A Preparation Method of a Piezoelectric Sensing Array for a Multi-Frequency Imaging Sonar

Abstract

The present invention discloses a method for preparing a piezoelectric sensor array for multi-frequency imaging sonar. The method adopts PVDF or P (VDF-TrFE) piezoelectric film as the core material, and integrates processes such as automatic coating, spin coating and thinning, laser etching, screen printing, magnetron sputtering, graphic mask and vacuum packaging. It can prepare a square orthogonal array of ≤8 inches, which can be used for multi-frequency and multi-beam three-dimensional acoustic imaging with a broadband of ≥300kHz. The array electrodes are formed into patterned electrodes by magnetron sputtering, screen printing or a combination of the two to achieve one-time molding of high-density array elements. Combined with laser etching and alignment technology, the array size and array element position accuracy are ensured, and epoxy resin and vacuum packaging technology are used to enhance the interlayer bonding strength. The sensor array has electrical consistency, an array element abnormality rate of <0.5%, can work stably under high voltage difference and high pressure environment, and an imaging distance greater than or equal to ten meters. It is suitable for detection of seabed landforms and target identification.

Description

Technical Field

[0001] The present invention relates to the technical field of underwater acoustic transducers, and in particular to a method for preparing a piezoelectric sensor array for 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 operation (typically <100kHz) and low-density array element designs (e.g., linear arrays, cross arrays, and 8×8 arrays). Their spatial resolution is generally insufficient (typically >10cm), and their signal dimensionality is limited, making it difficult to achieve detailed three-dimensional reconstruction of complex seafloor topography and identify the characteristics of small, weak targets. Existing sonar arrays often use PZT (lead zirconate titanate) piezoelectric ceramics as the transducer material. However, their inherent brittleness and high acoustic impedance (approximately 10 times that of water) can lead to acoustic wave interface reflection losses. Furthermore, in deep-sea high-pressure environments (>10MPa), deformation of the array structure can easily lead to material failure or piezoelectric performance degradation, limiting the reliability of long-term deep-sea detection.

[0003] In recent years, flexible piezoelectric materials such as PVDF (polyvinylidene fluoride) and its copolymer P(VDF-TrFE) (copolymer of vinylidene fluoride and trifluoroethylene) have become promising candidates for underwater acoustic transducers due to their acoustic impedance close to that of water (1.5 MRayl), broadband response (10 kHz to 10 MHz), and excellent mechanical flexibility. However, existing PVDF array fabrication technologies for imaging sonars suffer from the following challenges: a single imaging frequency, unable to simultaneously meet the requirements for long-range detection and close-range high resolution; limited array density and aperture; susceptibility to interlaminar delamination; insufficient element positioning accuracy, resulting in elevated sidelobe levels (>-15 dB) during beamforming; and existing packaging technologies, which often utilize non-hermetic structures, are unable to effectively withstand material deformation caused by deep-sea hydrostatic pressure. Therefore, a piezoelectric sensor array fabrication method that combines high element density, precise electrode patterning, strong interface bonding, and adaptability to deep-sea environments is needed to meet the requirements for high-resolution deep-sea acoustic imaging. Summary of the Invention

[0004] The present invention aims to provide a method for preparing a piezoelectric sensor array for multi-frequency imaging sonar. The array covers multiple sound sources, exhibits high sensitivity, withstands high pressure differentials and temperatures ≥50°C, and is suitable for use in deep-sea environments. The piezoelectric sensor array comprises an acoustic matching layer, a connected ground electrode (negative electrode), a single or multi-layer PVDF or P(VDF-TrFE) piezoelectric film, a patterned positive electrode, and a printed circuit board (PCB). The multi-frequency imaging sonar piezoelectric sensor array is a square orthogonal array ≤8 inches in size, with ≥24×24 elements. Virtual transition elements are positioned in the outermost circle, and the element center spacing is ≤1 wavelength of the operating frequency. The elements are square, with side lengths ≥70% of the element center spacing.

