Metal foreign matter detection system

Abstract

The utility model relates to a metal foreign matter detection system. The metal foreign matter detection system comprises an excitation module, a sensing module and a detection module, wherein the excitation module comprises an excitation coil and a magnetic core, the excitation coil is wound on the magnetic core, and the excitation module is used for providing an alternating magnetic field; the sensing module comprises a differential coil and a movable iron core, the differential coil is wound on the magnetic core, the iron core is arranged in a balance area of the alternating magnetic field, and the differential coil is used for inducing the alternating magnetic field and generating induced electromotive force; the detection module is connected with the sensing module and used for detecting the induced electromotive force signal output by the sensing module, and when the detection module detects that the variation amplitude of the induced electromotive force signal exceeds a preset threshold value, it is judged that the metal foreign matter exists on the surface of the detected object. The problems of material detection limitation, low small particle detection rate and false detection existing in metal foreign matter detection are solved.

Description

Technical Field

[0001] This application relates to the field of metal foreign object detection, and in particular to a metal foreign object detection system. Background Technology

[0002] In lithium battery manufacturing, the entry of metallic foreign objects into the battery can cause significant damage. For example, when a metallic foreign object is located between the electrode core surface and the MYLAR film, it may puncture the MYLAR film, leading to a short circuit between the negative electrode and the aluminum casing. Alternatively, when a metallic foreign object is located between the electrodes, it will first oxidize at the positive electrode during battery formation and then be reduced at the negative electrode. As the metallic element accumulates at the negative electrode, it may form dendrites, puncturing the separator and causing an internal short circuit, leading to increased self-discharge rate, and in severe cases, potentially causing fire or explosion. Currently commonly used methods for detecting metallic foreign objects include:

[0003] (1) Adding a magnet to the surface of the electrode or electrode core to attract magnetic materials, but it is impossible to detect non-magnetic materials;

[0004] (2) The HIPOT test is used to detect the conduction caused by foreign objects piercing the diaphragm or MYLAR membrane, but the detection rate is greatly affected by particle size, pressure and location.

[0005] (3) Implementing X-ray 100% inspection can detect metallic foreign objects, but the detection rate of particles smaller than 300μm is limited, and relying on image judgment is prone to false detection (over-detection or under-detection).

[0006] Currently, there is no effective solution to the problems of material detection limitations, low detection rate of small particles, and false detection in the detection of metal foreign objects. Utility Model Content

[0007] Therefore, it is necessary to provide a metal foreign object detection system that can overcome the limitations of material detection, improve the detection rate of small particles, and reduce the false detection rate, addressing the aforementioned technical problems. This system includes: an excitation module, a sensing module, and a detection module; wherein...

[0008] The excitation module includes an excitation coil and a magnetic core, the excitation coil being wound around the magnetic core, and the excitation module being used to provide an alternating magnetic field.

[0009] The sensing module includes a differential coil and a movable iron core. The differential coil is wound around the magnetic core, and the iron core is located in the equilibrium region of the alternating magnetic field. The differential coil is used to sense the alternating magnetic field and generate an induced electromotive force.

[0010] The detection module is connected to the sensing module. The detection module is used to detect the induced electromotive force signal output by the sensing module. When the detection module detects that the change amplitude of the induced electromotive force signal exceeds a preset threshold, it determines that there is a metallic foreign object on the surface of the object being detected.

[0011] In some embodiments, the magnetic core includes a first magnetic core and a second magnetic core, which are disposed opposite to each other, and the excitation coil is wound around the first magnetic core and the second magnetic core.

[0012] In some embodiments, the differential coil includes a first detection coil and a second detection coil, which are wound symmetrically, wherein the first detection coil is wound on the first magnetic core and the second detection coil is wound on the second magnetic core.

[0013] In some embodiments, the initial position of the iron core is located in the equilibrium region of the alternating magnetic field between the first detection coil and the second detection coil.

[0014] In some embodiments, the detection module includes a signal processing unit and an oscilloscope. The signal processing unit is connected to the oscilloscope and is used to process the induced electromotive force signal and output it to the oscilloscope. The oscilloscope is used to display the waveform of the induced electromotive force signal.

