Gradient porous piezoelectric ceramic, hydrophone and preparation method thereof

Abstract

The application provides a gradient porous piezoelectric ceramic, a hydrophone and a preparation method thereof. By establishing a gradient porous structure model in which porosity decreases from outside to inside along a radial direction, and by adopting a photocuring 3D printing technology to shape ceramic slurry, integrated construction of macro-pores and micro-pores is realized, and a low-frequency hydrophone with low acoustic impedance, high voltage sensitivity and good structural reliability is obtained.

Description

Technical Field

[0001] This invention relates to the field of piezoelectric ceramics and underwater acoustic sensing technology, and particularly to a gradient porous piezoelectric ceramic, a hydrophone, and a method for preparing the same. Background Technology

[0002] Hydrophones are the core receiving devices in underwater acoustic detection and passive sonar systems. Their main function is to convert underwater sound pressure signals into electrical signals. Low-frequency and ultra-low-frequency underwater acoustic signals are typically characterized by long propagation distances, low amplitudes, and strong background noise interference. Therefore, hydrophone sensitive elements are required to have low acoustic impedance, high sensitivity, and high voltage response.

[0003] Piezoelectric ceramics, with their high piezoelectric coefficient, fast response speed, and mature fabrication process, are one of the main materials for the sensitive elements of hydrophones. Introducing pores into piezoelectric ceramics can reduce the dielectric constant and acoustic impedance of the material, improve its acoustic matching with the water medium, and enhance the piezoelectric voltage response. However, increased porosity also reduces the effective piezoelectric phase, weakens stress transmission, and reduces structural strength. Therefore, how to maintain a high piezoelectric response while reducing acoustic impedance and dielectric constant is a key issue in the design of porous piezoelectric ceramic hydrophones.

[0004] Existing porous piezoelectric ceramics are mainly prepared using methods such as sacrificial template method, pore-forming agent sintering method, gel casting method, and freeze-drying method. However, the pore structures formed by these methods are usually highly random, and it is difficult to precisely control the pore size distribution, pore orientation, connectivity, and spatial distribution. It is also difficult to achieve continuous and controllable gradient pore changes to avoid step-like abrupt changes in acoustic impedance, and it is even more difficult to achieve the integrated construction of macroscopic porous structures and microscopic pore structures. Therefore, it is difficult to simultaneously meet the comprehensive performance requirements of low acoustic impedance, high voltage sensitivity, low frequency response, and structural reliability.

[0005] Photopolymer 3D printing technology boasts advantages such as high forming precision, mold-free operation, and high freedom in structural design, providing a new technological path for the precise design and integrated forming of complex porous structures. It holds promise for optimizing the acoustic impedance, sensitivity, and structural reliability of hydrophone sensing elements through structural control. However, current research and applications of photopolymer-printed porous piezoelectric ceramics primarily focus on the forming of macroscopic pore structures, with insufficient attention paid to the size control of micropores, connectivity design, and their synergistic regulation with macroscopic structures. Single-scale pore structure design struggles to effectively coordinate the contradictory relationships between acoustic matching, dielectric properties, piezoelectric response, and structural strength, hindering the development of high-performance hydrophone sensing elements. Summary of the Invention

[0006] In view of this, the present invention provides a gradient porous piezoelectric ceramic for hydrophones and its preparation method. The macroscopic porous structure with continuously decreasing porosity from the outside to the inside is realized by photopolymerization 3D printing technology, while uniformly distributed micropores are formed inside the ceramic matrix. This achieves the integrated construction of macropores and micropores, and obtains a hydrophone sensitive element with low acoustic impedance, high voltage sensitivity and good structural reliability.

[0007] This invention provides a gradient porous piezoelectric ceramic for hydrophones, comprising a piezoelectric ceramic matrix, wherein the porosity of the piezoelectric ceramic matrix continuously decreases radially from the outside to the inside, forming a peripheral high porosity region, an intermediate gradient transition region, and a central relatively dense region; The porosity of the peripheral high-porosity zone is 50%~70%; The porosity of the relatively dense central region is 10%~20%; The porosity of the intermediate gradient transition zone decreases continuously.

