A piezoelectric transducer and method for directionally exciting and receiving non-dispersive torsional guided waves

Abstract

The present invention provides a piezoelectric transducer and method for directionally exciting and receiving non-dispersive torsional guided waves, which relates to the technical field of ultrasonic non-destructive testing. It includes a first circumferential array composed of a plurality of first piezoelectric units and a plurality of first time-delay units; and a second circumferential array composed of a plurality of second piezoelectric units and a plurality of second time-delay units. The present invention constructs a piezoelectric transducer capable of directionally exciting and receiving non-dispersive torsional guided waves through thickness-shear type piezoelectric units and time-delay units with height differences. Whether it is unidirectional excitation or unidirectional reception, there is no need for an external circuit or device to provide time delay, reducing the complexity and cost of the overall structure. Moreover, in this application, time-delay units are used instead of piezoelectric units to be combined with the pipeline in a curved surface, which can avoid the problem that the piezoelectric units are not well-matched with the detection pipeline due to too small flexibility, thereby improving the fitting degree, ensuring signal transmission, and making the detection more efficient and accurate.

Description

Technical Field

[0001] The present invention relates to the technical field of non-destructive testing of pipelines, and in particular, to a piezoelectric transducer and method for directionally exciting and receiving non-dispersive torsional guided waves. Background Art

[0002] Due to its excellent medium transmission characteristics, pipeline structures are widely used in industrial fields such as petrochemical and nuclear power. However, during long-term service, pipelines are susceptible to defects such as structural deformation, wall thickness reduction, and crack propagation under the influence of factors such as corrosion by the transported medium and environmental load effects, which may lead to medium leakage, environmental pollution, and even major safety accidents. The ultrasonic guided wave detection technology has shown significant advantages in pipeline detection due to its unique propagation characteristics.

[0003] However, the guided wave transducers used in existing commercial detection systems are all bidirectional transducers, that is, ultrasonic guided waves are simultaneously transmitted to both ends of the pipeline, resulting in limited defect localization ability, and only the axial distance of the defect can be determined without being able to identify its specific orientation 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, developing a new excitation device that can achieve directional excitation and reception of axial guided waves has important engineering application value for improving the accuracy of pipeline defect detection and reducing the detection cost. Summary of the Invention

[0004] The purpose of the present invention is to provide a piezoelectric transducer and method for directionally exciting and receiving non-dispersive torsional guided waves to improve the above problems. To achieve the above purpose, the technical solutions adopted by the present invention are as follows:

[0005] In a first aspect, the present application provides a piezoelectric transducer for directionally exciting and receiving non-dispersive torsional guided waves, comprising:

[0006] A first circumferential array, which is composed of a plurality of first piezoelectric units and a plurality of first time delay units. The first time delay unit is a block structure, with a rectangular cross-section on its upper surface and an arc-shaped cross-section on its lower surface. The first piezoelectric unit is a cuboid, and the first piezoelectric unit is fixed above the first time delay unit. The lower surface of the first piezoelectric unit has the same size as the upper surface of the first time delay unit. The overall formed by the first piezoelectric unit and the first time delay unit is evenly distributed circumferentially;

[0007] 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 with a rectangular cross-section on its upper surface and an arc-shaped cross-section on its lower surface. The second piezoelectric unit is a cuboid, and the second piezoelectric unit is fixed above the second time-delay unit. The lower surface of the second piezoelectric unit has the same size as the upper surface of the second time-delay unit. The whole formed by the second piezoelectric unit and the second time-delay unit is evenly distributed circumferentially. The height of the second time-delay unit is greater than the height of the first time-delay unit.

[0008] 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-shaped cross-section of the first time-delay unit in the first circumferential array is consistent with the radian of the annular base layer. The arc-shaped cross-section of the second time-delay unit in the second circumferential array is consistent with the radian of the annular base layer.

[0009] 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.

[0010] The first piezoelectric unit is a cuboid with 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 , and the first piezoelectric unit generates shear deformation in the plane. The second piezoelectric unit is the same as the first piezoelectric unit.

[0011] 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. 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.

