A non-equidistant pitch zigzag coil electromagnetic ultrasonic transducer

Abstract

A non-equidistant zigzag coil electromagnetic ultrasonic transducer comprises a magnet, a test piece and a coil, wherein the coil comprises 9 non-equidistant wires, the 9 wires are numbered from left to right according to Arabic numerals, the spacing between the wires with odd numbers is fixed, and the spacing between the wires with even numbers is not fixed, and the arrangement of the 9 non-equidistant wires is defined as: removing the wires with odd numbers of the equidistant zigzag coil electromagnetic ultrasonic transducer, retaining the wires with even numbers as wires 1, 3, 5, and 7, adding four wires at four points where the horizontal magnetic field and the vertical magnetic field of the equidistant zigzag coil electromagnetic ultrasonic transducer intersect, as wires 2, 4, 6, and 8, adding a wire below the end of the last magnet, as wire 9, and the current direction of wires 1, 2, 5, 6, and 9 is opposite to the current direction of wires 3, 4, 7, and 8. The Rayleigh wave and Lamb wave amplitudes generated by the invention are large, and the energy conversion efficiency is high.

Description

Technical Field

[0001] The invention relates to the field of ultrasonic detection, and in particular to an electromagnetic ultrasonic transducer with non-equidistant meandering coils. Background Art

[0002] The zigzag coil electromagnetic ultrasonic transducer is mainly used to generate ultrasonic waves that propagate along the surface of the specimen. According to the thickness of the specimen on which the zigzag coil electromagnetic ultrasonic transducer acts, it can be divided into Rayleigh wave and Lamb wave electromagnetic ultrasonic transducers. When the thickness of the specimen is thicker, the zigzag coil electromagnetic ultrasonic transducer generates Rayleigh waves. The energy of the Rayleigh wave is mainly concentrated within a wavelength depth on the surface of the specimen. After exceeding this depth, the amplitude of the Rayleigh wave drops rapidly. Therefore, the Rayleigh wave is mainly used to detect shallow surface defects of the specimen. Under the action of the Rayleigh wave, the motion trajectory of the particles in the specimen is elliptical, so it can be divided into in-plane displacement and out-of-plane displacement components. The in-plane displacement is smaller than the out-of-plane displacement, and the phase difference between the two is π / 2. When the wavelength of the Rayleigh wave is larger than the defect depth, most of the Rayleigh waves bypass the defect and continue to propagate forward, forming a transmitted wave; when the wavelength of the Rayleigh wave is smaller than the defect depth, most of the Rayleigh waves will be reflected back by the defect to form a reflected wave. Therefore, the effect of defects on Rayleigh waves is like a low-pass filter in electronic components. The propagation speed of Rayleigh waves in aluminum specimens does not need to consider the influence of frequency. When the zigzag coil electromagnetic ultrasonic transducer acts on thin-walled parts, Lamb waves will be generated in the specimen. The propagation speed of Lamb waves in the specimen is not only related to the frequency but also to the thickness of the thin plate. In addition, Lamb waves contain various symmetrical waves (S0, S1, S2...) and asymmetrical waves (A0, A1, A2...). In practical applications, it is difficult to detect and analyze Lamb waves of different modes at the same time, and it is not necessary to use multiple modes of waves at the same time in actual detection. In addition to generating Rayleigh waves and Lamb waves, the zigzag coil electromagnetic ultrasonic transducer can reasonably design the spacing between adjacent wires of the zigzag coil so that the distance difference between the ultrasonic waves generated by adjacent wires and the focal point is half a wavelength to generate focused shear waves.

[0003] In the existing equally spaced meander coil electromagnetic ultrasonic transducer, the spacing between adjacent conductors is equal, the amplitudes of the generated Rayleigh waves and Lamb waves are small, and the energy conversion efficiency is low. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies of the above-mentioned background technology and provide a non-equidistant meander coil electromagnetic ultrasonic transducer, which generates Rayleigh waves and Lamb waves with larger amplitudes and higher transduction efficiency.

