A TR type pulsed eddy current probe structure capable of reducing the influence of lift-off fluctuation and a detection method

Abstract

This invention discloses a TR-type pulsed eddy current detection method that can reduce the influence of lift-off fluctuations, belonging to the field of electromagnetic nondestructive testing technology, and includes the following steps: S1: Establishing a simplified structure and establishing an induced voltage signal. △U The expression; according to △U S2: Use the actual expression to establish the integral formula; l omax Minimum spacing between the excitation coil and the receiving coil D min The method involves calculating the actual integral value and, based on the principle that the actual integral value remains constant, calculating different lift-offs and corresponding coil spacings; S3: performing curve fitting on the different lift-offs and coil spacings; S4: using the fitted curves to verify the correctness of reducing the lift-off effect. This method and probe structure can reduce the lift-off effect by changing the coil spacing at different lift-off times.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic nondestructive testing technology, specifically to a TR-type pulsed eddy current probe structure and testing method that can reduce the influence of lift-off fluctuations. Background Technology

[0002] Pulsed eddy current testing technology is a type of eddy current testing technology.

[0003] The distance between the probe and the specimen is one of the important factors affecting the accuracy of pulsed eddy current testing. Especially in field testing, due to uneven surface of the component or vibration of the scanning frame connecting the probe, the probe lift may be in a fluctuating state. The signal change caused by the lift fluctuation is easily regarded as a defect signal, which affects the accuracy of pulsed eddy current testing.

[0004] Some scholars have attempted to address the lift-off problem by improving the structure of pulsed eddy current probes. For example, studies have shown that a TR probe structure with separate excitation and receiving coils can reduce the lift-off effect. However, this only applies to cases where the lift-off remains constant. How to reduce the lift-off effect and improve the detection accuracy of the coil under conditions of lift-off fluctuations has not yet been investigated. Summary of the Invention

[0005] The present invention discloses a TR-type pulsed eddy current probe structure and detection method that can reduce the impact of lift-off fluctuations. It can change the coil spacing between the excitation coil and the receiving coil when the lift-off changes, thereby reducing the lift-off effect.

[0006] To achieve the above objectives, the present invention provides a TR-type pulsed eddy current detection method that can reduce the influence of lift-off fluctuations, comprising the following steps:

[0007] S1: Place the pulsed eddy current probe on the flat specimen, establish a simplified structure, and establish the induced voltage signal based on the simplified structure. △U The expression; according to △U The relevant parameters affecting the lift-off effect in the expression are used to establish an integral formula;

[0008] The integral formula is:

[0009] (1)

[0010] J 0( x ) represents the zeroth-order Bessel function; e -2αlo The lift-off factor is ; the coil spacing between the excitation coil and the receiving coil is . D ; l o For removal;

[0011] S2: Utilize the known actual maximum lift-off valuel omax Based on the known minimum spacing between the excitation and receiving coils D min Substitute into equation (1) to calculate the actual integral value of equation (1). Based on the principle that the actual integral value remains unchanged, calculate the different lift-offs and corresponding coil spacing.

[0012] S3: Perform curve fitting on the different lift-offs and corresponding coil spacings in S2;

[0013] S4: Using the curve fitted in S3, obtain different lift-offs and corresponding coil spacings, and verify the correctness of reducing the lift-off effect using different lift-offs and coil spacings.

[0014] Furthermore, in step S1,

[0015] The simplified structure has three layers, from bottom to top: air, flat specimen, and probe lift-off; the pulsed eddy current probe is located on top of the simplified structure.

[0016] With the axis of symmetry of the excitation coil as z Axis, with z A cylindrical coordinate system is established with the intersection of the axis and the point where the probe is lifted off the upper surface as the origin. r , θ , z );

[0017] Induced voltage signal △U It can be represented as:

[0018] ;

[0019] in, R'' 4,3 ( α () represents the generalized reflection coefficient of the three-layer structure. e -2αlo The lift-off coefficient, S'' ( α ) represents the coil coefficient of the pulsed eddy current probe. J 0( x ) and J 1( x () denote the zeroth and first-order Bessel functions, respectively. ω and I ( ω These represent the angular frequency and the amplitude of the harmonic excitation current, respectively. j It is the imaginary unit. μ 0 is the permeability of free space. μ r2 It is the relative permeability. σ 2 is the electrical conductivity of the metal plate; n ,r 1, r 2, l These are the number of coil turns, inner diameter, outer diameter, and height, respectively, with the subscripts T and R representing the excitation coil and the receiving coil, respectively.

