Torsional mode adjustable in-pipe electromagnetic ultrasonic guided wave transducer and working method thereof

Abstract

The application belongs to the technical field of pipeline ultrasonic guided wave detection, and proposes a twist mode adjustable in-pipe electromagnetic ultrasonic guided wave transducer and a working method thereof. The application comprises multiple circumferential magnet arrays arranged along the axial direction. The circumferential magnet array comprises multiple main magnets and multiple auxiliary magnets staggered along the circumferential direction. The magnetization direction of the main magnet and the magnetization direction of the auxiliary magnet are alternately orthogonal in the circumferential plane. By embedding the circumferential magnetization auxiliary magnet between the radial magnetization main magnet, the radial bias magnetic field strength of the pipe wall area is significantly enhanced, and the electromagnetic interference of the back area of the transducer is effectively suppressed. Without increasing the volume of the magnet, the electromagnetic ultrasonic conversion efficiency and the excitation amplitude of the pipeline twist guided wave are improved. By adjusting the current excitation direction of the spiral coil at different positions to change the axial distribution period of the Lorentz force at the pipe wall, the selective excitation and flexible regulation of the pipeline twist mode can be realized without changing the geometric structure of the transducer.

Description

Technical Field

[0001] This invention belongs to the field of pipeline ultrasonic guided wave detection technology, and particularly relates to an in-pipe electromagnetic ultrasonic guided wave transducer with adjustable torsional mode and its working method. Background Technology

[0002] Torsional guided waves possess advantages such as long propagation distance, wide coverage, and high detection efficiency, making them promising for damage identification and defect localization in oil and gas pipelines. However, the inherent dispersion and multimodal characteristics of ultrasonic guided waves increase the difficulty of signal analysis and processing, and reduce the response accuracy to minute structural defects. Therefore, achieving selective excitation of a single torsional mode through transducer structure design is crucial for ultrasonic guided wave detection of pipelines.

[0003] Electromagnetic ultrasonic transducers do not require coupling agents and can perform non-contact pipe inspection under harsh conditions such as high temperature and high pressure. However, compared with piezoelectric ultrasonic transducers, electromagnetic ultrasonic transducers have lower transduction efficiency and are more susceptible to electromagnetic interference, resulting in small echo signal amplitudes and severely affecting the accuracy of the inspection results. Furthermore, without changing the structural parameters, currently developed electromagnetic ultrasonic transducers can only excite torsional guided waves of a specific wavelength, making it impossible to flexibly control the guided wave excitation mode during pipe inspection. This limits the detection sensitivity of multi-mode torsional guided waves for different types of defects and makes it difficult to meet engineering inspection requirements. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes an in-pipe electromagnetic ultrasonic guided wave transducer with adjustable torsional modes and its operating method. It employs an array of alternately orthogonally magnetized circumferential magnets. By embedding circumferentially magnetized auxiliary magnets between radially magnetized main magnets, the radial bias magnetic field strength in the pipe wall region is significantly enhanced, while electromagnetic interference in the back region of the transducer is effectively suppressed. This improves the electromagnetic ultrasonic transduction efficiency and the excitation amplitude of the torsional guided wave in the pipe without increasing the magnet volume. Furthermore, each circumferential magnet array is wound with a helical coil. By adjusting the current excitation direction of the helical coils at different positions, the axial distribution period of the Lorentz force at the pipe wall is changed. Without altering the transducer geometry, selective excitation and flexible control of the pipe's torsional modes can be achieved.

[0005] To achieve the above objectives, in a first aspect, the present invention provides an in-tube electromagnetic ultrasonic guided wave transducer with torsional mode adjustable, employing the following technical solution: A torsional mode-tunable in-tube electromagnetic ultrasonic waveguide transducer includes multiple circumferential magnet arrays arranged along the axial direction; the circumferential magnet arrays include multiple main magnets and multiple auxiliary magnets distributed alternately along the circumferential direction; the magnetization directions of the main magnets and the magnetization directions of the auxiliary magnets are alternately orthogonal in the circumferential plane. Each circumferential magnet array is wound with a helical coil. By adjusting the current excitation direction of the helical coils at different positions, the axial distribution period of the Lorentz force at the tube wall is changed, thereby achieving the control of the torsional mode.

[0006] Furthermore, a spiral coil is wound around the main magnet in the circumferential magnet array; the inner and outer diameter arc surfaces of the main magnet and the auxiliary magnet are arranged with the pipe axis as the center, the vertex of the fan-shaped included angle of the main magnet is located on the pipe axis, and the vertex of the fan-shaped included angle of the auxiliary magnet is offset to the outside of the pipe wall.

[0007] Furthermore, the main magnet is magnetized radially along the pipe, and the magnetization directions of adjacent main magnets are opposite; the secondary magnet is magnetized circumferentially along the pipe, and the magnetization directions of adjacent secondary magnets are opposite.