[0005] The technical solution adopted by the present invention to solve the technical problem is a non-uniformly spaced meandering coil electromagnetic ultrasonic transducer, comprising a magnet, a test piece and a coil, wherein the magnet is located on the test piece, the number of the magnets is 5, and the 5 magnets are arranged in a single row to generate a static magnetic field, the polarities of all the magnets are in the vertical direction, and the polarities of two adjacent magnets are opposite, the coil is located below the magnet, the coil comprises 9 non-uniformly spaced wires, the 9 wires are numbered from left to right according to Arabic numerals, the spacing between the wires with odd numbers is fixed, and the spacing between the wires with even numbers is not fixed, and the arrangement of the 9 non-uniformly spaced wires is defined as: The arrangement of the wires of the equally spaced zigzag coil electromagnetic ultrasonic transducer is adjusted, specifically, the odd-numbered wires of the equally spaced zigzag coil electromagnetic ultrasonic transducer are removed, and the even-numbered wires are retained as wires No. 1, 3, 5, and 7. Four wires are added at four points where the horizontal magnetic field and the vertical magnetic field of the equally spaced zigzag coil electromagnetic ultrasonic transducer intersect, as wires No. 2, 4, 6, and 8. A wire is added below the end of the last magnet, as wire No. 9. The current directions of the wires No. 1, 2, 5, 6, and 9 are opposite to the current directions of the wires No. 3, 4, 7, and 8.

[0006] Furthermore, the non-equidistant meander coil electromagnetic ultrasonic transducer is a non-equidistant meander coil Rayleigh wave electromagnetic ultrasonic transducer, each magnet has a height of 5 mm, a length of 40 mm, and a width of 6 mm, the thickness of the specimen is more than 50 mm, and the spacing between odd-numbered wires is 6 mm.

[0007] Furthermore, the non-equidistant meander coil electromagnetic ultrasonic transducer is a non-equidistant meander coil Lamb wave electromagnetic ultrasonic transducer, each magnet has a height of 5 mm, a length of 40 mm, and a width of 5 mm; the thickness of the specimen is 2 mm; and the spacing between odd-numbered wires is 5 mm.

[0008] Furthermore, the current direction of the wires No. 1, 2, 5, 6, and 9 is outward, and the current direction of the wires No. 3, 4, 7, and 8 is inward.

[0009] Furthermore, the thickness of the test piece is 60 mm.

[0010] Compared with the prior art, the advantages of the present invention are as follows: Based on the equidistant zigzag coil electromagnetic ultrasonic transducer, the present invention proposes a non-equidistant zigzag coil electromagnetic ultrasonic transducer. The non-equidistant zigzag coil electromagnetic ultrasonic transducer has the same magnet configuration as the equidistant zigzag coil electromagnetic ultrasonic transducer. The non-equidistant zigzag coil electromagnetic ultrasonic transducer places more wires in a stronger horizontal magnetic field, and the generated Rayleigh wave and Lamb wave have larger amplitudes and higher energy conversion efficiency. The non-equidistant zigzag coil Rayleigh wave electromagnetic ultrasonic transducer generates a larger Rayleigh wave amplitude, which can improve the Rayleigh wave energy conversion efficiency by about 40%; the non-equidistant zigzag coil Lamb wave electromagnetic ultrasonic transducer generates a larger Lamb wave amplitude, which can improve the Lamb wave energy conversion efficiency by 34%. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a schematic diagram of the structure of an existing equidistant meander coil Rayleigh wave electromagnetic ultrasonic transducer.

[0012] Figure 2 yes Figure 1 Schematic cross-section of .

[0013] Figure 3 (a) is a cloud diagram of the horizontal magnetic field distribution generated by the existing equally spaced zigzag coil Rayleigh wave electromagnetic ultrasonic transducer on the specimen; Figure 3 (b) is a cloud diagram of the vertical magnetic field distribution generated by the existing equally spaced zigzag coil Rayleigh wave electromagnetic ultrasonic transducer in the test piece.

[0014] Figure 4 It is a numerical diagram of the magnetic field distribution generated by the existing equally spaced zigzag coil Rayleigh wave electromagnetic ultrasonic transducer in the test piece.

[0015] Figure 5 It is a schematic structural diagram of the non-equidistant meander coil Rayleigh wave electromagnetic ultrasonic transducer according to Example 1 of the present invention.

[0016] Figure 6 yes Figure 5 Schematic cross-section of .

[0017] Figure 7 (a) is the distribution diagram of eddy currents generated by the existing equally spaced zigzag coil Rayleigh wave electromagnetic ultrasonic transducer at different times. Figure 7 (b) is the distribution diagram of eddy currents generated by the non-equidistant-pitch zigzag coil Rayleigh wave electromagnetic ultrasonic transducer at different times.

