An electromagnetic ultrasonic unidirectional transducer, a guided wave detection system and a defect detection method

Abstract

The invention discloses an electromagnetic ultrasonic unidirectional transducer, a waveguide detection system and a defect detection method. The electromagnetic ultrasonic unidirectional transducer comprises: a narrow plate; two periodic permanent magnet electromagnetic ultrasonic transducers, which are respectively arranged on the upper and lower sides of the narrow plate, and the two periodic permanent magnet electromagnetic ultrasonic transducers are staggered in the long side direction of the narrow plate; and a clamping electromagnetic ultrasonic unidirectional transducer housing is used to fix the periodic permanent magnet electromagnetic ultrasonic transducers. The two periodic permanent magnet electromagnetic ultrasonic transducers are fixed by the clamping electromagnetic ultrasonic unidirectional transducer housing, and the electromagnetic ultrasonic unidirectional transducers are quickly installed and disassembled by relying on the magnetic attraction of the periodic permanent magnet electromagnetic ultrasonic transducers. The two periodic permanent magnet electromagnetic ultrasonic transducers are staggered in the long side direction of the narrow plate, and an external dual-channel excitation signal is used to generate a forward SH waveguide, suppress the formation of a backward SH waveguide, increase the amplitude of the transducer excitation signal, and enhance the defect detection capability.

Description

Technical Field

[0001] The present invention relates to the field of sensor measurement technology, and in particular to an electromagnetic ultrasonic unidirectional transducer, a waveguide detection system and a defect detection method. Background Art

[0002] As an emerging non-destructive testing technology, ultrasonic guided waves have been widely used in the detection of in-service plates due to their advantages of long detection distance and high detection efficiency under single-point excitation. Among them, SH waves have less energy leakage during propagation, long propagation distance, and low-mode SH guided waves have no dispersion and mode conversion phenomenon, which is very suitable for the detection of plate welding defects, cracks, and corrosion defects.

[0003] Electromagnetic ultrasonic guided wave technology, magnetostrictive ultrasonic guided wave technology and piezoelectric ultrasonic guided wave technology can all stimulate SH guided waves in the plate. Compared with piezoelectric and magnetostrictive SH guided wave sensors, electromagnetic ultrasonic sensors do not require additional coupling methods to make the sensor and the test component fit closely, thus reducing the requirements for the surface finish of the plate components. The convenient detection method of installation, inspection and disassembly and non-contact make it play a huge potential in large-scale plate components and mobile detection.

[0004] Directional SH guided waves can be generated by periodic permanent magnet electromagnetic ultrasonic transducers, which have the characteristics of high signal-to-noise ratio and good energy concentration. Traditional periodic permanent magnet electromagnetic ultrasonic transducers will generate forward and backward SH waves at the same time, causing the backward propagating waves to mix with the defect echoes to be detected after reflection, resulting in missed detection and false detection of defects.

[0005] Some scholars have used the interference mechanism of two independent periodic force sources to generate SH waves in a single direction, and verified the feasibility of the model by calculating the radiation pattern of the unidirectional side-shifted dual PPM EMAT. However, from the results, the rear side lobe sound beam still exists obviously, and the unidirectionality is not superior enough. Later, some scholars proposed to use traditional periodic permanent magnets with dual linear coil arrays to excite unidirectional SH waves. The eddy currents in the area of ​​each permanent magnet are provided by part of the coils wrapped around the permanent magnet. Due to the complete alignment of the wave source in the length direction, there is no obvious rear side lobe in the sound field, which significantly reduces the probability of false detection of defects by the electromagnetic ultrasonic transducer. Although the above method has initially solved the problem of rear side lobes, there are still problems such as insufficient coil utilization, overly cumbersome installation, and uneven static magnetic field. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention designs an electromagnetic ultrasonic unidirectional transducer, comprising: a narrow plate; two periodic permanent magnet electromagnetic ultrasonic transducers, which are respectively arranged on the upper and lower sides of the narrow plate, and the two periodic permanent magnet electromagnetic ultrasonic transducers are staggered in the long side direction of the narrow plate; and a clamping electromagnetic ultrasonic unidirectional transducer housing for fixing the periodic permanent magnet electromagnetic ultrasonic transducers.

[0007] Preferably, the two periodic permanent magnet electromagnetic ultrasonic transducers are offset by one quarter of the SH0 wavelength in the long side direction of the narrow plate, the excitation signals input into the two periodic permanent magnet electromagnetic ultrasonic transducers have the same frequency, and the excitation signals input into the two periodic permanent magnet electromagnetic ultrasonic transducers differ in phase by one quarter of a cycle.

