Plane active focusing piezoelectric ultrasonic transducer based on Airy beam electrode structure

Abstract

The invention belongs to the field of ultrasonic nondestructive testing, and discloses a plane active focusing piezoelectric ultrasonic transducer based on an Airy beam structure, the plane active focusing piezoelectric ultrasonic transducer is provided with a piezoelectric plate, a matching layer, a backing, a shell and a resin gasket, the shell is internally provided with a first containing cavity and a second containing cavity which are through and communicated, the diameter of the first containing cavity is smaller than that of the second containing cavity, the backing is located in the first containing cavity, and the resin gasket is located in the second containing cavity. The cross section of the resin gasket is in an L shape, the resin gasket is located in the second containing cavity, the resin gasket is tightly attached to the shell, the piezoelectric plate is clamped at the L-shaped bending position of the resin gasket, the acoustic impedance matching layer is tightly attached to the piezoelectric plate, and the resin gasket can prevent the backing from moving towards an opening in one end of the shell. Vibration energy of the piezoelectric plate is transmitted to the backing through a hole in the center of the resin gasket, the transducer works in a thickness vibration mode, and the center frequency of the transducer ranges from 300 kHz to 5 MHz. The invention further discloses two transducers outside the center frequency. The transverse resolution of the transducer can be improved, and meanwhile, the sensitivity is improved.

Description

Technical Field

[0001] This invention belongs to the field of ultrasonic nondestructive testing, specifically relating to a planar active focusing piezoelectric ultrasonic transducer based on an Airy beam structure. Background Technology

[0002] Ultrasonic nondestructive testing is widely used in the electrical field. It has been introduced into various application scenarios, including external insulation discharge of electrical equipment (Yang Daiyong, Liu He, Lin Haidan, et al. Acoustic-optical synergistic detection and diagnostic technology for external insulation discharge of power equipment [J]. Electric Porcelain Arrester, 2023, (06): 209-218.), partial discharge (Zhang Yupeng, Yang Yongming, Yang Chenghe, et al. Ultrasonic detection method for partial discharge of electrical equipment [J]. Piezoelectricity and Acousto-optics, 2010, 32(03): 414-416.), and contact interface stress detection (Liu Chunbo, Zhao Chunming, Yang Daiyong, et al. A review of research on ultrasonic-based contact interface stress detection technology for electrical equipment [J / OL]. Insulating Materials, 1-12 [2025-10-26].), effectively ensuring the safe, stable, and reliable operation of electrical equipment.

[0003] Ultrasonic transducers are the core components of ultrasonic testing technology. Focused piezoelectric ultrasonic transducers, in particular, can concentrate the sound beam onto a focal region, resulting in higher sensitivity and resolution during ultrasonic testing and imaging. High-performance focused piezoelectric ultrasonic transducers can further enhance the application potential of ultrasonic testing technology in the electrical field.

[0004] Common focusing methods include concave lenses (Zvietcovich F, Nair A, Ambekar YS, et al. Confocal air-coupled ultrasonic optical coherence elastography probe for quantitative biomechanics[J]. Optics Letters, 2020, 45(23): 6567-6570.), apodization (Unger A. Air Coupled Ultrasonic Transducers for Industrial Applications[J].2019.), and parabolic reflectors (Dai X, Zhu J, Tsai YT, et al. Use of parabolic reflector to amplify in-air signals generated during impact-echo testing[J].Journal of the Acoustical Society of America, 2011, 130(4):167-72.). Conventional passive focusing methods such as refractive lenses and apodization can disrupt acoustic impedance matching conditions, and parabolic reflectors are bulky and difficult to install, resulting in poor performance when applied to focused piezoelectric ultrasonic transducers.

