CN115032279B - Broadband magnetostrictive SH0 modal guided wave monitoring transducer - Google Patents
Broadband magnetostrictive SH0 modal guided wave monitoring transducer Download PDFInfo
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- 238000012544 monitoring process Methods 0.000 title claims abstract description 25
- 230000005291 magnetic effect Effects 0.000 claims abstract description 137
- 230000003068 static effect Effects 0.000 claims abstract description 52
- 239000002184 metal Substances 0.000 claims abstract description 38
- 229910052751 metal Inorganic materials 0.000 claims abstract description 38
- 238000012360 testing method Methods 0.000 claims abstract description 36
- 239000007822 coupling agent Substances 0.000 claims description 12
- 238000004088 simulation Methods 0.000 claims description 12
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 6
- 230000005415 magnetization Effects 0.000 claims description 5
- 230000035699 permeability Effects 0.000 claims description 5
- 239000003822 epoxy resin Substances 0.000 claims description 4
- 229920000647 polyepoxide Polymers 0.000 claims description 4
- 229910052742 iron Inorganic materials 0.000 claims description 3
- 230000000694 effects Effects 0.000 abstract description 9
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- 238000010361 transduction Methods 0.000 abstract description 9
- 230000005389 magnetism Effects 0.000 description 32
- 238000001514 detection method Methods 0.000 description 11
- 239000000463 material Substances 0.000 description 8
- 230000005284 excitation Effects 0.000 description 7
- 238000013461 design Methods 0.000 description 5
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- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
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- WABPQHHGFIMREM-UHFFFAOYSA-N lead(0) Chemical compound [Pb] WABPQHHGFIMREM-UHFFFAOYSA-N 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/22—Details, e.g. general constructional or apparatus details
- G01N29/24—Probes
- G01N29/2412—Probes using the magnetostrictive properties of the material to be examined, e.g. electromagnetic acoustic transducers [EMAT]
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/22—Details, e.g. general constructional or apparatus details
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/22—Details, e.g. general constructional or apparatus details
- G01N29/28—Details, e.g. general constructional or apparatus details providing acoustic coupling, e.g. water
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
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Abstract
The utility model provides a wide band magnetostriction SH0 mode guided wave monitoring transducer, has solved the problem how to improve magnetostriction transducer transduction efficiency based on reversal Wei Deman effect, belongs to nondestructive test technical field. The invention comprises permanent magnets, magnetostriction patches and a zigzag coil, wherein the magnetostriction patches are adhered to the outer surface of a tested metal test piece along the circumferential direction of the tested metal test piece, the zigzag coil is arranged on the surface of the magnetostriction patches, the permanent magnets are uniformly distributed along the circumferential direction of the tested metal test piece at equal intervals, the polarities of the adjacent two permanent magnets are opposite, the magnetizing direction is along the axial direction of the tested metal test piece, an axial static magnetic field is generated, the intervals of the permanent magnets are equal to the intervals of adjacent wires of the zigzag coil, the center line of each permanent magnet is aligned with the center line of the wire of the zigzag coil under the same, alternating current is introduced into the zigzag coil to provide a dynamic magnetic field, and the current directions in the adjacent wires at the same moment in the zigzag coil are opposite.
Description
Technical Field
The invention relates to a magnetostriction SH0 mode guided wave monitoring transducer structure based on a reverse Wei Deman effect, and belongs to the technical field of nondestructive testing.
Background
Defects such as cracks and corrosion are often generated in the service process of plates, pipes and the like, so that potential safety hazards are formed. In order to ensure safe operation and effective use of products, nondestructive detection has become a mandatory measure in the fields of petroleum and petrochemical industry, rail transit and the like. However, the existing detection technology has the problems of small detection range, low efficiency, high manual detection cost, large error and the like. The magnetostriction SH0 mode guided wave has a long propagation distance, and is suitable for long-term health monitoring of large plates and pipes.
