A multi-magnetic-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plate and a design method thereof

Abstract

The application discloses a kind of rough aluminium plate crack detection multi-magnetic pole electromagnetic ultrasonic transducer and design method, belong to electromagnetic ultrasonic transducer technical field, specifically include the following steps: S1, design structure;S2, construct two-dimensional finite element model, analyze characteristic;S3, structure optimization is carried out through orthogonal experiment and range analysis;S4, rough aluminium plate crack simulation detection is carried out, obtains the attenuation of Rayleigh wave with depth change under different aluminium plate surface state;S5, using reflection coefficient and transmission coefficient fitting curve to rough aluminium plate crack size quantitative analysis.The application adopts the above-mentioned rough aluminium plate crack detection multi-magnetic pole electromagnetic ultrasonic transducer and design method, can increase static magnetic flux density excitation energy stronger ultrasonic wave and increase the transduction efficiency of electromagnetic ultrasonic transducer, by exciting Rayleigh wave helps the accurate detection and quantitative analysis of surface crack in rough aluminium plate.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic ultrasonic transducer technology, and in particular to a multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates and its design method. Background Technology

[0002] Aluminum sheets are widely used in various industrial fields. Cracks and damage are prone to occur during the manufacturing and service of aluminum sheets, and when the surface of the aluminum sheet is rough, these damages can affect the normal operation of equipment and even cause safety accidents. Therefore, how to efficiently and accurately identify these damages is an important issue.

[0003] In traditional ultrasonic testing, piezoelectric transducers require direct contact with the test surface, and their accuracy depends heavily on the cleanliness of the sample surface. Conversely, electromagnetic acoustic transducers (EMAT) have attracted considerable attention because they do not require contact with the sample surface and are suitable for testing in harsh environments. However, existing EMAT transducers still suffer from low transduction efficiency, hindering their further development. Therefore, it is essential to invent an EMAT transducer capable of detecting cracks in rough aluminum plates. Summary of the Invention

[0004] The purpose of this invention is to provide a multi-pole electromagnetic ultrasonic transducer and its design method for detecting cracks in rough aluminum plates. This method can increase the static magnetic flux density to excite stronger ultrasonic waves and increase the transduction efficiency of the electromagnetic ultrasonic transducer. By exciting Rayleigh waves, it helps to accurately detect and quantitatively analyze surface cracks in rough aluminum plates. The optimal parameter combination of MP-EMAT with good crack detection performance in rough aluminum plates is obtained by using orthogonal experiments and range analysis. The polynomial fitting curve expressions of reflection coefficient and transmission coefficient obtained by MP-EMAT detection of cracks in rough aluminum plates are used to quantify cracks at different crack depths.

[0005] To achieve the above objectives, the present invention provides a design method for a multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates, specifically including the following steps: S1. Design the MP-EMAT structure; S2. Construct two-dimensional finite element models of MP-EMAT and cylindrical EMAT, and analyze the characteristics of MP-EMAT and cylindrical EMAT. S3. Optimize the structure by determining the optimal parameter combination of MP-EMAT through orthogonal experiments and range analysis; S4. The optimized MP-EMAT was used to simulate and detect cracks in rough aluminum plates, and the attenuation of the Rayleigh wave displacement amplitude excited by the optimized MP-EMAT under different aluminum plate surface conditions was obtained as a function of probe depth and crack depth. S5. Quantitative analysis of crack size in rough aluminum plate using curve fitting of reflection coefficient and transmission coefficient.