[0005] The thickness of the single-layer PVDF or P (VDF-TrFE) piezoelectric film is 40 μm-500 μm. The multi-layer 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:

[0006] (1) Take two pieces of PVDF membrane with a thickness of 200 μm and a size of ≥105 mm × 105 mm;

[0007] (2) Take two pieces of thermal release films of the same size as the PVDF membrane and stick them on the surface of the above PVDF membrane to prevent the surface from being contaminated by the following epoxy resin;

[0008] (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;

[0009] (4) Take a piece of PVDF membrane with a thermal release film 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.

[0010] (5) Place the film coated with epoxy resin in step (4) in a glue roller to remove excess epoxy resin on the surface. The speed of the glue roller is set to three stages: ≥800 rpm for 3 seconds, ≥2000 rpm for 20 seconds, and ≥3000 rpm for 20 seconds.

[0011] (6) Spread the sample obtained in the previous step 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 smooth the air bubbles between the two films; finally, press the two films with a heavy object, place them in a vacuum box, and let them stand for more than 24 hours to cure;

[0012] (7) After the epoxy resin is cured, remove the weight block and remove the thermal release film on the surface to obtain the laminated PVDF membrane.

[0013] The core of this piezoelectric sensor array fabrication technology lies in forming patterned electrodes on single-layer and multi-layer PVDF or P(VDF-TrFE) piezoelectric films. The specific methods include:

[0014] Magnetron sputtering method: According to the positive electrode pattern, the thermal release pattern mask tape of the positive electrode is laser-etched and covered on the surface of the piezoelectric film. The chromium and gold materials are sputtered onto the sample using a magnetron sputtering device. After the pattern mask tape is removed, a patterned positive electrode is formed. Subsequently, a chromium-gold electrode that fully covers the entire surface is magnetron sputtered on the back of the piezoelectric film.

[0015] 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 solidifies, use machine vision to flip the surface and align it, and then screen print the negative electrode on the other side of the piezoelectric film.

[0016] 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 solidifies, 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 and align the positive electrode of the array element with the negative electrode on the bottom platform. Then print the negative electrode on the other side of the piezoelectric film.

[0017] Combined method of magnetron sputtering and screen printing: a screen printing plate is made according to the negative electrode pattern, 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, so that 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.

[0018] Advantages and disadvantages of the three methods:

[0019] Magnetron sputtering method: It is impossible to prepare hollow back electrode patterns and the degree of interlayer adhesion cannot be directly observed.

[0020] Screen printing method 1: Requires the use of machine vision fully automatic screen printing equipment, and the processing cost is high.

[0021] Screen printing method 2: The accuracy of the alignment of the positive electrode and the negative electrode is the worst among the methods of the present invention, but the cost is the lowest.

[0022] 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.

[0023] To prepare the multi-frequency imaging sonar piezoelectric sensor array described above, processes such as quasi-femtosecond laser etching, screen printing, pattern masking, flip-over electrode alignment, magnetron sputtering electrode deposition, pattern bonding alignment, and vacuum curing electrical connection were adopted. Taking PVDF piezoelectric film as an example, the specific steps include:

[0024] S1. Select any of the above methods to make a double-sided electrode;

[0025] S2. PVDF membrane laser etching:

[0026] Using a quasi-femtosecond laser cutting machine, the edge profile of the PVDF membrane is laser-positioned and etched with the help of the four corner array elements of the electrode;

[0027] S3. Align the PVDF film and PCB circuit board:

[0028] S31. Place the PCB board into the PCB board fixture and buckle the mucosal positioning tool onto the PCB board;

[0029] S32. A conductive silver paste mask is made by quasi-femtosecond laser etching, and a conductive silver paste is coated on the mask. After each hole is filled with a conductive silver paste, the mask is removed;

[0030] Specifically, a thermal release film is taken and etched using a quasi-femtosecond laser cutting machine to cut into a circular hole array, where 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.