[0012] The upper surfaces of the first piezoelectric unit and the second piezoelectric unit are connected to the positive pole of the signal source through wires, and the lower surfaces of the first piezoelectric unit and the second piezoelectric unit are connected to the negative pole of the signal source through wires.

[0013] The axial length of the annular base layer 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.

[0014] In a second aspect, the present application also provides a method for a piezoelectric transducer to directionally excite and receive non-dispersive torsional guided waves, including:

[0015] The piezoelectric transducer is arranged on the surface of the pipeline to be detected through a coupling agent. The piezoelectric transducer includes an annular base layer, a plurality of first circumferential arrays, and a second circumferential array;

[0016] Determine a target circumferential array and a receiving circumferential array from the plurality of first circumferential arrays. Connect the positive poles of the first piezoelectric units in the target circumferential array and the positive poles of the second piezoelectric units in the second circumferential array to the positive pole of the power amplifier and the positive pole of the signal source in sequence through wires. Connect the negative poles of the first piezoelectric units in the target circumferential array and the negative poles of the second piezoelectric units in the second circumferential array to the negative pole of the power amplifier and the negative pole of the signal source in sequence through wires;

[0017] The signal source, the target circumferential array, and the second circumferential array receive the pulse signal and initiate the transmission of zero-order torsional guided waves in the pipeline to be detected;

[0018] After the zero-order torsional guided wave is reflected upon encountering the structural change in the pipeline to be detected, the receiving circumferential array receives the reflected echo signal and converts it into an electrical signal;

[0019] Input the electrical signal into the data acquisition system for time-domain and frequency-domain analysis to determine the specific position of the surface defect of the pipeline to be detected.

[0020] The beneficial effects of the present invention are as follows:

[0021] The present invention constructs a piezoelectric transducer capable of directionally exciting and receiving non-dispersive torsional guided waves through thickness-shear type piezoelectric units and time-delay units with height differences. Whether it is unidirectional excitation or unidirectional reception, no external circuit or device is required to provide time delay, reducing the complexity and cost of the overall structure. And in this application, time-delay units are used instead of piezoelectric units to be combined with the pipeline in a curved surface, which can avoid the problem that the piezoelectric units are not well-matched with the detection pipeline due to too small flexibility, thereby improving the fitting degree, ensuring signal transmission, and making the detection more efficient and accurate.

[0022] Other features and advantages of the present invention will be described in the subsequent specification, and, in part, will become apparent from the specification or be understood by implementing the embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, so they should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0024] Figure 1 It is a schematic diagram of the structure of the piezoelectric transducer in the embodiment of the present invention;

[0025] Figure 2 It is the front view of the piezoelectric transducer in the embodiment of the present invention;

[0026] Figure 3 It is a schematic flow diagram of the usage method of the piezoelectric transducer in the embodiment of the present invention;

[0027] Figure 4 It is a test schematic diagram of the piezoelectric transducer in the embodiment of the present invention for detecting axially symmetric defects of the pipeline to be detected;

[0028] Figure 5 It is a schematic diagram of the received signal of the signal receiving device placed in the direction of defect 1 when arrays A and B are excited simultaneously in the embodiment of the present invention;

[0029] Figure 6 It is a schematic diagram of the received signal of the signal receiving device placed in the direction of defect 2 when arrays A and B are excited simultaneously in the embodiment of the present invention;

[0030] Figure 7 It is a schematic diagram of the received signal of the signal receiving device placed in the direction of defect 2 when arrays B and C are excited simultaneously in the embodiment of the present invention;

[0031] Figure 8 It is a schematic diagram of the received signal of the signal receiving device placed in the direction of defect 1 when arrays B and C are excited simultaneously in the embodiment of the present invention;

[0032] Figure 9 It is a schematic diagram of the received signal of array C when arrays A and B are excited simultaneously in the embodiment of the present invention;

[0033] Figure 10 It is a schematic diagram of the received signal of array A when arrays B and C are excited simultaneously in the embodiment of the present invention;

[0034] Figure 11 It is the result diagram of the piezoelectric transducer detecting the defect in the direction of defect 1 in the embodiment of the present invention;

