Piezoelectric transducer and method for directionally exciting and receiving non-dispersion torsional guided waves

Abstract

The invention provides a piezoelectric transducer and method for directionally exciting and receiving non-dispersion torsional guided waves, and relates to the technical field of ultrasonic nondestructive testing, the piezoelectric transducer comprises a first circumferential array, and the first circumferential array is composed of a plurality of first piezoelectric units and a plurality of first time delay units; and the second circumferential array is composed of a plurality of second piezoelectric units and a plurality of second time delay units. The piezoelectric transducer capable of directionally exciting and receiving the non-dispersion torsional guided wave is constructed through the thickness shearing type piezoelectric unit and the height difference time delay unit, no matter unidirectional excitation or unidirectional receiving is needed, an additional circuit or equipment is not needed to provide time delay, and the complexity and cost of the whole structure are reduced. In addition, the time delay unit is adopted to replace a piezoelectric unit to be in curved surface combination with the pipeline, the problem that the piezoelectric unit is not matched with the detected pipeline due to too small flexibility can be avoided, then the fitting degree is improved, signal transmission is guaranteed, and detection is more efficient and accurate.

Description

Technical Field

[0001] The present invention relates to the technical field of pipeline nondestructive testing, and in particular to a piezoelectric transducer and method for directional excitation and reception of non-dispersive torsional guided waves. Background Art

[0002] Pipeline structures are widely used in petrochemical, nuclear power and other industrial fields due to their excellent medium transmission characteristics. However, during long-term service, pipelines are affected by factors such as transmission medium corrosion and environmental loads, and are prone to structural deformation, wall thickness reduction, crack expansion and other defects, which may cause medium leakage, environmental pollution and even major safety accidents. Ultrasonic guided wave detection technology has shown significant advantages in pipeline detection due to its unique propagation characteristics.

[0003] However, the waveguide transducers used in existing commercial detection systems are all bidirectional transducers, that is, they emit ultrasonic guided waves to both ends of the pipeline at the same time, which limits the defect location capability and can only determine the axial distance of the defect but cannot identify its specific position relative to the transducer. Although the above problems can be solved by configuring two sets of detection equipment, this method significantly increases the operation complexity and detection cost. Therefore, the development of a new excitation device that can realize directional excitation and reception of axial guided waves has important engineering application value for improving the accuracy of pipeline defect detection and reducing detection costs. Summary of the invention

[0004] The purpose of the present invention is to provide a piezoelectric transducer and method for directional excitation and reception of non-dispersive torsional guided waves to improve the above problems. In order to achieve the above purpose, the technical solution adopted by the present invention is as follows: In a first aspect, the present application provides a piezoelectric transducer for directional excitation and reception of non-dispersive torsional guided waves, comprising: A first circumferential array, wherein the first circumferential array is composed of a plurality of first piezoelectric units and a plurality of first time delay units, wherein the first time delay unit is a block structure, wherein the upper surface thereof is a rectangular cross section, and the lower surface thereof is an arc-shaped cross section, wherein the first piezoelectric unit is a cuboid, wherein the first piezoelectric unit is fixed above the first time delay unit, wherein the lower surface of the first piezoelectric unit has the same size as the upper surface of the first time delay unit, and wherein the first piezoelectric unit and the first time delay unit are uniformly distributed as a whole along the circumferential direction; The second circumferential array is composed of a plurality of second piezoelectric units and a plurality of second time delay units, the second time delay unit is a block structure, the upper surface of which is a rectangular cross-section, and the lower surface is an arc-shaped cross-section, the second piezoelectric unit is a cuboid, the second piezoelectric unit is fixed above the second time delay unit, the lower surface of the second piezoelectric unit is the same size as the upper surface of the second time delay unit, the second piezoelectric unit and the second time delay unit are uniformly distributed along the circumferential direction as a whole, and the height of the second time delay unit is greater than the height of the first time delay unit.

[0005] The piezoelectric transducer includes an annular base layer, the first circumferential array and the second circumferential array are fixed on the outer surface of the annular base layer, the arc cross-section of the first time delay unit in the first circumferential array is consistent with the curvature of the annular base layer, and the arc cross-section of the second time delay unit in the second circumferential array is consistent with the curvature of the annular base layer.

[0006] The number of the first circumferential arrays is 2, and the two first circumferential arrays are symmetrically distributed on both sides with the second circumferential array as the center.

[0007] The first piezoelectric unit has a length, width and height of The polarization direction of the first piezoelectric unit is along the length direction, the electrodes of the first piezoelectric unit are two opposite surfaces parallel to the polarization direction , the first piezoelectric unit is Shear deformation occurs in the plane, and the second piezoelectric unit is the same as the first piezoelectric unit.