[0006] Preferably, a scaling law model is constructed in S1, wherein the eddy current density induced by the excitation coil in the aluminum plate is... With excitation current and angular frequency Proportional, that is In the excitation current When kept constant, eddy current density Treating it as a constant, therefore the static Lorentz force density Directly proportional to static magnetic flux density ,Right now The amplitude of the excited ultrasonic displacement With static Lorentz force density Proportional, that is Ultrasonic output power Proportional to displacement amplitude The square of, that is Energy conversion efficiency Ultrasonic output power With input electromagnetic power The ratio of energy conversion efficiency to the input electromagnetic power, under the condition of constant input electromagnetic power. Proportional to ultrasonic output power Therefore, the core scaling relationship can be derived as follows: ; ; ; in, The density of the aluminum plate, The speed at which Rayleigh waves propagate in an aluminum plate. The impedance of the transducer is given.

[0007] Preferably, in S2, magnetic field analysis, eddy current analysis, Lorentz force analysis, and displacement field analysis are performed on the MP-EMAT and cylindrical EMAT, and the excitation current during finite element analysis is... The expression is as follows: ; in, For the excitation current amplitude, For the excitation frequency, The number of cycles.

[0008] Preferably, the influencing factors in S3 include coil lift-off. wire width Magnet lifting Wire thickness , radius of cylindrical magnet The ratio of the outer radius to the inner radius of a toroidal magnet and the number of coil turns Each parameter has three levels, and a suitable orthogonal array is selected and denoted as follows: The factors are assigned to an orthogonal table, simulation experiments are arranged according to the table and the results are recorded, and range analysis is used to obtain the ranking of the influence of each factor on the displacement amplitude and the optimal parameter combination.

[0009] Preferably, range analysis is used to rank the influence of each factor on the displacement amplitude and determine the optimal parameter combination. The calculation formula is shown below: ; ; ; ; in, This indicates that each factor is represented at each level. The arithmetic mean, For factor number, For horizontal sequence number, For the test number, For the test results ( M ).

[0010] Preferably, in S4, points P2 and P3 are used as receiving points for reflected and transmitted ultrasonic signals, respectively. The left edge of the crack is 200 mm from the center of MP-EMAT, the crack width is fixed at 0.5 mm, and the aluminum plate in the Rayleigh wave excitation area is set as a smooth surface and a rough surface, respectively.

[0011] Preferably, the reflection coefficient in S5 and transmission coefficient The calculation formula is as follows: ; ; in, The amplitude of the reflected wave displacement. The direct wave displacement amplitude, This represents the amplitude of the transmitted wave displacement.

[0012] This invention provides a multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates. The transducer is designed using the aforementioned design method and includes a PCB board with an integrated anti-bending coil. A support shell is positioned above the PCB board, with a multi-pole cylindrical magnet fixed inside and a multi-pole annular magnet fixed outside. The shape of the support shell is adapted to the shapes of the multi-pole cylindrical and annular magnets. The left half of both the multi-pole cylindrical and annular magnets has the south pole at the top and the north pole at the bottom, while the right half has the north pole at the top and the south pole at the bottom.

[0013] Therefore, the present invention employs the above-mentioned multi-pole electromagnetic ultrasonic transducer and design method for detecting cracks in rough aluminum plates. This method can increase the static magnetic flux density to excite stronger ultrasonic waves and increase the transduction efficiency of the electromagnetic ultrasonic transducer. By exciting Rayleigh waves, it helps to accurately detect and quantitatively analyze surface cracks in rough aluminum plates. The optimal parameter combination of MP-EMAT with good crack detection performance in rough aluminum plates is obtained by using orthogonal experiments and range analysis. The polynomial fitting curve expressions of reflection coefficient and transmission coefficient obtained by MP-EMAT detection of cracks in rough aluminum plates are used to quantify cracks at different crack depths.

