Air coupling broadband transducer based on double piezoelectric patches
By using a dual piezoelectric sheet structure and a variable thickness matching layer in the air-coupled broadband transducer, an ultrasonic signal containing fundamental waves and second harmonics is excitated, and the backing effect is achieved through the matching circuit, the problem of insufficient bandwidth and acoustic energy conversion efficiency of the existing transducer is solved, and the bandwidth and efficiency are significantly improved.
Patent Information
- Application Number
- CN202510359082.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-25
- Publication Date
- 2025-04-29
AI Technical Summary
Existing air-coupled broadband transducers have shortcomings in bandwidth and acoustic energy conversion efficiency, especially in application scenarios where high sensitivity and high resolution are required, and the acoustic signal cannot be effectively captured and converted.
Using a dual piezoelectric sheet structure, an ultrasonic signal containing fundamental waves and second harmonics is excitated through a non-consistent layer-thick double-layer piezoelectric structure, and acoustic impedance matching is achieved in a wide band range with a variable thickness matching layer, and the backing effect is achieved through a matching circuit.
The bandwidth and acoustic energy conversion efficiency of the transducer are significantly improved, breaking through the theoretical bandwidth upper limit of existing null-coupled transducers, so that the transducer can effectively receive and transmit ultrasonic signals within a wider frequency band range.
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Figure CN119897264A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of acoustic transducers, and in particular to an air-coupled broadband transducer based on dual piezoelectric sheets. Background Art
[0002] Air-coupled ultrasonic nondestructive testing technology has the characteristics of non-contact, non-invasive, and completely non-destructive. It can be used for in-situ testing and has a good application prospect. Air-coupled broadband transducers are widely used in large-scale infrastructure, rail transit, food safety, new composite materials, medical imaging and new energy, medical imaging and non-destructive testing.
[0003] At present, both at home and abroad, the bandwidth of the transducer is mainly improved from the perspective of matching layers and piezoelectric sheets. From the perspective of matching layers, a multi-matching layer design can be used to improve the bandwidth of the transducer. Although the multi-layer matching design can improve the relative bandwidth of the air-coupled transducer, the more matching layers there are, the more difficult it is to achieve, and the expected effect is often not achieved. From the perspective of piezoelectric sheets, the introduction of 1-3 type PMN-PT piezoelectric single crystal composite materials to make transducers can also improve the relative bandwidth. Although the above two methods can improve the bandwidth of the transducer to a certain extent, there is still a theoretical upper limit to the bandwidth. That is, due to the physical characteristics of thickness vibration, peaks can only be generated at the fundamental and other odd harmonic frequencies, and even harmonics are suppressed. Therefore, there is a clear theoretical bandwidth upper limit for the excited ultrasonic signal. Using a double-layer ferroelectric single crystal with non-uniform layer thickness can generate peaks at both odd and even harmonic frequencies. Due to the characteristics of the air-coupled transducer without backing and the large difference in peak-to-valley values between different resonance peaks, the frequency response of the transducer cannot be connected, which limits the transducer from obtaining a larger bandwidth signal.
[0004] The single piezoelectric transducer in the prior art has deficiencies in broadband performance and acoustic energy conversion efficiency, especially in application scenarios requiring high sensitivity and high resolution, and cannot effectively capture and convert acoustic wave signals. Summary of the invention
[0005] In view of this, it is necessary to provide an air-coupled broadband transducer based on a dual piezoelectric patch to solve the problem of how to improve the bandwidth and acoustic energy conversion efficiency of the transducer.
[0006] In order to solve the above problems, the present invention provides an air-coupled broadband transducer based on a dual piezoelectric patch, comprising: Variable thickness matching layer, front piezoelectric sheet, rear piezoelectric sheet, housing, rear cover, interface and matching circuit; The rear piezoelectric sheet, the front piezoelectric sheet and the variable thickness matching layer are arranged in the housing; The rear cover plate is fixedly connected to the end of the shell and forms a hollow cylindrical structure with the shell; the interface is fixedly arranged on the rear cover plate; the interface is used to receive ultrasonic signals; The negative electrode of the rear piezoelectric sheet is bonded to the negative electrode of the front piezoelectric sheet; The positive electrode of the front piezoelectric sheet and the circular surface through which the variable thickness matching layer passes are sequentially bonded; The positive electrode of the front piezoelectric sheet and the positive electrode of the rear piezoelectric sheet are connected by a wire; The thickness of the rear piezoelectric sheet and the front piezoelectric sheet are different; The positive electrode of the front piezoelectric sheet is connected to the positive electrode of the rear piezoelectric sheet, and the negative electrode of the front piezoelectric sheet is connected to the negative electrode of the rear piezoelectric sheet; The front piezoelectric sheet and the rear piezoelectric sheet are connected to the output end of the matching circuit through a wire; and the input end of the matching circuit is connected to the interface through a wire.