[0008] The polarization directions of all the first piezoelectric units in the first circumferential array are the same, the polarization directions of all the second piezoelectric units in the second circumferential array are the same, and the polarization directions of all the first piezoelectric units in the first circumferential array are opposite to the polarization directions of all the second piezoelectric units in the second circumferential array.

[0009] The upper surfaces of the first piezoelectric unit and the second piezoelectric unit are connected to the positive electrode of the signal source through a wire, and the lower surfaces of the first piezoelectric unit and the second piezoelectric unit are connected to the negative electrode of the signal source through a wire.

[0010] The axial length of the annular base layer is the sum of the central axial distance between the first circumferential array and the second circumferential array and the width of the first piezoelectric unit.

[0011] In a second aspect, the present application also provides a piezoelectric transducer method for directional excitation and reception of non-dispersive torsional guided waves, comprising: The piezoelectric transducer is arranged on the surface of the pipeline to be inspected through a coupling agent, wherein the piezoelectric transducer comprises an annular base layer, a plurality of first circumferential arrays and a second circumferential array; Determine a target circumferential array and a receiving circumferential array from a plurality of first circumferential arrays, connect the positive electrode of the first piezoelectric unit in the target circumferential array and the positive electrode of the second piezoelectric unit in the second circumferential array to the positive electrode of the power amplifier and the positive electrode of the signal source in sequence through a wire, and connect the negative electrode of the first piezoelectric unit in the target circumferential array and the negative electrode of the second piezoelectric unit in the second circumferential array to the negative electrode of the power amplifier and the negative electrode of the signal source in sequence through a wire; The target circumferential array of the signal source and the second circumferential array receive the pulse signal and induce the zero-order torsional guided wave to be transmitted in the pipeline to be detected; The zero-order torsional guided wave is reflected after encountering a structural change in the pipeline to be detected, and the receiving circumferential array receives the reflected echo signal and converts it into an electrical signal; The electrical signal is input into a data acquisition system for time domain and frequency domain analysis to determine the specific location of the surface defect of the pipeline to be detected.

[0012] The beneficial effects of the present invention are: The present invention constructs a piezoelectric transducer capable of directionally exciting and receiving non-dispersive torsional guided waves through a thickness shear type piezoelectric unit and a time delay unit with a height difference. No external circuit or device is required to provide time delay for either unidirectional excitation or unidirectional reception, thereby reducing the complexity and cost of the overall structure. In addition, the use of a time delay unit instead of a piezoelectric unit in this application to combine the pipe with a curved surface can avoid the problem of the piezoelectric unit not being compatible with the detection pipe due to its low flexibility, thereby improving the fit, ensuring signal transmission, and making the detection more efficient and accurate.

[0013] Other features and advantages of the present invention will be set forth in the following description, and in part will become apparent from the description, or may be understood by practicing embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0015] Figure 1 A schematic diagram of the structure of a piezoelectric transducer in an embodiment of the present invention; Figure 2 is a front view of a piezoelectric transducer in an embodiment of the present invention; Figure 3 A schematic diagram of a method for using a piezoelectric transducer according to an embodiment of the present invention; Figure 4 This is a schematic diagram of a test of using a piezoelectric transducer to detect axially symmetrical defects in a pipeline to be inspected in an embodiment of the present invention; Figure 5 This is a schematic diagram of receiving signals of a signal receiving device placed in the direction of defect 1 when array A and array B are excited simultaneously in an embodiment of the present invention; Figure 6 This is a schematic diagram of a signal received by a signal receiving device placed in the direction of defect 2 when array A and array B are excited simultaneously in an embodiment of the present invention; Figure 7 It is a schematic diagram of receiving signals of a signal receiving device placed in the direction of defect 2 when array B and array C are excited simultaneously in an embodiment of the present invention; Figure 8 This is a schematic diagram of receiving signals of a signal receiving device placed in the direction of defect 1 when array B and array C are excited simultaneously in an embodiment of the present invention; Fig. 9 Schematic diagram of the received signal of array C when array A and array B are excited simultaneously in an embodiment of the present invention; Fig.10 This is a schematic diagram of the received signal of array A when array B and array C are excited simultaneously in an embodiment of the present invention; Fig.11 This is a result diagram of the piezoelectric transducer detecting defect 1 in the embodiment of the present invention; Fig.12 In the embodiment of the present invention Fig.11 Schematic diagram of axial position comparison in the result diagram; Fig.13 In the embodiment of the present invention Fig.11 Schematic diagram of angle comparison in the result graph; Fig.14 This is a result diagram of the piezoelectric transducer detecting defect 2 in the embodiment of the present invention; Fig.15 In the embodiment of the present invention Fig.14 Schematic diagram of axial position comparison in the result diagram; Fig.16 In the embodiment of the present invention Fig.14 Schematic diagram of angle comparison in the result graph; Fig.17 It is a curve diagram of the group velocity dispersion of the bending and torsion guided waves of the pipeline to be tested in an embodiment of the present invention; Fig.18 Graph showing the phase velocity dispersion of the time delay unit in an embodiment of the present invention.