[0008] Furthermore, in the circumferential magnet array, the circumferential magnetization directions of the auxiliary magnets on both sides of the radially outward magnetized main magnet all point towards the main magnet; the circumferential magnetization directions of the auxiliary magnets on both sides of the radially inward magnetized main magnet all turn away from the main magnet.

[0009] Furthermore, the geometric centers of the main magnet and the secondary magnet are radially opposite each other, and the circumferential arc length of the main magnet is greater than that of the secondary magnet.

[0010] Furthermore, the spiral coil is wound radially around the main magnet of the circumferential magnet array, and the spiral coils of adjacent main magnets are wound in opposite directions; the spiral coils between adjacent main magnets are arranged circumferentially across the back side of the auxiliary magnet.

[0011] Furthermore, the circumferential magnet array consists of multiple arrays arranged along the axial direction, and the radial magnetization directions of the main magnets in adjacent circumferential magnet arrays along the axial direction are opposite.

[0012] Furthermore, the spiral coils of the circumferential magnet array are connected to a multi-channel current controller, which adjusts the current excitation direction of different spiral coils through circuit control.

[0013] Furthermore, when it is necessary to improve the local energy conversion efficiency of the transducer and the amplitude of the excitation signal, the sector angle ratio of the auxiliary magnet should be increased; when it is necessary to prioritize the uniformity of the excitation sound field, the sector angle ratio of the main magnet should be increased; under the premise of ensuring that the period of the magnet array determines the waveguide wavelength, when it is necessary to enhance the amplitude of the excitation signal or improve the energy coupling efficiency, the coil width should be increased; when it is necessary to avoid excessive coupling at high frequencies, the coil width should be reduced.

[0014] To achieve the above objectives, in a second aspect, the present invention also provides a method for operating an in-tube electromagnetic ultrasonic guided wave transducer with torsional mode adjustable, employing the following technical solution: A control method for an in-tube electromagnetic ultrasonic guided wave transducer with adjustable torsional mode is disclosed. The method utilizes the in-tube electromagnetic ultrasonic guided wave transducer with adjustable torsional mode as described in the first aspect. The torsional mode is controlled by adjusting the current excitation direction of the spiral coils at different positions to change the axial distribution period of the Lorentz force at the tube wall.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The in-pipe electromagnetic ultrasonic guided wave transducer of the present invention includes multiple circumferential magnet arrays arranged along the axial direction. The circumferential magnet arrays include multiple main magnets and multiple auxiliary magnets distributed alternately along the circumferential direction. The magnetization directions of the main magnets and the auxiliary magnets are alternately orthogonal in the circumferential plane. By using an alternating orthogonal magnetized circumferential magnet array and embedding circumferentially magnetized auxiliary magnets between the radially magnetized main magnets, the radial bias magnetic field strength in the pipe wall region is significantly enhanced, while the electromagnetic interference in the back region of the transducer is effectively suppressed. Without increasing the magnet volume, the electromagnetic ultrasonic transduction efficiency and the excitation amplitude of the pipe torsional guided wave are improved. At the same time, a helical coil is wound on each circumferential magnet array. By adjusting the current excitation direction of the helical coils at different positions, the axial distribution period of the Lorentz force at the pipe wall is changed. Without changing the geometry of the transducer, selective excitation and flexible control of the pipe torsional mode can be achieved.

[0016] 2. In this invention, the circumferential magnet array is made up of sector permanent magnets that are coaxially arranged but whose sector angle vertices do not overlap. By adjusting the sector angles of the main and auxiliary magnets, the circumferential arc length of the main magnet on the tube wall side is greater than that of the auxiliary magnet, thereby expanding the high-intensity coverage area of ​​the radial bias magnetic field and effectively improving the average magnetic induction intensity below the excitation coil.

[0017] 3. This invention arranges a circumferential magnet array closely along the axial direction inside the pipe. By controlling the current excitation direction of the spiral coil, the axial distribution period of the Lorentz force at the pipe wall can be adjusted. Without changing the transducer geometry, selective excitation and flexible control of the torsional mode of the pipe can be achieved, solving the problem that existing electromagnetic ultrasonic guided wave transducers can only excite torsional guided waves of specific modes and have low detection efficiency. Attached Figure Description

[0018] The accompanying drawings, which form part of this embodiment, are used to provide a further understanding of this embodiment. The illustrative embodiments and their descriptions are used to explain this embodiment and do not constitute an improper limitation of this embodiment.