According to the definition of Wei Deman effect, the ferromagnetic plate and the pipe can generate SH0 mode guided waves under the combined action of a horizontal static magnetic field perpendicular to the propagation direction of the sound wave and an alternating magnetic field parallel to the propagation direction of the sound wave. The transducer of the magnetostrictive guided wave detection system at the present stage adopts a pre-magnetized magnetostrictive patch and a zigzag coil, the magnetostrictive patch is stuck along the circumferential direction of a pipeline or the direction perpendicular to the propagation direction of sound waves of a plate, a permanent magnet 1 is used for magnetizing a magnetostrictive material along the direction, then the zigzag coil is placed on the upper surface of a magnetostrictive patch in the same direction, and an alternating magnetic field along the propagation direction of the sound waves is generated after alternating current is introduced. On the one hand, the structure transducer has smaller bias magnetic field caused by pre-magnetization, the magnetostrictive material cannot exert the optimal magnetostriction performance and cannot be monitored for a long time due to demagnetization, and on the other hand, the circumferential zigzag coil structure forms a band-pass filter with fixed center frequency, namely, the coil needs to be manually replaced to change the working frequency of SH0 guided waves, so that the magnetostrictive SH0 guided wave technology can only be applied to point-by-point detection, and industrial plates and pipe fittings are difficult to monitor for a long time.
The torsion guided wave magnetostrictive transducer based on the reverse Wei Deman effect uses a plurality of permanent magnets to be uniformly distributed along the circumferential direction of the pipeline and to be magnetized along the axial direction in the same direction. In order to excite torsional guided waves propagating in the axial direction in the pipe, it is necessary to generate a dynamic magnetic field distributed in the pipe circumferential direction in the magnetostrictive patch, and therefore a coil to which an alternating current is supplied is wound in the form of a solenoid on the magnetostrictive patch. However, the design mode of the transducer causes that a layer of coil is clamped between the lower surface of the magnetostrictive patch and the outer surface of the tested piece, so that the coupling effect of the transducer is seriously affected, and finally the transduction efficiency is reduced. In addition, the coil is wound on the magnetostrictive patch in the form of a solenoid, resulting in a significant increase in transducer manufacturing and installation costs.
Disclosure of Invention
Aiming at the problem of how to improve the transduction efficiency of the magnetostrictive transducer based on the reverse Wei Deman effect, the invention provides a broadband magnetostrictive SH0 mode guided wave monitoring transducer.
The invention relates to a broadband magnetostriction SH0 mode guided wave monitoring transducer which comprises a permanent magnet 1, a magnetostriction patch 3 and a zigzag coil 4;
The magnetostriction patch 3 is adhered to the outer surface of the tested metal test piece 6 along the circumferential direction of the tested metal test piece 6, the zigzag coils 4 are arranged on the surface of the magnetostriction patch 3, the permanent magnets 1 are uniformly distributed along the circumferential direction of the tested metal test piece 6 at equal intervals, the polarities of the adjacent two permanent magnets 1 are opposite, the magnetizing direction is along the axial direction of the tested metal test piece 6, an axial static magnetic field is generated, the intervals of the permanent magnets 1 are equal to the intervals of adjacent wires of the zigzag coils 4, the center line of each permanent magnet 1 is aligned with the center line of the wire of the zigzag coil 4 under the same, alternating current is introduced into the zigzag coils 4 to provide a dynamic magnetic field, and the current directions in the adjacent wires in the zigzag coils 4 at the same time are opposite.
Preferably, the monitoring transducer further comprises a magnetism collecting structure 2 with magnetic permeability, wherein the magnetism collecting structure 2 is arranged at two magnetic poles of each permanent magnet 1, a distance exists between the permanent magnet 1 and the magnetostriction patch 3, the two magnetic poles of the permanent magnet 1 are connected with the tested metal test piece 6 and the magnetostriction patch 3 through the magnetism collecting structure 2, and the permanent magnet 1, the magnetism collecting structure 2 and the magnetostriction patch 3 form a closed loop.
Preferably, the magnetism collecting structure 2 adopts a two-section structure connected, wherein one end of the first-section structure is adsorbed on the magnetic pole of the permanent magnet 1, the other end of the first-section structure is contacted with the outer surface of the tested metal test piece 6 and is connected with one end of the second-section structure, and the second-section structure extends towards the magnetostrictive patch 3 on the outer surface of the tested metal test piece 6 and is contacted with the magnetostrictive patch 3.