[0015] In some embodiments, the signal processing unit includes a preamplifier, a filter, and a lock-in amplifier connected in sequence; wherein,

[0016] The preamplifier is used to amplify the induced electromotive force signal and input the amplified induced electromotive force signal to the filter.

[0017] The filter is used to filter the amplified induced electromotive force signal and input the filtered induced electromotive force signal to the lock-in amplifier;

[0018] The lock-in amplifier is used to extract the phase angle of the filtered induced electromotive force signal.

[0019] In some embodiments, the oscilloscope is provided with a target area, and when the amplitude of the change in the induced electromotive force signal exceeds the preset threshold, the waveform of the induced electromotive force signal exceeds the target area.

[0020] In some embodiments, the detection module further includes an array of probes, and the detection module is connected to the sensing module through the array of probes.

[0021] In some embodiments, the system further includes a signal generation module connected to the excitation module, the signal generation module being used to output an excitation signal, the frequency of which is determined based on the defect burial depth of the object being detected.

[0022] In some embodiments, the system further includes a shield disposed on the outside of the magnetic core.

[0023] The aforementioned metal foreign object detection system generates an alternating magnetic field by applying an excitation signal to the excitation module; it generates an induced electromotive force based on the sensing module sensing the alternating magnetic field; and it detects the induced electromotive force signal output by the sensing module based on the detection module. When the detection module detects that the change amplitude of the induced electromotive force signal exceeds a preset threshold, it determines that there is a metal foreign object on the surface of the object being detected. This overcomes the limitations of material detection, improves the detection rate of small particles, and reduces the false detection rate. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the architecture of a metal foreign object detection system in one embodiment;

[0025] Figure 2 This is a schematic diagram of the structure of a metal foreign object detection system in one embodiment;

[0026] Figure 3 This is a schematic diagram of the detection module in one embodiment;

[0027] Figure 4 This is a schematic diagram of the oscilloscope interface in one embodiment;

[0028] Figure 5 This is a schematic diagram of the oscilloscope interface in one embodiment;

[0029] Figure 6 This is a schematic diagram of the metal foreign object detection system in another embodiment;

[0030] Figure 7 This is a flowchart of a method for detecting metallic foreign objects in one embodiment.

[0031] Figure label:

[0032] 1. Excitation module; 11. Excitation coil; 12. First magnetic core; 13. Second magnetic core;

[0033] 2. Sensing module; 21. Iron core; 22. First detection coil; 23. Second detection coil;

[0034] 3. Detection module; 31. Signal processing unit; 311. Preamplifier; 312. Filter; 313. Lock-in amplifier; 32. Oscilloscope;

[0035] 4. Signal generating module; 5. Shielding enclosure;

[0036] M, the object being detected; N, a metallic foreign object; F, an alternating magnetic field; S, an induced electromotive force signal; P, the target area. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this application clearer, the application is described and illustrated below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application. Furthermore, it is understood that although the efforts made in such a development process may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, modifications to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0038] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application may be combined with other embodiments without conflict.

[0039] Unless otherwise defined, the technical or scientific terms used in this application shall have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms “a,” “an,” “an,” “the,” and similar words used in this application do not indicate quantity limitation and may indicate singular or plural. The terms “comprising,” “including,” “having,” and any variations thereof used in this application are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or device that includes a series of steps or modules (units) is not limited to the listed steps or units, but may also include steps or units not listed, or may include other steps or units inherent to these processes, methods, products, or devices. The terms “connected,” “linked,” “coupled,” and similar words used in this application are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. “Multiple” used in this application means two or more. “And / or” describes the relationship between related objects, indicating that three relationships may exist; for example, “A and / or B” can represent: A alone, A and B simultaneously, and B alone. The terms “first,” “second,” “third,” etc., used in this application are merely to distinguish similar objects and do not represent a specific ordering of the objects.