[0007] In a possible implementation manner, the variable thickness matching layer is in the shape of a cylinder; and the top surface of the cylinder is a concave spherical surface.
[0008] In a possible implementation, the thickness of the variable thickness matching layer ranges from 0.7 mm to 1.5 mm.
[0009] In a possible implementation manner, the rear piezoelectric sheet, the front piezoelectric sheet, and the variable thickness matching layer are sequentially bonded by epoxy resin glue.
[0010] In a possible implementation, the rear piezoelectric sheet and the front piezoelectric sheet are bonded together by pressing.
[0011] In a possible implementation manner, the matching circuit is a second-order L-type circuit.
[0012] In a possible implementation manner, the diameters of the variable thickness matching layer, the front piezoelectric sheet, and the rear piezoelectric sheet are the same.
[0013] In a possible implementation manner, the variable thickness matching layer, the front piezoelectric sheet, and the rear piezoelectric sheet are coaxially arranged.
[0014] In a possible implementation, the front piezoelectric sheet and the rear piezoelectric sheet are both made of 1-3 type piezoelectric composite materials.
[0015] In a possible implementation, the variable thickness matching layer is made of an epoxy glass bead composite material.
[0016] The beneficial effects of the present invention are as follows: the air-coupled broadband transducer based on dual piezoelectric sheets provided by the present invention, by adopting rear piezoelectric sheets and front piezoelectric sheets with different layer thicknesses, can excite an ultrasonic signal containing both the fundamental wave and the second harmonic using a dual-layer piezoelectric structure with non-uniform layer thickness, thereby generating a higher bandwidth. In combination with a variable thickness matching layer, acoustic impedance matching can be achieved within a sufficiently wide frequency band, and the signal containing odd and even harmonics generated by the dual-layer piezoelectric structure can be converted into a broadband signal that can be transmitted and received into an air medium. A backing effect can be achieved through a matching circuit, thereby breaking through the theoretical bandwidth upper limit of existing air-coupled transducers, significantly improving the bandwidth, and thus improving the acoustic energy conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS
[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.
[0018] Figure 1 A cross-sectional view of an embodiment of an air-coupled broadband transducer based on a dual piezoelectric patch provided by the present invention; Figure 2 A schematic diagram of an embodiment of a method for bonding a piezoelectric sheet provided by the present invention; Figure 3 A front view of an embodiment of a variable thickness matching layer provided by the present invention; Figure 4 A schematic diagram of an embodiment of a method for preparing a variable thickness matching layer provided by the present invention; Figure 5 A schematic diagram of the structure of an embodiment of the circuit model provided by the present invention; Reference numerals: 1: variable thickness matching layer; 2: front piezoelectric sheet; 3: rear piezoelectric sheet; 4: housing; 5: rear cover; 6: interface; 7: matching circuit; 8: wire. DETAILED DESCRIPTION
[0019] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.
[0020] In the description of the embodiments of the present invention, unless otherwise specified, "multiple" means two or more than two. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, "A and / or B" may mean: A exists alone, A and B exist at the same time, and B exists alone.
[0021] The descriptions of "first", "second", etc. involved in the embodiments of the present invention are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the technical features defined as "first" or "second" may explicitly or implicitly include at least one of the features.
[0022] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.
