Piezoelectric transducer and method for unidirectional excitation and reception of non-dispersive ultrasonic guided waves

Abstract

The present invention discloses a piezoelectric transducer and method for unidirectional excitation and reception of non-dispersive ultrasonic guided waves. The piezoelectric transducer of the present invention adopts a method of unidirectional excitation and reception of non-dispersive ultrasonic guided waves, wherein two polarization directions are opposite and the thickness shear piezoelectric coefficient d is set to 0. 15 The piezoelectric transducer plates are respectively arranged on the surfaces of the short-side and high-side delay pillars, inducing the SH0 wave or T (0, 1) wave generated by the measured waveguide to propagate in both directions. The distance and height difference between the short-side and high-side delay pillars meet the interference conditions, so the interference is canceled in the direction of the high-side delay pillar, and the non-dispersive ultrasonic guided waves propagating in the direction of the short-side delay pillar are enhanced by interference. Therefore, the piezoelectric transducer can excite the non-dispersive ultrasonic guided waves propagating in one direction within a wide frequency range, and as a sensor, it filters out the non-dispersive ultrasonic guided waves on the weakened side and only receives the non-dispersive ultrasonic guided waves on the enhanced side. Regardless of unidirectional excitation or unidirectional reception, the present invention does not require an external circuit or device to provide time delay.

Description

Technical Field

[0001] The present invention relates to a structural health monitoring technology, and in particular to a piezoelectric transducer for unidirectionally exciting and receiving non-dispersive ultrasonic guided waves and an implementation method thereof. Background Art

[0002] Ultrasonic guided wave flaw detection (Ultrasonic Guided Wave) is considered a highly promising nondestructive testing and online monitoring technology due to its long detection range and high sensitivity. However, due to the complex propagation characteristics of ultrasonic guided waves in actual structures, current nondestructive testing and structural health monitoring methods based on ultrasonic guided waves are primarily in the laboratory research stage, with limited practical industrial application. The complexity of guided waves is primarily manifested in their multimodality and dispersion. Multimodality refers to the simultaneous propagation of multiple modes of guided waves within a waveguide structure at the same frequency. This multimodality not only makes it difficult to excite a single mode of guided waves but also makes it prone to conversion to other modes at locations with varying impedances (such as defects and boundaries), resulting in highly complex echo signals. Dispersion refers to the property of the guided wave velocity varying with frequency and structure size. Dispersion causes signal distortion during propagation, complicating signal processing. The use of single-mode non-dispersive guided waves can effectively reduce the complexity of the signal. Therefore, the development of transducers that can excite and receive single-mode non-dispersive guided waves in structures is of great significance for promoting the application of ultrasonic guided wave detection or monitoring technology in engineering. In addition, it is usually desirable to control the direction of the incident wave, such as directional emission of guided waves in one direction, which can effectively reduce the noise signal caused by non-defect scatterers. Currently, unidirectional propagation of guided waves is usually obtained by two-dimensional phased arrays. However, the phased array method has high requirements for the uniformity between each array source transducer and requires relatively complex and expensive control circuits. Therefore, there is an urgent need to develop new technologies that can achieve directional excitation of single-mode non-dispersive guided waves using a single transducer.

[0003] Zero-order horizontal shear waves (SH0 waves) in plate and shell structures are among the few non-dispersive guided waves in structures. SH0 waves can be excited by either a tangential line force or in-plane shear deformation in the waveguide structure. Both methods are physically equivalent to tangential force-induced SH0 waves, but the acoustic fields they induce in the waveguide structure differ. A tangential line force generates SH0 waves perpendicular to the line force, while Lamb waves are generated along the line force. A pair of antisymmetric line forces effectively suppresses Lamb waves, thereby exciting SH0 waves in opposite directions perpendicular to the line force. Based on this principle, as early as the 1970s, Thompson et al. developed a Lorentz-force electromagnetic ultrasonic transducer (EMAT) capable of exciting bidirectional SH0 waves. After continuous optimization, Lorentz-force EMATs are now commercially available. Based on the acoustic field they stimulate, they can be categorized as cylindrical SH0-wave EMATs and bidirectional SH0-wave EMATs. Recently, Alan C. Kubrusly of the Catholic University of Rio de Janeiro, Brazil, and Professor Steve Dixon's research group at the University of Warwick, UK, collaborated to develop an EMAT capable of unidirectionally exciting SH0 waves (Kubrusly AC, Kang L, Dixon S. Unidirectional shear horizontal wave generation with side-shifted periodic permanent magnets electromagnetic acoustic transducer. IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS AND FREQUENCY CONTROL, 2020, 67(12):2757-60.). This transducer is essentially constructed using two bidirectional EMATs in a phased array configuration. Therefore, a more complex circuit is required to generate a time delay, and it can only operate at a fixed frequency. Directional reception cannot be achieved without introducing an additional delay circuit. Linear force can also be generated by piezoelectric materials in thickness shear mode. Li Faxin's research group at Peking University constructed a bidirectional SH0 wave piezoelectric transducer based on two antisymmetrically arranged thickness shear piezoelectric ceramic strips, and on this basis, realized unidirectional excitation of SH0 waves through the phased array principle (Chen MT, Huan Q, Li F X. Aunidirectional SH wave transducer based on phase-controlled antiparallelthickness-shear (d 15) piezoelectric strips. Theoretical and Applied Mechanics Letters, 2020, 10(5):299-306.). However, like the unidirectional EMAT, the unidirectional SHO wave piezoelectric transducer can only operate at a fixed frequency and requires additional delay time.

[0004] Unlike linear force loading, in-plane shear deformation generates SH0 waves in four orthogonal principal directions and Lamb waves in the principal strain direction. Miao Hongchen's research group at Southwest Jiaotong University proposed that using two symmetrical in-plane shear deformations can eliminate SH0 waves in the symmetry axis direction and effectively suppress Lamb waves in the principal strain direction. Based on this principle, Miao Hongchen et al. developed a piezoelectric transducer that can excite SH0 waves in two opposite directions over a wide frequency range (HC Miao, Q. Huan, FX Li, GZ Kang. A variable-frequency bidirectional shear horizontal (SH) wavetransducer based on dual face-shear (d24) piezoelectric wafers. Ultrasonics, 2018, 89, 13–21.). Based on the same principle, the research group of Professor Bernd Köhler at the Fraunhofer Institute for Ceramic Technology and Systems in Germany developed a piezoelectric fiber composite transducer to achieve bidirectional SH0 wave excitation (B. Köhler, Y.Kim, K. Chwelatiuk, K. Tschoke, F. Schubert, L. Schubert. A mode-switchableguided elastic wave transducer. J. Nondestruct. Evaluat. 2020,39). Based on the similarities and differences in the acoustic field generation between in-plane shear piezoelectric transducers and thickness shear transducers, Miao Hongchen's research group recently proposed a piezoelectric transducer that can excite unidirectional SH0 waves in a wide frequency range. However, it still requires an additional time delay and cannot achieve unidirectional reception (JC Cai, H. Zhang, HC Miao. Excitation of unidirectional SH wavewithin a frequency range of 50 kHz by piezoelectric transducers withoutfrequency-dependent time delay. Ultrasonics, 2022,118, 106579.).In-plane shear deformation can also be generated by the Wiedemann effect in magnetostriction. The research groups led by Professor Kwun of the Southwest Research Institute in the United States and Professor Kim of Seoul National University in South Korea have done a lot of work on magnetostrictive SH0 wave transducers. They have also achieved bidirectional SH0 wave excitation (S. Lee, YY Kim, SH Cho. Beam-focused shear-horizontal wave generation in a plate by a circular magnetostrictive patch transducer employing a planar solenoid array. Smart Materials and Structures, 2009, 18, 015009.), but have not yet achieved unidirectional SH0 wave excitation.

