Multi-pole magnetized Rayleigh wave electromagnetic ultrasonic transducer for detecting small defects of aluminum plate

Abstract

The invention discloses a multi-pole magnetized Rayleigh wave electromagnetic ultrasonic transducer for detecting small defects of an aluminum plate. The multi-pole magnetized Rayleigh wave electromagnetic ultrasonic transducer comprises a permanent magnet assembly, a fixed shell and a zigzag coil, the permanent magnet assembly comprises a rectangular magnet and an annular magnet; the rectangular magnet and the annular magnet are fixed through the fixing shell. The permanent magnet assembly is fixed to the fixing shell through 3D printing. And the zigzag coil is integrated into the flexible printed circuit board, is arranged right below the permanent magnet assembly, and is used for exciting ultrasonic waves and receiving reflected or transmitted ultrasonic wave signals. The Rayleigh wave electromagnetic ultrasonic transducer comprises the multi-pole magnetized rectangular magnet and the multi-pole magnetized annular magnet, the magnetization proportion of the inner side and the outer side of the annular magnet is variable, the electromagnetic ultrasonic transducer can increase the horizontal magnetic flux density, and accurate detection and quantitative analysis of variable-size submillimeter-scale cracks in an aluminum plate are facilitated.

Description

Technical Field

[0001] The present invention belongs to the technical field of electromagnetic ultrasonic nondestructive testing, and in particular relates to a multi-pole magnetized Rayleigh wave electromagnetic ultrasonic transducer for detecting small defects in aluminum plates. Background Art

[0002] Aluminum sheet is of great importance in industries such as automotive, marine, petrochemical, and aerospace. Submillimeter cracks in aluminum sheet caused by fatigue damage or corrosion can pose a safety hazard. Therefore, timely and accurate identification of these cracks can help prevent safety incidents.

[0003] Ultrasonic testing methods are widely used in the field of non-destructive testing and have unique advantages. In ultrasonic testing, traditional piezoelectric transducers require a relatively clean testing surface and coupling agent to ensure optimal contact between the sensor and the sample, which is not suitable for testing in harsh environments. However, the emergence of electromagnetic ultrasonic transducers (EMAT) has effectively solved these problems. Electromagnetic ultrasonic transducers do not need to be attached to the surface of the sample, so the sample to be tested does not need to be surface treated. In addition, electromagnetic ultrasonic transducers are also suitable for online monitoring of high-temperature environments and moving targets.

[0004] In aluminum sheet defect detection applications, Rayleigh waves are a unique type of guided wave that relies solely on a single propagation boundary, making them excellent for detecting defects in samples of greater thickness. Furthermore, due to their non-dispersive nature, Rayleigh waves are more suitable for detecting surface and near-surface defects than other wave modes.

[0005] However, existing Rayleigh wave electromagnetic ultrasonic transducers generally only provide a small horizontal magnetic flux density, making it difficult to accurately detect or quantify submillimeter cracks in aluminum plates. Therefore, it is necessary to invent a Rayleigh wave electromagnetic ultrasonic transducer with a larger horizontal magnetic flux density. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention proposes a multi-pole magnetized Rayleigh wave electromagnetic ultrasonic transducer for detecting small defects in aluminum plates to solve the problems existing in the above-mentioned prior art.

[0007] To achieve the above objectives, the present invention provides a multi-pole magnetized Rayleigh wave electromagnetic ultrasonic transducer for detecting small defects in aluminum plates, comprising:

[0008] Permanent magnet assembly, fixed shell, zigzag coil;

[0009] The permanent magnet assembly includes a rectangular magnet and an annular magnet; the rectangular magnet and the annular magnet are fixed in position by a fixed shell; the fixed shell is fixed to the permanent magnet assembly by 3D printing;

[0010] The meander coil is integrated into a flexible printed circuit board and placed directly below the permanent magnet assembly for exciting ultrasonic waves and receiving reflected or transmitted ultrasonic signals.

[0011] Optionally, the polarization directions of the left half and the right half of the rectangular magnet are opposite, the polarization directions of the outer side and the inner side of the left half of the annular magnet are opposite, and the polarization direction of the right half is opposite to that of the left half.

[0012] Optionally, the fixed shell is cylindrical, and a rectangular cavity with a square cross-section passes through the center of the cylindrical body for accommodating a rectangular magnet; wherein the left half of the rectangular magnet has the south pole at the top and the north pole at the bottom.

