Eddy current probe and detection method based on "eight" shape excitation

Abstract

The application discloses a kind of eddy current probe based on " eight " shape excitation and detection method, the probe includes probe shell and be arranged in shell two excitation coils and receiving coil;Two excitation coils are " eight " shape distribution, receiving coil is located below excitation line.This application designs the structure of " eight " shape excitation eddy current probe.First, by theoretical analysis, it is found that the direction of the primary magnetic field generated by the excitation coil is not the sensitive direction of the magnetic field of the receiving coil, so this structure can reduce the influence of direct coupling effect;At the same time, the eddy current field region in the test piece is mainly located below the two feet of the " eight " shape excitation coil, and this region is close to the receiving coil, so the detection capability of the probe can be guaranteed.The probe can detect crack defects at 10mm lift-off, and has good detection performance for crack defects.The problem of poor detection capability when the lift-off is large in the prior art is solved.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic nondestructive testing devices, specifically relating to an eddy current probe and testing method based on figure-eight excitation. Background Technology

[0002] Eddy current testing is a detection technology based on the principle of electromagnetic induction. It is sensitive to surface and near-surface cracks, inclusions or corrosion defects, and has the advantages of strong versatility, high efficiency and no need for coupling agent, so it has a good application prospect.

[0003] Eddy current testing technology has been extensively studied and applied in the inspection of metallic materials. Especially in recent years, with the continuous development of probe manufacturing processes, flexible planar eddy current probes have gradually become a research focus in eddy current testing technology. Eddy current probes designed based on flexible substrates can detect structures with complex surfaces, are highly adaptable, and can reduce the impact of lift-off on the signal, thus gaining increasing attention.

[0004] However, while flexible coils can improve the detection capability of probes for defects, their detection capability is generally poor at large lift-off ratios due to the relatively weak energy of the coils. How to improve the detection capability of flexible probes at large lift-off ratios is a problem that needs to be effectively solved. Summary of the Invention

[0005] The purpose of this invention is to provide an eddy current probe and detection method based on figure-eight excitation, which solves the technical problem in the prior art that the detection capability is poor when the lift-off ratio is large due to the weak energy of the flexible coil.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: An eddy current probe based on figure-eight excitation includes a probe housing and two excitation coils and a receiving coil disposed in the housing; The two excitation coils are arranged in a figure-eight shape, and the receiving coil is located below the excitation line.

[0007] An eddy current probe structure with a figure-eight excitation was designed. First, theoretical analysis revealed that since the direction of the primary magnetic field generated by the excitation coil is not the sensitive direction of the magnetic field of the receiving coil, this structure can reduce the influence of direct coupling. At the same time, the eddy current field region in the specimen is mainly located below the two legs of the figure-eight excitation coil, and this region is close to the receiving coil, thus ensuring the probe's detection capability.

[0008] Further optimization involves making the two excitation coils identical in structure and symmetrical about the vertical plane between them.

[0009] Further optimization involves placing the upper ends of the two excitation coils close together, with an included angle of 15° to 90°.

[0010] Further optimization resulted in an angle of 60° between the two excitation coils.

[0011] Further optimization involves setting the receiving coil parallel to the upper surface of the specimen. When viewed along the plane parallel to the excitation coil, the sides of the two excitation coils and the receiving coil form an isosceles triangle.

[0012] A non-destructive testing method based on an eddy current probe with figure-eight excitation includes the following steps: Step 1: Set up the testing platform: The testing platform includes a signal generator, power amplifier, data acquisition card, signal conditioning circuit, DC power supply, scanning frame, eddy current probe, and computer; fix the probe on the bracket, and install the bracket on the scanning frame; the DC power supply provides centralized power to all circuits; Step 2: The scanning frame moves the support and eddy current probe along the surface of the workpiece to be inspected for defect detection. The eddy current probe is lifted by 0-10mm. The signal generator produces two sinusoidal signals. One signal is amplified and sent to the excitation coil in the probe, while the other is sent to the phase shifter in the conditioning circuit to be converted into two orthogonal reference signals. The induced voltage signal generated by the receiving coil is processed by the conditioning circuit and outputs two DC signals containing characteristic information. The data acquisition card synchronously acquires the data and reads and stores it through the DAQExpress software on the computer. Step 3: Analyze the detection signal from the eddy current probe to confirm the workpiece.

