Piezoelectric sensing array preparation method of multi-frequency imaging sonar

Abstract

The invention discloses a preparation method of a piezoelectric sensing array of a multi-frequency imaging sonar. According to the method, a PVDF or P (VDF-TrFE) piezoelectric film is adopted as a core material, automatic coating, spin-coating thinning, laser etching, silk-screen printing, magnetron sputtering, pattern masking, vacuum packaging and other processes are integrated, a square orthogonal array smaller than or equal to 8 inches can be prepared, and the method can be used for multi-frequency multi-beam three-dimensional acoustic imaging with the broadband larger than or equal to 300 kHz. An array electrode forms a patterned electrode through a magnetron sputtering method, a silk-screen printing method or a combination of the magnetron sputtering method and the silk-screen printing method, one-time forming of a high-density array element is achieved, the laser etching and alignment technology is combined, the array size and the array element position precision are ensured, and the interlayer bonding strength is enhanced through epoxy resin and the vacuum packaging technology. The sensing array has electrical consistency and array element abnormal rate lt; the system can stably work in high pressure difference and high pressure environments, the imaging distance is larger than or equal to ten meters, and the system is suitable for submarine landform detection and target identification.

Description

Technical Field

[0001] The invention relates to the technical field of underwater acoustic transducers, and in particular to a method for preparing a piezoelectric sensor array of a multi-frequency imaging sonar. Background Art

[0002] High-precision detection of marine topography, mineral deposits and biological resources is of great strategic significance to national security, resource development and environmental protection. Traditional multi-beam sonar systems are limited by low-frequency working modes (usually <100kHz) and low-density array element designs (such as linear arrays, cross arrays, 8×8 arrays). Their spatial resolution is generally insufficient (usually >10cm), and the signal dimension is single, making it difficult to achieve three-dimensional fine reconstruction of complex seabed topography and feature recognition of weak targets. Existing sonar arrays mostly use PZT (lead zirconate titanate) piezoelectric ceramics as transducer piezoelectric materials, but their inherent brittleness and high acoustic impedance (about 10 times that of water) can easily lead to acoustic wave interface reflection losses, and in deep-sea high-pressure environments (>10MPa), material failure or piezoelectric performance attenuation is easily caused by deformation of the array structure, which restricts the reliability of deep-sea long-term detection.

[0003] In recent years, flexible piezoelectric materials PVDF (polyvinylidene fluoride) and its copolymer P (VDF-TrFE) (copolymer of vinylidene fluoride and trifluoroethylene) have become one of the ideal candidate materials for underwater acoustic transducers due to their acoustic impedance close to that of water (1.5 MRayl), wide-band response (10kHz~10MHz) and excellent mechanical flexibility. However, the existing imaging sonar PVDF array preparation technology has the following problems: the imaging frequency is single, which cannot meet the requirements of long-distance detection and close-range high resolution at the same time; the array density and aperture are limited; interlayer peeling is prone to occur between materials; the insufficient positioning accuracy of the array element causes the sidelobe level to increase during beamforming (>-15dB); the existing packaging technology mostly uses a non-airtight structure, which cannot effectively cope with the material deformation caused by deep-sea hydrostatic pressure. Therefore, a piezoelectric sensor array preparation method that takes into account high array element density, precise electrode patterning, strong interface bonding and adaptability to deep-sea environment is developed to break through the requirements of deep-sea high-resolution acoustic imaging technology. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a piezoelectric sensor array with a multi-frequency imaging sonar, so as to cover multi-frequency sound sources, have high sensitivity, can not deform under high pressure difference and ≥50°C environment, and can be used in deep sea environment. The piezoelectric sensor array includes an acoustic matching layer, a connected ground electrode (negative electrode), a single-layer or multi-layer PVDF or P (VDF-TrFE) piezoelectric film, a patterned positive electrode, and a PCB circuit board. A multi-frequency imaging sonar piezoelectric sensor array is a square orthogonal array with a size of ≤8 inches, the number of array elements is ≥24×24, and virtual transition array elements are arranged in the outermost circle. The center spacing of the array elements is ≤1 wavelength of the working frequency. The array elements are square, and the side length is ≥70% of the center spacing of the array elements.