Preferably, the cross section of the first section structure is rectangular, the cross section of the second section structure is isosceles right trapezoid, one right-angle side rectangular surface of the second section structure is connected with the other end of the first section structure, and the other right-angle side rectangular surface of the second section structure is contacted with the outer surface of the tested metal test piece 6 and contacted with the magnetostriction patch 3.
Preferably, the magnetic focusing structure 2 is made of electrical pure iron with a relative permeability of about 2000.
Preferably, the width of the magnetostrictive patch 3 is 0.5 times the SH0 mode guided wave wavelength corresponding to the center frequency.
Preferably, the width of the magnetostrictive patch 3 is 1.5 times the SH0 mode guided wave wavelength corresponding to the center frequency.
Preferably, the monitoring transducer further comprises a coupling agent 5;
The magnetostrictive patch 3 is adhered to the tested metal test piece 6 through a coupling agent 5, and the coupling agent 5 is used for transmitting vibration generated by the magnetostrictive patch 3 to the tested metal test piece 6.
Preferably, the coupling agent 5 is made of epoxy resin.
Preferably, the thickness of the permanent magnet 1 at the time of the optimal static magnetic field is determined by finite element simulation.
The transducer provided by the invention has the beneficial effects that the axial magnetizing alternating permanent magnet array with the magnetic circuit is used for providing the static bias magnetic field, and the zigzag coil is used for providing the alternating magnetic field, so that the transduction efficiency of the transducer can be improved, the coil and the magnetostriction patch can be completely separated, and the manufacturing and mounting difficulty of the transducer is effectively reduced.
Drawings
FIG. 1 is a schematic and exploded view of the present invention;
FIG. 2 is a schematic diagram of a meandering coil structure and winding pattern;
FIG. 3 is a graph of experimental results of inversion Wei Deman effect versus pre-magnetization mode;
FIG. 4 is a graph comparing simulation results with and without magnetic circuits;
FIG. 5 is a schematic diagram of a magnetic circuit device, wherein (a) is a rectangular magnetic circuit, (b) is a trapezoidal magnetic circuit, (c) is a rectangular magnetism collecting structure, and (d) is an isosceles triangle magnetism collecting structure;
FIG. 6 is a schematic diagram of the signal superposition relationship when the force load width is half of the SH0 mode guided wave wavelength;
FIG. 7 is a schematic diagram of a magnetic circuit structure;
Fig. 8 shows the influence of magnetic path parameters on the static magnetic field, wherein, (a) the influence of the length of the permanent magnet 1 on the horizontal component of the static magnetic field, (b) the influence of the width of the magnetic path on the horizontal component and the vertical component of the static magnetic field, (c) the influence of the width of the magnetism collecting structure on the horizontal component and the vertical component of the static magnetic field, (d) the influence of the thickness of the permanent magnet 1 on the horizontal component and the vertical component of the static magnetic field, and (e) the influence of the lift-off distance on the horizontal component and the vertical component of the static magnetic field;
Fig. 9 shows SH0 mode guided wave signals at 300kHz with and without magnetic circuits.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other.
The invention is further described below with reference to the drawings and specific examples, which are not intended to be limiting.
