A hydrophone based on electric double layer capacitance sensing principle

Abstract

A hydrophone based on double electric layer capacitance sensing principle, the hydrophone comprises a sound-transparent polyurethane rubber shell, a BOPP electrode film, a gel polymer sensitive film, a threaded through-hole metal ring electrode, a conductive screw, a threaded through-hole metal lower electrode, a ring-shaped hard polyurethane gasket, a fixing support, a fluorine rubber sealing ring, a BNC noise reduction cable, a castor oil, a locking ring and a signal acquisition circuit; the connection mode of each component of the hydrophone is simple and universal; when underwater sound waves make the BOPP electrode film vibrate and drive the periodic deformation of the gel polymer sensitive film inside the BOPP electrode film, the double electric layer capacitance formed by the gel polymer sensitive film and the hydrophone electrode is changed to perform sensing; compared with the traditional hydrophone based on the piezoelectric principle, the hydrophone formed by using the high-sensitivity double electric layer capacitance sensing principle and the simple and reliable structure design has an absolute advantage of low frequency and high sensitivity, and can be used in the fields of underwater sound wave monitoring and underwater acoustic signal sensing.

Description

Technical Field

[0001] This invention relates to the field of underwater acoustic sensor technology, and specifically to a hydrophone based on the principle of double-layer capacitance sensing. Background Technology

[0002] Although the electric double-layer sensing principle has only been developing for about 10 years, it has unique applications in health monitoring, environmental signal recognition, and motion monitoring due to its advantages such as extremely high sensing sensitivity, low detection noise, and anti-interference characteristics. The so-called electric double-layer capacitance refers to the "ion-electron" interface capacitance formed when an ionic material and a metal come into contact. Because the thickness of the contact interface is only on the order of nanometers, the capacitance of this electric double layer is enormous, typically in the range of μF / cm². 2 The magnitude of the capacitance is far greater than that of traditional dielectric capacitors. Through reasonable structural design, sensors utilizing the double-layer capacitance sensing principle will exhibit a rapid change in double-layer capacitance under load. Due to the significant change in electrical quantity under unit load, i.e., high sensing sensitivity, double-layer capacitance sensors are typically used for sensing and acquiring weak signals. Early ionic materials were usually liquid ionic solutions, which posed a risk of leakage, causing considerable difficulties for further application. With the development of gel polymer sensing materials in recent years, this bottleneck has been overcome. Gel polymer sensing materials are polymeric materials composed of a three-dimensional polymer network containing sensing ions, possessing excellent mechanical properties such as low modulus, high toughness, and impact resistance. When they are combined with metals to form a "metal-ion electrolyte-metal" system, a stable double-layer capacitance is generated at the contact interface. Because they are solid materials, leakage problems do not occur. Currently, domestic and international research focuses on the design and application of gel polymer sensing materials, but limited by the inherent frequency of polymer materials, most applications are still concentrated in static or quasi-static sensing fields such as health monitoring.

[0003] Hydrophones, also known as underwater acoustic sensors, are devices used to sense sound signals in water and are widely used in underwater acoustic monitoring, underwater communication, and other fields. As the basic unit for receiving sound waves, improving the performance of hydrophones is meaningful and necessary. Currently, hydrophones use rigid materials such as piezoelectric ceramics and optical fibers as sensing elements, combined with the piezoelectric effect and optical interference principles for underwater acoustic sensing. However, they suffer from problems such as low low-frequency sensitivity and poor shock resistance. Therefore, there is an urgent need to develop hydrophones based on new principles to improve the current situation. To improve this situation, scholars at home and abroad have made many attempts, such as piezoresistive sensing principle hydrophones and MEMS process hydrophones, but all of them have their shortcomings. It is worth mentioning that some researchers have proposed using the double-layer capacitance sensing principle for underwater sound signal acquisition, but it is still limited by the inherent frequency of the polymer soft material, making it sensitive only to low-frequency sound signals of 5-15Hz. At the same time, the DC power supply acquisition circuit they used greatly reduced the sensor lifespan, and the application is limited to the laboratory level.

