阅读说明：本技术 一种管道检测复合振子结构导波激励换能器 (Guided wave excitation transducer of pipeline detection composite vibrator structure ) 是由 姜银方 胡华健 童炳祥 郭永强 于 2019-09-12 设计创作，主要内容包括：本发明属于无损检测技术领域,尤其是一种管道检测复合振子结构导波激励换能器,针对现有技术中存在磁致伸缩换能器的输出振子幅值低,与管道任意表面的耦合程度较低,结构较大,且换能器磁致伸缩材料与管道长期接触容易造成线圈漏电以及在外力作用下容易断裂,降低换能器使用寿命的问题,现提出如下方案,其包括换能器,换能器包括连接器、外壳顶盖、外壳底座、振子元件、弹性基底、螺线管线圈、永磁铁、背衬单元,由于本发明振子元件与弹性基底组成的特殊复合结构,能实现换能器在管道任意表面检测,同时也避免了现有磁致伸缩换能器振子材料直接与管道接触造成换能器的损耗和失效,延长了使用寿命。(The invention belongs to the technical field of nondestructive detection, in particular to a guided wave excitation transducer of a composite vibrator structure for pipeline detection, which aims at solving the problems that the amplitude of an output vibrator of a magnetostrictive transducer is low, the coupling degree with any surface of a pipeline is low, the structure is large, the magnetostrictive material of the transducer is easy to cause coil leakage after being contacted with the pipeline for a long time and is easy to break under the action of external force, and the service life of the transducer is shortened in the prior art, and the following proposal is provided, wherein the transducer comprises a connector, a shell top cover, a shell base, a vibrator element, an elastic substrate, a solenoid coil, a permanent magnet and a backing unit, because of the special composite structure formed by the vibrator element and the elastic substrate, the transducer can be detected on any surface of the pipeline, and simultaneously, the loss and the failure of the transducer caused by the direct contact of the vibrator material of the magnetostrictive transducer with the pipeline are avoided, the service life is prolonged.)

1. The guided wave excitation transducer of the pipeline detection composite vibrator structure comprises a transducer and is characterized in that the transducer comprises a connector (1), a shell top cover (2), a shell base (3), a vibrator element (4), an elastic substrate (5), a solenoid coil (6), a permanent magnet (7) and a backing unit (8);

the vibrator element (4) and the elastic substrate (5) form a composite structure;

the oscillator element (4) is terbium dysprosium iron Terfeno1-D and is in a cuboid shape;

the elastic substrate (5) is beryllium bronze, is cuboid, 0.8mm in thickness and 10mm in length, is bonded and baked with the vibrator element (4) into a whole by adopting epoxy resin, and the bottom of the elastic substrate (5) is coupled with the surface of the pipeline;

the height dimension of the backing unit (8) is 1 mm-3 mm; the solenoid coil (6) is wound on the vibrator element (4) and is bonded and insulated by insulating paint, the diameter range of the solenoid coil (6) is 0.1-0.3 mm, and the number of wound layers is 50-200 turns;

the permanent magnets (7) are symmetrically arranged on two sides of the oscillator element (4), one end of each permanent magnet (7) is fixed on the end face of the oscillator element (4), and the other end of each permanent magnet is connected with the shell base (3).

2. The guided wave excitation transducer of the pipeline detection composite vibrator structure according to claim 1, characterized in that the length dimension of the vibrator element (4) is calculated and designed according to the detection frequency by the following formula, and the width and thickness dimension of the vibrator element (4) should be smaller than 1/4-1/8 of the length;

in formula 1) < CHEM >_TIs the length of the material, f₀Is the resonant frequency, E_TIs the elastic coefficient of the material, p_TIs the material density.

3. The guided wave excitation transducer of the pipeline detection composite oscillator structure according to claim 1, characterized in that the backing unit (8) is a high-attenuation and low-impedance backing layer, the formula is prepared by silicon carbide, tungsten powder, epoxy resin and polysulfide rubber according to the proportion of 6: 1: 3: 2, the length and width dimensions of the backing unit (8) are consistent with the dimensions of the oscillator element (4), and the thickness of the backing unit (8) is designed according to the attenuation formula 2);

in the formula 2), α represents a material energy attenuation rate of the backing unit (8), and d represents a thickness of the backing unit (8).