[0005] In summary, although a few transducers currently exist that can achieve unidirectional SH0 wave excitation, they all require complex and expensive circuitry to implement time delays, and their effective operating frequency is narrow, preventing unidirectional reception. Therefore, it is necessary to develop new transducers capable of unidirectional SH0 wave excitation. Furthermore, research has shown that the zero-order torsional guided wave (T(0, 1)) in thin-walled circular tubes is equivalent to the SH0 wave in flat plate structures. Therefore, theoretically, a transducer capable of unidirectional SH0 wave excitation and reception can also unidirectionally excite and receive T(0, 1) waves. T(0, 1) waves are the only non-dispersive guided wave mode propagating axially in pipeline structures and hold considerable promise for application in pipeline inspection. Designing and fabricating new transducers capable of unidirectionally exciting and receiving non-dispersive guided waves (SH0 or T(0, 1) waves) over a wide frequency range would greatly advance the application of ultrasonic guided waves in fields such as nondestructive testing and structural health monitoring. Summary of the Invention

[0006] In response to the current lack of transducers capable of unidirectionally exciting and receiving non-dispersive ultrasonic guided waves within a wide frequency range, the present invention proposes a piezoelectric transducer for unidirectionally exciting and receiving non-dispersive ultrasonic guided waves and an implementation method thereof. The non-dispersive ultrasonic guided waves include SH0 waves in a flat plate structure and T(0,1) waves in a pipe structure. They can excite non-dispersive ultrasonic guided waves that propagate in one direction without time delay within a wide frequency range. In addition, the piezoelectric transducer is also unidirectional when used as a sensor to receive non-dispersive ultrasonic guided waves.

[0007] An object of the present invention is to provide a piezoelectric transducer for unidirectionally exciting and receiving non-dispersive ultrasonic guided waves.

[0008] The piezoelectric transducer for unidirectional excitation and reception of non-dispersive ultrasonic guided waves of the present invention comprises m basic units, where m is a natural number ≥ 1; each basic unit comprises two piezoelectric transducer plates, a short-side delay support, a high-side delay support and a substrate for connecting the unit; wherein the shape of the piezoelectric transducer plate is l × w × h The cuboid satisfies h< 0.5 l , the thickness of the cuboid is h , the length is l , with a width of w , the two areas are l × w The upper and lower surfaces are respectively along the length l The direction is the first direction, along the width w The direction of the piezoelectric transducer plate is the second direction; the polarization direction of the piezoelectric transducer plate is along the first direction, and has a thickness shear piezoelectric coefficient d 15 ; The upper surface and lower surface of the piezoelectric transducer plate are respectively used as electrode surfaces, and electrodes are prepared on the electrode surfaces; the short-side delay pillar and the high-side delay pillar are in the shape of a cuboid, and the cross-sectional shape of the cuboid is consistent with the electrode surface of the piezoelectric transducer plate; the lower surfaces of the two piezoelectric transducer plates are respectively pasted on the upper surfaces of the short-side delay pillar and the high-side delay pillar, and the polarization directions of the two piezoelectric transducer plates are opposite; the bottoms of the short-side delay pillar and the high-side delay pillar are connected through the intra-unit connection substrate; the bottoms of the m basic units are connected through the inter-unit connection substrate; each short-side delay pillar, high-side delay pillar, intra-unit connection substrate and inter-unit connection substrate are connected into a whole to form a delay substrate; the electrodes located on the upper and lower surfaces of the 2m piezoelectric transducer plates are respectively electrically connected by a wire, thereby connecting the 2m piezoelectric transducer plates in parallel; in each basic unit, the distance between the short-side delay pillar and the high-side delay pillar is , the height difference is ,satisfy , and ,in, is the wave velocity of the shear-like guided wave generated by the piezoelectric transducer plate in the short-side delay pillar and the high-side delay pillar, is the wave velocity of SH0 wave or T(0,1) wave in the waveguide being measured, f is the vibration frequency of the generated quasi-shear guided wave and SH0 wave or T (0, 1) wave; in each basic unit, the side where the short-side delay pillar is located is the enhancement side, and the side where the high-side delay pillar is located is the weakening side. In each basic unit, the enhancement side and the weakening side are consistent, and the polarization direction of the piezoelectric transducer plate attached to the short-side delay pillar is the same; the spacing between adjacent basic units is , the height difference is ,satisfy ;

[0009] As an actuator or sensor, the piezoelectric transducer can excite SH0 waves and detect the waveguide under test with a flat plate structure, and can also excite T (0, 1) waves and detect the waveguide under test with a pipe structure;

[0010] The waveguide under test has a flat plate structure. A piezoelectric transducer is set on the waveguide under test. The bottom surface of the delay substrate of the piezoelectric transducer is flat:

[0011] When used as an actuator, the electrodes on the upper and lower surfaces are each electrically connected to a single signal source using a wire; the signal source sends an AC signal to simultaneously excite 2m piezoelectric transducer plates, which are then energized by the inverse piezoelectric effect. 15 The mode generates thickness shear deformation, thereby generating quasi-shear guided waves with a set phase difference in the short-side delay pillar and the high-side delay pillar. The quasi-shear guided waves are transmitted to the waveguide under test through the short-side delay pillar and the high-side delay pillar respectively. In a basic unit, the polarization directions of the two piezoelectric transducer plates are opposite, and the shear stresses generated in the short-side delay pillar and the high-side delay pillar are opposite, so the quasi-shear guided waves generated in the short-side delay pillar and the high-side delay pillar have opposite phases. The short-side delay pillar and the high-side delay pillar have a height difference. , which makes the quasi-shear guided wave in the short-side delay pillar reach the waveguide under test before the shear guided wave in the high-side delay pillar. After the quasi-shear guided wave reaches the waveguide under test, it induces the waveguide under test to generate SH0 wave and further propagate to both sides; the time when the SH0 wave caused by the short-side delay pillar is transmitted to one side of the high-side delay pillar, that is, the weakened side, and reaches the bottom of the high-side delay pillar is exactly equal to the time when the quasi-shear guided wave in the high-side delay pillar lags behind the quasi-shear guided wave in the short-side delay pillar, so that the SH0 waves caused by the short-side delay pillar and the high-side delay pillar reach the waveguide under test under the high-side delay pillar at the same time, and the SH0 generated in the waveguide under test induced by the short-side delay pillar and the high-side delay pillar meet, and the phases are opposite. On the contrary, the interference on the high-side delay pillar, i.e. the weakening side, is destructive; and the spacing between the basic units meets the conditions for interference enhancement, so the interference enhancement is achieved for the SH0 wave propagating along the enhanced side, thereby achieving the effect of exciting the unidirectional propagation of the SH0 wave; at the same time, the effect of the quasi-shear guided wave in the low-side delay pillar and the high-side delay pillar on the measured waveguide is equivalent to two anti-parallel tangential distributed forces, so the Lamb waves induced by the two along the shear stress direction will also interfere and destruct due to the symmetry principle, thereby ensuring the purity of the SH0 wave excited by the piezoelectric transducer and propagating only along one main direction of the 360° plane direction, i.e. the enhanced side, thereby achieving the excitation of the SH0 wave propagating in one direction;

[0012] When used as a sensor, when an SH0 wave in the measured waveguide propagates to the piezoelectric transducer, it first causes a shear-like guided wave in the short-side delay pillar and the high-side delay pillar, and then the shear-like guided wave is transmitted to the corresponding piezoelectric transducer plates respectively, causing the piezoelectric transducer plates to produce thickness shear deformation, and the piezoelectric transducer plates generate electrical signals through the positive piezoelectric effect; according to the reciprocity principle of waves, the SH0 wave propagating from the weakening side causes the electrical signals in the two piezoelectric transducer plates to have opposite phases, so the total signal obtained by adding them is weakened by interference, while the SH0 wave propagating from the enhancing side causes the electrical signals in the two piezoelectric transducer plates to have enhanced phases, so the total signal obtained is enhanced by interference, that is, the SH0 wave on the weakening side is filtered out, and only the SH0 wave on the enhancing side is received, thereby realizing one-way reception of the SH0 wave;

[0013] The waveguide under test is a pipe structure. Multiple identical piezoelectric transducers are evenly arranged along the circumference of the pipe to form a circumferential array. The first direction of each piezoelectric transducer is perpendicular to the central axis of the pipe structure, and the second direction is parallel to the central axis of the pipe structure. The short-side delay struts and high-side delay struts of all piezoelectric transducers are located on the same side, and the short-side delay struts, i.e., the enhancement side, face the measured part of the pipe structure. The bottom surface of the delay base of the piezoelectric transducer has the same curvature as the outer surface of the pipe structure:

