Omnidirectional SH wave piezoelectric metamaterial transducer

Abstract

The invention discloses an omnidirectional SH wave piezoelectric metamaterial transducer which comprises a torsional mode piezoelectric metamaterial and an electrode. The torsional mode piezoelectric metamaterial comprises at least N structural units, wherein N is an integer not less than 3; the structural unit is of a beam-slab composite structure and comprises a thin plate and a beam located on the surface of the thin plate. The torsional mode piezoelectric metamaterial is of a three-dimensional structure and is of a hollow prism structure formed by sequentially connecting the connecting faces of structural units. In the torsional mode piezoelectric metamaterial, each structural unit is polarized along the direction vertical to the surface of the corresponding thin plate; the electrodes comprise inner electrodes and outer electrodes, the inner electrodes are communicated with each other, and the outer electrodes are communicated with each other. The omnidirectional horizontal shear wave transducer provided by the invention can realize excellent electrically induced torsion response under excitation of a single-channel electric field, so that omnidirectional horizontal shear waves are excited; in addition, the high omnidirectional performance is still kept in a wide frequency range.

Description

Technical Field

[0001] This invention relates to the field of piezoelectric transducers, and more specifically, to an omnidirectional SH wave piezoelectric metamaterial transducer. The invention may also be titled an omnidirectional horizontal shear wave transducer and its applications. Background Technology

[0002] Piezoelectric transducers, with their high electroacoustic conversion efficiency and considerable power capacity, are widely used in various fields, such as sensing, non-destructive testing (NDT), and biomedical engineering. These applications all utilize the multiple electromechanical modes inherent in piezoelectric materials. However, natural piezoelectric ceramics possess only five non-zero piezoelectric coefficients (dp). 31 ,d 32 ,d 33 ,d 15 ,d 24 This greatly limits the design and application of piezoelectric devices. Specifically, in the field of nondestructive testing, tensile vibration modes (d...) 31 d 33 Shear modes are often used to excite Lamb waves; unfortunately, these waves exhibit multimodal and dispersive propagation characteristics, making signal analysis and defect identification more complex. In contrast, shear modes (d... 15 d 24 This can excite dispersion-free horizontal shear waves (SH waves), and these waves exhibit extremely low mode transitions, thus generating clearer signals. Furthermore, planar shear modes (d...) realized in piezoelectric single crystals and piezoelectric ceramics... 36 This can solve the depolarization problem caused by the misalignment of the electric field and polarization direction.

[0003] The horizontal shear waves (SH waves) generated by the aforementioned piezoelectric transducers exhibit strong directionality; therefore, a large number of transducers are typically required to cover the entire monitoring area. To overcome this limitation, researchers have developed various omnidirectional horizontal shear wave (SH wave) transducers. Initially, several transducers based on the magnetostrictive effect and Lorentz force were proposed and subsequently applied. However, due to their large size and high power requirements, these transducers have not achieved widespread adoption. In contrast, piezoelectric transducers offer advantages such as light weight and high energy conversion efficiency, making them highly suitable for non-destructive testing (NDT) and structural health monitoring (SHM). Therefore, researchers have developed all-SH wave piezoelectric transducers (OSH-PTs) by arranging piezoelectric ceramic units of different shapes into a ring array and utilizing their different shear modes. For example, using d... 15 The sector primitive of the thickness shear mode, and the use of d 15 d 24 d 36 Trapezoidal or triangular primitives for surface shear modes.

[0004] Chinese Patent Document 1 (Application No.: 201210125086.1, Application Date: 2012.04.25) discloses an omnidirectional SH guided wave electromagnetic ultrasonic transducer, including an annular iron-nickel alloy strip with an opening, a folded coil attached to one side of the alloy strip, and the end of the folded coil located at the opening of the alloy strip; in the radial direction, the spatial period of the folded coil 1 is 1.5 to 4.5, with a step size of 0.5 spatial periods between two adjacent conductors. Chinese Patent Document 2 (Application No.: 201410329406.4, Application Date: 2014.07.07) discloses an omnidirectional horizontal shear waveguide transducer based on the piezoelectric principle, including multiple piezoelectric sensitive elements and a temporary adhesive tape substrate. The multiple piezoelectric sensitive elements are arranged in a ring to form an axisymmetric sensor array. The lower surface of the sensor array is pre-attached to the temporary adhesive tape substrate to fix the shape of the sensor array and ensure that the generated waveform is continuous and uniform around the transducer. Each individual piezoelectric sensitive element has two electrodes. A wire is used to connect the positive electrodes of all piezoelectric sensitive elements in series, and another wire is used to connect the negative electrodes in series. The piezoelectric sensitive elements are cut from a relaxor ferroelectric single crystal material at a certain angle, so that their d... 36 The piezoelectric coefficient is not zero, meaning that applying an electric field along its thickness will cause shear deformation in the plane. This shear deformation is used to excite and detect horizontal shear guided waves. However, the above omnidirectional SH-wave transducers still suffer from complex manufacturing and assembly processes.

