A non-packaged flexible hydrophone and a manufacturing method thereof

Abstract

The present invention relates to the technical field of underwater acoustic sensors, and in particular to a non-packaged flexible hydrophone and a manufacturing method thereof. The non-packaged flexible hydrophone comprises a porous flexible diaphragm, a microstructured flexible sensing material layer and a flexible substrate with interdigitated electrodes stacked in sequence; the flexible substrate with interdigitated electrodes is composed of a three-layer structure stacked together, the upper layer is a polyimide film layer with a central circular hole, the middle layer is a periodic interdigitated electrode layer, the electrode center area of ​​the interdigitated electrode layer is located in the central circular hole of the polyimide film, and the lower layer is a non-porous polyimide film layer. The present invention creatively proposes a non-packaged design, which has a simple structure, is easy to implement, has a low cost, a small size, and a light weight. It greatly improves the flexibility and bendability of the device, has good durability, and is highly corrosion-resistant. It can be used in a high-salinity underwater environment for a long time, and has a wider application prospect in deep-sea oil and gas, mineral resource exploration, national defense, environmental monitoring and industrial fields.

Description

Technical Field

[0001] The invention relates to the technical field of underwater acoustic sensors, and in particular to a non-packaged flexible hydrophone and a manufacturing method thereof. Background Art

[0002] Electromagnetic waves decay very quickly underwater, so sound waves are widely distributed underwater as the only medium for underwater communication and signal transmission. As a passive receiving unit in the underwater acoustic transducer system, the hydrophone can record the amplitude and frequency information of underwater sound waves, and is of great importance in the fields of national defense, military, marine equipment technology, etc. Since the sound waves generated by most underwater natural phenomena and man-made equipment are in the low-frequency range of about 1Hz to 600Hz, and their amplitude is relatively low, the overall trend of hydrophones is to develop in the direction of low frequency and high sensitivity. For example, at the bow of a submarine, the cylindrical array and spherical array composed of rigid hydrophone array elements are improving their low-frequency underwater acoustic reception capabilities by improving the hydrophone array elements to large-sized array surfaces to increase the base array aperture.

[0003] On the one hand, traditional hydrophones (such as piezoelectric ceramic hydrophones) are generally made of rigid materials, and this structure is difficult to maintain good contact and sensitivity in complex underwater environments. For example, in high turbulence or irregular surface environments, rigid devices may cause signal loss or increased noise. On the other hand, traditional hydrophones usually require complex waterproof packaging to maintain the performance of internal components while resisting the corrosive environment of high salinity underwater. This packaging not only increases manufacturing costs, but may also reduce the sensitivity of the hydrophone, especially when detecting low-frequency signals.

[0004] Flexible hydrophones are suitable for fitting complex surfaces and reducing interface impedance due to their deformable and lightweight characteristics, and are particularly good at capturing wide-band acoustic signals. For example: a flexible hydrophone based on polyvinylidene fluoride (PVDF) encapsulated in a flexible polymer material (Sensors & Actuators: A. Physica l 364 (2023) 114822), which uses polydimethylsiloxane (PDMS) to encapsulate an aluminum film substrate and a sandwich sensing structure (silver film-PVDF-silver film) to form a flexible hydrophone. A flexible hydrophone based on MEMS processing technology (Sensor Review: 44 (2024) 395-403), which uses MEMS processing technology to prepare a cross-beam-shaped flexible PI film with a piezoresistive effect, and fixes hard polymer cilia at the intersection of the cross beams to form a flexible hydrophone. However, the former, because the PVDF material is insensitive to low-frequency vibrations, has poor performance in low-frequency underwater acoustic sensing. The latter has a complex manufacturing process and is difficult to achieve flexible underwater acoustic sensing. At the same time, due to the particularity of the structure, the low-frequency underwater acoustic sensing performance is also poor. The above-mentioned existing technologies are used in high-salinity underwater environments for a long time, so they all need to be encapsulated to ensure structural stability and waterproof performance, which increases the production cost. The encapsulation materials are mostly polymer materials. Long-term service makes them face the risk of ion penetration and cause the hydrophone to fail, limiting their potential applications. Summary of the invention

[0005] In view of the problem in the prior art that the hydrophone fails due to the risk of ion penetration during long-term service, the present invention provides a non-packaged flexible hydrophone.