[0020] Furthermore, in step S3, the curve is fitted using a quadratic polynomial.

[0021] Furthermore, in step S2, the actual maximum lift-off value is... l omax =10 mm; minimum coil spacing D min =10mm.

[0022] Furthermore, a TR-type pulsed eddy current probe structure that can reduce the impact of lift-off fluctuations, used in the TR-type pulsed eddy current detection method for reducing the impact of lift-off fluctuations as described in any one of claims 1-4, is characterized in that it includes a housing, a receiving cavity provided in the housing, and an excitation coil assembly and a receiving coil assembly provided in the receiving cavity;

[0023] The excitation coil assembly includes:

[0024] The excitation coil frame is fixed to the inner wall of the receiving cavity;

[0025] The excitation coil is wound on the excitation coil frame, with its central axis set vertically.

[0026] The receiving coil assembly includes:

[0027] The mounting frame is slidably connected to the inner wall of the receiving cavity by means of a slide rail; the sliding direction of the mounting frame is horizontal, i.e., the X direction.

[0028] The receiving coil frame is fixed on the mounting frame;

[0029] The receiving coil is wound around the receiving coil frame, and the central axis of the receiving coil is set vertically; the receiving coil is outside the excitation coil and is not sleeved on the excitation coil.

[0030] It also includes a drive assembly that moves the mounting frame along the slide rail; and excitation coil connectors and receiving coil connectors that are respectively connected to the excitation coil and the receiving coil.

[0031] Furthermore, the driving component includes:

[0032] The probe is movably mounted on the inner wall of the receiving cavity and can move vertically.

[0033] The limiting spring and the limiting plate are located above the probe and are fixed to the inner wall of the receiving cavity. One end of the limiting spring is fixedly connected to the limiting plate and the other end is fixedly connected to the upper end of the probe. The limiting spring is always in a compressed state.

[0034] The slider is fixedly connected to the probe.

[0035] The rack is vertically positioned and fixedly connected to the slider.

[0036] The transmission rod is rotatably connected to the receiving cavity. One end is fixed with a transmission gear, which coincides with the axis of the transmission rod and meshes with the rack. The other end is fixed with a driving bevel gear, which coincides with the axis of the transmission rod. The axis of the transmission rod is parallel to the X direction.

[0037] The driven rod is rotatably connected to the inner wall of the receiving cavity, and its axis is set vertically.

[0038] The driven bevel gear is fixed on the driven rod, coincides with the axis of the driven rod, and meshes with the driving bevel gear;

[0039] A cam for moving the mounting frame is horizontally positioned with its outer edge abutting against the mounting frame; it is detachably connected to the driven rod.

[0040] The spring used to reset the mounting frame is always in a compressed state. One end is fixedly connected to the spring limiting plate fixed on the inner wall of the receiving cavity, and the other end is fixedly connected to the surface wall of the mounting frame. The cam and the spring are located on opposite sides of the surface wall of the mounting frame. Beneficial effects

[0041] This method can change the coil spacing when the lift-off changes, so that the integral in equation (1) remains unchanged, thereby reducing the lift-off effect. Attached Figure Description

[0042] Figure 1 This is a schematic diagram showing the TR probe positioned above the three-layer structure.

[0043] Figure 2 Top view of the TR probe;

[0044] Figure 3 for D Follow l A quadratic polynomial curve with varying o;

[0045] Figure 4 TR probe detection signal Δ for 0 and 10 mm lift-off U ;

[0046] Figure 5 For different lo and D The detection signal △ of the lower TR probe U ;

[0047] Figure 6 The detection signal Δ of the TR probe at 10 mm and 0 mm lift-off. U ;

[0048] Figure 7 The detection signal △ for a 10mm thick plate U ;

[0049] Figure 8 The detection signal △ for the aluminum plate U ;

[0050] Figure 9 The detection signal Δ of probe 2 U ;

[0051] Figure 10 This is a pulsed eddy current probe structure that can reduce the impact of lift-off fluctuations;

[0052] Figure 11 This is a schematic diagram of the overall structure of the outer shell.