[0035] Figure 12 In the embodiment of the present invention Figure 11 Schematic diagram of axial position comparison in the result diagram;

[0036] Figure 13 In the embodiment of the present invention Figure 11 Schematic diagram of angle comparison in the result diagram;

[0037] Figure 14 It is the result diagram of the piezoelectric transducer detecting the defect in the direction of defect 2 in the embodiment of the present invention;

[0038] Figure 15 In the embodiment of the present invention Figure 14Schematic diagram of axial position comparison in the result diagram;

[0039] Figure 16 In the embodiment of the present invention Figure 14 Schematic diagram of angle comparison in the result diagram;

[0040] Figure 17 Dispersion curve of the bending and torsional guided wave group velocity of the pipeline to be measured in the embodiment of the present invention;

[0041] Figure 18 Dispersion curve of the phase velocity of the time delay unit in the embodiment of the present invention.

[0042] 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 implementation manners

[0043] To make the objectives, 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 with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and illustrated herein usually can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the present invention provided in the accompanying drawings below is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0044] It should be noted that: similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. At the same time, in the description of the present invention, terms such as "first" and "second" are only used for descriptive distinction and cannot be construed as indicating or implying relative importance.

[0045] Embodiment 1:

[0046] This embodiment provides a piezoelectric transducer for directionally exciting and receiving non-dispersive torsional guided waves, including:

[0047] 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, with a rectangular cross-section on its upper surface and an arc-shaped cross-section on its lower surface. The first piezoelectric unit 1 is a cuboid, and 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 whole formed by the first piezoelectric unit 1 and the first time-delay unit 2 is evenly distributed circumferentially;

[0048] 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 its upper surface and an arc-shaped cross-section on its lower surface. The second piezoelectric unit 4 is a cuboid, and 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 whole formed by the second piezoelectric unit 4 and the second time-delay unit 3 is evenly distributed circumferentially, and the height of the second time-delay unit 3 is greater than the height of the first time-delay unit 2.

[0049] For the sake of convenience in description, hereinafter, the first piezoelectric unit 1 and the second piezoelectric unit 4 are collectively referred to as piezoelectric units, and the first time-delay unit 2 and the second time-delay unit 3 are collectively referred to as time-delay units for description.

[0050] In the embodiments of the present application, the piezoelectric units are all thickness-shear type piezoelectric units. As Figure 1 shown, the arrows located on the piezoelectric units in the figure indicate the polarization directions of the piezoelectric units. The length, width and height of the piezoelectric units are , the length and width of the upper surface of the first time-delay unit 2 are , the distance from the center point of the upper surface of the first time-delay unit 2 to the center point of the lower surface is , the length and width of the upper surface of the second time-delay unit 3 are , the distance from the center point of the upper surface of the second time-delay unit 3 to the center point of the lower surface is .

[0051] In the present invention, the material of the piezoelectric unit can be piezoelectric ceramics or piezoelectric single crystals, etc., and can also be other piezoelectric materials capable of generating corresponding deformation modes, which are not particularly limited here. The time-delay unit works in cooperation with the piezoelectric unit, and by controlling the height difference between the first time-delay unit 2 and the second time-delay unit 3, waves with a specific phase difference are generated in the piezoelectric unit, realizing the excitation and reception control of zero-order torsional guided waves and improving the detection resolution and accuracy.

[0052] The piezoelectric transducer includes 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 arc-shaped cross-section of the first time-delay unit 2 in the first circumferential array is consistent with the radian of the annular base layer 5, and the arc-shaped cross-section of the second time-delay unit 3 in the second circumferential array is consistent with the radian of the annular base layer 5. The annular base layer 5 is in the shape of a hollow cylinder, and its inner diameter is the same as the outer diameter of the pipeline to be detected, so as to ensure perfect fit 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. The arc-shaped cross-sections of the first time-delay unit 2 and the second time-delay unit 3 are consistent with the radian of the annular base layer, which not only ensures perfect fit between the piezoelectric transducer and the pipeline surface, but also guarantees the tightness and stability of the connection between components, effectively avoiding energy loss during signal transmission, improving signal transmission quality, and further enhancing the accuracy and reliability of detection.