4. The guided wave excitation transducer with the pipeline detection composite vibrator structure as claimed in claim 1, wherein the solenoid coil (6) is formed by closely winding enameled copper wires on the backing unit (8) and the vibrator element (4), the duty ratio of the coil of the solenoid coil (3) is designed according to formula 3), the duty ratio of the coil is controlled within the range of 6.3% -25%, the leakage of the magnetic flux of the sensor is reduced, the uniformity of the magnetic field intensity and the magnetic field is increased, and the maximum strain is achieved,

in formula 3), S_TDenotes the cross-sectional area of the GMM material, S_CRepresenting the alternating coil cross-sectional area and gamma the coil duty ratio.

5. The guided wave excitation transducer of the pipeline detection composite vibrator structure as claimed in claim 1, wherein the permanent magnet (7) is made of N52-brand circular neodymium iron boron magnetized in the thickness direction, the diameter range is 5 mm-8 mm, and the number range is 2-8 pieces.

Technical Field

The invention relates to the technical field of nondestructive testing, in particular to a pipeline testing composite vibrator structure guided wave excitation transducer.

Background

Pipeline transportation is an important transportation mode, especially plays an irreplaceable role in the aspects of petroleum, chemical industry, natural gas, urban water supply and the like, but pipeline leakage caused by pipeline damage caused by abrasion, corrosion and accidental injury happens occasionally, great harm is brought to the property and safety of the nation and people, the environment is seriously polluted, and the ecology is influenced. In order to reduce or even avoid such hazards, industrial pipeline safety inspection is particularly important.

At present, the conventional methods for nondestructive testing of pipelines mainly comprise: ultrasonic, ray, magnetic powder, eddy and infiltration technologies, but all of them must detect point by point, and the detection speed is slow, and they cannot be applied to long-distance industrial pipeline detection. In order to solve the problems, the ultrasonic guided wave technology is developed, the ultrasonic guided wave technology overcomes the defects to a great extent, has the characteristics of small attenuation along a propagation path and long propagation distance, and the received signals carry the whole information of the pipeline from an excitation point to a receiving point, can detect the pipeline with long distance, liquid filling and a coating layer on line, has obvious advantages in the aspect of on-line detection of the long-distance industrial pipeline, and is a nondestructive detection technology which has a great research value and is worth popularizing.

There are several existing transmitting transducers, and the earliest magnetostrictive material was usually a transducer made of stacked nickel plate, which is inefficient and costly. Since the 60 s, piezoelectric transducers made of piezoelectric ceramic materials have been the most common transducers, and the efficiency of the piezoelectric transducers is greatly improved compared with transducers made of nickel sheets, so that the piezoelectric transducers can meet the engineering use requirements under general conditions. However, due to the limitation of the performance of the piezoelectric ceramic, the driving force is not high enough, the excitation energy is small, the energy conversion efficiency is low, and the signal-to-noise ratio is low. In the 70's of the 20 th century, the us a.e. clark discovered rare earth alloys with giant magnetostrictive effect, the maximum strain of which due to magnetostrictive effect is 6-20 times greater than that of piezoelectric ceramics used in conventional underwater acoustic transducers, the energy density is about 10-20 times that of piezoelectric ceramics, and the sound velocity is only 2/3-3/4 of piezoelectric ceramics. Therefore, under the condition of the same volume, the resonant frequency of the giant magnetostrictive electroacoustic transducer is 2/3-3/4 lower than that of the piezoelectric ceramic underwater acoustic transducer. Because the transducer made of the rare earth giant magnetostrictive material has the characteristics of large transmitting power, small volume and light weight, the transducer is sufficiently valued and applied to the aspects of developing low-frequency high-power underwater acoustic transducers and the like. In the 80 s, developed countries such as the United states have developed various rare earth transducers and are used in the military field. Flextensional rare earth transducers with acoustic power up to 151KW have been successfully developed for minesweeping in sweden.

Patent document CN2458091Y discloses a magnetostrictive ultrasonic transducer, in which a magnetostrictive material generates a vibrator under the action of a bias magnetic field and an excitation coil, and the vibrator is transmitted through an amplitude transformer. The transducer vibrator is generated by magnetostrictive materials, but the generated vibrator is indirectly transmitted through the amplitude transformer, so that the vibrator output of the amplitude transformer only accounts for one part of the magnetostrictive material vibrator, the energy loss of the transducer is large, and the efficiency is low.