[0031] S33. Using a mucosal positioning tool, the PVDF membrane prepared with positive and negative electrodes and laser-etched is bonded to the PCB board using a conductive silver paste, with the patterned positive electrode facing the PCB board;

[0032] S34. Cover the piezoelectric film with a plastic protective film slightly smaller than the PVDF in length and width, insert a pressing weight, and then cure for ≥ 24 hours;

[0033] S4. Vacuum-cure the electrical connection. Apply epoxy resin around the PVDF film. Before curing, use a polytetrafluoroethylene weight to press the piezoelectric film 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.

[0034] S5. Fabricate the acoustic matching layer. Using a potting mold, use a one-step back-filling method. Assemble the matching layer molding mold to the front of the housing and secure with removable fasteners. The housing features a 1 / 4-wavelength thickness positioning slot. Place the sample into the housing and use the slot to position it. Mix the matching layer potting material thoroughly, vacuum-degassing it, and then pour it into the matching layer through the potting port. During pouring, tilt the sample and vacuum-draw for 30 minutes or longer. Then, place the entire sample in an oven and dry it at 40°C for 24 hours or longer. Fabrication is complete.

[0035] The present invention has the following beneficial effects:

[0036] (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;

[0037] (2) The prepared sensor array can withstand high pressure difference and 50°C without deformation and can be used in deep-sea environments;

[0038] (3) 3D imaging distance ≥ 10m;

[0039] (4) The overall electrical consistency is good, and the array element abnormality rate is <0.5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. 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 any creative work.

[0041] Figure 1 Schematic diagram of the overall design of the multi-frequency imaging sonar piezoelectric ultrasonic sensor array.

[0042] Figure 2 Schematic diagram of the patterned positive electrode.

[0043] Figure 3 Schematic diagram of connected ground electrode.

[0044] Figure 4 Schematic diagram of bonding PVDF or P (VDF-TrFE) piezoelectric film to PCB board.

[0045] Figure 5 Schematic diagram of auxiliary tools for preparing sensor arrays.

[0046] Figure 6 Schematic diagram of the matching layer potting mold.

[0047] Figure 7 This is the square array capacitor consistency test result.

[0048] Figure 8 The continuity test result of the array element receiving phase.

[0049] Figure 9 This is the test result of the array element receiving signal.

[0050] 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 top 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 top angle positioned by laser etching, 6 is an acoustic matching layer, 7 is a PCB board fixture, 8 is a mucosa 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 the piezoelectric layer bonded. DETAILED DESCRIPTION

[0051] 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 the various embodiments of the present invention can be combined accordingly without conflicting with each other. Without departing from the spirit and essence of the present invention, any modification or replacement of the method, steps or conditions of the present invention falls within the scope of the present invention.

[0052] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the materials and reagents used are commercially available reagents and materials unless otherwise specified.

[0053] refer to Figures 1 to 3 The PVDF or P (VDF-TrFE) piezoelectric film 4 used in the present invention has a thickness ranging from 40 μm to 500 μm. Piezoelectric films 4 with a thickness exceeding 200 μm can be obtained using a lamination method. Multilayer PVDF or P (VDF-TrFE) piezoelectric materials are prepared by laminating piezoelectric film + epoxy resin + piezoelectric film. Taking the preparation of a 400 μm thick laminated PVDF film as an example, the specific steps are as follows:

[0054] (1) Take two pieces of PVDF membrane with a thickness of 200 μm and a size of ≥105 mm × 105 mm;

[0055] (2) Take two pieces of thermal release films of the same size as the PVDF membrane and stick them on the surface of the above PVDF membrane to prevent the surface from being contaminated by the following epoxy resin;

[0056] (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;

[0057] (4) Take a piece of sample from (2) and place it on a vacuum adsorption platform with the PVDF membrane 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.