[0005] Compared to shear-mode-based arrays, torsional-mode devices can generate omnidirectional shear deformation. To date, researchers have developed various piezoelectric devices with torsional modes, such as 45° interdigitated electrode (IDE) beams, helical torsional actuators, dual concentric ring actuators with tension-to-torsion conversion capabilities, and segmented polarized torsional tubes. Furthermore, piezoelectric metamaterials based on piezoelectric element sequences and three-phase lattice structures can achieve full electromechanical modes, but their application still faces challenges, mainly due to the need for complex polarization circuits and multi-channel actuation.

[0006] Therefore, there is an urgent need to provide a torsional mode piezoelectric metamaterial transducer for omnidirectional SH waves that is simple to fabricate and does not require complex polarization circuits and multi-channel driving, which can be applied to large structures or large-scale non-destructive testing. Summary of the Invention

[0007] In view of this, the present invention provides an integrated design of a piezoelectric metamaterial structure that can be directly fabricated in 3D, for achieving an electro-torsional effect and serving as an omnidirectional SH wave piezoelectric metamaterial transducer. SH wave stands for horizontal shear wave.

[0008] The first aspect of this application provides an omnidirectional horizontal shear wave transducer, comprising:

[0009] A piezoelectric metamaterial in torsion mode consisting of at least N structural units, where N is an integer not less than 3;

[0010] The structural unit is a beam-slab composite structure, comprising a thin plate and beams located on the surface of the thin plate. The thin plate is rectangular, comprising an upper and lower end face parallel to the horizontal direction, and a front, left, rear, and right end face perpendicular to the horizontal direction and connected in sequence. The front, left, rear, and right end faces are respectively connected to the upper and lower end faces. The front and rear end faces are parallel to each other, and the left and right end faces are parallel to each other. The upper and / or the lower end face are... The horizontal extension length of the lower end face is equal to the width of the rectangular sheet; the extension length of the front end face and / or the rear end face in a first direction is equal to the length of the long side of the rectangular sheet, wherein the first direction is perpendicular to the upper end face and / or the lower end face; the extension length of the left end face and / or the right end face in a second direction is equal to the thickness of the rectangular sheet, wherein the second direction is perpendicular to the front end face and / or the rear end face; the beam is located on the front end face or the rear end face, and the left end face and / or the right end face are connecting surfaces;

[0011] The beam is located at the diagonal of the front or rear face of the thin plate; the angle between the beam and the long side of the thin plate is 15° to 75°.

[0012] The omnidirectional horizontal shear wave transducer has a three-dimensional structure, consisting of a hollow prism structure formed by the sequential connection surfaces of the structural units, wherein the beam is located on the outer surface of the hollow prism structure.

[0013] The omnidirectional horizontal shear wave transducer further includes electrodes, which include inner electrodes and outer electrodes. The inner electrodes are interconnected, and the outer electrodes are interconnected. The inner electrodes are located on the front end face or the rear end face within the cavity of the hollow prism structure, and the outer electrodes are located on the first side face of the beam, wherein the first side face is parallel to the front end face or the rear end face.

[0014] In the omnidirectional horizontal shear wave transducer, each structural unit is polarized along a direction perpendicular to the corresponding front end face or rear end face, including:

[0015] Each of the structural units is polarized in a vertically inward direction, wherein the vertically inward direction of each structural unit is a direction perpendicular to each of the front end face or the rear end face, pointing from the outer surface of the hollow prism structure to the inner surface of the hollow prism structure;

[0016] Alternatively, in the horizontal shear wave transducer, each of the structural units is polarized in a vertically outward direction, wherein the vertically outward direction of each structural unit is a direction perpendicular to each of the front end face or the rear end face, pointing from the inner surface of the hollow prism structure to the outer surface of the hollow prism structure.

[0017] In the omnidirectional horizontal shear wave transducer, the thickness of the thin plate in each structural unit is consistent;

[0018] In the omnidirectional horizontal shear wave transducer, the aspect ratio of the thin plate in each structural unit is constant.

[0019] Optionally, the base material of the piezoelectric metamaterial is at least one of piezoelectric ceramics and piezoelectric single crystals.

[0020] Optionally, the electrode is at least one of a silver electrode, a copper electrode, and a gold electrode.

[0021] Optionally, when the thin plate is square, the inclination angle of the beam is 45°;

[0022] When the thin plate is a non-square rectangle, the inclination angle of the beam is greater than or equal to 15° and less than 45°, or greater than 45° and less than or equal to 75°.

[0023] A second aspect of this application provides an application of the above-described omnidirectional horizontal shear wave transducer in structural health monitoring, non-destructive testing, and ultrasonic guided waves.