Patent document CN105954362A discloses an ultrasonic wave generator for rapid detection, in which a magnetic circuit body is made of rare earth giant magnetostrictive material, and the upper end of the magnetic circuit body abuts against the end face of the lower end of a permanent magnet, and the upper end of the magnetic circuit body passes through the lower side edge of a window and abuts against the end face of a detected pipeline. The generator is only limited to the detection of the end face of the pipeline, and the detection on any surface of the pipeline cannot be realized, so that the application of the generator is greatly limited, and the generator cannot be used in the actual detection work.

Patent document CN1276272C discloses a rare earth giant magnetostrictive multifunctional logging acoustic wave emitting seismic source. The vibration source is a transducer driven by magnetostrictive material, and is provided with two semicircular rods as sound generating plates, a magnetostrictive element is clamped between the two semicircular rods, the two semicircular rods are combined together through screws, and the magnetostrictive element arranged in the middle along the radial direction of the rods is clamped to form a cylindrical structure. When a driving magnetic field is applied to the magnetostrictive element through the driving coil, the magnetostrictive material deforms, so that the semicircular bar sound-generating plate clamping the magnetostrictive element generates flexural deformation and emits sound waves. The generator has small output amplitude, and no wave absorbing material is designed to eliminate aftershock, and no matching layer is designed to enhance the sound intensity transmissivity of the transducer.

Disclosure of Invention

The invention aims to solve the defects that in the prior art, the amplitude of an output vibrator of a magnetostrictive transducer is low, the coupling degree with any surface of a pipeline is low, the structure is large, the magnetostrictive material of the transducer is easy to cause coil leakage due to long-term contact with the pipeline and is easy to break under the action of external force, and the service life of the transducer is shortened.

In order to achieve the purpose, the invention adopts the following technical scheme:

a pipeline detection composite oscillator structure guided wave excitation transducer comprises a transducer, wherein the transducer comprises a connector, a shell top cover, a shell base, an oscillator element, an elastic substrate, a solenoid coil, a permanent magnet and a backing unit;

the vibrator element is Tb-Dy-Fe Terfenol-D and is in a cuboid shape, a solenoid coil is wound outside the vibrator element, the elastic substrate and the vibrator element are bonded into a whole through epoxy resin glue to form an upper-lower composite structure type, the bottom surface of the elastic substrate is coupled with the surface of the pipeline, the vibrator element is used for transmitting, and the vibrator is stretched in the length direction; the transducer shell top cover is internally provided with a connector, two ends of the solenoid coil are connected with the connector, and the shell base is internally provided with a vibrator element, an elastic substrate, a back lining unit and a permanent magnet; the vibrator element and the back lining layer are bonded into a whole by epoxy resin glue; the solenoid coil is closely wound on the vibrator element and is bonded and insulated by insulating paint; the permanent magnets are symmetrically arranged at two ends of the vibrator element in the length direction, one ends of the permanent magnets are fixed on the end face of one end of the vibrator element, and the other ends of the permanent magnets are connected with the shell base; the transducer is internally provided with a closed magnetic loop formed by a solenoid coil, an elastic substrate, a shell base, a shell top cover, a permanent magnet and a vibrator element.

In the scheme, the vibrator element comprises an unbonded elastic base part used for winding a coil, the vibrator element is connected with the elastic base, the bottom surface of the elastic base is used for coupling and transmitting the vibrator with the surface of a pipeline, the vibrator element stretches and contracts in the length direction of the vibrator element and transmits the vibrator to the elastic base through connection and constraint, the width and thickness of the vibrator element are smaller than 1/4-1/8 of the length, the length of the vibrator element is calculated and designed according to the detection frequency by the following formula,

in formula 1) < CHEM >_TIs the length of the material, f₀Is the resonant frequency, E_TIs the elastic coefficient of the material, p_TIs the material density.

In the scheme, the elastic substrate is made of beryllium bronze, the thickness of the substrate is 0.8mm, and the length and the width of the substrate are the same as those of the vibrator element.

In the scheme, the backing unit is a high-attenuation and low-impedance backing layer, and the formula is prepared by silicon carbide, tungsten powder, epoxy resin and polysulfide rubber according to the proportion of 6: 1: 3: 2.

In the scheme, the length and width of the backing unit are consistent with the size of the oscillator element, the thickness of the backing unit is designed according to the following attenuation formula, and the height of the backing unit is 2 mm.