As shown in fig. 1, a broadband magnetostrictive SH0 mode guided wave monitoring transducer of the present embodiment includes a permanent magnet 1, a magnetostrictive patch 3, and a meandering coil 4;
The magnetostriction patch 3 is adhered to the outer surface of the tested metal test piece 6 along the circumferential direction of the tested metal test piece 6, the zigzag coils 4 are arranged on the surface of the magnetostriction patch 3, the permanent magnets 1 are uniformly distributed at equal intervals along the circumferential direction of the tested metal test piece 6, polarities of two adjacent permanent magnets 1 are opposite, a magnetizing direction is along the axial direction of the tested metal test piece 6, an axial static magnetic field is generated, the intervals of the adjacent permanent magnets 1 are equal to the intervals of adjacent wires of the zigzag coils 4, the center line of each permanent magnet 1 is aligned with the center line of the wire of the zigzag coil 4 under the same, alternating current is introduced into the zigzag coils 4 to provide a dynamic magnetic field, and in order to avoid mutual cancellation of torsional guided waves excited by the magnetostriction patch under the adjacent permanent magnets 1, current directions in the adjacent wires in the zigzag coils 4 are opposite at the same time. The winding mode of the zigzag coil is shown in fig. 2, the zigzag coil is tightly wound by single-turn or multi-turn wires side by side, and the magnetostrictive patch 3 is made of magnetostrictive materials with high saturation magnetostriction coefficient, such as nickel, iron-cobalt alloy, iron-gallium alloy and the like;
When the transducer of the embodiment works, SH0 mode guided waves propagating along the axial direction of the tested metal test piece 6 are excited and received. The permanent magnet 1 provides a static magnetic field along the axial direction of the tested metal test piece 6, an alternating current signal is fed into the zigzag coil 4 to generate a dynamic magnetic field, and the dynamic magnetic field and the static magnetic field generated by the permanent magnet 1 act together to enable the magnetostrictive patch 3 to generate SH0 mode guided waves with the same frequency as the alternating current signal, namely, the dynamic magnetic field direction is perpendicular to the SH0 mode guided wave propagation direction, and the static magnetic field direction is parallel to the SH0 mode guided wave propagation direction. According to the inversion Wei Deman effect, the magnetostrictive patch 3 generates SH0 mode guided waves and propagates axially along the pipe under the combined action of a static magnetic field parallel to the acoustic wave propagation direction and a dynamic magnetic field perpendicular to the acoustic wave propagation direction. Since the static magnetic fields generated by the adjacent permanent magnets 1 are opposite in direction, the directions of currents in the wires below the adjacent permanent magnets 1 are also opposite, so that the directions of vibrations generated in the magnetostrictive patches 3 at the same time are the same.
According to the embodiment, the alternating permanent magnet arrays with NS poles along the axial direction of the pipeline are adopted, the permanent magnet arrays are uniformly distributed along the circumferential direction of the pipeline, the magnetic poles of the adjacent permanent magnets 1 are opposite, the permanent magnet array structure can enable the zigzag coil 4 to be completely placed on the upper surface of the magnetostrictive patch 3, the structure is used for designing the magnetostrictive torsion guided wave transducer, the problem that the traditional transducer structure is used for enabling the zigzag coil to be clamped between the magnetostrictive patch 3 and the pipeline to influence the coupling effect is solved, the zigzag coil 4 and the magnetostrictive patch 3 can be completely separated, the difficulty of designing and installing the transducer is reduced, and the electrical part of the transducer is more easily packaged independently.
Compared with the existing magnetostrictive SH0 mode guided wave detection transducer based on Wei Deman effect, the magnetostrictive SH0 mode guided wave detection transducer based on the inversion Wei Deman effect in the embodiment has the advantages that the direction of the static magnetic field and the direction of the alternating magnetic field are interchanged, the horizontal static magnetic field along the axial direction of the pipeline is easier to obtain in the pipe fitting, and the design difficulty of the transducer is reduced.
The present embodiment employs a permanent magnet 1 to provide a static magnetic field. Compared with the existing magnetostriction SH0 mode guided wave detection transducer adopting the pre-magnetization mode, the problem that demagnetization occurs on the magnetostriction patch 3 along with the increase of time is solved, the magnetostriction sensor can be used for long-term monitoring, and the optimal static magnetic field can be provided by adjusting the parameters of the permanent magnet 1, so that the transduction efficiency can be effectively improved, and when the excitation conditions are the same, the amplitude of SH0 mode guided wave signals excited by the transducer is improved by more than 2 times compared with that of the pre-magnetization mode under the optimal static magnetic field as shown in fig. 3.
In the preferred embodiment, the monitoring transducer of the embodiment further comprises a magnetism collecting structure 2 with magnetic permeability, wherein the magnetism collecting structure 2 is arranged at two magnetic poles of each permanent magnet 1, a distance exists between the permanent magnet 1 and the magnetostriction patch 3, the two magnetic poles of the permanent magnet 1 are connected with the tested metal test piece 6 and the magnetostriction patch 3 through the magnetism collecting structure 2, and the permanent magnet 1, the magnetism collecting structure 2 and the magnetostriction patch 3 form a closed loop.