[0014] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0015] Figure 1 This is a flowchart of a design method for a multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates according to the present invention. Figure 2 This is the excitation current waveform diagram of the design method of a multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates according to the present invention. Figure 3 This is the MP-EMAT finite element model mesh diagram of the design method of a multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates according to the present invention. Figure 4 This is a static magnetic flux density curve diagram of cylindrical EMAT and MP-EMAT for a design method of a multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates according to the present invention; wherein, Figure 4 (a) in the figure is the static magnetic flux density curve of the horizontal component; Figure 4 (b) in the figure is the static magnetic flux density curve of the vertical component; Figure 5 The diagram shows the induced eddy current distribution of cylindrical EMAT and MP-EMAT in the design method of a multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates according to the present invention. Figure 6This is a diagram showing the horizontal Lorentz force distribution of cylindrical EMAT and MP-EMAT in the design method of a multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates according to the present invention; wherein, Figure 6 (a) in the diagram is the distribution of the horizontal Lorentz force on the cylindrical EMAT. Figure 6 (b) in the figure is the horizontal Lorentz force distribution diagram of MP-EMAT; Figure 7 This is a diagram showing the vertical Lorentz force distribution of cylindrical EMAT and MP-EMAT in the design method of a multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates according to the present invention; wherein, Figure 7 (a) in the figure is the vertical Lorentz force distribution diagram of the cylindrical EMAT; Figure 7 (b) in the figure is the vertical Lorentz force distribution diagram of MP-EMAT; Figure 8 This is a displacement curve of cylindrical EMAT and MP-EMAT at point P1, representing the design method of a multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates according to the present invention. Figure 9 This invention relates to a design method for a multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates. The MP-EMAT two-dimensional finite element model of the rough aluminum plate is shown when the crack size is 0.5 mm. Figure 10 This invention relates to a design method for a multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates. The diagram shows the displacement amplitude curves of the aluminum plate under different surface conditions, where the probe depth and crack depth are proportional to the Rayleigh wave wavelength. Figure 10 (a) in the figure is a curve showing the change in displacement amplitude when the probe depth is proportional to the Rayleigh wave wavelength; Figure 10 (b) in the figure shows the amplitude curves of the reflected wave displacement and the transmitted wave displacement when the crack depth is proportional to the Rayleigh wave wavelength. Figure 11 This invention relates to a design method for a multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates, specifically the displacement envelopes of reflected and transmitted waves when the crack depth changes under different surface conditions of the aluminum plate; wherein... Figure 11 In the image, (a) represents a wave reflected from a smooth surface; Figure 11 (b) in the image represents a wave transmitted through a smooth surface. Figure 11 (c) in the equation represents the wave reflected from the rough surface. Figure 11 In the diagram, (d) represents the transmitted wave over a rough surface; Figure 12 This invention relates to a design method for a multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates, and includes a fitting curve of the reflection coefficient and transmission coefficient. Figure 12 In this context, (a) represents the reflection coefficient; Figure 12 In this context, (b) represents the transmission coefficient; Figure 13This is a schematic diagram of the structure of the MP-EMAT multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates according to the present invention. Figure 14 This is a diagram showing the polarization direction and dimensions of each component of the MP-EMAT multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates according to the present invention. Detailed Implementation

[0016] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0017] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0018] Example 1 like Figure 1 As shown, this invention provides a design method for a multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates, specifically including the following steps: S1. Design the structure of an MP-EMAT (Multi-pole Electromagnetic Acoustic Transducer) containing a pair of cylindrical and annular concentric permanent magnets with multiple magnetic poles. Construct a scaling law model, in which the eddy current density induced by the excitation coil in the aluminum plate is... With excitation current and angular frequency Proportional, that is In the excitation current When kept constant, eddy current density Treating it as a constant, therefore the static Lorentz force density Directly proportional to static magnetic flux density ,Right now The amplitude of the excited ultrasonic displacement With static Lorentz force density Proportional, that is Ultrasonic output power Proportional to displacement amplitude The square of, that is Energy conversion efficiency Ultrasonic output power With input electromagnetic power The ratio of energy conversion efficiency to the input electromagnetic power, under the condition of constant input electromagnetic power. Proportional to ultrasonic output power Therefore, the core scaling relationship can be derived as follows: ; ; ; in, The density of the aluminum plate, The speed at which Rayleigh waves propagate in an aluminum plate. The impedance of the transducer is given.