[0018] Figure 8The present invention is a distribution diagram of eddy currents generated on the surface of a test piece by existing equidistant-pitch zigzag-coil Rayleigh wave electromagnetic ultrasonic transducers and non-equidistant-pitch zigzag-coil Rayleigh wave electromagnetic ultrasonic transducers.

[0019] Fig. 9 (a) is a schematic diagram of the Lorentz force generated by the existing equidistant zigzag coil Rayleigh wave electromagnetic ultrasonic transducer. Fig. 9 (b) is a schematic diagram of the Lorentz force generated by the non-equidistant-pitch zigzag coil Rayleigh wave electromagnetic ultrasonic transducer.

[0020] Fig.10 (a) is the ultrasonic cloud diagram generated by the existing equally spaced zigzag coil Rayleigh wave electromagnetic ultrasonic transducer at different times. Fig.10 (b) is the ultrasonic cloud diagram generated by the non-equidistant zigzag coil Rayleigh wave electromagnetic ultrasonic transducer at different times.

[0021] Fig.11 (a) is a numerical diagram of ultrasonic waves generated by an existing equidistant meander coil Rayleigh wave electromagnetic ultrasonic transducer. Fig.11 (b) is a numerical diagram of the ultrasonic wave generated by the non-equidistant-pitch zigzag coil Rayleigh wave electromagnetic ultrasonic transducer.

[0022] Fig.12 It is a schematic diagram of the structure of an existing equally spaced meandering coil Lamb wave electromagnetic ultrasonic transducer.

[0023] Fig.13 yes Fig.12 Schematic cross-section of .

[0024] Fig.14 (a) is a cloud diagram of the horizontal magnetic field distribution generated by the existing equally spaced zigzag coil Lamb wave electromagnetic ultrasonic transducer on the specimen; Fig.14 (b) is a cloud diagram of the vertical magnetic field distribution generated by the existing equally spaced zigzag coil Lamb wave electromagnetic ultrasonic transducer in the test piece.

[0025] Fig.15 It is a numerical diagram of the magnetic field distribution generated by the existing equally spaced zigzag coil Lamb wave electromagnetic ultrasonic transducer in the test piece.

[0026] Fig.16 It is a schematic structural diagram of the non-equidistant meander coil Lamb wave electromagnetic ultrasonic transducer according to Example 2 of the present invention.

[0027] Fig.17 yes Fig.16 Schematic cross-section of .

[0028] Fig.18It is a distribution diagram of eddy currents generated on the surface of a test piece by existing equidistant-pitch zigzag-coil Lamb wave electromagnetic ultrasonic transducers and non-equidistant-pitch zigzag-coil Lamb wave electromagnetic ultrasonic transducers.

[0029] Fig.19 (a) is a schematic diagram of Lamb waves generated by an existing equidistant meander coil Lamb wave electromagnetic ultrasonic transducer. Fig.19 (b) is a schematic diagram of the Lamb wave generated by the non-equidistant meander coil Lamb wave electromagnetic ultrasonic transducer.

[0030] In the figure: 1—magnet, 2—coil, 3—test piece, 4—conductor. DETAILED DESCRIPTION

[0031] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] Example 1

[0033] Reference Figure 1 , Figure 2 The existing equidistant meander coil Rayleigh wave electromagnetic ultrasonic transducer comprises a magnet 1, a test piece 3 and a coil 2. The magnet 1 is located on the test piece 3. There are 5 magnets 1, which are arranged in a single row to generate a static magnetic field. The polarities of all magnets 1 are in the vertical direction, and the polarities of two adjacent magnets 1 are opposite. The height of each magnet 1 is 5 mm, the length is 40 mm, and the width is 6 mm. The coil 2 is located below the magnet 1. The thickness of the test piece 3 is more than 50 mm, and in this embodiment, it is 60 mm. mm; the coil 2 includes 9 equally spaced wires 4, which are numbered according to Arabic numerals from left to right, the wires 4 with odd numbers are located directly below the center of each magnet 1, and the wires 4 with even numbers are located directly below the contact surface between every two magnets 1, the current direction of wires No. 1, 2, 5, 6, and 9 is opposite to the current direction of wires No. 3, 4, 7, and 8, the current direction of wires No. 1, 2, 5, 6, and 9 is outward, and the current direction of wires No. 3, 4, 7, and 8 is inward, and the spacing between adjacent wires 4 is 3 mm.