[0008] Preferably, the periodic permanent magnet electromagnetic ultrasonic transducer comprises: an embedded electromagnetic ultrasonic transducer housing and a periodic permanent magnet array, a buffer layer, a PCB flexible runway coil and a wear-resistant layer which are sequentially arranged in the embedded electromagnetic ultrasonic transducer housing.

[0009] Preferably, the periodic permanent magnet array includes a plurality of permanent magnets, and a spacing between the plurality of permanent magnets in the long side direction of the narrow plate is half the SH0 wavelength, and a spacing between the plurality of permanent magnets in the wide side direction of the narrow plate is zero.

[0010] Preferably, a through hole is provided on the top of the housing of the embedded electromagnetic ultrasonic transducer, and the through hole is used to fix the periodic permanent magnet array.

[0011] Preferably, the material of the buffer layer is sponge, the PCB flexible track coil is a double-layer flexible PCB coil, and the material of the wear-resistant layer is nylon.

[0012] Based on the same design concept, the present invention provides a waveguide detection system using an electromagnetic ultrasonic unidirectional transducer, characterized in that it includes a power amplifier module, an excitation signal source module, a human-machine interface and control module, a digital signal processing module, an AD acquisition module, a signal filtering module and a signal amplification module connected in sequence, wherein the power amplifier module and the signal amplification module are both connected to the periodic permanent magnet electromagnetic ultrasonic transducer in the electromagnetic ultrasonic unidirectional transducer.

[0013] Based on the same design concept, the present invention provides a defect detection method using a guided wave detection system, which is characterized in that it includes the following steps: S1, an excitation signal source module generates a first sinusoidal wave signal and a second sinusoidal wave signal, the first sinusoidal wave signal is delayed by a quarter of a period, amplified by a power amplifier module, and input into one of the periodic permanent magnet electromagnetic ultrasonic transducers in the electromagnetic ultrasonic unidirectional transducer, and the second sinusoidal wave signal is amplified by the power amplifier module and input into another periodic permanent magnet electromagnetic ultrasonic transducer in the electromagnetic ultrasonic unidirectional transducer, so as to generate a forward propagating SH0 modal guided wave; S2, a first sinusoidal wave signal is generated by a first excitation signal source module, and a second sinusoidal wave signal is generated by a second excitation signal source module, and a second sinusoidal wave signal is generated by a second excitation signal source module, and a second sinusoidal wave signal is input into another periodic permanent magnet electromagnetic ultrasonic transducer in the electromagnetic ultrasonic unidirectional transducer, and a forward propagating SH0 modal guided wave is generated; S3, a second sinusoidal wave signal is generated by a first excitation signal source module, and a second sinusoidal wave signal is generated by a second excitation signal source module, and a second sinusoidal wave signal is input into another periodic permanent magnet electromagnetic ultrasonic transducer in the electromagnetic ultrasonic unidirectional transducer, and a forward propagating SH0 modal guided wave is generated; S4, a first excitation signal source module is used to generate a first excitation signal source, and a second sinusoidal wave signal is generated by a second excitation signal source, and a second sinusoidal wave signal is generated by a first ... 2. The SH0 mode waveguide propagates to the right, and after the defect is detected, it is reflected to generate an echo signal. After the echo signal is received by the periodic permanent magnet electromagnetic ultrasonic transducer in the electromagnetic ultrasonic unidirectional transducer, it is processed in sequence by the signal amplification module, the signal filtering module, the AD acquisition module and the digital signal processing module, and then stored in the human-machine interface and control module for display; S3. After the second sinusoidal wave signal is advanced by three quarters of a cycle, the two periodic permanent magnet electromagnetic ultrasonic transducer receiving signals in the electromagnetic ultrasonic unidirectional transducer are added to obtain the final echo signal diagram; S4. The defect position is calculated based on the final echo signal diagram.

[0014] Compared with the closest prior art, the beneficial effects of the present invention are:

[0015] 1. The present invention installs two periodic permanent magnet electromagnetic ultrasonic transducers of the same specifications in the axial direction of the length direction on both sides of the narrow plate, wherein the two periodic permanent magnet electromagnetic ultrasonic transducers are offset by a quarter of the SH0 wavelength in the long side direction of the narrow plate and are connected to an external dual-channel excitation signal to generate forward SH guided waves and suppress the formation of backward SH guided waves.