[0058] (5) Place the film coated with epoxy resin in step (4) in a glue roller to remove excess epoxy resin on the surface. The speed of the glue roller is set to three stages: ≥800 rpm for 3 seconds, ≥2000 rpm for 20 seconds, and ≥3000 rpm for 20 seconds.

[0059] (6) Spread the sample obtained in the previous step 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 the two films to remove the bubbles between them; finally, press the two films with a heavy object, place them in a vacuum box, and let them stand for more than 24 hours to cure;

[0060] (7) After the epoxy resin is cured, remove the weight block and remove the thermal release film on the surface to obtain the laminated PVDF membrane.

[0061] Example 1 (Magnetron Sputtering Method)

[0062] This embodiment provides a sensor array for a multi-frequency imaging sonar, the structural components of which include 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.

[0063] In this embodiment, double-sided electrodes are prepared by magnetron sputtering. The sensing 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. The material is PVDF or P (VDF-TrFE) piezoelectric film 4.

[0064] Preparation method:

[0065] (1) Take a piece of thermal release film and cut a square hole array in its center using a laser cutting machine to make a positive electrode mask;

[0066] (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;

[0067] (3) The film obtained in step (2) is attached to a glass sheet with the mask side facing upwards, 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 and target material are eccentrically rotated for ≥1 time. After the sputtering is completed, the mask is removed;

[0068] (4) Using a laser cutting machine, the film from step (3) is positioned and cut into the designed size according to the four corners 303 of the square array;

[0069] (5) Place the film from step (4) on a glass sheet with the side 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 ≥50 nm. Remove the film after sputtering is completed.

[0070] (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 its center using a laser cutter;

[0071] (7) Stick the film obtained in step (6) on the PCB board according to the silk screen and array position of the PCB board, and place the PCB board into the PCB board fixture 7;

[0072] (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;

[0073] (9) If 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 plastic film with the same size as the array design is placed on the membrane surface, and a pressing weight block 9 is placed inside to press for 24 hours.

[0074] (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;

[0075] (11) Use a syringe with a pinhole size of 0.5-1.5 mm to extract the epoxy resin prepared in step (10);

[0076] (12) After the conductive silver paste is solidified, remove the pressing weight block 9 and the mucosa positioning tool 8 in (9), and use a syringe to apply a small amount of epoxy resin around the PVDF membrane;

[0077] (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 vacuum pump power supply and maintain pressure curing for ≥ 24 hours, where the vacuum degree of the vacuum box is ≤ -0.1MPa;

[0078] (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 it at room temperature for ≥24h to obtain a circuit board 12 with a completed piezoelectric layer bonded;

[0079] (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. Place the sample 12 in step (14) upside down into the housing, that is, the PCB circuit board electrical connector 101 faces outward and is limited by the positioning slot 1001, as shown in FIG. Figure 6 As shown. The matching layer potting material is mixed evenly and poured from the matching layer potting port after vacuum degassing. During pouring, tilt the sample and vacuum for 30 minutes or longer. Then, place the entire sample in an oven and dry it at 40°C for 24 hours or longer. After the matching layer material solidifies, remove the fasteners and mold, and the production is complete.

[0080] Example 2 (screen printing)

[0081] 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 one wavelength of the target frequency, and the material is PVDF or P (VDF-TrFE) piezoelectric film 4. Screen printing includes:

[0082] (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;

[0083] (2) Fix the positive electrode screen printing plate on the printing table, take a piece of piezoelectric film 4 that is larger than the array design size 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 with tape around it to prevent it from shifting during the printing process;

[0084] Screen printing method 1:

[0085] (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;

[0086] (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;

[0087] Screen Printing Method 2:

[0088] (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;

[0089] (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 the electrode pattern side, use a scraper to apply a certain pressure on the conductive silver paste on the screen printing plate, and move it toward the other end of the electrode pattern of the screen printing plate, so that the negative electrode array element 501 and the negative electrode virtual transition array element 502 pattern 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. The positive electrode on the piezoelectric film 4 is aligned with the negative electrode on the bottom surface through the position of the array element, and the piezoelectric film 4 is fixed with tape. During this process, the position of the printing plate remains unchanged. Then, a proper amount of conductive silver paste is poured on the printing plate using the same method. A certain amount of pressure is applied to the conductive silver paste on the screen printing plate with a squeegee while moving toward the other end of the electrode pattern on the screen printing plate. After ensuring that the printing is complete, the printing plate is gently lifted, and the piezoelectric film 4 is removed. The negative electrode array element 501 and the negative electrode virtual transition array element 502 are completed.