[0014] When used as an actuator, the electrodes on the upper and lower surfaces of each piezoelectric transducer are electrically connected by a wire, and all piezoelectric transducers are electrically connected in parallel and connected to the same signal source; the signal source sends an AC signal to simultaneously excite all the piezoelectric transducer plates in multiple piezoelectric transducers, and the inverse piezoelectric effect is used to generate the d 15 The mode generates thickness shear deformation, thereby generating quasi-shear guided waves with a set phase difference in the short-side delay pillar and the high-side delay pillar. The quasi-shear guided waves are transmitted radially to the surface of the waveguide to be measured through the short-side delay pillar and the high-side delay pillar respectively, thereby causing circumferentially uniformly distributed shear stress on the surface of the waveguide to be measured; the number of piezoelectric transducers should be able to make the load they apply symmetrically distributed along the axis of the pipeline structure; in the pipeline structure, the only guided wave mode in which the vibration displacement is symmetrically distributed along the circumference is the torsional guided wave mode, so below the cutoff frequency of the first-order torsional guided wave, only a single-mode zero-order torsional guided wave T (0, 1) wave will be excited; in the basic unit of each transducer, the polarization directions of the two piezoelectric transducer plates are opposite, and the quasi-shear guided waves generated in the short-side delay pillar and the high-side delay pillar are opposite in phase, thereby causing circumferential shear stresses with opposite phases on the surface of the pipeline structure; the short-side delay pillar and the high-side delay pillar have a height difference , so that the quasi-shear guided wave in the short-side delay pillar reaches the surface of the measured waveguide before the shear guided wave in the high-side delay pillar. After the quasi-shear guided wave reaches the surface of the measured waveguide, it induces the measured waveguide to generate a zero-order torsional guided wave T (0, 1) and further propagates to both sides in a direction parallel to the central axis; the time when the T (0, 1) wave caused by the short-side delay pillar is transmitted to the side of the high-side delay pillar, that is, the weakened side, and reaches the bottom of the high-side delay pillar is exactly equal to the time when the quasi-shear guided wave in the high-side delay pillar lags behind the quasi-shear guided wave in the short-side delay pillar The time of waveguide guidance is determined by the time delay between the short side delay pillar and the high side delay pillar, so that the T (0, 1) waves caused by the short side delay pillar and the high side delay pillar reach the surface of the waveguide under test below the high side delay pillar at the same time. The T (0, 1) waves induced by the short side delay pillar and the high side delay pillar in the waveguide under test meet each other with opposite phases. Therefore, the interference is canceled on the weakening side of the high side delay pillar. In addition, the spacing between the basic units meets the conditions for interference enhancement. For the T (0, 1) wave propagating along the enhancement side, interference enhancement is achieved, thereby achieving the excitation of the T (0, 1) wave propagating in one direction.

[0015] When used as a sensor, when a T (0, 1) wave in the measured waveguide propagates to the piezoelectric transducer, it first induces shear-like guided waves in the short-side delay pillar and the high-side delay pillar, and then the shear-like guided waves are respectively transmitted to the corresponding piezoelectric transducer plates, causing the piezoelectric transducer plates to produce thickness shear deformation, and the piezoelectric transducer plates generate electrical signals through the positive piezoelectric effect; according to the reciprocity principle of waves, the T (0, 1) wave propagating from the weakening side causes the electrical signals in the two piezoelectric transducer plates to have opposite phases, so the total signal obtained by adding them is weakened by interference, while the T (0, 1) wave propagating from the enhancing side causes the electrical signals in the two piezoelectric transducer plates to have enhanced phases, so the total signal obtained is enhanced by interference, that is, the T (0, 1) wave on the weakening side is filtered out, and only the T (0, 1) wave on the enhancing side is received, thereby realizing unidirectional reception of the T (0, 1) wave.

[0016] The piezoelectric transducer plate is made of piezoelectric material, which is polarized to form the piezoelectric transducer plate. The piezoelectric material can be ferroelectric ceramics, ferroelectric piezoelectric single crystals, or non-ferroelectric piezoelectric single crystals. The piezoelectric material should be able to produce thickness shear deformation under the action of an external electric field. Conversely, when an external force forces the piezoelectric material to produce thickness shear deformation, it should be able to produce electric displacement on the electrode surface, converting mechanical energy into electrical energy. The delay substrate is made of isotropic metal materials such as aluminum and steel, or ceramic materials such as alumina and unpolarized PZT ceramics. When the waveguide surface to be measured is curved, a material with a low elastic modulus and high elasticity, such as rubber, is used.

[0017] The waveguide under test has a flat plate structure, and N identical piezoelectric transducers are arranged on a plane. The bottoms of the delay substrates of adjacent piezoelectric transducers are connected into a whole. The bottoms of the delay substrates of all piezoelectric transducers are located on the same plane, forming a regular N-gon annular array of piezoelectric transducers. Each piezoelectric transducer is located on one side of the regular N-gon. The angle θ between the center lines of adjacent piezoelectric transducers parallel to the second direction is 360° / N. The center lines of the N piezoelectric transducers parallel to the second direction all pass through the center of the regular polygon. The center line of each piezoelectric transducer parallel to the first direction is located on the same regular N. On a corresponding side of the edge, that is, the first direction of each piezoelectric transducer is parallel to a corresponding side of the regular N-gon, and the short-side delay pillars of all piezoelectric transducers are located on the outside, and the high-side delay pillars are located on the inside, and N is a natural number ≥ 3; in the regular polygonal ring array of piezoelectric transducers, each piezoelectric transducer is connected to an independent signal source for independent excitation, or all piezoelectric transducers are connected to the same signal source for overall excitation; when individually excited, one or more piezoelectric transducers in the regular N-gon ring array of piezoelectric transducers are selected to excite, which can achieve acoustic beam deflection similar to a phased array. Similarly, when used as a sensor, it can selectively receive SH0 waves propagating in different directions.

[0018] Piezoelectric transducer plate l Meet 1 mm ~ 50 mm.

[0019] Another object of the present invention is to provide a method for realizing a piezoelectric transducer for unidirectionally exciting and receiving non-dispersive ultrasonic guided waves.

[0020] The method for realizing a piezoelectric transducer for unidirectionally exciting and receiving non-dispersive ultrasonic guided waves of the present invention comprises the following steps:

[0021] 1) Preparation of piezoelectric transducer:

[0022] a) According to the vibration frequency of the quasi-shear guided wave and SH0 wave or T(0,1) wave to be excited, calculate the dispersion curve of the quasi-shear guided wave generated in the short side delay pillar and the high side delay pillar, and design the delay base so that in each basic unit, the distance between the short side delay pillar and the high side delay pillar is and height difference satisfy , and ,in, is the wave velocity of the shear-like guided wave generated by the piezoelectric transducer plate in the short-side delay pillar and the high-side delay pillar, is the wave velocity of SH0 wave or T(0,1) wave in the waveguide being measured, f is the vibration frequency of the generated shear-like guided wave and SH0 wave or T (0, 1) wave; and the spacing between adjacent basic units and height difference satisfy ;

[0023] b) processing delay substrate;

[0024] c) Providing a piezoelectric material for the piezoelectric transducer plate and polarizing the piezoelectric material to have a piezoelectric coefficient d 15 ;

[0025] d) Cut the polarized piezoelectric material into l × w × h The cuboid is used as a piezoelectric transducer plate, where the thickness of the cuboid is h , the length is l , with a width of w , the two areas are l × w The upper and lower surfaces are respectively along the length l The direction is the first direction, along the width w The direction of the piezoelectric transducer plate is along the first direction;

[0026] e) The upper and lower surfaces of the piezoelectric transducer plate serve as electrode surfaces, respectively, and electrodes are prepared on the electrode surfaces, while ensuring that the polarization state of the transducer plate is not changed during the electrode preparation process;

[0027] f) bonding the lower surface of the piezoelectric transducer plate to the time-delay substrate;

[0028] 2) The waveguide under test has a flat plate structure. A piezoelectric transducer is set on the waveguide under test. The bottom surface of the delay substrate of the piezoelectric transducer is flat:

[0029] i as actuator:

[0030] a) The electrodes on the upper and lower surfaces are each electrically connected to a single signal source using a wire;

[0031] b) The signal source sends an AC signal to stimulate 2m piezoelectric transducers at the same time, and the d 15 The mode generates thickness shear deformation, thereby generating quasi-shear guided waves with a set phase difference in the short-side delay pillar and the high-side delay pillar. The quasi-shear guided waves are transmitted to the waveguide under test through the short-side delay pillar and the high-side delay pillar respectively.