[0019] Figure 1 This is a schematic diagram of the overall structure of the circumferential magnet array according to an embodiment of the present invention; Figure 2 This is a partial structural schematic diagram of the circumferential magnet array according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the winding of a helical coil in a circumferential magnet array according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the overall structure of the axial magnet array and multi-channel current controller according to an embodiment of the present invention; Figure 5 These are schematic diagrams of the experimental systems for Embodiments 1 and 3 of the present invention; Figure 6 This is a graph showing the frequency response characteristics test results of Embodiment 1 of the present invention; Figure 7 This is a schematic diagram of the experimental system for a conventional electromagnetic ultrasonic transducer in Embodiment 2 of the present invention; Figure 8 This is a graph showing the test results of the torsional waveguide excitation efficiency of a conventional transducer in Embodiment 2 of the present invention; Figure 9 The graph shows the test results of the torsional waveguide excitation efficiency of the optimized transducer in Embodiment 2 of the present invention. Figure 10 The torsional waveguide phase velocity dispersion curve of the steel pipe with an inner diameter of 437 mm and a wall thickness of 10 mm in Example 3 of this invention; Figure 11 This is a schematic diagram of the axial distribution of the circumferential Lorentz force at the tube wall when the current excitation directions of every two adjacent spiral coils are opposite in Embodiment 3 of the present invention. Figure 12 This is an illustration of the torsional guided wave modes that the electromagnetic ultrasonic guided wave transducer can excite when the current excitation directions of every two adjacent spiral coils are opposite in Example 3. Figure 13 This is a schematic diagram of the axial distribution of the circumferential Lorentz force at the tube wall when the current excitation directions of each adjacent spiral coil are opposite. Figure 14 This is an illustration of the torsional guided wave modes that the electromagnetic ultrasonic guided wave transducer can excite when the current excitation directions of each adjacent spiral coil are opposite in Embodiment 3 of the present invention. Among them, 1. Circumferential magnet array; 101. Main magnet; 102. Secondary magnet; 2. Axial magnet array; 3. Helical coil; 4. Multi-channel current controller; 5. Steel pipe; 6. Multi-channel signal generator; 7. Multi-channel high-voltage amplifier; 8. Electromagnetic ultrasonic guided wave transducer; 9. Traditional electromagnetic ultrasonic transducer; 10. Oscilloscope. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0022] Pipelines are crucial transport carriers for traditional oil and gas, as well as new energy media such as hydrogen. During long-term service, they are susceptible to material degradation and cracking due to complex factors such as environmental corrosion and fatigue loads, seriously threatening the safe operation of oil and gas facilities. Torsional guided waves, as a type of mechanically elastic wave constrained and guided by structural boundaries, offer advantages such as long propagation distance, wide coverage, and high detection efficiency, showing great promise for damage identification and defect localization in oil and gas pipelines. However, the inherent dispersion and multimodal characteristics of ultrasonic guided waves increase the difficulty of signal analysis and processing, and reduce the response accuracy to minute structural defects. Therefore, achieving selective excitation of a single torsional mode through transducer structure design is crucial for ultrasonic guided wave detection of pipelines.

[0023] As described in the background section, electromagnetic ultrasonic transducers do not require coupling agents and can perform non-contact pipe inspection under harsh conditions such as high temperature and high pressure. However, compared with piezoelectric ultrasonic transducers, electromagnetic ultrasonic transducers have lower transduction efficiency and are more susceptible to electromagnetic interference, resulting in small echo signal amplitudes and severely affecting the accuracy of the inspection results. Furthermore, without changing the structural parameters, currently developed electromagnetic ultrasonic transducers can only excite torsional guided waves of a specific wavelength, making it impossible to flexibly control the guided wave excitation mode during pipe inspection. This limits the detection sensitivity of multi-mode torsional guided waves for different types of defects, making it difficult to meet engineering inspection requirements.

[0024] To solve at least one of the above problems, such as Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown, one embodiment of the present invention provides a torsional mode adjustable in-tube electromagnetic ultrasonic waveguide transducer 8, including a circumferential magnet array 1, an axial magnet array 2, a helical coil 3, and a multi-channel current controller 4, etc.; wherein, the circumferential magnet array 1 is closely arranged along the axial direction inside the tube to form the axial magnet array 2 of the transducer; each circumferential magnet array 1 has an independent helical coil 3 wound inside, and is connected to the multi-channel current controller 4 inside the transducer.

[0025] Specifically, such as Figure 1 , Figure 2 , Figure 3 and Figure 4As shown, the circumferential magnet array 1 is composed of a group of fan-shaped permanent magnets whose vertices do not overlap. The circumferential magnet array 1 includes multiple main magnets 101 and multiple auxiliary magnets 102, which are staggered along the circumference. Optionally, the circumferential magnet array 1 includes 10 main magnets 101 and 10 auxiliary magnets 102, or other numbers of main magnets 101 and auxiliary magnets 102. Optionally, a spiral coil 3 is wound around each main magnet 101. The inner and outer diameter arc surfaces of the main magnets 101 and the auxiliary magnets 102 are arranged with the pipe axis as the center, and the vertices of the fan-shaped vertices of the main magnets 101 are located on the pipe axis, while the vertices of the fan-shaped vertices of the auxiliary magnets 102 are offset to the outside of the pipe wall.