[0034] Depend on Figure 3 It can be seen that the magnetic field generated by the equally spaced zigzag coil Rayleigh wave electromagnetic ultrasonic transducer is mainly concentrated in the shallow surface layer of the specimen 3; the horizontal magnetic field and the vertical magnetic field are alternating; the peak directions of two adjacent horizontal magnetic fields are opposite, and the vertical magnetic field also follows this law. In the middle of two horizontal magnetic fields or two vertical magnetic fields is a magnetic field in another direction. Eddy currents only exist within the skin depth of the surface of specimen 3. Correspondingly, only this part of the area will produce the Lorentz force that excites ultrasonic waves.

[0035] The magnetic field distribution on the surface of specimen 3 is as follows: Figure 4 shown. Figure 4There is a certain gap between each peak value of the horizontal magnetic field and the vertical magnetic field, but the overall change is basically consistent with the periodic change. The phase difference between the vertical magnetic field Bsy and the horizontal magnetic field Bsx is about π / 2. The horizontal magnetic field has 6 peaks; the vertical magnetic field has 5 peaks. Figure 4 In the figure, the dotted line represents the position of the wire 4, and the wire 4 is located at the peak of the horizontal or vertical magnetic field. The middle and lower part of each magnet 1 is in the vertical magnetic field, and the lower part of the contact surface of every two adjacent magnets 1 is in the horizontal magnetic field. The wires 4 with odd numbers are located in the vertical magnetic field, and the wires 4 with even numbers are located in the horizontal magnetic field. Figure 4 The four black dots are the points where the horizontal magnetic field and the vertical magnetic field intersect, and the magnetic field here has both strong horizontal and vertical magnetic fields. Compared with the wire 4 with an odd number, the vertical magnetic field at the black dots is only weakened by less than 20%, but has a significantly improved horizontal magnetic field. Therefore, it is reasonable to infer that the Rayleigh wave amplitude generated by arranging the wire 4 at the black dots is larger than the Rayleigh wave amplitude generated by the wire 4 with an odd number.

[0036] The non-equidistant meander coil electromagnetic ultrasonic transducer of this embodiment is a non-equidistant meander coil Rayleigh wave electromagnetic ultrasonic transducer, and the non-equidistant meander coil Rayleigh wave electromagnetic ultrasonic transducer is improved on the basis of the equidistant meander coil Rayleigh wave electromagnetic ultrasonic transducer.

[0037] Reference Figure 5 , Figure 6In this embodiment, the non-equidistant zigzag coil Rayleigh wave electromagnetic ultrasonic transducer includes a magnet 1, a test piece 3 and a coil 2. The magnet 1 is located on the test piece 3. The number of magnets 1 is 5. The 5 magnets 1 are arranged in a single row to generate a static magnetic field. The polarities of all magnets 1 are in the vertical direction. The polarities of two adjacent magnets 1 are opposite. The height of each magnet 1 is 5 mm, the length is 40 mm, and the width is 6 mm. The thickness of the test piece 3 is more than 50 mm, and is 60 mm in this embodiment; the coil 2 is located below the magnet 1. The coil 2 includes 9 non-equidistant wires 4. The 9 wires 4 are numbered according to Arabic numerals from left to right. The spacing between the wires 4 with odd numbers is 6 mm, and the spacing between the wires 4 with even numbers is not fixed. The arrangement of the 9 non-equidistant wires 4 is defined as: the equidistant zigzag wires 4 are arranged in a vertical direction. The length of the wires 4 is 40 mm, and the width of the wires 4 is 60 mm. The arrangement of the wires 4 of the zigzag coil Rayleigh wave electromagnetic ultrasonic transducer is adjusted, specifically, the wires 4 with odd numbers of the equidistant zigzag coil Rayleigh wave electromagnetic ultrasonic transducer are removed, and the wires 4 with even numbers are retained as wires 1, 3, 5, and 7. Four wires are added at four points where the horizontal magnetic field and the vertical magnetic field of the equidistant zigzag coil Rayleigh wave electromagnetic ultrasonic transducer intersect, as wires 2, 4, 6, and 8. A wire is added below the end of the last magnet 1, as wire 9. The current direction of wires 1, 2, 5, 6, and 9 is opposite to that of wires 3, 4, 7, and 8. In this embodiment, the current direction of wires 1, 2, 5, 6, and 9 is outward, and the current direction of wires 3, 4, 7, and 8 is inward.