[0053] The annular base layer 5, the first time-delay unit 2, and the second time-delay unit 3 of the piezoelectric transducer are made of the same material and are integrally formed by machining. The material used can be a metal material, such as aluminum, steel, etc.; or a ceramic material, such as alumina, unpolarized piezoelectric ceramics, etc., without special restrictions here.

[0054] 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.

[0055] The first piezoelectric unit 1 is a cuboid with 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 , and the first piezoelectric unit 1 generates shear deformation in the plane. The second piezoelectric unit 4 is the same as the first piezoelectric unit 1.

[0056] The polarization directions of all the first piezoelectric units 1 in the first circumferential array are the same, and the polarization directions of all the second piezoelectric units 4 in the second circumferential array are the same. 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. As Figure 2 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.

[0057] The upper surfaces of the first piezoelectric unit 1 and the second piezoelectric unit 4 are connected to the positive pole of the signal source through wires, and the lower surfaces of the first piezoelectric unit 1 and the second piezoelectric unit 4 are connected to the negative pole of the signal source through wires. The signal source applies a voltage pulse signal to each piezoelectric unit, and each piezoelectric unit generates a shear deformation according to the inverse piezoelectric effect, thereby exciting shear-like guided waves with a set phase difference in the time-delay units at different heights. After the shear-like guided waves are transmitted to the pipe surface through the time-delay units and the annular base layer 5, they will trigger a wave propagating in only one direction in the pipe, i.e., the zero-order torsional guided wave with axially symmetric energy distribution.

[0058] 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 ; where is the axial length of the annular base layer 5; is the central axial spacing between the first circumferential array and the second circumferential array; is the width of the first piezoelectric unit 1.

[0059] The above design makes the entire piezoelectric transducer structure compact, and each component fits closely, avoiding looseness or displacement caused by size mismatch, enhancing the stability of the device in complex environments, and ensuring the stable and reliable progress of the detection work.

[0060] Embodiment 2:

[0061] As Figure 3 shown, this embodiment provides a method for a piezoelectric transducer to directionally excite and receive non-dispersive torsional guided waves. The figure shows that this method includes step S10, step S20, step S30, step S40, step S50, and step S60:

[0062] Step S10. Set the piezoelectric transducer on the surface of the pipeline to be detected through a couplant. The piezoelectric transducer includes an annular base layer 5, a plurality of first circumferential arrays, and a second circumferential array;

[0063] Specifically, set the piezoelectric transducer on the surface of the pipeline to be detected through a couplant. The couplant can effectively fill the tiny gaps 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.

[0064] Among them, 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 second circumferential array is composed of a plurality of second piezoelectric units 4 and a plurality of second time-delay units 3. Moreover, the whole composed of the first piezoelectric unit 1 and the first time-delay unit 2 corresponds one-to-one with the whole composed of the second piezoelectric unit 4 and the second time-delay unit 3, and the quantities are the same. That is, the quantities of the first piezoelectric unit 1, the first time-delay unit 2, the second piezoelectric unit 4, and the second time-delay unit 3 are the same, all being , and the quantity The calculation formula is:

[0065] ;

[0066] ;

[0067] Among them, is the quantity of the first piezoelectric unit 1, the first time-delay unit 2, the second piezoelectric unit 4, or the second time-delay unit 3 included in the first circumferential array; is the flexural-torsional guided wave The highest circumferential order.

[0068] Step S20. Determine the target circumferential array and the receiving circumferential array from the multiple first circumferential arrays. Connect the positive electrodes of the first piezoelectric units 1 in the target circumferential array and the positive electrodes of the second piezoelectric units 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 wires. Connect the negative electrodes of the first piezoelectric units 1 in the target circumferential array and the negative electrodes of the second piezoelectric units 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 wires;

[0069] Step S30. The signal source applies a pulse signal to the target circumferential array and the second circumferential array;

[0070] Step S40. The target circumferential array and the second circumferential array receive the pulse signal and initiate the transmission of the zero-order torsional guided wave in the pipeline to be detected;

[0071] Specifically, as Figure 1 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.

