Metal detection device

Abstract

The present application relates to a metal detection device. The device includes: a transmitting coil, a first receiving coil, and a second receiving coil; the transmitting coil is arranged relatively parallel to the first receiving coil and the second receiving coil, the first receiving coil and the second receiving coil are arranged on the same side of the transmitting coil, the electromagnetic fields in the first region and the second region of the first receiving coil and the second receiving coil are in opposite directions, and when no metal is detected, the magnetic field flux in the first region is equal to the magnetic field flux in the second region, the first region is the region overlapping with the projection of the transmitting coil; the second region is the region not overlapping with the projection of the transmitting coil; the first receiving coil and the second receiving coil have the same winding direction, and one end of the first receiving coil is connected to the second receiving coil. Compared with existing metal detection devices, this metal detection device has higher metal detection sensitivity.

Description

Technical Field

[0001] The present application relates to the field of detection technology, and in particular to a metal detection device. Background Art

[0002] With the rapid development of microelectronics and computer technology, traditional metal detection systems are also moving towards newer directions. Metal detection devices are increasingly used in modern society and industrial production, such as travel security, food, counter-terrorism, metallurgy, and pharmaceuticals. The main purpose of metal detection devices is to detect and locate metal objects. They mainly use the principle of electromagnetic induction. A coil passing alternating current generates a rapidly changing magnetic field. This magnetic field can induce eddy currents within the metal object. The eddy currents generate magnetic fields, which in turn affect the original magnetic field and cause the detector to emit a beep.

[0003] Traditional metal detection devices utilize a receiving coil system consisting of two sets of opposing first and second receiving coils. By adjusting parameters such as the relative position and amplification of the first and second receiving coils, when the detection device is in a metal-free environment, the output voltages of the first and second receiving coils are kept as equal as possible but with opposite signs. This results in the total output voltage approaching zero due to the mutual cancellation of the two coil voltages. However, the presence of metal in the detection area alters the electromagnetic field distribution, disrupting the original voltage balance between the two receiving coils, causing the total output voltage to vary from zero and become available for signal processing circuitry to receive, amplify, and analyze. However, when metal objects are present in the detection area, the induced voltages in the two receiving coils also cancel each other out to a considerable degree, reducing the overall sensitivity of the detection device.

[0004] However, existing metal detection devices have the problem of low sensitivity. Summary of the Invention

[0005] Based on this, it is necessary to provide a more sensitive metal detection device to address the above technical problems.

[0006] The present application provides a metal detection device. The device includes: a transmitting coil, a first receiving coil and a second receiving coil;

[0007] The transmitting coil is arranged parallel to the first receiving coil and the second receiving coil. The first receiving coil and the second receiving coil are arranged on the same side of the transmitting coil. The electromagnetic fields in the first region and the second region of the first receiving coil and the second receiving coil are directed in opposite directions. When no metal is detected, the magnetic field flux in the first region is equal to the magnetic field flux in the second region. The first region is an area overlapping with the projection of the transmitting coil; the second region is an area not overlapping with the projection of the transmitting coil.

[0008] The first receiving coil and the second receiving coil have the same winding direction, and one end of the first receiving coil is connected to one end of the second receiving coil.

[0009] In one embodiment, the metal detection device further includes a connecting wire, and one end of the first receiving coil is connected to one end of the second receiving coil via the connecting wire.

[0010] In one embodiment, the metal detection device further includes a power supply, and the transmitting coil is connected to the power supply.

[0011] In one embodiment, the first receiving coil and the second receiving coil are located in the same plane.

[0012] In one embodiment, the first receiving coil and the second receiving coil are equal in size.

[0013] In one embodiment, the first receiving coil and the second receiving coil are two semicircles of equal area, and the area enclosed by the first areas of the first receiving coil and the second receiving coil is equal in size to the transmitting coil.

[0014] In one embodiment, the projection areas of the transmitting coil in the first receiving coil and the second receiving coil are equal.

[0015] In one embodiment, the metal detection device further includes a switch module and a signal analysis circuit, and the other ends of the first receiving coil and the second receiving coil are connected to the signal analysis circuit via the switch module.

