Foreign object detection device for wireless charging system

Abstract

The present invention discloses a foreign object detection device for a wireless charging system, which has a transmitting side detector, and the transmitting side detector is arranged at the transmitting end of the wireless charging system; the transmitting side detector includes: a first antenna set and an excitation circuit connected in sequence; the first antenna set includes multiple first antennas; each of the first antennas has a transmitting function and a receiving function; the excitation circuit is connected to one of the first antennas, so that the first antenna turns on the transmitting function and acts as a transmitting antenna to transmit signals; the first antennas other than the transmitting antenna turn on the receiving function and act as receiving antennas to receive signals. The foreign object detection device for a wireless charging system of the present invention detects foreign objects through a transmitting side detector and a receiving side detector, and the detectors on both sides detect foreign objects through antennas to avoid the danger of foreign objects entering during charging.

Description

Technical Field

[0001] The present invention relates to the field of wireless charging, and in particular to a foreign object detection device for a wireless charging system. Background Art

[0002] If there is a metal foreign body on the power transmitting coil during the wireless charging process, the temperature will rise sharply due to the eddy current effect generated by the magnetic field on the metal foreign body, and there may even be dangers such as fire. There are many designs at present, such as adding a detection coil such as a balance coil, and detecting foreign bodies by measuring the change of parameters such as the impedance of the detection coil. The existing method can detect foreign bodies attached to the surface of the transmitting coil, but foreign bodies in the space, such as bottles with metal caps, objects wrapped in metal, etc., cannot be detected by the above methods. This is still a hidden danger of wireless charging, especially high-power wireless charging such as electric vehicles.

[0003] In addition to metal foreign body detection, wireless charging of electric vehicles also poses the risk of organisms such as infants and pets entering the power transmission area, so it is necessary to increase the function of protecting living things to detect the intrusion of living things. The existing living thing detection is more common by setting up multiple Doppler radars around the transmitting coil. When an organism approaches the transmitting coil, the Doppler effect of the radar wave is used to detect the organism, thereby triggering a shutdown alarm. When the organism leaves, charging is resumed. However, there is a possibility that if an organism enters the power transmission area after the charging system is shut down, the wireless charging system may not be able to detect the entry of the organism and resume power transmission. In this case, there is still the possibility of harm to the health of the organism. Summary of the invention

[0004] The present invention provides a foreign object detection device for a wireless charging system to realize foreign object detection.

[0005] The foreign object detection device of the wireless charging system of the present invention has a transmitting side detector, which is arranged at the transmitting end of the wireless charging system; the transmitting side detector includes: a first antenna set and an excitation circuit connected in sequence; the first antenna set includes multiple first antennas; each of the first antennas has a transmitting function and a receiving function; the excitation circuit is connected to one of the first antennas, so that the first antenna turns on the transmitting function and acts as a transmitting antenna to transmit signals; the first antennas other than the transmitting antenna turn on the receiving function and act as receiving antennas to receive signals.

[0006] Preferably, the foreign object detection device also has a receiving side detector, which includes: a second antenna set, a second signal processing circuit and a second controller connected in sequence; wherein the second antenna set has at least one second antenna, and the second antenna is used to receive the signal transmitted by the transmitting antenna.

[0007] Preferably, the excitation circuit includes a signal generator, a driving circuit and a power amplifier which are connected to each other, wherein the power amplifier is connected to the switching switch.

[0008] Preferably, the transmitting side detector also includes: a first detection circuit and a controller connected to each other; the first detection circuit is connected to the receiving antenna; the first detection circuit has a first amplifier and a first filter connected to each other; the first detection circuit obtains the signal received by the receiving antenna, processes it through the first amplifier and the first filter, and sends it to the controller.

[0009] Preferably, the transmitting side detector also includes: a second detection circuit and a controller connected to each other; the second detection circuit is connected to the receiving antenna; the second detection circuit includes a second filter and a signal measurer connected to each other; the second detection circuit obtains the signal received by the receiving antenna, and sends it to the controller after being processed by the second filter and the signal measurer.

[0010] Preferably, the second signal processing circuit comprises: a receiving signal processor, a receiving amplifier and a receiving filter connected to each other.