[0032] c) In a basic unit, the polarization directions of the two piezoelectric transducer plates are opposite, and the shear stress generated in the short-side delay pillar and the high-side delay pillar are opposite, so the shear-like guided waves generated in the short-side delay pillar and the high-side delay pillar have opposite phases; the short-side delay pillar and the high-side delay pillar have a height difference , so that the quasi-shear guided wave in the short-side delay pillar reaches the waveguide under test before the shear guided wave in the high-side delay pillar. After the quasi-shear guided wave reaches the waveguide under test, it induces the waveguide under test to generate an SH0 wave and further propagate to both sides; the time for the SH0 wave caused by the short-side delay pillar to propagate toward one side of the high-side delay pillar, i.e., the weakening side, to the bottom of the high-side delay pillar is exactly equal to the time that the quasi-shear guided wave in the high-side delay pillar lags behind the quasi-shear guided wave in the short-side delay pillar. Therefore, the SH0 waves caused by the short-side delay pillar and the high-side delay pillar reach the waveguide under test under the high-side delay pillar at the same time, and the SH0s induced by the short-side delay pillar and the high-side delay pillar in the waveguide under test meet, and have opposite phases, so they interfere and cancel each other at the high-side delay pillar, i.e., the weakening side.

[0033] d) The spacing between the basic units satisfies the conditions for interference enhancement, which enables interference enhancement of the SH0 wave propagating along the enhanced side, thereby achieving the effect of stimulating unidirectional propagation of the SH0 wave;

[0034] e) At the same time, the effect of the quasi-shear guided waves in the short-side delay pillar and the high-side delay pillar on the measured waveguide is equivalent to two antiparallel tangential distributed forces. Therefore, the Lamb waves induced by the two along the shear stress direction will also interfere and cancel each other due to the principle of symmetry, thereby ensuring the purity of the SH0 wave excited by the piezoelectric transducer and propagating only along one main direction of the 360° plane, that is, enhancing the side propagation, thereby achieving the excitation of the SH0 wave propagating in one direction;

[0035] ii As a sensor:

[0036] a) When an SH0 wave propagates from the measured waveguide to the piezoelectric transducer, it first induces shear-like guided waves in the short-side delay pillar and the high-side delay pillar. The shear-like guided waves are then transmitted to the corresponding piezoelectric transducer plates, causing thickness shear deformation of the piezoelectric transducer plates. The piezoelectric transducer plates then generate electrical signals through the positive piezoelectric effect.

[0037] b) According to the reciprocity principle of waves, the SH0 wave propagating from the weakening side causes the electrical signals in the two piezoelectric transducer plates to have opposite phases, so the total signal obtained by adding them is weakened by interference. On the other hand, the SH0 wave propagating from the strengthening side causes the electrical signals in the two piezoelectric transducer plates to have enhanced phases, so the total signal obtained is enhanced by interference. That is, the SH0 wave on the weakening side is filtered out, and only the SH0 wave on the strengthening side is received, thus achieving one-way reception of the SH0 wave.

[0038] 3) The waveguide to be measured is a pipe structure. Multiple identical piezoelectric transducers are evenly arranged along the circumference of the pipe to form a circumferential array. The first direction of each piezoelectric transducer is perpendicular to the central axis of the pipe structure, and the second direction is parallel to the central axis of the pipe structure. The short-side delay struts and high-side delay struts of all piezoelectric transducers are located on the same side, and the short-side delay struts, i.e., the enhancement side, face the measured part of the pipe structure. The bottom surface of the delay base of the piezoelectric transducer has the same curvature as the outer surface of the pipe structure:

[0039] i as actuator:

[0040] a) The electrodes on the upper and lower surfaces of each piezoelectric transducer are electrically connected by a wire, and all piezoelectric transducers are electrically connected in parallel and connected to the same signal source;

[0041] b) The signal source sends an AC signal to stimulate all the piezoelectric transducer plates in the multiple piezoelectric transducers at the same time, and the d 15 The mode generates thickness shear deformation, thereby generating quasi-shear guided waves with a set phase difference in the short-side delay pillar and the high-side delay pillar. The quasi-shear guided waves are respectively transmitted radially to the surface of the waveguide under test through the short-side delay pillar and the high-side delay pillar, thereby inducing circumferentially uniformly distributed shear stress on the surface of the waveguide under test.

[0042] c) The number of piezoelectric transducers should be such that the applied load is distributed symmetrically along the axis of the pipeline structure; in the pipeline structure, the only waveguide mode in which the vibration displacement is symmetrically distributed along the circumferential direction is the torsional waveguide mode, so below the cutoff frequency of the first-order torsional waveguide, only a single-mode zero-order torsional waveguide T (0, 1) wave will be excited; in each basic unit of the transducer, the polarization directions of the two piezoelectric transducer plates are opposite, and the shear-like waveguides generated in the short-side delay strut and the high-side delay strut have opposite phases, thus causing circumferential shear stresses with opposite phases on the surface of the pipeline structure; the short-side delay strut and the high-side delay strut have a height difference , so that the quasi-shear guided wave in the short-side delay pillar reaches the surface of the waveguide under test before the shear guided wave in the high-side delay pillar. After the quasi-shear guided wave reaches the surface of the waveguide under test, it induces the waveguide under test to generate a zero-order torsional guided wave T (0, 1) and further propagates to both sides in a direction parallel to the central axis; the time for the T (0, 1) wave caused by the short-side delay pillar to propagate toward one side of the high-side delay pillar, i.e., the weakening side, to the bottom of the high-side delay pillar is exactly equal to the time that the quasi-shear guided wave in the high-side delay pillar lags behind the quasi-shear guided wave in the short-side delay pillar, so that the T (0, 1) waves caused by the short-side delay pillar and the high-side delay pillar reach the surface of the waveguide under test below the high-side delay pillar at the same time, and the T (0, 1) waves induced by the short-side delay pillar and the high-side delay pillar to generate in the waveguide under test meet, and have opposite phases, so they interfere and cancel each other at the high-side delay pillar, i.e., the weakening side;

[0043] d) The spacing between the basic units satisfies the conditions for interference enhancement, which achieves interference enhancement for the T(0, 1) wave propagating along the enhanced side, thereby stimulating the T(0, 1) wave propagating in one direction;

[0044] ii As a sensor:

[0045] a) When a T(0,1) wave propagates from the measured waveguide to the piezoelectric transducer, it first induces shear-like guided waves in the short-side delay pillar and the high-side delay pillar. The shear-like guided waves then propagate to the corresponding piezoelectric transducer plates, causing thickness shear deformation of the piezoelectric transducer plates. The piezoelectric transducer plates then generate electrical signals through the direct piezoelectric effect.

[0046] b) According to the reciprocity principle of root waves, the T (0, 1) wave propagating from the weakening side causes the electrical signals in the two piezoelectric transducer plates to have opposite phases, so the total signal obtained by adding them is weakened by interference. On the other hand, the T (0, 1) wave propagating from the enhancing side causes the electrical signals in the two piezoelectric transducer plates to have enhanced phases, so the total signal obtained is enhanced by interference. That is, the T (0, 1) wave on the weakening side is filtered out, and only the T (0, 1) wave on the enhancing side is received, thus achieving one-way reception of the T (0, 1) wave.

[0047] In step 1) b), the delay substrate is processed by mechanical processing or additive manufacturing; the delay substrate adopts isotropic metal materials such as aluminum, steel, etc.; or ceramic materials such as alumina, unpolarized PZT ceramics, etc.; when the waveguide structure has a large curvature, a material with low elastic modulus and high elasticity, such as rubber, is adopted.