[0013] Optionally, the annular magnet wraps the fixed shell and the rectangular magnet, and the outer north pole of the left half of the annular magnet is at the top and the inner north pole is at the bottom.

[0014] Optionally, the permanent magnets in the permanent magnet assembly are all N52 sintered neodymium iron boron.

[0015] Optionally, seven factors are selected through orthogonal experiments, including the magnetization ratio of the inner and outer sides of the annular magnet, the outer radius, the width of the rectangular magnet, the coil lift-off, the wire width, the magnet lift-off and the number of coil turns. Three level values ​​are set for each factor, and a finite element model is used to simulate the performance under different parameter combinations. The Rayleigh wave displacement amplitude is extracted as the evaluation index, and the degree of influence of each factor on the performance is determined by range analysis, and finally the optimal structural parameter combination that maximizes the displacement amplitude is obtained.

[0016] Optionally, the parameters of the meander coil include a wire width of 0.3-0.9 mm, a wire spacing of 1.465 mm, a coil lift distance of 0.2-1.0 mm, and a coil turn number of 8-12; and the spacing between adjacent wires is half the wavelength of the Rayleigh wave.

[0017] Compared with the prior art, the present invention has the following advantages and technical effects:

[0018] The present invention provides a Rayleigh wave electromagnetic ultrasonic transducer comprising multi-pole magnetized rectangular and annular magnets, and the magnetization ratio of the inner and outer sides of the annular magnet is variable. This electromagnetic ultrasonic transducer can increase the horizontal magnetic flux density, which is beneficial for the accurate detection and quantitative analysis of submillimeter-scale cracks of variable sizes in aluminum plates. By comparing the finite element simulation results of the present invention with those of the multi-pole magnetized annular magnet electromagnetic ultrasonic transducer, it is shown that the present invention has better Lorentz force and displacement performance. In addition, when comparing the direct wave and reflected echo displacement when cracks of the same size are present, the displacement amplitude of the present invention is greater than that of the multi-pole magnetized rectangular magnet electromagnetic ultrasonic transducer, the multi-pole magnetized annular magnet electromagnetic ultrasonic transducer and the traditional cylindrical magnet electromagnetic ultrasonic transducer. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0020] Figure 1 Schematic diagram of the structure of MPRR-EMAT according to an embodiment of the present invention;

[0021] Figure 2 Schematic diagram of the polarization direction and dimensions of each component of the MPRR-EMAT according to an embodiment of the present invention;

[0022] Figure 3 is a flow chart of an embodiment of the present invention;

[0023] Figure 4 A two-dimensional finite element model of the MPRR-EMAT according to an embodiment of the present invention;

[0024] Figure 5 The static magnetic flux density distribution of the annular EMAT and MPRR-EMAT according to the embodiment of the present invention; (a) is a schematic diagram of the horizontal component distribution; (b) is a schematic diagram of the vertical component distribution;

[0025] Figure 6 The induced eddy current distribution of the annular EMAT and MPRR-EMAT according to the embodiment of the present invention;

[0026] Figure 7 Horizontal Lorentz force contributions of the annular EMAT and MPRR-EMAT according to an embodiment of the present invention; (a) is the annular EMAT; (b) is the MPRR-EMAT;

[0027] Figure 8 The vertical Lorentz force contributions of the annular EMAT and MPRR-EMAT according to the embodiment of the present invention are shown in FIG. (a) is the annular EMAT; (b) is the MPRR-EMAT.

[0028] Figure 9 1 is the displacement curve of the annular EMAT and the MPRR-EMAT at point P1 according to an embodiment of the present invention;

[0029] Figure 10 The displacement curves of different EMATs when there is a 0.5 mm crack in the embodiment of the present invention; (a) is the corresponding curve of MPRR-EMAT; (b) is the corresponding curve of rectangular EMAT; (c) is the corresponding curve of traditional cylindrical magnet EMAT; (d) is the corresponding curve of annular EMAT;

[0030] Figure 11Schematic diagram of a two-dimensional finite element model when detecting a 0.5 mm crack using the optimized MPRR-EMAT according to an embodiment of the present invention;