[0013] Further optimization involves the eddy current probe having identical parameters for its receiving and excitation coils: 30 mm long, 20 mm wide, 0.08 mm wire diameter, 0.18 mm wire spacing, two layers, and a total of 41 turns; the excitation current frequency is 100 kHz. Compared with the prior art, the present invention has the following beneficial effects: 1) This invention designs an eddy current probe structure with an "eight"-shaped excitation. First, theoretical analysis reveals that since the direction of the primary magnetic field generated by the excitation coil is not the sensitive direction of the magnetic field of the receiving coil, this structure can reduce the influence of direct coupling. At the same time, the eddy current field region in the specimen is mainly located below the two legs of the "eight"-shaped excitation coil, and this region is close to the receiving coil, thus ensuring the probe's detection capability.

[0014] 2) This probe can detect crack defects with a lift of 10mm, demonstrating excellent detection performance. This solves the problem of poor detection capability in existing technologies when the lift ratio is large. Attached Figure Description

[0015] Figure 1 This is a schematic diagram illustrating the detection principle of a flexible eddy current probe. Figure 2 This is a schematic diagram of the Comsol numerical simulation model described in this invention; Figure 3 The eddy current distribution on the surface of the specimen when the probe is located in an intact area of ​​the specimen; Figure 4 The eddy current distribution on the specimen surface is shown when the probe moves along the specimen surface from far to near, and an excitation coil is located above the defect. Figure 5 This is a diagram showing the eddy current distribution on the specimen surface when the probe is directly above the defect. Figure 6 This is a diagram of the probe's detection signal during simulation. Figure 7 This is a schematic diagram of the experimental platform; Figure 8 This is a schematic diagram of the support structure; Figure 9 A comparison chart of detection signals when the "eight"-shaped excitation coil is subjected to different included angles; Figure 10 Peak-to-peak value diagrams of the signal when the excitation coil is at different angles; Figure 11 The image shows the detection signal when the probe detects cracks at different depths. Figure 12 The graph shows the detection signals of the probe under different lifting conditions. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] The detection principle of the flexible eddy current probe is the same as that of conventional eddy current testing, such as... Figure 1 As shown, a current with a frequency of is passed through the excitation coil. f When a sinusoidal alternating current is applied, a primary magnetic field of the same frequency is generated in space. This magnetic field induces eddy currents on the surface of the specimen. The changes in these eddy currents on the specimen surface generate a magnetic field in the opposite direction to the primary magnetic field, called the secondary magnetic field. Both the primary and secondary magnetic fields induce an electromotive force (EMF) across the induction coil, which is the detection signal. Clearly, the primary magnetic field is directly coupled to the signal generated by the receiving coil. U0 is independent of the test specimen, while the signal Δ generated by the secondary magnetic field coupled into the receiving coil is independent of the test specimen. U It contains information about component defects and is the signal required for detection. For flexible eddy current probes, when the excitation and receiving coils are designed with parallel upper and lower layers (such as the receiving coil...), Figure 1 (As shown by the dashed red line in the middle), directly coupled signal U 0 significantly interferes with the detection signal; however, when the excitation and receiving coils are designed as a left-right structure (such as the receiving coil...), Figure 1 (As shown by the dashed blue line), although the interference generated by direct coupling is relatively small, the large distance between the receiving coil and the eddy current field region in the specimen leads to Δ U The signal density is also relatively small, which reduces the coil's detection capability. Therefore, for flexible coils, it is necessary to ensure the coil's detection capability while reducing the direct coupling signal.

[0018] In response, this application has designed the following: Figure 2 The diagram shows a flexible eddy current probe based on a figure-eight excitation. It includes a probe housing and two excitation coils 21 and a receiving coil 22 housed within the housing. The two excitation coils 21 have identical structures and are symmetrically arranged about a vertical plane between them, forming a figure-eight shape. The receiving coil 22 is positioned parallel to the surface 1 of the specimen and below the excitation coils, specifically within the projection area of ​​the excitation coils onto the specimen surface. Viewed along the plane parallel to the excitation coils, the sides of the two excitation coils and the receiving coil form an isosceles triangle.

[0019] In this embodiment, the number of receiving coils 22 is one, constituting an absolute coil. In other embodiments, the number of receiving coils can be two, constituting a differential coil.

[0020] In this embodiment, the included angle between the two excitation coils is 60°. In other embodiments, the included angle between the two excitation coils can be any angle within the range of 15° to 90°.

[0021] Since the direction of the primary magnetic field generated by the excitation coil is not the direction of the magnetic field sensitivity of the receiving coil, the probe structure of this application can reduce the influence of direct coupling. At the same time, according to the magnetic field distribution law, the eddy current field region in the specimen is mainly located below the two legs of the figure-eight excitation coil, that is, the projection area of ​​the excitation coil on the specimen. This region is close to the receiving coil, thus ensuring the detection capability of the probe.