[0005] CN119897263A discloses a planar active focusing air-coupled ultrasonic transducer, which includes: a piezoelectric element and a matching layer both disposed within a housing; a rear cover plate covering the end of the housing; an interface disposed on the housing; multiple concentric ring-shaped electrodes disposed on the first surface of the piezoelectric element; the width of each concentric ring in the multiple concentric ring-shaped electrodes increases sequentially from the outside to the inside; a second electrode disposed on the second surface of the piezoelectric element; and the piezoelectric element is connected to the interface via wires led out from the multiple concentric ring-shaped electrodes and the full-surface electrode. The planar active focusing air-coupled ultrasonic transducer provided by this invention achieves active focusing of the planar sound beam by changing the electrode structure of the piezoelectric element and setting multiple concentric ring-shaped electrode structures on one side of the piezoelectric element. Combined with a planar acoustic impedance matching layer of uniform thickness, it improves the sensitivity of the focusing air-coupled transducer without affecting the transducer's lateral resolution.

[0006] The performance of the aforementioned existing technologies in focused piezoelectric ultrasonic transducers needs further improvement. Summary of the Invention

[0007] The purpose of this invention is to address the problem of sacrificing sensitivity in a focusing transducer to improve lateral resolution. A planar focusing piezoelectric ultrasonic transducer based on an Airy beam structure is proposed. This transducer achieves beam focusing through a series of concentric ring structures, thereby improving both the transducer's lateral resolution and sensitivity.

[0008] To achieve the above objectives, this invention provides three implementation methods for planar focused piezoelectric ultrasonic transducers based on Airy beams: (1) For piezoelectric ultrasonic transducers with a center frequency of 300 kHz - 5 MHz, this invention provides a design method for a planar active focused piezoelectric ultrasonic transducer based on an Airy beam electrode structure. The transducer consists of a piezoelectric element, an acoustic impedance matching layer, and a backing. The piezoelectric element operates in the thickness vibration mode. Using screen printing technology, the upper surface electrode of the piezoelectric element is fabricated into a concentric ring electrode structure based on an Airy beam structure; (2) For piezoelectric ultrasonic transducers with a center frequency higher than 5 MHz, this invention provides a design method for a high-frequency focused piezoelectric ultrasonic transducer based on an Airy beam piezoelectric structure. Using 3D printing technology, a concentric ring piezoelectric structure based on an Airy beam is directly fabricated on a thin metal substrate; (3) For piezoelectric ultrasonic transducers with a center frequency lower than 300 kHz, this invention provides a design method for a planar active focused piezoelectric ultrasonic transducer based on an Airy beam structure. A design method for a low-frequency focusing piezoelectric ultrasonic transducer with a beam baffle structure, wherein the transducer consists of a piezoelectric element, a housing, and a baffle, operates in a bending vibration mode, and a planar baffle based on an Airy beam structure is clamped on the transducer housing.

[0009] This application discloses a planar focused piezoelectric ultrasonic transducer based on an Airy beam structure, comprising a piezoelectric element, an acoustic impedance matching layer, and a backing. Its features include: a cylindrical metal shell and a resin gasket; the metal shell has a through-hole first cavity, and one end of the metal shell has a second cavity; the first cavity and the second cavity are connected, and the diameter of the first cavity is smaller than the diameter of the second cavity; the backing is located within the first cavity and engaged with the inner wall of the metal shell; the resin gasket has an L-shaped cross-section and is located within the second cavity, tightly attached to the metal shell; the piezoelectric element is engaged at the L-shaped bend of the resin gasket; the acoustic impedance matching layer is tightly attached to the piezoelectric element; the resin gasket can prevent the backing from moving towards the opening at one end of the metal shell; the vibration energy of the piezoelectric element is transmitted to the backing through the central hole of the resin gasket; the electrode structure of the piezoelectric element is a concentric ring electrode structure based on an Airy beam, wherein the radius of each concentric ring is based on the Airy beam structure. The beam structure is given; the transducer operates in the thickness vibration mode, and the center frequency of the transducer is 300 kHz - 5 MHz.

[0010] The planar focusing piezoelectric ultrasonic transducer based on the Airy beam structure described above is characterized in that: the piezoelectric element is made of type 1-3 composite material, the acoustic impedance of the piezoelectric element is 10 MRayl, the diameter is 30 mm, and the thickness of the piezoelectric element is half the wavelength corresponding to the center frequency of the ultrasonic signal.