[0026] Optional, such as Figure 1 As shown, both the main magnet 101 and the auxiliary magnet 102 are made of neodymium iron boron (NdFeB) material, with their magnetization directions alternating orthogonal in the circumferential plane. NdFeB material has advantages such as small size, light weight, and strong magnetism. The main magnet 101 is magnetized radially along the pipe, and the magnetization directions of adjacent main magnets 101 are opposite. The radial magnetic field gradient generated by the main magnet 101 is spatially modulated by the introduced circumferential magnetic flux density. The auxiliary magnet 102 is magnetized circumferentially along the pipe, and the magnetization directions of adjacent auxiliary magnets 102 are opposite. In order to enhance the radial magnetic field strength on the pipe wall side and weaken the electromagnetic interference on the pipe axis side, for the radially outward magnetized main magnet 101, the circumferential magnetization directions of the auxiliary magnets 102 on both sides are pointing towards the main magnet 101, while for the radially inward magnetized main magnet 101, the circumferential magnetization directions of the auxiliary magnets 102 on both sides are away from the main magnet 101.

[0027] The geometric centers of the main magnet 101 and the auxiliary magnet 102 are radially opposite each other. The circumferential arc length of the main magnet 101 on the tube wall side is greater than that of the auxiliary magnet 102 on the tube wall side, which can further expand the coverage area of ​​the radial bias magnetic field.

[0028] like Figure 2 As shown, the inner and outer diameter arc surfaces of both the main magnet 101 and the auxiliary magnet 102 are centered on the pipe axis. The vertex of the sector-shaped included angle of the main magnet 101 is located on the pipe axis, and its inner diameter... 186mm radial thickness 30mm, sector angle The angle is 45°; while the vertex of the sector-shaped included angle of the auxiliary magnet 102 is offset to the outside of the tube wall, and the geometric center of the auxiliary magnet 102 is offset to the outside of the tube wall, its inner diameter is 45°; 186mm radial thickness 30mm, sector angle The angle is 11°; it is worth noting that the sector angle of the main magnet 101 and the auxiliary magnet 102 is not the same as the circumferential angle with reference to the pipe axis.

[0029] In some embodiments, the fan-shaped angle and circumferential proportion of the main magnet 101 and the auxiliary magnet 102 mainly affect the radial bias magnetic field strength at the pipe wall and the circumferential coverage of the spiral coil 3, and can be optimized and adjusted according to different pipe diameters, diameter-to-thickness ratios, and other actual working conditions and testing requirements. Specifically, for pipes with different diameter-to-thickness ratios, the fan-shaped angle proportions of the main magnet 101 and the auxiliary magnet 102 need to be adapted to match the spatial distribution of the radial bias magnetic field with the geometric characteristics of the pipe, thereby obtaining better electromagnetic excitation efficiency.

[0030] For pipes of the same specifications, when it is necessary to improve the local energy conversion efficiency of the transducer and the amplitude of the excitation signal, the sector angle ratio of the auxiliary magnet 102 can be appropriately increased. This parameter adjustment can further enhance the radial bias magnetic field strength at the pipe wall below the main magnet 101; however, it will correspondingly reduce the circumferential arc length of the main magnet 101 on the pipe wall side, resulting in a reduction in the circumferential coverage area of ​​the helical coil 3 at the pipe wall, making the excited induced eddy currents and Lorentz forces more concentrated in the circumferential direction, thereby reducing the spatial uniformity of the guided wave energy distribution. Conversely, when it is necessary to prioritize the uniformity of the excitation sound field, the sector angle ratio of the main magnet 101 can be appropriately increased to increase the circumferential arc length of the main magnet 101 on the pipe wall side and expand the circumferential coverage area of ​​the helical coil 3 at the pipe wall, making the alternating eddy currents and Lorentz forces generated on the pipe wall surface more widely distributed, thereby effectively improving the uniformity of the guided wave energy distribution.

[0031] The spiral coil 3 is made of copper-clad aluminum enameled wire and is wound radially around the main magnet 101 in the circumferential magnet array 1. The coil has 7 turns and a coil width of... The coil spacing is 1mm. The diameter is 3mm, and the winding directions of adjacent main magnets 101 are opposite; the spiral coils 3 between adjacent main magnets 101 are arranged circumferentially across the back side of the auxiliary magnet to avoid generating ineffective induced eddy currents at the tube wall.