[0048] In step 1) c), the piezoelectric transducer plate is made of piezoelectric material, and the piezoelectric material is polarized to form the piezoelectric transducer plate; the piezoelectric material is made of ferroelectric ceramics or ferroelectric piezoelectric single crystals, or non-ferroelectric piezoelectric single crystals; the piezoelectric material should be able to produce thickness shear deformation under the action of an external electric field, and conversely, when an external force forces the piezoelectric material to produce thickness shear deformation, it should be able to form electric displacement on the electrode surface, that is, convert mechanical energy into electrical energy.

[0049] In step 1) e), the electrode is prepared by ion sputtering or chemical plating.

[0050] In step 1) f), if the delay substrate is made of conductive material, insulation treatment is performed between the lower surface of the piezoelectric transducer plate and the upper surface of the delay substrate to ensure that the electrodes of the piezoelectric transducer plate and the delay substrate are not conductive.

[0051] Advantages of the present invention:

[0052] The piezoelectric transducer of the present invention can, within a frequency range of 20 kHz to 5 MHz for engineering applications, design the spacing and height difference between the short-side delay pillar and the high-side delay pillar according to the vibration frequency of the required shear-like guided wave and SH0 wave or T (0, 1) wave to be excited, excite the SH0 wave or T (0, 1) wave propagating in one direction at the designed vibration frequency, and can serve as a sensor to filter out the SH0 wave or T (0, 1) wave on the weakened side and only receive the SH0 wave or T (0, 1) wave on the enhanced side; in addition, regardless of unidirectional excitation or unidirectional reception, the piezoelectric transducer of the present invention does not require an external circuit or device to provide time delay. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 Schematic diagram of an embodiment of a piezoelectric transducer for unidirectionally exciting and receiving non-dispersive ultrasonic guided waves according to the present invention;

[0054] Figure 2 The experimental results of the first embodiment of the present invention for unidirectional excitation and reception of non-dispersive ultrasonic guided waves as an actuator to excite SH0 waves on a 1 mm thick aluminum plate, where (a) is the in-plane shear d 24 The waveform of the PZT piezoelectric transducer as a sensor on the enhanced side is shown in (b). 24 (c) The waveform received by the PZT piezoelectric transducer as a sensor on the weakened side, and (d) the acoustic field of the transducer obtained by experimental measurement, theoretical prediction and finite element simulation;

[0055] Figure 3 The experimental results of Example 2 of the piezoelectric transducer for unidirectional excitation and reception of non-dispersive ultrasonic guided waves of the present invention used as a sensor to receive SHO waves from different directions, where (a) is the result of the SHO wave measurement from the enhanced side, and (b) is the result of the SHO wave measurement from the weakened side;

[0056] Figure 4 Schematic diagram of the arrangement of a piezoelectric transducer for unidirectionally exciting and receiving non-dispersive ultrasonic guided waves according to a third embodiment of the present invention, wherein (a) is a side view and (b) is a perspective view;

[0057] Figure 5 Schematic diagram of the arrangement of a fourth embodiment of the piezoelectric transducer for unidirectionally exciting and receiving non-dispersive ultrasonic guided waves according to the present invention, wherein (a) is a top view, (b) is a schematic diagram of one of the piezoelectric transducers, and (c) is a schematic diagram during detection;

[0058] Figure 6 Schematic diagram of the arrangement of a fifth embodiment of the piezoelectric transducer for unidirectionally exciting and receiving non-dispersive ultrasonic guided waves according to the present invention, wherein (a) is a side view and (b) is a stereogram. DETAILED DESCRIPTION

[0059] The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings.

[0060] like Figure 1 As shown, the piezoelectric transducer for unidirectional excitation and reception of non-dispersive ultrasonic guided waves in this embodiment includes two basic units; each basic unit includes two piezoelectric transducer plates 10, a short-side delay support 11, a high-side delay support 12 and a substrate for connecting the unit; wherein the shape of the piezoelectric transducer plate is l × w × h The thickness of the cuboid is h , the length is l , with a width of w , the two areas are l × w The upper and lower surfaces are respectively along the length l The direction is the first direction, along the width w The direction of the piezoelectric transducer plate is along the first direction. Figure 1 Where P represents the polarization vector and has a thickness shear piezoelectric coefficient d 15 ; The upper surface and lower surface of the piezoelectric transducer plate are respectively used as electrode surfaces, and electrodes are prepared on the electrode surfaces; the short-side delay pillar and the high-side delay pillar are in the shape of a cuboid, and the cross-sectional shape of the cuboid is consistent with the electrode surface of the piezoelectric transducer plate; the lower surfaces of the two piezoelectric transducer plates are respectively pasted on the upper surfaces of the short-side delay pillar and the high-side delay pillar, and the polarization directions of the two piezoelectric transducer plates are opposite; the bottoms of the short-side delay pillar and the high-side delay pillar are connected through the intra-unit connecting substrate; the bottoms of the two basic units are connected through the inter-unit connecting substrate; each short-side delay pillar, the high-side delay pillar, the intra-unit connecting substrate and the inter-unit connecting substrate are connected into a whole to form a delay substrate; the electrodes located on the upper and lower surfaces of the four piezoelectric transducer plates are respectively electrically connected by a wire, thereby connecting the four piezoelectric transducer plates in parallel; in each basic unit, the distance between the short-side delay pillar and the high-side delay pillar is , the height difference is ,satisfy , and ,in, is the wave velocity of the shear-like guided wave generated by the piezoelectric transducer plate in the short-side delay pillar and the high-side delay pillar, is the wave velocity of SH0 wave in the waveguide under test, f is the vibration frequency of the generated quasi-shear guided wave and SH0 wave; in each basic unit, the side where the short-side delay pillar is located is the enhancement side, and the side where the high-side delay pillar is located is the weakening side. In each basic unit, the enhancement side and the weakening side are consistent; the spacing between adjacent basic units is , the height difference is ,satisfy The spacing between adjacent basic units is the distance between the centers of the two basic units; the height difference between adjacent basic units is the height difference between the high-side delay pillars of the adjacent basic units.

[0061] Example 1

[0062] In this embodiment, the piezoelectric transducer includes a basic unit. The piezoelectric transducer plate is made of PZT-5H ceramics. The design size of each side is l =20 mm, w =2 mm, h =1 mm; the delay base is made of aluminum alloy, the cross-section of the two rectangular strips in the delay base is the same as the size of the transducer plate, and the distance between the short side delay pillar and the high side delay pillar is and height difference 3 mm and 2.7 mm respectively.

[0063] The piezoelectric transducer for unidirectionally exciting and receiving non-dispersive ultrasonic guided waves of this embodiment, as an actuator, includes the following steps:

[0064] 1) Preparation of piezoelectric transducer:

[0065] a) Based on the vibration frequencies of the quasi-shear guided wave and the SH0 wave, calculate the dispersion curves of the quasi-shear guided wave generated in the short-side delay pillar and the high-side delay pillar, and design the delay base, which only includes one basic unit. The spacing between the short-side delay pillar and the high-side delay pillar is and height difference 3 mm and 2.7 mm respectively;

[0066] b) machining the time-delay substrate by CNC machine tools;

[0067] c) providing a PZT-5H ceramic, and polarizing the PZT-5H ceramic, wherein the polarization vector P is along a first direction, so that the PZT-5H ceramic has a piezoelectric coefficient d 15 ;

[0068] d) The poled PZT-5H ceramic is cut into a 20 mm × 2 mm × 1 mm cuboid, with the polarization direction of the piezoelectric transducer plate along the first direction with a length of 20 mm.

[0069] e) The upper and lower surfaces of the piezoelectric transducer plate are used as electrode surfaces, and electrodes are prepared on the electrode surfaces using an ion sputtering apparatus, while ensuring that the polarization state of the transducer plate is not changed during the electrode preparation process;

[0070] f) Using epoxy glue, bond the lower surface of the piezoelectric transducer plate to the time-delay substrate;

[0071] 2) As an actuator:

[0072] a) The electrodes on the upper and lower surfaces are each electrically connected to a single signal source using a wire;

[0073] b) The signal source sends an AC signal to stimulate the two piezoelectric transducer plates at the same time, and the d 15 The mode generates thickness shear deformation, thereby generating quasi-shear guided waves with a set phase difference in the short-side delay pillar and the high-side delay pillar. The quasi-shear guided waves are transmitted to the waveguide under test through the short-side delay pillar and the high-side delay pillar respectively.