[0006] In order to achieve the above object, the present invention is implemented by the following technical solutions: a non-packaged flexible hydrophone, comprising a porous flexible diaphragm, a microstructured flexible sensing material layer and a flexible substrate with interdigitated electrodes stacked in sequence;

[0007] The flexible substrate with interdigitated electrodes is composed of three stacked layers, the upper layer is a polyimide film layer with a central circular hole, the middle layer is a periodic interdigitated electrode layer, the electrode center area of ​​the interdigitated electrode layer is located in the central circular hole of the polyimide film, and the lower layer is a non-porous polyimide film layer.

[0008] Furthermore, the porous flexible diaphragm is made of a biaxially stretched polyethylene glycol phthalate film as a substrate, which is cut by a laser cutting machine to form a uniform porous structure.

[0009] Furthermore, the above-mentioned microstructured flexible sensing material is a thin film structure synthesized by spin coating and curing on a sandpaper mold of a specific mesh size using platinum-catalyzed silica gel as a raw material using a spin coater.

[0010] Furthermore, the porous flexible diaphragm material is polyethylene glycol, polyimide, polydimethylsiloxane or thermoplastic polyurethane, with a thickness of 5 μm to 100 μm, a circular hole diameter of 100 μm to 1 mm, and a spacing of 100 μm to 1 mm.

[0011] Furthermore, the above-mentioned microstructured flexible sensing material is polydimethylsiloxane (PDMS), platinum-catalyzed silica gel (Ecoflex) or thermoplastic polyurethane (TPU), and the microstructure thereon is micro-pyramid type, micro-column type, micro-sphere type or random type.

[0012] Furthermore, the interdigital electrode layer includes rectangular interdigital electrodes, circular spiral interdigital electrodes or circular concentric interdigital electrodes, and the electrode material is pure gold, copper plated with gold or zinc plated with gold.

[0013] Furthermore, the materials of the upper and lower thin films in the above-mentioned flexible substrate with interdigitated electrodes are micro-polyimide or polyethylene glycol phthalate.

[0014] Furthermore, the manufacturing method of the above-mentioned unpackaged flexible hydrophone is to apply in-plane tension to the porous flexible diaphragm, and apply a certain amount of pre-compression to the microstructure flexible sensing material in combination with the flexible substrate, and complete the manufacturing of the unpackaged flexible hydrophone by seamlessly gluing the three layers of "porous flexible diaphragm-microstructure flexible sensing material-flexible electrode substrate".

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] (1) The present invention creatively proposes a non-packaged design, which allows ion-containing liquids to freely enter and exit the hydrophone, so that the hydrophone does not need to consider the risk of ion penetration. At the same time, the internal interdigital electrodes of the device are made of corrosion-resistant gold material, and there is no need to avoid device failure due to high salinity of the liquid, and it can adapt to complex underwater environments (such as irregular surfaces, high pressure, and corrosive environments); at the same time, packaging materials (such as metal shells, ceramic protective layers, etc.) are usually expensive, and the non-packaged design of the present invention can reduce dependence on these high-priced materials, thereby further saving expenses; because the non-packaged flexible hydrophone reduces the packaging structure, it is small in size and light in weight, which can meet the needs of portable and miniaturized equipment, and has broader application prospects in the fields of national defense, environmental monitoring and industry;

[0017] (2) The flexible substrate with interdigitated electrodes of the present invention arranges the positive and negative electrodes of the device on the same side, that is, it is designed as a single-sided interdigitated electrode and placed in the flexible substrate layer. By improving the traditional opposing electrode structure, the flexibility and bendability of the device are greatly improved, and the durability is good. Its flexibility and bendability are greatly improved; because under the action of sound pressure, the flexible sensing material undergoes periodic deformation, and under the action of positive sound pressure, the flexible sensing material is further compressed, so that the contact area between the flexible sensing material and the electrode increases, that is, the contact area between the liquid environment and the electrode decreases, and the double electric layer capacitance formed is reduced; under the action of negative sound pressure, the hydrophone undergoes the opposite change, so that high-sensitivity underwater acoustic sensing can be performed for monitoring the sound of marine life and environmental noise;