[0032] In some embodiments, the coil width Coil spacing The main factors affecting electromagnetic transduction efficiency and the spatial distribution characteristics of induced eddy currents can be optimized and adjusted according to different detection requirements. Specifically, while ensuring the period of the magnet array determines the waveguide wavelength, the coil width can be appropriately increased when it is necessary to enhance the amplitude of the excitation signal or improve the energy coupling efficiency. Or reduce the coil spacing This parameter adjustment can enhance the spatial continuity of induced eddy currents between adjacent coils, reduce the peak value of local current density, thereby suppressing eddy current concentration and improving the uniformity of field distribution.

[0033] For small-diameter pipes with large curvature or applications using highly conductive materials, the coil spacing can be further reduced. This improves the consistency of eddy current coupling and the stability of guided wave excitation. Conversely, when it is necessary to avoid excessive coupling at high frequencies or reduce system energy loss, the coil spacing can be appropriately increased. Or reduce the coil width This is to improve the excitation stability of the transducer and the overall matching characteristics of the system.

[0034] Specifically, the circumferential magnet array 1 is arranged closely along the axial direction inside the tube, and its axial width is... The axial spacing is 10mm. The diameter is 2 mm; the radial magnetization directions of the main magnets 101 in the adjacent circumferential magnet array 1 are opposite to ensure that the transducer can provide a uniform and stable radial bias magnetic field on the tube wall side.

[0035] In some embodiments, the axial width of the circumferential magnet array 1 Axial spacing The main factor determining the minimum guided wave wavelength that the transducer can excite is the periodicity of the axial Lorentz force generated at the tube wall. This can be optimized and adjusted according to the actual required target guided wave wavelength range. Specifically, the guided wave excitation wavelength of the torsional mode is equal to the axial distribution period of the circumferential Lorentz force generated at the tube wall. When the current excitation directions of the helical coils 3 in adjacent circumferential magnet arrays 1 alternately reverse, the minimum axial distribution period of the Lorentz force is formed at the tube wall. At this time, the minimum guided wave wavelength that the transducer can excite is strictly limited to the axial span of two adjacent circumferential magnet arrays 1, i.e., twice the axial width. Axial spacing The sum of. Therefore, the axial width Axial spacing The size of the transducer directly determines the lower limit of its ability to control the wavelength of the torsional guide wave.

[0036] When actual testing requires expanding the transducer's modulation range for short-wavelength torsional modes, the axial width needs to be appropriately reduced. or axial spacing This shortens the minimum axial distribution period of the Lorentz force, thereby enabling selective excitation of shorter wavelength modes; conversely, if the wavelength corresponding to the target detection mode is longer, the axial width can be increased accordingly. or axial spacing To adapt to the distribution period of long-wavelength guided waves. By reasonably configuring the axial dimension parameters of the circumferential magnet array 1, the lower limit of the transducer's wavelength control can be accurately set, achieving optimal matching with different detection frequency bands and modal requirements.

[0037] Specifically, the spiral coil 3 of each circumferential magnet array 1 is connected to the multi-channel current controller 4 inside the transducer. By adjusting the current excitation direction of different spiral coils 3 through circuit control, the axial distribution period of the Lorentz force at the tube wall can be changed. This enables selective excitation and flexible control of a single torsional mode, wherein the guided wave excitation wavelength of the torsional mode... The axial distribution period of the Lorentz force generated by the transducer equal.

[0038] An embodiment of the present invention also provides a method for operating an in-tube electromagnetic ultrasonic guided wave transducer with adjustable torsional mode, using the aforementioned electromagnetic ultrasonic guided wave 8, including: changing the axial distribution period of the Lorentz force at the tube wall by adjusting the current excitation direction of the helical coils at different positions to achieve torsional mode control. Specifically, the current excitation direction of the helical coils 3 in the circumferential magnet array 1 is adjusted by the multi-channel current controller 4 to spatially adjust the periodic Lorentz force distribution excited at the tube wall by the axial magnet array 2, thereby controlling the excitation wavelength of the torsional guided wave mode.

[0039] When a high-frequency alternating current is passed through the coil inside the transducer, eddy currents of the same frequency opposite to the direction of the excitation current are generated at the skin depth of the tube wall. The radial bias magnetic field provided by the circumferential magnet array interacts with the induced eddy currents to generate a circumferential Lorentz force at the tube wall, thereby causing high-frequency vibration of the tube wall particles. This vibration propagates in the form of waves along the axial direction of the tube to form ultrasonic guided waves. Without changing the transducer structural design, by controlling the current excitation direction of the helical coil in the circumferential magnet array, circumferential Lorentz forces with different periodic distributions can be formed along the axial direction of the tube, thereby achieving selective excitation of specific torsional mode guided waves, where the guided wave wavelength is equal to the axial distribution period of the circumferential Lorentz force.