[0016] Markings in the figure: 1, first piezoelectric unit; 2, first time delay unit; 3, second time delay unit; 4, second piezoelectric unit; 5, annular base layer. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0018] It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings. At the same time, in the description of the present invention, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0019] Embodiment 1: This embodiment provides a piezoelectric transducer for directional excitation and reception of non-dispersive torsional guided waves, including: The first circumferential array is composed of a plurality of first piezoelectric units 1 and a plurality of first time delay units 2. The first time delay unit 2 is a block structure, the upper surface of which is a rectangular cross-section, and the lower surface is an arc-shaped cross-section. The first piezoelectric unit 1 is a cuboid. The first piezoelectric unit 1 is fixed above the first time delay unit 2. The lower surface of the first piezoelectric unit 1 has the same size as the upper surface of the first time delay unit 2. The first piezoelectric unit 1 and the first time delay unit 2 are uniformly distributed as a whole along the circumferential direction; The second circumferential array is composed of a plurality of second piezoelectric units 4 and a plurality of second time delay units 3. The second time delay unit 3 is a block structure with a rectangular cross section on the upper surface and an arc cross section on the lower surface. The second piezoelectric unit 4 is a rectangular parallelepiped. The second piezoelectric unit 4 is fixed above the second time delay unit 3. The lower surface of the second piezoelectric unit 4 has the same size as the upper surface of the second time delay unit 3. The second piezoelectric unit 4 and the second time delay unit 3 are uniformly distributed as a whole along the circumferential direction. The height of the second time delay unit 3 is greater than the height of the first time delay unit 2.

[0020] For the convenience of description, the first piezoelectric unit 1 and the second piezoelectric unit 4 are collectively referred to as piezoelectric units, and the first delay unit 2 and the second delay unit 3 are collectively referred to as delay units for description.

[0021] In the embodiment of the present application, the piezoelectric units are all thickness shear type piezoelectric units, such as Figure 1 As shown, the arrow on the piezoelectric unit in the figure indicates the polarization direction of the piezoelectric unit. The length, width and height of the piezoelectric unit are , the length and width of the upper surface of the first delay unit 2 are , the distance from the center point of the upper surface to the center point of the lower surface of the first delay unit 2 is The length and width of the upper surface of the second delay unit 3 are , the distance from the center point of the upper surface to the center point of the lower surface of the second delay unit 3 is .

[0022] The material of the piezoelectric unit in the present invention can be piezoelectric ceramics or piezoelectric single crystals, etc., and can also be other piezoelectric materials that can produce corresponding deformation modes, which are not particularly limited here. The delay unit works in conjunction with the piezoelectric unit, and the height difference between the first delay unit 2 and the second delay unit 3 is controlled to make the piezoelectric unit generate a wave with a specific phase difference, thereby realizing the excitation and reception control of the zero-order torsional waveguide and improving the detection resolution and accuracy.

[0023] The piezoelectric transducer includes an annular base layer 5, and the first circumferential array and the second circumferential array are fixed on the outer surface of the annular base layer 5. The arc section of the first time delay unit 2 in the first circumferential array is consistent with the curvature of the annular base layer 5, and the arc section of the second time delay unit 3 in the second circumferential array is consistent with the curvature of the annular base layer 5. The shape of the annular base layer 5 is a hollow cylinder, and its inner diameter is the same as the outer diameter of the pipeline to be detected, so as to ensure that it can fit perfectly with the pipeline surface. The first circumferential array and the second circumferential array are fixed on the outer surface of the annular base layer 5, and the arc section of the first time delay unit 2 and the second time delay unit 3 is consistent with the curvature of the annular base layer, which not only ensures that the piezoelectric transducer fits perfectly with the pipeline surface, but also ensures the tightness and stability of the connection between the components, effectively avoiding energy loss during signal transmission, improving signal transmission quality, and thus improving the accuracy and reliability of detection.

[0024] The annular base layer 5, the first delay unit 2 and the second delay unit 3 of the piezoelectric transducer are made of the same material and are made into a whole by mechanical processing. The material used can be metal materials, such as aluminum, steel, etc.; or ceramic materials, such as alumina, unpolarized piezoelectric ceramics, etc., and there is no special limitation here.

[0025] The number of the first circumferential arrays is 2, and the two first circumferential arrays are symmetrically distributed on both sides with the second circumferential array as the center.

[0026] The first piezoelectric unit 1 has a length, width and height of The polarization direction of the first piezoelectric unit 1 is along the length direction, the electrodes of the first piezoelectric unit 1 are two opposite surfaces parallel to the polarization direction , the first piezoelectric unit 1 is Shear deformation occurs in the plane, and the second piezoelectric unit 4 is the same as the first piezoelectric unit 1 .