[0019] The dimensions of each component in MP-EMAT and the excitation current parameters are shown in Table 1.

[0020] Table 1 MP-EMAT Structure and Current Parameters

[0021] S2. Construct two-dimensional finite element models of MP-EMAT and cylindrical EMAT, and analyze the characteristics of MP-EMAT and cylindrical EMAT. In this invention, sintered NdFeB magnets are used throughout. The theoretical propagation speed of Rayleigh waves in aluminum. C It's 2930 m / s, the wavelength here. λ It is 2.93mm. Figure 2 The waveform of the excitation signal is shown. A boundary layer mesh was added to the skin layer of the aluminum plate, and the left, right, and bottom boundaries of the aluminum plate were set as low-reflection boundaries. Figure 3 This is a mesh diagram of the MP-EMAT two-dimensional finite element model. The excitation current during finite element analysis is also shown. The expression is as follows: ; in, For the excitation current amplitude, For the excitation frequency, The number of cycles.

[0022] Magnetic field analysis, eddy current analysis, Lorentz force analysis, and displacement field analysis were performed on MP-EMAT and cylindrical EMAT.

[0023] Magnetic field analysis: Figure 4Figures (a) and (b) show the horizontal and vertical static magnetic flux density distributions of two magnet configurations of EMAT along the X-axis at 0.05 mm below the upper surface of the aluminum plate, respectively. It is clear from the figures that the MP-EMAT significantly increases the magnetic flux density compared to the cylindrical EMAT, raising the maximum horizontal magnetic flux density by approximately 25%, which contributes to the generation of a larger Rayleigh wave vertical displacement component. Since the Rayleigh wave displacement is predominantly vertical, this indicates an increase in Rayleigh wave intensity.

[0024] Eddy current analysis: Figure 5 The figure shows that the two EMATs have the same eddy current distribution near the aluminum plate surface when the time is 3 μs. In this figure, the eddy current density is the largest and the values ​​are equal directly below each conductor, and the eddy current directions are opposite below adjacent conductors.

[0025] Lorentz force analysis: Figure 6 The figure shows the Lorentz force distribution of the two EMATs in the horizontal direction at 3 μs. The figure indicates that the maximum Lorentz force of the two EMATs occurs directly below the conductor, and the Lorentz force at the center of the EMAT is smaller than that on the left and right sides. It is also clearly visible that the value of MP-EMAT is larger.

[0026] Figure 7 The Lorentz force distribution of the two EMATs in the vertical direction at 3 μs is shown. The maximum Lorentz force is observed below the conductors of both EMATs. Unlike the horizontal Lorentz force distribution, the Lorentz force decreases from the center of the EMAT towards the left and right sides. Furthermore, the maximum vertical Lorentz force of the cylindrical EMAT is smaller than that of the MP-EMAT.

[0027] Displacement analysis: Figure 8 The displacement curves of the two EMATs at P1 (30, 9.95) are shown. It can be seen that the displacement amplitude generated by the MP-EMAT is significantly greater than that of the cylindrical EMAT. Further analysis extracts the total displacement amplitude of the cylindrical EMAT and the MP-EMAT at P1. . The values ​​are: 1.13 × 10 -7 mm, 1.70×10 -7 mm. Calculations show that the transduction efficiency of MP-EMAT is approximately 126% higher than that of cylindrical EMAT.

[0028] S3. Optimize the structure by determining the optimal parameter combination of MP-EMAT through orthogonal experiments and range analysis; Influencing factors include coil lift-off distance wire width Magnet lifting Wire thickness , radius of cylindrical magnet The ratio of the outer radius to the inner radius of a toroidal magnet and the number of coil turns Each parameter has three levels, as shown in Table 2. The range of variation for the MP-EMAT structural parameters is shown below: 0.5-1.5mm 0.2-0.6mm 0.4-1.2mm 0.1-0.3mm : 6.0-9.0mm, 1.3-1.7 10-18 turns. Choose a suitable orthogonal array denoted as... The displacement amplitude at point P1 (30, 9.95) was extracted for conducting orthogonal experiments, as shown in Table 3. As evaluation indicators, see the last column of Table 3.