[0011] Preferably, the first antenna set is connected to a switching switch, and the switching switch selectively connects at least one of the first antennas to the excitation circuit, so that the at least one first antenna is used as a transmitting antenna to transmit signals; and the other first antennas are used as receiving antennas.

[0012] The foreign object detection device of the wireless charging system of the present invention detects foreign objects through a transmitting side detector and a receiving side detector. The detectors on both sides detect foreign objects through antennas to avoid danger caused by foreign objects entering during charging. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A schematic diagram of a foreign object detection device for a wireless charging system of the present application;

[0014] Figure 2 This is a schematic diagram of the operation of the first antenna set in the foreign object detection device of the wireless charging system of the present application.

[0015] Reference numerals:

[0016] First antenna set 11; switching switch 12; excitation circuit 13; first detection circuit 14; second detection circuit 15; controller 16; second antenna set 21; second signal processing circuit 22; second controller 23; signal generator 131; driving circuit 132; power amplifier 133; first amplifier 141; first filter 142; second filter 151; signal measurer 152; receiving signal processor 221; receiving amplifier 222; receiving filter 223; transmitting antenna 11t; receiving antenna 11r. DETAILED DESCRIPTION

[0017] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be interpreted as limiting the present invention.

[0018] The foreign object detection device of the wireless charging system of the present invention has a transmitting side detector. The transmitting side detector is arranged at the transmitting end of the wireless charging system. The transmitting end includes a power transmitting coil, and the receiving end includes a power receiving coil. During wireless charging, an alternating current of a certain frequency output by a high-frequency driving source is applied to the power transmitting coil to excite and generate an electromagnetic field of the same frequency. The power receiving coil located above the power transmitting coil generates current after inductive coupling to the magnetic field, thereby realizing wireless transmission of electric energy.

[0019] The power transmitting coil includes a transmitting coil winding, a magnetic material, a bottom plate and a housing, and of course also includes a transmitting side detector. Corresponding to the power transmitting coil, when wireless charging is performed, there is also a power receiving coil on the device to be charged, which includes a receiving coil winding, a magnetic material, a bottom plate and a housing, and also includes a receiving side detector.

[0020] The transmitting-side detector comprises: a first antenna set 11 and an excitation circuit 13 connected in sequence.

[0021] The first antenna set 11 includes a plurality of first antennas, each of which has a receiving function and a transmitting function. Generally, when working, each first antenna will turn on the transmitting function in turn to transmit signals, and the remaining first antennas will turn on the receiving function. The specific working principle and the effect of the first antenna turning on the receiving function will be described in detail below. In some embodiments, the transmitting or receiving function of the first antenna can be switched by switching the switch 12.

[0022] During operation, one of the first antennas is generally connected to the excitation circuit 13, so that the first antenna is used as a transmitting antenna 11t to transmit a signal. Each first antenna in the first antenna set 11 has its own code, that is, their structure, function and even size can be the same, but each has its own unique corresponding number for distinction. The "sequential" connection mentioned here does not necessarily mean sequential arrangement, but is carried out in a fixed order to ensure that when the receiving side detector receives the corresponding signal, it can match the pre-known order.

[0023] When working, at least one first antenna is connected to the excitation circuit 13, and acts as a transmitting antenna 11t to transmit a signal. The signal it transmits is generally an electromagnetic wave signal, which is received by other components used for detection to detect foreign objects. The detection components and principles will be explained later. Generally, there is only one first antenna at a time that acts as a transmitting antenna 11t to transmit a signal, but this application does not exclude the possibility that multiple transmitting antennas 11t can work at the same time. As long as the corresponding encoding or detection rules are adjusted when receiving the signal, it can also be used in this application. In some embodiments, the switching switch 12 can control which first antenna is connected to the excitation circuit, and the connected first antenna is used as the transmitting antenna 11t.

[0024] The first antennas are arranged to form an array, the first antenna set is located between the transmitting coil winding and the upper shell thereof, and the entire array of the first antennas covers the surface of the power transmitting coil and other areas requiring foreign body detection.

[0025] The excitation circuit 13 includes a signal generator 131, a driving circuit 132 and a power amplifier 133, which are preferably connected in sequence. Generally, the power amplifier 133 is connected to the first antenna (which serves as the transmitting antenna 11t at this time). When there is a switch 12, the excitation circuit 13 is directly connected to the switch 12.