[0090] (5) Take the piezoelectric film printed with positive and negative electrodes, use a laser cutting machine to identify the four top corners 303 of the array and cut it into a film of the designed size of the array;

[0091] (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 in the center of the film using a laser cutter;

[0092] (7) Stick the film obtained in step (6) on the circuit board according to the silk screen and array position of the circuit board, and place the PCB board into the PCB board fixture 7;

[0093] (8) Take the conductive silver paste and apply it evenly 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;

[0094] (9) If 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, place a piece of plastic film of the designed size on the membrane surface for protection, insert the pressing weight block 9 and press for ≥24 hours;

[0095] (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. The vacuum degree of the vacuum box is ≤-0.1MPa.

[0096] (11) Use a syringe with a pinhole size of 0.5-1.5 mm to extract the epoxy resin prepared in step (10);

[0097] (12) After the conductive silver paste solidifies, 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;

[0098] (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 vacuum pump power supply and maintain pressure curing for ≥ 24 hours, where the vacuum degree of the vacuum box is ≤ -0.1MPa;

[0099] (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 it at room temperature for ≥24h to obtain a circuit board 12 with a completed piezoelectric layer bonded;

[0100] (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. Place the sample 12 in step (14) upside down into the housing, that is, the PCB circuit board electrical connector 101 faces outward and is limited by the positioning slot 1001, as shown in FIG. Figure 6 As shown. The matching layer potting material is mixed evenly and poured from the matching layer potting port after vacuum degassing. During pouring, tilt the sample and vacuum for 20 minutes or more. Then, place the entire sample in an oven and dry it at 40°C for 24 hours or more. After the matching layer material solidifies, remove the fasteners and mold, and the production is complete.

[0101] Example 3 (screen printing + magnetron sputtering)

[0102] In this embodiment, the positive and negative electrodes are prepared by combining screen printing and magnetron sputtering. The sensing array is a square orthogonal array of ≥24×24, the array elements are square, the center spacing of the array elements is one wavelength of the target frequency, and the material is PVDF or P (VDF-TrFE) piezoelectric film 4:

[0103] (1) Make a screen printing plate according to the designed pattern of the connected ground electrode (negative electrode) 5;

[0104] (2) Fix the negative electrode screen printing plate on the printing table, take a piece of piezoelectric film 4 that is larger than the array design size 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 below the electrode pattern, and fix the PVDF film or P (VDF-TrFE) piezoelectric film 4 with tape to prevent it from shifting during the printing process;

[0105] (3) Pour an appropriate amount of conductive silver paste on one side of the electrode pattern of the negative electrode 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. 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;

[0106] (4) Take the film printed with the negative electrode, use a laser cutting machine to identify the four top corners 503 of the array and cut it into a film of the designed size of the array;

[0107] (5) Take a piece of thermal release film that is larger than the design size of the array, and use a laser cutting machine to cut a square hole array of the design size in the center of the film to make a positive electrode mask;

[0108] (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);

[0109] (7) Paste the sample in step (6) on a glass sheet larger than the array design size and with a thickness of ≤1mm, with the mask facing up, and place it in the 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 ≥50nm 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 times in the center, and the sample and the target are rotated and sputtered ≥1 times in the eccentric rotation. After the sputtering is completed, remove the mask;

[0110] (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 cutting machine;

[0111] (9) Stick the film obtained in step (8) on the PCB board according to the silk screen and array position of the PCB board, and place the PCB board into the PCB board fixture 7;

[0112] (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 is scraped off, the thermal release film is carefully removed, leaving a conductive silver paste point 2 on the PCB circuit board;

[0113] (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 Then, place a piece of thermal release film of the same size as the array design on the surface of the film for protection, and press it with a pressing weight block 9 for ≥ 24 hours;

[0114] (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. The vacuum degree of the vacuum box is ≤-0.1MPa.