[0029] Table 2. Range of MP-EMAT structural parameters

[0030] Table 3. Numerical calculation results of MP-EMAT combination parameters based on orthogonal experiments.

[0031] The factors are assigned to an orthogonal table, simulation experiments are arranged according to the table and the results are recorded. Range analysis is used to obtain the ranking of the influence of each factor on the displacement amplitude and the optimal parameter combination.

[0032] Range analysis was used to rank the influence of each factor on the displacement amplitude and to determine the optimal parameter combination. The calculation formula is shown below: ; ; ; ; in, This indicates that each factor is represented at each level. The arithmetic mean, For factor number, For horizontal sequence number, For the test number, The test result is the displacement amplitude. , , For example, K 11This represents the arithmetic mean of the results from the first-factor, first-level trial. It also represents the degree of influence of each factor. As shown in Table 4.

[0033] Table 4 Summary of orthogonal experiment results

[0034] The orthogonal experiment results show that the influence The primary factor is the coil lift-off distance. Secondly, the number of coil turns Magnet lifting l 2. Wire width Wire thickness , radius of cylindrical magnet The ratio of the outer radius to the inner radius of the toroidal magnet Minimal impact.

[0035] The optimal parameter combination obtained through orthogonal experiments and range analysis is as follows: Coil lift-off distance =0.5mm, wire width =0.4mm, magnet lift-off =0.4mm, wire thickness =0.1mm, radius of cylindrical magnet =9mm, the ratio of the outer radius to the inner radius of the toroidal magnet =1.5 and the number of coil turns =10 turns.

[0036] It is worth noting that this combination is not included in the orthogonal array, therefore optimizing the structural parameters using orthogonal experimental design is effective. A finite element model is established using this combination, and the displacement amplitude of the Rayleigh wave at point P1 is extracted. ,get =37.81 10 -8 mm, exceeding any record in the orthogonal array Furthermore, calculations show that the conversion efficiency of the optimized MP-EMAT is approximately five times that of the unoptimized version.

[0037] S4. The optimized MP-EMAT was used to simulate and detect cracks in rough aluminum plates, and the attenuation of the Rayleigh wave displacement amplitude excited by the optimized MP-EMAT under different aluminum plate surface conditions was obtained as a function of probe depth and crack depth. Points P2 (170, 9.95) and P3 (220, 9.95) were used as receiving points for reflected and transmitted ultrasonic signals, respectively. The left edge of the crack was 200 mm from the center of the MP-EMAT, and the crack width was fixed at 0.5 mm. The orthogonally optimized MP-EMAT was used to simulate and detect defects at different depths. To compare the difference in defect detection by MP-EMAT on aluminum plates with different surface conditions, the aluminum plate in the Rayleigh wave excitation region was set to a smooth surface and a rough surface, respectively. This Gaussian random rough surface was generated by MATLAB, and the relevant length... Set to 0.3mm, root mean square height Set to 0.1mm. Figure 9 A two-dimensional MP-EMAT finite element model of an aluminum plate with a rough surface excitation region is shown, where the air domain is hidden when the crack depth and width are 0.5 mm.

[0038] Considering that Rayleigh waves mainly propagate within a single wavelength depth in the aluminum plate, to illustrate the attenuation of Rayleigh waves with increasing depth, six probe points were sequentially set at a position of 30 mm on the horizontal axis, and the vertical axis was sequentially set below the surface of the aluminum plate. , ,......, , Here It is 2.93mm. For example... Figure 10 Figure (a) shows the Rayleigh wave displacement amplitude as a function of probe depth. It can be seen from the figure that the displacement amplitude decreases monotonically with increasing depth. When the depth increases from... Add a wavelength to The displacement amplitude decreased by approximately 55%. When the probe depth from... arrive The displacement amplitude is greater when the aluminum plate surface is smooth than when the surface is rough, and when the depth increases from... arrive The opposite is true at other times.