[0024] Compared with the prior art, the omnidirectional horizontal shear wave transducer provided by the present invention achieves at least the following beneficial effects:

[0025] The omnidirectional horizontal shear wave transducer proposed in this invention is a piezoelectric metamaterial transducer based on the coordination of electric field-induced deformation between a beam and a plate. By extending a single beam-plate unit into a hollow prism structure through chiral rotation, this transducer achieves superior electro-torsional response; furthermore, it maintains strong omnidirectional performance over a wide frequency range. This piezoelectric metamaterial transducer can be integrally fabricated using 3D printing, offering simplicity in terms of manufacturing process and drive circuitry.

[0026] Of course, any product implementing this invention does not necessarily need to achieve all of the technical effects described above at the same time.

[0027] Other features and advantages of the invention will become clear from the following detailed description of exemplary embodiments of the invention with reference to the accompanying drawings. Attached Figure Description

[0028] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments of the invention and, together with their description, serve to explain the principles of the invention.

[0029] Figure 1 In the figure, (a) shows the design route of the structural unit in this embodiment, (b) shows the structural schematic diagram of the sheet metamaterial and the direction of the internal electric field during polarization, (c) shows the schematic diagram of the sheet metamaterial → three-dimensional expansion (taking a quadrangular prism as an example), and (d) shows the schematic diagram of the three-dimensional structure (torsional deformation).

[0030] Figure 2 In the figure, (a)-(b) show the parameter analysis of the sheet-like piezoelectric metamaterial; (c)-(f) show the schematic diagram of the three-dimensional extended piezoelectric metamaterial structure with different side numbers; (g) shows the schematic diagram of the electro-torsional properties of three-dimensional metamaterials with different side numbers under the condition of fixed plate thickness; (h) shows the schematic diagram of the electro-torsional properties of three-dimensional metamaterials with different side numbers under the condition of fixed aspect ratio; (i)-(j) are the analysis diagram of the influence of different beam heights and beam widths on the performance.

[0031] Figure 3 These are electrical response analysis diagrams of sheet-like metamaterials obtained from finite element simulations at frequencies of 1kHz, 10kHz, 30kHz, 60kHz, 80kHz, and 100kHz.

[0032] Figure 4 Figures (a)-(d) show the displacement field of an omnidirectional horizontal shear wave transducer excited in an aluminum plate using finite element simulation. Figure (a) shows the shear displacement; (b) shows the radial displacement; (c) shows the normal displacement; (d) shows the total displacement; (e) shows the time-domain signal of the tangential displacement collected by the omnidirectional horizontal shear wave transducer at different angle receiving points; and (f) shows the SH wave excited by a sheet-like metamaterial in an aluminum plate under the same conditions.

[0033] Figure 5 In the figure, (a) shows the electrode positions of the sheet-like metamaterial; (b) shows the position of the outer electrode in the omnidirectional horizontal shear wave transducer; and (c) shows the position of the inner electrode in the omnidirectional horizontal shear wave transducer.

[0034] Figure 6 The sintering curve (time-temperature) during the fabrication of the omnidirectional horizontal shear wave transducer in this embodiment is shown.

[0035] Figure 7 In the figure, (a) is a schematic diagram of the experimental setup for measuring the omnidirectional horizontal shear wave transducer in this embodiment; (b) is the experimental result of the tangential displacement of the omnidirectional horizontal shear wave transducer excited in the aluminum plate under a center frequency of 50 kHz. Detailed Implementation

[0036] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention.

[0037] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the invention or its application or use.

[0038] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.

[0039] In all the examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0040] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures.

[0041] This embodiment provides an omnidirectional horizontal shear wave transducer, including a torsional mode piezoelectric metamaterial and electrodes; the torsional mode piezoelectric metamaterial includes at least N structural units, where N is an integer not less than 3;

[0042] The structural unit is a beam-slab composite structure, comprising a thin plate and beams located on the surface of the thin plate. The beam-slab composite structure is made of piezoelectric metamaterial. The thin plate is rectangular, comprising a top and bottom surface parallel to the horizontal direction, and a front, left, rear, and right surface perpendicular to the horizontal direction and connected sequentially. The front, left, rear, and right surfaces are connected to the top and bottom surfaces, respectively. The front and rear surfaces are parallel to each other, and the left and right surfaces are parallel to each other. The upper and / or lower end faces extend horizontally for the width of the rectangular sheet; the front and / or rear end faces extend in a first direction for the length of the long side of the rectangular sheet, wherein the first direction is perpendicular to the upper and / or lower end faces; the left and / or right end faces extend in a second direction for the thickness of the rectangular sheet, wherein the second direction is perpendicular to the front and / or rear end faces; the beam is located on the front or rear end face, and the left and / or right end faces are connecting surfaces;

[0043] The beam is located at the diagonal of the front or rear face of the thin plate; the angle between the beam and the long side of the thin plate is 15° to 75°.

[0044] The omnidirectional horizontal shear wave transducer has a three-dimensional structure, consisting of a hollow prism structure composed of connecting surfaces of structural units connected in sequence, wherein the beam is located on the outer surface of the hollow prism structure.