In formula 2), α represents a material energy decay rate of the backing unit, and d represents a thickness of the backing unit.

In the scheme, the permanent magnet is made of N52 round neodymium iron boron magnetized in the thickness direction, the diameter range is 5-8 mm, and the thickness range is 2-6 mm.

In the scheme, the solenoid coil is formed by densely winding enameled copper wires on the backing unit and the oscillator element (4), the diameter range of the solenoid coil is 0.1-0.3 mm, and the number of winding layers is 50-200 turns.

In the scheme, the duty ratio of the solenoid coil is designed according to the following formula, the duty ratio of the coil is controlled within the range of 6.3% -25%, the leakage of the magnetic flux of the transducer is reduced, the magnetic field intensity and the magnetic field uniformity are increased, and the maximum strain capacity is achieved,

in formula 3), S_TDenotes the cross-sectional area, S, of the magnetostrictive material_CRepresenting the alternating coil cross-sectional area and gamma the coil duty ratio.

In the scheme, the bottom of the top cover of the shell is provided with a rectangular boss, and the center of the rectangular boss is provided with a second circular through groove; the top of the shell base is provided with a rectangular through groove, and the rectangular through groove is provided with a first circular groove;

the rectangular lug boss is arranged in the rectangular through groove, the first circular through groove corresponds to the second circular through groove in position, the connector is arranged in the second circular through groove, and two ends of the solenoid coil are connected with the connector through the first circular through groove.

In the above scheme, the connector is an MCX connector.

Compared with the prior art, the invention has the beneficial effects that:

1. due to the special composite structure formed by the vibrator element and the elastic substrate, the transducer can be detected on any surface of the pipeline, the loss and the failure of the transducer caused by the direct contact of the vibrator material of the conventional magnetostrictive transducer and the pipeline are avoided, and the service life is prolonged.

2. Due to the special structure of the elastic substrate, the coupling degree and stability of the transducer and the surface of the pipeline are improved, the phenomenon that the existing knife-type magnetostrictive transducer oscillator structure is easy to topple due to asymmetry is avoided, and the coupling degree of the surface of the pipeline is reduced.

3. The transducer is internally provided with a backing unit which is a backing wave-absorbing material prepared according to a certain formula, can effectively absorb the vibrator in the thickness direction of a composite structure consisting of the vibrator element and the elastic substrate, and improves the signal-to-noise ratio of signals.

4. The magnetic loop is formed by a solenoid coil, a vibrator element, an elastic substrate, a shell base, a shell top cover, a permanent magnet and a vibrator element, and a closed magnetic loop is formed to prevent a magnetic field from leaking.

5. The connector adopts an MCX connector, which is beneficial to the reduction of the size of the probe, adopts a push-in type connection mode, so that the connection and the separation of the connector are very quick, and the installation time of the connector is shortened

Drawings

Fig. 1 is a front view of a transducer of the present invention.

Fig. 2 is a top view of a transducer of the present invention.

Fig. 3 is a three-view diagram of the composite vibrator structure of the transducer of the present invention.

Fig. 4 is a front view of the housing base of the transducer of the present invention.

FIG. 5 is a top view of the housing base of the transducer of the present invention.

FIG. 6 is a front view of a housing top cover of a transducer of the present invention.

Fig. 7 is a left side view of the top cover of the housing of the transducer of the present invention.

Fig. 8 is a schematic diagram of the excitation effect of the transducer of the present invention.

Fig. 9 is a diagram of the excitation effect of a transducer without a designed backing element.

Fig. 10 is a graph showing the relationship between the strain of terbium dysprosium iron and the magnetic field strength.

FIG. 11 is a phase velocity dispersion curve of a carbon steel pipe having a diameter of 108 mm.

Fig. 12 is a graph showing the experimental result of the relationship between the length dimension of the composite vibrator structure and the resonant frequency in the length direction.

FIG. 13 is a graph of experimental results of different materials of elastic substrates and echo voltage amplitudes.

Fig. 14 is a graph of experimental results of different arrangements of permanent magnets.

FIG. 15 is a graph showing the results of an experiment concerning the number of permanent magnets.

Fig. 16 is a graph of experimental results of solenoid coil parameters.

Fig. 17 is a graph of experimental results of duty ratio versus relative sensitivity.