[0016] 2. The two periodic permanent magnet electromagnetic ultrasonic transducers of the present invention are clamped on a narrow plate through a clamping electromagnetic ultrasonic unidirectional transducer housing. The rapid installation and disassembly of the electromagnetic ultrasonic unidirectional transducer are achieved by relying on the magnetic attraction of the periodic permanent magnet electromagnetic ultrasonic transducer. Through the adaptive design of the mold, unidirectional SH wave detection of a narrow plate structure with a large range of cross-sectional dimensions can be achieved.

[0017] 3. The transducer structure of the present invention is simple, and the design of the clamp-type transducer can not only solve the defect misdetection caused by the bidirectional propagation of traditional SH waves, but also improve the amplitude of the transducer excitation signal and enhance the defect detection capability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the structure of the electromagnetic ultrasonic unidirectional transducer of the present invention.

[0019] Figure 2 It is a schematic diagram of the structure of the periodic permanent magnet electromagnetic ultrasonic transducer of the present invention.

[0020] Figure 3 This is the SH wave dispersion curve in the 4 mm thick steel narrow plate of the present invention.

[0021] Figure 4 This is a simulation diagram of the electromagnetic ultrasonic unidirectional transducer comsol of the present invention.

[0022] Figure 5 Schematic diagram of the guided wave detection system of the present invention.

[0023] Figure 6 It is an echo signal diagram corresponding to a specific implementation example of the present invention.

[0024] Reference numerals:

[0025] 1-narrow plate, 2-clamped electromagnetic ultrasonic unidirectional transducer housing, 3-periodic permanent magnet electromagnetic ultrasonic transducer, 31-embedded electromagnetic ultrasonic transducer housing, 32-periodic permanent magnet array, 33-buffer layer, 34-PCB flexible runway coil, 35-wear-resistant layer, 4-power amplifier module, 5-excitation signal source module, 6-human-machine interface and control module, 7-digital signal processing module, 8-AD acquisition module, 9-signal filtering module, 10-signal amplification module. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0027] like Figure 1-Figure 2As shown, the present invention provides an electromagnetic ultrasonic unidirectional transducer, comprising: a narrow plate 1; two periodic permanent magnet electromagnetic ultrasonic transducers 3, which are respectively arranged on the upper and lower sides of the narrow plate 1, and the two periodic permanent magnet electromagnetic ultrasonic transducers 3 are staggered in the long side direction of the narrow plate 1; and a clamping electromagnetic ultrasonic unidirectional transducer housing 2, which is used to fix the periodic permanent magnet electromagnetic ultrasonic transducer 3. The two periodic permanent magnet electromagnetic ultrasonic transducers 3 are staggered by a quarter of the SH0 wavelength in the long side direction of the narrow plate 1, and the excitation signals input into the two periodic permanent magnet electromagnetic ultrasonic transducers 3 have the same frequency, and the excitation signals input into the two periodic permanent magnet electromagnetic ultrasonic transducers 3 differ in phase by a quarter of a cycle. Two periodic permanent magnet electromagnetic ultrasonic transducers 3 of the same specification are installed in the axial direction of the length direction on both sides of the narrow plate 1, wherein the two periodic permanent magnet electromagnetic ultrasonic transducers 3 are staggered by a quarter of the SH0 wavelength in the long side direction of the narrow plate 1 and are connected to an external dual-channel excitation signal, generating a forward SH guided wave and suppressing the formation of a backward SH guided wave. The two periodic permanent magnet electromagnetic ultrasonic transducers 3 are clamped on the narrow plate 1 through the clamping electromagnetic ultrasonic unidirectional transducer housing 2. The electromagnetic ultrasonic unidirectional transducers are quickly installed and disassembled by relying on the magnetic attraction of the periodic permanent magnet electromagnetic ultrasonic transducers 3. Through the adaptive design of the mold, the unidirectional SH wave detection of the narrow plate 1 structure with a large range of cross-sectional dimensions can be achieved. The transducer has a simple structure, and the design of the clamping transducer can not only solve the defect misdetection caused by the bidirectional propagation of traditional SH waves, but also improve the amplitude of the transducer excitation signal and enhance the defect detection capability.

[0028] Preferably, the periodic permanent magnet electromagnetic ultrasonic transducer 3 includes: an embedded electromagnetic ultrasonic transducer housing 31 and a periodic permanent magnet array 32, a buffer layer 33, a PCB flexible runway coil 34 and a wear-resistant layer 35 which are sequentially arranged in the embedded electromagnetic ultrasonic transducer housing 31.