The permanent magnet 1 provides a static magnetic field along the axial direction of the tested metal test piece 6, the magnetic focusing structure 2 obviously enhances the static magnetic field along the axial direction of the pipeline, and the magnetic focusing structure 2 is adopted to optimize the static magnetic field. The static magnetic field size and consistency on the magnetostrictive patch 3 can be changed and optimized by adjusting the relevant parameters of the magnetic focusing structure 2. As shown in fig. 4, the addition of the magnetism collecting structure 2 can enhance the static magnetic field size on the magnetostrictive patch 3 as compared with the permanent magnet 1 alone. For a static magnetic field with a fixed required size, the permanent magnet 1 with smaller size or remanence is used, so that the same magnetic field size can be obtained, and the manufacturing cost of the transducer can be reduced. In order to obtain an accurate magnetic field magnitude, the dimensional parameters of the magnetic focusing structure 2 need to be determined by combining the permanent magnets 1 in a simulation or experimental manner.
In the preferred embodiment, the magnetism collecting structure 2 adopts a two-section structure connected, wherein one end of the first-section structure is adsorbed on the magnetic pole of the permanent magnet 1, the other end of the first-section structure is contacted with the outer surface of the tested metal test piece 6 and is connected with one end of the second-section structure, and the second-section structure extends towards the magnetostrictive patch 3 on the outer surface of the tested metal test piece 6 and is contacted with the magnetostrictive patch 3.
In order to make the transducer excited and receive the torsional guided wave with pure mode, the static magnetic field in the magnetostriction patch is required to be horizontal and the magnetic field is uniformly distributed, and the vertical component of the magnetic field is zero. In the embodiment, the magnetic circuit device is built, so that the magnetostriction patch, the permanent magnet 1 and the magnetic circuit device form a closed loop, the horizontal component of the static magnetic field in the magnetostriction patch is further enhanced, and the vertical component is reduced. The magnetic circuit device structure used in this embodiment is shown in fig. 4, and the magnetic circuit device material is electrical pure iron, wherein fig. b uses a trapezoidal magnetic circuit, and fig. c and d respectively add a rectangular magnetism collecting structure and an isosceles triangle magnetism collecting structure at the adjacent positions of the magnetic circuit device and the magnetostrictive patch edge. The rectangular magnetic circuit adjacent to the isosceles triangle magnetic focusing structure in the structure shown in the figure (d) is used for adjusting the distance between the edge of the magnetic circuit and the edge of the magnetostrictive patch so as to ensure that the magnetic circuit can be attached to the edges of the magnetostrictive patches with different sizes.
The two-dimensional finite element simulation is carried out on the magnetic circuit structure by using finite element simulation software, the size of the permanent magnet 1 is 30mm multiplied by 1mm, the residual magnetism is 1.2T, the width of the magnetic circuit is 1mm, the height is 16mm, the relative magnetic conductivity is 2000, the upper bottom edge of the trapezoid magnetic circuit is 1mm, the lower bottom edge of the trapezoid magnetic circuit is 3mm, the rectangular magnetism collecting structure is 2m in height, the right-angle side length of the isosceles triangle magnetism collecting structure is 2m, the size of the magnetostriction patch is 24mm multiplied by 0.1mm, the relative magnetic conductivity is calculated by a material BH curve, and the thickness of a tested piece is 2mm. The result shows that the isosceles triangle magnetic focusing structure can improve the horizontal magnetic field intensity and uniformity in the magnetostrictive strip, and can inhibit the vertical magnetic field intensity at the edge of the magnetostrictive patch. In the embodiment, the isosceles triangle magnetic focusing structure is characterized in that the cross section of the first section structure is rectangular, the cross section of the second section structure is isosceles right trapezoid, one right-angle side rectangular surface of the second section structure is connected with the other end of the first section structure, and the other right-angle side rectangular surface of the second section structure is contacted with the outer surface of the tested metal test piece 6 and contacted with the magnetostriction patch 3.