[0004] Based on the above background research, this invention employs a novel sensing technology that combines a gel polymer sensitive material with a metal to generate impedance characteristics under weak alternating current. This, combined with the pre-stretching of the electrode film and the pre-compression of the gel polymer material, results in a hydrophone based on the double-layer capacitive sensing principle. This improves upon the current state of underwater acoustic sensing, solving problems such as narrow low-frequency bandwidth and short lifespan in current cutting-edge research using the double-layer principle for underwater acoustic signal sensing, thus better promoting the development of double-layer capacitive hydrophones in the underwater acoustic field. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention aims to provide a hydrophone based on the principle of double-layer capacitance sensing. By leveraging the high sensitivity of double-layer capacitance sensing combined with a pre-loaded structural design, the technical bottleneck of soft polymer materials being unable to sense high-frequency signals is overcome. The successful design and fabrication of this hydrophone based on the double-layer capacitance sensing principle broadens the application of this new sensing principle in the field of underwater acoustic signal acquisition and compensates for the technical shortcomings of existing hydrophones.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] A hydrophone based on the principle of double-layer capacitance sensing, the hydrophone includes a sound-permeable polyurethane rubber shell 1, a BOPP electrode film 2, a gel polymer sensitive membrane 3, a metal ring electrode with threaded through holes 4, a conductive screw 5, a metal lower electrode with threaded through holes 6, a ring-shaped rigid polyurethane gasket 7, a fixing bracket 8, a rubber sealing ring 9, a BNC noise reduction cable 10, castor oil 11, a locking ring 12, and a signal acquisition circuit 13;

[0008] The hydrophone connection method is as follows: First, the threaded through-hole metal lower electrode 6 and the fixing bracket 8 are tightly fitted together by the conductive screw 5 at the rear of the fixing bracket 8 (near the tail of the hydrophone). At the same time, the negative wire of the BNC noise-canceling cable 10 is connected to the conductive screw 5 through the wire clamp to maintain contact and form the negative electrode of the hydrophone. Second, the threaded through-hole metal ring electrode 4 is fixed to contact the BOPP electrode film 2 on its surface by adhesive bonding. At the same time, the entire assembly is fixed to the fixing bracket 8 by fitting the conductive screw 5 at the front of the fixing bracket 8 (near the head of the hydrophone) onto the outer circumference of the threaded through-hole metal lower electrode 6. The BNC noise-canceling cable 10 is also connected to the fixing bracket 8 by the wire clamp on the back of the fixing bracket 8. The positive wire of the noise-canceling cable 10 is connected to a conductive screw passing through a threaded through-hole metal ring electrode 4 to form the positive electrode of the hydrophone; next, a gel polymer sensitive membrane 3 is placed between the positive and negative electrodes of the hydrophone, and a ring-shaped rigid polyurethane gasket 7 of a predetermined thickness is used to separate the gel polymer sensitive membrane 3 from the positive and negative electrodes of the hydrophone, ensuring the initial pre-compression strain of the gel polymer sensitive membrane 3; finally, the sound-permeable polyurethane rubber shell 1 is fitted onto the outside of the fixing bracket 8, and the contact part is assembled with a rubber sealing ring 9 using an interference fit, and the sound-permeable polyurethane rubber shell 1 and the BO Castor oil 11 is filled between the hydrophone sensitive element, which consists of a PP electrode film 2, a gel polymer sensitive film 3, a metal ring electrode with a threaded through hole 4, a conductive screw 5, a metal lower electrode with a threaded through hole 6, and an annular rigid polyurethane gasket 7. Finally, the sound-permeable polyurethane rubber shell 1 is further pressed onto the fixed bracket 8 by a locking ring 12 to form a sealed hydrophone. The gap between the BNC noise-reducing cable 10 and the fixed bracket 8 is filled and sealed with sealant. The signal acquisition circuit 13 is placed in the annular cavity at the tail of the fixed bracket 8, close to the hydrophone sensitive element to maximize the reduction of output signal noise.

