Piezoelectric metasurface, method and ultrasonic transducer capable of generating specific sound field

Abstract

The present invention discloses a piezoelectric metasurface capable of generating a specific sound field, comprising a piezoelectric material, on which a pre-designed pattern electrode is plated, and after the pattern electrode is positively and negatively polarized, a phase difference distribution of 0 and π is formed on the surface of the piezoelectric material to generate a sound field with a specific pattern. The piezoelectric metasurface of the present invention can generate a sharp high-frequency focused or vortex sound field, as well as other specific sound fields, underwater, and has important applications in underwater wave field modulation, acoustic tweezers, biomedical imaging, industrial non-destructive testing, and neural regulation.

Description

Technical Field

[0001] The present invention relates to the technical field of acoustic materials, and in particular to a piezoelectric metasurface, method and ultrasonic transducer capable of generating a specific sound field. Background Art

[0002] Acoustic field manipulation plays an important role in many applications such as ultrasonic imaging, nondestructive testing, cell and particle manipulation, etc. Traditional acoustic field control methods can be divided into two parts. One part is active acoustic field control, which is represented by phased array. Active acoustic field regulation achieves spatial control of the acoustic field by adding electrical signal excitation delay to the unit. Phase distribution is usually generated by discrete and independently driven ultrasonic sources, but its cost is high and the operation process is complicated. Another method is to add lenses or subsurfaces to the surface of the transducer to achieve acoustic field control. The disadvantage is that the structure is complex and difficult to implement. Summary of the invention

[0003] The main purpose of the present invention is to provide a piezoelectric metasurface that can control the sound field and can be mass-produced, as well as a method for realizing the piezoelectric metasurface, and use it to make a programmable ultrasonic transducer.

[0004] The technical solution adopted by the present invention is:

[0005] A piezoelectric metasurface capable of generating a specific sound field is provided, comprising a piezoelectric material on which a pre-designed pattern electrode is plated. After the pattern electrode is positively and negatively polarized, a phase difference distribution of 0 and π is formed on the surface of the piezoelectric material to generate a sound field with a specific pattern.

[0006] According to the above technical solution, the pattern electrode is a plurality of independent ring-shaped electrodes or a single spiral electrode.

[0007] According to the above technical solution, the pattern electrode is a Fresnel spiral metal electrode.

[0008] Following the above technical solution, the specific sound field is a focused sound field, and the distribution of the pattern electrodes is based on the modified Airy distribution formula It is deduced that, in the formula, represents the sound pressure distribution, represents the Airy function, represents the radial distance, represents the initial radius of the main ring, represents the scale factor for length units, represents the exponential decay factor.

[0009] Following the above technical solution, the specific sound field is a vortex sound field, and the distribution of the pattern electrode is based on the spiral curve formula of the Mth arm It can be deduced that, is the focal length of the focus, is the wavelength of the sound field, Defined as the radius of the first inner helical circle, is the topological number of the acoustic vortex.

[0010] Following the above technical solution, M =1, the pattern electrode is a Fresnel spiral electrode, and the sound waves diffracted from opposite angles arrive at the focus with opposite phases, forming a focused vortex sound field.

[0011] The present invention also provides a method for preparing a piezoelectric metasurface that can generate a specific sound field. Pattern electrodes are plated on a piezoelectric material and a coded piezoelectric metasurface for sound wave manipulation is prepared by a polarization method. After positive and negative polarization, a phase difference distribution of 0 and π is formed on the surface of the piezoelectric material to generate a sound field with a specific pattern.

[0012] According to the above technical solution, the pattern electrode is obtained by a photolithography process.

[0013] Following the above technical solution, the positive and negative polarization methods of the electrodes are to perform high voltage polarization according to the characteristics of the piezoelectric material, so as to form a sound field consistent with a specific pattern on the surface of the piezoelectric material.

[0014] The present invention also provides an ultrasonic transducer, comprising a copper shell, the copper shell fixing a piezoelectric metasurface, the copper shell and the piezoelectric metasurface being connected by conduction, and the piezoelectric metasurface is the piezoelectric metasurface that can generate a specific sound field as described in the above technical solution.