[0005] The thickness of the single-layer PVDF or P (VDF-TrFE) piezoelectric film is 40 μm-500 μm, and the multi-layer PVDF or P (VDF-TrFE) piezoelectric material is prepared by laminating piezoelectric film + epoxy resin + piezoelectric film. Taking the preparation of a laminated PVDF film with a thickness of 400 μm as an example, the specific steps are as follows: (1) Take two pieces of PVDF membrane with a thickness of 200 μm and a size of ≥105 mm × 105 mm; (2) Take two pieces of thermal release films of the same size as the PVDF film and stick them on the surface of the PVDF film to prevent the surface from being contaminated by the epoxy resin described below; (3) Prepare epoxy resin glue, take epoxy resin A glue and epoxy resin B glue, mix and stir evenly, then put them into a vacuum box to remove bubbles for ≥ 20 minutes, where the vacuum degree of the vacuum box is ≤-0.1MPa; (4) Take a piece of PVDF membrane with a thermal release film in (2) and place it on a vacuum adsorption platform with the PVDF membrane side facing up, pour the epoxy resin prepared in (3) on one side of the PVDF membrane, and use a coater to evenly apply the epoxy resin starting from one side of the PVDF membrane; (5) placing the film coated with epoxy resin in step (4) in a coating machine to remove excess epoxy resin on the surface, and setting the speed of the coating machine in three stages: ≥800 speed for 3 seconds, ≥2000 speed for 20 seconds, and ≥3000 speed for 20 seconds; (6) Spread the sample obtained in the previous step flat on a clean table, and stick the other film from (2) on the sample (where the PVDF film side is in contact with the epoxy resin glue), then use a scraper to scrape and remove the bubbles between the two films; finally, press the two films with a heavy block, put them in a vacuum box, and let them stand for more than 24 hours to cure; (7) After the epoxy resin is cured, remove the weight block and the thermal release film on the surface to obtain a laminated PVDF membrane.

[0006] The core of the piezoelectric sensor array preparation technology is to form patterned electrodes on single-layer and multi-layer PVDF or P (VDF-TrFE) piezoelectric films. The specific method includes: Magnetron sputtering method: According to the positive electrode pattern, laser etch the thermal release pattern mask tape of the positive electrode, cover it on the surface of the piezoelectric film, use magnetron sputtering equipment to sputter chromium and gold materials onto the sample, remove the pattern mask tape to form a patterned positive electrode, and then magnetron sputter a full-surface chromium-gold electrode on the back of the piezoelectric film.

[0007] Screen printing method 1: Make screen printing plates according to the positive and negative electrode patterns respectively. Use screen printing technology to print the positive electrode on one side of the piezoelectric film. After the positive electrode silver paste is cured, use machine vision to flip and align it, and screen print the negative electrode on the other side of the piezoelectric film.

[0008] Screen printing method 2: Make screen printing plates according to the positive and negative electrode patterns respectively, use manual screen printing to print the positive electrode on one side of the piezoelectric film, after the positive electrode silver paste is cured, print the negative electrode pattern on the bottom platform and cover it with a layer of PET transparent film, place the piezoelectric film on the transparent film, align the array element positive electrode with the negative electrode on the bottom platform, and then print the negative electrode on the other side of the piezoelectric film.

[0009] Combined method of magnetron sputtering and screen printing: a screen printing plate is made according to the negative electrode pattern, and the negative electrode is first printed on one side of the piezoelectric film by screen printing. The edge contour of the piezoelectric film and the thermal release pattern mask tape of the positive electrode are laser etched, and the pattern mask tape is covered on the other side of the piezoelectric film using an adhesive positioning tool. The hollow area of ​​the mask tape is aligned with the position of the screen-printed negative electrode array element, and chromium and gold materials are sputtered on the surface using a magnetron sputtering device. After removing the pattern mask tape, a patterned positive electrode is formed.

[0010] Advantages and disadvantages of the three methods: Magnetron sputtering method: It is impossible to prepare hollow back electrode patterns and the degree of interlayer adhesion cannot be directly observed.

[0011] Screen printing method 1: It requires the use of machine vision fully automatic screen printing equipment, and the processing cost is high.

[0012] Screen printing method 2: The accuracy of the flipping and alignment of the positive electrode and the negative electrode is the worst among the several methods of the present invention, but the cost is the lowest.

[0013] Combined method of magnetron sputtering and screen printing: It takes into account direct observation and precision of interlayer adhesion, but the process steps are the most complicated.

[0014] In order to prepare the multi-frequency imaging sonar piezoelectric sensor array as described above, quasi-femtosecond laser etching, screen printing, pattern masking, flip electrode alignment, magnetron sputtering electrode spraying, pattern bonding alignment, vacuum curing electrical connection and other processes are adopted. Taking PVDF piezoelectric film as an example, the specific steps include: S1. Select any of the above methods to make a double-sided electrode; S2. PVDF membrane laser etching: A quasi-femtosecond laser cutting machine was used to perform laser positioning and etching of the edge contour of the PVDF membrane with the help of the four corner array elements of the electrode; S3.Alignment of PVDF film and PCB circuit board: S31. Place the PCB board into the PCB board fixture, and buckle the mucosal positioning tool on the PCB board; S32. A conductive silver paste mask is made by quasi-femtosecond laser etching, and a conductive silver paste is coated on the mask, and the mask is removed after each hole is filled with the conductive silver paste; Specifically, a thermal release film is taken and etched using a quasi-femtosecond laser cutting machine to cut into a circular hole array, wherein the array element aperture is ≤35% of the array element size, and the mask size, number of array elements, and array element center spacing are consistent with the patterned positive electrode.