[0045] The omnidirectional horizontal shear wave transducer also includes electrodes, which include inner electrodes and outer electrodes. The inner electrodes are interconnected, and the outer electrodes are interconnected. The inner electrodes are located on the front or rear face of the hollow prism structure, and the outer electrodes are located on the first side face of the beam, wherein the first side face is parallel to the front or rear face.

[0046] In an omnidirectional horizontal shear wave transducer, each structural unit is polarized along a direction perpendicular to its corresponding front or rear face, including:

[0047] Each structural unit is polarized in a vertical inward direction, wherein the vertical inward direction of each structural unit is a direction perpendicular to each front or rear face, pointing from the outer surface of the hollow prism structure to the inner surface of the hollow prism structure.

[0048] Alternatively, in a horizontal shear wave transducer, each structural unit is polarized in a vertically outward direction, wherein the vertically outward direction of each structural unit is a direction perpendicular to each front or rear face, pointing from the inner surface of the hollow prism structure to the outer surface of the hollow prism structure.

[0049] In an omnidirectional horizontal shear wave transducer, the thickness of the thin plates in each structural unit is consistent;

[0050] In an omnidirectional horizontal shear wave transducer, the aspect ratio of the thin plate in each structural unit is constant.

[0051] It should be noted that in this embodiment, the omnidirectional SH wave transducer (TPMT) uses a beam-plate composite structure as the basic structural unit, which is extended into a hollow prism structure through chiral rotation. Under electric field excitation, the beams and plates in each unit will generate different tensile displacements due to their different polarization directions. It is this difference in tensile displacement that triggers deformation coordination: under the constraint of the plate, the beams undergo bending deformation, which in turn drives the entire metamaterial to undergo torsional deformation. This mechanical behavior has been verified by finite element analysis and experimental results. Experiments on SH wave excitation in aluminum plates show that the proposed TPMT can generate SH waves with uniform amplitude in all directions. In addition, the TPMT also has stable operating performance, structural integration, and ease of assembly. These advantages together make it a novel solution for non-destructive testing (NDT) and structural health monitoring (SHM) of large engineering structures.

[0052] Specifically, the omnidirectional SH wave transducer in this application is a three-dimensional structure, and therefore requires at least three structural units, i.e., N≥3. When N=3, the omnidirectional SH wave transducer is a triangular prism structure; when N=4, the omnidirectional SH wave transducer is a quadrangular prism structure; when N=6, the omnidirectional SH wave transducer is a hexagonal prism structure; and when N is infinitely large, the omnidirectional SH wave transducer is close to a cylindrical structure.

[0053] It should be noted that the design route of this application is as follows: Figure 1 As shown in Figure (a), the basic structural unit of the sheet metamaterial consists of a thin plate in the middle and antisymmetric beams (intersecting each other) on both sides. The entire structure is uniformly polarized along the y-direction, which only indicates the direction perpendicular to the thin plate in the structural unit. In the three-dimensional structure, the polarization direction of each side (i.e. each structural unit) is perpendicular to the surface of the thin plate of that structural unit.

[0054] It should be noted that the principle of the torsional mode piezoelectric metamaterial in this application is achieved through the deformation coordination between beams and thin plates with different polarization states (i.e., different polarization directions) under the action of an electric field. For example... Figure 5 As shown in (a), the electrodes are arranged only on the surface perpendicular to the polarization direction of the beam; the blue area in the figure represents the electrode positions. Figure 1 As shown in Figure (b), this electrode arrangement induces an in-plane electric field within the thin plate, with the direction of the electric field pointing from the diagonal of the top beam to the diagonal of the bottom beam.

[0055] When an electric field is applied along the polarization direction, the deformation of the beam in the x and z directions is mainly determined by d. 31 The deformation of the thin plate in these two directions is mainly determined by d. 33 Dominant. Due to the prevalence of d in most piezoelectric ceramics 31 With d 33 Since the signs are opposite, the beam and the thin plate will deform in opposite directions under the action of the electric field. Under the constraint of the thin plate, the beams on both sides undergo bending deformation, which in turn causes the thin plate in the middle to produce an overall electro-torsional effect.

[0056] To balance torsional stability with practical assembly requirements, basic units consisting of individual beams and thin plates were extended through chiral rotation to construct a three-dimensional torsional piezoelectric metamaterial, the structure of which is as follows: Figure 1 As shown in Figure (c), the polarization direction of each element in this three-dimensional structure is consistent with that of the two-dimensional metamaterial element. Electrodes are arranged on the outer surface of the beam and the inner surface of the plate connected to the beam (one electrode is required on the inner and outer sides of each side, such as...). Figure 5 As shown in (a), the blue area represents the electrode location. Under the influence of an applied electric field, each unit undergoes torsional deformation, and these units are connected end-to-end and work together to give the entire three-dimensional metamaterial the appearance of... Figure 1 The overall torsional deformation effect is shown in (d).

[0057] It should be noted that, as Figure 1 As shown in Figure (c), the inclination angle of the beams remains consistent in each structural unit.