[0008] This invention also provides a method for preparing a gradient porous piezoelectric ceramic hydrophone, comprising the following steps: Step S1: Using a parametric modeling method, establish a three-dimensional structural model of the gradient porous piezoelectric ceramic; Step S2: Prepare ceramic slurry and use photopolymerization 3D printing technology to prepare piezoelectric ceramic blanks; Step S3: Remove organic matter from the piezoelectric ceramic green body and perform sintering treatment to obtain porous piezoelectric ceramic.

[0009] Preferably, step S1 specifically includes: dividing the model radially into an outer region, an intermediate region, and a central region; constructing each region using a three-period minimal surface (TPMS) structure; and setting the structure type and structural parameters of each region respectively, so that the porosity of the outer region, the intermediate region, and the central region continuously decreases from the outside to the inside.

[0010] Based on the above scheme, in a further preferred embodiment, in step S1, the three-period minimal surface structure is selected from one or more of the following types: Gyroid, Diamond, Primitive, or I-WP.

[0011] This invention constructs a macroscopic gradient porous structure model by controlling the unit size, wall thickness, and isosurface parameters of a three-dimensional structural model. This model comprises a high-porosity outer region, a gradient transition region in the middle, and a relatively dense central region. 3D printing technology is used to fabricate this macroscopic gradient porous piezoelectric ceramic, resolving the technical contradiction in existing porous piezoelectric ceramic hydrophones of simultaneously achieving low acoustic impedance, high voltage sensitivity, and high structural reliability. Its mechanism of action is as follows: the high-porosity outer region reduces apparent density and elastic modulus, making the acoustic impedance approach that of water, thus improving the acoustic matching with the water medium and ensuring efficient sound energy penetration; the gradient transition region achieves a smooth transition in acoustic impedance and structural stiffness from the outside to the inside, avoiding reflection loss at the interface of abrupt changes in porosity (i.e., impedance abrupt changes), while also eliminating local stress concentration caused by abrupt changes in porosity, improving resistance to hydrostatic pressure; the relatively dense central region maintains the high-voltage phase content, contributing high voltage response and sufficient mechanical strength after polarization treatment, providing structural support for the entire component. The three functional areas work together to enable the sensitive element to simultaneously achieve low acoustic impedance, high sensitivity, wide bandwidth response, and excellent structural reliability.

[0012] Based on the above technical solutions, preferably, the ceramic slurry in step S3 includes ceramic powder, photocurable monomer, photoinitiator, phase separation component and dispersant.

[0013] Photocurable monomers include one or more of acrylate monomers and acrylate oligomers.

[0014] The phase separation component is at least one of polyethylene glycol (PEG), polypropylene glycol (PPG), polyvinylpyrrolidone (PVP), and polyvinyl alcohol (PVA).

[0015] The piezoelectric paste contains 70%–85% ceramic powder by mass, 3%–5% phase separation components by mass, 10%–25% photocurable monomers by mass, and 0.5%–3.0% photoinitiator by mass.

[0016] In the piezoelectric paste, the ceramic powder has a mass fraction of 70%–85%, which is used to ensure the integrity and formability of the ceramic skeleton after sintering; the phase separation component has a mass fraction of 3%–5%, which is used to form micropores during the subsequent debinding and sintering process, while avoiding a decrease in structural strength due to excessive content; the photocurable monomer has a mass fraction of 10%–25%, which is used to adjust the fluidity of the paste and ensure photocuring formation; and the photoinitiator has a mass fraction of 0.5%–3.0%, which is used to ensure that the paste has a suitable photocuring reaction rate and curing depth.

[0017] Preferably, the removal of organic matter from the piezoelectric ceramic green body in step S3 includes cleaning and degreasing the piezoelectric ceramic green body to remove non-photopolymerization phase separation components, forming micropores, and obtaining a macro- and micro-porous green body.

[0018] The present invention also provides a hydrophone, comprising the aforementioned gradient porous piezoelectric ceramic for hydrophones.