[0027] The polarization directions of all first piezoelectric units 1 in the first circumferential array are the same, the polarization directions of all second piezoelectric units 4 in the second circumferential array are the same, and the polarization directions of all first piezoelectric units 1 in the first circumferential array are opposite to the polarization directions of all second piezoelectric units 4 in the second circumferential array. Figure 2 As shown, the polarization directions of all the second piezoelectric units 4 in the figure are counterclockwise, and the polarization directions of all the first piezoelectric units 1 in the figure are clockwise, that is, the polarization directions of the first piezoelectric unit 1 and the second piezoelectric unit 4 are completely opposite.

[0028] The upper surfaces of the first piezoelectric unit 1 and the second piezoelectric unit 4 are connected to the positive electrode of the signal source through a wire, and the lower surfaces of the first piezoelectric unit 1 and the second piezoelectric unit 4 are connected to the negative electrode of the signal source through a wire. The signal source applies a voltage pulse signal to each piezoelectric unit, and each piezoelectric unit produces shear deformation according to the inverse piezoelectric effect, thereby exciting a quasi-shear guided wave with a set phase difference in the time delay unit with different heights. After the shear guided wave is transmitted to the surface of the pipeline through the time delay unit and the annular base layer 5, it will induce a wave propagating in only one direction in the pipeline. Wave, that is, zero-order torsional guided wave with axisymmetric energy distribution.

[0029] The axial length of the annular base layer 5 is the sum of the central axial spacing between the first circumferential array and the second circumferential array and the width of the first piezoelectric unit 1. The axial length of the annular base layer 5 satisfies ;in, is the axial length of the annular base layer 5; is the center axial spacing between the first circumferential array and the second circumferential array; is the width of the first piezoelectric unit 1 .

[0030] The above design makes the entire piezoelectric transducer structure compact and the components fit tightly together, avoiding looseness or displacement caused by size mismatch, enhancing the stability of the equipment working in complex environments, and ensuring that the detection work is carried out stably and reliably.

[0031] Embodiment 2: like Figure 3As shown, this embodiment provides a piezoelectric transducer method for directional excitation and reception of non-dispersive torsional guided waves. The figure shows that the method includes steps S10, S20, S30, S40, S50 and S60: Step S10. The piezoelectric transducer is arranged on the surface of the pipeline to be detected through a coupling agent, wherein the piezoelectric transducer comprises an annular base layer 5, a plurality of first circumferential arrays and a second circumferential array; Specifically, the piezoelectric transducer is set on the surface of the pipeline to be detected through a coupling agent. The coupling agent can effectively fill the tiny gap between the piezoelectric transducer and the pipeline surface, reduce the obstruction of the air layer to the ultrasonic signal, greatly improve the signal transmission efficiency, and make the detection signal clearer and more accurate.

[0032] The first circumferential array is composed of a plurality of first piezoelectric units 1 and a plurality of first time delay units 2, the second circumferential array is composed of a plurality of second piezoelectric units 4 and a plurality of second time delay units 3, and the whole composed of the first piezoelectric unit 1 and the first time delay unit 2 corresponds to the whole composed of the second piezoelectric unit 4 and the second time delay unit 3 in one-to-one correspondence, that is, the number of the first piezoelectric unit 1, the first time delay unit 2, the second piezoelectric unit 4 and the second time delay unit 3 is the same, and both are ,quantity The calculation formula is: ; ; in, is the number of first piezoelectric units 1 or first time delay units 2 or second piezoelectric units 4 or second time delay units 3 included in the first circumferential array; Bending-torsion guided wave The highest circumferential order.

[0033] Step S20. Determine a target circumferential array and a receiving circumferential array from a plurality of first circumferential arrays, connect the positive electrode of the first piezoelectric unit 1 in the target circumferential array and the positive electrode of the second piezoelectric unit 4 in the second circumferential array to the positive electrode of the power amplifier and the positive electrode of the signal source in sequence through a wire, and connect the negative electrode of the first piezoelectric unit 1 in the target circumferential array and the negative electrode of the second piezoelectric unit 4 in the second circumferential array to the negative electrode of the power amplifier and the negative electrode of the signal source in sequence through a wire; Step S30. The signal source applies a pulse signal to the target circumferential array and the second circumferential array; Step S40. The target circumferential array and the second circumferential array receive the pulse signal and induce the zero-order torsional guided wave to be transmitted in the pipeline to be detected; Specifically, Figure 1As shown, the second circumferential array is composed of a plurality of second piezoelectric units 4 and second time delay units 3 , and the height of the second time delay unit 3 is greater than the height of the first time delay unit 2 .