[0040] Example 1: To test the performance of the torsional mode-tunable in-tube electromagnetic ultrasonic guided wave transducer proposed in this invention, this embodiment provides a test system including the torsional mode-tunable in-tube electromagnetic ultrasonic guided wave transducer, which realizes the frequency response characteristics test of the electromagnetic ultrasonic guided wave transducer, specifically: Optionally, the test object is steel pipe 5, with an inner diameter of 437 mm, a wall thickness of 10 mm, and a length of 1000 mm. The experimental system is as follows: Figure 5As shown, the system includes a steel pipe 5, a multi-channel signal generator 6, a multi-channel high-voltage amplifier 7, an electromagnetic ultrasonic guided wave transducer 8, and an oscilloscope 10. The multi-channel signal generator 6 outputs a sinusoidal pulse signal modulated by a Hanning window as the signal source, which can reduce the spectral sidelobes of the excitation signal, making the frequency of the excited guided wave signal closer to a single frequency and the energy more concentrated. The multi-channel high-voltage amplifier 7 can increase the voltage amplitude of the signal source. The electromagnetic ultrasonic guided wave transducer 8 is used to excite and receive the torsional guided wave signal in the steel pipe 5. The oscilloscope 10 is used to export the waveform information of the received signal for post-processing. The steel pipe 5 can be a Q235 steel pipe.

[0041] A frequency sweep experiment was performed on the electromagnetic ultrasonic guided wave transducer 8. Optionally, the electromagnetic ultrasonic guided wave transducer 8, acting as an excitation transducer, was positioned 300 mm from the left end face of the steel pipe, and the electromagnetic ultrasonic guided wave transducer 8, acting as a receiving transducer, was positioned 300 mm from the right end face of the steel pipe. The axial distance between the excitation and receiving transducers was 400 mm. The excitation signal source could be a five-cycle sinusoidal pulse wave modulated by a Hanning window. The starting frequency of the frequency sweep experiment could be 60 kHz, increasing to 160 kHz in 10 kHz steps. A one-excitation-one-emission experimental method was used to extract the peak-to-peak value of the received wave at each frequency, resulting in the frequency response characteristic curve of the electromagnetic ultrasonic guided wave transducer 8, as shown below. Figure 6 As shown, the actual center frequency of the electromagnetic ultrasonic guided wave transducer 8 is 98kHz, which is basically consistent with the theoretical center frequency of 103kHz, with a relative error of only 4.9%.

[0042] Example 2: To further test the performance of the torsional mode-tunable in-tube electromagnetic ultrasonic waveguide transducer of this invention, this embodiment provides a test system including the torsional mode-tunable in-tube electromagnetic ultrasonic waveguide transducer. Through comparative experiments, the excitation efficiency of the electromagnetic ultrasonic waveguide transducer was tested, specifically as follows: Optionally, the test object is steel pipe 5, with an inner diameter of 437 mm, a wall thickness of 10 mm, and a length of 1000 mm. The experimental system is as follows: Figure 5 and Figure 7 As shown, the system includes a steel pipe 5, a multi-channel signal generator 6, a multi-channel high-voltage amplifier 7, an electromagnetic ultrasonic guided wave transducer 8, a conventional electromagnetic ultrasonic transducer 9, and an oscilloscope 10. The multi-channel signal generator 6 outputs a sinusoidal pulse signal modulated by a Hanning window as the signal source, which can reduce the spectral sidelobes of the excitation signal, making the frequency of the excited guided wave signal closer to a single frequency and the energy more concentrated. The multi-channel high-voltage amplifier 7 can increase the voltage amplitude of the signal source. The conventional electromagnetic ultrasonic transducer 9 is used to excite and receive the torsional guided wave signal in the steel pipe 5. The oscilloscope 10 is used to export the waveform information of the received signal for post-processing.

[0043] To test the torsional mode excitation efficiency of the electromagnetic ultrasonic guided wave transducer 8 and compare it with that of a traditional electromagnetic ultrasonic transducer, an excitation efficiency test experiment was designed. Optionally, the electromagnetic ultrasonic guided wave transducer 8, acting as the excitation transducer, is positioned 300mm from the left end face of the steel pipe, and the electromagnetic ultrasonic guided wave transducer 8, acting as the receiving transducer, is positioned 300mm from the right end face of the steel pipe. The axial distance between the excitation and receiving transducers is 400mm. The excitation signal source can be a five-cycle sinusoidal pulse wave modulated by a Hanning window, with a center frequency of 110kHz. A one-excitation-one-emission experimental method is used, and the obtained torsional guided wave signal is as follows: Figure 8 and Figure 9 As shown, the amplitude of the torsional mode signal excited and received by the electromagnetic ultrasonic guided wave transducer 8 is 3.2 Vpp, while the amplitude of the torsional mode signal excited and received by the conventional electromagnetic ultrasonic transducer 9 is 2.04 Vpp. This indicates that the electromagnetic ultrasonic guided wave transducer used in this embodiment has a higher transduction efficiency. By designing a circumferentially arranged and alternately orthogonally magnetized permanent magnet array, the radial magnetic field strength of the transducer on the tube wall side is significantly enhanced, thereby improving the in-tube excitation efficiency of the torsional guided wave.