Fig. 18 is a demagnetization curve of a conventional permanent magnetic material.

FIG. 19A is a graph of the results of an experiment in which the height of the backing was 3 mm.

FIG. 19B is a graph of the results of an experiment in which the height of the backing was 2 mm.

FIG. 19C is a graph of the results of an experiment in which the backing height was 1 mm.

Fig. 19D is a graph of the results of the experiment without the backing.

In the figure: the transducer comprises a connector 1, a housing top cover 2, a housing base 3, a vibrator element 4, an elastic substrate 5, a solenoid coil 6, a permanent magnet 7, a backing unit 8, a rectangular through groove 9, a first circular through groove 10, a groove 11, a second circular through groove 12, a rectangular boss 13 and an elastic substrate lower surface 14.

Detailed Description

The invention designs a guided wave excitation transducer of a pipeline detection composite vibrator structure, and the transducer can be coupled with any surface of a pipeline due to a special composite structure consisting of a vibrator element and an elastic substrate, so that the magnetostrictive element is protected while detection is realized; because the back lining unit with high attenuation and low impedance is designed in the transducer and is used for absorbing the residual shock of the Tb-Dy-Fe and the unnecessary micro-vibrator perpendicular to the pipeline direction brought by the composite structure, the signal-to-noise ratio of the detection signal is improved; a closed magnetic loop is formed in the transducer, so that the leakage of a magnetic field is prevented, and the electromechanical conversion efficiency is improved; the MCX connector is adopted as the transducer connector, so that the size reduction is facilitated, and the miniaturization of the transducer and the use of the annular array are facilitated.

The invention will be further explained with reference to the drawings

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments.

Referring to fig. 1, 2, 3, 4, 5, 6 and 7, the invention relates to an embodiment of a guided wave excitation transducer with a composite vibrator structure for pipeline inspection, the transducer includes a vibrator element 4, a backing unit 8 bonded with the upper surface of the vibrator element 4 by epoxy resin glue, a U-shaped elastic substrate 5 bonded with the lower surface of the vibrator element 4 by epoxy resin glue, a solenoid coil 6 tightly wound on the outer surfaces of the backing unit 8 and the vibrator element 4, neodymium iron boron permanent magnets 7 mounted at the two ends of the vibrator element 4, a housing base 3 with a rectangular through groove 9 at the top, a groove 11 at the bottom and a first circular through groove 10 at the top, a housing top cover 2 with a rectangular boss 13 and a second circular through groove 12, and an MCX connector 1 mounted in the circular through groove 12 of the housing top cover 2.

The upper surface of the vibrator element 4 is bonded with the backing unit 8 by epoxy resin glue, the solenoid coil 6 is wound on the outer surface of the vibrator element 4 to provide a driving magnetic field, and insulating paint is coated on the coil to prevent the coil from loosening and achieve the purpose of insulation; the lower bottom surface of a U-shaped elastic substrate 5 which is bonded by epoxy resin glue on the lower surface of the vibrator element 4 is coupled with the surface of the pipeline, and the vibrator is stretched in the length direction of the pipeline; the MCX connector 1 is arranged in the top cover 2 of the transducer shell and used for transmitting detection signals, and the vibrator element 4, the elastic substrate 5, the backing unit 8 and the permanent magnet 7 are arranged in the groove 11 of the shell base 3; one end of a permanent magnet 7 is fixed on the end face of the oscillator element 4, the other end of the permanent magnet 7 is attracted with the shell base 3 made of ferromagnetic materials by virtue of attraction, the permanent magnet 7 provides a bias magnetic field to eliminate the frequency doubling effect, a closed magnetic loop is arranged in the transducer, and the magnetic loop is formed by the solenoid coil 6, the oscillator element 4, the elastic substrate 5, the shell base 3, the shell top cover 2, the permanent magnet 7 and the oscillator element 4 to prevent the leakage of the magnetic field.