[0034] Specifically, step S40 specifically includes step S41 and step S42: Step S41. The first piezoelectric unit 1 of the target circumferential array and the second piezoelectric unit 4 of the second circumferential array receive the pulse signal and generate shear deformation based on the inverse piezoelectric effect, and excite shear-like guided waves in the first time delay unit 2 and the second time delay unit 3 with different heights; Step S41. The shear-like guided wave is transmitted to the surface of the pipeline to be inspected via the annular base layer 5, and based on the interaction between the energy carried by the shear-like guided wave and the material of the pipeline to be inspected, a zero-order torsional guided wave is induced; Specifically, in the present application, the number of the first circumferential array is 2, and the number of the second circumferential array is 1. Figure 4 As shown, based on the order of the first circumferential array and the second circumferential array in the figure, they are named array A, array B and array C from left to right. According to the direction currently required to be detected, it is flexibly selected to apply pulses to only part of the circumferential arrays.

[0035] In order to ensure that the emitted signal propagates in only one direction, a signal receiving device is placed in this application to verify the direction of wave transmission.

[0036] First, array A and array B of piezoelectric transducers are used for excitation, such as Figure 5 As shown, the signal receiving device in the direction of defect 1 received a zero-order torsional guided wave with a high signal-to-noise ratio. ;like Figure 6 As shown, the signal receiving device in the direction of defect 2 detected The amplitude of the wave is weakened; by comparing the signal amplitude on both sides, it is found that the unidirectional performance can reach 15dB. Use the arrays B and C of piezoelectric transducers for excitation, such as Figure 7 As shown, the signal receiving device in the direction of defect 2 receives Wave, such as Figure 8 As shown, the signal receiving device in the direction of defect 1 did not detect This means that the piezoelectric transducer of the present invention can selectively excite unidirectional zero-order torsional guided waves in the pipeline. , no additional electronics are required to provide excitation signals with different time delays.

[0037] In the actual operation of the piezoelectric transducer of the present application, when it is necessary to detect in the direction of defect 1, array A and array B are used as brakes to excite the signal, and array C is used as a sensor to receive the reflected wave sent back from direction 1, that is, array A is the target circumferential array, array C is the receiving circumferential array, and based on the wave propagation characteristics and the characteristics of the received signal, the pipeline condition in the direction of defect 1 is detected and analyzed, thereby achieving effective detection in the direction of defect 1. The corresponding detection results are as follows Fig. 9 As shown in the figure, there is an obvious reflected echo, i.e., defect echo signal, in the direction of defect 1. By calculating the time difference between the reflected echo and the excitation signal, the axial position of defect 1 can be determined.

[0038] When it is necessary to detect in the direction of defect 2, array C and array B are used as brakes to excite signals, and array A is used as a sensor to receive the reflected waves sent back from the 2 directions, that is, array C is the target circumferential array, and array A is the receiving circumferential array. Based on the propagation characteristics of the wave and the characteristics of the received signal, the pipeline condition in the direction of defect 2 is detected and analyzed, thereby achieving effective detection in the direction of defect 2. The corresponding detection results are shown in Figure 2. Fig.10 As shown in the figure, there is an obvious reflected echo, i.e., defect echo signal, in the direction of defect 2. By calculating the time difference between the reflected echo and the excitation signal, the axial position of defect 2 can be determined. The present application can greatly reduce the influence of the reflected signal on the other side by independently detecting a single direction, especially when there are defects on both sides.

[0039] When it is necessary to detect in the direction of defect 1, the piezoelectric units in arrays A and B produce thickness shear deformation based on the inverse piezoelectric effect. Due to the different heights of the delay units in arrays A and B, this deformation excites a shear-like guided wave with a set phase difference in the delay unit. When the cutoff frequency is , the shear-like guided wave will propagate to the surface of the pipeline to be tested through the time delay unit and the annular base layer 5, and then induce the zero-order torsional guided wave in the pipeline to be tested, realizing the excitation process of the wave required for the detection of the pipeline to be tested. It is necessary to detect in the direction of defect 2, and the corresponding principle is the same, which will not be repeated here.