[0011] The planar focusing piezoelectric ultrasonic transducer based on the Airy beam structure described above is characterized in that: when the center frequency is 500 kHz, the parameters of the concentric ring electrodes conform to the following table:

[0012]

[0013] Where: r n n=1, 2, 3... represents the nth radius from the center of the circle outwards.

[0014] The planar focusing piezoelectric ultrasonic transducer based on the Airy beam structure described above is characterized in that: the concentric ring electrode is fabricated by removing the upper surface electrode of the piezoelectric sheet, and using conductive silver paste based on screen printing technology to fabricate the upper surface electrode based on the Airy beam structure, while the lower surface electrode remains unchanged.

[0015] The planar focusing piezoelectric ultrasonic transducer based on the Airy beam structure described above is characterized in that: the matching layer is a composite material made of epoxy resin and diamond powder mixed in a certain proportion, and the thickness of the matching layer is one-quarter wavelength corresponding to the center frequency of the ultrasonic signal.

[0016] The planar focusing piezoelectric ultrasonic transducer based on the Airy beam structure described above is characterized in that: the backing is a composite material made by mixing and curing epoxy resin and tungsten powder in a certain proportion, and the volume ratio of tungsten powder at the end closer to the piezoelectric element should be greater than that at the end farther from the piezoelectric element during the mixing and curing process.

[0017] This application discloses another planar focusing piezoelectric ultrasonic transducer based on an Airy beam structure, comprising a piezoelectric element; characterized in that it further comprises a cylindrical metal shell and a resin gasket, the metal shell having a through first cavity, and a second cavity inside one end of the metal shell, the first cavity and the second cavity being connected, the diameter of the first cavity being smaller than the diameter of the second cavity, the resin gasket having an L-shaped cross-section, the resin gasket being located inside the second cavity, the resin gasket being tightly attached to the metal shell, the piezoelectric element being engaged at the L-shaped bend of the resin gasket, and the resin gasket preventing the piezoelectric element from moving to the other end of the metal shell; the piezoelectric element is fabricated using 3D printing technology, directly on a thin metal substrate to create a concentric ring-shaped piezoelectric structure based on an Airy beam, wherein the radius of each concentric ring is given based on the Airy beam structure; the transducer operates in thickness vibration mode, and the center frequency of the transducer is higher than 5 MHz.

[0018] This application discloses another planar focusing piezoelectric ultrasonic transducer based on an Airy beam structure, comprising a piezoelectric element and a housing; characterized in that it further comprises a baffle, the housing having a concave cross-section, the piezoelectric element being located at the bottom of the concave shape within the housing, the baffle being mounted on the housing and covering the effective acoustic radiation surface of the transducer, the polarization direction of the piezoelectric element being the thickness direction, the piezoelectric element being made of PZT4 piezoelectric ceramic, the housing being made of hollow microspheres / epoxy resin composite material, the baffle being made of aluminum, and the baffle being a concentric ring structure based on an Airy beam, wherein the radius of each concentric ring is given based on the Airy beam structure, the transducer operating in a bending vibration mode, and the center frequency of the transducer being below 300 kHz.

[0019] The advantages of this invention are: the sound beam is focused by a series of concentric ring structures, which improves the transducer's lateral resolution and sensitivity. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a planar focused piezoelectric ultrasonic transducer based on an Airy beam electrode structure, with a center frequency range of 300 kHz - 5 MHz, provided by the present invention.

[0021] Figure 2 This is a schematic diagram of a high-frequency planar focused piezoelectric ultrasonic transducer based on an Airy beam structure with a center frequency higher than 5 MHz, provided by the present invention.

[0022] Figure 3 This is a schematic diagram of a low-frequency planar focused piezoelectric ultrasonic transducer based on an Airy beam structure with a center frequency of less than 300 kHz, provided by the present invention.

[0023] Figure 4This is a top view of the concentric ring structure based on the Airy beam structure in this invention. Detailed Implementation

[0024] The planar focusing piezoelectric ultrasonic transducer based on the Airy beam structure described in this invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0025] This section reveals three implementation methods for planar focused piezoelectric ultrasonic transducers based on the Airy beam structure.