[0058] The specific electrode placement includes the outer surface of the beam and the entire inner surface of the plate connected to the beam.

[0059] For sheet-like piezoelectric metamaterials within structural units, the tilt angle of the beam is a key factor influencing the electric field distribution within the thin plate, thus significantly affecting its electro-torsional properties. Finite element analysis (FEM) simulations showed that the metamaterial exhibited electro-torsional properties across beam tilt angles ranging from 15° to 75°. Specifically, at a tilt angle of 45°, the thin plate was square; at other angles, the plate was rectangular (excluding squares). The FEM results indicate that the metamaterial exhibits optimal electro-torsional properties when the beam tilt angle is 45° and the thin plate is square.

[0060] Further parameter analysis was conducted using a 5mm thin plate width as the baseline dimension, and the results are as follows: Figure 2 As shown, (a)-(b) are parameter analyses of sheet-like piezoelectric metamaterials; (c)-(f) are schematic diagrams of three-dimensional extended piezoelectric metamaterial structures with different numbers of sides; (g) is a schematic diagram of the electro-torsional properties of three-dimensional metamaterials with different numbers of sides under a fixed plate thickness; (h) is a schematic diagram of the electro-torsional properties of three-dimensional metamaterials with different numbers of sides under a fixed aspect ratio; and (i)-(j) are analysis diagrams of the influence of different beam heights and beam widths on performance.

[0061] like Figure 2 As shown in Figures (a) and (b), the thickness of the sheet plays a dominant role in the electro-torsional properties: with increasing thickness (see Figures (a) and (b)), the electro-torsional properties increase. Figure 2 In Figures (i) and (j), the torsion angle gradually decreases. This is because the torsional deformation of the metamaterial depends on the bending deformation generated by the beam-driven thin plate. Increasing the thickness of the thin plate will increase its bending stiffness, thereby suppressing the overall torsion. The influence of beam height and beam width on performance is similar. As beam height and beam width increase (see Figures (i) and (j)), the torsion angle gradually decreases. Figure 2 In Figures (i) and (j), the torsion angle first increases and then decreases. Considering both electro-torsional properties and structural strength, a beam height of 0.25 mm, a beam width of 0.75 mm, and a sheet thickness of 0.8 mm were ultimately selected as the sample preparation parameters and applied to subsequent experiments. Finite element analysis was performed on the electrical response of the sheet-like metamaterial at frequencies of 1 kHz, 10 kHz, 30 kHz, 60 kHz, 80 kHz, and 100 kHz, such as... Figure 3As shown, the sheet-like metamaterials exhibit electro-torsional properties under excitation frequencies of at least 1–100 kHz. That is, the finite element analysis results confirm that under these parameters, the sheet-like piezoelectric metamaterials exhibit stable electro-torsional properties over a wide frequency range. It should be noted that the plate width, plate thickness, beam height, and beam width selected in this embodiment are only baseline dimensions and can be scaled up or down according to actual needs.

[0062] It should be noted that the subsequent finite element analysis of the three-dimensional omnidirectional horizontal shear wave transducer was performed at frequencies of 30 kHz between 50 kHz, 70 kHz, and 90 kHz-210 kHz.

[0063] In this application, two principles are followed when extending the two-dimensional structure to three dimensions: first, maintaining a consistent plate thickness in structures with different numbers of sides; and second, maintaining a constant aspect ratio for each structural element. The electrotorsional behavior of metamaterials with different numbers of sides under the two extension methods is systematically compared using the finite element method (FEM). Figure 2 Figures (c)-(f) illustrate the structural schematics based on the second principle. To accurately assess torsional performance, the tangential displacements at all corner points were calculated in the simulation, and their arithmetic mean was then used as the equivalent torsional angle of the three-dimensional metamaterial.

[0064]

[0065] Among them, u k Let r be the tangential displacement of the k-th corner point, and r be the distance from the corner point to the center of torsion. k / r can be approximated as the torsion angle, and this formula averages the torsion angles of k corner points.

[0066] When the number of extended sides is large, the structure can be approximated as a cylinder, such as... Figure 2 As shown in Figure (f). Figure 2 Figure (g) illustrates the electro-torsional properties of metamaterials with different numbers of sides when expanded according to the first principle, showing that the quadrangular prism structure performs optimally. Further, based on the second principle, the influence of the aspect ratio of the structural unit on the performance was analyzed, such as... Figure 2 As shown in Figure (h), the results indicate that the hexagonal prism exhibits the largest torsion angle at smaller aspect ratios. As the aspect ratio increases, the torsion angle first increases and then decreases, with relatively small overall fluctuations. The octagonal prism structure performs the worst, showing almost no torsional deformation at larger aspect ratios. The quadrangular prism structure, however, shows the best performance with a continuously increasing aspect ratio, reaching its optimal value above 0.75 and stabilizing around 1.4. Therefore, the quadrangular prism was ultimately chosen as the extended configuration for the three-dimensional piezoelectric metamaterial.