[0031] Figure 12 Schematic diagram of the displacement curve of the optimized MPRR-EMAT when cracks are present according to an embodiment of the present invention; (a) is the displacement curve of the optimized MPRR-EMAT when a 0.5 mm crack is present; (b) is the reflected wave displacement curve of a 0.3 mm longitudinal crack and a transverse crack; (c) is the reflected wave displacement curve of a 0.4 mm longitudinal crack and a transverse crack; (d) is the reflected wave displacement curve of a 0.6 mm longitudinal crack and a transverse crack; (e) is the reflected wave displacement curve of a 0.7 mm longitudinal crack and a transverse crack; (f) is the reflected wave displacement curve of a 0.8 mm longitudinal crack and a transverse crack;

[0032] Figure 13 : The displacement envelope of the reflected wave when longitudinal cracks and transverse cracks exist in the embodiment of the present invention; (a) is the longitudinal crack; (b) is the transverse crack;

[0033] Figure 14 Schematic diagrams of MPRR-EMAT with different magnetizing ratios of annular magnets according to an embodiment of the present invention; (a) is a schematic diagram of an MPRR-EMAT with a magnetizing ratio of 0.5, (b) is a schematic diagram of an MPRR-EMAT with a magnetizing ratio of 1, and (c) is a schematic diagram of an MPRR-EMAT with a magnetizing ratio of 2;

[0034] Figure 15 This is the range analysis result of the embodiment of the present invention. DETAILED DESCRIPTION

[0035] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0036] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0037] Example 1

[0038] This embodiment provides a multi-pole magnetized Rayleigh wave electromagnetic ultrasonic transducer for detecting small defects in aluminum plates, comprising: a multi-pole magnetized magnet assembly, a fixed shell, and a zigzag coil. Figure 1 As shown, the permanent magnet assembly consists of a rectangular and a ring magnet, fixed by a 3D-printed fixed shell, and the meander coil is integrated into the flexible printed circuit board (PCB). Figure 2The polarization directions of the rectangular and ring magnets in the MPRR-EMAT are shown. The left half of the rectangular magnet has the south pole at the top and the north pole at the bottom, while the right half has the opposite polarization direction. The left half of the ring magnet has the outer north pole at the top and the inner north pole at the bottom. Correspondingly, the right half of the ring magnet has the opposite polarization direction. The dimensions of the components in the MPRR-EMAT are shown in Table 1.

[0039] Table 1

[0040]

[0041] In EMAT, three energy conversion mechanisms can occur: the Lorentz force mechanism, the magnetostrictive force mechanism, and the magnetizing force mechanism. The Lorentz force mechanism only occurs in non-ferromagnetic conductors, such as copper and aluminum. In ferromagnetic materials such as steel, these three forces are simultaneously generated, with the magnetostrictive force and the Lorentz force being dominant. Since the application object of this embodiment is an aluminum plate, only the Lorentz force is considered.

[0042] When using a Rayleigh wave electromagnetic ultrasonic transducer to detect defects in aluminum sheets, the excitation principle of the Rayleigh wave is as follows: a high-frequency pulse current is input into a zigzag coil, with the currents in adjacent conductors flowing in opposite directions. Simultaneously, an alternating magnetic field is induced around the coil, which in turn induces eddy currents in the aluminum sheet's skin layer that are equal in magnitude but opposite in direction to the excitation current.

[0043]

[0044] In formula (1), H d is the dynamic magnetic field strength, J c is the excitation pulse. In formula (2), B d is the dynamic magnetic induction intensity, A is the magnetic vector potential. In formula (3), J e is the induced eddy current, and σ represents the electrical conductivity of aluminum. Under the action of static and dynamic magnetic fields, the induced eddy current generates a Lorentz force, which in turn causes the particles in the sample to vibrate and propagate through the aluminum plate in the form of ultrasonic waves.

[0045] F L =F s +F d (4)

[0046] F s =J e ×B s (5)

[0047] F d =J e ×B d (6)

[0048] In formula (4), F L is the total Lorentz force, Fs is the static Lorentz force, F d is the dynamic Lorentz force.