The oscillator element 4 of the transducer is terbium dysprosium iron (Terfenol-D), which is an alloy compound of rare earth elements terbium (Tb), dysprosium (Dy) and iron (Fe), and the shape of the oscillator element is a rectangular structure; the oscillator element 4 is bonded with the backing unit 8 by adopting Kasutte epoxy resin; the lower surface of the vibrator element 4 is bonded with the elastic substrate 5 by epoxy resin glue to form a composite vibrator structure; as shown in fig. 3: the vibrator element 4 generates a vibrator and transmits the vibrator to the elastic substrate 5 under the combined action of a driving magnetic field and a bias magnetic field, the vibrator element 4 and the elastic substrate lower surface 14 expand and contract along the length direction to generate a guided wave for detection through the coupling of the elastic substrate lower surface 14 and the pipeline surface, the vibrator element 4 and the elastic substrate lower surface 14 expand and contract along the length direction, the vibrator element 4 along the length direction needs the vibrator with the width and thickness dimension smaller than 1/4-1/8 of the length, the length dimension is calculated according to the resonance frequency, the resonance frequency is approximately equal to the central frequency of the guided wave detection, the central frequency range of the guided wave detection is determined by a frequency dispersion curve, when the detected pipeline is a carbon pipeline with the inner diameter of 98mm and the outer diameter of 108mm, a phase velocity frequency dispersion diagram within the frequency range of 0-150 kHz is shown in figure 11, and for an L (0, 2) mode (17), the phase velocity is basically consistent within the frequency range of 50-, this means that the dispersion is small, that is, the temporal length variation of the wave packet is small in the actual image, and the number of modes appearing in this frequency range is relatively small, so we set our working range to be about 50KHZ to 160KHZ, the length dimension of the transducer element 4 is calculated and designed according to the detection frequency by the following formula,

in formula 1) < CHEM >_TIs the length of the material, f₀Is the resonant frequency, E_TIs the elastic coefficient of the material, p_TIs the material density.

Taking Tb-Dy-Fe and having an elastic coefficient of 3.5X 10¹⁰N/m²Density 9250kg/m³The frequency is in the range of 30 KHZ-120 KHZ, and the size range is 6.1-20 mm. Considering that the calculated length of the oscillator is too short at high frequency to cause insufficient excitation energy, and because the subsequent components such as the elastic substrate 5 and the coil cause the increase of the center frequency, and the detection frequency is too high to increase the dispersion of the guided wave and shorten the detection distance, the design should be performed by setting a lower resonance frequency when calculating the size of the tb-dy-iron element, so that 50kHz is selected to calculate the length of the tb-dy-iron element, and (1) is substituted to obtain the length of the tb-dy-iron element of 20 mm. When the square magnetostrictive element performs element by axial expansion, according to the quarter-wavelength theory, the width and height of the square magnetostrictive element should be less than a quarter of the length value, so the length, width and height of the terbium dysprosium iron element of the giant magnetostrictive transducer herein are set to be 20mm 4mm 1 mm.

The elastic substrate 5 of the transducer is of a cuboid structure, the length and the width of the lower surface 14 of the elastic substrate are the same as those of the vibrator unit 4, and the thickness of the substrate wall is 0.8 mm. The method is characterized in that experimental research is carried out on transducers made of vibrators with different material substrates, and the influence of elastic substrate materials on the excitation performance of the transducers is analyzed. As shown in fig. 13, the guided wave transducer manufactured by using the beryllium bronze material as the substrate has the largest echo coefficient of the weld joint under the condition of the same alternating magnetic field, bias magnetic field and excitation voltage.

The backing unit 8 is made of high-attenuation and low-impedance materials, the formula is prepared by silicon carbide, tungsten powder, epoxy resin and polysulfide rubber according to the proportion of 6: 1: 3: 2, the epoxy resin glue is used for bonding the back surface of the oscillator element 4, the oscillator generated by the oscillator element 4 can radiate towards the back surface, so that the backing unit 8 is designed for absorbing the energy radiated towards the back surface by the oscillator element 4, the oscillator element 4 can stop the oscillator as soon as possible, the axial resolution of the transducer is improved, the energy is small because the detection adopts ultrasonic guided waves and has low frequency, the energy is greatly influenced by the backing layer with high impedance on the energy transmitted into a detection medium, the excitation effect of the transducer with the backing unit 8 with low impedance and high attenuation is adopted, as shown in figure 8, figure 9 is a transducer excitation effect graph without the backing unit, and as shown in figure 8, the noise wave is small, the echoes of the three welding seams and the end faces are clearly visible, while the clutter is larger in the figure 9 except the three welding seams and the end faces, the identification of the welding seams is influenced, the backing unit 8 plays a great role in improving the signal-to-noise ratio of the excitation signal, the sensitivity of defect identification is improved, the length and the width of the backing unit 8 are consistent with the size of the oscillator element 4, the height is selected through the thickness according to the attenuation formula,