[0009] When sound waves act on the BOPP electrode film 2, the vibration of the BOPP electrode film 2 causes the gel polymer sensitive film 3 to undergo periodic deformation, thereby changing the system impedance of the "metal-ion electrolyte-metal" system formed by the contact between the gel polymer sensitive film 3 and the positive and negative electrodes of the hydrophone for sensing.

[0010] Under the alternating current provided by the signal acquisition circuit 13, the interface between the gel polymer and the metal in the hydrophone forms a pair of "ion-electron" interface capacitors, also known as double-layer capacitors. Inside the gel polymer material far from the contact interface, ions form an equivalent form of alternating current resistance. Therefore, the system impedance of the "metal-ion electrolyte-metal" system formed by the contact of the gel polymer sensitive membrane 3 with the positive and negative electrodes of the hydrophone refers to the alternating current resistance and the series connection of the two double-layer capacitors, where the double-layer capacitors account for the main component of the impedance. The impedance of the gel polymer sensitive membrane changes under the action of sound waves, thereby changing the voltage across the series voltage divider resistor to output a voltage signal.

[0011] The hydrophone based on the double-layer capacitive sensing principle is characterized in that:

[0012] While ensuring good contact between the threaded through-hole metal ring electrode 4 and the BOPP electrode film 2, it is important to avoid short-circuiting the hydrophone when the conductive screw 5 passes through the front of the fixed bracket 8 to fix the threaded through-hole metal ring electrode 4 and the BOPP electrode film 2 on the fixed bracket 8.

[0013] The hydrophone based on the double-layer capacitance sensing principle is characterized in that electrical insulation is provided between the conductive screw 5 and the threaded through-hole metal lower electrode 6.

[0014] The hydrophone based on the double-layer capacitive sensing principle is characterized in that: the BOPP electrode film has internal tension generated by biaxial pre-stretching in its two surfaces.

[0015] The hydrophone based on the double-layer capacitive sensing principle is characterized in that the pre-compression degree of the gel polymer sensitive membrane 3 between the positive and negative electrodes of the hydrophone depends on the thickness of the annular rigid polyurethane gasket 7.

[0016] The hydrophone based on the double-layer capacitance sensing principle is characterized in that: the hydrophone is used for underwater acoustic signal acquisition and analysis, and vibration signal sensing in liquid environments.

[0017] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0018] (A) The design strategy of this invention utilizes the double-layer capacitance in the impedance of the "metal-ion electrolyte-metal" system formed by the contact between the gel polymer sensitive material and the metal for sensing. Sound waves act on the BOPP electrode film 2 with in-plane biaxial pre-stretching, causing deformation of the gel polymer sensitive material and thus changing the size of the double-layer capacitance. This fully utilizes the high sensitivity of the double-layer sensing principle to achieve highly sensitive acoustic signal sensing in the hydrophone.

[0019] (B) The structural design of the BOPP electrode film 2 with in-plane biaxial pre-stretching and the gel polymer sensitive film 3 with pre-compression of the present invention can overcome the problem of narrow low-frequency bandwidth of hydrophones caused by the low inherent frequency of gel polymer sensitive materials. At the same time, the bandwidth of hydrophones can be adjusted by adjusting different degrees of pre-stretching and pre-compression according to different underwater acoustic signal frequency ranges.

[0020] (C) The integrated signal acquisition circuit 13 of the present invention adopts AC power supply, which ensures the stability and reliability of the double-layer capacitor, and thus ensures the stability and reliability of the hydrophone based on the double-layer capacitor sensing principle.

[0021] (D) The hydrophone of this invention has a simple structural design, is easy to implement, and is low-cost in the field of hydrophones. However, its sensing performance is significantly improved compared to traditional hydrophones, expanding the application of the double-layer capacitive sensing principle in the field of hydrophones and making up for the shortcomings of existing hydrophones. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a hydrophone based on the double-layer capacitive sensing principle proposed in this invention.