[0015] S33. With the aid of a mucosal positioning tool, the PVDF membrane prepared with positive and negative electrodes and laser-etched is bonded to the PCB board through a conductive silver paste, wherein the patterned positive electrode side faces the PCB circuit board; S34. Cover the piezoelectric film with a plastic protective film slightly smaller in length and width than the PVDF size, insert a pressing weight block, and then cure for ≥24 hours; S4. Vacuum-cured electrical connection: apply epoxy resin around the PVDF film, press the piezoelectric film with a polytetrafluoroethylene weight before curing and use a vacuum pump with a vacuum degree of ≤10Pa to remove bubbles for ≥30 minutes, then cure in a vacuum box for more than 12 hours; after the edge epoxy resin is cured, use conductive silver paste to connect the ground electrode to the four ground holes of the PCB circuit board.

[0016] S5. Make the acoustic matching layer. With the help of the potting mold, use the back-filling method to form the matching layer mold. Assemble the matching layer molding mold to the front side of the shell and fix it with a detachable fastener. The shell is equipped with a 1 / 4 wavelength thickness positioning slot. Put the sample into the shell and limit it through the slot. Mix the matching layer potting glue material evenly, and pour it from the matching layer filling port after vacuum degassing. When pouring, tilt the sample to vacuum for ≥30 minutes, and then put all of them into the oven and dry them at 40℃ for ≥24 hours. The production is completed.

[0017] The present invention has the following beneficial effects: (1) The high-density ultrasonic sensor array prepared by the present invention can have an array element number of ≥24×24 formed at one time, which can obtain the pickup of ≥576 array signals; (2) The prepared sensor array can remain unchanged under high pressure difference and 50°C environment and can be used in deep sea environment; (3) 3D imaging distance ≥ 10m; (4) The overall electrical consistency is good, and the array element abnormality rate is less than 0.5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application, 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 application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 Schematic diagram of the overall design of the multi-frequency imaging sonar piezoelectric ultrasonic sensor array.

[0020] Figure 2 Schematic diagram of the patterned positive electrode.

[0021] Figure 3 Schematic diagram of connecting the ground electrode.

[0022] Figure 4 Schematic diagram of bonding PVDF or P (VDF-TrFE) piezoelectric film to PCB board.

[0023] Figure 5 Schematic diagram of auxiliary tools for preparing sensor arrays.

[0024] Figure 6 Schematic diagram of the matching layer potting mold.

[0025] Figure 7 This is the square array capacitor consistency test result.

[0026] Figure 8 It is the continuity test result of the array element receiving phase.

[0027] Fig. 9 This is the test result of the array element receiving signal.

[0028] Among them: 1 is a PCB circuit board, 101 is a PCB circuit board electrical connector, 2 is a conductive silver paste dot, 3 is a patterned positive electrode, 301 is a positive electrode array element, 302 is a positive electrode virtual transition array element, 303 is a vertex angle positioned by laser etching, 4 is a PVDF or P (VDF-TrFE) piezoelectric film, 5 is a connected ground electrode (negative electrode), 501 is a negative electrode array element, 502 is a negative electrode virtual transition array element, 503 is a vertex angle positioned by laser etching, 6 is an acoustic matching layer, 7 is a PCB board fixture, 8 is a mucosal positioning tool, 9 is a pressing weight block, 10 is a sensor array housing, 1001 is a positioning slot, 11 is a matching layer molding mold, and 12 is a circuit board with a piezoelectric layer bonded. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with specific examples. The following examples are only used to illustrate the present invention and are not intended to limit the scope of application of the present invention. The technical features of each embodiment of the present invention can be combined accordingly without conflicting with each other. Without departing from the spirit and essence of the present invention, the modifications or replacements made to the method, steps or conditions of the present invention all belong to the scope of the present invention.

[0030] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the materials and reagents used are reagents and materials that can be obtained from commercial channels unless otherwise specified.