[0049] When the reflected wave or transmitted wave after encountering the defect propagates into the receiving range of EMAT, it will cause the vibration of the particles in the metal sample. Due to the influence of the static bias magnetic field, the source current density J is induced in the skin layer of the aluminum plate. L At the same time, the source current in the receiving coil induces an alternating magnetic field B t , which is input into EMAT in the form of induced voltage V. The control equation of the ultrasonic receiving process is:

[0050] J L =σv×B s (7)

[0051] J t =σv×(B s +B t )+σE(8)

[0052]

[0053] In formula (7), v is the particle vibration velocity. In formula (8), J t is the total current density in the aluminum plate, E is the induced electric field strength. μ in formula (10) represents the magnetic permeability of the magnet.

[0054] Because the designed multi-pole magnet combination increases the horizontal static magnetic flux density, it can excite more energetic Rayleigh waves. Similarly, the received Rayleigh wave signal is also stronger.

[0055] To verify the effectiveness of the present invention, Figure 3 As shown, this embodiment first uses COMSOL Multiphysics software to establish a finite element model to compare the performance of MPRR-EMAT and multi-pole magnetized annular EMAT (in the present invention, the multi-pole magnetized rectangular magnet EMAT is referred to as rectangular EMAT, and the multi-pole magnetized annular magnet EMAT is referred to as annular EMAT). Then, an orthogonal experiment is designed to optimize the structure of the MPRR-EMAT. Furthermore, the influence of the structural parameters of the MPRR-EMAT on the Rayleigh wave displacement amplitude is studied through range analysis to obtain the optimal parameter combination. In addition, the direct wave and reflected wave displacement amplitudes of the MPRR-EMAT, rectangular EMAT, annular EMAT, and traditional cylindrical magnet EMAT under cracks of the same size are compared. Finally, the MPRR-EMAT with the optimal parameter combination is used to detect submillimeter cracks with varying depth and width, and the Spearman correlation coefficient is calculated to obtain the linear correlation relationship between the crack size and the reflected wave displacement amplitude.

[0056] The two-dimensional finite element models of MPRR-EMAT and annular EMAT were established using the finite element software COMSOL Multiphysics. The finite element models of the two EMATs are consistent except for the permanent magnets. Figure 4 Shown is the numerical model of MPRR-EMAT.

[0057] 1) Magnetic field analysis:

[0058] Figure 5 Figures (a) and (b) show the horizontal and vertical static magnetic flux density distributions of EMATs with different magnet configurations along the X-axis, respectively, at a depth of 0.05 mm below the surface of the aluminum plate. The figures clearly show that, compared to the annular EMAT, the MPRR-EMAT significantly increases the horizontal magnetic flux density without significantly reducing the vertical magnetic flux density, which contributes to a larger vertical displacement component of the Rayleigh wave. The fact that the vertical component of the Rayleigh wave displacement is dominant indicates an increase in the Rayleigh wave intensity.

[0059] 2) Eddy current analysis:

[0060] Figure 6 It shows that the two EMATs mentioned above have the same eddy current distribution near the surface of the aluminum plate at 3μs. In this figure, the eddy current density directly under each conductor is the largest and the values ​​are equal, and the eddy currents under adjacent conductors are in opposite directions.

[0061] 3) Lorentz force analysis:

[0062] Figure 7 The figure shows the Lorentz force contribution of the two EMATs in the horizontal direction at 3 μs. This figure shows that the maximum Lorentz force of the two EMATs appears just below the left and right sides of the wire, and the value of MPRR-EMAT is large.

[0063] Figure 8 The vertical Lorentz force contributions of the two EMATs at 3 μs are shown. The maximum Lorentz force is observed below the conductors of the two EMATs, similar to eddy currents. However, the maximum vertical Lorentz force of the ring-shaped EMAT is smaller than that of the MPRR-EMAT.

[0064] 4) Displacement analysis:

[0065] For MPRR-EMAT, at the intercept point P1 (25, 9.95), the horizontal displacement amplitude u of the Rayleigh wave is m and vertical displacement amplitude v m They are 6.38×10 -8 mm and 1.18×10 -7 mm. Figure 9The displacement curves of the two EMATs at P1 are shown. It can be seen that the displacement amplitude generated by the MPRR-EMAT is significantly larger than that of the ring-shaped EMAT.

[0066] 2. Orthogonal experiment and range analysis results

[0067] The best parameter combination obtained by orthogonal experiment and range analysis is as follows: W1 = 18 mm, l1 = 0.2 mm, W2 = 0.3 mm, l2 = 0.3 mm, P c =2, R2=13mm, n=8.