[0018] (3) The present invention uses a non-packaged design. Regardless of whether the ion concentration of the liquid environment is high or low, it can directly enter the interior of the device, making full use of the double-layer capacitance formed by the electrons in the interdigitated electrode and the ions in the liquid environment for sensing. It has obvious low-frequency and high-sensitivity characteristics, and the performance in low-frequency underwater acoustic sensing can be greatly improved. At the same time, it has high corrosion resistance and can be used for a long time in a high-salinity underwater environment. There is no risk of ion penetration, thereby eliminating the problem of hydrophone failure. It can play an important role in deep-sea oil and gas and mineral resource exploration.

[0019] (4) The structure of the present invention is simple, easy to implement, and low in cost. Since the non-packaged structure design is adopted in the manufacturing process, the risk of penetration and aging of the complex package structure is reduced. The high-sensitivity double-layer capacitance sensing principle and the non-packaged structure design greatly extend the service life of the device and reduce the maintenance and replacement costs caused by package failure; at the same time, due to the low cost of components, the non-packaged hydrophone is easy to maintain and update, which greatly reduces the maintenance cost of the flexible hydrophone and promotes the development of flexible hydrophones. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 An exploded view and an assembled schematic diagram of the non-packaged flexible hydrophone proposed by the present invention;

[0021] Figure 2 Schematic diagram for fabrication of microstructured flexible sensing materials;

[0022] Figure 3 Schematic diagram for fabricating a flexible substrate with interdigitated electrodes;

[0023] Figure 4 Schematic diagram for manufacturing porous flexible diaphragm;

[0024] Figure 5 is a typical sensitivity frequency response diagram of the present invention;

[0025] Figure 6The receiving sensitivity of an unpackaged flexible hydrophone at 300 Hz underwater sound waves as the bending degree increases. DETAILED DESCRIPTION

[0026] Specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent changes and improvements made on the basis of the technical solution of this application fall within the protection scope of the present invention.

[0027] See also Figure 1 The present invention provides a non-packaged flexible hydrophone, comprising a porous flexible diaphragm, a microstructured flexible sensing material layer and a flexible substrate with interdigitated electrodes stacked in sequence. The flexible substrate with interdigitated electrodes is composed of three stacked layers, the upper layer is a polyimide film layer with a central circular hole, the middle layer is a periodic interdigitated electrode layer, the electrode center area of ​​the interdigitated electrode layer is located in the central circular hole of the polyimide film, and the lower layer is a non-porous polyimide film layer. The three parts are described in detail below:

[0028] 1. The porous flexible diaphragm material can be polyethylene glycol, polyimide, polydimethylsiloxane or thermoplastic polyurethane, with a thickness of 5μm to 100μm, a circular hole diameter of 100μm to 1mm, and a spacing of 100μm to 1mm. The porous flexible diaphragm in this embodiment is made of a 10μm thick polyethylene glycol film as a substrate, and a laser cutting machine is used to cut the polymer film to form a diaphragm with a porous structure, such as Figure 4 As shown, a rectangular polyethylene terephthalate (PET) film with an outer size of 30mm×30mm is placed on the operating platform of a laser cutting machine and is punched by the laser cutting machine. An array of porous forms with a circular hole diameter of 200μm and a spacing of 200μm is formed to obtain the porous flexible diaphragm used in this embodiment. The porous structure in the porous flexible diaphragm can make the liquid flow into and out of the hydrophone better during the sensing process, that is, near the contact interface between the sensing material and the electrode, and can increase its dynamic response performance under sound pressure to enhance the dynamic sensing capability of the device.

