An intrinsic flexible electromagnetic ultrasonic guided wave probe for complex curved surface defect positioning

Abstract

The present application belongs to the technical field of electromagnetic ultrasonic testing, and particularly relates to an intrinsic flexible electromagnetic ultrasonic guided wave probe for complex curved surface defect positioning, comprising: a high magnetic permeability magnetic film, a permanent magnet array arranged in an array and embedded in the upper part of the high magnetic permeability magnetic film, and a flexible coil embedded in the lower part of the high magnetic permeability magnetic film. The present application discloses an intrinsic flexible electromagnetic ultrasonic guided wave probe for complex curved surface defect positioning. The probe is composed of a flexible coil, a Halbach permanent magnet array and a high magnetic permeability magnetic film, can adapt to the detection requirements of steel plates, steel pipes and curved surface components, and realizes large-scale rapid detection through guided waves. The design can reduce the lift-off distance, enhance the magnetic field strength in the coil area, improve the electromagnetic ultrasonic transduction efficiency and detection stability, and has good engineering application value.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic ultrasonic testing technology, specifically relating to an intrinsic flexible electromagnetic ultrasonic guided wave probe for locating defects on complex curved surfaces. Background Technology

[0002] The information disclosed in this background section is intended only to enhance some understanding of the overall background of this disclosure and is not necessarily to be construed as an admission or in any way an implication that the information constitutes prior art known to those skilled in the art.

[0003] Electromagnetic ultrasonic testing is a non-contact, non-destructive testing technique based on electromagnetic induction and electromagnetic force to excite and receive ultrasonic waves. When a high-frequency alternating current is passed through the excitation coil, an alternating electromagnetic field is generated around the coil, inducing eddy currents on the surface of the metal material being tested. These eddy currents interact with the static bias magnetic field provided by a permanent magnet or electromagnet, generating a periodic Lorentz force, thereby exciting ultrasonic waves in the metal material. During reception, the ultrasonic vibrations in the material cause relative motion or magnetic flux changes in the conductor within the magnetic field, inducing an electrical signal in the receiving coil, thus achieving the acquisition of the ultrasonic signal. Compared to contact ultrasonic testing, electromagnetic ultrasonic testing does not require a liquid coupling agent and can complete the excitation and reception of ultrasonic waves under non-contact or minimal lift-off conditions, making it suitable for complex testing environments such as high temperatures, rough surfaces, coated surfaces, and moving workpieces. Depending on the structure being tested and the testing requirements, electromagnetic ultrasonic transducers can excite various ultrasonic modes, including volume waves, surface waves, and guided waves. Among these, guided waves can propagate along the structural direction in boundary-constrained structures such as plates and pipes, exhibiting long propagation distances and large detection coverage, making them suitable for rapid testing of large metal structures.

[0004] However, most existing electromagnetic ultrasonic probes employ a rigid structural design. While these probes perform well when the object being tested is a planar metal structure, they struggle to achieve adequate contact with steel pipes, bends, components with small radii of curvature, or complex curved metal structures. This results in significant lift-off distances or fluctuations in lift-off distance. Since the transduction efficiency of electromagnetic ultrasound is closely related to the distance between the coil, the magnetic field source, and the surface of the metal being tested, an increased lift-off distance weakens the induced eddy current intensity and the effective magnetic field, thereby reducing ultrasonic excitation efficiency and the stability of the received signal. Therefore, designing flexible electromagnetic ultrasonic probes is of great importance.

[0005] In existing technologies, some solutions employ torsional mode magnetostrictive sensors arranged circumferentially around the pipe. Multiple coils and permanent magnet arrays form a detection structure around the pipe, utilizing the magnetostrictive effect to excite torsional mode guided waves within the pipe (Patent No.: CN108508085B). Other solutions utilize flexible guiding mechanisms, hinged connection structures, and magnetic positioning structures to enable ultrasonic thickness gauge probes to adapt to complex surfaces such as irregularly shaped boiler tubes, achieving localized thickness detection (Patent No.: CN121521038A). While these solutions can adapt to pipe or curved surface structures to some extent, the former primarily relies on a circumferential sensor structure, resulting in complex installation, and its flexibility mainly lies in structural adaptation to pipe diameter. The latter's flexibility primarily stems from external guiding or installation mechanisms, and its detection method remains focused on localized thickness measurement, making it difficult to locate defects over a large area.