[0029] Preferably, the periodic permanent magnet array 32 includes a plurality of permanent magnets, the spacing of the plurality of permanent magnets in the long side direction of the narrow plate 1 is half the SH0 wavelength, and the magnetic poles are opposite, so as to ensure the generation of a specific single mode waveguide corresponding to a wavelength at a certain frequency. The spacing in the wide side direction of the narrow plate 1 is zero, and the magnetic poles are opposite, so as to improve the utilization rate of the runway coil and enhance the excitation. The size of the straight part area of ​​the PCB flexible runway coil 34 is kept coincident with the bottom surface size of the periodic permanent magnet array 32.

[0030] Preferably, a through hole is provided on the top of the embedded electromagnetic ultrasonic transducer housing 31, and the through hole is used to fix the periodic permanent magnet array 32. After the periodic permanent magnet array 32 is installed, the structure is stable and a stable magnetic field is generated, and it is placed in the inner cavity of the embedded electromagnetic ultrasonic transducer housing 31, and adhesive is added from the through hole on the top of the embedded electromagnetic ultrasonic transducer housing 31 to fix the periodic permanent magnet array 32.

[0031] Preferably, the material of the buffer layer 33 is sponge, the PCB flexible track coil 34 is a double-layer flexible PCB coil, and the material of the wear-resistant layer 35 is nylon.

[0032] In another preferred embodiment, the processing design of the electromagnetic ultrasonic unidirectional transducer mainly includes the selection of the following parameters:

[0033] Wavelength: The relative position of the two periodic permanent magnet electromagnetic ultrasonic transducers 3 and the width of a single permanent magnet in the periodic permanent magnet array 32 are all determined by the wavelength of the selected mode waveguide. When conducting waveguide detection on narrow plate 1 type components, the SH0 mode is usually selected, which has the characteristics of single mode, non-dispersion, good directivity, etc. In this embodiment, the narrow plate 1 is selected as a steel narrow plate 1 with a length of 2m and a cross-sectional size of 40mm×4mm, a density of 7800kg / m3, a Poisson's ratio of 0.3, and a Young's modulus of 2.1×1011Pa. Figure 3 As for its group velocity dispersion curve, the SH0 modal guided wave velocity is 3217m / s, which does not change with the frequency and exists independently in the range of 0-402kHz. The waveguide frequency selected in this embodiment is 161kHz, and the corresponding SH0 wavelength is 20mm. Therefore, the two periodic permanent magnet electromagnetic ultrasonic transducers 3 are 5mm apart in the long side direction of the narrow plate 1, and the spacing between the single permanent magnets in the periodic permanent magnet array 32 in the long side direction of the narrow plate 1 is 10mm.

[0034] Size of periodic permanent magnet array 32: The size of periodic permanent magnet array mainly includes the length of a single magnet and the total length of permanent magnet array. The length of a single magnet determines the aperture size of the transducer and affects the acoustic beam angle of the excited waveguide. θ=2arcsin (0.442λ / W) is the formula for the acoustic beam angle, where θ is the acoustic beam angle of the excited SH wave, λ is the wavelength of the SH wave, and W is the length of the permanent magnet array. As W increases, the acoustic beam angle of the SH wave will decrease. For waveguide detection in the narrow plate 1, a smaller acoustic beam angle should be selected. The length of a single magnet selected in this embodiment is 12mm. The total length of the permanent magnet array is determined by the number of permanent magnet pairs. The more permanent magnet pairs there are, the larger the corresponding total length of the permanent magnet array is, and the higher the amplitude of the excited signal is. However, considering the high impedance caused by the excessively long runway coil and the simplicity of the transducer, the total length of the permanent magnet array selected in this embodiment is 50mm, and the height of a single permanent magnet is 20mm.

[0035] Size of PCB flexible runway coil 34: The overall size of the PCB flexible runway coil 34 is determined by the permanent magnet array, including the length and width of the straight part. The number of coil turns and the line spacing need to be considered additionally. The number of turns and the line spacing of the PCB flexible runway coil 34 are selected according to the inductance and impedance formula of the coil. The coil parameters used in this embodiment are 14 coil turns and 26 mil line spacing.