[0022] To verify the performance of the figure-eight-shaped excitation flexible eddy current probe, simulation and experiment were conducted.

[0023] I. Simulation:

[0024] To further verify the above analysis of the detection principle, the electromagnetic field frequency domain analysis of the designed probe was performed using the AC / DC module of the finite element simulation software COMSOL MultiPhysical. The established geometric model is as follows: Figure 2 As shown. The test block is made of carbon steel with a thickness of 4 mm; the crack length in the specimen is 15 mm, the depth is 2 mm, and the width is 0.35 mm; the dimensions of a single excitation coil and receiving coil are the same, with inner side length and width of 2 mm and 1 mm respectively, and outer side length and width of 6 mm and 5 mm respectively (the coil size used in the simulation is smaller to reduce the computational load); the included angle between the two excitation coils is 80 degrees.

[0025] Figure 3-5 This shows the eddy current distribution on the surface of the specimen when the probe is located at different positions. Figure 3 The eddy current distribution on the surface of the specimen when the probe is located in an intact area of ​​the specimen; Figure 4 The eddy current distribution on the surface of the specimen is shown when the probe moves along the surface of the specimen from far to near, and an excitation coil is located above the defect. Figure 5 This is a diagram showing the eddy current distribution on the specimen surface when the probe is directly above the defect. Figure 3-5 It can be seen that the eddy current field in the specimen is mainly concentrated in the projection area of ​​the figure-eight shaped excitation coil on the specimen surface, which is consistent with the theoretical analysis conclusions above. Furthermore, due to the distribution characteristics of the eddy current field on the specimen surface, the detection signal is stronger when the probe is close to and far from the crack; while when the probe is directly above the defect, the detection signal is 0V. Figure 6 The detection signal of the probe is represented by the horizontal coordinates of the peaks and troughs, which indicate the vertical distance of the probe from the defect location, respectively. The 0 coordinate indicates that the probe is directly above the defect.

[0026] II. Experimental Verification:

[0027] 1) Setting up the experimental platform: To verify the probe's performance, a system was built. Figure 7 The experimental platform shown is mainly composed of a signal generator 10, a power amplifier 11, a data acquisition card 7, a signal conditioning circuit 9, a DC power supply 8, a scanning frame 5, an eddy current probe 2, a carbon steel specimen 1, and a computer 6. The signal generator produces two sinusoidal signals; one is amplified by the power amplifier and sent to the excitation coil in the probe, while the other is sent to the phase shifter in the conditioning circuit to convert it into two orthogonal reference signals. The induced voltage signal generated by the receiving coil is processed by the conditioning circuit and outputs two DC signals containing characteristic information. The acquisition card synchronously acquires data and reads and stores it using the DAQExpress software on the computer. The DC power supply provides centralized power to all circuit components. Furthermore, for experimental convenience, a probe bracket is designed, with the probe 2 fixed on the bracket 3, as shown below. Figure 8 As shown, the bracket 3 is mounted on the scanning frame 5 via the clamping assembly 31, and the specimen is scanned under its clamping. The probe excitation and receiving coils used in the experiment are the same, with the following parameters: length 30 mm, width 20 mm, wire diameter 0.08 mm, wire spacing 0.18 mm, two layers, and a total of 41 turns; the excitation current frequency is 100 kHz; the specimen is a carbon steel plate specimen with through-crack defects of 0.5 mm width, 5 mm depth, 4 mm depth, and 3 mm depth.

[0028] 2) Probe angle optimization: Considering that changing the angle of the figure-eight excitation coil will affect the coupling between the primary magnetic field and the receiving coil, as well as the coupling between the secondary magnetic field generated by the eddy current field induced in the specimen and the receiving coil, and thus affect the detection signal, the included angle of the figure-eight excitation coil was first optimized through experiments. Figure 9 When the angle of the figure-eight excitation coil varies from 15 degrees to 90 degrees, the probe scans the detection signal of a crack defect with a width of 0.5 mm and a depth of 5 mm. As shown in the figure, the detection signal of the eddy current probe based on the figure-eight excitation exhibits a sinusoidal curve distribution, and when the probe is located in an intact area, its signal amplitude is almost 0V, which is consistent with the simulation results. Furthermore, the figure shows that the signal shape and signal-to-noise ratio change with the coil angle. The signal-to-noise ratio is best when the angle of the figure-eight excitation coil is 60 degrees. In addition, Figure 10 The graph shows the peak-to-peak value of the signal as a function of the excitation coil angle. As can be seen from the graph, the peak-to-peak value is highest when the angle of the figure-eight excitation coil is 60 degrees. Therefore, it is considered that the performance of the figure-eight excitation coil is best when the angle is 60 degrees. In subsequent experiments, an excitation coil with an angle of 60 degrees was selected.