[0068] 3. Comparative Experimental Results

[0069] In the present invention, point P2 (45, 9.95) is used as the ultrasonic signal receiving point, and the left edge of the crack is 240mm away from the center of the EMAT. When the crack depth changes, the width is fixed at 0.5mm; on the contrary, when the crack width changes, the depth is fixed at 0.5mm, and the crack depth and width increase from 0.3mm to 0.8mm at intervals of 0.1mm. Figure 10 In the figure, the displacements generated by conventional cylindrical magnet EMAT, rectangular EMAT, annular EMAT and MPRR-EMAT when there is a 0.5mm crack are compared. As can be seen from the figure, the displacement amplitudes M of the direct wave and reflected wave generated by MPRR-EMAT are d and M r Significantly larger than the other EMATs. Furthermore, the direct wave displacement amplitudes of the cylindrical, rectangular, and MPRR-EMAT are approximately 7.8, 10.6, and 11.5 times that of the annular EMAT, respectively; while the reflected wave displacement amplitudes are approximately 6.4, 9, and 9.8 times that of the annular EMAT. Furthermore, it is clear that the peak times of the MPRR-EMAT and rectangular EMAT are roughly the same, while the peak times of the cylindrical and annular EMATs are earlier than those of the aforementioned two EMATs.

[0070] 4. Small crack detection results

[0071] The orthogonally optimized MPRR-EMAT is used to detect sub-millimeter cracks of different sizes. Figure 11 A two-dimensional finite element model is shown, corresponding to a small crack with a depth and width of 0.5 mm. Figure 12 (a) shows the displacement curve of the optimized MPRR-EMAT at point P2 when the depth and width of the small crack are both 0.5 mm. As shown in the figure, the flight time (TOF) between the direct wave and the defect reflection echo is 138.4 μs, and the distance difference ΔS between the peaks is 390 mm. The wave velocity C calculated according to formula (12) is s =2818m / s.

[0072]

[0073] Simulated wave speed C s The error Δk=3.8% from the theoretical wave velocity C can be obtained from formula (13):

[0074]

[0075] This demonstrates that the optimized MPRR-EMAT can effectively excite and receive Rayleigh waves.

[0076] In this embodiment, the small cracks with varying depths are referred to as longitudinal cracks, and the small cracks with varying widths are referred to as transverse cracks. Figure 12 Figures (b)-(f) show a comparison of the reflected echo displacement at point P2 when longitudinal and transverse cracks of equal area are present. When the crack depth or width is 0.5 mm, the longitudinal crack is considered a transverse crack. Therefore, the comparison of the reflected wave displacement for a 0.5 mm crack is omitted in this discussion. These figures show that when the size changes are 0.3 mm and 0.4 mm, the reflected wave displacement amplitude of the transverse crack is greater than that of the longitudinal crack; conversely, for cracks with a size change ranging from 0.6 mm to 0.8 mm, the reflected wave displacement amplitude of the longitudinal crack is greater than that of the transverse crack. In other words, when the areas of the longitudinal crack and the transverse crack are equal, the deeper crack type produces a greater reflected wave displacement amplitude.

[0077] 5. Linear correlation analysis results between crack size and reflected wave displacement amplitude

[0078] Figure 13 Figures (a) and (b) show the reflected echo envelopes of longitudinal and transverse cracks, plotted using the findpeaks function in MATLAB software. This demonstrates that the orthogonally optimized MPRR-EMAT can effectively detect submillimeter cracks of varying sizes. The figures show that the displacement amplitude of the reflected wave increases with the depth and width of the small crack, and this change becomes more pronounced with increasing crack depth.

[0079] The Spearman correlation coefficient was further calculated to characterize the relationship between the crack size and the reflected echo displacement amplitude M of the longitudinal and transverse cracks. l and M h As shown in Table 2, the Spearman correlation coefficient ρ is 1.00 and the p value is 0.0028, indicating that the size of the small crack is positively correlated with the displacement amplitude of the reflected wave.

[0080] Table 2

[0081]

[0082] Finite element simulation results comparing the present invention with those of a multi-pole ring-shaped electromagnetic ultrasonic transducer demonstrate superior Lorentz force and displacement performance. Furthermore, when comparing the direct wave and reflected echo displacements in the presence of cracks of the same size, the present invention exhibits greater displacement amplitudes than those of a multi-pole rectangular magnet, a multi-pole ring-shaped electromagnetic ultrasonic transducer, and a conventional cylindrical magnet.