[0023] Figure 2 This is a diagram of the exploded component of a hydrophone based on the double-layer capacitive sensing principle proposed in this invention.

[0024] Figure 3 This is a cross-sectional view of the present invention.

[0025] Figure 4 This is a schematic diagram of the sensing principle of the present invention.

[0026] Figure 5 This is a schematic diagram of the double-layer capacitor in the sensing principle of this invention.

[0027] Figure 6 This is a schematic diagram of the equivalent circuit of the present invention.

[0028] Figure 7 This is the sensitivity level curve obtained by calibration of the present invention under the same electrode size but different gel polymer sensitive membrane diameters.

[0029] Figure 8 This is the sensitivity level curve calibrated and measured under the same electrode size and the ratio of the diameter of the gel polymer sensitive membrane.

[0030] Figure 9 This is a graph showing the performance stability over time in a specific embodiment of the present invention. Detailed Implementation

[0031] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent transformations and modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0032] Following the above technical solutions, such as Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 and Figure 9 As shown in the figure, this embodiment provides a hydrophone manufacturing process and calibration data based on the principle of double-layer capacitance sensing.

[0033] like Figure 1 and Figure 2As shown in the diagram, the hydrophone designed based on the double-layer capacitive sensing principle of this invention has a simple overall structure and high applicability. It includes a sound-permeable polyurethane rubber shell 1, a BOPP electrode film 2, a gel polymer sensitive membrane 3, a metal ring electrode with threaded through holes 4, conductive screws 5, a lower metal electrode with threaded through holes 6, a ring-shaped rigid polyurethane gasket 7, a fixing bracket 8, a rubber sealing ring 9, a BNC noise-canceling cable 10, castor oil 11, a locking ring 12, and a signal acquisition circuit 13. The connection method is as follows: First, the lower metal electrode with threaded through holes 6 and the fixing bracket 8 are tightly fitted together by four conductive screws 5 at the rear of the fixing bracket 8 (near the tail of the hydrophone). Simultaneously, the negative wire of the BNC noise-canceling cable 10 is connected to the conductive screws 5 through a wire clamp to maintain good contact and form the negative electrode of the hydrophone. Secondly, the threaded through-hole metal ring electrode 4 is bonded to its surface to form good contact with the BOPP electrode film 2. Simultaneously, the entire assembly is fixed to the outer circumference of the threaded through-hole metal lower electrode 6 using conductive screws 5. On the back of the fixing bracket 8, wire clips are used to connect the positive lead of the BNC noise-canceling cable 10 to the conductive screw passing through the threaded through-hole metal ring electrode 4, forming a highly conductive hydrophone positive electrode. Thirdly, a gel polymer sensitive membrane 3 is fixedly placed between the hydrophone positive and negative electrodes. A rigid polyurethane gasket 7 of a predetermined thickness separates the gel polymer sensitive membrane 3 from the hydrophone positive and negative electrodes, effectively ensuring the initial pre-compression strain of the gel polymer sensitive membrane 3. Finally, the acoustically permeable polyurethane rubber shell 1 is fitted onto the outside of the mounting bracket 8. The contact portion is assembled using three rubber sealing rings 9 with an interference fit. Castor oil 11 is filled between the acoustically permeable polyurethane rubber shell 1 and the hydrophone sensitive element, which consists of a BOPP electrode film 2, a gel polymer sensitive film 3, a threaded through-hole metal ring electrode 4, a conductive screw 5, a threaded through-hole metal lower electrode 6, and an annular rigid polyurethane gasket 7. Finally, the acoustically permeable polyurethane rubber shell 1 is further pressed onto the mounting bracket 8 using a locking ring 12 to form a simple and sealed hydrophone. The gap between the BNC noise-reducing cable 10 and the mounting bracket 8 is filled and sealed with sealant. The signal acquisition circuit 13 is placed in the annular cavity at the tail of the mounting bracket 8, close to the hydrophone sensitive element to maximize the reduction of output signal noise; from Figure 3 This can also be seen in the cross-sectional schematic diagram of the present invention. The above describes the structure and assembly method of a hydrophone based on the double-layer capacitive sensing principle.