The static magnetic field is optimized by the magnetic focusing structure 2. Under the same condition of the permanent magnet 1, the magnetism collecting structure 2 can strengthen the static magnetic field in the magnetostriction patch 3, optimize the consistency of magnetic fields, reduce the requirements on the size and the remanence of the permanent magnet 1 when the magnetic field with fixed size is required, increase the magnetism collecting structure 2, increase the transduction efficiency and save the cost.
In a preferred embodiment, the monitoring transducer of the present embodiment further comprises a coupling agent 5;
the magnetostrictive patch 3 is adhered to the tested metal test piece 6 through a coupling agent 5, and the coupling agent 5 is used for transmitting vibration generated by the magnetostrictive patch 3 to the tested metal test piece 6. The coupling agent 5 of the present embodiment is made of epoxy resin, and bonds the magnetostrictive patch 3 to a metal test piece for transmitting vibration generated by the magnetostrictive patch 3 to the test piece.
When an ultrasonic guided wave detection technology is used for detecting industrial equipment, guided wave detection signals with multiple frequencies are generally collected for analysis. Therefore, it is of great importance to study the influence factors of the center frequency of the transducer. In the embodiment, magnetostrictive patches with widths of 4mm, 6mm, 8mm, 10mm and 12mm are used for torsional guided wave excitation in a frequency range of 200 kHz-600 kHz, wherein the excitation frequency stepping value is 20kHz. The amplitude of the received signal at different frequencies was recorded for each magnetostrictive patch, and the results showed that the peak of the plot of amplitude versus excitation frequency for each received signal corresponds to frequencies of about 380kHz, 300kHz, 220kHz, 430kHz and 400kHz, with corresponding wavelengths of about 8.2mm, 10.3mm, 14.1mm, 7.1mm and 7.8mm. As shown by the results of the magnetostrictive patches with the widths of 4mm, 6mm and 8mm, as the width of the magnetostrictive patch increases, the excitation frequency corresponding to the peak value of the received signal gradually decreases, and the width of the magnetostrictive patch is 0.5-0.6 times of the wavelength corresponding to the peak value frequency. When the widths of the magnetostrictive patches are 10mm and 12mm, the widths of the magnetostrictive patches are approximately equal to 1.5-1.6 times the corresponding wavelengths of the peak signals. For a uniform force source of finite width, the signal amplitude peaks when the force source width is theoretically equal to the sum of an integer multiple of the wavelength and a half wavelength. Therefore, the experimental result is basically consistent with the theory, and the transducer of the embodiment has a wider bandwidth, and the center frequency of the transducer can be selected by adjusting the width of the magnetostrictive patch. The transducer structure of the embodiment has a wider bandwidth, the wavelength corresponding to the center frequency is lambda, and the magnetostrictive patch width is about 0.5lambda or 1.5lambda. Thus, the transducer operating frequency range can be selected by adjusting the magnetostrictive patch width. The center frequency and bandwidth of the transducer can be changed by changing the width of the magnetostrictive patch 3. The winding coil 4 does not need to be manually replaced, and SH0 mode guided wave signals with larger amplitude can be excited in a wider frequency range only by changing current frequency, so that the method is suitable for remote control excitation and reception of the guided wave signals.
In a preferred embodiment, the width of the magnetostrictive patch 3 is 0.5 times the SH0 mode guided wave wavelength corresponding to the center frequency. According to the transducer disclosed by the application, the width of the surface force load of the test piece is approximately equal to that of the magnetostrictive patch 3, and through qualitative analysis, as shown in fig. 6, when the force load applied to the test piece is uniformly distributed, the particles distributed along the propagation direction of SH0 mode guided waves are completely counteracted by the particles with the interval of l/2 wavelength. I.e. when the width of the force load is smaller than l/2 wavelength, the total displacement increases with increasing width of the force load; when the width of the force load exceeds l/2 wavelength, the width of the force load is increased, displacement offset is generated, and the transduction efficiency is reduced. The width w of the magnetostrictive patch 3 is generally considered to be approximately equal to the width of the test piece force load, so the transducer proposed by the present application constitutes a bandpass filter with a center frequency c/(2 w), the center frequency and bandwidth of which can be varied by adjusting the width w of the meandering coil 4. Wherein c is the SH0 mode guided wave speed.