[0031] refer to Figures 1 to 3 The PVDF or P (VDF-TrFE) piezoelectric film 4 used in the present invention has a thickness of 40 μm-500 μm. The piezoelectric film 4 with a thickness exceeding 200 μm can be obtained by a lamination method. The multilayer PVDF or P (VDF-TrFE) piezoelectric material is prepared by laminating a piezoelectric film + epoxy resin + piezoelectric film. Taking the preparation of a laminated PVDF film with a thickness of 400 μm as an example, the specific steps are as follows: (1) Take two pieces of PVDF membrane with a thickness of 200 μm and a size of ≥105 mm × 105 mm; (2) Take two pieces of thermal release films of the same size as the PVDF film and stick them on the surface of the PVDF film to prevent the surface from being contaminated by the epoxy resin described below; (3) Prepare epoxy resin glue. Take epoxy resin A glue and epoxy resin B glue, mix them evenly, and put them into a vacuum box to remove bubbles for ≥ 20 minutes, where the vacuum degree of the vacuum box is ≤-0.1MPa; (4) Take a piece of sample from (2) and place it on a vacuum adsorption platform with the PVDF membrane side facing up, pour the epoxy resin prepared in (3) on one side of the PVDF membrane, and use an applicator to evenly apply the epoxy resin starting from one side of the PVDF membrane; (5) placing the film coated with epoxy resin in step (4) in a coating machine to remove excess epoxy resin on the surface, and setting the speed of the coating machine in three stages: ≥800 speed for 3 seconds, ≥2000 speed for 20 seconds, and ≥3000 speed for 20 seconds; (6) Spread the sample obtained in the previous step flat on a clean table, and stick the other sample from (2) on the sample (where the PVDF film side is in contact with the epoxy resin glue), then use a scraper to scrape and remove the bubbles between the two films; finally, press the two films with a heavy block, put them in a vacuum box, and let them stand for more than 24 hours to cure; (7) After the epoxy resin is cured, remove the weight block and the thermal release film on the surface to obtain a laminated PVDF membrane.

[0032] Example 1 (Magnetron Sputtering Method) The present embodiment provides a sensor array for a multi-frequency imaging sonar, the structure of which includes an acoustic matching layer 6, a connected ground electrode (negative electrode) 5, a PVDF or P (VDF-TrFE) piezoelectric film 4, a patterned positive electrode 3, and a PCB circuit board 1.

[0033] In this embodiment, the double-sided electrodes are prepared by magnetron sputtering, the sensor array is a square orthogonal array of ≥24×24, the array elements are square, the center spacing of the array elements is 1 wavelength of the target frequency, and the material is PVDF or P (VDF-TrFE) piezoelectric film 4.

[0034] Preparation method: (1) Take a piece of thermal release film and cut a square hole array in the center of the film using a laser cutter to make a positive electrode mask. (2) Paste the positive electrode mask onto the surface of a PVDF or P (VDF-TrFE) piezoelectric film that is larger than the array design size; (3) The film obtained in step (2) is attached to a glass sheet with the mask side facing upward, and placed in a magnetron sputtering system to sputter a positive electrode 3, including a positive electrode array element 301 and a virtual transition array element 302. The sputtering thickness of chromium and gold materials is ≥50nm, and the surface resistance is ≤1Ω. To ensure the consistency of the surface resistance, the sample is aligned with the center of the target material and rotated for ≥1 time, and the sample is eccentrically rotated with the target material and sputtered for ≥1 time. After the