[0015] The beneficial effects of the present invention are as follows: the present invention achieves binary coding of the piezoelectric material by plating a pre-designed pattern electrode on the piezoelectric material, and after the pattern electrode is positively and negatively polarized, a phase difference distribution of 0 and π is formed on the surface of the piezoelectric material, and the excited coded piezoelectric metasurface can generate a sound field of a specific pattern, which provides a new method for ultrasonic sound field regulation and drives the development of ultrasonic applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0017] Figure 1a This is a structural diagram of a piezoelectric metasurface capable of generating a focused acoustic field according to Embodiment 1 of the present invention;

[0018] Figure 1b The sound pressure amplitude and phase distribution diagram of the piezoelectric metasurface capable of generating a focused sound field in embodiment 1 of the present invention;

[0019] Figure 1c The steps for manufacturing the piezoelectric metasurface transducer according to the first embodiment of the present invention;

[0020] Figure 1d This is a YZ-plane sound field intensity distribution diagram of a piezoelectric metasurface capable of generating a focused sound field in accordance with the first embodiment of the present invention;

[0021] Figure 1e This is an XY plane sound field intensity distribution diagram of a piezoelectric metasurface capable of generating a focused sound field in accordance with the first embodiment of the present invention;

[0022] Figure 1f for Figure 1c Normalized sound pressure intensity distribution of the fabricated piezoelectric transducer in the horizontal direction along the focal point;

[0023] Figure 1g It is the phase distribution diagram of the XY plane acoustic field at the focus of the piezoelectric transducer;

[0024] Figure 2a This is a structural diagram of a piezoelectric metasurface for generating a vortex acoustic field according to a second embodiment of the present invention;

[0025] Figure 2b The amplitude and phase distribution of the piezoelectric metasurface generating the vortex acoustic field in the direction of the horizontal symmetry axis in the second embodiment of the present invention;

[0026] Figure 2c This is a YZ surface sound pressure distribution diagram of the vortex sound field generated by the second embodiment of the present invention;

[0027] Figure 2d This is a distribution diagram of the sound field intensity in the XY plane at the focus of the piezoelectric transducer that generates the vortex sound field in the second embodiment of the present invention;

[0028] Figure 2e This is a phase distribution diagram of the XY plane sound field at the focus of the piezoelectric transducer that generates the vortex sound field in the second embodiment of the present invention;

[0029] Figure 2f The XY plane sound field intensity distribution diagram at the focus of the sound field transducer producing the specific pattern A produced by the method of the present invention;

[0030] Figure 2g The XY plane sound field phase distribution diagram at the focus of the sound field transducer producing the specific pattern A manufactured by the method of the present invention. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0032] The piezoelectric metasurface realized by the piezoelectric material polarization method of the present invention can reconstruct the diffraction-limited sound pressure field and realize the sound field of any given pattern, such as spiral sound field, focused sound field, etc. When the piezoelectric material that has been positively and negatively polarized is subjected to a small AC electric field, the piezoelectric crystal will be compressed or stretched, generating a longitudinal sound wave. Therefore, depending on the polarization direction, the sound wave generated can be in phase or out of phase with the external AC electric field. The positive and negative polarization of the piezoelectric material provides a binary phase modulation method for the sound field, and this binary phase information is independent of the frequency or amplitude of the signal. The piezoelectric metasurface prepared by the piezoelectric material polarization method can realize coded sound wave manipulation. Using it in a phase-controlled piezoelectric transducer can simplify the process of the transducer and facilitate large-scale industrial production.

[0033] The piezoelectric metasurface that can generate a specific sound field in the embodiment of the present invention includes a piezoelectric material, on which a pre-designed pattern electrode is plated, and after the pattern electrode is positively and negatively polarized, a phase difference distribution of 0 and π is formed on the surface of the piezoelectric material to generate a specific pattern of sound field. Figure 1a The ring pattern shown, such as Figure 2a The spiral pattern shown, such as Figure 2f The letter A pattern shown.