[0040] In one embodiment, Figure 1 A schematic diagram of a metal foreign object detection system is provided. The system includes an excitation module 1, a sensing module 2, and a detection module 3. The excitation module 1 provides an alternating magnetic field. The sensing module 2 senses the alternating magnetic field and generates an induced electromotive force (EMF). The detection module 3 is connected to the sensing module 2 and detects the induced EMF signal output by the sensing module 2. When the detection module 1 detects a change in the induced EMF signal exceeding a preset threshold, it determines that a metal foreign object exists on the surface of the object being detected.

[0041] Figure 2 A schematic diagram of the structure of the metal foreign object detection system is provided, such as... Figure 2 As shown:

[0042] The excitation module 1 includes an excitation coil 11 and a magnetic core, with the excitation coil 11 wound around the magnetic core. Specifically, the magnetic core includes a first magnetic core 12 and a second magnetic core 13, which are arranged opposite to each other, and the excitation coil 11 is wound around the first magnetic core 12 and the second magnetic core 13.

[0043] The sensing module 2 includes a differential coil and a movable iron core 21. The differential coil is wound around the magnetic core, and the iron core 21 is positioned in the equilibrium region of the alternating magnetic field F. The differential coil is used to sense the alternating magnetic field F and generate an induced electromotive force. Specifically, the differential coil includes a first detection coil 22 and a second detection coil 23, which are symmetrically wound. The first detection coil 22 is wound around the first magnetic core 12, and the second detection coil 23 is wound around the second magnetic core 13. The initial position of the iron core 21 is located in the equilibrium region of the alternating magnetic field F between the first detection coil 22 and the second detection coil 23.

[0044] The detection module 3 is connected to the sensing module 2. The detection module 3 is used to detect the induced electromotive force signal output by the sensing module 2. When the detection module 3 detects that the change amplitude of the induced electromotive force signal exceeds the preset threshold, it determines that there is a metal foreign object N on the surface of the object M.

[0045] When a conductor is placed in an alternating magnetic field, an induced current, or eddy current, will exist within it. Variations in various factors of the conductor itself (such as conductivity, permeability, shape, size, and defects) will cause variations in the eddy currents. For metallic foreign objects, the passage of alternating current will generate a changing magnetic field. When passing through the metallic material, it forms a closed loop, creating an alternating electric field. This alternating electric field, in turn, generates a magnetic field, leading to changes in magnetic flux and resulting in differences in electromotive force. By capturing this change with an oscilloscope, metallic foreign objects can be identified.

[0046] In this embodiment, an alternating magnetic field F is generated by applying an excitation signal (e.g., sinusoidal alternating current, with a voltage range of 0~6VPP or 6~10VPP) to the excitation module 1. The sensing module 2 senses the alternating magnetic field F and generates an induced electromotive force (EMF). The detection module 3 detects the induced EMF signal output by the sensing module 2 and determines whether a metallic foreign object N is present based on the induced EMF signal. The alternating magnetic field F acts on the detection object M, causing eddy currents to be generated in the detection object M, generating a reverse magnetic field disturbance that interferes with the distribution of the original alternating magnetic field. At this time, the induced EMF of the differential coil will fluctuate.

[0047] If there is no metallic foreign object N on the surface of the object M being tested, the reverse magnetic field disturbance is small, and the induced electromotive force will only fluctuate slightly. If there is a metallic foreign object N on the surface of the object M being tested, the reverse magnetic field disturbance is large, causing the iron core 21 to deviate from the equilibrium region, thereby amplifying the fluctuation phenomenon of the induced electromotive force and causing it to fluctuate violently. When the detection module 3 detects that the change amplitude of the induced electromotive force signal exceeds a preset threshold, it determines that there is a metallic foreign object N on the surface of the object M being tested. The object being tested can be a battery cell, and the surface of the battery cell can be coated with a 0.5mm thick plastic film.