[0016] In one embodiment, the signal analysis circuit includes an operational amplifier and a processor connected to each other, and the operational amplifier is connected to the first receiving coil and the second receiving coil respectively.

[0017] In one embodiment, the switch device includes a MOS (metal oxde semiconductor) tube or a transistor.

[0018] In the metal detection device, the transmitting coil is arranged parallel to the first and second receiving coils, and the first and second receiving coils are arranged on the same side of the transmitting coil. The electromagnetic fields in the first and second regions of the first and second receiving coils have opposite directions. When no metal is detected, the magnetic flux in the first region is equal to the magnetic flux in the second region. When no metal is detected, the magnetic flux in the first and second regions cancel each other out. Furthermore, the first and second receiving coils are wound in the same direction and connected at one end. The induced voltages generated in the two coils are superimposed, and the resulting total induced voltage is used as a basis for detecting the presence of metal objects. Compared to existing metal detection devices, the metal detection sensitivity is higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A schematic structural diagram of a metal detection device in one embodiment;

[0020] Figure 2 FIG. 1 is a schematic diagram showing the connection between a receiving coil and a signal analysis circuit in an embodiment. DETAILED DESCRIPTION

[0021] To make the above-mentioned objects, features, and advantages of the present invention more readily apparent, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. The following description sets forth numerous specific details to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0022] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0023] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0024] In the present invention, unless otherwise specified or limited, the terms "installed," "connected," "connect," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection; direct connection, or indirect connection through an intermediate medium; internal communication between two components, or interaction between two components, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0025] In the present invention, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediary. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0026] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be an intermediate element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be an intermediate element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only implementation methods.

[0027] In one embodiment, Figure 1 As shown, a metal detection device is provided, comprising a transmitting coil 100, a first receiving coil 200 and a second receiving coil 300;

[0028] The transmitting coil 100 is arranged parallel to the first receiving coil 200 and the second receiving coil 300. The first receiving coil 200 and the second receiving coil 300 are arranged on the same side of the transmitting coil 100. The electromagnetic fields in the first and second regions of the first receiving coil 200 and the second receiving coil 300 are in opposite directions. When no metal is detected, the magnetic field flux in the first region is equal to the magnetic field flux in the second region. The first region is the region that overlaps with the projection of the transmitting coil 100; the second region is the region that does not overlap with the projection of the transmitting coil 100.

[0029] The first receiving coil 200 and the second receiving coil 300 have the same winding direction, and one end of the first receiving coil 200 is connected to one end of the second receiving coil 300 .

[0030] Among them, the transmitting coil is a coil winding that continuously transmits an alternating electromagnetic field in the metal detection device; the receiving coil is a coil winding in the metal detection device for sensing and receiving the surrounding electromagnetic field (including the alternating electromagnetic field continuously transmitted by the transmitting coil); specifically, the transmitting coil 100 in the metal detection device is arranged relatively parallel to the first receiving coil 200 and the second receiving coil 300, the first receiving coil 200 and the second receiving coil 300 are located directly above the transmitting coil 100 and the first receiving coil 200 and the second receiving coil 300 are arranged on the same side of the transmitting coil 100, the first receiving coil 200 and the second receiving coil 300 are relatively parallel to the transmitting coil 100, and the transmitting coil 100 is relatively parallel to the transmitting coil 100. Part of the projection overlaps with the first receiving coil 200, and part of the projection overlaps with the projection of the second receiving coil 300. The area overlapping with the projection of the first receiving coil 200 or the second receiving coil 300 is the first area. The area that does not overlap with the projection of the transmitting coil 100 is the second area. The electromagnetic field directions in the first area and the second area are opposite. For example, the electromagnetic field direction in the first area is defined as +, and the electromagnetic field direction in the second area is defined as -. Select one of the first receiving coil 200 and the second receiving coil 300 and move it steadily from a position far away from the center of the transmitting coil 100 to a position close to the center. Then, the total electromagnetic field surrounded by the receiving coil is The flux is negative when far from the center of the transmitting coil 100 and positive when close to the center of the transmitting coil 100. The relative positions of the first receiving coil 200 and the transmitting coil 100 are adjusted until the magnetic flux in the first area and the second area cancel each other out. At this time, the total electromagnetic flux enclosed by the first receiving coil 200 is the sum of the magnetic flux in the first area and the second area, which is close to 0. The position of the second receiving coil 300 is then adjusted in the same way so that its total electromagnetic flux is as close to 0 as possible. When no metal is detected, the magnetic field flux in the first area and the magnetic field flux in the second area cancel each other out. At this time, the voltages generated by the first receiving coil 200 and the second receiving coil 300 are in a relatively balanced state. In addition, because the first receiving coil 200 and the second receiving coil 300 are connected at one end and both coils are wound in the same direction (either clockwise or counterclockwise), the total induced voltage output by the two receiving coils is the sum of their induced voltages. The induced voltage formula is E = nΔΦ / Δt, where E is the induced electromotive force (V), n is the number of turns in the induction coil, and ΔΦ / Δt is the rate of change of magnetic flux. For example, if the induced voltage output by the first receiving coil 200 is +0.01V and the induced voltage output by the second receiving coil 300 is +0.01V, the total induced voltage output is +0.02V. This change in the total induced voltage is easier to see than a +0.01V voltage. This enhances the sensitivity of the receiving coils to metal magnetic field induction, eliminates detection blind spots, and significantly improves metal detection accuracy.