[0023] Figure 1 A cross-sectional view of an embodiment of an air-coupled broadband transducer based on a dual piezoelectric patch provided by the present invention, as shown in FIG. Figure 1 As shown, the air-coupled broadband transducer based on dual piezoelectric patches includes: Variable thickness matching layer 1, front piezoelectric sheet 2, rear piezoelectric sheet 3, housing 4, rear cover plate 5, interface 6 and matching circuit 7; The rear piezoelectric sheet 3, the front piezoelectric sheet 2 and the variable thickness matching layer 1 are arranged in the housing 4; The rear cover plate 5 is fixedly connected to the end of the housing 4 to form a hollow cylindrical structure with the housing 4; the interface 6 is fixedly arranged on the rear cover plate 5; the interface 6 is used to receive ultrasonic signals; The negative electrode of the rear piezoelectric sheet 3 is bonded to the negative electrode of the front piezoelectric sheet 2; The positive electrode of the front piezoelectric sheet 2 is bonded to the circular surface of the variable thickness matching layer 1; The positive electrode of the front piezoelectric sheet 2 and the positive electrode of the rear piezoelectric sheet 3 are connected by a wire; The thickness of the rear piezoelectric sheet 3 and the front piezoelectric sheet 2 are different; The front piezoelectric sheet 2 and the rear piezoelectric sheet 3 are connected to the output end of the matching circuit 7 via a wire 8; the input end of the matching circuit 7 is connected to the interface 6 via a wire.
[0024] like Figure 1As shown, the rear piezoelectric sheet, the front piezoelectric sheet and the variable thickness matching layer are arranged in the transducer housing in sequence along the ultrasonic signal emission direction. The rear cover plate covers the end of the housing and is fixedly connected to the end of the housing to form a hollow cylindrical structure with the housing. The interface is fixed to the housing through the rear cover plate, and the interface is a universal interface for receiving ultrasonic signals.
[0025] The thickness of the rear piezoelectric sheet is different from that of the front piezoelectric sheet. The front piezoelectric sheet and the rear piezoelectric sheet are a double-layer piezoelectric structure, which is a structure in which the piezoelectric sheets are mechanically connected in series and connected in parallel in the circuit. The positive electrode of the front piezoelectric sheet is connected to the positive electrode of the rear piezoelectric sheet, and the negative electrode of the front piezoelectric sheet is connected to the negative electrode of the rear piezoelectric sheet, forming a structure in which the circuit is connected in parallel. That is, the rear piezoelectric sheet and the front piezoelectric sheet are mechanically connected in series and connected in parallel in the circuit.
[0026] The negative electrode of the rear piezoelectric sheet is directly attached to the negative electrode of the front piezoelectric sheet, the positive electrode of the front piezoelectric sheet is attached to the circular surface of the variable thickness matching layer, and the positive electrode of the front piezoelectric sheet is connected to the positive electrode of the rear piezoelectric sheet through a wire.
[0027] By using a double-layer piezoelectric structure with non-uniform layer thicknesses for the rear piezoelectric sheet and the front piezoelectric sheet, an ultrasonic signal containing both the fundamental wave and the second harmonic can be excited to produce a higher bandwidth.
[0028] The variable thickness matching layer is a matching layer with uneven thickness. By combining the variable thickness matching layer, acoustic impedance matching can be achieved within a sufficiently wide frequency band, and the signal containing odd and even harmonics generated by the double-layer piezoelectric structure can be converted into a broadband signal that can be transmitted and received into the air medium.
[0029] The front piezoelectric sheet and the rear piezoelectric sheet are connected through a matching circuit and an interface using wires led out from the electrodes, that is, the front piezoelectric sheet and the rear piezoelectric sheet are connected through wires and the output end of the matching circuit, and an opening can be set in the center of the rear cover plate to allow the wire to pass through, so that the input end of the matching circuit is connected to the interface through the wire. Through the impedance matching network, the backing effect can be achieved, the problem of air-coupled transducers without backing is solved, the theoretical bandwidth upper limit of existing air-coupled transducers is broken through, and the bandwidth is significantly improved.
[0030] The air-coupled broadband transducer based on dual piezoelectric sheets provided in an embodiment of the present invention can stimulate an ultrasonic signal containing both the fundamental wave and the second harmonic by using a dual-layer piezoelectric structure with non-uniform layer thicknesses, thereby generating a higher bandwidth. In combination with a variable thickness matching layer, acoustic impedance matching can be achieved within a sufficiently wide frequency band, and the signal containing odd and even harmonics generated by the dual-layer piezoelectric structure can be converted into a broadband signal that can be transmitted and received into an air medium. A backing effect can be achieved through a matching circuit, thereby breaking through the theoretical bandwidth upper limit of existing air-coupled transducers, significantly improving the bandwidth, and thus improving the efficiency of sound energy conversion.