[0036] Shell material: Both the clamped electromagnetic ultrasonic unidirectional transducer shell 2 and the embedded electromagnetic ultrasonic transducer shell 31 can be designed and processed using 3D printing technology. The processing materials can be nylon, photosensitive resin, etc., but solid processing must be ensured to resist the mutual attraction and repulsion between strong magnets during assembly. In addition, in order to eliminate the clutter interference caused by the spatial magnetic field and improve the signal-to-noise ratio of electromagnetic conversion, a copper shielding shell can be added to the shell.

[0037] After selecting and designing the transducer parameters according to the above steps, the optimal excitation of the SH0 shear wave in the narrow plate 1 structure of a specific size can be achieved in theory. Since the conversion efficiency of the Lorentz magnetic force of the electromagnetic ultrasonic transducer itself is low, it is very necessary to improve the excitation and receiving energy of the transducer through structural design.

[0038] like Figure 4 As shown in the figure, the electromagnetic ultrasonic unidirectional transducer excitation SH wave is simulated in comsol. The specific size is obtained from the above parameters. The excitation signal is a sine wave signal modulated by a 3-cycle Hanning window. The curved part of the runway coil does not affect the simulation results, so it is not modeled. The result is 5.2×10 -5 The waveguide propagation cloud diagram at time s only produces unidirectional propagating SH0 mode waveguide.

[0039] In another preferred embodiment, a waveguide detection system using an electromagnetic ultrasonic unidirectional transducer is provided, comprising a power amplifier module 4, an excitation signal source module 5, a human-machine interface and control module 6, a digital signal processing module 7, an AD acquisition module 8, a signal filtering module 9 and a signal amplifier module 10 connected in sequence, wherein the power amplifier module 4 and the signal amplifier module 10 are both connected to the periodic permanent magnet electromagnetic ultrasonic transducer 3 in the electromagnetic ultrasonic unidirectional transducer. When the single-transmit single-receive mode is adopted, two electromagnetic ultrasonic unidirectional transducers are required to be placed at a distance; when the pulse echo transceiver mode is adopted, only one magnetic ultrasonic unidirectional transducer is required to be placed in the required detection area.

[0040] In another preferred embodiment, a defect detection method using a guided wave detection system is provided, comprising the following steps:

[0041] Step 1: Install an electromagnetic ultrasonic unidirectional transducer on the central axis of the narrow plate 1 in the longitudinal direction, and excite the signal source module 5 to generate two different-channel sinusoidal wave signals with adjustable periods in the range of 1 to 5 and adjustable center frequencies in the range of 0 to 200 kHz, which are respectively a first sinusoidal wave signal and a second sinusoidal wave signal. Delay the first sinusoidal wave signal by a quarter of a period, amplify it through the power amplifier module 4, and input it into one of the periodic permanent magnet electromagnetic ultrasonic transducers 3 in the electromagnetic ultrasonic unidirectional transducer. Amplify the second sinusoidal wave signal through the power amplifier module 4, and input it into another periodic permanent magnet electromagnetic ultrasonic transducer 3 in the electromagnetic ultrasonic unidirectional transducer to generate a forward-propagating SH0 modal guided wave.

[0042] Step 2: The SH0 mode waveguide propagates to the right, and after detecting the defect, it reflects to generate an echo signal. After the echo signal is received by the periodic permanent magnet electromagnetic ultrasonic transducer 3 in the electromagnetic ultrasonic unidirectional transducer, it is processed in sequence by the signal amplification module 10, the signal filtering module 9, the AD acquisition module 8 and the digital signal processing module 7, and then stored in the human-machine interface and control module 6 for display.

[0043] Step 3: In the echo signal diagram, except for the initial wave, the first echo is the defect echo, the second echo is the right end face echo, and the third echo is the echo formed by the defect reflected by the left end face. In order to eliminate such interference waves as the third echo, the second sinusoidal wave signal is advanced by three quarters of a cycle, and the receiving signals of the two periodic permanent magnet electromagnetic ultrasonic transducers 3 in the electromagnetic ultrasonic unidirectional transducer are added to obtain the final echo signal diagram.

[0044] Step 4: Get the final echo signal as Figure 6 As shown in the figure, in actual application, there is a deviation between the SH0 wave velocity and the theoretical wave velocity, so it is necessary to first use the end echo to calculate the wave velocity c p Correction: c p =2s / t, where s is the distance between the end of the narrow plate 1 and the center of the transducer, and t is the time corresponding to the peak value of the end echo. In this case, the corrected wave velocity is 3030m / s. The position of the defect after wave velocity correction can be determined by 2s q =c p ×t q Get, where t q Indicates the time corresponding to the defect echo peak, s q is the distance between the defect and the center of the transducer. The calculated defect position is 0.495 m, which is consistent with the actual defect position of 0.5 m.