[0074] c) In a basic unit, the polarization directions of the two piezoelectric transducer plates are opposite, and the shear stress generated in the short-side delay pillar and the high-side delay pillar are opposite, so the shear-like guided waves generated in the short-side delay pillar and the high-side delay pillar have opposite phases; the short-side delay pillar and the high-side delay pillar have a height difference , so that the quasi-shear guided wave in the short-side delay pillar reaches the waveguide under test before the shear guided wave in the high-side delay pillar. After the quasi-shear guided wave reaches the waveguide under test, it induces the waveguide under test to generate an SH0 wave and further propagate to both sides; the time for the SH0 wave caused by the short-side delay pillar to propagate toward one side of the high-side delay pillar, i.e., the weakening side, to the bottom of the high-side delay pillar is exactly equal to the time that the quasi-shear guided wave in the high-side delay pillar lags behind the quasi-shear guided wave in the short-side delay pillar. Therefore, the SH0 waves caused by the short-side delay pillar and the high-side delay pillar reach the waveguide under test under the high-side delay pillar at the same time, and the SH0s induced by the short-side delay pillar and the high-side delay pillar in the waveguide under test meet, and have opposite phases, so they interfere and cancel each other at the high-side delay pillar, i.e., the weakening side.

[0075] d) At the same time, the effect of the quasi-shear guided waves in the short-side delay pillar and the high-side delay pillar on the waveguide under test is equivalent to two antiparallel tangential distributed forces. Therefore, the Lamb waves induced by the two along the shear stress direction will also interfere and cancel each other due to the principle of symmetry, thereby ensuring the purity of the SHO wave excited by the piezoelectric transducer and propagating only along one main direction of the 360° plane, that is, enhancing the side propagation, thereby achieving the excitation of SHO waves propagating in one direction within a wide frequency range.

[0076] Figure 2 The waveform of the piezoelectric transducer prepared in this embodiment as an actuator is shown in the figure. When the in-plane shear d 24 When the PZT piezoelectric transducer is used as a sensor to receive SH0 waves on the enhanced side, Figure 2 (a) SH0 wave with high signal-to-noise ratio is successfully excited, and the in-plane shear d 24The PZT piezoelectric transducer can excite and receive SHO waves, but the excited SHO waves are along four orthogonal main directions (Li Faxin, Miao Hongchen, Tan Chi. Piezoelectric transducer for exciting and receiving non-dispersive ultrasonic guided waves and its preparation method. Chinese invention patent, patent number: ZL201610213142.5, authorization announcement date: August 10, 2018.). When using in-plane shear d 24 When the PZT piezoelectric transducer is used as a sensor to receive SH0 waves on the weakening side, Figure 2 (b) shows that no SH0 wave is excited. Figure 2 (c) The acoustic field diagram of the SH0 wave excited by the transducer obtained by experimental measurement, theoretical prediction and finite element simulation is further given, and it is found that the energy of the excited SH0 wave is indeed focused on the enhanced side; combined with Figure 2 (a), (b), and (c) show that the experimentally measured ratio of the signal amplitude received on the amplified side to the signal amplitude received on the weakened side is 22 dB, confirming that the piezoelectric transducer of this embodiment is capable of exciting unidirectional SHO waves at 210 kHz. Further experimental results indicate that the piezoelectric transducer of this embodiment, as an actuator, is capable of exciting unidirectional SHO waves in the range of 180 kHz to 250 kHz. This demonstrates that the piezoelectric transducer of the present invention is capable of unidirectionally exciting SHO waves over a wide frequency range, a feature currently unattainable by other conventional transducers without modifying the transducer layout and time delay.

[0077] Example 2

[0078] In this embodiment, the piezoelectric transducer prepared in Example 1 is used as a sensor:

[0079] a) When an SH0 wave propagates from the measured waveguide to the piezoelectric transducer, it first induces shear-like guided waves in the short-side delay pillar and the high-side delay pillar. The shear-like guided waves are then transmitted to the corresponding piezoelectric transducer plates, causing thickness shear deformation of the piezoelectric transducer plates. The piezoelectric transducer plates then generate electrical signals through the positive piezoelectric effect.

[0080] b) According to the reciprocity principle of waves, the SH0 wave propagating from the weakening side causes the electrical signals in the two piezoelectric transducer plates to have opposite phases, so the total signal obtained by adding them is weakened by interference. On the other hand, the SH0 wave propagating from the enhancing side causes the electrical signals in the two piezoelectric transducer plates to have enhanced phases, so the total signal obtained is enhanced by interference. That is, the SH0 wave on the weakening side is filtered out, and only the SH0 wave on the enhancing side is received, thereby realizing one-way reception of the SH0 wave.

[0081] Figure 3 Demonstrates the use of in-plane shear d 24The experimental results show that the piezoelectric transducer is used as an actuator to excite 210 kHz SHO waves from the enhancement side and the weakening side of the piezoelectric transducer respectively, and the piezoelectric transducer prepared in Example 1 is used as a sensor to receive the waves. Figure 3 (a) shows that when the SH0 wave is incident from the enhanced side, the SH0 wave can be detected with a high signal-to-noise ratio. However, when the SH0 wave is incident from the weakened side, it cannot be detected, as shown in Figure 3 (b) Combination Figure 3 (a) and (b) demonstrate that the piezoelectric transducer of the present invention, when used as a sensor, also has directional reception of SHO waves, meaning it can only receive SHO waves from the amplified side. Further experiments show that the piezoelectric transducer of this embodiment can maintain unidirectional reception within a frequency range of 180 kHz to 250 kHz. This demonstrates that the present invention can selectively receive SHO waves across a wide frequency range, significantly reducing interference from echo signals such as boundary reflections on the received signal, and possesses significant application value. Currently, other types of transducers are unable to unidirectionally receive SHO waves across a wide frequency range.

[0082] Example 3

[0083] In this embodiment, it is used to detect rail defects. Figure 4 The detection diagram is given. Figure 4 (a) are symmetrically arranged on both sides of the rail waist, with the bottom surface of the delay base close to the side wall of the rail waist. Each piezoelectric transducer consists of a basic unit. The two piezoelectric transducers are electrically connected in parallel and excited simultaneously by the same signal excitation source, which can excite unidirectional SH0 waves in the rail waist, as shown in Figure 2. Figure 4 As shown in (b), Figure 4 The star symbol in (b) represents a defect. When the SHO wave encounters a defect, the reflected echo is detected by the piezoelectric transducer. Because the piezoelectric transducer of the present invention can only transmit SHO waves in one direction and receive echoes only in the transmitted direction, it can effectively identify rail defects.

[0084] Example 4

[0085] Figure 5 Another embodiment of the piezoelectric transducer of the present invention is given. Twelve piezoelectric transducers are arranged on the plane of the orthogonal anisotropic steel bridge deck, N=12, the angle θ between the center lines of adjacent piezoelectric transducers parallel to the second direction is 360° / 12=30°, the center lines of the N piezoelectric transducers parallel to the second direction all pass through the center of the regular polygon, and the center line of each piezoelectric transducer parallel to the first direction is located on a corresponding side of the same regular N side, that is, the first direction of each piezoelectric transducer is respectively parallel to a corresponding side of the regular N-sided polygon, and the short-side delay pillars of all piezoelectric transducers are located on the outside, and the high-side delay pillars are located on the inside. Each piezoelectric transducer is as follows. Figure 5 (b) It consists of a basic unit, twelve independent piezoelectric transducers Figure 5 (a) Stacked in a circular arrangement, the bottoms of the delay substrates of adjacent piezoelectric transducers are connected as a whole, forming a piezoelectric transducer regular N-gon annular array. In the piezoelectric transducer regular N-gon annular array, each piezoelectric transducer regular N-gon annular array is excited individually. Selective excitation of one or more piezoelectric transducers in the annular array can achieve acoustic beam deflection similar to a phased array. Similarly, when used as a sensor, the piezoelectric transducer regular N-gon annular array can selectively receive SH0 waves propagating in different directions. The piezoelectric transducer regular N-gon annular array can be used to detect or monitor defects in large plate and shell structures. Figure 5 (c) shows the piezoelectric transducer regular N-gon ring array, Figure 5 The star-shaped symbols in (c) represent defects, which means that defects in a large range of orthotropic steel bridge decks can be effectively identified.