[0038] The main idea of ​​traditional optimization of electromagnetic ultrasonic transducers is to improve the magnet configuration to produce a magnetic field distribution that is more conducive to exciting Rayleigh waves. Different from the traditional idea of ​​optimizing zigzag coil electromagnetic ultrasonic transducers, the non-equidistant zigzag coil Rayleigh wave electromagnetic ultrasonic transducer keeps the magnet configuration unchanged and changes the distribution of the wires in the coil to adapt to the distribution of the magnetic field. But in addition to the magnetic field, the eddy currents on the surface of the specimen will also directly affect the Lorentz force that generates ultrasonic waves. In order to investigate the improvement of the conversion efficiency of the non-equidistant zigzag coil Rayleigh wave electromagnetic ultrasonic transducer, it is necessary to study the eddy currents generated by the non-equidistant zigzag coil Rayleigh wave electromagnetic ultrasonic transducer on the surface of the specimen. Figure 7 It can be seen that the eddy current is mainly distributed in the shallow skin layer under the surface of the specimen. As time changes, the eddy current distribution in the specimen will also change. At the same time, the eddy current density generated by the non-uniformly spaced zigzag coil Rayleigh wave electromagnetic ultrasonic transducer is greater than the eddy current generated by the equidistantly spaced zigzag coil Rayleigh wave electromagnetic ultrasonic transducer.

[0039] In order to intuitively compare the eddy currents generated on the specimen surface by the equidistant-pitch Rayleigh wave electromagnetic ultrasonic transducer and the unequal-pitch Rayleigh wave electromagnetic ultrasonic transducer, the frequency domain solution of the eddy current density on the specimen surface is displayed in Figure 8 In. By Figure 8 It can be seen that the eddy current generated by the equally spaced zigzag coil Rayleigh wave electromagnetic ultrasonic transducer on the surface of the specimen has a total of five peaks, and the first four peaks are composed of two small peaks. This is because the first four peaks are generated by two wires with current in the same direction. Due to the large spacing between the wires, the eddy current does not form a single crest but two bifurcated crests. However, the spacing between the two wires with current in the same direction in the non-equally spaced zigzag coil Rayleigh wave electromagnetic ultrasonic transducer is small enough, so the generated eddy current forms a single crest. Due to the smaller spacing between the two wires with current in the same direction in the non-equally spaced zigzag coil Rayleigh wave electromagnetic ultrasonic transducer, the maximum value of the eddy current generated on the surface of the specimen is approximately 1.4 times the maximum value of the eddy current generated on the surface of the specimen by the equally spaced zigzag coil Rayleigh wave electromagnetic ultrasonic transducer.

[0040] The Lorentz force is the result of the interaction between the magnetic field and eddy current on the specimen surface. The horizontal Lorentz force and the vertical Lorentz force are shown in Fig. 9 The horizontal and vertical Lorentz forces generated by the equidistant zigzag coil Rayleigh wave electromagnetic ultrasonic transducer and the non-equidistant zigzag coil Rayleigh wave electromagnetic ultrasonic transducer basically conform to periodic changes. The horizontal Lorentz force is distributed in both positive and negative directions, with a stronger distribution in the positive direction and a weaker distribution in the negative direction. The vertical Lorentz force is relatively more evenly distributed in the positive and negative directions. The maximum values ​​of the horizontal Lorentz force generated by the equidistant zigzag coil Rayleigh wave electromagnetic ultrasonic transducer and the non-equidistant zigzag coil Rayleigh wave electromagnetic ultrasonic transducer are not much different; the vertical Lorentz force generated by the non-equidistant zigzag coil Rayleigh wave electromagnetic ultrasonic transducer is about 30% of that of the equidistant zigzag coil Rayleigh wave electromagnetic ultrasonic transducer. It can be seen from the fact that the horizontal magnetic field is more conducive to the excitation of Rayleigh waves that the vertical Lorentz force is more conducive to the generation of ultrasonic waves. Therefore, the non-equidistant zigzag coil Rayleigh wave electromagnetic ultrasonic transducer can generate stronger Rayleigh waves.