[0072] Specifically, step S40 specifically includes step S41 and step S42:

[0073] Step S41. The first piezoelectric units 1 of the target circumferential array and the second piezoelectric units 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 units 2 and the second time-delay units 3 with different heights;

[0074] Step S41. The shear-like guided wave is transmitted through the annular base layer 5 to the surface of the pipeline to be detected. Based on the interaction between the energy it carries and the material of the pipeline to be detected, a zero-order torsional guided wave is induced.

[0075] Specifically, in this application, the number of the first circumferential arrays is 2, and the number of the second circumferential arrays is 1. As Figure 4 shown, based on the sorting of the first circumferential array and the second circumferential array in the figure, they are named array A, array B, and array C in sequence from left to right. It is possible to flexibly select to apply pulses only to some of the circumferential arrays according to the current required detection direction.

[0076] In order to ensure that the emitted signal propagates only in one direction, in this application, a signal receiving device will be placed to verify the propagation direction of the wave.

[0077] First, use array A and array B of the piezoelectric transducer for excitation. As Figure 5 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 ; as Figure 6 shown, the signal receiving device in the direction of defect 2 detected a weakening of the wave amplitude; by comparing the signal amplitudes on both sides, it is found that the unidirectional performance can reach 15 dB. Use array B and C of the piezoelectric transducer for excitation. As Figure 7 shown, the signal receiving device in the direction of defect 2 received a wave. As Figure 8 shown, the signal receiving device in the direction of defect 1 did not detect a wave. This means that the piezoelectric transducer of this application can selectively excite a zero-order torsional guided wave that propagates unidirectionally in the pipeline , without additional electronic devices to provide excitation signals with different time delays.

[0078] When the piezoelectric transducer of this application is actually operated, when it is necessary to detect in the direction of defect 1, use array A and array B as actuators to excite signals, and use array C as a sensor to receive the reflected wave returned from the 1 direction. That is, array A is the target circumferential array, and array C is the receiving circumferential array. And based on the propagation characteristics of the wave and the characteristics of the received signal, the pipeline condition in the direction of defect 1 is detected and analyzed, so as to realize the effective detection in the direction of defect 1. The corresponding detection result is as Figure 9 shown. In the figure, there is an obvious reflected echo, that is, a 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.

[0079] When it is necessary to detect in the direction of Defect 2, Array C and Array B are used as brakes to excite signals, while Array A is used as a sensor to receive the reflected waves returned in the 2 direction. That is, Array C is the target circumferential array, and Array A is the receiving circumferential array. According to the propagation characteristics of the waves and the characteristics of the received signals, the condition of the pipeline in the direction of Defect 2 is detected and analyzed, so as to achieve effective detection in the direction of Defect 2. The corresponding detection results are as Figure 10 shown. In the figure, there is an obvious reflected echo, that is, a 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. In this application, by independently detecting a single direction, especially in the case where there are defects on both sides, the influence of the reflected signals on the other side can be greatly reduced.

[0080] When it is necessary to detect in the direction of Defect 1, the piezoelectric units in Array A and Array B generate thickness shear deformation based on the inverse piezoelectric effect. Since the height of the time delay units in Array A and Array B is different, this deformation excites shear-like guided waves with a set phase difference in the time delay units. When the excitation frequency is lower than the cut-off frequency of the flexural torsional guided wave, the shear-like guided wave will propagate through the time delay unit and the annular base layer 5 to the surface of the pipeline to be measured, and then trigger a zero-order torsional guided wave in the pipeline to be measured, realizing the excitation process of the waves required for detecting the pipeline to be measured. When it is necessary to detect in the direction of Defect 2, the corresponding principle is the same and will not be elaborated here.