[0026] The signal generator 131 generates an electromagnetic wave signal of a certain frequency, and loads a code corresponding to a first antenna of the first antenna set into the electromagnetic wave signal through signal modulation, and then amplifies the signal through the power amplifier 133. The power amplifier 133 is connected to the first antenna corresponding to the code, that is, the transmitting antenna 11t, and loads the electromagnetic signal onto the transmitting antenna 11t, and transmits it to the space above the power transmitting coil in the form of continuous or pulsed electromagnetic waves.

[0027] The emitted electromagnetic waves can be received by multiple detection devices. For example, three are exemplified in this article, one is the first detection circuit 14 located at the transmitting side detector; another is the second detection circuit 15 located at the transmitting side detector; and the third is the receiving side detector. They are described in detail below.

[0028] The first detection circuit 14:

[0029] The transmitting side detector also includes: a first detection circuit 14 and a controller 16 connected to each other; the first detection circuit 14 is connected to the receiving antenna 11r (in some embodiments, there is a switch 12, then it is directly connected to the switch 12). Generally, in a preferred embodiment, the receiving antenna 11r and the transmitting antenna 11t are different first antennas. The "different" mentioned here does not mean that the two use first antennas with different structures, but that the first antenna used as the receiving antenna 11r and the first antenna used as the transmitting antenna 11t are not the same first antenna. In combination with the above-mentioned that each first antenna has its own number, the "different" here means that the number of the first antenna used as the receiving antenna 11r is different from the number of the first antenna used as the transmitting antenna 11t. In short, the first antenna can realize the transmitting function or the receiving function in terms of function. In operation, at least one first antenna uses the transmitting function and is used as the transmitting antenna 11t, and the other first antennas use the receiving function and are used as the receiving antenna 11r. In other words, among all the first antennas, some are used as receiving antennas 11r and some are used as transmitting antennas 11t.

[0030] In other words, the transmitting antenna 11t and the receiving antenna 11r are both first antennas, but they play different roles at different times. The transmitting antennas 11t transmit signals in turn, and when one transmitting antenna 11t transmits a signal, the other first antennas act as receiving antennas 11r to receive the signal reflected by the signal transmitted by the transmitting antenna 11t when it encounters an obstacle.

[0031] It should be noted that the above is only a preferred embodiment. In other embodiments, the first antenna used as the transmitting antenna 11t can also be used as a receiving antenna at the same time, that is, the first antenna can start the transmitting and receiving functions at the same time. In this embodiment, at least one first antenna is used as the transmitting antenna 11t, and all first antennas can be used as the receiving antenna 11r at the same time.

[0032] In the first antenna, except for the transmitting antenna 11t, all antennas can be used as receiving antennas 11r. In this way, the transmitting antenna 11t only transmits signals. However, in some embodiments, the first antenna can start the receiving function while turning on the transmitting function. That is, while a transmitting antenna 11t transmits a signal, it can also serve as a receiving antenna 11r to receive the reflected signal. It should be noted that although there is a situation where two functions are turned on at the same time, it is generally not allowed to turn on the transmitting function of multiple first antennas at the same time to avoid signal confusion.

[0033] When the first detection circuit is working, each receiving antenna 11r receives the reflected wave of the electromagnetic signal sent by the transmitting antenna 11t, and sends it to the controller 16 for processing to finally obtain parameters such as frequency and phase.

[0034] The first detection circuit 14 has a first amplifier 141 and a first filter 142 that are connected to each other. The first detection circuit 14 is connected to the receiving antenna 11 r to obtain a signal, which is processed by the first amplifier 141 and the first filter 142 and then sent to the controller 16 .

[0035] like Figure 2 , the transmitting antenna 11t sends out an electrical signal. If there is a foreign object, the electrical signal will be reflected, and the receiving circuit 11r will receive the reflected signal to realize the judgment of the foreign object, especially the judgment of the living thing. The specific judgment method will be described below. Because the position of the foreign object is not fixed, the position and direction of the reflected signal may be different. Therefore, when one transmitting antenna 11t is working, all other first antennas work as receiving antennas 11r. In some embodiments, the transmitting antenna 11t can also realize the function of the receiving antenna 11r at the same time.