[0040] Step S50. The zero-order torsional guided wave is reflected after encountering a structural change in the pipeline to be detected, and the receiving circumferential array receives the reflected echo signal and converts it into an electrical signal; Specifically, when it is necessary to detect in the direction of defect 1, array A and array B act as brakes, i.e., signal transmitting end brakes. After receiving a specific pulse excitation, array A and array B cooperate to excite zero-order torsional guided waves based on the inverse piezoelectric effect. The guided wave propagates in the pipeline to be detected. When encountering changes or defects in the internal structure of the pipeline, the zero-order torsional guided wave may be transformed into a bending torsional guided wave, so the reflected echo is generally a superposition of the zero-order torsional guided wave and the bending torsional guided wave. When the reflected echo propagates to array C, array C acts as a sensor, i.e., a signal receiving end, and converts the reflected echo signal carrying the pipeline structure information into an electrical signal based on the piezoelectric effect. Subsequently, by analyzing and solving the characteristic parameters such as the amplitude, frequency, and phase of the electrical signal, combined with the pre-established mapping relationship between the signal characteristics and the pipeline structural health status, the structural health status of the pipeline to be detected can be accurately analyzed to determine whether the pipeline has defects. If there is a defect, the specific location of the defect in the pipeline is further determined by using the principles of wave propagation time difference, reflection and scattering characteristics, etc. The corresponding principles are the same when detecting in the direction of defect 2, and will not be repeated here.

[0041] Step S60: Input the electrical signal into the data acquisition system for time domain and frequency domain analysis to determine the specific location of the surface defect of the pipeline to be detected; Specifically, Figure 4 As shown in the figure, defect 1 and defect 2 have the same axial distance relative to the piezoelectric transducer, but different circumferential positions. If the center of the piezoelectric transducer is regarded as the origin of the cylindrical coordinate system, the positions of defect 1 and defect 2 can be expressed by the coordinate system. That is, it is expressed in the form of angle and axial distance. This application takes array A and array B as brakes and array C as a sensor as an example to elaborate on the principle of piezoelectric transducer positioning defects.

[0042] Take array A and array B as brakes and array C as a sensor as an example. First, apply an excitation pulse signal to array A and array B at the same time, collect and save the receiving signal of the first piezoelectric unit 1 in array C respectively, and get The number of time domain signals is the same as the number of the first piezoelectric unit 1, and the number of the first piezoelectric unit 1, the second piezoelectric unit 4, the first time delay unit 2 and the second time delay unit 3 are all the same. Then, the synthetic focusing algorithm is used to post-process the collected data to finally locate the specific position of the defect. The specific steps are as follows: The first step is to use the two-dimensional Fourier transform calculation array C to collect the frequency domain signal of the time domain signal: ; in, is the frequency domain signal; is the time domain signal received by the first piezoelectric unit 1 in the array C; Bending-torsion guided waves The circumferential order of is an imaginary unit; is the circular frequency; For time; The second step is to perform phase compensation on the frequency domain signal to obtain the compensated signal: ; in, is the compensation signal; is the frequency domain signal; Non-dispersive torsional guided wave The corresponding wave number; Zero-order torsional guided wave The corresponding wave number; is an imaginary unit; is the circular frequency.

[0043] The third step is to introduce pseudo wave number and pseudo group velocity: ; ; in, Non-dispersive torsional guided wave The corresponding wave number, Zero-order torsional guided wave The corresponding wave number; is the circular frequency; is the pseudo wave velocity; is the circular frequency; is the pseudo group velocity.

[0044] The fourth step is to substitute the pseudo wave number and pseudo group velocity to convert the frequency domain signal into the wave number domain signal: ; in, is the wavenumber domain signal; is the frequency domain signal; is the circular frequency; is the pseudo wave velocity; is the pseudo group velocity; is the axial distance.

[0045] The fifth step is to perform inverse Fourier transform on the wavenumber domain signal to obtain the reconstructed signal: ; in, To reconstruct the signal; is the wavenumber domain signal; is an imaginary unit; is the axial distance; Zero-order torsional guided wave The circumferential order of is the angle between the piezoelectric unit and the defect.

[0046] The value of the reconstructed signal corresponds to the pixel value of each point in the final image, and the defect can be located by the depth of the color. Similarly, if array B and array C are used as brakes and array A is used as a sensor, array C and array A in the above operation can be interchanged and the same operation can be performed.

[0047] like Figure 11-13 The figure shown is the result of locating defect 1 using a piezoelectric transducer according to the above steps. At this time, the brakes are arrays A and B, and the sensor is array C. For ease of observation, the pipeline to be inspected is unfolded into a planar structure of the same size to present the results. When arrays A and B are used as brakes, the emission direction of the piezoelectric transducer is direction 1 (left side). The theoretical target detection area is the left area of ​​the pipeline to be inspected relative to the piezoelectric transducer, so only the image results in the corresponding target area are given here. Fig.11 It can be seen that there is only one obvious white area in the target detection area, and the energy distribution of the corresponding area in the axial and circumferential directions is extracted, as shown in Fig.12 and Fig.13 As shown, the positions of the maximum axial and circumferential energy in this area are very close to the actual positions of defect 1, which shows that defect 1 is accurately located.