[0086] Example 5

[0087] Figure 6 Another embodiment of the piezoelectric transducer of the present invention is given. Figure 6 The method shown in (a) is evenly arranged along the circumference of the pipeline to form a circumferential array. The first direction of each piezoelectric transducer is perpendicular to the central axis of the pipeline structure, and the second direction is parallel to the central axis of the pipeline structure. The short-side delay pillars and high-side delay pillars of all piezoelectric transducers are located on the same side, and the short-side delay pillars, i.e., the enhanced side, face the measured part of the pipeline structure. The bottom surface of the delay substrate of the piezoelectric transducer has the same curvature as the outer surface of the pipeline structure. The number of piezoelectric transducers should be such that the circumferential shear stress caused by the circumferential array in the pipeline structure is axially symmetrically distributed. All piezoelectric transducers are electrically connected in parallel and excited simultaneously under the same signal excitation source, which can excite a unidirectionally propagating zero-order torsional guided wave T (0, 1) in the pipeline, as shown in 6 (b). Figure 6 The star symbol in (b) represents a defect. When the T(0, 1) wave encounters a defect, it is reflected and detected by the circumferential array. Because the circumferential array can only transmit T(0, 1) waves in one direction and receive echoes only in the transmitted direction, it can effectively identify pipeline defects.

[0088] Finally, it should be noted that the purpose of disclosing the embodiments is to facilitate a further understanding of the present invention. However, those skilled in the art will appreciate that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the contents disclosed in the embodiments; the scope of protection claimed by the present invention shall be determined by the scope defined in the claims.

Claims

1. A piezoelectric transducer for unidirectionally exciting and receiving non-dispersive ultrasonic guided waves, characterized in that: The piezoelectric transducer includes m basic units, where m is a natural number ≥ 1; each basic unit includes two piezoelectric transducer plates, a short-side delay pillar, a high-side delay pillar, and a connecting substrate within the unit; wherein the piezoelectric transducer plate is in the shape of a cuboid of l×w×h, satisfying h<0.5l, the thickness of the cuboid is h, the length is l, the width is w, the two surfaces with an area of ​​l×w are the upper surface and the lower surface respectively, the direction along the length l is the first direction, and the direction along the width w is the second direction; the polarization direction of the piezoelectric transducer plate is along the first direction, and has a thickness shear piezoelectric coefficient d 15 ; The upper surface and lower surface of the piezoelectric transducer plate are respectively used as electrode surfaces, and electrodes are prepared on the electrode surfaces; the shape of the short-side delay pillar and the high-side delay pillar is a cuboid, and the cross-sectional shape of the cuboid is consistent with the electrode surface of the piezoelectric transducer plate; the lower surfaces of the two piezoelectric transducer plates are respectively pasted on the upper surfaces of the short-side delay pillar and the high-side delay pillar, and the polarization directions of the two piezoelectric transducer plates are opposite; the bottoms of the short-side delay pillar and the high-side delay pillar are connected through the intra-unit connection substrate; the bottoms of the m basic units are connected through the inter-unit connection substrate; each short-side delay pillar, the high-side delay pillar, the intra-unit connection substrate and the inter-unit connection substrate are connected into a whole to form a delay substrate; the electrodes located on the upper and lower surfaces of the 2m piezoelectric transducer plates are respectively electrically connected by a wire, thereby connecting the 2m piezoelectric transducer plates in parallel; in each basic unit, the spacing between the short-side delay pillar and the high-side delay pillar is Δd, and the height difference is Δh, satisfying Δh / c1=Δd / c2, and Among them, c1 is the wave velocity of the quasi-shear guided wave generated by the piezoelectric transducer plate in the short-side delay pillar and the high-side delay pillar, c2 is the wave velocity of the SH0 wave or T(0,1) wave in the measured waveguide, and f is the vibration frequency of the generated quasi-shear guided wave and SH0 wave or T(0,1) wave; in each basic unit, the side where the short-side delay pillar is located is the enhancement side, and the side where the high-side delay pillar is located is the weakening side. In each basic unit, the enhancement side and the weakening side are consistent, and the polarization direction of the piezoelectric transducer plate attached to the short-side delay pillar is the same; the spacing between adjacent basic units is ΔD, and the height difference is ΔH, satisfying and ΔD ≤ c2 / f; As an actuator or sensor, the piezoelectric transducer can excite SHO waves and detect the waveguide under test with a flat plate structure, and can also excite T(0,1) waves and detect the waveguide under test with a pipe structure.

2. The piezoelectric transducer according to claim 1, wherein The material of the piezoelectric transducer plate is ferroelectric ceramics or ferroelectric piezoelectric single crystal, or non-ferroelectric piezoelectric single crystal.

3. The piezoelectric transducer according to claim 1, wherein The time-delay substrate is made of isotropic metal material or ceramic material.

4. The piezoelectric transducer according to claim 1, wherein N identical piezoelectric transducers are located on the same plane, and each piezoelectric transducer is located on an edge of a regular N-gon, forming a regular N-gon ring array of piezoelectric transducers; in the regular N-gon ring array of piezoelectric transducers, each piezoelectric transducer is connected to an independent signal source for independent excitation, or all piezoelectric transducers are connected to the same signal source for overall excitation; when individually excited, one or more piezoelectric transducers in the regular N-gon ring array of piezoelectric transducers are selected for excitation.