[0034] The threaded holes of the hydrophone's threaded lower metal electrode 6 and ring electrode 4 should fit tightly with the high conductivity screw 5, and the negative and positive terminals of the BNC noise reduction cable 10 should also fit tightly with the high conductivity screw 5 through the wire clamp, in order to avoid excessive noise from the hydrophone due to poor contact.

[0035] When the gel polymer sensing material comes into contact with the positive and negative electrodes (metal electrodes) of the hydrophone, forming a "metal-ion electrolyte-metal" system, its impedance model and the principle of sensing using double-layer capacitance are as follows: Figure 4 As shown, a basic double-layer capacitive sensing system is formed when a sensing element, formed by the interface contact between a metal-gel polymer electrolyte and a metal, is connected to an AC voltage via a series voltage divider resistor. Under AC voltage, the sensing element exhibits significant impedance characteristics, meaning that the AC current through the system shows a significant change in amplitude and phase compared to the AC voltage. The fundamental reason for this is that ionic electrolytes differ from electronic conductors; under the influence of AC current, ions and electrons form an ion-electron interface capacitor (also known as a double-layer capacitor) at the interface, exhibiting properties similar to a capacitor. Figure 5 As shown, due to the tight bonding between the ionic electrolyte material and the metal, the ion-electron interface thickness is very small, resulting in a very large double-layer capacitance C, typically in μF / cm². 2 The magnitude is on the order of magnitude. When factors such as ion concentration and ambient temperature are constant, the size of the electric double-layer capacitance is directly proportional to the contact area between the electrolyte and the metal. This is one of the differences between it and traditional dielectric capacitors. Therefore, with... Figure 4 The equivalent circuit model of thin-film sensing elements in AC circuits can typically be represented by a resistor R and two double-layer capacitors C1 and C2 connected in series, such as... Figure 6 Its basic sensing principle is that under the action of an external load, the sensitive element formed by the ionic gel polymer electrolyte and the metal deforms. This deformation causes significant changes in R, C1, and C2 in the circuit (mainly changes in the double-layer capacitance), thus achieving sensing. This is based on the series voltage divider resistor R... out By changing the voltage divider in the voltage divider circuit, the magnitude of the load acting on the system can be measured.

[0036] In one specific embodiment, the manufacturing process and performance calibration tests of the hydrophone are described in detail below:

[0037] Both the threaded through-hole metal lower electrode 6 and the threaded through-hole metal ring electrode 4 are manufactured using CNC stainless steel machining. The diameters of the stainless steel frustum of the threaded through-hole metal lower electrode are 20 mm and 40 mm, respectively, and the inner diameters of the threaded through-hole metal ring electrode correspond to these diameters. Two pairs of hydrophones with different diameters are prepared for fabrication. The gel polymer sensitive material adopts a thin film structure with a microstructure on one side and a flat surface on the other. A hydrogel material containing Li+ ions is used as the gel polymer sensitive membrane 3 of the hydrophone. In the experiment, 15 mL of an aqueous solution of 3.52 M (3.75 g) acrylamide (AAm), 2.0 wt% (0.075 g) N,N'-methylenebisacrylamide (MBAA), 0.2 wt% (0.0075 g) ammonium persulfate (APS), 0.375 μL N,N,N,N-tetramethylethylenediamine (TEMED), and 3 M (1.91 g) anhydrous lithium chloride (LiCl) was mixed in a 100 mL glass beaker. After thorough mixing, the solution was pipetted into the gap between a glass plate and an etched silicon wafer, with 500 μm thick annular silicone gaskets separating the gaps. The etched silicon wafer has a concave pyramidal microstructure, used to form a hydrogel with several rectangularly arranged, 50 μm-spaced, 50 μm-side-length convex pyramidal microstructures on one side. The prepolymerized liquid was then trapped in the gap and cured at room temperature for 4 hours to form a uniform, transparent, and flexible one-sided microstructured hydrogel film. During use, it is carefully peeled off from the silicon wafer and cut into circular samples using cutters with inner diameters of 10 mm, 15 mm, and 20 mm. The sound-permeable polyurethane rubber shell 1 is integrally molded using 3D printing. The BOPP electrode film 2 is bonded to the threaded through-hole metal ring electrode 4 using a biaxial stretching platform and conductive epoxy adhesive, and the in-plane tension of the BOPP electrode film 2 is tested with a tension meter and found to be 170 N / m. The conductive screw is made of copper. The thickness of the annular rigid polyurethane gasket is 16.5 μm to ensure that the pre-compression strain of the gel polymer sensitive membrane is 3%. The signal acquisition circuit of the hydrophone has a series voltage divider resistor with a resistance of 220 Ω, an AC frequency of 20 kHz, and an amplitude of 20 mV. The output AC voltage is amplified 10 times by a lock-in amplifier and then output as DC to obtain the hydrophone signal output.