[0034] Piezoelectric materials can be selected according to needs, including piezoelectric ceramics and piezoelectric single crystals. According to the characteristics of different piezoelectric materials, the appropriate voltage is selected for polarization treatment. Generally, after the preset electrode pattern is plated on the piezoelectric material, it is immersed in high-temperature silicone oil and heated to a certain temperature by a thermostat heater. Then a conductive electrode, such as a copper sheet (cathode), is connected to the bottom surface of the piezoelectric material as a ground layer, and another conductive electrode, such as a copper needle (anode), is used to connect the spiral electrode on the upper surface of the piezoelectric material. A DC power supply is used to generate a high voltage difference between the cathode and the anode. The applied voltage gradually increases from 0 to the polarization voltage.

[0035] Embodiment 1

[0036] Reference Figure 1a As shown, in this embodiment, a piezoelectric metasurface capable of generating a focused acoustic field is provided. The piezoelectric metasurface includes a piezoelectric material and a plurality of annular electrodes. In this embodiment, the diameter of the cylindrical piezoelectric material is selected to be 5 cm and the thickness is 1 mm.

[0037] Reference Figure 1aAs shown, the photolithography steps of the surface electrode pattern of the piezoelectric metasurface in this example are as follows, and the Cr / Au pattern is prepared by metal lift-off technology. First, the photolithography process is performed using a photolithography system, and a patterned photoresist layer with a thickness of 2.5μm is used as a mask. Then, a 50nm Cr film and a 100nm Au film are continuously coated by a radio frequency magnetron sputtering method. Finally, the photoresist mask is stripped in acetone, leaving the desired Cr / Au ring electrode pattern on the piezoelectric substrate.

[0038] Reference Figure 1a As shown, the polarization method of the circular ring electrode in this example is as follows: the piezoelectric material with the electrode pattern plated is immersed in high-temperature silicone oil and heated to 60° by a thermostat heater. A copper sheet (cathode) is connected to the bottom surface of the piezoelectric material as a ground layer, and another copper needle (anode) is used to select the circular electrode on the upper surface of the piezoelectric material. A DC power supply is used between the cathode and the anode to generate a high voltage difference. Each circular ring electrode is polarized for 5 minutes, and the applied voltage is gradually increased from 0 to 2500 V.

[0039] Reference Figure 1b As shown, Figure 1b The amplitude and phase distribution of the piezoelectric metasurface that can generate a focused acoustic field in this example along the horizontal symmetry axis are given.

[0040] Reference Figure 1c As shown in the figure, the polarized piezoelectric metasurface in this example has been Figure 1c The steps shown in the figure are used to make an ultrasonic transducer. First, the piezoelectric material PZT-4 is selected; then the circular electrode is made by the PVD gold plating process, and a wire is connected to the electrode; then the piezoelectric material is fixed by a copper shell, and another wire is connected to the copper shell; then the inner surface of the copper shell is filled with epoxy resin; then the back of the transducer is made by the gold plating process; finally, a layer of polyparaxylene film is applied to the surface of the transducer.

[0041] It can be seen that by directly plating electrodes on the piezoelectric material and polarizing it, the required sound field can be generated without the need to add additional lenses or use lasers to etch groove structures on the piezoelectric material. The required electric field can be generated according to the electrode pattern.

[0042] Furthermore, the excitation of the piezoelectric transducer is a 2 MHz 10-cycle sine wave, and the sound propagation medium is water. Figure 1d The YZ-plane acoustic pressure distribution of the above-mentioned piezoelectric transducer is given.

[0043] Further, Figure 1e The XY plane acoustic field intensity distribution diagram at the focus of the above piezoelectric transducer is given.

[0044] Further, Figure 1fThe normalized sound pressure intensity distribution of the piezoelectric transducer along the horizontal direction at the focus is given, where the half-height width of the focused beam is 0.63 (Simulation), 0.65 (experiment).

[0045] Further, Figure 1g The XY plane acoustic field phase distribution at the focus of the above piezoelectric transducer is given.

[0046] It should be noted that the purpose of making the piezoelectric metasurface capable of generating a focused acoustic field provided in this embodiment into a transducer is to facilitate the measurement of its acoustic field distribution. The thickness of the piezoelectric metasurface provided in the above invention embodiment is determined by its designed operating frequency. In this embodiment, the thickness of the piezoelectric metasurface is selected to be 1 mm, and the designed operating frequency is 2 MHz. The size of the piezoelectric metasurface provided in the above invention embodiment is determined by the designed operating frequency. Figure 1b To confirm, Figure 1b From the modified Airy distribution formula The parameters are set in this example. =1.5 mm, =0.75 mm, =0.05.