[0006] In summary, the existing technology has the following shortcomings: 1. Insufficient flexibility of the probe body: Most existing electromagnetic ultrasonic probes adopt a rigid structure, which is difficult to adapt to complex curved surfaces such as steel pipes and bends, and is prone to fluctuations in lift-off distance during detection; 2. Insufficient coil flexibility: Traditional EMAT mostly uses copper coils or rigid printed coils, which lack flexibility and stretchability, making it difficult to maintain a stable fit on curved surfaces; 3. The magnet structure is not conducive to flexibility: Traditional EMAT mostly uses a monolithic permanent magnet, which is bulky and not conducive to subsequent flexible design. 4. Low magnetic field utilization: Existing flexible EMAT carriers mostly use ordinary silicone or PDMS, which have low magnetic permeability, lack magnetic focusing ability, and insufficient effective magnetic flux density in the coil area. 5. Limited detection area: Ordinary thickness probes use volume wave detection, which is mainly used for local detection or thickness measurement. To achieve large-scale defect location, it is usually necessary to scan point by point or use a multi-probe array, which has problems such as low efficiency, high cost and complex layout. Summary of the Invention

[0007] To address the shortcomings of existing electromagnetic ultrasonic probes, such as insufficient flexibility, poor surface fit, and low magnetic field utilization, this invention discloses an intrinsically flexible electromagnetic ultrasonic guided wave probe for locating defects on complex curved surfaces. This probe comprises a flexible coil, a Heilbeck permanent magnet array, and a high-permeability magnetic film, making it adaptable to the inspection needs of steel plates, steel pipes, and curved components. It achieves large-area, rapid inspection through guided waves. This design reduces lift-off distance, enhances the magnetic field strength in the coil region, improves electromagnetic ultrasonic transduction efficiency and detection stability, and has significant engineering application value.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: An intrinsically flexible electromagnetic ultrasonic guided wave probe for locating defects on complex curved surfaces includes: a high-permeability magnetic film, an array of permanent magnets embedded in the upper part of the high-permeability magnetic film, and a flexible coil embedded in the lower part of the high-permeability magnetic film.

[0009] Preferably, the permanent magnet array is a Haberc permanent magnet array, an alternating magnetization array, or a co-directional magnetization array.

[0010] Preferably, the permanent magnet array is a Haberc permanent magnet array, in which case the magnetic field enhancement side faces the flexible coil side.

[0011] Preferably, the flexible coil is made of liquid metal material; or flexible printed circuit board; or conductive composite material made of carbon nanotubes and silicone rubber; or graphene composite conductive material.

[0012] Preferably, the flexible coil is made of liquid metal material.

[0013] Preferably, the high permeability flexible magnetic film is formed by combining PDMS and magnetic filler.

[0014] Preferably, the magnetic filler in the high permeability flexible magnetic film is carbonyl iron powder, neodymium iron boron powder, or iron powder.

[0015] Preferably, the magnetic filler is carbonyl iron powder.

[0016] Preferably, the flexible coil is made of liquid metal material and is coiled into a bow-shaped fold structure in the lower part of a high-permeability magnetic film. The two ends of the flexible coil are respectively connected to a positive electrode and a negative electrode through an encapsulation layer.

[0017] The beneficial effects of this invention, an intrinsically flexible electromagnetic ultrasonic guided wave probe for locating defects on complex curved surfaces, are as follows: 1. This invention employs a flexible folded coil structure to replace the traditional rigid coil structure, enabling the probe to maintain good conductivity while adapting to the surface contact testing requirements of steel pipes, bends, and metal components with different radii of curvature. The flexible coil effectively reduces the lift-off distance between the probe and the structure under test, improving stability during excitation and reception, thereby enhancing the quality of electromagnetic ultrasonic testing signals.

[0018] 2. This invention employs multiple small-sized permanent magnets to form a Heilbeck array. Compared to traditional monolithic permanent magnet structures, this magnet array has better flexibility and adaptability. By combining specific magnetization directions within the Heilbeck array, the magnetic field can be enhanced on the side closest to the coil and the metal structure under test, increasing the magnetic field strength in the coil's operating region. This, in turn, strengthens the coupling between eddy currents and the magnetic field, improving the Lorentz force excitation effect.