[0038] Hydrophones with an electrode diameter of 20mm and a gel diameter of 10mm are designated A01; those with an electrode diameter of 40mm and a gel diameter of 10mm are designated C01; those with an electrode diameter of 40mm and a gel diameter of 15mm are designated C02; and those with an electrode diameter of 40mm and a gel diameter of 20mm are designated C03. The sensitivity levels of the hydrophones were calibrated according to the national standard GB / T 4130-2017, "Calibration Method for Low-Frequency Hydrophones - Closed Cavity Comparison Method." The standard hydrophone used is the BK8104 scalar hydrophone. The specific formula for calculating the sensitivity level is as follows:

[0039]

[0040] in The sensitivity is that of a standard hydrophone (the sensitivity of the BK8104 is -180dB±3dB). The sensitivity of the hydrophone under test. This represents the peak-to-peak value of the open-circuit voltage output of a standard hydrophone. This represents the voltage output of the hydrophone under test at the same frequency and sound pressure level.

[0041] like Figure 7 As shown, taking the sensitivity level curve of the C01 hydrophone as an example, the bandwidth of this invention reaches 50-200Hz in the low-frequency range, which is a significant improvement compared to the results in the literature. Due to the pre-stretching of the BOPP electrode film, the hydrophone can avoid resonance affecting the bandwidth due to the low inherent frequency of the soft material. At the same time, it is not difficult to see from the figure that, while ensuring the electrode diameter is 40mm, increasing the gel diameter from 10mm in C01 to 15mm in C02 increases the sensitivity level of the hydrophone from -215±5dB to -145±5dB. This is because when the hydrogel area increases, the deformation area of ​​the hydrogel per unit sound pressure increases, resulting in a more drastic change in the impedance of the hydrophone's sensitive element. However, as the gel size further increases from 15 mm for CO2 to 20 mm for CO3, the hydrophone's sensitivity only improves to -142 ± 5 dB. This is because, while further increasing the gel size increases the gel area, the microstructure on one side of the gel hinders the vibration of the electrode film under sound waves. The increased gel size reduces the deflection of the upper electrode film under the same sound pressure, thus limiting gel deformation and reducing double-layer changes. Consequently, the hydrophone sensitivity initially increases sharply with increasing gel size and then slowly approaches a stable level.

[0042] like Figure 8 As shown, hydrophones A01 and C03 were compared, both with an electrode-to-gel diameter ratio of 2:1. The results indicate that when the electrode-to-gel sensitive membrane diameter ratio is fixed, a smaller overall device size results in a wider low-frequency bandwidth (50-600Hz), while a larger device size results in a narrower low-frequency bandwidth (50-200Hz). The sensitivity shows the opposite trend: device sensitivity is directly proportional to device size. Larger device sizes result in higher sensitivity (-142±5 dB).