[0047] Figure 1a The electrode distribution can also be derived through other annular curve formulas, not limited to the above formula, such as the Fresnel lens annular distribution.

[0048] Embodiment 2

[0049] According to Figure 2a As shown, in this embodiment, a piezoelectric metasurface capable of generating a vortex acoustic field is provided. The piezoelectric metasurface includes a piezoelectric material and a Fresnel spiral electrode. In this embodiment, the diameter of the cylindrical piezoelectric material is selected to be 5 cm and the thickness is 2 mm.

[0050] Reference Figure 2a As shown in Figure 1, the photolithography steps of the surface electrode pattern of the piezoelectric metasurface in this example are as follows. The Cr / Au pattern is prepared by metal lift-off technology. First, the photolithography process is performed using a photolithography system, and a patterned photoresist layer with a thickness of 2.5 μm is used as a mask. Then, a 50 nm Cr film and a 100 nm Au film are continuously coated by a radio frequency magnetron sputtering method. Finally, the photoresist mask is stripped in acetone, leaving the desired Cr / Au ring electrode pattern on the piezoelectric substrate.

[0051] Reference Figure 2aAs shown, the polarization method of the circular ring electrode in this example is as follows: the piezoelectric material with the electrode pattern plated is immersed in high-temperature silicone oil and heated to 60° by a thermostat heater. A copper sheet (cathode) is connected to the bottom surface of the piezoelectric material as a ground layer, and another copper needle (anode) is used to select the spiral electrode on the upper surface of the piezoelectric material. A DC power supply is used to generate a high voltage difference between the cathode and the anode. Each circle of electrodes is polarized for 5 minutes, and the applied voltage is gradually increased from 0 to 2500V.

[0052] Reference Figure 2b As shown, Figure 2b The amplitude and phase distribution of the piezoelectric metasurface that can generate a vortex acoustic field in this example along the horizontal symmetry axis are given.

[0053] Reference Figure 1c As shown in the figure, the polarized piezoelectric metasurface in this example has been Figure 1c The steps shown in the figure are used to make an ultrasonic transducer. First, the piezoelectric material PZT-4 is selected; then the spiral electrode is made by the PVD gold plating process, and a wire is connected to the electrode; then the piezoelectric material is fixed by a copper shell, and another wire is connected to the copper shell; then the copper shell is filled with epoxy resin; then the back of the transducer is made by the gold plating process; finally, a layer of polyparaxylene film is applied to the surface of the transducer.

[0054] Furthermore, the excitation of the piezoelectric transducer is a 1 MHz 10-cycle sine wave, and the sound propagation medium is water. Figure 2c The YZ-plane acoustic pressure distribution of the above-mentioned piezoelectric transducer is given.

[0055] Further, Figure 2d The XY plane sound field intensity distribution diagram at the focus of the above piezoelectric transducer is given. Further, Figure 2e The XY plane acoustic field phase distribution at the focus of the above piezoelectric transducer is given.

[0056] Further, Figure 2f The XY plane acoustic field intensity distribution diagram at the focus of the piezoelectric transducer with a specific pattern A electrode is given. Further, Figure 2g The XY plane acoustic field phase distribution at the focus of the piezoelectric transducer with a specific pattern A electrode is given.

[0057] The piezoelectric metasurfaces of the above two embodiments can generate sharp high-frequency focused or vortex acoustic fields underwater, and have important applications in underwater wave field modulation, acoustic tweezers, biomedical imaging, industrial nondestructive testing, and neural regulation.

[0058] It should be noted that the purpose of making the piezoelectric metasurface capable of generating a vortex acoustic field provided in this embodiment into a transducer is to facilitate the measurement of its acoustic field distribution. The thickness of the piezoelectric metasurface capable of generating a vortex acoustic field provided in the above invention embodiment is determined by its designed operating frequency. The size of the piezoelectric metasurface capable of generating a vortex acoustic field provided in the above invention embodiment is determined according to Figure 2b to be sure. Figure 2a The electrode distribution can be expressed by the spiral curve formula of the Mth arm: The parameters set in this example are: = 1.5 mm, = 30 mm, = 1.5 mm, = 1, = 1.