[0053] 10. Excitation coil assembly; 101. Excitation coil frame; 102. Excitation coil;

[0054] 20. Receiver coil assembly; 201. Mounting frame; 202. Slide rail; 203. Receiver coil frame; 204. Receiver coil; 205. Spring limiting plate;

[0055] 30. Drive assembly; 301. Limiting plate; 302. Probe; 303. Slider; 304. Rack; 305. Limiting spring; 306. Transmission gear; 307. Transmission rod; 308. Driving bevel gear; 309. Driven bevel gear; 310. Driven rod; 311. Spring; 312. Cam. Detailed Implementation

[0056] 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. Example 1

[0057] A TR-type pulsed eddy current detection method that can reduce the impact of lift-off fluctuations includes the following steps:

[0058] S1: Place the pulsed eddy current probe on the flat specimen, establish a simplified structure, and establish the induced voltage signal based on the simplified structure. △U The expression; according to △U Establish the integral formula using the relevant parameters in the expression;

[0059] Specifically, see Figure 1The placed flat plate specimen is considered as a simplified three-layer structure, viewed from bottom to top. The first layer is air, the second layer is the flat plate specimen, and its thickness is... c The third layer is for probe removal. l o The pulsed eddy current probe, consisting of an excitation coil and a receiving coil, is located in the fourth layer of a simplified three-layer structure, and the axial distance between the excitation coil and the receiving coil is... D (Hereinafter referred to as coil spacing) D The lower surfaces of the excitation coil and the receiving coil are located on the same plane, with the excitation coil outside the receiving coil. A top view of the excitation coil and the receiving coil is shown below. Figure 2 .

[0060] Considering that the excitation current is a circular current, a cylindrical coordinate system is chosen for ease of calculation. r , θ , z ),set up z The axis coincides with the axis of symmetry of the excitation coil, and the origin of the coordinate system is ( O The point is located on the upper surface of the three-layer structure; when the excitation current is a square wave signal, according to the Fourier transform, the square wave excitation can be regarded as a superposition of a series of harmonic excitations. Therefore, by adding the signals of each harmonic and performing a discrete inverse Fourier transform on the result, the time-domain induced voltage signal of the pulsed eddy current can be obtained. For each harmonic component, the induced voltage signal of the receiving coil... △U It can be represented as:

[0061] (1)

[0062] ;

[0063] in, R'' 4,3 ( α ) represents the generalized reflection coefficient of the three-layer structure. e -2αlo The lift-off coefficient, S'' ( α ) represents the coil coefficient of the TR probe. J 0( x ) and J 1( x () denote the zeroth and first-order Bessel functions, respectively. ω and I ( ω These represent the angular frequency and the amplitude of the harmonic excitation current, respectively. j It is the imaginary unit. μ 0 is the permeability of free space. μ r2 It is the relative permeability. σ 2 is the electrical conductivity of the metal plate. n, r 1, r 2, l These are the number of coil turns, inner diameter, outer diameter, and height, respectively. The subscripts T and R represent the excitation coil and the receiving coil, respectively.

[0064] From equation (1), we can see that △ U Mainly composed of R" 4,3 ( α ), S" ( α )and e -2αlo × J 0( αD These three decisions. Among them, R" 4,3 ( α It is only related to parameters such as the material of the specimen. S" ( α It depends only on the coil parameters (number of turns, inner diameter, outer diameter, and coil height). Therefore, R" 4,3 ( α )and S" ( α It will not be taken away. l o Changes occur when the parameters of the specimen and coil (number of turns, inner diameter, outer diameter, and height) are determined. R" 4,3 ( α )and S" ( α ) will also be determined at this time. △ U The expression can only take the value of... e -2αlo × J 0( αD This relates to the selection of an appropriate coil spacing. D， make e -2αlo × J 0( αD The value of ) does not change with lift-off, at which point Δ U This will remain unchanged, thus eliminating the effects of lifting.

[0065] In order to find the right D It is necessary to separate them in different ways. l o The corresponding coil spacing D Down e -2αlo × J 0( αD In this scheme, the integral shown in equation (6) (referred to as in this method) is used. l o– D To solve the above problem, we only need to integrate the points (i.e., as long as...). l o and D When changes occur, maintain l o – D If the integral value remains unchanged, then it is considered that e -2αlo × J 0( αD ) remains unchanged.