[0026] Example 1: See Figures 1 to 4 ,like Figure 1 As shown, a planar focused piezoelectric ultrasonic transducer based on the Airy beam structure is a focused piezoelectric ultrasonic transducer with a center frequency of 300 kHz - 5 MHz. The transducer operates in the thickness vibration mode and consists of a piezoelectric element, an acoustic impedance matching layer, and a backing.

[0027] The piezoelectric element of the planar active focusing piezoelectric ultrasonic transducer is made of type 1-3 composite material, with an acoustic impedance of 10 MRayl, a diameter of 30 mm, and a thickness of half the wavelength corresponding to the center frequency of the ultrasonic signal.

[0028] The preferred electrode structure of the piezoelectric element is a concentric ring electrode structure based on the Airy beam, wherein the radius of each concentric ring is given based on the Airy beam structure. The parameters of the concentric ring electrode at a center frequency of 500 kHz are shown in Table 1. The concentric ring electrode is fabricated as follows: the upper surface electrode of the piezoelectric element is removed, and the upper surface electrode based on the Airy beam structure is fabricated using conductive silver paste based on screen printing technology, while the lower surface electrode remains unchanged.

[0029] Table 1. Parameters of concentric ring electrodes based on Airy beam structure

[0030]

[0031] Where r n n = 1, 2, 3... represents the nth radius starting from the center of the circle. A top view of the concentric ring electrode structure is shown below. Figure 2 As shown.

[0032] The matching layer is a composite material made of epoxy resin and corundum mixed in a certain proportion, and the thickness of the matching layer is one-quarter wavelength corresponding to the center frequency of the ultrasonic signal.

[0033] The backing is a composite material made by mixing and curing epoxy resin and tungsten powder in a certain proportion. During the mixing and curing process, the volume ratio of tungsten powder at the end closer to the piezoelectric element should be greater than that at the end farther away from the piezoelectric element.

[0034] Example 2: Reference Figures 1 to 4 This embodiment is for a high-frequency focused piezoelectric ultrasonic transducer with a center frequency higher than 5 MHz, and its schematic diagram is shown below. Figure 2 As shown, concentric ring-shaped piezoelectric structures based on Airy beams are fabricated directly on a thin metal substrate using 3D printing technology. The radii of each concentric ring are given based on the Airy beam structure. No matching layer or backing is fabricated.

[0035] Example 3: Reference Figures 1 to 4 This embodiment focuses on a low-frequency focusing piezoelectric ultrasonic transducer with a center frequency below 300 kHz. The transducer operates in a bending vibration mode and consists of a piezoelectric element, a housing, and a baffle. The piezoelectric element's polarization direction is along its thickness. Taking a piezoelectric ultrasonic transducer with a center frequency of 25 kHz as an example, the piezoelectric material is PZT4 piezoelectric ceramic, with a thickness of 0.5 mm and a diameter of 9 mm. The housing material is a hollow microsphere / epoxy resin composite material, with a thickness of 2 mm and a diameter of 14 mm. The baffle is a concentric ring structure based on an Airy beam, where the radius of each concentric ring is given based on the Airy beam structure. The baffle material is aluminum, with a diameter of 14 mm, and is attached to the housing of the ultrasonic transducer, covering the effective acoustic radiation surface of the transducer.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A planar focusing piezoelectric ultrasonic transducer based on an Airy beam structure, comprising a piezoelectric element, an acoustic impedance matching layer, and a backing; characterized in that: It also features a cylindrical metal shell and a resin gasket. The metal shell has a through-hole first cavity, and a second cavity at one end of the metal shell. The first cavity and the second cavity are connected, and the diameter of the first cavity is smaller than the diameter of the second cavity. A backing is located in the first cavity and is engaged with the inner wall of the metal shell. The resin gasket has an L-shaped cross-section and is located in the second cavity, closely attached to the metal shell. A piezoelectric element is engaged at the L-shaped bend of the resin gasket. An acoustic impedance matching layer is closely attached to the piezoelectric element. The resin gasket can block the backing from moving towards the opening at one end of the metal shell. The vibration energy of the piezoelectric element is transmitted to the backing through the central hole of the resin gasket. The electrode structure of the piezoelectric element is a concentric ring electrode structure based on Airybeam, wherein the radius of each concentric ring is given based on the Airybeam structure. The transducer operates in the thickness vibration mode, and the center frequency of the transducer is 300 kHz - 5 MHz.