[0043] like Figure 9 As shown, the time stability of the hydrophone was tested. Due to the use of AC-powered signal acquisition circuit and good sealing technology, the sensitivity level of the hydrophone did not change significantly after 5 days underwater.

[0044] The specific embodiments in this group illustrate that the hydrophone based on the double-layer capacitive sensing principle of the present invention has the advantages of simple structure, high sensitivity, and stable and adjustable performance. This invention lays the foundation for expanding the application of the double-layer capacitive sensing principle in the field of underwater acoustics and provides design ideas for the configuration of high-performance polymer material underwater sensors.

[0045] Application scope:

[0046] The hydrophone based on the double-layer capacitance sensing principle can be used in fields such as underwater acoustic signal acquisition and analysis, and vibration signal sensing in liquid environments.

[0047] The potential economic benefits of this invention are:

[0048] The field of hydrophones is highly confidential, and market data on high-performance hydrophones abroad is not easily collected. Based on a review and analysis of the global and Chinese hydrophone markets, the global market size reached 765 million RMB in 2022, while the Chinese market size reached 300 million RMB. Analyzing the current status and future prospects of the global and Chinese hydrophone markets, it is predicted that the global market size will reach 990 million RMB by 2028, with an estimated compound annual growth rate of around 4.65%. High-performance hydrophones will fill the gaps in the market for sensor-based hydrophones, securing a place for themselves, and their future civilian market size may even exceed expectations. Conservatively estimated, the economic benefits of this invention are at least 500 million RMB by 2028.

[0049] Impact of this invention on the future technology market in China:

[0050] In the current technology market, hydrophones based on piezoelectric sensing principles dominate, while fiber optic sensing hydrophones are mainly used in towed arrays and shore-based arrays. MEMS hydrophones remain largely in the laboratory exploration stage. In recent years, the double-layer capacitive sensing principle has become a research hotspot due to its advantages such as high sensitivity, strong anti-interference capability, and low detection noise. Its application to underwater acoustic signal sensing offers absolute advantages in terms of high sensitivity and low noise. This invention applies the double-layer sensing principle to the field of underwater acoustic sensing, broadening its application scope and providing a new sensing approach in the hydrophone field. Furthermore, information on high-performance hydrophones is not readily available both domestically and internationally. This invention, as a supplement to the sensing principles and structural designs of high-performance hydrophones, has a significant advantage in the technology market.