5. A method for realizing a piezoelectric transducer for unidirectionally exciting and receiving non-dispersive ultrasonic guided waves according to claim 1, characterized in that: The implementation method comprises the following steps: 1) Preparation of piezoelectric transducer: a) Based on the vibration frequencies of the quasi-shear guided waves and SH0 waves or T(0,1) waves to be excited, calculate the dispersion curves of the quasi-shear guided waves generated in the short-side delay pillars and the high-side delay pillars, and design the delay base so that in each basic unit, the spacing Δd and the height difference Δh between the short-side delay pillars and the high-side delay pillars satisfy Δh / c1=Δd / c2, and Wherein, c1 is the wave velocity of the quasi-shear guided wave generated by the piezoelectric transducer plate in the short-side delay pillar and the high-side delay pillar, c2 is the wave velocity of the SH0 wave or T(0,1) wave in the measured waveguide, f is the vibration frequency of the generated quasi-shear guided wave and SH0 wave or T(0,1) wave; and the spacing ΔD and height difference ΔH of adjacent basic units satisfy and ΔD ≤ c2 / f; b) processing delay substrate; c) Providing a piezoelectric material for the piezoelectric transducer plate and polarizing the piezoelectric material to have a piezoelectric coefficient d 15 ; d) cutting the polarized piezoelectric material into a l×w×h cuboid to serve as a piezoelectric transducer plate, wherein the cuboid has a thickness of h, a length of l, and a width of w, and two surfaces with an area of ​​l×w are the upper surface and the lower surface, respectively; a direction along the length l is a first direction, and a direction along the width w is a second direction; and the polarization direction of the piezoelectric transducer plate is along the first direction; e) The upper and lower surfaces of the piezoelectric transducer plate serve as electrode surfaces, respectively, and electrodes are prepared on the electrode surfaces, while ensuring that the polarization state of the transducer plate is not changed during the electrode preparation process; f) bonding the lower surface of the piezoelectric transducer plate to the time-delay substrate; 2) The waveguide under test has a flat plate structure. A piezoelectric transducer is set on the waveguide under test, and the bottom surface of the delay substrate of the piezoelectric transducer is flat: i as actuator: a) The electrodes on the upper and lower surfaces are each electrically connected to a single signal source using a wire; b) The signal source sends an AC signal to stimulate 2m piezoelectric transducer plates at the same time, and the d 15 The mode generates thickness shear deformation, thereby generating quasi-shear guided waves with a set phase difference in the short-side delay pillar and the high-side delay pillar. The quasi-shear guided waves are transmitted to the waveguide under test through the short-side delay pillar and the high-side delay pillar respectively. c) Within a basic unit, the polarization directions of the two piezoelectric transducer plates are opposite, and the shear stresses generated in the short-side delay pillar and the high-side delay pillar are opposite, so the quasi-shear guided waves generated in the short-side delay pillar and the high-side delay pillar are in opposite phases; the short-side delay pillar and the high-side delay pillar have a height difference Δh, so that the quasi-shear guided waves in the short-side delay pillar reach the measured waveguide before the shear guided waves in the high-side delay pillar. After reaching the measured waveguide, the quasi-shear guided waves induce the measured waveguide to generate SHO waves and further propagate to both sides; The time it takes for the SH0 wave caused by the short-side delay pillar to propagate toward the side of the high-side delay pillar, i.e., the weakening side, and reach directly below the high-side delay pillar is exactly equal to the time it takes for the quasi-shear guided wave in the high-side delay pillar to lag behind the quasi-shear guided wave in the short-side delay pillar. As a result, the SH0 waves caused by the short-side delay pillar and the high-side delay pillar simultaneously reach the waveguide under test below the high-side delay pillar. The SH0 waves induced by the short-side delay pillar and the high-side delay pillar in the waveguide under test meet, and their phases are opposite. Therefore, they interfere with each other destructively at the high-side delay pillar, i.e., the weakening side. d) The spacing between the basic units satisfies the conditions for interference enhancement, which enables interference enhancement of the SHO wave propagating along the enhanced side, thereby achieving the effect of stimulating unidirectional propagation of the SHO wave; e) At the same time, the effect of the quasi-shear guided waves in the short-side delay pillar and the high-side delay pillar on the measured waveguide is equivalent to two antiparallel tangential distributed forces. Therefore, the Lamb waves induced by the two along the shear stress direction will also interfere and cancel each other due to the principle of symmetry, thereby ensuring the purity of the SHO wave excited by the piezoelectric transducer and propagating only along one main direction in the 360° direction of the plane, that is, enhancing the side propagation, thereby achieving the excitation of the SHO wave propagating in one direction; ii As a sensor: a) When an SHO wave propagates from the measured waveguide to the piezoelectric transducer, it first induces shear-like guided waves in the short-side delay pillar and the high-side delay pillar. The shear-like guided waves are then transmitted to the corresponding piezoelectric transducer plates, causing thickness shear deformation of the piezoelectric transducer plates. The piezoelectric transducer plates then generate electrical signals through the positive piezoelectric effect. b) According to the reciprocity principle of waves, the SHO wave propagating from the weakening side causes the electrical signals in the two piezoelectric transducer plates to have opposite phases, so the total signal obtained by adding them is weakened by interference. On the other hand, the SHO wave propagating from the strengthening side causes the electrical signals in the two piezoelectric transducer plates to have enhanced phases, so the total signal obtained is enhanced by interference. That is, the SHO wave on the weakening side is filtered out, and only the SHO wave on the strengthening side is received, thereby achieving one-way reception of the SHO wave; 3) The waveguide to be measured is a pipe structure. Multiple identical piezoelectric transducers are evenly arranged along the circumference of the pipe to form a circumferential array. The first direction of each piezoelectric transducer is perpendicular to the central axis of the pipe structure, and the second direction is parallel to the central axis of the pipe structure. The short-side delay struts and the high-side delay struts of all piezoelectric transducers are located on the same side, and the short-side delay struts, i.e., the enhancement side, face the measured part of the pipe structure. The bottom surface of the delay base of the piezoelectric transducer has the same curvature as the outer surface of the pipe structure: i as actuator: a) The electrodes on the upper and lower surfaces of each piezoelectric transducer are electrically connected by a wire, and all piezoelectric transducers are electrically connected in parallel and connected to the same signal source; b) The signal source sends an AC signal to stimulate all the piezoelectric transducer plates in multiple piezoelectric transducers at the same time, and the d 15 The mode generates thickness shear deformation, thereby generating quasi-shear guided waves with a set phase difference in the short-side delay pillar and the high-side delay pillar. The quasi-shear guided waves are respectively transmitted radially to the surface of the waveguide under test through the short-side delay pillar and the high-side delay pillar, thereby inducing circumferentially uniformly distributed shear stress on the surface of the waveguide under test. c) The number of piezoelectric transducers should be such that the load applied by them is distributed symmetrically along the axis of the pipeline structure; in the pipeline structure, the only waveguide mode in which the vibration displacement is symmetrically distributed along the circumferential direction is the torsional waveguide mode, so below the cutoff frequency of the first-order torsional waveguide, only a single-mode zero-order torsional waveguide T(0,1) wave will be excited; in the basic unit of each transducer, the polarization directions of the two piezoelectric transducer plates are opposite, and the quasi-shear waveguides generated in the short-side delay pillar and the high-side delay pillar have opposite phases, thereby causing circumferential shear stresses with opposite phases on the surface of the pipeline structure; the short-side delay pillar and the high-side delay pillar have a height difference Δh, so that the quasi-shear waveguide in the short-side delay pillar reaches the surface of the waveguide under test before the shear waveguide in the high-side delay pillar After the quasi-shear guided wave reaches the surface of the waveguide under test, it induces the waveguide under test to generate a zero-order torsional guided wave T(0, 1) and further propagates to both sides in a direction parallel to the central axis; the time for the T(0, 1) wave caused by the short-side delay pillar to propagate toward one side of the high-side delay pillar, i.e., the weakening side, to the bottom of the high-side delay pillar is exactly equal to the time that the quasi-shear guided wave in the high-side delay pillar lags behind the quasi-shear guided wave in the short-side delay pillar, so that the T(0, 1) waves caused by the short-side delay pillar and the high-side delay pillar simultaneously reach the surface of the waveguide under test below the high-side delay pillar, and the T(0, 1) waves induced by the short-side delay pillar and the high-side delay pillar to generate in the waveguide under test meet and have opposite phases, so they interfere and cancel each other at the high-side delay pillar, i.e., the weakening side; d) The spacing between the basic units satisfies the conditions for interference enhancement, thus achieving interference enhancement for the T(0, 1) wave propagating along the enhanced side, thereby achieving the effect of stimulating unidirectional propagation of the T(0, 1) wave; ii As a sensor: a) When a T(0,1) wave propagates from the measured waveguide to the piezoelectric transducer, it first induces shear-like guided waves in the short-side delay pillar and the high-side delay pillar. The shear-like guided waves then propagate to the corresponding piezoelectric transducer plates, causing thickness shear deformation of the piezoelectric transducer plates. The piezoelectric transducer plates then generate electrical signals through the direct piezoelectric effect. b) According to the reciprocity principle of root waves, the T(0, 1) wave propagating from the weakening side causes the electrical signals in the two piezoelectric transducer plates to have opposite phases, so the total signal obtained by adding them is weakened by interference. On the other hand, the T(0, 1) wave propagating from the strengthening side causes the electrical signals in the two piezoelectric transducer plates to have enhanced phases, so the total signal obtained is enhanced by interference. That is, the T(0, 1) wave on the weakening side is filtered out, and only the T(0, 1) wave on the strengthening side is received, thereby achieving one-way reception of the T(0, 1) wave.

6. The implementation method according to claim 5, characterized in that: In step b) of step 1), the time-delay substrate is processed by mechanical processing or additive manufacturing; the time-delay substrate is made of isotropic metal material or ceramic material.

7. The implementation method according to claim 5, characterized in that: In step 1) c), the piezoelectric transducer plate is made of piezoelectric material, which is polarized to form the piezoelectric transducer plate; the piezoelectric material is made of ferroelectric ceramics or ferroelectric piezoelectric single crystal, or non-ferroelectric piezoelectric single crystal.

8. The implementation method according to claim 5, characterized in that: In step e) of step 1), the electrode is prepared by ion sputtering or chemical plating.

9. The implementation method according to claim 5, characterized in that: In step 1) f), if the delay substrate is made of conductive material, insulation treatment is performed between the lower surface of the piezoelectric transducer plate and the upper surface of the delay substrate to ensure that the electrodes of the piezoelectric transducer plate and the delay substrate are not conductive.

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