[0083] Example:

[0084] 1. Finite Element Modeling

[0085] In this embodiment, all permanent magnets are N52 sintered NdFeB. The excitation current I is 100A, the signal excitation frequency f is 1 MHz, and a six-cycle cosine pulse modulated by a Hanning window is used. Furthermore, the magnet height h1, the inner diameter R1 of the ring magnet, and the coil thickness t are set to 30 mm, 10 mm, and 0.2 mm, respectively. The theoretical propagation velocity C of Rayleigh waves in aluminum is 2930 m / s, and the wavelength λ in this example is 2.93 mm.

[0086] In order to utilize the principle of constructive interference of current signals in adjacent conductors to enhance the amplitude of ultrasonic signals, the distance d between adjacent conductors should be set to half the wavelength, i.e. 1.465mm. Since induced eddy currents and electromagnetic forces are generated within the skin layer of the aluminum plate, and Rayleigh waves mainly propagate at a depth approximately equal to their wavelength. Therefore, 3mm below the upper surface of the aluminum plate is set as the volume load area. In order to reduce interference from reflected waves, the left, right, and bottom boundaries of the aluminum plate are set as low-reflection boundaries. According to the formula:

[0087]

[0088] Here the skin depth of the sample is δ0.0815mm, ρ m =2.62×10 -8 ω / m is the resistivity of the aluminum plate.

[0089] μ=μ0μ r (15)

[0090] Where μ is the magnetic permeability of the aluminum plate, μ0 represents the magnetic permeability of vacuum, and μ r is the relative magnetic permeability of the aluminum plate, μ r =1.

[0091] In EMAT finite element modeling, each wavelength should contain at least eight elements to ensure accurate solutions. Furthermore, the size of the air domain affects the accuracy of the static and dynamic magnetic field calculations. Therefore, an infinite element domain was set outside the air domain to approximate the infinite propagation of ultrasound in air, with an ultrafine mesh size. Furthermore, a boundary layer mesh was added to the volume loading region to ensure complete coverage of the skin layer. The number of layers was set to eight, with the first layer thickness set to 0.05 mm and a stretch factor of 1.2.

[0092] 2. Orthogonal Experiment

[0093] The influence of seven factors on the MPRR-EMAT signal amplitude was studied by orthogonal experimental method. These factors include the magnetization ratio P of the inner and outer sides of the ring magnet. c , the outer radius R2 of the ring magnet, the width W1 of the rectangular magnet, the coil lift-off l1, the width W2 of the conductor, the magnet lift-off l2 and the number of turns n of the coil. Figure 14 Schematic diagram of MPRR-EMAT with different magnetization ratios of the ring magnet is shown.

[0094] In this embodiment, three levels are selected for each factor, as shown in Table 3. The variation ranges of the MPRR-EMAT structural parameters are as follows: W1: 13-18 mm, l1: 0.2-1.0 mm, W2: 0.3-0.9 mm, l2: 0.3-2.3 mm, P c :0.5-2, R2:13-19mm, n:8-12. Therefore, L 18 (3 7 ) The orthogonal table is selected to carry out the orthogonal experiment, as shown in Table 4. The horizontal displacement amplitude u of the Rayleigh wave at point P1 is extracted m and vertical displacement amplitude v m As evaluation indicators, see the last two columns of Table 4.

[0095] Table 3

[0096]

[0097] Table 4

[0098]

[0099]

[0100] 3. Range Analysis

[0101] After obtaining the experimental results according to the orthogonal table, we can calculate u for each factor at each level. m and v m The arithmetic mean of the factors is used to show the influence of each factor on the signal amplitude (where Z represents the factor number and N represents the level number; for example, K11 Indicates the arithmetic mean of the experimental results of the first level of the first factor). Influence degree T Z As shown in Table 5.

[0102]

[0103] T Z =R maxZ -R minZ (17)

[0104] R maxZ =max{K Z1 ,K Z2 ,K Z3}(18)

[0105] R minZ =min{K Z1 ,K Z2 ,K Z3}(19)

[0106] In formula (16), i is the experimental number, m=6, n=18, and y is the experimental result; here y is u m and v m .