[0031] In the above-mentioned metal detection device, the transmitting coil 100 is arranged in parallel with the first receiving coil 200 and the second receiving coil 300, and the first receiving coil 200 and the second receiving coil 300 are arranged on the same side of the transmitting coil 100. The electromagnetic fields in the first area and the second area of ​​the first receiving coil 200 and the second receiving coil 300 are in opposite directions, and when no metal is detected, the magnetic field flux in the first area is equal to the magnetic field flux in the second area. When no metal is detected in the surrounding area, the magnetic flux in the first area and the second area can cancel each other out. At this time, the first receiving coil 200 and the second receiving coil 300 are in a relatively balanced voltage state, and the output induced voltages are both Close to 0, for example, the induced voltage output by the first receiving coil 200 is +0.01, and the induced voltage output by the second receiving coil 300 is +0.01. At the same time, the first receiving coil 200 and the second receiving coil 300 have the same winding direction and are connected at one end to each other. The induced voltage generated in the first receiving coil 200 and the induced voltage generated in the second receiving coil 300 are superimposed, and the change in the total induced voltage is used as a basis for detecting whether a metal object is present. Compared with existing metal detection devices, this device maintains metal detection sensitivity while having a simpler structure, thereby reducing production costs.

[0032] In one embodiment, the metal detection device further includes a connecting wire, and one end of the first receiving coil 200 is connected to one end of the second receiving coil 300 via the connecting wire.

[0033] Specifically, the ends of the first receiving coil 200 and the second receiving coil 300 are connected via a connecting wire to form a complete electrical circuit. Since the connecting wire will also cause some changes in the induced voltage, after the two receiving coils are connected, the semicircular antenna of one receiving coil can be slightly moved closer to or further away from the center of the transmitting coil 100 to make the total output induced voltage closer to zero.

[0034] In this embodiment, one end of the first receiving coil 200 and the second receiving coil 300 are connected via a connecting wire, and the other end is used to output the total induced voltage of the two coils, forming a complete electrical circuit for subsequently transmitting the total induced voltage generated in the first receiving coil 200 or the second receiving coil 300 to the signal analysis circuit.

[0035] In one embodiment, the metal detection device further includes a power supply, and the transmitting coil 100 is connected to the power supply.

[0036] Specifically, the condition for the transmitting coil 100 to generate an alternating electromagnetic field is that it needs to be connected to a circuit that generates an alternating current. Therefore, in the metal detection device of this application, the transmitting coil 100 is connected to a power supply within the metal detection device, thereby connecting to the circuit. When the power is turned on, the transmitting coil 100 will emit a continuous alternating magnetic field.