[0059] Figure 2a The electrode distribution can also be derived by other spiral curve formulas, not limited to the above spiral curve formulas, such as Archimedean spirals.

[0060] It should also be noted that the described embodiments are only some embodiments of the present invention, not all embodiments. Usually, different parameters and materials can be selected to design piezoelectric metasurfaces with different functions, and the above specific embodiments are only exemplary. Any modification, change or replacement made on this basis is within the scope of protection of the present invention.

[0061] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all these improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. A piezoelectric metasurface capable of generating a specific sound field, characterized in that: Including piezoelectric materials, selecting appropriate voltages to polarize the piezoelectric materials according to the characteristics of different piezoelectric materials; The piezoelectric material is plated with a pre-designed pattern electrode. After the preset electrode pattern is plated on the piezoelectric material, it is immersed in high-temperature silicone oil and heated to a certain temperature by a thermostat heater. Then, a conductive electrode is connected to the bottom surface of the piezoelectric material as a ground layer, and another conductive electrode is used to connect the pattern electrode on the upper surface of the piezoelectric material. The two conductive electrodes are polarized with high voltage according to the characteristics of the piezoelectric material, and the voltage is gradually increased from 0 to the polarization voltage. After the pattern electrode is polarized, a phase difference distribution of 0 and π is formed on the surface of the piezoelectric material, generating a sound field with a specific pattern. The pattern electrodes are a plurality of independent ring electrodes, spiral electrodes or letter A electrodes.

2. The piezoelectric metasurface capable of generating a specific sound field according to claim 1, characterized in that: When the pattern electrodes are multiple independent ring electrodes, the specific sound field is a focused sound field, and the distribution of the pattern electrodes is based on the modified Airy distribution formula It is derived that, where P0(r) represents the sound pressure distribution, Ai(·) represents the Airy function, r represents the radial distance, r0 represents the initial radius of the main ring, w represents the scale factor of the length unit, and α represents the exponential decay factor.

3. The piezoelectric metasurface capable of generating a specific sound field according to claim 1, characterized in that: When the pattern electrode is a spiral electrode, the specific sound field is a vortex sound field, and the distribution of the pattern electrode is based on the spiral curve formula of the Mth arm. It can be deduced that, where F is the focal length of the focus, λ is the wavelength of the sound field, Defined as the radius of the first inner spiral circle, M is the topological number of the acoustic vortex.

4. The piezoelectric metasurface capable of generating a specific sound field according to claim 3, characterized in that: M=1, the pattern electrode is a Fresnel spiral electrode, and the sound waves diffracted from opposite angles reach the focus with opposite phases, forming a focused vortex sound field.

5. A method for preparing a piezoelectric metasurface capable of generating a specific acoustic field, characterized in that: A preset pattern electrode is plated on the piezoelectric material, which is immersed in high-temperature silicone oil and heated to a certain temperature by a thermostat heater. Then, a conductive electrode is connected to the bottom surface of the piezoelectric material as a grounding layer, and another conductive electrode is used to connect the pattern electrode on the upper surface of the piezoelectric material. The two conductive electrodes are polarized with high voltage according to the characteristics of the piezoelectric material, and the voltage gradually increases from 0 to the polarization voltage. A coded piezoelectric metasurface for sound wave manipulation is prepared by the polarization method. After the pattern electrode is polarized, a phase difference distribution of 0 and π is formed on the surface of the piezoelectric material to generate a sound field with a specific pattern. The pattern electrode is a plurality of independent ring electrodes, a spiral electrode or a letter A electrode.

6. The method for preparing a piezoelectric metasurface capable of generating a specific sound field according to claim 5, characterized in that: The patterned electrodes are obtained by photolithography.

7. An ultrasonic transducer, characterized in that: It comprises a copper shell, which fixes a piezoelectric metasurface, and the copper shell and the piezoelectric metasurface are connected by conduction. The piezoelectric metasurface is the piezoelectric metasurface capable of generating a specific sound field as described in any one of claims 1 to 4.

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