[0044] Example 3: To further test the performance of the torsional mode-tunable in-tube electromagnetic ultrasonic waveguide transducer of this invention, this embodiment provides a test system including the torsional mode-tunable in-tube electromagnetic ultrasonic waveguide transducer, verifying the feasibility of torsional mode control of the electromagnetic ultrasonic waveguide transducer, specifically as follows: The object of the test is steel pipe 5, with an inner diameter of 437 mm, a wall thickness of 10 mm, and a length of 1000 mm. The experimental system is as follows: Figure 5 As shown, the system includes a steel pipe 5, a multi-channel signal generator 6, a multi-channel high-voltage amplifier 7, an electromagnetic ultrasonic guided wave transducer 8, and an oscilloscope 10. The multi-channel signal generator 6 outputs a sinusoidal pulse signal modulated by a Hanning window as the signal source, which reduces the spectral sidelobes of the excitation signal, making the frequency of the excited guided wave signal closer to a single frequency and the energy more concentrated. The multi-channel high-voltage amplifier 7 increases the voltage amplitude of the signal source. The electromagnetic ultrasonic guided wave transducer 8 is used to excite and receive the torsional guided wave signal in the steel pipe 5. The oscilloscope 10 is used to export the waveform information of the received signal for post-processing.

[0045] Figure 10 The diagram shows the torsional guided wave phase velocity dispersion curve of the aforementioned steel pipe. Optionally, the electromagnetic ultrasonic guided wave transducer 8, acting as the excitation transducer, is positioned 300 mm from the left end face of the steel pipe, and the electromagnetic ultrasonic guided wave transducer 8, acting as the receiving transducer, is positioned 300 mm from the right end face of the steel pipe. The axial distance between the excitation transducer and the receiving transducer is 400 mm. The excitation signal source can be a five-cycle sinusoidal pulse wave modulated by a Hanning window, using a one-excitation-one-emission experimental method.

[0046] The current excitation direction of the helical coil 3 can be adjusted by the multi-channel current controller 4. For example, the current excitation directions of the helical coils in every two adjacent circumferential magnet arrays are opposite. At this time, the axial distribution period of the circumferential Lorentz force at the tube wall is also adjusted. It is 48mm, such as Figure 11 As shown; the center frequencies of the excitation signals are set to 68kHz and 177kHz respectively, and the torsional mode signal is received using the electromagnetic ultrasonic guided wave transducer 8, as follows. Figure 12 As shown, after processing, it was found that the transducer can excite a single torsional mode point, Mode1 and Mode2, which intersect with the dashed line.

[0047] The current excitation direction of the helical coil 3 can be adjusted by the multi-channel current controller 4. For example, the current excitation directions of the helical coils in each adjacent circumferential magnet array are opposite. At this time, the axial distribution period of the circumferential Lorentz force at the tube wall is also adjusted. It is 24mm, such as Figure 13 As shown; the center frequencies of the excitation signals are set to 307kHz and 420kHz respectively, and the torsional mode signal is received using the electromagnetic ultrasonic guided wave transducer 8, as follows. Figure 14 As shown, after processing, it was found that the transducer can excite a single torsional mode point, Mode3 and Mode4, which intersect with the dashed line.

[0048] This discovery reveals that by using an independent helical coil for each circumferential magnet array and adjusting the current excitation direction of the helical coil through a multi-channel current controller, selective excitation and flexible control of the torsional guided wave mode within the pipeline can be achieved without altering the transducer geometry.

[0049] Specifically, before or during actual pipeline inspection, the number of adjacent circumferential magnet arrays with the same current excitation direction can be dynamically adjusted according to the type and size of the target defect and the required inspection range. The basis and effect of this adjustment is that by increasing or decreasing the number of adjacent circumferential magnet arrays with the same current direction, the axial distribution period L of the Lorentz force at the pipe wall can be directly and significantly changed, thereby altering the wavelength λ of the excited torsional guided wave.

[0050] In practical applications, when conducting rapid overall screening of long-distance, large-area pipelines, or when the target defect is large, such as extensive corrosion thinning, the number of adjacent circumferential magnet arrays with the same current direction can be increased. This adjustment method increases the Lorentz force distribution period L, exciting a longer wavelength torsional guided wave. Longer wavelength guided waves experience less energy attenuation during propagation, which is beneficial for increasing the detection distance. Conversely, when performing high-precision scanning in a specific area, or when the target defect is small, such as micro-cracks or localized pitting corrosion, the number of adjacent circumferential magnet arrays with the same current direction needs to be reduced to shorten the Lorentz force distribution period L, exciting a shorter wavelength torsional guided wave, thereby improving the sensitivity and resolution of the guided wave for detecting small defects. Furthermore, after determining the required Lorentz force distribution period L, by adjusting the center frequency of the excitation signal, a single torsional guided wave mode, such as Mode 1 to Mode 4, can be accurately located and excited in the dispersion curve, effectively avoiding signal interference caused by multi-mode superposition and greatly reducing the difficulty of processing and identifying defect echo signals.