[0081] Step S50. The zero-order torsional guided wave reflects after encountering the structural changes in the pipeline to be detected, and the receiving circumferential array receives the reflected echo signal and converts it into an electrical signal;

[0082] Specifically, when it is necessary to detect in the direction of Defect 1, Array A and Array B are used as brakes, that is, the signal transmitting end brakes. After receiving a specific pulse excitation, based on the inverse piezoelectric effect, they cooperate to excite a zero-order torsional guided wave. This guided wave propagates in the pipeline to be detected. When it encounters the internal structural changes or defects in the pipeline, the zero-order torsional guided wave may turn into a flexural torsional guided wave. Therefore, the reflected echo is generally a superposition of the zero-order torsional guided wave and the flexural torsional guided wave. When the reflected echo propagates to Array C, Array C is used as a sensor, that is, the signal receiving end, and based on the piezoelectric effect, it converts the reflected echo signal carrying the pipeline structure information into an electrical signal. Subsequently, by analyzing and calculating the characteristic parameters such as the amplitude, frequency, and phase of the electrical signal, and combining the pre-established mapping relationship between the signal characteristics and the pipeline structure health condition, the structural health condition of the pipeline to be detected can be accurately analyzed, and it can be judged whether there are defects in the pipeline. If there are defects, using the principles such as the wave propagation time difference, reflection and scattering characteristics, etc., the specific position of the defect in the pipeline can be further determined. When detecting in the direction of Defect 2, the corresponding principle is the same and will not be elaborated here.

[0083] Step S60. Input the electrical signal into the data acquisition system for time-domain and frequency-domain analysis to determine the specific position of the surface defect of the pipeline to be detected;

[0084] Specifically, as Figure 4 shown, the axial distances of defect 1 and defect 2 relative to the piezoelectric transducer are the same, but the circumferential positions are different. 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 represented by coordinates in the form of angle and axial distance. Taking the way that array A and array B are used as brakes and array C is used as a sensor as an example, the principle of defect positioning by the piezoelectric transducer is described in detail.

[0085] Taking the way that array A and array B are used as brakes and array C is used as a sensor as an example. First, apply an excitation pulse signal to array A and array B simultaneously, and respectively collect and save the received signals of the first piezoelectric unit 1 in array C, and time-domain signals can be obtained. The number of time-domain signals is the same as the number of the first piezoelectric unit 1, and the numbers 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, use the synthetic focusing algorithm to post-process the collected data, and finally realize the specific position positioning of the defect. The specific steps are as follows:

[0086] The first step is to calculate the frequency-domain signal of the time-domain signal collected by array C by using two-dimensional Fourier transform:

[0087] ;

[0088] where, is the frequency-domain signal; is the time-domain signal received by the first piezoelectric unit 1 in array C; is the circumferential order of the flexural-torsional guided wave ; is the imaginary unit; is the circular frequency; is the time;

[0089] The second step is to perform phase compensation on the frequency-domain signal to obtain the compensated signal:

[0090] ;

[0091] where, is the compensated signal; is the frequency-domain signal; is the wave number corresponding to the non-dispersive torsional guided wave ; is the wave number corresponding to the zero-order torsional guided wave ; is the imaginary unit; is the circular frequency.

[0092] Step 3: Introduce the pseudo wavenumber and pseudo group velocity:

[0093] ;

[0094] ;

[0095] where is the wavenumber corresponding to the non-dispersive torsional guided wave ; is the wavenumber corresponding to the zero-order torsional guided wave ; is the circular frequency; is the pseudo wave speed; is the circular frequency; is the pseudo group velocity.

[0096] Step 4: Substitute the pseudo wavenumber and pseudo group velocity to convert the frequency-domain signal into a wavenumber-domain signal:

[0097] ;

[0098] where is the wavenumber-domain signal; is the frequency-domain signal; is the circular frequency; is the pseudo wave speed; is the pseudo group velocity; is the axial distance.

[0099] Step 5: Perform the inverse Fourier transform on the wavenumber-domain signal to obtain the reconstructed signal:

[0100] ;

[0101] where is the reconstructed signal; is the wavenumber-domain signal; is the imaginary unit; is the axial distance; is the circumferential order of the zero-order torsional guided wave ; is the angle between the piezoelectric element and the defect.

[0102] Among them, the value of the reconstructed signal corresponds to the pixel value of each point in the final imaging image, and the defect can be located by the depth of the color. Similarly, if array B and array C are used as actuators, and array A is used as a sensor, by swapping array C and array A in the above operations and then performing the same operations, the same result can be obtained.