[0019] The present invention has the following advantages over the prior art: (1) By setting a macroscopic gradient porous structure in the piezoelectric ceramic for hydrophones, three different functional regions with decreasing porosity are constructed, so that the hydrophone forms a functional gradient. Its acoustic impedance can reach 6.5MRayl, the receiving sensitivity at 1 kHz can reach -194.5 dB, the piezoelectric coefficient is still maintained above 171.5 pC / N, and the compressive strength is maintained above 2.1 MPa. This significantly improves the acoustic matching between the piezoelectric ceramic and the water medium, and achieves the effect of maintaining high piezoelectric response and structural stability while reducing acoustic impedance and dielectric constant. (2) The continuous gradient pore structure achieved by photopolymerization 3D printing in this invention has a smooth and gradual change in porosity from the outside to the inside, and no sudden change in acoustic impedance at the interface, which can effectively avoid stress concentration, thereby achieving low acoustic impedance matching while having higher receiving sensitivity and structural reliability.

[0020] (3) By utilizing the synergistic effect of ultraviolet light polymerization and induced phase separation, the integrated construction of macroscopic porous structure and microscopic pores is realized, which enables the hydrophone sensitive element to achieve a better balance between low acoustic impedance and high structural reliability, and effectively improves the piezoelectric response and its receiving sensitivity. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a magnified schematic diagram of the overall structure and micropores of the gradient porous piezoelectric ceramic of the present invention; Figure 2 This is a schematic diagram of the axial cross-sectional structure of the hydrophone of the present invention and the corresponding top view; Figure 3 The test results show the acoustic impedance and receiving sensitivity of the hydrophone of this invention. Figure 4 The test results show the piezoelectric coefficient and compressive strength of the gradient porous piezoelectric ceramic of this invention. Explanation of reference numerals in the attached figures: 1-Sealing layer 1; 2-Positive electrode; 3-Gradient porous piezoelectric ceramic; 4-Hydrophone housing; 5-Negative electrode; 6-Sealing layer 2; 7-Wire; Ⅰ-Central relatively dense region; Ⅱ-Intermediate gradient transition region; Ⅲ-Outer high porosity region. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] In the following specific embodiments, the lead zirconate titanate-based piezoelectric ceramic powder (PZT-5H) was purchased from Zibo Yuhai Electronic Ceramics Co., Ltd., and PEGDA400, PEG200, TPO (diphenyl-(2,4,6-trimethylbenzoyl)phosphorus oxide), tripropylene glycol diacrylate (TPGDA), polypropylene glycol (PPG), polyurethane acrylate (PUA1000), and polyvinylpyrrolidone (PVP) were all purchased from Sinopharm Chemical Reagent Co., Ltd., and BYK-111 (dispersant) was purchased from BYK Chemical Co., Ltd.

[0025] Example 1 This embodiment provides a method for manufacturing a hydrophone, including: Step 1: Establish a gradient three-period minimum surface (TPMS) structural model using 3D modeling software recognized in the field.

[0026] First, a cylindrical model with a diameter of 40 mm and a height of 15 mm is established, and it is divided into three regions from the inside to the outside along the radial direction: region I, region II, and region III. The radial range of region I is 0–7 mm, the radial range of region II is 7–15 mm, and the radial range of region III is 15–20 mm.

[0027] Zone I is set as a relatively dense central region, using a Gyroid-type TPMS structure with a unit cell size of 6.2 mm, a wall thickness of 0.58 mm, and a porosity of 10%; Zone III is set as a high-porosity peripheral region, using a Diamond-type TPMS structure with a unit cell size of 5.0 mm, a wall thickness of 0.50 mm, and a porosity of 50%.

[0028] Region II is set as a gradient transition region. By setting fusion parameters that change continuously with radial position, the Gyroid structure gradually transitions to the Diamond structure. At the same time, the unit cell size, wall thickness and isosurface threshold are continuously adjusted so that the porosity of this region gradually increases from the side closer to Region I to the side closer to Region III, and the porosity gradually increases from 10% to 50%.

[0029] After setting the parameters, a three-dimensional TPMS fusion structure is generated in the software, resulting in a complete gradient porous piezoelectric ceramic model. The established three-dimensional structural model is then sliced ​​layer by layer to generate slice images for each layer.

[0030] Step 2: Using lead zirconate titanate piezoelectric ceramic powder (PZT-5H) as raw material, with an average particle size of 1μm, 80g of PZT-5H powder, 12g of PEGDA400 (polyethylene glycol diacrylate), 2g of TPO (diphenyl-(2,4,6-trimethylbenzoyl)phosphine oxide), 3g of BYK-110 (dispersant), and 3g of PEG200 (polyethylene glycol) were mixed uniformly under light-protected conditions. The above components were added to a ball mill jar, with a zirconium oxide grinding ball to material mass ratio of 1.5:5. The mixture was ball-milled at 220 r / min for 4 hours, followed by vacuum degassing for 1 hour to obtain a uniform and stable piezoelectric ceramic slurry.