[0036] The transmitting antenna 11t and receiving antenna 11r mentioned above are divisions of the first antenna according to different divisions of labor, which does not mean that there are two or different first antennas. Any first antenna can be used as a transmitting antenna 11t and also as a receiving antenna 11r.

[0037] It should be noted that Figure 1 and Figure 2 The first antenna (transmitting antenna 11t, receiving antenna 11r) and the second antenna are schematic diagrams, showing the external structure in two shapes, but all "antennas" in this application are not limited by the drawings and should be set according to actual work needs, such as the common use of planar spiral coils.

[0038] Before wireless charging is started or during wireless charging power transmission, when an active organism enters the detection range, the radio waves (electromagnetic waves) emitted by the transmitting antenna 11t will be reflected, and the frequency of the reflected wave will change with the moving state of the object encountered. If the position of the object encountered by the electromagnetic wave is fixed, the frequency of the reflected wave is equal to the frequency of the transmitted wave; if the object moves in the direction of transmission, the reflected wave will be compressed, that is, the frequency of the reflected wave will increase; conversely, when the object moves away from the transmission direction, the frequency of the reflected wave will decrease accordingly. When the transmitting antenna 11t is working, the remaining first antenna is used as the receiving antenna 11r to receive the reflected wave, and the frequency of the received electromagnetic reflected wave is compared with the frequency of the emitted electromagnetic wave. If the frequency change value exceeds the safety threshold, it can be determined that there is an active object in the protection area of ​​the transmitting coil. When the activity amplitude of the organism is not large or stationary, the frequency of the electromagnetic reflected wave changes little or does not change, but the micro-movement of the chest wall or the heartbeat signal caused by the breathing movement of the organism causes the reflected signal to produce a time-varying phase shift. The communication controller can also detect the organism after extracting the body movement signal that meets the life parameters such as infants from the received electromagnetic reflection signal. When the foreign object detection device detects the presence of a living organism within the working area, it sends the living organism protection abnormality information to the wireless charging system main controller, stops or does not start the wireless charging power transmission and sends an alarm message.

[0039] The second detection circuit 15:

[0040] The transmitting side detector also includes: a second detection circuit 15 and a controller 16 connected to each other; the second detection circuit 15 is connected to the receiving antenna 11r. The second detection circuit 15 includes a second filter 151 and a signal measurer 152 connected to each other; the second detection circuit 15 obtains the signal received by the receiving antenna 11r, and sends it to the controller 16 after being processed by the second filter 151 and the signal measurer 152. The second signal processing circuit 22 includes: a receiving signal processor 221, a receiving amplifier 222 and a receiving filter 223 connected to each other. In terms of the connection with the first antenna, the second detection circuit 15 is the same as the first detection circuit 14, that is, they share the receiving antenna 11r.

[0041] The second detection circuit 15 and the first detection circuit 14 can share the controller 16. Moreover, the receiving antennas 11r used by them are the same, that is, the signal received by the receiving antenna 11r can be received by both detection circuits.

[0042] Metal foreign matter on the surface above or near the power transmitting coil housing can also be equivalent to inductance and resistance, and has equivalent mutual inductance with the nearby transmitting antenna 11t. When the metal foreign matter is close to the transmitting antenna 11t, the equivalent inductance and resistance of the transmitting antenna 11t will change. Therefore, for metal foreign matter close to the power transmitting coil housing, the second detection circuit 15 can be used for detection. The second filter 151 transmits the signal of the transmitting antenna 11t to the signal measuring device 152 after filtering. The signal measuring device 152 detects the change of one or more parameters such as the output impedance of the transmitting antenna, the phase of the electromagnetic wave signal, and the frequency. When the parameter change value exceeds the safety threshold, it can be determined that there is a metal foreign matter on the surface or near the power transmitting coil.

[0043] The receiving side detector is described below. The receiving side detector is independent of the transmitting side detector. Taking an electric car as an example, the receiving side detector is installed on the car, that is, installed on the receiving side of the wireless power. The receiving side detector includes: a second antenna set 21, a second signal processing circuit 22 and a second controller 23 connected in sequence.

[0044] The second antenna set 21 also includes a plurality of second antennas, which can receive signals transmitted by the transmitting antenna 11t. The plurality of second antennas can also form an array.