Claims

1. A hydrophone based on the principle of double-layer capacitive sensing, characterized in that: The hydrophone includes a sound-permeable polyurethane rubber shell (1), a BOPP electrode film (2), a gel polymer sensitive membrane (3), a metal ring electrode with threaded through holes (4), a conductive screw (5), a metal lower electrode with threaded through holes (6), an annular rigid polyurethane gasket (7), a fixing bracket (8), a rubber sealing ring (9), a BNC noise reduction cable (10), castor oil (11), a locking ring (12), and a signal acquisition circuit (13). The hydrophone connection method is as follows: First, the threaded through-hole metal lower electrode (6) and the fixed bracket (8) are tightly fitted together by the conductive screw (5) at the rear of the fixed bracket (8) near the end of the hydrophone. At the same time, the negative wire of the BNC noise reduction cable (10) is connected to the conductive screw (5) through the wire clamp to maintain contact and form the negative electrode of the hydrophone. Second, the threaded through-hole metal ring electrode (4) is fixed to contact the BOPP electrode film (2) on its surface by adhesive bonding. At the same time, the entire electrode is fixed to the fixed bracket (8) by the conductive screw (5) at the front of the fixed bracket (8) near the head of the hydrophone, by fitting it onto the outer circumference of the threaded through-hole metal lower electrode (6). Similarly, the BNC noise reduction cable (10) is fixed to the fixed bracket (8) by the wire clamp on the back of the fixed bracket (8). The positive wire of the noise reduction cable (10) is connected to the conductive screw passing through the metal ring electrode (4) with a threaded through hole to form the positive electrode of the hydrophone; next, a gel polymer sensitive membrane (3) is placed between the positive and negative electrodes of the hydrophone, and a ring-shaped rigid polyurethane gasket (7) of a preset thickness is used to separate the gel polymer sensitive membrane (3) from the positive and negative electrodes of the hydrophone to ensure the initial pre-compression strain of the gel polymer sensitive membrane (3); finally, the sound-permeable polyurethane rubber shell (1) is put on the outside of the fixing bracket (8), and the contact part is assembled with a rubber sealing ring (9) in an interference fit, and the sound-permeable polyurethane rubber shell (1) and the BOPP electrode are connected to the positive electrode. Castor oil (11) is filled between the hydrophone sensitive element, which consists of a thin film (2), a gel polymer sensitive film (3), a metal ring electrode with threaded through holes (4), a conductive screw (5), a metal lower electrode with threaded through holes (6), and an annular rigid polyurethane gasket (7). Finally, the sound-permeable polyurethane rubber shell (1) is further pressed onto the fixed bracket (8) by the locking ring (12) to form a sealed hydrophone. The gap between the BNC noise reduction cable (10) and the fixed bracket (8) is filled and sealed with sealant. The signal acquisition circuit (13) is placed in the annular cavity at the tail of the fixed bracket (8) close to the hydrophone sensitive element to maximize the reduction of output signal noise. When sound waves act on the BOPP electrode film (2), the vibration of the BOPP electrode film (2) causes the gel polymer sensitive film (3) to undergo periodic deformation, thereby changing the system impedance of the "metal-ion electrolyte-metal" formed by the contact between the gel polymer sensitive film (3) and the positive and negative electrodes of the hydrophone for sensing. Under the alternating current provided by the signal acquisition circuit (13), the interface between the gel polymer and the metal in the hydrophone will form a pair of "ion-electron" interface capacitors, also known as double-layer capacitors. Inside the gel polymer material far from the contact interface, ions will form an equivalent form of alternating current resistance under the action of alternating current. Therefore, the system impedance of the "metal-ion electrolyte-metal" formed by the contact between the gel polymer sensitive membrane (3) and the positive and negative electrodes of the hydrophone refers to the alternating current impedance formed by the series connection of the alternating current resistance and the two double-layer capacitors, in which the double-layer capacitor accounts for the main component of the impedance. The impedance of the gel polymer sensitive membrane changes under the action of sound waves, thereby changing the voltage across the series voltage divider resistor to output a voltage signal.

2. A hydrophone based on the double-layer capacitive sensing principle according to claim 1, characterized in that: While ensuring good contact between the threaded through-hole metal ring electrode (4) and the BOPP electrode film (2), avoid the conductive screw (5) from passing through the front of the fixed bracket (8) to fix the threaded through-hole metal ring electrode (4) and the BOPP electrode film (2) on the fixed bracket (8), so that the front conductive screw (5) contacts the threaded through-hole metal lower electrode (6) and short-circuit the hydrophone.

3. A hydrophone based on the double-layer capacitive sensing principle according to claim 1, characterized in that: Electrical insulation is provided between the conductive screw (5) and the threaded through-hole metal lower electrode (6).

4. A hydrophone based on the double-layer capacitive sensing principle according to claim 1, characterized in that: The BOPP electrode film (2) has internal tension generated by biaxial pre-stretching in its in-plane.

5. A hydrophone based on the double-layer capacitive sensing principle according to claim 1, characterized in that: The degree of pre-compression of the gel polymer sensitive membrane (3) between the positive and negative electrodes of the hydrophone depends on the thickness of the annular rigid polyurethane gasket (7).

6. A hydrophone based on the double-layer capacitive sensing principle according to claim 1, characterized in that: The hydrophone is used for underwater acoustic signal acquisition and analysis, and vibration signal sensing in liquid environments.

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