[0031] Step 3: Add the piezoelectric ceramic slurry to the slurry tank of the surface-exposure photopolymerization 3D printer. Apply the slurry using a doctor blade to form a uniform slurry layer with a thickness of 50 μm. Then, selectively expose the target area to ultraviolet light according to the slice pattern from Step 1. The ultraviolet light wavelength used for printing is 355 nm, the irradiance at the exposed surface is 11 mW / cm², and the single-layer exposure time is 5 s. After each layer is exposed, adjust the relative position of the forming platform and the doctor blade to the preset layer thickness for the next layer. Repeat the above slurry application and exposure process, accumulating layer by layer until the entire sample is formed, obtaining a piezoelectric ceramic green body.

[0032] Step 4: Immerse the piezoelectric ceramic green body completely in ethanol at room temperature for 24 hours to remove the enriched phase, unreacted photopolymerizable components, and other soluble low-molecular-weight components. This leaves micropores in situ within the green body, resulting in a porous piezoelectric ceramic green body. Dry the porous piezoelectric ceramic green body in a 60°C oven for 10 hours to remove residual ethanol from the interior and surface of the green body.

[0033] Step 5: Place the dried porous piezoelectric ceramic green body in a vacuum tube furnace. Under continuous nitrogen protection, raise the temperature from 50℃ to 600℃ at a heating rate of 0.5℃ / min. Hold the green body at 150℃, 250℃, 350℃, 500℃ and 600℃ for 2 hours respectively to allow the residual PEG, crosslinked PEGDA400, TPO and BYK-111 to gradually pyrolyze and be removed, thus obtaining the piezoelectric ceramic preform.

[0034] The piezoelectric ceramic preform was transferred to a muffle furnace, and the above heating and holding process was repeated in an air atmosphere. The temperature was increased from 50°C to 600°C at a heating rate of 0.5°C / min, and held at 150°C, 250°C, 350°C, 500°C and 600°C for 2 hours respectively to oxidize and remove the residual carbon formed during the nitrogen pyrolysis process, thus obtaining the impurity-free piezoelectric ceramic preform.

[0035] The impurity-removed piezoelectric ceramic preform was placed in a sintering furnace for sintering. The temperature was increased from 50℃ to 1200℃ at a heating rate of 5℃ / min and held at 1200℃ for 3 hours. Finally, it was cooled to 50℃ at a cooling rate of 5℃ / min to obtain a porous piezoelectric ceramic sintered body.

[0036] Step 6: Clean the surface of the sintered porous piezoelectric ceramic body and prepare electrodes on the predetermined surface. Silver electrode paste is screen-printed onto the upper and lower surfaces of the sintered body, and after drying and heat treatment at 850℃, a dense silver electrode layer is formed. The sintered body with prepared electrodes is then polarized at a polarization temperature of 140℃, a polarization electric field of 3kV / mm, and a preferred polarization time of 5min. After polarization, the body is cooled while maintaining the electric field or under short-circuit conditions. After reaching room temperature, the electric field is removed, resulting in a porous piezoelectric ceramic element with piezoelectric properties.

[0037] Step 7: Place the porous piezoelectric ceramic element (e.g., after electrode fabrication and polarization treatment) into the substrate. Figure 2 (As shown in mark 3) is used as the receiving element of the hydrophone and is fixed to the hydrophone housing (e.g., using epoxy resin adhesive). Figure 2 As shown in Figure 4, lead out electrode wires to connect the positive and negative electrodes of the receiving element (e.g., ...). Figure 2 (As shown in marks 2 and 5) is connected to the wire, and then connected to the external preamplifier and signal conditioning circuit via a watertight cable. A polyurethane sealing layer (such as...) with insulation, waterproofing, and sound transmission properties is provided on the acoustic incident side of the receiving element. Figure 2 (As shown in marks 1 and 6).

[0038] Through the above steps, a hydrophone containing gradient porous piezoelectric ceramic is obtained.