[0019] 3. This invention uses a carbonyl iron powder-PDMS composite magnetic film as the carrier for the permanent magnet array and flexible coil. This composite magnetic film has high permeability, enabling it to guide and concentrate the magnetic field, allowing more magnetic flux to be concentrated in the coil's operating area, further improving the effective magnetic field utilization and electromagnetic ultrasonic transduction efficiency. Simultaneously, the PDMS substrate ensures the flexibility of the magnet structure, allowing the probe to better adapt to complex curved surfaces.

[0020] 4. This invention employs electromagnetic ultrasonic guided wave detection, which differs from traditional local thickness measurement. The guided wave can propagate long distances along steel plate or pipe structures, enabling large-area structural inspection under single-point or limited-point excitation conditions, reducing the complexity and cost of array-based inspection systems. Through the synergistic design of flexible coils, Helbeck arrays, and high-permeability composite magnetic films, this invention balances surface conformability with guided wave wide-area inspection capabilities, making it suitable for efficient, stable, non-contact, and non-destructive testing of large steel plates, pipes, and complex curved metal structures. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure during the detection process of the present invention.

[0022] Figure 2 This is a flowchart of electromagnetic ultrasonic testing.

[0023] Figure 3 This is a structural diagram of a flexible coil.

[0024] Figure 4 This is a simulation diagram of a dynamic magnetic field.

[0025] Figure 5 This is a comparison chart of eddy current intensity in coils.

[0026] Figure 6 This is a resistance comparison chart.

[0027] Figure 7 This is a diagram of the magnet's structure.

[0028] Figure 8 This is a comparison diagram of the simulated structures.

[0029] Figure 9 This is a comparison chart of magnetic adsorption capabilities.

[0030] Figure 10 This is a graph comparing magnetic flux.

[0031] Figure 11 This is a comparison chart of the experimental results.

[0032] In the figure, 1 is a permanent magnet array; 2 is a flexible coil; 3 is a high permeability magnetic film; 4 is the device under test; 5 is an encapsulation layer; and 6 is a lead-out electrode. Detailed Implementation

[0033] The following description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0034] In this embodiment, the present invention provides an intrinsically flexible electromagnetic ultrasonic guided wave probe for locating defects on complex curved surfaces, such as... Figure 1 , 3 As shown in Figures 7 and 8, the device includes: a high permeability magnetic film 3, an array of permanent magnets 1 embedded in the upper part of the high permeability magnetic film 3, and a flexible coil 2 embedded in the lower part of the high permeability magnetic film 3.

[0035] In this embodiment, as Figure 7 As shown, the permanent magnet array 1 is a Haberc permanent magnet array, an alternating magnetization array, or a co-directional magnetization array.

[0036] In this embodiment, as Figure 1 , 3 As shown, the flexible coil 2 is made of liquid metal material; or flexible printed circuit board; or conductive composite material made of carbon nanotubes and silicone or rubber; or graphene composite conductive material.

[0037] In this embodiment, as Figure 1 , 3 As shown in Figures 7 and 8, the high permeability flexible magnetic film 3 is formed by combining PDMS and magnetic filler, and the magnetic filler is carbonyl iron powder, neodymium iron boron powder, or iron powder.

[0038] In this embodiment, as Figure 3 As shown, the flexible coil is made of liquid metal material and is coiled into a bow-shaped structure in the lower part of the high permeability magnetic film 3. The two ends of the flexible coil are respectively connected to positive and negative electrodes through the encapsulation layer 5. The positive and negative electrodes are connected to an external signal generator, which inputs the high-frequency pulse signal after being amplified by the power amplifier into the flexible coil, so that it induces eddy currents on the surface of the metal structure being tested.

[0039] Working principle of the invention: 1. For example Figure 1 As shown, during testing, the flexible electromagnetic ultrasonic probe is attached to the surface of a structural steel plate or pipe to reduce the lift-off distance between the probe and the test piece. A signal generator produces a high-frequency excitation signal, which, after power amplification, is input to the flexible coil. The coil induces eddy currents on the metal surface. These eddy currents interact with the static magnetic field generated by the permanent magnet array to form a Lorentz force, thereby exciting the ultrasonic guided wave.