in formula 2, α represents the material energy decay rate of the backing layer;

according to the measurement, if the attenuation coefficient alpha of the backing layer is 3.2-6.5, the height of the backing layer unit is 1 mm-3 mm, and the signal to noise ratio of the tested echo signal is adjusted, wherein fig. 19A shows that the backing layer height is 3mm, fig. 19B shows that the backing layer height is 2mm, fig. 19C shows that the backing layer height is 1mm, fig. 19D shows that no backing layer exists, the backing layer height is 1mm through the test, at this time, the signal to noise ratio is higher, and the defect identification rate is better.

Fig. 5 and fig. 6 are a front view and a top view of the transducer housing top cover 2, the housing top cover 2 is made of a metal material with high magnetic permeability, as shown in fig. 5 and fig. 6, a rectangular boss 13 is arranged at the bottom of the housing top cover 2 and is used for matching with the housing base 3, a second circular through groove 12 is formed in the center of the rectangular boss 13 and is used for installing the connector 1, the connector 1 is bonded around the second circular through groove 12 in the top cover 2 by epoxy resin glue to prevent loosening, one end of the solenoid coil 6 is welded with a central pin of the connector 1 to be used as an anode, the other end of the solenoid coil 6 is welded with another pin of the connector 1 to be used as a cathode, and a male lead-out electrode of the connector 1 is used for inputting signals.

Transducer housing base 3 is as shown in fig. 4 and fig. 5, adopt the metal material of high magnetic conductivity to make, it has horizontal recess 11 to be used for installing backing unit 8 to open the bottom, oscillator element 4 and elastic substrate 5, and it is fixed with the epoxy glue, open at housing base 3's top center has rectangle through groove 9, it has first circular through groove 10 to open on the rectangle through groove 9, a cooperation for housing top cap 2's rectangle boss 13, realize housing top cap 2 and housing base 3's assembly, and the lower surface at housing top cap 2 and the upper surface of housing base 3 are scribbled with the epoxy glue, realize fixing.

FIG. 18 is a demagnetization curve of a conventional permanent magnet material, in which ferrite I, AlNiCo II, and rare earth III are used, and the AlNiCo permanent magnet material has a large Br but a small Hc; the ferrite permanent magnet material is larger than the Hc of the aluminum-nickel material, the Br and Hc of the neodymium-iron-boron permanent magnet material are both larger, the demagnetization curve is basically a straight line, the magnetic energy products corresponding to different points on the demagnetization curve of the permanent magnet are different, the maximum value is called the maximum magnetic energy product and is marked as (BH) max, for the permanent magnet material, the larger the magnetic energy is generally required to be, the better the magnetic energy is, the bias magnetic field of the permanent magnet 7 adopts a circular neodymium-iron-boron permanent magnet which is magnetized in the thickness direction and is of the brand number N52, for the permanent magnet material, the magnetic energy product is generally required to be larger and is an important performance index of the permanent magnet material, the arrangement mode of the permanent magnet 7 is determined by a test mode, as shown in FIG. 14, when the permanent magnet is symmetrically arranged and asymmetrically, the defect echo amplitude is firstly increased and then reduced, and the echo amplitude is; the defect echo amplitude of the permanent magnets in symmetrical arrangement is obviously larger than that of asymmetrical arrangement, which shows that when the permanent magnets in the same number are in symmetrical arrangement, the leakage of magnetic flux is reduced, the magnetic field strength in the composite vibrator area is larger and the uniformity is better, the number of the permanent magnets is determined in a test mode, as shown in fig. 15, the defect echo amplitude is gradually increased along with the increase of the number of the permanent magnets, mainly because the number of the permanent magnets is increased, the provided bias magnetic field strength is increased, the strain of the composite vibrator is increased, but the increase speed of the echo amplitude is gradually reduced; as shown in the strain relationship of the magnetic field intensity diagram of the material in FIG. 10, when the number of the permanent magnets is 2-8, the magnetic field intensity is about 400-1200 e, and is in a linear change region, in order to make the excitation and the reception of the transducer in the optimal condition, the number of the permanent magnets is 6, and 3 pieces are respectively arranged at two ends.