[0031] In some embodiments of the present invention, the rear piezoelectric sheet 3, the front piezoelectric sheet 2 and the variable thickness matching layer 1 are sequentially bonded by epoxy resin glue.
[0032] In some embodiments of the present invention, the rear piezoelectric sheet 3 and the front piezoelectric sheet 2 are bonded together by pressing.
[0033] By using a double-layer piezoelectric structure with non-uniform layer thickness, an ultrasonic signal containing both fundamental wave and second harmonic can be excited. The double-layer piezoelectric structure is a structure in which piezoelectric sheets are mechanically connected in series and electrically connected in parallel.
[0034] Figure 2 A schematic diagram of an embodiment of a method for bonding a piezoelectric sheet provided by the present invention is shown in FIG. Figure 2 As shown, metal electrodes are plated on the positive and negative surfaces of the two piezoelectric sheets, the negative electrodes of the two piezoelectric sheets are in contact with each other, and the negative electrodes of the piezoelectric sheets are led out with conductive tape.
[0035] It must be strictly ensured that there is no air gap between the two piezoelectric sheets to avoid affecting the vibration transmission between the front and rear piezoelectric sheets. Therefore, a threaded pressing mechanism is used to press the front and rear piezoelectric sheets bonded with epoxy resin glue together with appropriate external force (excessive pressure will cause damage to the piezoelectric sheets) to ensure that there is no gap between the two piezoelectric sheets, forming a mechanical series connection, with negative electrodes connected to negative electrodes and positive electrodes connected to positive electrodes to form a parallel connection structure in the circuit.
[0036] When the thickness of each layer in a double-layer piezoelectric structure is inconsistent, under the action of the inverse piezoelectric effect, the mechanical output of the piezoelectric sheet produces peaks at both odd and even harmonic frequencies, thereby overcoming the characteristic of the thickness-molded piezoelectric air-coupled transducer that the even harmonics are suppressed, and breaking through the upper bandwidth limit of the transducer. For a double-layer piezoelectric structure, the piezoelectric sheet material is preferably a 1-3 type piezoelectric composite material with an acoustic impedance of 15MRayl.
[0037] In some embodiments of the present invention, the diameters of the variable thickness matching layer 1 , the front piezoelectric sheet 2 , and the rear piezoelectric sheet 3 are the same.
[0038] In some embodiments of the present invention, the variable thickness matching layer 1, the front piezoelectric sheet 2 and the rear piezoelectric sheet 3 are coaxially arranged.
[0039] In some embodiments of the present invention, the materials of the front piezoelectric sheet 2 and the rear piezoelectric sheet 3 are both 1-3 type piezoelectric composite materials.
[0040] The following is an example of a novel broadband transducer with a double-layer piezoelectric structure having non-uniform layer thicknesses and center frequencies of 1 MHz and 500 kHz, and a variable thickness matching layer.
[0041] For example, the thickness b1 of the front piezoelectric sheet is 2 mm, and the diameter d1 is 30 mm. The thickness of the front piezoelectric sheet is half the wavelength, which is calculated by formula (1).
[0042] (1) in, is the wavelength, c is the speed of sound, and f is the center frequency of the piezoelectric patch.
[0043] The diameter d2 of the rear piezoelectric sheet is 30 mm, and the thickness b2 is 4 mm, which are calculated according to formula (1).
[0044] The air-coupled broadband transducer based on dual piezoelectric sheets provided in an embodiment of the present invention uses a dual-layer piezoelectric structure with non-uniform layer thickness to stimulate an ultrasonic signal that contains both the fundamental wave and the second harmonic, thereby generating a higher bandwidth. When the thickness of each layer in the dual-layer piezoelectric structure is inconsistent, under the action of the inverse piezoelectric effect, the mechanical output of the piezoelectric sheet produces peaks at both odd and even harmonic frequencies, thereby overcoming the characteristic of the thickness-molded piezoelectric air-coupled transducer that the even harmonics are suppressed, thereby breaking through the bandwidth upper limit of the transducer.
[0045] In some embodiments of the present invention, the variable thickness matching layer 1 is in the shape of a cylinder; and the top surface of the cylinder is a concave spherical surface.