[0048] When arrays B and C are used as actuators and array A is used as a sensor, the target detection area of ​​the piezoelectric transducer will be transformed into the area corresponding to the defect 2 direction, that is, the right area of ​​the pipeline to be detected. Fig.14 It shows that there is only one white area in the target detection area. Fig.15 and Fig.16 The results show that the white area corresponds to the position of defect 2. From the above, it can be seen that the piezoelectric transducer can successfully identify and locate axially symmetrical defects in the pipeline, while the existing bidirectional transducer technology cannot achieve the above function.

[0049] It should be noted that, regarding the device in the above embodiment, the specific manner in which each module performs the operation has been described in detail in the embodiment of the method, and will not be elaborated here.

[0050] Embodiment 3: This embodiment provides a method for preparing a piezoelectric transducer for directional excitation and receiving non-dispersive guided waves for different pipelines to be inspected: In this application, it is assumed that the pipeline to be tested is an aluminum tube with an outer diameter of 102 mm and a thickness of 2.2 mm. First, the operating frequency of the piezoelectric transducer is determined to be 380 kHz, corresponding to the wavelength of the zero-order torsional guided wave. Based on the semi-analytical finite element algorithm, the dispersion curve of the aluminum tube, i.e. the pipeline to be tested, is calculated, as shown in Fig.17 As shown, it can be seen that under the design frequency of the piezoelectric transducer, the highest circumferential order zero-order torsional guided wave is ,Right now , then the number of piezoelectric units and time delay units should be an integer greater than 15.4, so Take 16. After determining the number of time delay units and piezoelectric units, design the length of the first time delay unit 2 and the second time delay unit 3 according to the outer circumference of the pipeline to be detected. According to experimental experience, the size of the piezoelectric unit can be determined to be 18mm×2mm×1mm, and the width of the delay unit The axial distance between the first circumferential array and the second circumferential array is 2 mm, and the upper surface of the delay unit is a rectangular cross-section of 18 mm × 2 mm. 3mm, which meets the value range , that is 1.64mm-3.28mm.

[0051] The height of the first delay unit 2 and the height of the second delay unit 3 , calculate the height difference Previously, the propagation velocity of the shear-like guided wave in the time-delay unit needs to be calculated. Based on the semi-analytical finite element algorithm, the dispersion curve of the guided wave in the time-delay unit can be obtained, such as Fig.17 and Fig.18 It can be seen that when the operating frequency is 380kHz, the wave velocity of the zero-order torsional waveguide is is 3122m / s, while the velocity of shear wave is 2777m / s, so according to the calculation formula , we can find the height difference between the two delay units About 2.7mm. As for the annular base layer, its inner diameter is the same as the outer diameter of the pipe to be tested, ensuring that it can fit perfectly with the surface of the pipe to be tested. The axial length of the base layer is , calculated as 8mm, and all key parameters of the piezoelectric transducer are determined. The parameters calculated for different materials and sizes of the pipeline to be detected may not be the same, and no special restrictions are made here.

[0052] Typically, the annular base layer 5 and the time-delay unit are made of 6061 aluminum alloy and are integrated by CNC processing; the piezoelectric unit is a PZT-5H piezoelectric ceramic and is fixed to the upper surface of the time-delay unit with epoxy glue.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0054] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A piezoelectric transducer for directional excitation and reception of non-dispersive torsional guided waves, characterized in that: include: A first circumferential array, the first circumferential array being composed of a plurality of first piezoelectric units (1) and a plurality of first time delay units (2), the first time delay unit (2) being a block structure, the upper surface of which is a rectangular cross section, and the lower surface of which is an arc-shaped cross section, the first piezoelectric unit (1) being a rectangular parallelepiped, the first piezoelectric unit (1) being fixed above the first time delay unit (2), the lower surface of the first piezoelectric unit (1) being the same size as the upper surface of the first time delay unit (2), and the first piezoelectric unit (1) and the first time delay unit (2) being uniformly distributed as a whole along the circumferential direction; A second circumferential array, wherein the second circumferential array is composed of a plurality of second piezoelectric units (4) and a plurality of second time delay units (3), the second time delay unit (3) is a block structure, the upper surface of which is a rectangular cross-section and the lower surface of which is an arc-shaped cross-section, the second piezoelectric unit (4) is a rectangular parallelepiped, the second piezoelectric unit (4) is fixed above the second time delay unit (3), the lower surface of the second piezoelectric unit (4) is the same size as the upper surface of the second time delay unit (3), the second piezoelectric unit (4) and the second time delay unit (3) are uniformly distributed along the circumferential direction, and the height of the second time delay unit (3) is greater than the height of the first time delay unit (2).

2. The piezoelectric transducer for directional excitation and reception of non-dispersive torsional guided waves according to claim 1, characterized in that: The piezoelectric transducer comprises an annular base layer (5), the first circumferential array and the second circumferential array are fixed on the outer surface of the annular base layer (5), the arcuate cross-section of the first time delay unit (2) in the first circumferential array is consistent with the curvature of the annular base layer (5), and the arcuate cross-section of the second time delay unit (3) in the second circumferential array is consistent with the curvature of the annular base layer (5).