[0041] Reference Fig.10In addition to Rayleigh waves, a small amount of shear waves and longitudinal waves are also excited by the two Rayleigh wave electromagnetic ultrasonic transducers. The Rayleigh waves in the specimen are mainly concentrated on the surface of the specimen and decay rapidly after exceeding a certain depth. Both the equidistant zigzag coil Rayleigh wave electromagnetic ultrasonic transducer and the non-equidistant zigzag coil Rayleigh wave electromagnetic ultrasonic transducer excite Rayleigh waves in both the left and right directions. In order to reduce the interference between the reflected wave and the incident wave, the two sides of the specimen are set as low-reflection boundaries. It can be observed that the amplitude of the Rayleigh waves generated by the non-equidistant zigzag coil Rayleigh wave electromagnetic ultrasonic transducer is significantly stronger than that generated by the equidistant zigzag coil Rayleigh wave electromagnetic ultrasonic transducer.

[0042] In order to directly compare the amplitude of Rayleigh waves generated by equidistant zigzag coil Rayleigh wave electromagnetic ultrasonic transducer and unequal zigzag coil Rayleigh wave electromagnetic ultrasonic transducer, the improvement of the conversion efficiency of unequal zigzag coil Rayleigh wave electromagnetic ultrasonic transducer is studied. The in-plane and out-of-plane displacements of the ultrasonic waves generated by equidistant zigzag coil Rayleigh wave electromagnetic ultrasonic transducer and unequal zigzag coil Rayleigh wave electromagnetic ultrasonic transducer on the surface of the specimen are displayed. Fig.11 In. By Fig.11 It can be seen that the difference in the in-plane displacement of the ultrasonic wave excited by the equidistant-pitch Rayleigh wave electromagnetic ultrasonic transducer and the unequal-pitch Rayleigh wave electromagnetic ultrasonic transducer is π / 2. The in-plane displacement is smaller than the out-of-plane displacement. The enhancement of the in-plane and out-of-plane displacement amplitudes of the ultrasonic waves generated by the non-equidistant zigzag coil Rayleigh wave electromagnetic ultrasonic transducer are:

[0043]

[0044]

[0045] Therefore, the non-equidistant-pitch meander coil Rayleigh wave electromagnetic ultrasonic transducer proposed in the embodiment can significantly improve the energy conversion efficiency of the Rayleigh wave electromagnetic ultrasonic transducer.

[0046] Example 2

[0047] Reference Fig.12 , 13The existing equally spaced meandering coil Lamb wave electromagnetic ultrasonic transducer includes a magnet 1, a specimen 3 and a coil 2. The magnet 1 is located on the specimen 3. There are 5 magnets 1. The 5 magnets 1 are arranged in a single row to generate a static magnetic field. The polarities of all magnets 1 are in the vertical direction. The polarities of two adjacent magnets 1 are opposite. The height of each magnet 1 is 10 mm, the length is 40 mm, and the width is 5 mm. The thickness of the specimen 3 is 2 mm. The coil 2 is located below the magnet 1. The coil 2 includes 9 The wires 4 are equally spaced, and 9 wires 4 are numbered according to Arabic numerals from left to right. The wires 4 with odd numbers are located directly below the center of each magnet 1, and the wires 4 with even numbers are located directly below the contact surface between every two magnets 1. The current direction of wires 1, 2, 5, 6, and 9 is opposite to that of wires 3, 4, 7, and 8. The current direction of wires 1, 2, 5, 6, and 9 is outward, and the current direction of wires 3, 4, 7, and 8 is inward. The spacing between adjacent wires 4 is 2.5 mm.

[0048] The magnetic field generated by the Lamb wave electromagnetic ultrasonic transducer with equal spacing meander coils is similar to the magnetic field generated by the Rayleigh wave electromagnetic ultrasonic transducer with equal spacing meander coils. Fig.14 It can be seen that the magnetic field generated by the equally spaced zigzag coil Lamb wave electromagnetic ultrasonic transducer is mainly concentrated in the shallow surface layer of the specimen 3; the horizontal magnetic field and the vertical magnetic field are alternating; the peak directions of the two adjacent horizontal magnetic fields are opposite, and the vertical magnetic field also follows this law. In the middle of the two horizontal magnetic fields or the two vertical magnetic fields is a magnetic field in another direction. Eddy currents only exist within the skin depth of the surface of the specimen 3. Correspondingly, only this part of the area will produce the Lorentz force that excites the ultrasonic wave.