[0040] 2. The flexible electromagnetic ultrasonic guided wave probe of this invention is an intrinsically flexible probe. Its flexibility does not originate from external guiding mechanisms, hinge connection mechanisms, or adjustable mounting brackets, but is achieved by the probe body structure itself, enabling the probe as a whole to adapt to the bending deformation of the surface of the metal structure being measured. When inspecting steel pipes, bent pipes, and metal structures with different radii of curvature, no additional disassembly, reassembly, or mechanical adjustment of the probe is required to achieve contact with the surface being measured.

[0041] 3. During the inspection process, the ultrasonic guided wave propagates along the direction of the plate or pipe structure. When there are cracks, corrosion thinning, boundaries, or other structural discontinuities in the propagation path, reflection, scattering, or waveform changes will occur. The probe receives the returned guided wave signal, and the defect location is determined based on the echo arrival time and amplitude changes. Compared with local volume wave detection methods, this invention utilizes the characteristics of guided wave propagation over long distances, enabling large-area detection under single-point or limited-point excitation conditions. This reduces the need for point-by-point scanning and array arrangement, improving the inspection efficiency of large steel plates and pipe structures. The electromagnetic ultrasonic probe inspection flowchart is shown below. Figure 2 As shown.

[0042] 4. This invention designs a flexible folding coil structure for electromagnetic ultrasonic guided wave excitation, such as... Figure 3 As shown. The coil mainly consists of a flexible substrate composed of a high-permeability magnetic film 3, a periodic folded conductive channel composed of flexible coils 2, lead-out electrodes 6, and an encapsulation layer 5. Adjacent conductor segments maintain a set spacing, and the current directions in adjacent conductors are opposite. After a high-frequency pulse signal is applied to the coil, an alternating electromagnetic field is generated around the conductors, inducing periodic eddy currents on the surface of the tested metal. To verify the electromagnetic field distribution characteristics of this folded coil, an electromagnetic field simulation model between the coil and the metal workpiece was established, and the dynamic magnetic field distribution between the coil and the workpiece under the action of pulse current was analyzed, such as... Figure 4 As shown. Simulation results show that the folded coil can form a periodic dynamic magnetic field distribution on the workpiece surface, providing conditions for subsequent coupling with the static bias magnetic field generated by the permanent magnet array, thereby forming a periodic Lorentz force on the metal surface and realizing the excitation of the guided wave.

[0043] 5. To verify the electromagnetic coupling advantages of flexible folding coils in the inspection of curved structures, a comparative electromagnetic field model of flexible and rigid coils on the same curved workpiece surface was established, and the eddy current density distribution at the cut-off line near the workpiece surface was extracted, such as... Figure 6As shown in the simulation results, the eddy current density generated by the flexible coil on the workpiece surface is significantly higher than that of the rigid coil, and exhibits a more continuous distribution along the cross-section. This is because the flexible coil can deform with the curved workpiece surface, maintaining a relatively stable lift-off distance between each conductor of the coil and the workpiece, thereby enhancing the electromagnetic coupling between the coil and the metal workpiece. In contrast, the rigid coil is difficult to conform to the curved surface structure, resulting in a larger local lift-off distance and thus a lower and less uniform induced eddy current intensity. These results indicate that the flexible folded coil can improve the induced eddy current intensity on the workpiece surface under curved surface detection conditions, providing favorable conditions for subsequent coupling with the static bias magnetic field to form a stronger Lorentz force, thereby helping to improve the excitation efficiency of electromagnetic ultrasonic guided waves.

[0044] 6. The folding coil in this invention is made of flexible conductive material or liquid metal. The flexible substrate (high permeability magnetic film 3) is formed by combining PDMS and carbonyl iron powder, which enables the coil to maintain flexibility while having a certain magnetic field guiding ability, thereby improving its ability to adhere to steel pipes, bends and metal surfaces with different radii of curvature.

[0045] 7. In the flexible composite conductive material coil design, carbon nanotubes and silicone rubber are mixed in a preset ratio, and after stirring and dispersion, a conductive composite filler is formed. The conductive composite filler is then coated into a preset folded channel using a scraper, and after curing, a continuous conductive network is formed. This structure can achieve flexible conductivity to a certain extent and meet the requirements for coil bending and fitting.