[0066] (6)

[0067] S2: Utilize the known maximum lift. l omax The minimum spacing between the excitation coil and the receiving coil is combined. D min Substituting into equation (6), we can calculate... l o – D The actual value of the integral, and then based on lo–θ Integrate the actual value to calculate the coil spacing between the excitation coil and the receiving coil under different lift-off conditions.

[0068] Specifically, since the maximum lift-off of the probe during the detection process can be estimated, and the minimum spacing of the coils is known, these two values ​​can be used to determine... l o – D The integral value of . Then it can be defined as:

[0069] (7)

[0070] in, l omax yes l o The maximum value, D min yes D The minimum value.

[0071] In practice, when using probe 1 to inspect the rail, the probe lift fluctuates between 0 and 10 mm. l omax =10 mm, and then according to the parameters of probe 1 in Table 1, we get D min = r 2T + r 2R =2 r 2 = 10 mm. (The rest of the text appears to be incomplete and requires further context.) l omax andD min Substituting into equation (7), we can calculate the result. Int ( l omax ，D min The value is 38.5. Then, based on the obtained... Int ( l omax ，D min ) Calculations differ l o Down D The values ​​are shown in Table 2. According to Table 2, optimizing the coil spacing under different lift-off conditions can reduce the lift-off effect.

[0072] Table 1. Parameters of the excitation coil and receiving coil of probe 1

[0073]

[0074] Table 2. Coil spacing values ​​under different lift-off conditions

[0075]

[0076] S3: Based on the coil spacing under different lift-off conditions in S2, a quadratic polynomial is used to fit the relationship between lift-off and coil spacing.

[0077] Specifically, based on the data in Table 2, the fitted curve is shown below. Figure 3 The expression for the fitted curve is: D = -0.18 l o 2 + 0.34l o + 24.82 .

[0078] The coil spacing of this probe can be adjusted in real time according to changes in lift-off, so as to reduce the impact of the lift-off effect and improve detection accuracy.

[0079] S4: Using the fitted curve from S3, obtain different lift-offs and corresponding coil spacings, and verify the correctness of reducing the lift-off effect using different lift-offs and corresponding coil spacings.

[0080] Specifically, relevant verifications were conducted to demonstrate that a TR probe with optimized coil spacing can reduce the lift-off effect. Figure 4 To detect the signal of a 20 mm thick ferromagnetic metal plate with probe 1 at 0 mm and 10 mm lift-off without changing the coil spacing;

[0081] Figure 5 and Figure 6 For in differentl o and D The detection signal of a 20 mm thick ferromagnetic metal plate, among which... Figure 5 The detection signals shown are based on those listed in Table 2. l o and D Obtained. To highlight signal differences, from Figure 5 Two signals under maximum and minimum lift-off conditions were extracted, and the results are as follows: Figure 6 .Will Figure 4 and Figure 6 A comparison shows that, Figure 6 The signal difference in the middle is less than Figure 4 The signal differences are more pronounced in the latter half of the signal. This indicates that, according to l o – D Integral optimization of coil spacing D This can reduce the lift-off effect.

[0082] From equation (7), we can see that l o – D Points only with l omax and D min Related to, among them D min Depends on the outer diameter of the coil ， at the same time, l o – D The integration is unaffected by other parameters of the specimen and probe (number of turns, inner diameter, and height). Therefore, the probe performance is analyzed under conditions of different specimen thicknesses, different materials, and different probe parameters.

[0083] To demonstrate that the optimized coil spacing can be used for plate detection of other thicknesses, a 10 mm thick ferromagnetic metal plate was designed, and its detection signal is as follows: Figure 7 As shown. Figure 7 The results show that the detection signal difference of the TR probe is small at 0 mm and 10 mm lift-off, indicating that the optimized coil spacing in Table 2 can be used to reduce the lift-off effect of a 10 mm thick metal plate. Figure 6 and Figure 7 This demonstrates that it can be used to reduce the lift-off effect of metal plates of different thicknesses.