The solenoid coil 6 is formed by closely winding enamelled copper wires on a backing unit 8 and a vibrator element 4, the enamelled copper wires are insulated by insulating paint and bonded by epoxy resin adhesive, the diameter range of the solenoid coil 6 is 0.1-0.3 mm, the number of wound layers is 2-5, a magnetic field in the length direction is provided for terbium dysprosium iron, one end of the solenoid coil 6 is welded with a central pin of a connector 1 to be used as a positive pole, the other end of the solenoid coil 6 is welded with the other pin of the connector to be used as a negative pole, the magnetic field generated by the solenoid coil 6 is calculated and designed by the following formula, as shown in fig. 10, a relation graph of the magnetic field strength and the terbium dysprosium iron is shown in a graph of the relation of the magnetic field strength and the terbium dysprosium iron strain, when the magnetic field is designed, the magnetic field strength is controlled to be as much as possible within a range of 400-12000 e of a curve,

estimating the thickness of the coil:

R₂-R₁＝N·d/L 4)

in formulae 3) and 4)H is the magnetic field strength, L is the coil length, d is the diameter of the coil, R₁Is the inner radius of the coil, R₂The outer radius of the coil, N the number of coil layers and I the effective value of the exciting current.

In the embodiment, because a voltage source function generator is adopted, parameters of the solenoid are determined by comparing the echo coefficients of the welding seams by adopting an experimental method, as shown in fig. 8, the experiment adopts enamelled copper wires with the diameters of 0.1mm, 0.15mm, 0.2mm, 0.25mm and 0.3mm and the number of layers of 2-5, and as can be seen in fig. 16, the echo coefficient is the highest when the diameter is 0.15mm and the number of turns is 150.

A magnetic circuit of the transducer is a closed magnetic loop formed by the solenoid coil 6, the vibrator element 4, the elastic substrate 5, the shell base 6, the shell top cover 2, the permanent magnet 7 and the vibrator element 4, and leakage of a magnetic field is prevented.

The duty ratio of the solenoid coil and the magnetic field intensity on the center line of the alternating coil are related to the inner diameter and the outer diameter of the coil, the magnetic flux change around the coil can generate induced electromotive force, the design of the duty ratio of the solenoid coil is designed according to the following formula, the duty ratio of the coil is controlled within the range of 6.3% -16%, the leakage of the magnetic flux of the transducer is reduced, the magnetic field intensity and the magnetic field uniformity are increased, and the maximum dependent variable is achieved,

in formula 5), S_TDenotes the cross-sectional area, S, of the magnetostrictive material_CThe cross section area of an alternating coil is shown, gamma represents the duty ratio of the coil, the parameter of the duty ratio of the coil determines the parameter of the solenoid through an experimental method, and as can be seen from the following graph 17, the change trends of the echo coefficients of different duty ratios are basically consistent, the change trends are firstly increased and then reduced, the change trend is highest around the central frequency of 120kHz, secondly, the defect echo coefficient is higher when the duty ratio is larger, the experimental effect of the selected 16% duty ratio is the best, 11% and 8% and 6.3% are poor, the defect echo signal is basically difficult to identify, and the defect echo signal is basically lost when the duty ratio is smaller than 8%The detection capability, generally speaking, should be as large as possible, since the duty ratio is 16%.

When the transducer works, the length direction of the transducer is parallel to the axial direction of a pipeline and is placed on the surface of the pipeline to excite the guided wave in an L (0, 2) mode to detect, an MCX connector male head is inserted into an MCX connector female head, a lead is led out, the led-out lead is connected with a function generator, at the moment, a 10-period sine signal modulated by a Hanning window can be input, an alternating magnetic field is generated in a solenoid coil 6, a vibrator element 4 generates a periodic vibrator and transmits the periodic vibrator to an elastic substrate 5 under the combined action of a bias magnetic field provided by a permanent magnet 7 and the alternating magnetic field provided by the solenoid coil 6, the vibrator generates guided wave in the pipeline through the coupling of the elastic substrate 5 and the surface of the pipeline to be detected, the guided wave is reflected back to the receiving transducer after reaching the end surface of the pipeline to be detected, and the defects can generate reflection due to different acoustic impedances in the guided wave propagation process, the invention has the advantages of high electromechanical conversion efficiency, large guided wave excitation amplitude, high signal-to-noise ratio, short response time, high coupling degree with a pipeline, long service life and the like.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.