[0046] 8. In the liquid metal coil design, a folded microchannel is pre-formed inside the flexible substrate. Liquid metal is injected into the microchannel to form a conductive path, and a flexible encapsulation layer is used to seal and protect it. This design can achieve lower conductor resistance and better current transmission capability while maintaining the coil's flexibility and deformability.

[0047] 9. Through experimental comparison, such as Figure 5 As shown, compared with carbon nanotube-silicone rubber composite conductive filler, liquid metal coils exhibit lower resistance and better conductivity, which can effectively reduce energy loss during the excitation process and increase the excitation current intensity in the coil. Therefore, they are more suitable for the fabrication of coil structures for flexible electromagnetic ultrasonic probes.

[0048] 10. This invention designs a magnet structure suitable for flexible electromagnetic ultrasonic probes, such as... Figure 7As shown. Traditional electromagnetic ultrasonic probes mostly use a monolithic permanent magnet as the magnetic field source. Although this type of structure can provide a strong static magnetic field, its overall stiffness is relatively high, which is not conducive to the flexible design of the probe, and it is difficult to fully fit the surface being tested when inspecting curved structures. To improve the flexibility and adaptability of the magnet structure and the efficiency of magnetic field utilization, this invention uses an array of multiple small-sized permanent magnets to replace the traditional monolithic permanent magnet, and embeds it in a flexible magnetic film carrier. This allows the magnet structure to undergo a certain degree of bending deformation along with the overall probe, thereby adapting to the inspection needs of steel plates, steel pipes, and metal surfaces with different radii of curvature.

[0049] 11. The small-sized permanent magnets are arranged in a Halbach array configuration. Compared to ordinary co-directional permanent magnet structures, the Halbach array can achieve directional magnetic field concentration by using a specific combination of the magnetization directions of adjacent magnets to enhance the magnetic field on one side while relatively weakening the magnetic field on the other side. Simulation results are as follows... Figure 8 As shown, this invention directs the magnetic field enhancement side toward the flexible folding coil and the surface of the metal structure being tested, concentrating more magnetic flux in the coil's effective region and increasing the static magnetic induction intensity near the coil. After a high-frequency excitation current is applied to the coil, the enhanced static magnetic field can interact with the induced eddy currents on the metal surface to generate a stronger Lorentz force, thereby improving the electromagnetic ultrasonic transduction efficiency.

[0050] 12. To further improve the magnetic field focusing capability, the high-permeability magnetic film 3 of this invention is made of carbonyl iron powder and PDMS composite material, which serves as the carrier of the electromagnetic ultrasonic probe. The carbonyl iron powder is uniformly dispersed in the PDMS matrix to form a flexible composite magnetic film with high permeability. Compared with ordinary silicone or pure PDMS carriers, this composite magnetic film can guide and focus the magnetic field, causing magnetic field lines to concentrate more on the surface area of ​​the coil and the measured structure, thereby improving the effective magnetic flux utilization rate. At the same time, the PDMS matrix ensures the flexibility and bendability of the magnet carrier, enabling it to meet the requirements of magnetic field enhancement and curved surface fit.

[0051] 13. In the preparation process, PDMS prepolymer and curing agent are mixed in a certain proportion, and then a certain amount of carbonyl iron powder is added. After stirring and vacuum degassing, the mixture is poured into a pre-set mold and then heated to cure and form. By controlling the carbonyl iron powder content, the magnetic permeability and flexibility of the composite magnetic film can be adjusted.

[0052] 14. To verify the magnetic field enhancement effect of the magnet structure designed in this invention, the prepared magnet samples were compared with samples of "silicone substrate-Haelbeck array" and "magnetic film substrate-ordinary permanent magnet array". During the test, each group of samples was placed on the surface of a structural steel plate, and a tension gauge was used to pull the sample at a constant speed along a direction perpendicular to the steel plate surface until the sample was completely detached from the structural steel plate. The maximum pull-out force required during the detachment process was recorded. The experimental results are as follows: Figure 9 As shown, compared to the comparative sample, the magnet structure designed in this invention requires a greater pull-out force to detach from the steel plate, indicating that it has a stronger magnetic adsorption capacity for the structural steel plate.