sputtering is completed, the mask is removed; (4) Using a laser cutting machine, the film of step (3) is positioned and cut into the designed size according to the four vertices 303 of the square array; (5) Place the film from step (4) on a glass sheet with the side of the film not sputtered facing upwards, and place it in a magnetron sputtering system to sputter a full-through ground electrode. The thickness of the chromium and gold electrodes should be ≥50nm. After sputtering, take it out; (6) Take a piece of thermal release film that is larger than the design size of the array and cut a circular hole array in the center using a laser cutter; (7) Stick the film obtained in step (6) on the PCB board according to the screen printing and array position of the PCB board, and place the PCB board into the PCB board fixture 7; (8) Take the conductive silver paste and evenly apply it on the surface of the film in step (6). After each hole is filled with the conductive silver paste, scrape off the excess silver paste and carefully remove the thermal release film, leaving a conductive silver paste point 2 on the PCB circuit board; (9) Figure 5 As shown, the adhesive film positioning tool 8 is buckled into the PCB board in step (8), and the film of the sputtered electrode in step (5) is pasted on the PCB board in step (8) with the help of the alignment tool, wherein the patterned positive electrode 3 faces the PCB board, as shown in FIG. Figure 4 Then, a piece of plastic film with the design size of the array is placed on the surface of the film, and a pressing weight block 9 is put in and pressed for 24 hours; (10) Prepare epoxy resin. Take epoxy resin A glue and epoxy resin B glue, mix and stir evenly, then put them into a vacuum box to remove bubbles for ≥ 20 minutes, where the vacuum degree of the vacuum box is ≤ -0.1MPa; (11) Use a syringe with a pinhole size of 0.5-1.5 mm to extract the epoxy resin prepared in step (10); (12) After the conductive silver paste is cured, remove the pressing weight block 9 and the mucosal positioning tool 8 in (9), and use a syringe to apply a small amount of epoxy resin around the PVDF membrane; (13) Place a polytetrafluoroethylene weight block on the surface of the piezoelectric film 4 of the above sample, and then put them into a vacuum box to evacuate the air, further remove the epoxy resin bubbles, and exhaust the air between the contact surface of the PVDF film and the circuit board. After no obvious bubbles are exhausted, turn off the power of the vacuum pump, maintain pressure and cure for ≥ 24 hours, where the vacuum degree of the vacuum box is ≤ -0.1MPa; (14) Take the sample obtained in step (13), connect the ground electrode to the four ground holes of the PCB circuit board 1 with conductive silver paste, and cure at room temperature for ≥ 24 hours to obtain a circuit board 12 with a piezoelectric layer bonded; (15) Brush a layer of release agent on the matching layer forming mold 11 and assemble it to the front side of the housing 10 and fix it with a detachable fastener. The housing 10 is provided with a 1 / 4 wavelength thickness positioning slot 1001. The sample 12 in step (14) is placed upside down in the housing, that is, the PCB circuit board electrical connector 101 faces outward and is limited by the positioning slot 1001. Figure 6 As shown. The matching layer potting glue material is mixed evenly, and after vacuum degassing treatment, it is poured from the matching layer potting port. When pouring, the sample is tilted and vacuumed for ≥30 minutes, and then all are placed in an oven and dried at 40℃ for ≥24 hours. After the matching layer material is cured, the fasteners and molds are removed, and the production is completed.