[0037] In this embodiment, the transmitting coil 100 is connected to an internal power supply to generate an alternating current, thereby emitting a continuous alternating magnetic field. The receiving coil receives the alternating magnetic field emitted by the transmitting coil 100. Within a first region overlapping with the projection of the transmitting coil 100, the first receiving coil 200 outputs an induced voltage E1 after receiving the alternating magnetic field emitted by the transmitting coil 100. The second receiving coil 300 also outputs an induced voltage E2 after receiving the alternating magnetic field emitted by the transmitting coil 100. Because the first receiving coil 200 and the second receiving coil 300 have the same winding direction, the induced voltage E1 output by the first receiving coil 200 and the induced voltage E2 output by the second receiving coil 300 have the same sign. The total induced voltage output by the receiving coils is the sum of the two induced voltages, i.e., E=E1+E2. The total induced voltage of the two coils is used as a basis for detecting the presence of metal.

[0038] In one embodiment, the first receiving coil 200 and the second receiving coil 300 are located in the same plane.

[0039] Specifically, the first receiving coil 200 and the second receiving coil 300 are located in the same plane. The first receiving coil 200 and the second receiving coil 300 together constitute a receiving coil system. The transmitting coil 100 is evenly projected into the receiving coil system to avoid a large difference in the magnetic flux received by the two receiving coils due to the inconsistent distance between the transmitting coil 100 and the first receiving coil 200 and the second receiving coil 300, thereby causing a large difference in the obtained induced voltage, which affects the accuracy and precision of metal detection. The total induced voltage output by the receiving coil system is the sum of the induced voltages generated by the first receiving coil 200 and the second receiving coil 300. Since the first receiving coil 200 and the second receiving coil 300 have the same winding direction, the total induced voltage is obtained by superimposing the induced voltages generated by the two coils. When the presence of metal is detected in the surrounding area, the change in the total induced voltage is used as the basis for detecting whether there is metal in the surrounding area. If the change in the total induced voltage is too large, it can be determined that there is metal in the surrounding area.

[0040] In this embodiment, the first receiving coil 200 and the second receiving coil 300 are located in the same plane, which can effectively avoid the inconsistent distances between the transmitting coil 100 and the first receiving coil 200 and the second receiving coil 300, resulting in an excessively large difference in the magnetic flux received by the two receiving coils, thereby causing an excessively large difference in the obtained induced voltages, thereby reducing errors and improving the accuracy and precision of metal detection.

[0041] In one embodiment, the first receiving coil 200 and the second receiving coil 300 are equal in size.

[0042] Specifically, the first receiving coil 200 and the second receiving coil 300 are of equal size, the transmitting coil 100 is evenly projected between the first receiving coil 200 and the second receiving coil 300200, the two coils sense and receive the alternating magnetic field of the transmitting coil 100 in the same range, and the magnetic flux enclosed by the two coils is approximately equal.

[0043] In this embodiment, the first receiving coil 200 and the second receiving coil 300 are of equal size, ensuring that the two coils sense and receive the alternating magnetic field of the transmitting coil 100 in the same range. This ensures that the magnetic flux enclosed by the two coils is approximately equal, resulting in a minimal difference in the induced voltages. This prevents interference with metal detection due to a large difference in the induced voltages, thereby affecting the accuracy and precision of metal detection.

[0044] In one embodiment, the first receiving coil 200 and the second receiving coil 300 are two semicircles of equal area, and the area enclosed by the first areas of the first receiving coil 200 and the second receiving coil 300 is equal in size to the transmitting coil 100 .

[0045] Specifically, the first receiving coil 200 and the second receiving coil 300 have equal areas and are both semicircular in shape, and are symmetrically distributed. This facilitates the mutual cancellation of the positive and negative magnetic fluxes in the first and second regions of the first receiving coil 200 and the second receiving coil 300, so that the output induced voltage is close to zero. At the same time, the area enclosed by the first regions of the first receiving coil 200 and the second receiving coil 300 is equal in size to the transmitting coil 100. That is, the collective area of ​​the overlapping portions of the projections of the transmitting coil 100 and the two receiving coils is equal in size to the transmitting coil 100. The first receiving coil 200 and the second receiving coil 300 divide the transmitting coil 100 100 into two equal parts, so that half of the transmitting coil 100 is projected into the first receiving coil 200, and the other half is projected into the second receiving coil 300.