[0045] The second antenna set 21 can be integrated inside the power receiving coil and above the receiving coil winding, or it can be set outside the power receiving coil and located above the power receiving coil, that is, between the power receiving coil and the power transmitting coil. The receiving range covered by the array composed of the second antenna can be greater than the array range composed of the first antenna. Within the normal offset working range between the power transmitting coil and the power receiving coil, the second antenna set 21 can receive the electromagnetic wave signal emitted by the transmitting antenna 11t.

[0046] The receiving side detector directly receives the electrical signal transmitted by the transmitting antenna 11t by concentrating multiple second antennas through the second antenna. In addition, the second signal processing circuit 22 and the second controller 23 of the receiving side detector implement monitoring and analysis of the processing of the electrical signal. Generally, the second controller 23 can obtain the number of each first antenna in advance. Specifically, it can be obtained by wireless signal transmission, or it can be directly prefabricated.

[0047] The second signal processing circuit of the second antenna set includes a receiving signal processor 221, a receiving amplifier 222 and a receiving filter 223. Preferably, the second antenna of the second antenna set is connected to the receiving amplifier 222, and the electromagnetic signals received by the multiple second antennas are sent to the signal processor 221 for processing to generate an electromagnetic signal, which is amplified after being input to the receiving amplifier 222, and the amplified signal is sent to the receiving filter 223 for filtering to remove clutter, especially the interference signal generated by the coupling of the power transmission magnetic field on the second antenna. The signal output by the receiving filter 223 is sent to the second controller 23 for detection, and the parameters such as signal strength, phase, frequency, etc. are measured, and the code corresponding to the transmitting antenna is demodulated.

[0048] Before wireless charging is started or during the wireless charging power transmission process, the excitation circuit 13 connects to one transmitting antenna 11t at a time to transmit electromagnetic waves, and the circuit of the receiving side detector simultaneously connects to all second antennas, obtains the electromagnetic waves emitted by the transmitting antenna 11t, detects the parameters of the electromagnetic wave signal, and demodulates the corresponding code of the transmitting antenna 11t. The electromagnetic wave signal emitted by the transmitting antenna 11t may be scattered, and it is not certain which second antenna will receive it, so all second antennas are turned on at the same time, and all received signals are superimposed at the receiving end and restored to one signal.

[0049] Each first antenna acts as a transmitting antenna 11t in turn, repeating and looping the above process, so that the signal strength and other parameters of each first antenna when acting as a transmitting antenna 11t can be continuously detected. When there is a metal foreign body above the transmitting coil shell, including the surface or the space between the power transmitting coil and the power receiving coil, the metal will generate eddy currents due to electromagnetic induction, resulting in transmission energy loss, thereby destroying the transmission relationship between the transmitting antenna 11t and the second antenna, and the energy and signal parameters of the electromagnetic wave signal received by the second antenna change. The intensity of the electromagnetic wave emitted by each transmitting antenna 11t received by the second antenna can be calibrated in advance before leaving the factory, and the signal strength value and the corresponding transmitting antenna 11t code have been sent to the communication controller of the receiving end by the communication controller of the transmitting end through wireless communication before the system is started (it can also be transmitted in other ways). When the electromagnetic wave emitted by more than one transmitting antenna 11t received by the second antenna is lower than the calibrated signal strength, and the change in signal strength exceeds the safety threshold, it can be determined that there is a metal foreign body on the surface or in the upper space of the power transmitting coil, and the location of the foreign body can be determined according to the code value of the transmitting antenna 11t. When the second controller 23 determines that a metal foreign body is found, it will send foreign body protection abnormality information to the communication controller of the wireless charging system transmitter, stop or do not start the wireless charging power transmission and send out an alarm message. The specific component that sends the foreign body protection abnormality information can be the controller 23 or an independent communication device, which can be obtained by those skilled in the art.

[0050] In some embodiments of the present invention, the second detection circuit 15 is used in combination with the above-mentioned receiving side detector to further improve the effectiveness of metal foreign body detection. The first detection circuit 14 can also be combined, that is, the three detection methods can exist at the same time.