[0035] Example 2 (screen printing) In this embodiment, the double-sided electrodes are prepared by screen printing, the sensor array is a square orthogonal array of ≥24×24, the array elements are square, the center spacing of the array elements is 1 wavelength of the target frequency, and the material is PVDF or P (VDF-TrFE) piezoelectric film 4. Screen printing includes: (1) Design and manufacture the corresponding screen printing plates for the positive and negative electrodes according to the positive and negative electrode patterns and taking into account the cross marks required for flipping and alignment; (2) Fix the positive electrode screen printing plate on the printing table, take a piece of piezoelectric film 4 that is larger than the design size of the array and lay it flat on the printing table, adjust the position of the piezoelectric film 4 so that it is placed directly under the electrode pattern, and fix the PVDF film around with tape to prevent displacement during printing; Screen printing method 1: (3) Pour an appropriate amount of conductive silver paste on one side of the electrode pattern of the screen printing plate, and use a machine vision fully automatic screen printing dedicated equipment to print a positive electrode pattern on one side of the surface of the piezoelectric film 4, including a positive electrode array element 301 and a positive electrode virtual transition array element 302. Remove the piezoelectric film 4 and let it stand at room temperature for ≥24 hours. The patterned positive electrode 3 is completed; (4) Fix the negative electrode side of the piezoelectric film 4 on the screen printing table, use the machine vision of the equipment and the cross mark on the piezoelectric film 4 to realize the flipping and alignment of the positive and negative electrode patterns, screen print the negative electrode on the other side of the piezoelectric film 4, remove the piezoelectric film 4, and let it stand at room temperature for ≥24 hours. The negative electrode 5 is completed; Screen Printing Method 2: (3) Pour an appropriate amount of conductive silver paste on one side of the electrode pattern of the screen printing plate, apply a certain amount of pressure to the conductive silver paste on the screen printing plate with a squeegee, and move toward the other end of the electrode pattern of the screen printing plate at the same time. After ensuring that the printing is complete, gently lift the printing plate, including the positive electrode array element 301 and the positive electrode virtual transition array element 302, remove the piezoelectric film 4, and let it stand at room temperature for ≥ 24 hours. The patterned positive electrode 3 is completed, including the positive electrode array element 301 and the positive electrode virtual transition array element 302; (4) Fix the negative electrode screen printing plate on the printing table, pour an appropriate amount of conductive silver paste on the negative electrode screen printing plate along one side of the electrode pattern, use a squeegee to apply a certain pressure on the conductive silver paste on the screen printing plate, and move toward the other end of the electrode pattern of the screen printing plate at the same time, so that the negative electrode array element 501 and the negative electrode virtual transition array element 502 are printed on the bottom platform, lift the printing plate, take a PET transparent film larger than the array design size and cover it on the electrode pattern of the bottom platform, and place the film printed with the positive electrode (3) on the PET film. Through the position of the array element, the positive electrode on the piezoelectric film 4 is aligned with the negative electrode on the bottom surface, and the piezoelectric film 4 is fixed around with tape. During the process, the position of the printing plate remains unchanged. Then, a proper amount of conductive silver paste is poured on the printing plate in the same way, and a certain pressure is applied to the conductive silver paste on the screen printing plate with a squeegee. At the same time, it moves toward the other end of the electrode pattern of the screen printing plate. After ensuring that the printing is complete, the printing plate is gently lifted, and the piezoelectric film 4 is removed. It is left to stand at room temperature for ≥24 hours. The negative electrode array element 501 and the negative electrode virtual transition array element 502 are completed. (5) Take the piezoelectric film printed with positive and negative electrodes, identify the four vertices 303 of the array with a laser cutting machine, and position and cut it into a film of the designed size of the array; (6) Take a piece of thermal release film that is larger than the design size of the array, and cut a circular hole array of the design size at its center using a laser cutter; (7) Stick the film obtained in step (6) on the circuit board according to the screen printing and array position of the circuit board, and place the PCB board into the PCB board fixture 7; (8) Take the conductive silver paste and evenly apply it on the PCB board with the mask. After each hole is filled with the conductive silver paste, scrape off the excess silver paste on the surface and carefully remove the thermal release film, leaving a conductive silver paste point 2 on the PCB circuit board; (9) Figure 5 As shown, the mucosal positioning tool 8 is buckled into the PCB board of step (8), and the sample of step (5) is pasted on the PCB board of step (8) with the help of the alignment tool, wherein the patterned positive electrode 3 faces the PCB board, as shown in FIG. Figure 4 Then, a plastic film of the designed size of the array is placed on the surface of the membrane for protection, and a pressing weight block 9 is put in and pressed for ≥24 hours; (10) Prepare epoxy resin. Take epoxy resin A glue and epoxy resin B glue, mix them evenly, and put them into a vacuum box to remove bubbles for ≥ 20 minutes, where the vacuum degree of the vacuum box is ≤-0.1MPa; (11) Use a syringe with a pinhole size of 0.5-1.5 mm to extract the epoxy resin prepared in step (10); (12) After the conductive silver paste is solidified, remove the weight block and alignment module in (9), and use a syringe to apply a small amount of epoxy resin around the piezoelectric film 4; (13) Place a polytetrafluoroethylene weight block on the surface of the piezoelectric film 4 of the above sample, and then put them into a vacuum box to evacuate the air, further remove the epoxy resin bubbles, and exhaust the air between the contact surface of the piezoelectric film 4 and the circuit board. After no obvious bubbles are exhausted, turn off the power of the vacuum pump and maintain the pressure for curing for ≥ 24 hours, wherein the vacuum degree of the vacuum box is ≤ -0.1MPa; (14) Take the sample obtained in step (13), connect the ground electrode to the four ground holes of the PCB circuit board 1 with conductive silver paste, and cure at room temperature for ≥ 24 hours to obtain a circuit board 12 with a piezoelectric layer bonded; (15) Brush a layer of release agent on the matching layer forming mold 11 and assemble it to the front side of the housing 10 and fix it with a detachable fastener. The housing 10 is provided with a 1 / 4 wavelength thickness positioning slot 1001. The sample 12 in step (14) is placed upside down in the housing, that is, the PCB circuit board electrical connector 101 faces outward and is limited by the positioning slot 1001. Figure 6 As shown. The matching layer potting glue material is mixed evenly, and after vacuum degassing, it is poured from the matching layer potting port. When pouring, the sample is tilted and vacuumed for ≥20 minutes, and then all are placed in an oven and dried at 40℃ for ≥24 hours. After the matching layer material is cured, the fasteners and molds are removed, and the production is completed.