[0084] To demonstrate that the optimized coil spacing can be used to inspect flat plates of other materials, a 20 mm thick aluminum plate was used. Figure 8 The signal obtained by using a TR probe to detect an aluminum plate. Figure 8This indicates that the TR probe structure of the present invention can be used to reduce the lift-off effect of the aluminum plate. Combined with... Figure 6 and Figure 8 This indicates that the probe can also be made of other materials.

[0085] Furthermore, to prove that the optimization of the coil spacing is only related to the outer diameter of the coil, probe 2 was designed, wherein the outer diameter of probe 2 is... r 2 is the same as probe 1, but all other parameters are different from probe 1. Figure 9 The detection signal obtained by probe 2 based on the lift-off and coil spacing changes in Table 2. Figure 9 This indicates that the signal from probe 2 is also almost unaffected by the lift-off effect, proving the results listed in Table 2. D This can be used to optimize the coil spacing of probe 2. This also shows that coil spacing optimization is only related to the probe's outer diameter, making probe optimization easier.

[0086] In summary, this application proposes a pulsed eddy current TR probe structure capable of automatically adjusting the coil spacing and demonstrates that this probe structure can reduce the influence of the lift-off effect. It should be noted that this invention only considers the maximum lift-off effect. l omax =10 mm and minimum coil spacing D min Taking 10 mm as an example, but not limited to this application scenario. That is, in other application scenarios, as long as it is known... l omax and D min The value of can also be obtained from equation (7). l o – D integral Int ( l omax ，D min The value of ) is then used to determine the spacing of the lower coils at different lift-off points.

[0087] Example 2

[0088] See Figure 10 A TR-type pulsed eddy current probe structure that can reduce the impact of lift-off fluctuations is used to fabricate probe 1 or probe 2 in Example 1.

[0089] The probe structure includes a housing (see...) Figure 11 (The outer frame 407 and the cover plate 408 are connected as a whole by bolts. The outer shell is a rectangular frame with a receiving cavity in it. The receiving cavity contains an excitation coil assembly 10, a receiving coil assembly 20 and a driving assembly 30.)

[0090] Excitation coil assembly 10 includes:

[0091] Excitation coil frame 101 is fixed to the inner wall of the receiving cavity;

[0092] The excitation coil 102 is wound around the excitation coil frame 101. The central axis of the excitation coil 102 is set vertically.

[0093] The receiving coil assembly 20 includes:

[0094] The mounting frame 201 is slidably connected to the inner wall of the receiving cavity by means of a slide rail 202, and the slide rail 202 is fixed to the inner wall of the receiving cavity; assuming that the sliding direction of the mounting frame 201 is horizontal, that is... Figure 10 In the X direction;

[0095] The receiving coil frame 203 is fixed on the mounting frame 201 and moves with the mounting frame 201.

[0096] The receiving coil 204 is wound around the receiving coil frame 203 and moves with the mounting frame 201. The central axis of the receiving coil 204 is vertically arranged. In this embodiment, the excitation coil 103 is located outside the receiving coil 204, and the two are not nested together.

[0097] The cover plate is connected to an excitation coil connector 402 and a receiving coil connector 403, which are respectively connected to the excitation coil 102 and the receiving coil 203. The excitation coil connector 402 is used to generate an excitation signal for the excitation coil 102, and the receiving coil connector 403 is used to receive the induced signal.

[0098] The driver components include:

[0099] The probe 302 has its axis set vertically and is movably mounted on the inner wall of the receiving cavity. The probe 302 can move vertically. A probe protective shell 405 is fixed on the inner wall of the receiving cavity and wraps around the probe 302. The lower end of the probe 302 extends out of the receiving cavity and abuts against the upper surface wall of the object to be tested.

[0100] The limiting spring 305 and the limiting plate 301 are located above the probe 302 and are fixed to the inner wall of the receiving cavity. One end of the limiting spring 305 is fixedly connected to the limiting plate 301, and the other end is fixedly connected to the upper end of the probe 302. The limiting spring 305 is always in a compressed state.

[0101] The slider 303 and probe 302 are fixedly connected to the slider 303 via a probe bracket; the slider 303 moves as the probe 302 moves.

[0102] The rack 304 is fixed on the slider 303 and is arranged vertically.