2. The planar focusing piezoelectric ultrasonic transducer based on the Airy beam structure according to claim 1, characterized in that: The piezoelectric element is made of type 1-3 composite material, with an acoustic impedance of 10 MRayl, a diameter of 30 mm, and a thickness that is half the wavelength corresponding to the center frequency of the ultrasonic signal.

3. A planar focusing piezoelectric ultrasonic transducer based on an Airy beam structure according to claim 1 or claim 2, characterized in that: When the center frequency is 500 kHz, the parameters of the concentric ring electrode conform to the following table: ， Where: r n n=1, 2, 3... represents the nth radius from the center of the circle outwards.

4. A planar focusing piezoelectric ultrasonic transducer based on an Airy beam structure according to claim 3, characterized in that: The concentric ring electrode is fabricated as follows: the upper surface electrode of the piezoelectric sheet is removed, and the upper surface electrode based on the Airy beam structure is fabricated using conductive silver paste based on screen printing technology, while the lower surface electrode remains unchanged.

5. A planar focusing piezoelectric ultrasonic transducer based on an Airy beam structure according to claim 4, characterized in that: The matching layer is a composite material made of epoxy resin and corundum mixed in a certain proportion, and the thickness of the matching layer is one-quarter wavelength corresponding to the center frequency of the ultrasonic signal.

6. A planar focusing piezoelectric ultrasonic transducer based on an Airy beam structure according to claim 5, characterized in that: The backing is a composite material made by mixing and curing epoxy resin and tungsten powder in a certain proportion. During the mixing and curing process, the volume ratio of tungsten powder at the end closer to the piezoelectric element should be greater than that at the end farther from the piezoelectric element.

7. A planar focusing piezoelectric ultrasonic transducer based on an Airy beam structure, comprising a piezoelectric element; characterized in that: It also features a cylindrical metal shell and a resin gasket. The metal shell has a through-hole first cavity, and one end of the metal shell has a second cavity. The first cavity and the second cavity are connected, and the diameter of the first cavity is smaller than the diameter of the second cavity. The resin gasket has an L-shaped cross-section and is located inside the second cavity. The resin gasket is in close contact with the metal shell, and the piezoelectric sheet is engaged at the L-shaped bend of the resin gasket. The resin gasket can prevent the piezoelectric sheet from moving to the other end of the metal shell. The piezoelectric sheet is fabricated using 3D printing technology, directly creating a concentric ring piezoelectric structure based on Airy beam on a thin metal substrate. The radius of each concentric ring is given based on the Airy beam structure. The transducer operates in the thickness vibration mode, and the center frequency of the transducer is higher than 5 MHz.

8. A planar focusing piezoelectric ultrasonic transducer based on an Airy beam structure, comprising a piezoelectric element and a housing; characterized in that: It also has a baffle, the cross-section of the outer shell is U-shaped, the piezoelectric sheet is located at the bottom of the U-shape inside the outer shell, the baffle is attached to the outer shell and covers the effective acoustic radiation surface of the transducer, the polarization direction of the piezoelectric sheet is the thickness direction, the transducer operates in bending vibration mode, and the center frequency of the transducer is below 300 kHz.

9. A planar focusing piezoelectric ultrasonic transducer based on an Airy beam structure according to claim 8, characterized in that: The piezoelectric element is made of PZT4 piezoelectric ceramic, the outer shell is made of hollow microspheres / epoxy resin composite material, and the baffle is made of aluminum.

10. A planar focusing piezoelectric ultrasonic transducer based on an Airy beam structure according to claim 9, characterized in that: The baffle is a concentric ring structure based on the Airy beam, where the radius of each concentric ring is given based on the Airy beam structure.

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