[0103] Such as Figures 11 - 13As shown, it is the result diagram 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 sensors are array C. For the convenience of observation, the pipeline to be detected 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 the 1 direction (left side). The theoretically target detection area is the left area of the pipeline to be detected relative to the piezoelectric transducer. Therefore, only the image results within the corresponding target area are given here. From Figure 11 it can be seen that there is only one obvious white area within the target detection area. The energy distributions in the axial and circumferential directions of the corresponding area are extracted, as Figure 12 and Figure 13 shown. The positions of the maximum values of the axial and circumferential energies in this area are very close to the actual position of defect 1, indicating that defect 1 is accurately located.

[0104] When array B and array C are used as brakes and array A is used as a sensor, the target detection area of this piezoelectric transducer will be transformed into the area corresponding to the direction of defect 2, that is, the right area of the pipeline to be detected. Similarly, Figure 14 it shows that there is only one white area within the target detection area. Combining the results of Figure 15 and Figure 16 can prove that the position corresponding to this white area is that of defect 2. As can be seen from the above, this piezoelectric transducer can successfully identify and locate the axially symmetric defects in the pipeline, while the existing bidirectional transducer technology cannot achieve the above functions.

[0105] It should be noted that regarding the device in the above embodiments, the specific manners in which each module performs operations have been described in detail in the embodiments related to the method, and will not be elaborated here.

[0106] Embodiment 3:

[0107] This embodiment provides a preparation method for a piezoelectric transducer for directional excitation and receiving non-dispersive guided waves for different pipelines to be detected:

[0108] In this application, it is assumed that the pipeline to be detected is an aluminum pipe 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, and the wavelength corresponding to the zero-order torsional guided wave is 8.2 mm. Based on the semi-analytical finite element algorithm, the dispersion curve of this aluminum pipe, that is, the pipeline to be detected, is calculated, as Figure 17 shown. It can be seen that under the design frequency of this piezoelectric transducer, the highest circumferential order of the zero-order torsional guided wave is , that is, , then the number of piezoelectric units and time-delay units Take 16. After determining the number of time-delay units and piezoelectric units, according to the outer circumference of the pipeline to be detected, design the lengths of the first time-delay unit 2 and the second time-delay unit 3 to be 18 mm. According to experimental experience, the size of the piezoelectric unit can be determined as 18 mm × 2 mm × 1 mm, and the width of the time-delay unit is all 2 mm, and the upper surface of the time-delay unit is a rectangular cross-section of 18 mm × 2 mm. The axial distance between the first circumferential array and the second circumferential array is 3 mm, meeting the value range , that is, 1.64 mm - 3.28 mm.

[0109] The height of the first time-delay unit 2 and the height of the second time-delay unit 3 . Before calculating the height difference , it is necessary to first calculate the propagation speed of the pseudo-shear guided wave in the time-delay unit. Based on the semi-analytical finite element algorithm, the dispersion curve of the guided wave in the time-delay unit can be obtained. As Figure 17 and Figure 18 can be seen, when the operating frequency is 380 kHz, the wave speed of the zero-order torsional guided wave is 3122 m / s, while the speed of the pseudo-shear guided wave is 2777 m / s. Therefore, according to the calculation formula , the height difference between the two time-delay units can be obtained is approximately 2.7 mm. Regarding the annular base layer, its inner diameter is the same as the outer diameter of the pipeline to be detected, ensuring perfect fit with the surface of the pipeline to be detected. The axial length of the base layer , calculated as 8 mm, determines all the key parameters in the piezoelectric transducer. The parameters calculated for different materials and sizes of the pipelines to be detected are not necessarily the same, and no special restrictions are imposed here.

[0110] Generally, the materials of the annular base layer 5 and the time-delay unit are 6061 aluminum alloy and are made into one body by CNC machining; the piezoelectric unit is PZT-5H piezoelectric ceramic and is fixed on the upper surface of the time-delay unit with epoxy glue.

[0111] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0112] As described above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to 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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