[0029] 3) Probe performance analysis: Figure 11 The detection signals were obtained by sequentially scanning cracks 5mm, 4mm, and 3mm deep using an optimized probe. As shown in the figure, the probe can detect all defects with a high signal-to-noise ratio. Furthermore, the signal peak value and peak-to-peak value vary significantly with defect depth, thus they can be used as characteristic quantities to quantify crack defect size.

[0030] also, Figure 12 The figure shows the detection signal of a 0.5mm wide and 5mm deep crack when the probe lift varies from 0 to 10mm. As can be seen from the figure, although the peak value and peak-to-peak value of the signal decrease with increasing lift, the probe can still detect the 0.5mm wide and 5mm deep crack defect at a lift of 10mm, and the signal-to-noise ratio is high. This proves that the probe still has good detection performance under large lifts.

[0031] In summary, the eddy current probe based on the figure-eight excitation described in this application reduces the influence of direct coupling because the direction of the primary magnetic field generated by the excitation coil is not in the sensitive direction of the receiving coil's magnetic field. Furthermore, the eddy current field region in the specimen is mainly located below the two legs of the figure-eight excitation coil, and this region is close to the receiving coil, thus ensuring the probe's detection capability. Secondly, the probe's design and performance were optimized through experiments. Experimental results show that the probe exhibits the strongest detection capability for the carbon steel specimen used in this paper when the included angle between the two excitation coils is 60 degrees. Simultaneously, the designed probe can distinguish crack defects of different depths and can detect crack defects 0.5 mm wide and 5 mm deep with a 10 mm lift. This demonstrates that the probe has excellent detection performance for crack defects.

[0032] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. An eddy current probe based on figure-eight excitation, characterized in that, Includes a probe housing and a receiving coil and two excitation coils housed within the housing; The two excitation coils are arranged in a figure-eight shape, and the receiving coil is located below the excitation line; The upper ends of the two excitation coils are close together, with an included angle of (15°, 90°). The receiving coil is arranged parallel to the upper surface of the specimen and is located in the projection area of ​​the excitation coil on the surface of the specimen; when viewed along the direction parallel to the plane where the excitation coil is located, the sides of the two excitation coils and the receiving coil form an isosceles triangle.

2. The eddy current probe based on "eight"-shaped excitation according to claim 1, characterized in that, The two excitation coils have identical structures and are symmetrically arranged about the vertical plane between them.

3. The eddy current probe based on "eight"-shaped excitation according to claim 2, characterized in that, The included angle between the two excitation coils is 60°.

4. The eddy current probe based on "eight"-shaped excitation according to claim 3, characterized in that, The number of receiving coils is one or two.

5. A non-destructive testing method based on an eddy current probe with "eight"-shaped excitation, characterized in that, The eddy current probe based on any one of claims 1-4 includes the following steps: Step 1: Set up the testing platform: The testing platform includes a signal generator, power amplifier, data acquisition card, signal conditioning circuit, DC power supply, scanning frame, eddy current probe, and computer; fix the probe on the bracket, and install the bracket on the scanning frame; the DC power supply provides centralized power to all circuits; Step 2: The scanning frame moves the support and eddy current probe along the surface of the workpiece to be inspected for defect detection. The eddy current probe is lifted by 0-10mm. The signal generator produces two sinusoidal signals. One signal is amplified and sent to the excitation coil in the probe, while the other is sent to the phase shifter in the conditioning circuit to be converted into two orthogonal reference signals. The induced voltage signal generated by the receiving coil is processed by the conditioning circuit and outputs two DC signals containing characteristic information. The data acquisition card synchronously acquires the data and reads and stores it through the DAQExpress software on the computer. Step 3: Analyze the detection signal from the eddy current probe to confirm the workpiece.

6. The nondestructive testing method according to claim 5, characterized in that, The receiving coil and excitation coil of the eddy current probe have the same parameters: 30 mm in length, 20 mm in width, 0.08 mm in wire diameter, 0.18 mm in wire spacing, two layers, and a total of 41 turns; the excitation current frequency is 100 kHz.

Images