[0067] Therefore, using an overall width of 5 mm and an aspect ratio of 1.4 as the baseline dimensions, parametric analysis was performed on the three-dimensional piezoelectric metamaterial, and the results are as follows: Figure 2As shown in Figures (i) and (j), since only the outer beam structure of the plate is retained in the 3D extension, and the electrodes are covered on the entire outer surface of the plate and grounded, the influence of the plate thickness on the torsion angle is significantly reduced. Based on the finite element results, the plate thickness of 0.8 mm and the beam height of 0.3 mm were finally determined as the preparation parameters for the 3D sample.

[0068] In some optional embodiments provided by this invention, the base material of the piezoelectric metamaterial is at least one of piezoelectric materials such as piezoelectric ceramics and piezoelectric single crystals. In this embodiment, barium titanate (BTO) piezoelectric ceramic is used as the base material. In actual applications, there are no specific requirements for the piezoelectric metamaterial.

[0069] In some optional embodiments provided by the present invention, the electrode is at least one of the electrode materials such as silver electrode, copper electrode, and gold electrode; in this embodiment, the electrode is a silver electrode.

[0070] In some optional embodiments provided by the present invention, when the thin plate is square, the inclination angle of the beam is 45°;

[0071] When the thin plate is a non-square rectangle, the inclination angle of the beam is 15 to 75°, excluding 45°.

[0072] In this application, COMSOL Multiphysics finite element software was used to simulate and analyze the SH wave modes and omnidirectional performance excited by the proposed omnidirectional horizontal shear wave transducer (cylindrical metamaterial) and sheet metamaterial in an aluminum plate. The waveguide in the simulation was an aluminum plate with dimensions of 400mm × 400mm × 1mm. The material parameters of the waveguide were: Young's modulus 69 GPa, Poisson's ratio 0.33, and density 2700 kg / m³. 3 A sheet-like metamaterial was simulated by bonding it to the center of an aluminum plate using a thin layer of material. The metamaterial itself was made of PZT-5H piezoelectric ceramic (d 31 = -274pC / N,d 33 =593pC / N). Considering structural symmetry, a displacement sampling point was set every 10° within a range of 0° to 90° around the omnidirectional horizontal shear wave transducer (columnar metamaterial) and the sheet metamaterial. The excitation signal was a five-cycle sine wave modulated by a Hanning window, with a center frequency set at 65kHz, consistent with the torsional resonance frequency of the metamaterial of this size, and a driving voltage of 400V.

[0073] Figure 4The total displacement field in the aluminum plate at 69.4 μs and the distribution of its components in cylindrical coordinates are shown. Figures (a)-(d) represent the displacement field excited by the TPMT in the aluminum plate using finite element simulation. Figure (a) shows the shear displacement, which is the target mode of this application; (b) shows the radial displacement; (c) shows the normal displacement; (d) shows the total displacement; (e) shows the time-domain signal of the tangential displacement collected by the omnidirectional horizontal shear wave transducer (cylindrical metamaterial) at different angle receiving points; (f) shows the SH wave excited in the aluminum plate under the same conditions using a sheet metamaterial. Figures (a)-(d) illustrate that the tangential displacement is dominant, achieving the objective of this application. The tangential displacement represents the SHO wave component, while the radial and out-of-plane displacements reflect the S0 and A0 wave components, respectively. Figure 4 As can be seen in Figure (a), the tangential displacement exhibits a completely axisymmetric circular distribution, indicating that the excited SHO wave has a high degree of omnidirectionality. Figure 4 Figure (b) and Figure 4(c) show that although there are radial and out-of-plane displacements with certain omnidirectional characteristics, their amplitudes are much lower than those of the tangential displacements. Combined with... Figure 4 As shown in Figure (d), the total displacement distribution indicates that the SH0 wave dominates the overall fluctuation. These results demonstrate that the designed transducer can excite a high-purity omnidirectional SH0 wave, while the amplitudes of the generated S0 and A0 modes are small and negligible in practical applications.

[0074] To further verify the omnidirectional performance of the SHO wave, Figure 4 Figure (e) shows the time-domain signals of tangential displacement collected at different angle receiving points of the omnidirectional horizontal shear wave transducer (cylindrical metamaterial). It can be seen that all the signals at the measuring points exhibit a five-cycle sinusoidal waveform modulated by a Hanning window, consistent with the excitation signal, and all signals within the range of 0° to 90° completely overlap, fully demonstrating that the excited SHO wave has perfect omnidirectional consistency during propagation. Figure (f) shows the SHO wave excited in an aluminum plate under the same conditions of sheet metamaterial; it can be seen that... Figure 4 Compared to Figure (e) (results of columnar metamaterials), there is no omnidirectionality.