[0053] 15. To verify the magnetic field enhancement effect of flexible magnet structures in curved surface inspection, a magnetic field simulation model of flexible and rigid magnets under the same workpiece conditions was established, and the magnetic flux density distribution at the cut-off point near the coil's active area was extracted, such as... Figure 10 As shown in the figure, the results indicate that the flexible magnet exhibits a higher magnetic flux density level within the effective region of the coil, superior to that of the rigid magnet, demonstrating its ability to generate a stronger effective bias magnetic field on curved surfaces. In contrast, the rigid magnet, unable to adapt to the curved surface, experiences increased lift-off distances between its sides and the workpiece, resulting in significant magnetic field attenuation at the edges and an overall less uniform magnetic field distribution. The flexible magnet structure better conforms to the curved workpiece surface, making the magnetic field distribution more continuous and stable within the working region, thereby increasing the effective magnetic flux density in the coil region.

[0054] 16. To further verify the actual detection capability of the flexible electromagnetic ultrasonic guided wave probe, the received signals of the flexible EMAT and the rigid EMAT under the same curved surface conditions were compared and analyzed, such as... Figure 11 As shown in the figure, the experimental results show that both probes can receive the excited guided wave signal and subsequent reflected echo. The flexible EMAT probe receives a higher amplitude of the excited wave and exhibits a more pronounced reflected echo in the subsequent time period, indicating that the flexible probe has a more stable electromagnetic coupling effect under curved surfaces or non-ideal contact conditions. In contrast, the rigid EMAT probe receives a lower amplitude signal and has a relatively weaker echo characteristic, suggesting that the rigid structure is more susceptible to changes in lift-off distance and unstable contact during the detection process. This demonstrates that flexible coil and flexible magnet structures can improve the stability between the probe and the measured structure, which is beneficial for enhancing the amplitude of the guided wave signal and the ability to identify defect echoes.

Claims

1. An intrinsically flexible electromagnetic ultrasonic guided wave probe for locating defects on complex curved surfaces, characterized in that: include: A high-permeability magnetic film, an array of permanent magnets embedded in the upper part of the high-permeability magnetic film, and a flexible coil embedded in the lower part of the high-permeability magnetic film.

2. The intrinsically flexible electromagnetic ultrasonic guided wave probe for locating defects on complex curved surfaces as described in claim 1, characterized in that: The permanent magnet array is a Haberc permanent magnet array, an alternating magnetization array, or a co-directional magnetization array.

3. The intrinsically flexible electromagnetic ultrasonic guided wave probe for locating defects on complex curved surfaces as described in claim 2, characterized in that: The permanent magnet array is a Haberc permanent magnet array, and in this case, the magnetic field enhancement side faces the flexible coil side.

4. The intrinsically flexible electromagnetic ultrasonic guided wave probe for locating defects on complex curved surfaces as described in claim 1, characterized in that: The flexible coil is made of liquid metal material; or flexible printed circuit board; or conductive composite material made of carbon nanotubes and silicone rubber; or graphene composite conductive material.

5. The intrinsically flexible electromagnetic ultrasonic guided wave probe for locating defects on complex curved surfaces as described in claim 4, characterized in that: The flexible coil is made of liquid metal material.

6. The intrinsically flexible electromagnetic ultrasonic guided wave probe for locating defects on complex curved surfaces as described in claim 1, characterized in that: The high-permeability flexible magnetic film is formed by combining PDMS and magnetic fillers.

7. The intrinsically flexible electromagnetic ultrasonic guided wave probe for locating defects on complex curved surfaces as described in claim 6, characterized in that: The magnetic filler in the high-permeability flexible magnetic film is carbonyl iron powder, neodymium iron boron powder, or iron powder.

8. The intrinsically flexible electromagnetic ultrasonic guided wave probe for locating defects on complex curved surfaces as described in claim 7, characterized in that, The magnetic filler is carbonyl iron powder.

9. The intrinsically flexible electromagnetic ultrasonic guided wave probe for locating defects on complex curved surfaces as described in claim 5, characterized in that, The flexible coil is coiled into a bow-shaped folded structure in the lower part of the high permeability magnetic film, and the two ends of the flexible coil are respectively connected to the positive electrode and the negative electrode through the encapsulation layer.

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