[0036] Example 3 (screen printing + magnetron sputtering) In this embodiment, the positive and negative electrodes are prepared by combining screen printing and magnetron sputtering. The sensor array is a square orthogonal array of ≥24×24, the array elements are square, the center spacing of the array elements is 1 wavelength of the target frequency, and the material is PVDF or P (VDF-TrFE) piezoelectric film 4: (1) Making a screen printing plate according to the designed pattern of the connected ground electrode (negative electrode) 5; (2) Fix the negative electrode screen printing plate on the printing table, take a piece of piezoelectric film 4 larger than the design size of the array and lay it flat on the printing table, adjust the position of the PVDF film or P (VDF-TrFE) piezoelectric film 4 so that it is placed directly under the electrode pattern, and fix the PVDF film or P (VDF-TrFE) piezoelectric film 4 with tape to prevent it from shifting during printing; (3) Pour a proper amount of conductive silver paste on one side of the electrode pattern of the negative electrode screen printing plate, apply a certain pressure on the conductive silver paste on the screen printing plate with a squeegee, and move toward the other end of the electrode pattern of the screen printing plate at the same time. After ensuring that the printing is complete, gently lift the printing plate, remove the PVDF film or P (VDF-TrFE) piezoelectric film 4, and let it stand at room temperature for ≥ 24 hours. The negative electrode array element 501 and the negative electrode virtual transition array element 502 are completed; (4) Take the film printed with the negative electrode, identify the four top corners 503 of the array with a laser cutting machine, and position and cut it into a film of the designed size of the array; (5) Take a piece of thermal release film that is larger than the design size of the array, and use a laser cutter to cut a square hole array of the design size in the center of the film to obtain a positive electrode mask; (6) Using the mucosal positioning tool 8, the positive electrode mask is pasted onto the non-electrode printed surface of the piezoelectric film 4 in step (4); (7) Paste the sample in step (6) on a glass sheet larger than the array design size and with a thickness of ≤1 mm, with the mask side facing up, and place it in a magnetron sputtering system to sputter the array element electrodes, including the positive electrode array element 301 and the positive electrode virtual transition array element 302. The chromium and gold are sputtered ≥50 nm each, and the surface resistance is ≤1Ω. To ensure the consistency of the surface resistance, the sample and the target are rotated and sputtered ≥1 time at the center, and the sample and the target are rotated and sputtered ≥1 time at the eccentricity. After the sputtering is completed, remove the mask; (8) Take a piece of thermal release film that is larger than the design size of the array, and cut it into a circular hole array of the design size at its center using a laser cutter; (9) Stick the film obtained in step (8) on the PCB board according to the screen printing and array position of the PCB board, and place the PCB board into the PCB board fixture 7; (10) Take the conductive silver paste and evenly apply it on the surface of the film in step (9). After each hole is filled with the conductive silver paste and the excess silver paste on the surface is scraped off, the thermal release film is carefully removed, leaving a conductive silver paste point 2 on the PCB circuit board; (11) Figure 5 As shown, the mucosal positioning tool 8 is buckled into the PCB board of step (10), and the sample of step (7) is pasted on the PCB board of step (10) with the help of the alignment tool, wherein the patterned positive electrode 3 faces the PCB board, as shown in FIG. Figure 4 As shown. Then, a piece of thermal release film of the same size as the array design is placed on the surface of the film for protection, and a pressing weight block 9 is used for pressing for ≥ 24 hours; (12) Prepare epoxy resin. Take epoxy resin A glue and epoxy resin B glue, mix them evenly, and put them into a vacuum box to remove bubbles for ≥ 20 minutes, where the vacuum degree of the vacuum box is ≤-0.1MPa; (13) Use a syringe with a pinhole size of 0.5-1.5 mm to extract the epoxy resin after the bubbles are extracted in step (12); (14) After the conductive silver paste is dry, remove the weight block and alignment module in (11), and use a syringe to apply a small amount of epoxy resin around the piezoelectric film 4; (15) Place a polytetrafluoroethylene weight block on the surface of the piezoelectric film 4 of the above sample, and then put them into a vacuum box to evacuate the air, further remove the bubbles in the epoxy resin, and exhaust the air between the contact surface of the PVDF film and the circuit board. After no obvious bubbles are exhausted in the epoxy resin, turn off the power of the vacuum pump, maintain pressure and cure for ≥ 24 hours, wherein the vacuum degree of the vacuum box is ≤ -0.1MPa; (16) Take the sample obtained in step (15), connect the ground electrode to the four ground holes of the PCB circuit board 1 with conductive silver paste, and cure at room temperature for ≥ 24 hours to obtain a circuit board 12 with a piezoelectric layer bonded; (17) Brush a layer of release agent on the matching layer forming mold 11 and assemble it to the front side of the housing 10 and fix it with a detachable fastener. The housing 10 is provided with a 1 / 4 wavelength thickness positioning slot 1001. The sample in step (16) is placed upside down in the housing, that is, the PCB circuit board electrical connector 101 faces outward and is limited by the slot 1001. Figure 6 As shown. The matching layer potting glue material is mixed evenly, and after vacuum degassing treatment, it is poured from the matching layer potting port. When pouring, the sample is tilted and vacuumed for ≥30 minutes, and then all are placed in an oven and dried at 40℃ for ≥24 hours. After the matching layer material is cured, the fasteners and molds are removed, and the production is completed.