[0075] Example 1

[0076] like Figure 5 As shown, the omnidirectional horizontal shear wave transducer provided in this embodiment has a hollow quadrangular prism structure, including four polarized structural units; the four structural units are connected in sequence to form a hollow quadrangular prism structure; the structural units are as follows: Figure 1As shown in Figure c, this is a beam-plate composite structure. The structural unit includes a thin plate and a beam located on the surface of the thin plate. The material of the beam-plate composite structure is a piezoelectric metamaterial, specifically BTO piezoelectric ceramic. The thin plate is square in shape, wherein the length of the upper / lower end face extending horizontally is the width, and the length of the end face perpendicular to the upper / lower end face (including the front end face, left end face, rear end face, and right end face) extending vertically is the length of the thin plate. The length of the left / right end face extending perpendicular to the front / rear end face is the thickness of the thin plate. The beam is located on the front or rear end face, and the end face and / or the right end face are the connecting surfaces.

[0077] The thickness of the plates in each structural unit is uniform, all being 0.8 mm. In the omnidirectional horizontal shear wave transducer, the aspect ratio of the plates in each structural unit is constant, all being 1.4, with an overall width of 5 mm and a beam height of 0.3 mm. The beams are located at the diagonal of the square surface, i.e., at an angle of 45° with the sides of the square; the inclination angles and directions of the beams on the four sides are consistent.

[0078] like Figure 5 As shown, the beam is located on the outer surface of the hollow quadrangular prism structure.

[0079] The omnidirectional horizontal shear wave transducer also includes electrodes, which are silver electrodes, comprising inner and outer electrodes, such as... Figure 1 As shown in Figure (c); the inner electrodes are interconnected, and the outer electrodes are interconnected; the inner electrodes are located on the front or rear face of the cavity within the hollow prism structure, i.e. Figure 5 The blue area shown in Figure (c) indicates that the external electrode is located on the first side of the beam, where the first side is parallel to the front or rear face, as shown in Figure (c). Figure 5 The blue area shown in Figure (b);

[0080] In an omnidirectional horizontal shear wave transducer, each structural unit is polarized in a direction perpendicular to the front or rear face of the structural unit. Specifically, in an omnidirectional horizontal shear wave transducer, each structural unit is polarized in a vertical outward direction, wherein the vertical outward direction of each structural unit is a direction perpendicular to each front or rear face, pointing from the inner surface of the hollow prism structure to the outer surface of the hollow prism structure.

[0081] The above-mentioned method for fabricating an omnidirectional horizontal shear wave transducer includes:

[0082] S1. Sample using a 3D-printed omnidirectional horizontal shear wave transducer;

[0083] S2. The omnidirectional horizontal shear wave transducer sample was sintered. Details of the sintering temperature and time changes are provided below. Figure 6 , to obtain sintered samples;

[0084] S1. The sintered sample was polarized using a Bailibo OBP series oil bath polarizer. The oil bath polarization was used with a boost time of 600s, a polarization time of 3600s, and a polarization voltage of 2.5kV / mm to obtain an omnidirectional horizontal shear wave transducer.

[0085] Under electric field excitation, the beams and plates in each unit will produce different tensile displacements due to different polarization directions. The different polarization directions specifically refer to the different polarization directions of each side, which are perpendicular to each side and directed inward / outward (either simultaneously inward or simultaneously outward). In this embodiment, since the theoretical beam thickness is 0.3 mm, the plate thickness is 0.8 mm, the shrinkage rate after sintering is 29%, and the actual total thickness is 0.781 mm, a voltage of 2.5 kV / mm, i.e., 1950 V, is selected for polarization.

[0086] To evaluate the actual performance of the designed three-dimensional piezoelectric metamaterial as an omnidirectional SH-wave transducer, experimental tests were conducted on the omnidirectional SH-wave transducer obtained in Example 1. The experimental setup was basically the same as the finite element simulation setup, such as... Figure 7 As shown in Figure (a), an aluminum plate with dimensions of 1000mm × 1000mm × 1mm was used as the waveguide medium, and the transducer was attached to the center of the aluminum plate. On a circle 360mm away from the transducer, d-shaped elements were arranged at 15° intervals within a range of 0° to 90°. 24 The PZT sensor is used to receive SH wave signals. The excitation signal is a five-cycle sine wave modulated by a Hanning window, generated by a function generator (Tektronix, AFG31000), amplified by a power amplifier (ATA-304C), and then drives the transducer. The received signal is acquired and recorded using an oscilloscope (Tektronix, TBS2000B).

[0087] First, the transducer's performance was evaluated near its resonant frequency. Due to differences in experimental constraints (such as the aluminum plate bonding method) and clamping conditions during previous independent metamaterial tests, the actual resonant frequency deviated slightly. Therefore, 50kHz and 70kHz were selected as the center frequencies for excitation, and the driving voltage was set to 80V. Figure 7 Figure (b) shows the electrical signal waveforms acquired by seven receivers at a frequency of 50 kHz. It can be seen that the proposed transducer successfully excites the SHO guided wave mode with a high signal-to-noise ratio. The signal waveforms from each receiver are consistent and have a high degree of overlap, with a peak amplitude deviation of 2.94%, indicating that the excited SH wave has good omnidirectional consistency, high overlap at the wave packet displacement, and a high signal-to-noise ratio.