[0051] The above description is merely a preferred embodiment of this practice and is not intended to limit the scope of this practice. Various modifications and variations can be made to this practice by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this practice should be included within the protection scope of this practice.

Claims

1. A torsional mode-tunable in-tube electromagnetic ultrasonic guided wave transducer, characterized in that, It includes multiple circumferential magnet arrays arranged along the axial direction; the circumferential magnet arrays include multiple main magnets and multiple auxiliary magnets that are staggered along the circumferential direction; the magnetization directions of the main magnets and the magnetization directions of the auxiliary magnets are alternately orthogonal in the circumferential plane; Each circumferential magnet array has a spiral coil wound around it. The spiral coil is wound radially along the main magnet of the circumferential magnet array. By adjusting the current excitation direction of the spiral coil at different positions, the axial distribution period of the Lorentz force at the tube wall is changed, thereby achieving the control of the torsional mode.

2. The torsional mode-tunable in-tube electromagnetic ultrasonic waveguide transducer as described in claim 1, characterized in that, The main magnet in the circumferential magnet array is wound with a spiral coil; the inner and outer diameter arc surfaces of the main magnet and the auxiliary magnet are arranged with the pipe axis as the center, the vertex of the fan-shaped included angle of the main magnet is located on the pipe axis, and the vertex of the fan-shaped included angle of the auxiliary magnet is offset to the outside of the pipe wall.

3. The torsional mode-tunable in-tube electromagnetic ultrasonic waveguide transducer as described in claim 1, characterized in that, The main magnet is magnetized radially along the pipe, and the magnetization directions of adjacent main magnets are opposite; the secondary magnet is magnetized circumferentially along the pipe, and the magnetization directions of adjacent secondary magnets are opposite.

4. The torsional mode-tunable in-tube electromagnetic ultrasonic guided wave transducer as described in claim 3, characterized in that, In the circumferential magnet array, the circumferential magnetization directions of the auxiliary magnets on both sides of the radially outward magnetized main magnet all point towards the main magnet; the circumferential magnetization directions of the auxiliary magnets on both sides of the radially inward magnetized main magnet all turn away from the main magnet.

5. The torsional mode-tunable in-tube electromagnetic ultrasonic waveguide transducer as described in claim 1, characterized in that, The geometric centers of the main magnet and the secondary magnet are radially opposite each other, and the circumferential arc length of the main magnet is greater than that of the secondary magnet.

6. The torsional mode-tunable in-tube electromagnetic ultrasonic waveguide transducer as described in claim 1, characterized in that, The spiral coil is wound radially around the main magnet of the circumferential magnet array, and the spiral coils of adjacent main magnets are wound in opposite directions; the spiral coils between adjacent main magnets are arranged circumferentially across the back side of the auxiliary magnet.

7. The torsional mode-tunable in-tube electromagnetic ultrasonic waveguide transducer as described in claim 1, characterized in that, The circumferential magnet array consists of multiple arrays arranged along the axial direction, and the radial magnetization directions of the main magnets in adjacent circumferential magnet arrays along the axial direction are opposite.

8. The torsional mode-tunable in-tube electromagnetic ultrasonic waveguide transducer as described in claim 1, characterized in that, The spiral coils of the circumferential magnet array are connected to a multi-channel current controller, which adjusts the current excitation direction of different spiral coils through circuit control.

9. The torsional mode-tunable in-tube electromagnetic ultrasonic waveguide transducer as described in claim 1, characterized in that, When it is necessary to improve the local energy conversion efficiency of the transducer and the amplitude of the excitation signal, the sector angle ratio of the auxiliary magnet should be increased. When it is necessary to prioritize the uniformity of the excitation sound field, the sector angle ratio of the main magnet should be increased. Under the premise of ensuring that the period of the magnet array determines the waveguide wavelength, when it is necessary to enhance the amplitude of the excitation signal or improve the energy coupling efficiency, the coil width should be increased. When it is necessary to avoid excessive coupling at high frequencies, the coil width should be reduced.

10. A control method for an in-tube electromagnetic ultrasonic guided wave transducer with adjustable torsional mode, characterized in that, The torsional mode adjustable in-tube electromagnetic ultrasonic guided wave transducer as described in any one of claims 1-9 is used. By adjusting the current excitation direction of the spiral coils at different positions, the axial distribution period of the Lorentz force at the tube wall is changed, thereby achieving the control of the torsional mode.

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