[0107] Table 5

[0108]

[0109] Figure 15 The arithmetic mean of each level under the seven factors and the effect of each factor on u are shown. m and v m The figure shows that the influence of u m The primary factor is the coil lift-off l1, followed by the magnet lift-off l2 and the ring magnet magnetization ratio P c , coil width W2, rectangular magnet width W1 and coil turns n, the outer radius R2 of the ring magnet has the least effect. m , except W1 and W2 with u m On the contrary, the influence of other factors is related to u m At the same time, it is obvious that increasing l1, l2 and W2 will reduce the amplitude of the signal. In addition, when the inner and outer sides of the ring magnet are magnetized in equal proportions, the displacement amplitude is the smallest. c When =2, the displacement amplitude is the largest.

[0110] The best parameter combination is as follows: W1 = 18 mm, l1 = 0.2 mm, W2 = 0.3 mm, l2 = 0.3 mm, P c=2, R2=13mm, n=8. It is worth noting that this combination is not included in the orthogonal table, so it is effective to use the orthogonal experimental method to optimize the structural parameters. Experimenting with this combination yields u m =28.1×10 -8 mm and v m =5.23×10 -7 mm, both of which exceed any u recorded in the orthogonal table m and v m .

[0111] The above are merely preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A multi-pole magnetized Rayleigh wave electromagnetic ultrasonic transducer for detecting small defects in aluminum plates, characterized in that: include: Permanent magnet assembly, fixed shell, zigzag coil; The permanent magnet assembly includes a rectangular magnet and a ring magnet; The rectangular magnet and the annular magnet are fixed in position by a fixed shell; the fixed shell is fixed to the permanent magnet assembly by 3D printing; The meander coil is integrated into a flexible printed circuit board and placed directly below the permanent magnet assembly for exciting ultrasonic waves and receiving reflected or transmitted ultrasonic signals.

2. The multi-pole magnetized Rayleigh wave electromagnetic ultrasonic transducer for detecting small defects in aluminum plates according to claim 1, characterized in that: The polarization directions of the left half and the right half of the rectangular magnet are opposite, the polarization directions of the outer side and the inner side of the left half of the annular magnet are opposite, and the polarization direction of the right half is opposite to that of the left half.

3. The multi-pole magnetized Rayleigh wave electromagnetic ultrasonic transducer for detecting small defects in aluminum plates according to claim 2, characterized in that: The fixed shell is cylindrical, and a rectangular cavity with a square cross-section passes through the center of the cylindrical body for accommodating a rectangular magnet; wherein the left half of the rectangular magnet has the south pole at the top and the north pole at the bottom.

4. The multi-pole magnetized Rayleigh wave electromagnetic ultrasonic transducer for detecting small defects in aluminum plates according to claim 3, characterized in that: The annular magnet wraps the fixed shell and the rectangular magnet, and the outer north pole of the left half of the annular magnet is at the top and the inner north pole is at the bottom.

5. The multi-pole magnetized Rayleigh wave electromagnetic ultrasonic transducer for detecting small defects in aluminum plates according to claim 4, characterized in that: The permanent magnets in the permanent magnet assembly are all N52 sintered neodymium iron boron.

6. The multi-pole magnetized Rayleigh wave electromagnetic ultrasonic transducer for detecting small defects in aluminum plates according to claim 5, characterized in that: Seven factors were selected through orthogonal experiments, including the magnetization ratio of the inner and outer sides of the annular magnet, the outer radius, the width of the rectangular magnet, the coil lift-off, the wire width, the magnet lift-off and the number of coil turns. Each factor was set to three levels, and a finite element model was used to simulate the performance under different parameter combinations. The Rayleigh wave displacement amplitude was extracted as the evaluation index, and the degree of influence of each factor on the performance was determined through range analysis. Finally, the optimal structural parameter combination that maximizes the displacement amplitude was obtained.

7. The multi-pole magnetized Rayleigh wave electromagnetic ultrasonic transducer for detecting small defects in aluminum plates according to claim 1, characterized in that: The parameters of the zigzag coil include a wire width of 0.3-0.9 mm, a wire spacing of 1.465 mm, a coil lift distance of 0.2-1.0 mm, and a coil number of 8-12 turns; the spacing between adjacent wires is half the wavelength of the Rayleigh wave.

Images