[0088] Example 2

[0089] The omnidirectional SH wave transducer obtained in Example 1 can excite omnidirectional SH waves in an aluminum plate. Due to its omnidirectional nature, it can reduce the number of transducers required in large structures or large-scale non-destructive testing; specifically, it can be applied to structural health monitoring, non-destructive testing (NDT), and ultrasonic guided waves.

[0090] As can be seen from the above embodiments, the omnidirectional horizontal shear wave transducer provided by the present invention achieves at least the following beneficial effects:

[0091] The omnidirectional horizontal shear wave transducer proposed in this invention is a piezoelectric metamaterial transducer (TPMT) based on the coordination of electric field-induced deformation between beams and plates. By extending a single beam-plate unit into a quadrangular prism structure through chiral rotation, this transducer achieves superior electro-torsional response; furthermore, it maintains strong omnidirectional performance over a wide frequency range. This piezoelectric metamaterial transducer (TPMT) can be integrally fabricated using 3D printing, offering simplicity in terms of manufacturing process and drive circuitry.

[0092] While specific embodiments of the invention have been described in detail by way of examples, those skilled in the art should understand that the examples are for illustrative purposes only and not intended to limit the scope of the invention. Those skilled in the art should understand that modifications can be made to the above embodiments without departing from the scope and spirit of the invention. The scope of the invention is defined by the appended claims.

Claims

1. An omnidirectional horizontal shear wave transducer, characterized in that, include: A piezoelectric metamaterial in torsion mode consisting of at least N structural units, where N is an integer not less than 3; The structural unit is a beam-slab composite structure, comprising a thin plate and beams located on the surface of the thin plate. The thin plate is rectangular, comprising an upper and lower end face parallel to the horizontal direction, and a front, left, rear, and right end face perpendicular to the horizontal direction and connected in sequence. The front, left, rear, and right end faces are respectively connected to the upper and lower end faces. The front and rear end faces are parallel to each other, and the left and right end faces are parallel to each other. The upper and / or the lower end face are... The horizontal extension length of the lower end face is equal to the width of the rectangular sheet; the extension length of the front end face and / or the rear end face in a first direction is equal to the length of the long side of the rectangular sheet, wherein the first direction is perpendicular to the upper end face and / or the lower end face; the extension length of the left end face and / or the right end face in a second direction is equal to the thickness of the rectangular sheet, wherein the second direction is perpendicular to the front end face and / or the rear end face; the beam is located on the front end face or the rear end face, and the left end face and / or the right end face are connecting surfaces; The beam is located at the diagonal of the front or rear face of the thin plate; the angle between the beam and the long side of the thin plate is 15° to 75°. The omnidirectional horizontal shear wave transducer has a three-dimensional structure, consisting of a hollow prism structure formed by the sequential connection surfaces of the structural units, wherein the beam is located on the outer surface of the hollow prism structure. The omnidirectional horizontal shear wave transducer further includes electrodes, which include inner electrodes and outer electrodes. The inner electrodes are interconnected, and the outer electrodes are interconnected. The inner electrodes are located on the front end face or the rear end face within the cavity of the hollow prism structure, and the outer electrodes are located on the first side face of the beam, wherein the first side face is parallel to the front end face or the rear end face. In the omnidirectional horizontal shear wave transducer, each structural unit is polarized along a direction perpendicular to the corresponding front end face or rear end face, including: Each of the structural units is polarized in a vertically inward direction, wherein the vertically inward direction of each structural unit is a direction perpendicular to each of the front end face or the rear end face, pointing from the outer surface of the hollow prism structure to the inner surface of the hollow prism structure; Alternatively, in the horizontal shear wave transducer, each of the structural units is polarized in a vertically outward direction, wherein the vertically outward direction of each structural unit is a direction perpendicular to each of the front end face or the rear end face, pointing from the inner surface of the hollow prism structure to the outer surface of the hollow prism structure. In the omnidirectional horizontal shear wave transducer, the thickness of the thin plate in each structural unit is consistent; In the omnidirectional horizontal shear wave transducer, the aspect ratio of the thin plate in each structural unit is constant.

2. The omnidirectional horizontal shear wave transducer according to claim 1, characterized in that, The matrix material of the piezoelectric metamaterial is at least one of piezoelectric ceramics and piezoelectric single crystals.

3. The omnidirectional horizontal shear wave transducer according to claim 1, characterized in that, The electrode is at least one of a silver electrode, a copper electrode, and a gold electrode.

4. The omnidirectional horizontal shear wave transducer according to claim 1, characterized in that, When the thin plate is square, the inclination angle of the beam is 45°; When the thin plate is a non-square rectangle, the inclination angle of the beam is greater than or equal to 15° and less than 45°, or greater than 45° and less than or equal to 75°.

5. The application of an omnidirectional horizontal shear wave transducer according to any one of claims 1 to 4 in structural health monitoring, non-destructive testing, and ultrasonic guided waves.

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