[0048] The metal foreign object detection system of this embodiment, employing the electromagnetic eddy current detection principle, is applicable to both conductive and magnetic materials, overcoming limitations in material detection. This system supports non-contact detection, does not damage the cell's external dimensions, and can detect depths from 0.5 to 1 mm. Electromagnetic eddy current detection is insensitive to the size of metal foreign objects, thus not being limited by their dimensions, and can detect particles smaller than 300 μm, which helps protect the mylar membrane, separator, or electrode from puncture. The differential coil design reduces the impact of lift-off and edge effects, minimizing over- and under-detection. Compared to HIPOT pressure testing and X-ray dismantling of scrapped NG cells, electromagnetic eddy current detection is performed before casing; if there is no surface damage, the cells can be released normally, reducing waste. X-ray detection involves radiation and requires a lead-lined enclosure, while electromagnetic eddy current detection is radiation-free and offers high safety.

[0049] In some embodiments, Figure 3 A structural diagram of the detection module is provided, such as... Figure 3 As shown, the detection module 3 includes a signal processing unit 31 and an oscilloscope 32. The signal processing unit 31 is connected to the oscilloscope 32. The signal processing unit 31 processes the induced electromotive force signal and outputs it to the oscilloscope 32. The oscilloscope 32 is used to display the waveform of the induced electromotive force signal.

[0050] The signal processing unit 31 includes a preamplifier 311, a filter 312, and a lock-in amplifier 313 connected in sequence. The preamplifier 311 amplifies the induced electromotive force signal and inputs the amplified induced electromotive force signal to the filter 312. The filter 312 filters the amplified induced electromotive force signal and inputs the filtered induced electromotive force signal to the lock-in amplifier 313. The lock-in amplifier 313 extracts the phase angle of the filtered induced electromotive force signal.

[0051] For the preamplifier 311, the gain will affect the sensitivity of eddy current detection. When adjusting the gain of the preamplifier 311, if the gain is too large, the interference signal will be enhanced, which may easily lead to false defect detection; if the gain is too small, the sensitivity will be insufficient, and defects may be missed. Therefore, the phase angle of the defect signal can be clearly distinguished from the lift-off and edge interference signals by adjusting the X / Y direction gain ratio.

[0052] For filter 312, by properly configuring low-pass, high-pass, and band-pass filters, interference signals can be effectively suppressed and the signal-to-noise ratio improved.

[0053] For the lock-in amplifier 313, the phase angle is adjusted at the defect-free position to move the lifting line horizontally to the left, so as to separate the defect signal from the interference signal as much as possible.

[0054] Figure 4 This is a schematic diagram of an oscilloscope interface. Figure 5 The second diagram shows the interface of an oscilloscope. Figure 4 and Figure 5 As shown, the oscilloscope 32 has a target region P. Figure 4 As shown, when there are no metallic foreign objects on the surface of the object being detected, the amplitude of the change in the induced electromotive force signal S does not exceed the preset threshold, and the waveform of the induced electromotive force signal S is within the target area P. Figure 5 As shown, when a metallic foreign object is present on the surface of the object being detected, the amplitude of the induced electromotive force (EMF) signal S exceeds a preset threshold, and the waveform of the induced EMF signal S extends beyond the target area P. Therefore, the presence of a metallic foreign object can be determined based on the relative positional relationship between the waveform of the induced EMF signal S and the target area P. If the waveform of the induced EMF signal S is within the target area P, it is determined that no metallic foreign object exists; if the waveform of the induced EMF signal S extends beyond the target area P, it is determined that a metallic foreign object exists.

[0055] In some embodiments, Figure 6 Another metal foreign object detection system is provided, in Figures 1 to 5 In addition to the above, the system also includes a signal generation module 4, which is connected to the excitation module 1 and is used to output an excitation signal. The signal generation module 4 is connected to the excitation coil 11 via a probe, and the frequency of the excitation signal (referred to as the detection frequency) is determined based on the defect burial depth of the detection object M.

[0056] Specifically, the detection frequency and the defect burial depth of the detection object M satisfy the following calculation formula:

[0057]

[0058] Where δ represents the skin depth, π represents pi, σ represents electrical conductivity, μ represents magnetic permeability, and f represents the detection frequency. This setting ensures that the effective penetration depth of the eddy current is greater than the burial depth of the defect.

