readable medium” can be any medium that can contain or store the program for use by or in connection with the instruction execution system, apparatus, or device. The computer readable medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus or device, a portable computer diskette (magnetic), a random access memory (RAM) (magnetic), a read-only memory (ROM) (magnetic), an erasable programmable read-only memory (EPROM) (magnetic), a portable optical disc such a CD, CD-R, CD-RW, DVD, DVD-R, or DVD-RW, or flash memory such as compact flash cards, secured digital cards, USB memory devices, memory sticks, and the like.
The invention described and claimed herein is not to be limited in scope by the specific preferred embodiments disclosed herein, as these embodiments are intended as illustrations of several aspects of the invention. Indeed, various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims.

Claims

What is claimed is:

1. An automated laser calibration kit for calibrating a distance between a testing device and a device-under-test (DUT) of a wireless charging system, wherein the calibration kit is positioned on a wireless charging testing system, and the testing system comprises a testing plane to hold the DUT and a clamp arm to hold the testing device, the calibration kit comprising:

a laser pointer configured to emit a laser beam;

a reflection mirror positioned on the clamp arm and configured to reflect the laser beam to form a light point on the testing plane; and

a camera configured to monitor a position of the light point.

2. The calibration kit of claim 1, wherein the DUT is a TX coil.

3. The calibration kit of claim 1, wherein the testing device is a RX coil.

4. The calibration kit of claim 1, wherein the reflection mirror is positioned with an angle with respect to the testing plane so that a change in the position of the light point is proportional to a change in the distance between the DUT and the testing device.

5. The calibration kit of claim 1, wherein when the position of the light point overlaps with a reference position, the distance between the DUT and testing device is set as a known value, and wherein both the reference position and the known value are predetermined by a user.

6. The calibration kit of claim 1, further comprising a controller computer configured to receive the position of the light point and automatically control the distance between the DUT and the testing device.

7. The calibration kit of claim 1, further comprising a spatial filter, wherein the spatial filter comprises a convex lens, a concave lens, and a shielding box.

8. A wireless charging testing system for testing a wireless charging system, comprising:

a clamp arm configured to hold a testing device;

a testing plane configured to hold a DUT; and

an automated laser calibration kit for calibrating a distance between the testing device and the DUT, wherein the calibration kit comprises:

a laser pointer configured to emit a laser beam;

a camera configured to monitor a position of the light point.

9. The testing system of claim 8, wherein the DUT is a TX coil.

10. The testing system of claim 8, wherein the testing device is a RX coil.

11. The testing system of claim 8, wherein the reflection mirror is positioned with an angle with respect to the testing plane so that a change in the position of the light point is proportional to a change in the distance between the DUT and the testing device.

12. The testing system of claim 8, wherein when the position of the light point overlaps with a reference position, the distance between the DUT and testing device is set as a known value, and wherein both the reference position and the known value are predetermined by a user.

13. The testing system of claim 8, further comprising a controller computer configured to receive the position of the light point and automatically control the distance between the DUT and the testing device.

14. The testing system of claim 8, further comprising a spatial filter, wherein the spatial filter comprises a convex lens, a concave lens and a shielding box.

15. A method for calibrating a distance between a testing device and a DUT of a wireless charging system by using an automated laser calibration kit installed on a wireless charging testing system, wherein the testing system comprises a testing plane to hold the DUT, a clamp arm to hold the testing device, and a laser pointer mounted on the clamp arm and configured to form a light point on the testing plane, the method comprising:

setting a reference position for the light point on the testing plane;

moving the clamp arm relative to the testing plane until the light point coincide with the reference position on the testing plane.

16. The method of claim 15, wherein the DUT is a TX coil, and the testing device is a RX coil.