[0046] In some embodiments of the present invention, the thickness of the variable thickness matching layer 1 ranges from 0.7 mm to 1.5 mm.
[0047] In some embodiments of the present invention, the variable thickness matching layer 1 is made of epoxy glass microbead composite material.
[0048] For the variable thickness matching layer, the acoustic impedance is between the piezoelectric material and the air, which can improve the matching between the piezoelectric material and the air medium and increase the sensitivity. The best matching material acoustic impedance is determined by formula (2), where Z1 is the matching layer acoustic impedance, Z0 is the piezoelectric material acoustic impedance, and Z2 is the air acoustic impedance. Therefore, the matching layer material is selected to be epoxy glass microbead composite material.
[0049] (2) The thickness of the matching layer changes evenly from the minimum thickness (i.e., the center of the matching layer) to the maximum thickness (i.e., the edge of the matching layer), and the maximum and minimum thicknesses are set according to a quarter wavelength corresponding to the center frequencies of 500kHz and 1MHz, respectively.
[0050] Take the maximum thickness The minimum thickness is 1.5mm is 0.7 mm, and h is calculated according to formula (3), where is the wavelength, c is the speed of sound, and f is the center frequency of the piezoelectric patch.
[0051] (3) For the transition between the two thicknesses, a concave spherical surface is used. Figure 3 A front view of an embodiment of a variable thickness matching layer provided by the present invention.
[0052] The concave spherical surface forming method uses a sphere with a radius of R to hit the upper surface of a cylinder with a diameter of d to form a concave spherical surface. Figure 4 A schematic diagram of an embodiment of a method for preparing a variable thickness matching layer provided by the present invention is shown in FIG. Figure 4 As shown, the radius R can be determined by Figure 4 Calculated.
[0053] Similarly, epoxy resin glue is used as an adhesive to bond the variable thickness matching layer in front of the double-layer piezoelectric structure, such as Figure 3 As shown. Then, conventional plastic shells and rear covers are used to encapsulate the bonded variable thickness matching layer, front piezoelectric sheet, rear piezoelectric sheet and other parts. The lead wires of the piezoelectric sheet electrodes are connected to the interface through the rear cover, and the interface is a universal interface.
[0054] The air-coupled broadband transducer based on dual piezoelectric sheets provided in an embodiment of the present invention can improve the matching between the piezoelectric material and the air medium through a variable thickness matching layer, thereby increasing the sensitivity, and can achieve acoustic impedance matching within a sufficiently wide frequency band, thereby converting the signal containing odd and even harmonics generated by the dual-layer piezoelectric structure into a broadband signal that can be transmitted and received into the air medium.
[0055] In some embodiments of the present invention, the matching circuit 7 is a second-order L-type circuit.
[0056] Optionally, in order to solve the problem of the air-coupled transducer having no backing, an impedance matching circuit is introduced in an embodiment of the present invention, which is added between the excitation source and the transducer to convert the transducer into a simple circuit model.
[0057] Figure 5 A schematic diagram of the structure of an embodiment of the circuit model provided by the present invention, the matching circuit and the transducer circuit model are as follows Figure 5 As shown, in order to make the transducer have a better bandwidth, a two-order simple L-type circuit is used to achieve a lower Q value to match a wider frequency excitation signal.
[0058] Here is a set of capacitance and inductance data for a matching circuit: L1=27.296μH, L2=18.3μH, C1=1.6637nF, C2=0.887nF.
[0059] The air-coupled broadband transducer based on a dual piezoelectric patch provided in an embodiment of the present invention converts the transducer into a simple circuit model by introducing a matching circuit between the excitation source and the transducer. A two-order simple L-type circuit is used to enable the transducer to have a better bandwidth to achieve a lower Q value to match a wider frequency excitation signal.