[0046] In this embodiment, the first receiving coil 200 and the second receiving coil 300 are two semicircles of equal area. The alternating magnetic field received by the two semicircles has the same range and encloses substantially the same magnetic flux. This ensures that the difference in induced voltages generated by the two coils is minimal, thereby avoiding interference with metal detection due to excessively large differences in induced voltages, thereby affecting the accuracy and precision of metal detection.

[0047] In one embodiment, the projected areas of the transmitting coil 100 in the first receiving coil 200 and the second receiving coil 300 are equal.

[0048] Specifically, half of the transmitting coil 100 is projected onto the first receiving coil 200 , and the other half is projected onto the second receiving coil 300 , forming two equal projected areas. The alternating magnetic field in the transmitting coil 100 is evenly distributed around the first and second receiving coils 300 .

[0049] In this embodiment, the transmitting coil 100 is evenly projected onto the first receiving coil 200 and the second receiving coil 300, forming equal projected areas. This ensures that the magnetic fluxes enclosed by the first receiving coil 200 and the second receiving coil 300 are substantially consistent, thereby ensuring a small difference in the induced voltages output by the two coils. This prevents interference with metal detection due to an excessively large difference in the induced voltages, thereby affecting the accuracy and precision of metal detection.

[0050] In one embodiment, Figure 2 As shown, the metal detection device further includes a switch module and a signal analysis circuit. The other ends of the first receiving coil 200 and the second receiving coil 300 are connected to the signal analysis circuit via the switch module.

[0051] Among them, the signal analysis circuit refers to a circuit that can receive, amplify and analyze metal signals; specifically, the first receiving coil 200 and the second receiving coil 300 each output an induced voltage, outputting a total induced voltage. The other ends of the first receiving coil 200 and the second receiving coil 300 are connected to the signal analysis circuit 400 through a switch module. The total induced voltage obtained is received, amplified and analyzed by the signal analysis circuit to obtain the final metal detection result.

[0052] In this embodiment, the two receiving coils are connected to the signal analysis circuit through a switch module, and the change in the total induced voltage is used as the basis for judging whether there is metal around. After the signal analysis circuit receives, amplifies and analyzes the metal signals of the two coils, accurate metal detection results can be obtained.

[0053] In one embodiment, Figure 2 As shown, the signal analysis circuit includes an operational amplifier and a processor connected to each other, and the operational amplifier is connected to the first receiving coil 200 and the second receiving coil 300 respectively.

[0054] Among them, the operational amplifier is a special integrated circuit that can perform various functions or operations (such as amplification, addition and subtraction); specifically, in order for the signal analysis circuit to realize the functions of receiving, amplifying and analyzing metal signals, it needs to include an operational amplifier and a signal processor. The operational amplifier is connected to the first receiving coil 200 and the second receiving coil 300 respectively. The total induced voltage output by the first receiving coil 200 and the second receiving coil 300 is first amplified by the operational amplifier 401, so that it can be analyzed by the subsequent processor 402 to obtain accurate metal detection results.

[0055] In this embodiment, an operational amplifier is connected to the first receiving coil 200 and the second receiving coil 300 respectively. After the total induced voltage output by the two receiving coils is amplified by the operational amplifier, it is convenient for the processor to analyze and obtain accurate metal detection results.

[0056] In one embodiment, the switch device is a MOS transistor or a triode.

[0057] Specifically, the switch device includes a MOS tube or a triode. Both the triode and the MOS tube are very commonly used electronic components. Both can be used as electronic switch tubes, and in many occasions the two can be used interchangeably.

[0058] In order to better illustrate this technical solution, a complete description of the implementation process and technical principles of the entire solution is given.