[0103] The transmission rod 307 has a horizontal axis and the axis of the transmission rod 307 is parallel to the X direction. The transmission rod 307 is rotatably connected to the inner wall of the receiving cavity by the limiting frame 406. The limiting frame 406 is fixed to the inner wall of the receiving cavity, and the transmission rod 307 can rotate relative to the limiting frame 406.

[0104] The transmission gear 306 is aligned with the axis of the transmission rod 307, fixed on the transmission rod 307, and meshes with the rack 304.

[0105] The active bevel gear 308 coincides with the axis of the transmission rod 307 and is fixed on the transmission rod 307. The active bevel gear 308 and the transmission gear 306 are located at the two ends of the transmission rod 307, respectively.

[0106] Driven rod 310 is rotatably connected to the inner wall of the receiving cavity, and its axis is set vertically;

[0107] The driven bevel gear 309 coincides with the axis of the driven rod 310, is fixed on the driven rod 310, and meshes with the driving bevel gear 308.

[0108] Cam 312, detachably connected to driven rod 310, is horizontally positioned. The outer circumferential wall of cam 312 abuts against one side surface wall of mounting frame 201. Cam 312 and excitation coil assembly 10 are located on the same side of mounting frame 201. Probe 302 moves mounting frame 201 sequentially via slider 303, rack 304, transmission rod 305, driven rod 310, and cam 312, thereby increasing the coil spacing. D Change;

[0109] Spring 311 has one end fixedly connected to spring limiting plate 205 fixed in the receiving cavity, and the other end fixedly connected to the surface wall of mounting frame 201. Cam 312 and spring 311 are located on opposite side surfaces of mounting frame 201. Spring 311 is always in a compressed state to push mounting frame 201 to move. When cam 312 does not generate a force to move mounting frame, the elastic force of spring 311 is used to reset mounting frame 201.

[0110] Except for the spring 311, the excitation coil 103, and the receiving coil 204, all other components in this design are made of non-conductive materials.

[0111] Change the coil spacing D The process is as follows:

[0112] The lower end of the probe 302 is in contact with the surface of the object being measured. When the probe 302 detects a change in lifting, the probe 302 will move accordingly under the elastic force of the limit spring 305; the slider 303 also moves with the movement of the probe 302.

[0113] Since the slider 303 meshes with the transmission gear 306 through the rack 304, and the transmission rod 307 is rotatably connected to the receiving cavity, the vertical movement of the slider 303 will drive the transmission gear 306 to rotate, the transmission gear 306 will then cause the transmission rod 307 to rotate, and in turn the active bevel gear 308 will rotate.

[0114] Since the active bevel gear 308 meshes with the driven bevel gear 309, the active bevel gear 308 drives the driven bevel gear 309 to rotate, which in turn causes the driven rod 310 to rotate.

[0115] Rotation of the driven rod 310 causes the cam 312 to rotate in the horizontal plane. Since the outer circumferential wall of the cam 312 abuts against the mounting frame 201, the mounting frame 201 will move along the slide rail 202 when the cam 312 rotates, resulting in an increase in the coil spacing. D The outer edge of cam 312 is ground according to the actual situation, corresponding to the coil spacing in Example 1. D The fitting curve of the quadratic term is set, that is, the coil spacing is adjusted. D The data in Table 2 of Example 1 are satisfied.

[0116] 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. A TR-type pulsed eddy current detection method that can reduce the influence of lift-off fluctuations, characterized in that, Includes the following steps: S1: Place the pulsed eddy current probe on the flat specimen, establish a simplified structure, and establish the induced voltage signal based on the simplified structure. △U The expression; according to △U The relevant parameters affecting the lift-off effect in the expression are used to establish an integral formula; The integral formula is: ; J 0( x ) represents the zeroth-order Bessel function; e -2αlo The lift-off factor is ; the coil spacing between the excitation coil and the receiving coil is . D ; l o For removal; In step S1, the simplified structure has three layers, from bottom to top: air, flat specimen, and probe lifting; the pulsed eddy current probe is located above the simplified structure. With the axis of symmetry of the excitation coil as z Axis, with z A cylindrical coordinate system is established with the intersection of the axis and the point where the probe is lifted off the upper surface as the origin. r , θ , z ); S2: Utilize the known actual maximum lift-off value l omax Based on the known minimum spacing between the excitation and receiving coils D min Substitute into equation (1) to calculate the actual integral value of equation (1). Based on the principle that the actual integral value remains unchanged, calculate the different lift-offs and corresponding coil spacing. S3: Perform curve fitting on the different lift-offs and corresponding coil spacings in S2; S4: Using the curve fitted in S3, obtain different lift-offs and corresponding coil spacings, and verify the correctness of reducing the lift-off effect using different lift-offs and coil spacings.