[0049] The magnetic field distribution on the surface of specimen 3 is as follows: Fig.15 shown. Fig.15 There is a certain gap between each peak value of the horizontal magnetic field and the vertical magnetic field, but the overall change is basically consistent with the periodic change. The phase difference between the vertical magnetic field Bsy and the horizontal magnetic field Bsx is about π / 2. The horizontal magnetic field has 6 peaks; the vertical magnetic field has 5 peaks. Fig.15 In the figure, the dotted line represents the position of the wire 4, and the wire 4 is located at the peak of the horizontal or vertical magnetic field. The middle and lower part of each magnet 1 is in the vertical magnetic field, and the lower part of the contact surface of every two adjacent magnets 1 is in the horizontal magnetic field. The wires 4 with odd numbers are located in the vertical magnetic field, and the wires 4 with even numbers are located in the horizontal magnetic field. Fig.15The four black dots are the points where the horizontal magnetic field and the vertical magnetic field intersect. The magnetic field here has both strong horizontal and vertical magnetic fields. Compared with the wire 4 with an odd number, the vertical magnetic field at the black dots is only weakened by less than 20%, but has a significantly improved horizontal magnetic field. Therefore, it is reasonable to infer that the Lamb wave amplitude generated by arranging the wire 4 at the black dots is larger than the Lamb wave amplitude generated by the wire 4 with an odd number.

[0050] The non-equidistant meander coil electromagnetic ultrasonic transducer of this embodiment is a non-equidistant meander coil Lamb wave electromagnetic ultrasonic transducer, which is improved on the basis of the equidistant meander coil Lamb wave electromagnetic ultrasonic transducer.

[0051] Reference Fig.16 , 17 The non-uniformly spaced zigzag coil Lamb wave electromagnetic ultrasonic transducer of this embodiment includes a magnet 1, a test piece 3 and a coil 2. The magnet 1 is located on the test piece 3. The number of magnets 1 is 5. The 5 magnets 1 are arranged in a single row to generate a static magnetic field. The polarities of all magnets 1 are in the vertical direction. The polarities of two adjacent magnets 1 are opposite. The height of each magnet 1 is 5 mm, the length is 40 mm, and the width is 5 mm. The thickness of the test piece 3 is 2 mm. The coil 2 is located below the magnet 1. The coil 2 includes 9 non-uniformly spaced wires 4. The 9 wires 4 are numbered according to Arabic numerals from left to right. The spacing between the wires 4 with odd numbers is 5 mm, and the spacing between the wires 4 with even numbers is not fixed. The arrangement of the 9 non-uniformly spaced wires 4 is defined as: the equally spaced zigzag coils are arranged in a vertical direction. The arrangement of the wires 4 of the Lamb wave electromagnetic ultrasonic transducer is adjusted, specifically, the wires 4 with odd numbers of the equally spaced zigzag coil Lamb wave electromagnetic ultrasonic transducer are removed, and the wires 4 with even numbers are retained as wires 1, 3, 5, and 7. Four wires are added at four points where the horizontal magnetic field and the vertical magnetic field of the equally spaced zigzag coil Lamb wave electromagnetic ultrasonic transducer intersect, as wires 2, 4, 6, and 8. A wire is added below the end of the last magnet 1, as wire 9. The current direction of wires 1, 2, 5, 6, and 9 is opposite to that of wires 3, 4, 7, and 8. In this embodiment, the current direction of wires 1, 2, 5, 6, and 9 is outward, and the current direction of wires 3, 4, 7, and 8 is inward.

[0052] Depend on Fig.18It can be seen that both Lamb wave electromagnetic ultrasonic transducers have five peaks. The first four peaks of the Lamb wave electromagnetic ultrasonic transducer with equal spacing meander coils include two independent small peaks, because the spacing between adjacent wires of its meander coil is large. In the coil of the Lamb wave electromagnetic ultrasonic transducer with non-equal spacing meander coils, the spacing between adjacent wires with the same current direction is small, so there is only a single peak. The maximum eddy current density generated on the surface of the specimen by the Lamb wave electromagnetic ultrasonic transducer with non-equal spacing meander coils is about 40% higher than the eddy current density generated on the surface of the specimen by the Lamb wave electromagnetic ultrasonic transducer with equal spacing meander coils.

[0053] Depend on Fig.19 It can be seen that the positions of the Lamb waves in the A0 and S0 modes coincide with the wave velocity of the selected working point. The signal amplitudes of the A0 and S0 modes of the Lamb waves generated by the non-uniformly spaced zigzag coil Lamb wave electromagnetic ultrasonic transducer are greater than the Lamb wave signal amplitudes generated by the equidistantly spaced zigzag coil Lamb wave electromagnetic ultrasonic transducer. The specific improvement of the in-plane and out-of-plane displacements of the A0 mode Lamb wave is:

[0054]

[0055] This shows that the Lamb wave electromagnetic ultrasonic transducer with non-equidistant meandering coils is also suitable for improving the conversion efficiency of Lamb wave EMAT, but the conversion efficiency improvement is slightly lower than that of Rayleigh wave.