[0029] 2. The microstructure flexible sensing material is polydimethylsiloxane (PDMS), platinum catalyzed silica gel (Ecoflex) or thermoplastic polyurethane (TPU), and the microstructure thereon is micro-pyramid, micro-column, micro-sphere or random. The microstructure flexible sensing material described in this embodiment is an elastic microstructure thin film sensing material synthesized by spin coating and curing on a sandpaper mold using platinum catalyzed silica gel as raw material. Figure 2As shown in the figure, 240-grit sandpaper is applied to a float glass sheet to form a sandpaper mold, and then the prepolymer solution of Ecoflex is poured into the center of the sandpaper mold. The rotation speed of the spin coater is adjusted to 1200 rpm and the rotation time is 15 s to form a microstructured Ecoflex film with uniform thickness. The microstructured Ecoflex film is carefully peeled off from the sandpaper mold to obtain a microstructured flexible sensing material layer. The microstructures thereon are random, and their size ranges from 30 to 50 μm.

[0030] 3. Use the flexible circuit board etching process to manufacture a flexible substrate layer with interdigitated electrodes, such as Figure 3 As shown, the interdigital electrode layer is manufactured by a flexible circuit board etching process. First, a polyimide (PI) film with uniform thickness is used as the substrate, and the interdigital electrode layer is formed through conventional etching, surface treatment and gold deposition processes. Then, a polyimide film (PI film) with a central circular hole is used as the top layer, the interdigital electrode layer is the middle layer, and the non-porous polyimide film is used as the bottom layer. The electrode center area of ​​the flexible interdigital electrode layer, that is, the central interdigital part and the lead part are exposed, and a flexible substrate with interdigital electrodes can be obtained.

[0031] The above-mentioned unpackaged flexible hydrophone uses electromechanical coupling simulation design to optimize the type of flexible sensing material, microstructure form and structural parameters; designs the corresponding interdigitated gold electrode structure and parameters according to the structural parameters of the microstructure flexible sensing material; and selects a porous flexible diaphragm material.

[0032] After the material system is determined, in-plane tension is applied to the porous flexible diaphragm, and a certain amount of pre-compression is applied to the microstructured flexible sensing material in combination with the flexible substrate. The non-packaged flexible hydrophone is manufactured by seamlessly gluing the three layers of "porous flexible diaphragm-microstructured flexible sensing material-flexible electrode substrate". The microstructure side of the microstructured flexible sensing material placed between the porous flexible diaphragm and the flexible electrode substrate directly forms initial contact with the electrode center area of ​​the interdigitated electrode layer in the flexible electrode substrate.

[0033] Specifically, this embodiment is prepared by stacking a 10μm thick porous flexible diaphragm, a 100μm thick microstructure flexible sensing material layer, and a 100μm thick flexible substrate. The in-plane size of the formed hydrophone is 75mm, wherein the thickness of the interdigital electrode layer in the flexible substrate is 3μm, the central area of ​​the interdigital electrode is a circle with a diameter of 60mm, and the width and spacing of the interdigital electrode are 40μm.

[0034] The unpackaged flexible hydrophone test environment was prepared according to the ion types and concentrations shown in Table 1, and the sensitivity frequency response test of the unpackaged flexible hydrophone prepared in the embodiment of the present invention was carried out using a low-frequency hydroacoustic calibration test experimental device to verify its hydroacoustic performance.

[0035] Table 1 Types and concentrations of ions in the seawater test environment

[0036]

[0037]

[0038] The specific test process is as follows:

[0039] First, the unpackaged flexible hydrophone was placed in a prepared simulated seawater test environment and allowed to stand for a long time to allow the environmental liquid to flow into the contact interface between the microstructure flexible sensing material layer and the central area of ​​the interdigitated electrode layer. The standard hydrophone RHC-14 was placed at the same sound field test position as the unpackaged flexible hydrophone; secondly, the sensitivity frequency response test experiment of the unpackaged flexible hydrophone was carried out using a 20Hz to 1000Hz hydroacoustic signal. The sensitivity frequency response characteristics of the unpackaged flexible hydrophone can be obtained using the closed cavity comparison method; finally, a flexible carbon fiber backboard was used as the acoustic backboard of the unpackaged flexible hydrophone, and basic hydroacoustic tests were carried out on it at different bending curvatures.