3. The piezoelectric transducer for directional excitation and reception of non-dispersive torsional guided waves according to claim 1, characterized in that: The number of the first circumferential arrays is 2, and the two first circumferential arrays are symmetrically distributed on both sides with the second circumferential array as the center.

4. The piezoelectric transducer for directional excitation and reception of non-dispersive torsional guided waves according to claim 1, characterized in that: The first piezoelectric unit (1) has a length, width and height of The polarization direction of the first piezoelectric unit (1) is along the length direction, the electrodes of the first piezoelectric unit (1) are two opposite surfaces parallel to the polarization direction , the first piezoelectric unit (1) is Shear deformation occurs within the plane, and the second piezoelectric unit (4) is the same as the first piezoelectric unit (1).

5. The piezoelectric transducer for directional excitation and reception of non-dispersive torsional guided waves according to claim 4, characterized in that: The polarization directions of all the first piezoelectric units (1) in the first circumferential array are the same, the polarization directions of all the second piezoelectric units (4) in the second circumferential array are the same, and the polarization directions of all the first piezoelectric units (1) in the first circumferential array are opposite to the polarization directions of all the second piezoelectric units (4) in the second circumferential array.

6. The piezoelectric transducer for directional excitation and reception of non-dispersive torsional guided waves according to claim 1, characterized in that: The upper surfaces of the first piezoelectric unit (1) and the second piezoelectric unit (4) are connected to the positive electrode of the signal source through a wire, and the lower surfaces of the first piezoelectric unit (1) and the second piezoelectric unit (4) are connected to the negative electrode of the signal source through a wire.

7. The piezoelectric transducer for directional excitation and reception of non-dispersive torsional guided waves according to claim 2, characterized in that: The axial length of the annular base layer (5) is the sum of the central axial distance between the first circumferential array and the second circumferential array and the width of the first piezoelectric unit (1).

8. A method for directional excitation and reception of non-dispersive torsional guided waves by a piezoelectric transducer, characterized in that: include: A piezoelectric transducer is arranged on the surface of the pipeline to be inspected through a coupling agent, wherein the piezoelectric transducer comprises an annular base layer (5), a plurality of first circumferential arrays and a second circumferential array; Determining a target circumferential array and a receiving circumferential array from a plurality of first circumferential arrays, connecting the positive electrode of the first piezoelectric unit (1) in the target circumferential array and the positive electrode of the second piezoelectric unit (4) in the second circumferential array to the positive electrode of the power amplifier and the positive electrode of the signal source in sequence through a wire, and connecting the negative electrode of the first piezoelectric unit (1) in the target circumferential array and the negative electrode of the second piezoelectric unit (4) in the second circumferential array to the negative electrode of the power amplifier and the negative electrode of the signal source in sequence through a wire; A signal source applies a pulse signal to the target circumferential array and the second circumferential array; The target circumferential array and the second circumferential array receive the pulse signal and induce zero-order torsional guided waves to be transmitted in the pipeline to be inspected; The zero-order torsional guided wave is reflected after encountering a structural change in the pipeline to be detected, and the receiving circumferential array receives the reflected echo signal and converts it into an electrical signal; The electrical signal is input into a data acquisition system for time domain and frequency domain analysis to determine the specific location of the surface defect of the pipeline to be detected.

9. The piezoelectric transducer method for directional excitation and reception of non-dispersive torsional guided waves according to claim 8, characterized in that: The first circumferential array is composed of a plurality of first piezoelectric units (1) and a plurality of first time delay units (2), and the number of the first piezoelectric units (1) or the first time delay units (2) is: ； ； in, is the number of first piezoelectric units (1) or first time delay units (2) included in the first circumferential array; Bending-torsion guided waves The highest circumferential order.

10. The method for directional excitation and reception of non-dispersive torsional guided waves of a piezoelectric transducer according to claim 9, characterized in that: The second circumferential array is composed of a plurality of second piezoelectric units (4) and a second time delay unit (3), the height of the second time delay unit (3) being greater than the height of the first time delay unit (2), the target circumferential array and the second circumferential array receiving the pulse signal and inducing zero-order torsional guided waves to be transmitted in the pipeline to be detected, comprising: The first piezoelectric unit (1) of the target circumferential array and the second piezoelectric unit (4) of the second circumferential array receive the pulse signal and generate shear deformation based on the inverse electric effect, and excite shear-like guided waves in the first time delay unit (2) and the second time delay unit (3) with different heights; The quasi-shear guided wave is transmitted to the surface of the pipeline to be inspected via the annular base layer (5), and based on the interaction between the energy it carries and the material of the pipeline to be inspected, a zero-order torsional guided wave is induced.

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