[0045] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0046] In addition, the terms "above" and "below" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "above" and "below" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0047] In this application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or communication with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0048] In the present application, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0049] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention are included in the scope of the claims of the present invention to be approved.

Claims

1. An electromagnetic ultrasonic unidirectional transducer, characterized in that: include: Narrow board (1); Two periodic permanent magnet electromagnetic ultrasonic transducers (3) are arranged on the upper and lower sides of the narrow plate (1), respectively, and the two periodic permanent magnet electromagnetic ultrasonic transducers (3) are offset by a quarter of the SH0 wavelength in the long side direction of the narrow plate (1), the excitation signals input into the two periodic permanent magnet electromagnetic ultrasonic transducers (3) have the same frequency, and the excitation signals input into the two periodic permanent magnet electromagnetic ultrasonic transducers (3) differ in phase by a quarter of a period; A clamping type electromagnetic ultrasonic unidirectional transducer housing (2) used for fixing the periodic permanent magnet electromagnetic ultrasonic transducer (3); The periodic permanent magnet electromagnetic ultrasonic transducer (3) comprises: an embedded electromagnetic ultrasonic transducer housing (31), and a periodic permanent magnet array (32), a buffer layer (33), a PCB flexible track coil (34), and a wear-resistant layer (35) which are sequentially arranged in the embedded electromagnetic ultrasonic transducer housing (31); The periodic permanent magnet array (32) comprises a plurality of permanent magnets, wherein the spacing between the plurality of permanent magnets in the long side direction of the narrow plate (1) is half the SH0 wavelength, and the spacing between the plurality of permanent magnets in the wide side direction of the narrow plate (1) is zero.

2. The electromagnetic ultrasonic unidirectional transducer according to claim 1, characterized in that: A through hole is provided on the top of the embedded electromagnetic ultrasonic transducer housing (31), and the through hole is used to fix the periodic permanent magnet array (32).

3. The electromagnetic ultrasonic unidirectional transducer according to claim 1, characterized in that: The material of the buffer layer (33) is sponge, the PCB flexible track coil (34) is a double-layer flexible PCB coil, and the material of the wear-resistant layer (35) is nylon.

4. A guided wave detection system, characterized in that: The invention comprises an electromagnetic ultrasonic unidirectional transducer as claimed in any one of claims 1 to 3, and a power amplifier module (4), an excitation signal source module (5), a human-machine interface and control module (6), a digital signal processing module (7), an AD acquisition module (8), a signal filtering module (9) and a signal amplifier module (10) connected in sequence, wherein the power amplifier module (4) and the signal amplifier module (10) are both connected to a periodic permanent magnet electromagnetic ultrasonic transducer (3) in the electromagnetic ultrasonic unidirectional transducer.

5. A defect detection method, characterized in that: Utilizing the guided wave detection system as claimed in claim 4, the method comprises the following steps: S1, the excitation signal source module (5) generates a first sine wave signal and a second sine wave signal, delays the first sine wave signal by a quarter of a cycle, amplifies it through the power amplifier module (4), and then inputs it into one of the periodic permanent magnet electromagnetic ultrasonic transducers (3) in the electromagnetic ultrasonic unidirectional transducer, and amplifies the second sine wave signal through the power amplifier module (4), and then inputs it into another periodic permanent magnet electromagnetic ultrasonic transducer (3) in the electromagnetic ultrasonic unidirectional transducer, thereby generating a forward propagating SH0 modal guided wave; The S2 and SH0 mode guided waves propagate to the right, and after the defect is detected, the reflected waves generate echo signals. After the echo signals are received by the periodic permanent magnet electromagnetic ultrasonic transducer (3) in the electromagnetic ultrasonic unidirectional transducer, they are processed in sequence by the signal amplification module (10), the signal filtering module (9), the AD acquisition module (8), and the digital signal processing module (7), and then stored in the human-machine interface and control module (6) for display; S3, after advancing the second sine wave signal by three quarters of a cycle, adding the received signals of the two periodic permanent magnet electromagnetic ultrasonic transducers (3) in the electromagnetic ultrasonic unidirectional transducer to obtain a final echo signal diagram; S4. Calculate the defect location based on the final echo signal image.

Images