[0037] The capacitance test results of the sensor array of the multi-frequency imaging sonar are as follows: Figure 7 As shown, the horizontal axis corresponds to the connector number of the 64 channels, with a total of 9 columns of connectors. The array element abnormality rate is <0.5%. An external sound source is placed in the front and upper part of the sensor array to test the key performance of the overall array element, namely phase consistency. The phase continuity test results are shown in Figure 8As shown, blue represents a small time delay. From the time delay distribution of the array element signal, it can be seen that the distance between the array element and the external sound source from the top to the bottom of the array is from near to far, which is in line with the actual law and the array element distribution is normal; the array element receiving signal test results are as follows Fig. 9 As shown in the figure, there are a total of 576 array elements receiving signals. The vertical axis is the number of channels and the horizontal axis is the number of points at 4M sampling rate. It can be seen that all array elements can receive signals and work normally. The yield rate of array element signal reception is 100%.

[0038] The above-described embodiments are only preferred solutions of the present invention and are not intended to limit the present invention. A person skilled in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A method for preparing a piezoelectric sensor array for a multi-frequency imaging sonar, characterized in that: The array form is a square array with a size of ≤8 inches, the array elements are square, the number of array elements is ≥24×24, the imaging frequency is ≥300kHz, and the PVDF and P (VDF-TrFE) sensor arrays are integrated and packaged on the PCB circuit board by laser etching, screen printing, magnetron sputtering or graphic mask technology; The core of the preparation process is to form patterned electrodes with single-layer and multi-layer PVDF or P (VDF-TrFE) piezoelectric films. The patterned electrode method specifically includes: Magnetron sputtering method: laser etch the thermal release pattern mask tape of the positive electrode according to the positive electrode pattern, cover it on the surface of the piezoelectric film, use magnetron sputtering equipment to sputter chromium and gold materials onto the sample, remove the pattern mask tape to form a patterned positive electrode, and then magnetron sputter the back of the piezoelectric film to form a full-surface chromium-gold electrode; or Screen printing method 1: Make screen printing plates according to the positive and negative electrode patterns respectively, and print the positive electrode on one side of the piezoelectric film using screen printing technology. After the positive electrode silver paste is cured, use machine vision to flip the surface and align it, and screen print the negative electrode on the other side of the piezoelectric film; or Screen printing method 2: Make screen printing plates according to the positive and negative electrode patterns respectively, use manual screen printing to print the positive electrode on one side of the piezoelectric film, after the positive electrode silver paste is cured, print the negative electrode pattern on the bottom platform and cover it with a layer of PET transparent film, place the piezoelectric film on the transparent film, align the array element positive electrode with the negative electrode on the bottom platform, and then print the negative electrode on the other side of the piezoelectric film; or Combined method of magnetron sputtering and screen printing: a screen printing plate is made according to the negative electrode pattern, and the negative electrode is first printed on one side of the piezoelectric film by screen printing. The edge contour of the piezoelectric film and the thermal release pattern mask tape of the positive electrode are laser etched, and the pattern mask tape is covered on the other side of the piezoelectric film using an adhesive positioning tool. The hollow area of ​​the mask tape is aligned with the position of the screen-printed negative electrode array element, and chromium and gold materials are sputtered on the surface using a magnetron sputtering device. After removing the pattern mask tape, a patterned positive electrode is formed.

2. The preparation method according to claim 1, characterized in that The center spacing of the array elements of the square array is ≤ 1 wavelength of the operating frequency, and the length and width of the array elements are ≥ 70% of the center spacing of the array elements.

3. The preparation method according to claim 1, characterized in that: The method for bonding the piezoelectric film to the PCB circuit is: first laser etching a heat-release mask tape, then pasting it on the PCB circuit board and evenly applying conductive silver paste, after removing the mask tape, only retaining the conductive silver paste at the array element position, and bonding the piezoelectric film to the PCB circuit board with the help of the viscosity of the conductive silver paste.

4. The preparation method according to claim 1, characterized in that: The edge of the PVDF or P (VDF-TrFE) piezoelectric film bonded to the PCB circuit board is coated with epoxy resin glue. Before curing, a polytetrafluoroethylene weight block is pressed on the piezoelectric film and a vacuum box with a vacuum degree of ≤10Pa is used to remove the air between the layers; The size of the PTFE weight is designed to be 90% of the size of the piezoelectric film.

5. The preparation method according to claim 1, characterized in that: The multi-layer PVDF or P (VDF-TrFE) piezoelectric material is formed by uniformly coating epoxy resin on each layer of piezoelectric film with a coating machine, thinning it by spin coating, and then bonding multiple piezoelectric films together. The thickness of the epoxy resin bonding layer is ≤10 μm.

6. The preparation method according to claim 1, characterized in that: The magnetron sputtering method is to first plate chromium and then gold, the sample is aligned with the center of the target material and rotated and sputtered ≥1 time, the sample and the target material are eccentrically rotated and sputtered ≥1 time, and the thickness of the electrode composed of chromium and gold materials is ≥50nm.

7. The preparation method according to claim 1, characterized in that: The temperature of thermal release pattern mask tape heating and peeling is less than half of the Curie temperature of PVDF and P (VDF-TrFE) piezoelectric materials.

8. The preparation method according to claim 1, characterized in that: The bonding positioning auxiliary tool comprises a PCB circuit board positioning fixture, a piezoelectric film bonding positioning module, and a piezoelectric film pressing module.

9. The preparation method according to claim 1, characterized in that: The array elements in the screen-printed negative electrode pattern are connected to each other through a cross pattern.

10. The preparation method according to claim 1, characterized in that: The positive electrode patterns of the screen printing method 1 and the screen printing method 2 have cross-shaped positioning marks for flipping and aligning.

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