[0039] When the crack depth is proportional to the Rayleigh wave wavelength, the amplitude of the reflected wave displacement at point P2 and the amplitude of the transmitted wave displacement at point P3 were extracted (the amplitude of the reflected wave on the smooth surface is expressed as...). The amplitude of the transmitted wave on a smooth surface is expressed as The amplitude of the reflected wave from the rough surface is expressed as The amplitude of transmitted waves on a rough surface is expressed as ),like Figure 10 As shown in (b) of the figure, it can be seen that the amplitude curves of reflected and transmitted waves on both smooth and rough surfaces exhibit the same trend with crack depth. When the crack depth increases from... Increase to When the crack depth increases, the amplitude of the reflected wave displacement increases significantly while the amplitude of the transmitted wave displacement decreases significantly; when the crack depth increases from... Increase to At that time, the amplitude of both reflected and transmitted wave displacements first increased and then decreased; when the crack depth increased from... Increase to At the same time, the amplitude of the reflected wave displacement increases while the amplitude of the transmitted wave displacement decreases. When the crack depth is... The amplitude of reflected wave displacement is greater on rough surfaces than on smooth surfaces, while the amplitude of transmitted wave displacement is even greater on smooth surfaces. For all other crack depths, the amplitudes of both reflected and transmitted wave displacements are greater on smooth surfaces. Furthermore, due to… Figure 10 (b) also shows that regardless of the roughness of the aluminum plate surface, only when the crack depth is... The amplitude of the transmitted wave displacement is greater than that of the reflected wave displacement, while the amplitude of the reflected wave displacement is greater than that of the transmitted wave displacement as the crack depth increases.

[0040] To illustrate the performance of the optimized MP-EMAT in detecting sub-millimeter cracks, the crack depth was increased from 0.3 mm to 0.9 mm in increments of 0.1 mm. Figure 11 Figures (a) to (d) show the envelopes of reflected and transmitted wave displacement curves for different surface conditions of an aluminum plate, plotted using the `findpeaks` function in MATLAB. Figure 11 As can be seen from (a) and (c), except for the case with a rough surface where the crack depth of 0.3 mm corresponds to a reflected wave displacement amplitude greater than 0.4 mm, the reflected wave displacement amplitude increases with increasing crack depth in all other cases. Figure 11 As shown in (b) and (d), the displacement amplitude of the transmitted wave on both smooth and rough aluminum plate surfaces decreases with increasing crack depth. This is consistent with... Figure 10 (b) arrive This phenomenon is observed. Furthermore, when the aluminum plate surface is smooth, the transmitted wave displacement amplitude is greater than the reflected wave displacement amplitude when the crack depth is in the range of 0.3 mm to 0.6 mm; however, the result is reversed in the range of 0.7 mm to 0.9 mm. When the aluminum plate surface is rough, the transmitted wave displacement amplitude is greater than the reflected wave displacement amplitude when the crack depth is in the range of 0.3 mm to 0.7 mm; however, the result is reversed in the range of 0.8 mm to 0.9 mm. Table 5 shows the reflected and transmitted wave displacement amplitudes when the crack depth changes under different surface conditions of the aluminum plate. It can be seen that at a crack depth of 0.3 mm, the reflected wave displacement amplitude is smaller when the aluminum plate surface is smooth than when it is rough, while the transmitted wave displacement amplitude is greater when the aluminum plate surface is smooth than when it is rough. In the range of 0.4 mm to 0.9 mm, both the reflected and transmitted wave displacement amplitudes are larger on the smooth surface.