[0059] The metal detection device includes a transmitting coil 100, a first receiving coil 200, and a second receiving coil 300. The transmitting coil 100 is arranged parallel to the first receiving coil 200 and the second receiving coil 300. The first receiving coil 200 and the second receiving coil 300 are located on the same side and in the same plane. The two receiving coils are equal in size and are two semicircles of equal area. The transmitting coil 100 is connected to a power supply inside the metal detection device and emits a continuous alternating magnetic field, which is evenly projected on the first receiving coil 200 and the second receiving coil 300. The portion of the two receiving coils that overlaps with the projection of the transmitting coil 100 is a first area, and the portion that does not overlap with the projection of the transmitting coil 100 is a second area. The transmitting coil 100 is located between the first receiving coil 200 and the second receiving coil 300. 0 is equal to the projected area of ​​the second receiving coil 300. The electromagnetic fields in the first and second regions are in opposite directions. The magnetic flux in the first region can be defined as +, and the magnetic flux in the second region can be defined as -. In both receiving coils, there is an intermediate position where the magnetic flux in the first region and the magnetic flux in the second region cancel each other out. At this time, the magnetic flux enclosed by the two receiving coils is the sum of the magnetic flux in the first region and the magnetic flux in the second region. The induced voltage generated by the magnetic flux is close to 0 and within a preset range, which is used as a critical condition for determining that there is no metal in the surrounding area. At the same time, one end of the first receiving coil 200 and the second receiving coil 300 are connected by a wire, and the other end is connected to the signal analysis circuit through a switch module to form a complete electrical circuit. Because the first receiving coil 200 and the second receiving coil 300 are wound in the same direction, the induced voltages generated by the two receiving coils in response to the magnetic flux they enclose are directed in the same direction. The total induced voltage output is the sum of the induced voltages generated by the two receiving coils. For example, if the induced voltage generated by the first receiving coil 200 is +0.01V, the induced voltage generated by the second receiving coil 300 is also +0.01V, resulting in a total induced voltage of +0.02V. The signal analysis circuit then receives the output induced voltage, amplifies it by an operational amplifier, and then analyzes it through a processor. Based on the change in the total induced voltage, the presence of metal is determined. If the total induced voltage exceeds a preset range, metal is determined to be present.

[0060] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0061] The above embodiments merely illustrate several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art may make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims.

Claims

1. A metal detection device, characterized in that: comprising a transmitting coil, a first receiving coil and a second receiving coil; The transmitting coil is arranged parallel to the first receiving coil and the second receiving coil. The first receiving coil and the second receiving coil are arranged on the same side of the transmitting coil. The electromagnetic fields in a first region and a second region of the first receiving coil and the second receiving coil are in opposite directions. When no metal is detected, the magnetic field flux in the first region is equal to the magnetic field flux in the second region. The first region is an area overlapping with the projection of the transmitting coil; the second region is an area not overlapping with the projection of the transmitting coil. The first receiving coil and the second receiving coil have the same winding direction and are connected to one end of the second receiving coil; the first receiving coil and the second receiving coil are two semicircles of equal area, and the area enclosed by the first area of ​​the first receiving coil and the second receiving coil is equal in size to the transmitting coil; The metal detection device further includes a connecting wire, and one end of the first receiving coil is connected to one end of the second receiving coil via the connecting wire.

2. The metal detection device according to claim 1, characterized in that: A power supply is also included, and the transmitting coil is connected to the power supply.

3. The metal detection device according to claim 1, characterized in that: The first receiving coil and the second receiving coil are located in the same plane.

4. The metal detection device according to claim 1, characterized in that: The first receiving coil and the second receiving coil are equal in size.

5. The metal detection device according to claim 1, characterized in that: The projected areas of the transmitting coil in the first receiving coil and the second receiving coil are equal.

6. The metal detection device according to claim 1, characterized in that: It also includes a switch module and a signal analysis circuit; The other ends of the first receiving coil and the second receiving coil are connected to the signal analysis circuit through the switch module.

7. The metal detection device according to claim 6, characterized in that: The signal analysis circuit includes an operational amplifier and a processor connected to each other, and the operational amplifier is connected to the first receiving coil and the second receiving coil respectively.

8. The metal detection device according to claim 6 or 7, characterized in that: The switch module includes a MOS tube or a triode.

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