2. The TR-type pulsed eddy current detection method for reducing the influence of lift-off fluctuations according to claim 1, characterized in that, Induced voltage signal △U It can be represented as: ; ; ; ; ; in, R'' 4,3 ( α () represents the generalized reflection coefficient of the three-layer structure. e -2αlo The lift-off coefficient, S'' ( α ) represents the coil coefficient of the pulsed eddy current probe. J 0( x ) and J 1( x () denote the zeroth and first-order Bessel functions, respectively. ω and I ( ω These represent the angular frequency and the amplitude of the harmonic excitation current, respectively. j It is the imaginary unit. μ 0 is the permeability of free space. μ r2 It is the relative permeability. σ 2 is the electrical conductivity of the metal plate; n , r 1, r 2, l These are the number of coil turns, inner diameter, outer diameter, and height, respectively, with the subscripts T and R representing the excitation coil and the receiving coil, respectively.

3. The TR-type pulsed eddy current detection method for reducing the influence of lift-off fluctuations according to claim 1, characterized in that, In step S3, a quadratic polynomial is used to fit the curve.

4. The TR-type pulsed eddy current detection method for reducing the influence of lift-off fluctuations according to claim 1, characterized in that, In step S2, the actual maximum lift-off value is... l omax =10 mm; minimum coil spacing D min =10mm.

5. A TR-type pulsed eddy current probe structure that can reduce the influence of lift-off fluctuations, used in the TR-type pulsed eddy current detection method for reducing the influence of lift-off fluctuations as described in any one of claims 1-4, characterized in that, The system includes a housing, which contains a receiving cavity, and the receiving cavity contains an excitation coil assembly and a receiving coil assembly. The excitation coil assembly includes: The excitation coil frame is fixed to the inner wall of the receiving cavity; The excitation coil is wound on the excitation coil frame, with its central axis set vertically. The receiving coil assembly includes: The mounting frame is slidably connected to the inner wall of the receiving cavity by means of a slide rail; the sliding direction of the mounting frame is horizontal, i.e., the X direction. The receiving coil frame is fixed on the mounting frame; The receiving coil is wound around the receiving coil frame, and the central axis of the receiving coil is set vertically; the receiving coil is outside the excitation coil and is not sleeved on the excitation coil. It also includes a drive assembly that moves the mounting frame along a slide rail; and excitation coil connectors and receiving coil connectors that are respectively connected to the excitation coil and the receiving coil.

6. The TR-type pulsed eddy current probe structure for reducing the influence of lift-off fluctuations according to claim 5, characterized in that, The driving component includes: The probe is movably mounted on the inner wall of the receiving cavity and can move vertically. The limiting spring and the limiting plate are located above the probe and are fixed to the inner wall of the receiving cavity. One end of the limiting spring is fixedly connected to the limiting plate and the other end is fixedly connected to the upper end of the probe. The limiting spring is always in a compressed state. The slider is fixedly connected to the probe. The rack is vertically positioned and fixedly connected to the slider. The transmission rod is rotatably connected to the receiving cavity. One end is fixed with a transmission gear, which coincides with the axis of the transmission rod and meshes with the rack. The other end is fixed with a driving bevel gear, which coincides with the axis of the transmission rod. The axis of the transmission rod is parallel to the X direction. The driven rod is rotatably connected to the inner wall of the receiving cavity, and its axis is set vertically. The driven bevel gear is fixed on the driven rod, coincides with the axis of the driven rod, and meshes with the driving bevel gear; A cam for moving the mounting frame is horizontally positioned with its outer edge abutting against the mounting frame; it is detachably connected to the driven rod. The spring used to reset the mounting frame is always in a compressed state. One end is fixedly connected to the spring limiting plate fixed on the inner wall of the receiving cavity, and the other end is fixedly connected to the surface wall of the mounting frame. The cam and the spring are located on opposite sides of the surface wall of the mounting frame.

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