[0041] Table 5. Displacement amplitude of reflected and transmitted waves when crack depth changes under different surface conditions of aluminum plates.

[0042] S5. Quantitative analysis of crack size in rough aluminum plate using curve fitting of reflection coefficient and transmission coefficient; Calculate the reflection coefficient of aluminum plate under different surface conditions and crack depths. and transmission coefficient The fitting curves are plotted as follows: Figure 12 As shown in (a) and (b) in the table, the expressions for the fitted curves of the reflection coefficient and transmission coefficient are shown in Table 6. Reflection coefficient and transmission coefficient The calculation formula is as follows: ; ; in, The amplitude of the reflected wave displacement. The direct wave displacement amplitude, This represents the amplitude of the transmitted wave displacement.

[0043] like Figure 12 In (a), when the crack depth is greater than 0.7 mm, the rate of change of the reflection coefficient fitting curve gradually decreases, and the sensitivity of MP-EMAT to changes in crack depth decreases. From... Figure 12 As shown in (b), the rate of change of the transmission coefficient fitting curve does not decrease significantly when the crack depth is in the range of 0.3 mm to 0.9 mm. Therefore, when the submillimeter crack depth is small, the crack can be quantitatively evaluated by combining the reflection coefficient and transmission coefficient fitting curves, while when the submillimeter crack depth is large, it is more appropriate to use the transmission coefficient fitting curve for quantitative crack evaluation.

[0044] Table 6 Summary of Fitted Curves

[0045] like Figure 13 As shown, this invention provides a multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates. The transducer is designed using the aforementioned design method and includes a PCB board. An anti-zigzag coil is integrated on the PCB board, which serves as the substrate and precisely fixes the anti-zigzag coil traces, ensuring consistent coil spacing and orientation. When an alternating excitation current is applied to the anti-zigzag coil, an eddy current field is induced on the surface of the aluminum plate. The anti-zigzag trace structure forms a periodic reverse current distribution, matching the multi-pole magnetic field arrangement and enhancing electromagnetic coupling strength. To address the unevenness of the rough aluminum plate surface, the planar layout of the coils weakens the influence of lift-off distance fluctuations on eddy current excitation, ensuring the stability of the crack detection signal. A support shell is positioned above the PCB board. A multi-pole cylindrical magnet is fixed inside the support shell, and a multi-pole annular magnet is fixed outside. The shape of the support shell matches the shapes of the multi-pole cylindrical and annular magnets, enabling precise coaxial positioning and fixation of the multi-pole annular and cylindrical magnets. Figure 14 As shown, the left half of both the multi-pole cylindrical magnet and the multi-pole toroidal magnet has the south pole at the top and the north pole at the bottom, while the right half of both has the north pole at the top and the south pole at the bottom.

[0046] Therefore, the present invention employs the above-mentioned multi-pole electromagnetic ultrasonic transducer and design method for detecting cracks in rough aluminum plates. This method can increase the static magnetic flux density to excite stronger ultrasonic waves and increase the transduction efficiency of the electromagnetic ultrasonic transducer. By exciting Rayleigh waves, it helps to accurately detect and quantitatively analyze surface cracks in rough aluminum plates. The optimal parameter combination of MP-EMAT with good crack detection performance in rough aluminum plates is obtained by using orthogonal experiments and range analysis. The polynomial fitting curve expressions of reflection coefficient and transmission coefficient obtained by MP-EMAT detection of cracks in rough aluminum plates are used to quantify cracks at different crack depths.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A design method for a multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates, characterized in that: Specifically, the steps include: S1. Design the MP-EMAT structure; S2. Construct two-dimensional finite element models of MP-EMAT and cylindrical EMAT, and analyze the characteristics of MP-EMAT and cylindrical EMAT. S3. Optimize the structure by determining the optimal parameter combination of MP-EMAT through orthogonal experiments and range analysis; S4. The optimized MP-EMAT was used to simulate and detect cracks in rough aluminum plates, and the attenuation of the Rayleigh wave displacement amplitude excited by the optimized MP-EMAT under different aluminum plate surface conditions was obtained as a function of probe depth and crack depth. S5. Quantitative analysis of crack size in rough aluminum plate using curve fitting of reflection coefficient and transmission coefficient.