In a preferred embodiment, the thickness of the permanent magnet 1 at the optimal static magnetic field is determined by finite element simulation.
In the present embodiment, a permanent magnet 1 is used to provide a static magnetic field. The size of the static magnetic field is changed by adjusting the parameters of the permanent magnet 1, and finally the optimal static magnetic field is obtained. As shown in fig. 3, compared with the pre-magnetizing mode adopted at the present stage mentioned in the background, the transducer structure not only solves the problem of demagnetization and realizes long-term monitoring, but also obviously improves the transducer transduction efficiency. In order to obtain an optimal static magnetic field, it is first necessary to experimentally determine the optimal static magnetic field size required for the magnetostrictive patch 3. Then, according to the optimal static magnetic field size, the relevant parameters of the permanent magnet 1 are determined through a simulation or experiment mode, including, but not limited to, the number of the permanent magnet 1, the size of the permanent magnet 1, the lifting distance between the permanent magnet 1 and the magnetostrictive patch 3, and the like.
The invention provides a transducer structure, which is used for exciting and receiving SH0 mode guided waves of 300kHz in a carbon steel pipe with a nominal diameter of 100mm and a wall thickness of 3.5 mm.
First, the optimal static magnetic field size of the magnetostrictive patch 3 material is determined, and the amplitude of the SH0 mode guided wave signal received by the transducer under different static magnetic field sizes is measured through an experimental mode, as shown in fig. 3. From the measurement results, the transducer has the maximum transduction efficiency when the static magnetic field on the surface of the magnetostrictive patch 3 material is about 200 Gs.
Then, using comsol software, the relevant parameters of the permanent magnet 1 and the magnetic focusing structure 2 are determined by finite element simulation. The number and size of the permanent magnet 1, the lifting distance between the permanent magnet 1 and the zigzag coil 4, the size of the magnetism collecting structure 2, the shape of the tail end and the like all have influence on the size of the static magnetic field, and in order to simplify the design flow, the size of the static magnetic field is adjusted by adopting a mode of adjusting the thickness of the permanent magnet 1. Firstly, parameters of a magnetism gathering structure 2 are determined, the size of a fixed permanent magnet 1 is 30mm multiplied by 10mm multiplied by 5mm, the magnetizing direction is the minimum surface for magnetizing, and the magnetism gathering structure 2 is shown in figure 7. Wherein l is the length of the permanent magnet 1, h1 is the thickness of the permanent magnet 1, h2 is the lifting distance between the permanent magnet 1 and the magnetostriction patch 3, w1 is the width of the magnetism collecting structure 2, and w2 is the extension length of the magnetism collecting structure 2. The influence of the parameters of the magnetism collecting structure 2 on the static magnetic field is studied through finite element simulation, and the simulation result is shown in fig. 8, and the result shows that 1) the width w1 of the magnetism collecting structure 2, the width w2 of the magnetism collecting structure and the length l of the permanent magnet 1 have no influence on the static magnetic field in the magnetostrictive patch 3, the magnetic field intensity at the edge of the magnetostrictive patch 3 is obviously larger than that of a middle area, the length of the permanent magnet 1 and the length of the magnetostrictive patch 3 are increased, the length of a uniform static magnetic field distribution area can be increased, 2) the thickness h1 of the permanent magnet 1 is increased, the static magnetic field size in the magnetostrictive patch 3 can be effectively increased, but the vertical component of the static magnetic field is obviously increased, the lifting distance between the permanent magnet 1 and the magnetostrictive patch 3 is increased, the uniform distribution area of the horizontal magnetic field in the magnetostrictive patch 3 is increased, the vertical component of the static magnetic field is reduced, and the horizontal magnetic field size is obviously reduced. According to simulation results, the device with the magnetic focusing structure 2 is designed, the width w1 of the magnetic focusing structure 2 is 1mm, the width w2 of the magnetic focusing structure is 1mm, the length l of the permanent magnet 1 is 30mm, the thickness of the permanent magnet 1 is 8mm, and the distance between the permanent magnet 1 and the magnetostrictive strip is 7mm. On the basis, the thickness of the permanent magnet 1 is determined after fine adjustment in a simulation mode. The thickness of the permanent magnet 1 can also be determined directly by means of experimental tests. In the embodiment, the permanent magnet 1 with the thickness of 8mm is finally used, and the permanent magnet 1 is formed by stacking 8 NdFeB permanent magnets 1 with the brands of 30mm multiplied by 10mm multiplied by 1mm and N35. The number of the permanent magnets 1 is determined by the size of the pipeline and the size of the permanent magnets 1, the circumference of the outer surface of the pipeline is 108mm multiplied by 3.14 approximately 340mm, and the distance between the adjacent permanent magnets 1 is 10mm, so that 34 permanent magnets 1 are arranged along the circumferential direction of the pipeline in the embodiment.