[0060] That is, the embodiment of the present invention provides a broadband air-coupled ultrasonic transducer based on a dual piezoelectric film with non-uniform layer thickness and a variable thickness matching layer structure, which is composed of a front piezoelectric film, a rear piezoelectric film, a housing, a rear cover, a variable thickness matching layer, a second-order electrical impedance matching network and an interface. The best material selected for the two piezoelectric films is a 1-3 type piezoelectric composite material. The interface is a universal interface, which is connected to the lead wires of the piezoelectric films. The matching layer material is an epoxy glass bead composite material. The variable thickness matching layer, the front piezoelectric film, the rear piezoelectric film, and each part are sequentially bonded with epoxy resin glue and encapsulated with a plastic housing. Compared with conventional ultrasonic detection technology, the air-coupled ultrasonic detection technology does not require the use of coupling agents, which greatly broadens the scope of application. By using a double-layer piezoelectric structure with non-uniform layer thickness, an ultrasonic signal containing both the fundamental wave and the second harmonic is stimulated to produce a higher bandwidth. Combined with a variable thickness matching layer, acoustic impedance matching can be achieved within a sufficiently wide frequency band, and the signal containing odd and even harmonics generated by the double-layer piezoelectric structure is converted into a broadband signal that can be transmitted and received into the air medium. Through an electrical impedance matching network, the backing effect is achieved, solving the problem of air-coupled transducers without backing, breaking through the theoretical bandwidth upper limit of existing air-coupled transducers, and significantly improving the bandwidth.
[0061] Those skilled in the art will appreciate that all or part of the processes of the above-mentioned embodiments can be implemented by instructing related hardware (such as a processor, a controller, etc.) through a computer program, and the computer program can be stored in a computer-readable storage medium, wherein the computer-readable storage medium is a disk, an optical disk, a read-only storage memory, or a random access memory, etc.
[0062] The above is a detailed introduction to the air-coupled broadband transducer based on dual piezoelectric plates provided by the present invention. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as a limitation on the present invention.
Claims
1. An air-coupled broadband transducer based on a dual piezoelectric patch, characterized in that: include: Variable thickness matching layer, front piezoelectric sheet, rear piezoelectric sheet, housing, rear cover, interface and matching circuit; The rear piezoelectric sheet, the front piezoelectric sheet and the variable thickness matching layer are arranged in the housing; The rear cover is fixedly connected to the end of the shell to form a hollow cylindrical structure with the shell; the interface is fixedly arranged on the rear cover; the interface is used to receive ultrasonic signals; the negative electrode of the rear piezoelectric sheet is attached to the negative electrode of the front piezoelectric sheet; The positive electrode of the front piezoelectric sheet is bonded to the circular surface of the variable thickness matching layer; The positive electrode of the front piezoelectric sheet and the positive electrode of the rear piezoelectric sheet are connected by a wire; The thickness of the rear piezoelectric sheet and the front piezoelectric sheet are different; The front piezoelectric sheet and the rear piezoelectric sheet are connected to the output end of the matching circuit through a wire; and the input end of the matching circuit is connected to the interface through a wire.
2. The air-coupled broadband transducer based on dual piezoelectric plates according to claim 1, characterized in that: The variable thickness matching layer is in the shape of a cylinder; the top surface of the cylinder is a concave spherical surface.
3. The air-coupled broadband transducer based on dual piezoelectric plates according to claim 2, characterized in that: The thickness of the variable thickness matching layer ranges from 0.7 mm to 1.5 mm.
4. The air-coupled broadband transducer based on dual piezoelectric plates according to claim 1, characterized in that: The rear piezoelectric sheet, the front piezoelectric sheet and the variable thickness matching layer are sequentially bonded by epoxy resin glue.
5. The air-coupled broadband transducer based on dual piezoelectric plates according to claim 1, characterized in that: The rear piezoelectric sheet and the front piezoelectric sheet are bonded together by pressing.
6. The air-coupled broadband transducer based on dual piezoelectric plates according to claim 1, characterized in that: The matching circuit is a second-order L-type circuit.
7. The air-coupled broadband transducer based on dual piezoelectric plates according to claim 1, characterized in that: The variable thickness matching layer, the front piezoelectric sheet and the rear piezoelectric sheet have the same diameter.
8. The air-coupled broadband transducer based on dual piezoelectric plates according to claim 1, characterized in that: The variable thickness matching layer, the front piezoelectric sheet and the rear piezoelectric sheet are coaxially arranged.
9. The air-coupled broadband transducer based on dual piezoelectric plates according to claim 1, characterized in that: The materials of the front piezoelectric sheet and the rear piezoelectric sheet are both 1-3 type piezoelectric composite materials.
10. The air-coupled broadband transducer based on dual piezoelectric plates according to claim 1, characterized in that: The material of the variable thickness matching layer is epoxy glass microbead composite material.