[0040] like Figure 5 The figure shows the sensitivity frequency response diagram of the unpackaged flexible hydrophone at three different water depths. At 20Hz, the sensitivity of the hydrophone can reach -167dB. As the sound wave frequency increases, its sensitivity will stabilize to -195±3dB in the frequency range of 100Hz to 350Hz, and as the sound frequency further increases, its sensitivity decays rapidly. Through the underwater acoustic test at different depths, it can be seen that the sensitivity of the unpackaged flexible hydrophone provided by the present invention is less affected by the water depth, and its sensitivity mean value fluctuates by less than 1.2dB at different water depths in the frequency range of 100Hz to 350Hz.

[0041] like Figure 6 As shown in the figure, when the sound wave frequency is 300Hz, when the bending degree of the unpackaged flexible hydrophone increases, its receiving sensitivity gradually decreases. From the flat state (R=∞) to the bending radius of 45cm and then to the bending radius of 30cm, the receiving sensitivity of the flexible hydrophone decreases from -196dB to -207.5dB.

[0042] Compared with the flexible hydrophone based on flexible polymer material encapsulating polyvinylidene fluoride (PVDF) (Sensors & Actuators: A. Physica l 364 (2023) 114822), the low-frequency sensitivity of the flexible hydrophone formed by polydimethylsiloxane (PDMS) encapsulating aluminum film substrate and sandwich sensing structure (silver film-PVDF-silver film) is -211dB, and the maximum underwater acoustic receiving sensitivity of the present invention is -167dB. The sensitivity of the present invention is significantly improved by 44dB. That is, under the same signal sound pressure, the open-circuit output of the present invention is two orders of magnitude higher.

[0043] 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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A non-packaged flexible hydrophone, characterized in that: It includes a porous flexible diaphragm, a microstructured flexible sensing material layer and a flexible substrate with interdigitated electrodes which are stacked in sequence; The flexible substrate with interdigitated electrodes is composed of three stacked layers, the upper layer is a polyimide film layer with a central circular hole, the middle layer is a periodic interdigitated electrode layer, the electrode center area of ​​the interdigitated electrode layer is located in the central circular hole of the polyimide film, and the lower layer is a non-porous polyimide film layer.

2. The non-packaged flexible hydrophone according to claim 1, characterized in that: The porous flexible diaphragm uses a biaxially stretched polyethylene glycol film as a substrate, which is cut by a laser cutting machine to form a uniform porous structure.

3. The non-packaged flexible hydrophone according to claim 2, characterized in that: The microstructured flexible sensing material is a thin film structure synthesized by spin coating and curing on a sandpaper mold with a specific mesh size using a spin coater, using platinum catalyzed silica gel as a raw material.

4. The non-packaged flexible hydrophone according to claim 3, characterized in that: The porous flexible diaphragm material is polyethylene glycol, polyimide, polydimethylsiloxane or thermoplastic polyurethane, with a thickness of 5 μm to 100 μm, a circular hole diameter of 100 μm to 1 mm, and a spacing of 100 μm to 1 mm.

5. The non-packaged flexible hydrophone according to claim 4, characterized in that: The microstructured flexible sensing material is polydimethylsiloxane, platinum catalyzed silica gel or thermoplastic polyurethane, and the microstructure thereon is micro-pyramid type, micro-column type, micro-sphere type or random type.

6. The non-packaged flexible hydrophone according to claim 5, characterized in that: The interdigital electrode layer includes rectangular interdigital electrodes, circular spiral interdigital electrodes or circular concentric interdigital electrodes, and the electrode material is pure gold, copper plated with gold or zinc plated with gold.

7. The non-packaged flexible hydrophone according to claim 6, characterized in that: The materials of the upper and lower thin films in the flexible substrate with interdigitated electrodes are micro-polyimide or polyethylene glycol phthalate.

8. The method for manufacturing a non-packaged flexible hydrophone according to claim 1, characterized in that: In-plane tension is applied to the porous flexible diaphragm, and a certain amount of pre-compression is applied to the microstructure flexible sensing material in combination with the flexible substrate. The non-packaged flexible hydrophone is manufactured by seamlessly gluing the three layers of "porous flexible diaphragm-microstructure flexible sensing material-flexible electrode substrate".

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