[0039] The piezoelectric ceramic and hydrophone structure prepared in this embodiment are as follows: Figure 1 and Figure 2As shown, the piezoelectric ceramic structure includes a relatively dense central region (such as...) Figure 1 As shown in the middle (marked as I), the intermediate gradient transition region (such as...) Figure 1 (as shown by the mark II in the middle) and the outer high porosity zone (such as...) Figure 1 As shown in the middle (marked III), the interior of the solid skeleton is further distributed with micropores formed by photopolymerization-induced phase separation.

[0040] Example 2 The difference between this embodiment and Embodiment 1 is as follows: In step 1: Zone I has a unit cell size of 6.0 mm, a wall thickness of 0.55 mm, and a porosity of 15%; Zone III has a unit cell size of 4.5 mm, a wall thickness of 0.45 mm, and a porosity of 60%.

[0041] The porosity in zone II gradually increases from 15% to 60%.

[0042] In step 2, 70g of PZT-5H powder, 18g of trimethylolpropane triacrylate (TMPTA), 7g of 1,6-hexanediol diacrylate (HDDA), 1g of photoinitiator TPO, 1g of dispersant (DISPERBYK-110) and 3g of PVP are mixed.

[0043] In step 3, the slurry layer thickness is 100μm, the ultraviolet light wavelength is 405nm, the irradiation intensity at the exposure surface is 40mW / cm2, and the single-layer exposure time is 20s.

[0044] The sintering process in step 5 is as follows: First, the temperature is raised from 50℃ to 600℃ at a heating rate of 10℃ / min, and held at 600℃ for 2 hours; then, the temperature is raised from 600℃ to 900℃ at a heating rate of 5℃ / min, and held at 900℃ for 3 hours; then, the temperature is raised from 900℃ to 1050℃ at a heating rate of 3℃ / min, and held at 1050℃ for 3 hours; finally, the temperature is cooled to 50℃ at a cooling rate of 10℃ / min to obtain a porous piezoelectric ceramic sintered body.

[0045] The remaining steps and parameters are the same as in Example 1.

[0046] The porosity of the outer region of the hydrophone prepared in this embodiment is 60%, the porosity of the intermediate transition zone gradually transitions from 15% to 60%, and the porosity of the central region is 15%.

[0047] Example 3 The difference between this embodiment and Embodiment 1 is as follows: Step 1: The unit cell size of region I is 5.8 mm, the wall thickness is 0.52 mm, and the porosity is 20%; the unit cell size of region III is 4.2 mm, the wall thickness is 0.40 mm, and the porosity is 70%.

[0048] The porosity in zone II gradually increases from 20% to 70%.

[0049] Step 2 uses PZT-5H powder as raw material, with an average particle size of 500nm. By mass percentage, 85g of PZT-5H powder, 10g of polyurethane acrylate (PUA), 1g of TPO, 1g of BYK-110 and 3g of polyvinyl alcohol are mixed.

[0050] In step 3, the slurry layer thickness is 75μm, the ultraviolet light wavelength used for printing is 385nm, the irradiation intensity at the exposure surface is 30mW / cm2, and the single-layer exposure time is 10s.

[0051] The sintering process in step 5 is as follows: First, the temperature is raised from 50℃ to 600℃ at a heating rate of 10℃ / min, and held at 600℃ for 2 hours; then, the temperature is raised from 600℃ to 900℃ at a heating rate of 5℃ / min, and held at 900℃ for 3 hours; then, the temperature is raised from 900℃ to 1300℃ at a heating rate of 3℃ / min, and held at 1300℃ for 1 hour; finally, the temperature is cooled to 50℃ at a cooling rate of 10℃ / min to obtain a porous piezoelectric ceramic sintered body.

[0052] The remaining steps and parameters are the same as in Example 1.

[0053] The porosity of the outer region of the hydrophone prepared in this embodiment is 70%, the porosity of the intermediate transition region gradually transitions from 20% to 70%, and the porosity of the central region is 20%.

[0054] Comparative Example 1 The difference between this comparative example and Example 1 is that the parameter settings in step 1 are adjusted to make the pores uniformly distributed and the porosity 70%. The remaining steps and parameters are the same as in Example 1.

[0055] Comparative Example 2 The difference between this comparative example and Example 1 is that the parameter settings in step 1 are adjusted to make the pores uniformly distributed with a porosity of 10%. The remaining steps and parameters are the same as in Example 1.