[0059] In some embodiments, under the same conditions, a higher frequency of the excitation signal results in higher detection sensitivity. The frequency of the excitation signal can be selected by combining the performance of the signal processing unit 31 and the probe. Furthermore, the detection objective and material characteristics can be considered, ultimately determining a suitable detection frequency through a trade-off. For example, the detection frequency can be selected based on the size of the weld slag particles and the detection rate sensitivity, thereby ultimately deciding whether to use a low-pass, band-pass, or high-pass mode.

[0060] Continue to refer to Figure 6 In some embodiments, the system further includes a shield 5 disposed on the outside of the magnetic core. Specifically, the shield 5 isolates the first magnetic core 12 and the second magnetic core 13 from the external environment.

[0061] It is understandable that the detection module 3 is connected to the differential coil through its own probe, and the signal generation module 4 is connected to the excitation coil through its own probe. The shield 5 can reduce the interference of the alternating magnetic field on the signal detection of the detection module 3 and the signal output of the signal generation module 4, thus achieving magnetic shielding.

[0062] To improve detection efficiency, detection module 3 can employ an array probe. Detection module 3 is connected to sensing module 2 via the array probe, enabling a single inspection width of up to 64mm and a scanning speed of 1m / s. This embodiment uses an array probe and differential coil induction, which can reduce noise factors caused by height changes, dimensions, and edge effects, thus minimizing their impact on detection results.

[0063] In one embodiment, based on the same inventive concept as the aforementioned metal foreign object detection system... Figure 7 A flowchart of a method for detecting metal foreign objects is also provided, applicable to the metal foreign object detection system of any of the above embodiments. The process includes the following steps:

[0064] Step S101: Apply an excitation signal to excitation module 1 to generate an alternating magnetic field;

[0065] Step S102: Based on the alternating magnetic field sensed by the sensing module 2, an induced electromotive force is generated;

[0066] Step S103: Based on the induced electromotive force signal output by the detection module 3 and the sensing module, when the detection module 3 detects that the change amplitude of the induced electromotive force signal exceeds a preset threshold, it is determined that there is a metal foreign object N on the surface of the detection object M.

[0067] When a conductor is placed in an alternating magnetic field, an induced current, or eddy current, will exist within it. Variations in various factors of the conductor itself (such as conductivity, permeability, shape, size, and defects) will cause variations in the eddy currents. For metallic foreign objects, the passage of alternating current will generate a changing magnetic field. When passing through the metallic material, it forms a closed loop, creating an alternating electric field. This alternating electric field, in turn, generates a magnetic field, leading to changes in magnetic flux and resulting in differences in electromotive force. By capturing this change with an oscilloscope, metallic foreign objects can be identified.

[0068] In this embodiment, an alternating magnetic field F is generated by applying an excitation signal (e.g., sinusoidal alternating current, with a voltage range of 0~6VPP or 6~10VPP) to the excitation module 1. The sensing module 2 senses the alternating magnetic field F and generates an induced electromotive force (EMF). The detection module 3 detects the induced EMF signal output by the sensing module 2 and determines whether a metallic foreign object N is present based on the induced EMF signal. The alternating magnetic field F acts on the detection object M, causing eddy currents to be generated in the detection object M, generating a reverse magnetic field disturbance that interferes with the distribution of the original alternating magnetic field. At this time, the induced EMF of the differential coil will fluctuate.

[0069] If there is no metallic foreign object N on the surface of the object M being tested, the reverse magnetic field disturbance is small, and the induced electromotive force will only fluctuate slightly. If there is a metallic foreign object N on the surface of the object M being tested, the reverse magnetic field disturbance is large, causing the iron core 21 to deviate from the equilibrium region, thereby amplifying the fluctuation phenomenon of the induced electromotive force and causing it to fluctuate violently. When the detection module 3 detects that the change amplitude of the induced electromotive force signal exceeds a preset threshold, it determines that there is a metallic foreign object N on the surface of the object M being tested. The object being tested can be a battery cell, and the surface of the battery cell can be coated with a 0.5mm thick plastic film.