[0115] (13) Use a syringe with a pinhole size of 0.5-1.5 mm to extract the epoxy resin after the bubbles are removed in step (12);

[0116] (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;

[0117] (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 and maintain the pressure for curing for ≥24 hours, wherein the vacuum degree of the vacuum box is ≤-0.1MPa;

[0118] (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 it at room temperature for ≥24h to obtain a circuit board 12 with a completed piezoelectric layer bonded;

[0119] (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 6As shown. The matching layer potting material is mixed evenly and poured from the matching layer potting port after vacuum degassing. During pouring, tilt the sample and vacuum for 30 minutes or longer. Then, place the entire sample in an oven and dry it at 40°C for 24 hours or longer. After the matching layer material solidifies, remove the fasteners and mold, and the production is complete.

[0120] 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-channel, 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 entire array element, namely phase consistency. The phase continuity test results are shown below. Figure 8 As 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 elements and the external sound source from the top to the bottom of the array is from close 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 Figure 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 the 4M sampling rate. It can be seen that all array elements can receive signals and work normally, and the yield rate of array element signal reception is 100%.

[0121] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Persons skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent substitution or equivalent transformation falls within the scope of protection 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 is a square array with a size of ≤8 inches, a square array element, a number of array elements ≥24×24, an imaging frequency ≥300kHz, and uses laser etching, screen printing, magnetron sputtering or pattern mask technology. The PVDF and P (VDF-TrFE) sensor arrays are integrated and packaged on a PCB circuit board. The core of the preparation process is to form patterned electrodes from single-layer and multi-layer PVDF or P (VDF-TrFE) piezoelectric films. The patterned electrode method specifically includes: Combined method of magnetron sputtering and screen printing: a screen printing plate is made according to the negative electrode pattern, 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, so that 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, wherein The center distance between the elements of the square array is ≤ 1 wavelength of the operating frequency, and the length and width of the elements are ≥ 70% of the center distance between the elements.

3. The preparation method according to claim 1, wherein The method for integrating and packaging the PVDF and P(VDF-TrFE) sensor array on a PCB circuit board is as follows: first, laser etching a heat-release masking tape, then pasting it on the PCB circuit board and evenly applying conductive silver paste; after removing the masking tape, only the conductive silver paste at the array element position remains; and using the viscosity of the conductive silver paste to bond the piezoelectric film to the PCB circuit board.

4. The preparation method according to claim 1, wherein The edges of the PVDF or P(VDF-TrFE) piezoelectric film bonded to the PCB are coated with epoxy resin glue. Before curing, a polytetrafluoroethylene weight 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, wherein The multilayer PVDF or P (VDF-TrFE) piezoelectric material is formed by evenly coating each layer of piezoelectric film with epoxy resin using 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, wherein The steps of sputtering chromium and gold materials on the surface using magnetron sputtering equipment are: first chromium plating and then gold plating, the sample and the target material are aligned and rotated and sputtered for ≥1 time, the sample and the target material are eccentrically rotated and sputtered for ≥1 time, and the thickness of the electrode composed of chromium and gold materials is ≥50nm.

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

8. The preparation method according to claim 1, wherein The bonding and positioning tool includes a PCB circuit board positioning fixture, a piezoelectric film bonding and positioning module, and a piezoelectric film pressing module.

9. The preparation method according to claim 1, wherein The array elements in the negative electrode pattern are connected to each other through a cross pattern.

Images