[0051] The first antenna and the second antenna can be planar antennas. The antennas can be wound by metal wires, or can be made by printing, etching, printing, and metal deposition on a PCB board. For the convenience of explanation, the first antenna and the second antenna are collectively referred to as "antennas". The antennas can include various shapes such as folded lines, rings, sheets, and spirals, but avoid using block metal bodies that produce eddy current effects to reduce the eddy current losses caused by the antenna coupling the power transmission magnetic field during power transmission. The polarization direction of the antenna, that is, the electromagnetic wave is perpendicular to the antenna plane in the maximum radiation direction or the maximum receiving direction, wherein the electromagnetic wave emitted by the first antenna (transmitting antenna 11t) forms two main lobes, one upward and one downward. The downward lobe is absorbed by the magnetic core material inside the power transmitting coil (in some embodiments, the first antenna that does not transmit electromagnetic waves as the transmitting antenna 11t can also be used as a receiving antenna 11r. The upward lobe can be received by other transmitting antennas after encountering foreign objects or reflected by the receiving coil, and can be recorded as the receiving antenna 11r. The details are explained below). When there is a receiving coil above the transmitting coil, the upward lobe can be obtained by the receiving antenna in the receiving coil.

[0052] In summary, the foreign body detection device of the present application can integrate three detection methods at the same time, which can effectively improve the detection efficiency and accuracy.

[0053] The above describes in detail the structure, features and effects of the present invention based on the embodiments shown in the drawings. The above is only a preferred embodiment of the present invention, but the present invention is not limited to the scope of implementation shown in the drawings. Any changes made according to the concept of the present invention, or modifications to equivalent embodiments with equivalent changes, which still do not exceed the spirit covered by the description and drawings, should be within the protection scope of the present invention.

Claims

1. A foreign object detection device for a wireless charging system, characterized in that: The foreign object detection device has a transmitting side detector, and the transmitting side detector is arranged at the transmitting end of the wireless charging system; The transmitting side detector comprises: a first antenna set (11) and an excitation circuit (13) connected in sequence; the first antenna set (11) comprises a plurality of first antennas; each of the first antennas has a transmitting function and a receiving function; The excitation circuit (13) is connected to one of the first antennas, so that the first antenna starts the transmission function and acts as a transmitting antenna (11t) to transmit a signal, wherein the transmitted signal is an electromagnetic wave signal and is transmitted to the space above the power transmitting coil; the first antennas other than the transmitting antenna (11t) start the receiving function and act as receiving antennas (11r) to receive signals; The transmitting side detector further comprises: a first detection circuit (14) and a controller (16) which are connected to each other; The first detection circuit (14) is connected to the receiving antenna (11r); the first detection circuit (14) has a first amplifier (141) and a first filter (142) that are connected to each other; the first detection circuit (14) obtains a signal received by the receiving antenna (11r), processes the signal through the first amplifier (141) and the first filter (142), and sends the signal to the controller (16); The transmitting side detector further comprises: a second detection circuit (15) and a controller (16) which are connected to each other; the second detection circuit (15) is connected to the receiving antenna (11r); the second detection circuit (15) comprises a second filter (151) and a signal measurer (152) which are connected to each other; the second detection circuit (15) obtains a signal received by the receiving antenna (11r), processes the signal through the second filter (151) and the signal measurer (152), and then sends the signal to the controller (16); The second detection circuit (15) and the first detection circuit (14) share a controller (16).

2. The foreign object detection device of the wireless charging system according to claim 1, characterized in that: The foreign object detection device also has a receiving side detector, which includes: a second antenna set (21), a second signal processing circuit (22) and a second controller (23) connected in sequence; wherein the second antenna set (21) has at least one second antenna, and the second antenna is used to receive the signal transmitted by the transmitting antenna (11t).

3. The foreign object detection device of the wireless charging system according to claim 1, characterized in that: The excitation circuit (13) comprises a signal generator (131), a drive circuit (132), and a power amplifier (133) which are connected to each other, wherein the power amplifier (133) is connected to the switching switch (12).

4. The foreign object detection device for a wireless charging system according to claim 2, characterized in that: The second signal processing circuit (22) comprises: a receiving signal processor (221), a receiving amplifier (222) and a receiving filter (223) which are connected to each other.

5. The foreign object detection device of the wireless charging system according to claim 1, characterized in that: The first antenna set is connected to a switch (12), and the switch (12) selectively connects at least one of the first antennas to the excitation circuit (13), so that the at least one of the first antennas serves as a transmitting antenna (11t) to transmit signals; And the other first antenna is used as a receiving antenna (11r).

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