Next, the magnetostrictive patch 3 size was calculated. The magnetostrictive patch 3 needs to be wound on the outer wall of the pipeline, so that the length of the magnetostrictive patch 3 is equal to the circumference of the outer surface of the pipeline, namely 108mm multiplied by 3.14 approximately equal to 340mm, the width of the magnetostrictive patch 3 is determined by the optimal working frequency of the transducer, the sound velocity of SH0 mode guided wave in the carbon steel pipeline used in the embodiment is about 3200m/s, the working frequency is 300kHz, the wavelength of SH0 mode guided wave is about 10mm according to the formula of wavelength=sound velocity/frequency, and the width of the magnetostrictive patch 3 is half the wavelength, namely 5mm. Thus, a 5mm 340mm 0.1mm magnetostrictive patch 3 was used, and the thickness of the magnetostrictive patch 3 was 0.1mm of the standard thickness of the strip material provided by the manufacturer.
Next, the meander coil 4 parameters are designed. And due to the adoption of a zigzag coil structure, the distance between adjacent wires in the zigzag coil is equal to the distance between the permanent magnets 1, so that the distance between the adjacent wires in the zigzag coil is 10mm, and the total length of the zigzag coil is about 340mm. The wire is composed of 10 turns of enameled wires with the width of 0.3mm which are closely distributed side by side along the same direction, and the number of turns of the enameled wires and the width of the wire in the wire have no definite design requirement, so long as the width of the wire enables the zigzag coil 4 to bear the current intensity when the transducer works. The meander coil 4 is fabricated using a flexible PCB process.
Finally, the transducer is installed and guided wave excitation/reception, and is of a self-receiving structure and can be used for exciting and receiving SH0 mode guided waves. As shown in fig. 1, epoxy resin is uniformly coated on one surface of the magnetostrictive patch 3, and the magnetostrictive patch 3 is adhered to the outer surface of the pipeline to form a complete annular structure. Then, a meandering coil is placed around the surface of the magnetostrictive patch 3. Finally, 34 permanent magnets 1 are placed above the zigzag coil 4 according to the transducer structure provided by the application, the magnetic poles of the adjacent permanent magnets 1 are opposite in direction, the central line of each permanent magnet 1 is aligned with the central line of a lead wire of the zigzag coil 4, the magnetism collecting structure 2 is adsorbed on two sides of the permanent magnets 1, the other side of the magnetism collecting structure 2 is contacted on a pipeline, and the tail end of the magnetism collecting structure 2 points to the magnetostriction patch 3. The RITEC RAM-5000SNAP ultrasonic transmitting and receiving device is used for exciting the transducer, so that SH0 mode guided waves are excited in the carbon steel pipeline. And under the condition of experimental comparison of the same array of the permanent magnets 1, the non-magnetic focusing structure 2 has no lifting distance and SH0 mode guided wave signals received after the structure of the non-magnetic focusing structure 2 is increased. As shown in FIG. 9, the amplitude of the SH0 mode-guided wave signal excited after the addition of the magneto-polymeric structure 2 is enhanced by about 2 times according to the design method proposed by the present application.
Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the different dependent claims and the features described herein may be combined in ways other than as described in the original claims. It is also to be understood that features described in connection with separate embodiments may be used in other described embodiments.
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