[0056] Comparative Example 3 The difference between this comparative example and Example 1 is that PEG is not added, while the remaining steps and parameters are the same as in Example 1.

[0057] Performance testing The piezoelectric coefficient and compressive strength of the gradient porous piezoelectric ceramic were tested, and the acoustic impedance and receiving sensitivity of the hydrophone were tested.

[0058] Depend on Figure 3 and Figure 4It can be seen that as the peripheral porosity increases from 50% to 70%, the acoustic impedance decreases from 10.8 MRayl to 8.2 MRayl and 6.5 MRayl, respectively, and the receiving sensitivity at 1 kHz increases from -198.5 dB to -195.7 dB and -194.5 dB, respectively. This indicates that increasing the peripheral porosity can effectively reduce the acoustic impedance, improve underwater acoustic matching, and increase the receiving sensitivity. At the same time, the piezoelectric coefficient decreases from 210.3 pC / N to 194.1 pC / N and 171.5 pC / N, and the compressive strength decreases from 3.4 MPa to 2.8 MPa and 2.1 MPa, but still maintains good piezoelectric and mechanical properties. Comparative Example 1, employing a 70% uniform high-porosity structure, achieved a reduced acoustic impedance of 4.5 MRayl, but its piezoelectric coefficient and compressive strength were only 62.7 pC / N and 0.8 MPa, respectively, with a receiving sensitivity of -196.5 dB, lower than Example 3. This indicates that excessively high and uniformly distributed porosity significantly weakens the continuity of the ceramic framework and the effective piezoelectric phase. Comparative Example 2, using a 10% uniform low-porosity structure, achieved a piezoelectric coefficient and compressive strength of 253.4 pC / N and 5.4 MPa, respectively, but its acoustic impedance was as high as 24 MRayl, with a receiving sensitivity of only -207 dB, indicating poor underwater acoustic matching performance. Comparative Example 3, without introducing phase-separated micropores, had an acoustic impedance of 18.5 MRayl and a receiving sensitivity of -201 dB, also lower than Example 1. This demonstrates that the present invention, through the synergistic design of the outer high porosity region, the intermediate gradient transition region, and the central relatively dense region, can reduce acoustic impedance and improve receiving sensitivity while maintaining high piezoelectric performance and structural strength, thus achieving a comprehensive balance between underwater acoustic performance, piezoelectric performance, and structural reliability.

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A gradient porous piezoelectric ceramic for hydrophones, characterized in that, It includes a piezoelectric ceramic matrix, the porosity of which decreases continuously from the outside to the inside in the radial direction, forming a high porosity outer region, a gradient transition region in the middle, and a relatively dense central region.

2. The gradient porous piezoelectric ceramic for hydrophones as described in claim 1, characterized in that, The porosity of the peripheral high-porosity zone is 50%~70%; The porosity of the relatively dense central region is 10%~20%; The porosity of the intermediate gradient transition zone decreases continuously.

3. The method for preparing gradient porous piezoelectric ceramics for hydrophones as described in claim 1 or 2, characterized in that, Includes the following steps: Step S1: Using a parametric modeling method, establish a three-dimensional structural model of the gradient porous piezoelectric ceramic; Step S2: Prepare ceramic slurry and use photopolymerization 3D printing technology to prepare piezoelectric ceramic blanks; Step S3: Remove organic matter from the piezoelectric ceramic green body and perform sintering treatment to obtain porous piezoelectric ceramic.

4. The method for preparing gradient porous piezoelectric ceramics for hydrophones as described in claim 3, characterized in that, Step S1 specifically includes: dividing the model radially into an outer region, an intermediate region, and a central region; constructing each region using a three-period minimal surface structure; and setting the structure type and structural parameters for each region so that the porosity of the outer region, the intermediate region, and the central region continuously decreases from the outside to the inside.

5. The method for preparing gradient porous piezoelectric ceramics for hydrophones as described in claim 4, characterized in that, In step S1, the three-period minimal surface structure is selected from one or more of the following types: Gyroid, Diamond, Primitive, or I-WP.

6. A hydrophone, characterized in that, Includes the gradient porous piezoelectric ceramic for hydrophones as described in claim 1 or 2.

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