[0070] The metal foreign object detection system of this embodiment, employing the electromagnetic eddy current detection principle, is applicable to both conductive and magnetic materials, overcoming limitations in material detection. This system supports non-contact detection, does not damage the cell's external dimensions, and can detect depths from 0.5 to 1 mm. Electromagnetic eddy current detection is insensitive to the size of metal foreign objects, thus not being limited by their dimensions, and can detect particles smaller than 300 μm, which helps protect the mylar membrane, separator, or electrode from puncture. The differential coil design reduces the impact of lift-off and edge effects, minimizing over- and under-detection. Compared to HIPOT pressure testing and X-ray dismantling of scrapped NG cells, electromagnetic eddy current detection is performed before casing; if there is no surface damage, the cells can be released normally, reducing waste. X-ray detection involves radiation and requires a lead-lined enclosure, while electromagnetic eddy current detection is radiation-free and offers high safety.

[0071] This embodiment overcomes the limitations of material detection, improves the detection rate of small particles, and reduces the false detection rate. The metal foreign object detection system can be referred to the description in the above embodiment, and will not be repeated here.

[0072] The technical features of the above embodiments can be combined in any way. For the sake of brevity, 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.

[0073] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A metal foreign object detection system, characterized in that, include: The module consists of an excitation module, a sensing module, and a detection module; among which, The excitation module includes an excitation coil and a magnetic core, the excitation coil being wound around the magnetic core, and the excitation module being used to provide an alternating magnetic field. The sensing module includes a differential coil and a movable iron core. The differential coil is wound around the magnetic core, and the iron core is located in the equilibrium region of the alternating magnetic field. The differential coil is used to sense the alternating magnetic field and generate an induced electromotive force. The detection module is connected to the sensing module. The detection module is used to detect the induced electromotive force signal output by the sensing module. When the detection module detects that the change amplitude of the induced electromotive force signal exceeds a preset threshold, it determines that there is a metallic foreign object on the surface of the object being detected.

2. The metal foreign object detection system according to claim 1, characterized in that, The magnetic core includes a first magnetic core and a second magnetic core, which are arranged opposite to each other, and the excitation coil is wound around the first magnetic core and the second magnetic core.

3. The metal foreign object detection system according to claim 2, characterized in that, The differential coil includes a first detection coil and a second detection coil, which are wound symmetrically. The first detection coil is wound on the first magnetic core, and the second detection coil is wound on the second magnetic core.

4. The metal foreign object detection system according to claim 3, characterized in that, The initial position of the iron core is located in the equilibrium region of the alternating magnetic field between the first detection coil and the second detection coil.

5. The metal foreign object detection system according to claim 1, characterized in that, The detection module includes a signal processing unit and an oscilloscope. The signal processing unit is connected to the oscilloscope. The signal processing unit processes the induced electromotive force signal and outputs it to the oscilloscope. The oscilloscope displays the waveform of the induced electromotive force signal.

6. The metal foreign object detection system according to claim 5, characterized in that, The signal processing unit includes a preamplifier, a filter, and a lock-in amplifier connected in sequence; wherein... The preamplifier is used to amplify the induced electromotive force signal and input the amplified induced electromotive force signal to the filter. The filter is used to filter the amplified induced electromotive force signal and input the filtered induced electromotive force signal to the lock-in amplifier; The lock-in amplifier is used to extract the phase angle of the filtered induced electromotive force signal.

7. The metal foreign object detection system according to claim 5, characterized in that, The oscilloscope has a target area. When the change amplitude of the induced electromotive force signal exceeds the preset threshold, the waveform of the induced electromotive force signal exceeds the target area.

8. The metal foreign object detection system according to claim 1, characterized in that, The detection module also includes an array of probes, and the detection module is connected to the sensing module through the array of probes.

9. The metal foreign object detection system according to claim 1, characterized in that, The system also includes a signal generation module connected to the excitation module. The signal generation module is used to output an excitation signal, the frequency of which is determined based on the defect burial depth of the object being detected.

10. The metal foreign object detection system according to claim 1, characterized in that, The system also includes a shield, which is disposed on the outside of the magnetic core.

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