2. The design method of a multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates according to claim 1, characterized in that: A scaling law model is constructed in S1, where the eddy current density induced by the excitation coil in the aluminum plate is... With excitation current and angular frequency Proportional, that is In the excitation current When kept constant, eddy current density Treating it as a constant, therefore the static Lorentz force density Directly proportional to static magnetic flux density ,Right now The amplitude of the excited ultrasonic displacement With static Lorentz force density Proportional, that is Ultrasonic output power Proportional to displacement amplitude The square of, that is Energy conversion efficiency Ultrasonic output power With input electromagnetic power The ratio of energy conversion efficiency to the input electromagnetic power, under the condition of constant input electromagnetic power. Proportional to ultrasonic output power Therefore, the core scaling relationship can be derived as follows: ； ； ； in, The density of the aluminum plate, The speed at which Rayleigh waves propagate in an aluminum plate. The impedance of the transducer.

3. The design method of a multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates according to claim 2, characterized in that: In S2, magnetic field analysis, eddy current analysis, Lorentz force analysis, and displacement field analysis are performed on MP-EMAT and cylindrical EMAT. The excitation current during finite element analysis is also considered. The expression is as follows: ； in, For the excitation current amplitude, For the excitation frequency, The number of cycles.

4. The design method of a multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates according to claim 3, characterized in that: Influencing factors in S3 include coil lift-off. wire width Magnet lifting Wire thickness , radius of cylindrical magnet The ratio of the outer radius to the inner radius of a toroidal magnet and the number of coil turns Each parameter has three levels, and a suitable orthogonal array is selected and denoted as follows: The factors are assigned to an orthogonal table, simulation experiments are arranged according to the table and the results are recorded. Range analysis is used to obtain the ranking of the influence of each factor on the displacement amplitude and the optimal parameter combination.

5. The design method of a multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates according to claim 4, characterized in that: Range analysis was used to rank the influence of each factor on the displacement amplitude and to determine the optimal parameter combination. The calculation formula is shown below: ； ； ； ； in, This indicates that each factor is represented at each level. The arithmetic mean, For factor number, For horizontal sequence number, For the test number, The test result is the displacement amplitude. .

6. The design method of a multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates according to claim 5, characterized in that: In S4, points P2 and P3 are used as receiving points for reflected and transmitted ultrasonic signals, respectively. The left edge of the crack is 200 mm from the center of MP-EMAT, and the crack width is fixed at 0.5 mm. The aluminum plate in the Rayleigh wave excitation area is set to a smooth surface and a rough surface, respectively.

7. The design method of a multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates according to claim 6, characterized in that: Reflectance coefficient in S5 and transmission coefficient The calculation formula is as follows: ； ； in, The amplitude of the reflected wave displacement. The direct wave displacement amplitude, This represents the amplitude of the transmitted wave displacement.

8. A multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates, designed using the design method for a multi-pole electromagnetic ultrasonic transducer for detecting cracks in rough aluminum plates as described in any one of claims 1-7, characterized in that: The system includes a PCB board with an integrated anti-bend coil. A support shell is located above the PCB board. A multi-pole cylindrical magnet is fixed inside the support shell, and a multi-pole annular magnet is fixed outside the support shell. The shape of the support shell is adapted to the shape of the multi-pole cylindrical magnet and the multi-pole annular magnet. The left half of both the multi-pole cylindrical magnet and the multi-pole annular magnet has the south pole at the top and the north pole at the bottom, while the right half of both the multi-pole cylindrical magnet and the multi-pole annular magnet has the north pole at the top and the south pole at the bottom.

Images