[0056] Since the horizontal magnetic field is more conducive to the excitation of Rayleigh waves and Lamb waves, in order to improve the conversion efficiency of the zigzag coil electromagnetic ultrasonic transducer, the present invention proposes a non-equidistant zigzag coil electromagnetic ultrasonic transducer based on the equidistant zigzag coil electromagnetic ultrasonic transducer. The magnet configuration of the non-equidistant zigzag coil electromagnetic ultrasonic transducer is consistent with that of the equidistant zigzag coil electromagnetic ultrasonic transducer. The design idea of ​​the non-equidistant zigzag coil electromagnetic ultrasonic transducer is to place more wires in a stronger horizontal magnetic field. The following conclusions were obtained by studying and comparing the eddy current density, Lorentz force and ultrasonic amplitude on the surface of the specimen:

[0057] (1) The non-uniformly spaced meandering coil Rayleigh wave electromagnetic ultrasonic transducer can improve the conversion efficiency of Rayleigh waves by about 40%.

[0058] (2) The non-uniformly spaced zigzag coil Lamb wave electromagnetic ultrasonic transducer can improve the Lamb wave conversion efficiency by 34%.

[0059] Those skilled in the art may make various modifications and variations to the present invention. If these modifications and variations are within the scope of the claims of the present invention and their equivalents, then these modifications and variations are also within the protection scope of the present invention.

[0060] The contents not described in detail in the specification are prior art known to those skilled in the art.

Claims

1. A non-uniformly spaced meandering coil electromagnetic ultrasonic transducer, comprising a magnet, a test piece and a coil, wherein the magnet is located on the test piece, the number of the magnets is 5, the 5 magnets are arranged in a single row to generate a static magnetic field, the polarities of all the magnets are in the vertical direction, the polarities of two adjacent magnets are opposite, and the coil is located below the magnet, characterized in that: The coil includes 9 non-equally spaced wires, which are numbered according to Arabic numerals from left to right, with a fixed spacing between the wires with odd numbers, and a non-fixed spacing between the wires with even numbers. The arrangement of the 9 non-equally spaced wires is defined as: adjusting the arrangement of the wires of the equally spaced zigzag coil electromagnetic ultrasonic transducer, specifically removing the odd-numbered wires of the equally spaced zigzag coil electromagnetic ultrasonic transducer, retaining the even-numbered wires as wires No. 1, 3, 5, and 7, adding four wires at four points where the horizontal magnetic field and the vertical magnetic field of the equally spaced zigzag coil electromagnetic ultrasonic transducer intersect, as wires No. 2, 4, 6, and 8, adding a wire below the end of the last magnet, as wire No. 9, and the current directions of the wires No. 1, 2, 5, 6, and 9 are opposite to the current directions of the wires No. 3, 4, 7, and 8.

2. The non-equidistant meander coil electromagnetic ultrasonic transducer according to claim 1, characterized in that: The non-equidistant meander coil electromagnetic ultrasonic transducer is a non-equidistant meander coil Rayleigh wave electromagnetic ultrasonic transducer, each magnet has a height of 5 mm, a length of 40 mm, and a width of 6 mm, the thickness of the test piece is more than 50 mm, and the spacing between the odd-numbered wires is 6 mm.

3. The non-equidistant meander coil electromagnetic ultrasonic transducer according to claim 1, characterized in that: The non-equidistant meander coil electromagnetic ultrasonic transducer is a non-equidistant meander coil Lamb wave electromagnetic ultrasonic transducer, each magnet has a height of 5 mm, a length of 40 mm, and a width of 5 mm; the thickness of the test piece is 2 mm; and the spacing between the odd-numbered wires is 5 mm.

4. The non-equidistant meander coil electromagnetic ultrasonic transducer according to claim 2 or 3, characterized in that: The current direction of the wires No. 1, 2, 5, 6, and 9 is outward, and the current direction of the wires No. 3, 4, 7, and 8 is inward.

5. The non-equidistant meander coil electromagnetic ultrasonic transducer according to claim 2, characterized in that: The thickness of the test piece was 60 mm.

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