Flexible underwater acoustic detection skin and underwater acoustic sensor

Abstract

The application provides a flexible underwater acoustic detection skin and an underwater acoustic sensor. The flexible underwater acoustic detection skin comprises an upper electrode signal line, a lower electrode signal line, and a top flexible waterproof layer, an upper electrode layer, a PVDF piezoelectric layer, a lower electrode layer, a high Young's modulus film backing and a flexible substrate layer arranged in sequence from top to bottom; the upper electrode signal line is connected with the upper electrode layer, and the lower electrode signal line is connected with the lower electrode layer; the skin has good flexibility as a whole and can be conformally installed on a surface with different curvature radii. In the application, the high Young's modulus film backing has both high Young's modulus and thin thickness. Through reasonable setting of the layer structure and design and specification of the material, thickness and Young's modulus of the layer structure, the application verifies that the negative influence of acoustic detection performance is reduced by using the experimental method and taking the signal-to-noise ratio and the flatness of the response curve as the basis.

Description

Technical Field

[0001] This invention relates to the field of underwater sensors, specifically to a flexible underwater acoustic detection skin, and particularly to a flexible underwater acoustic sensor. Background Technology

[0002] Unmanned underwater vehicles (UUVs) play a vital role in underwater search and rescue, resource exploration, and other fields. Underwater acoustic detection is an important means for UUVs to achieve environmental awareness in these tasks. However, UUVs have limited size and payload capacity, which must be allocated to batteries and various types of sensors. Therefore, small-sized and lightweight hydrophones have significant application value.

[0003] Conformal mounting is an effective way to reduce volume, while using low-density materials can reduce the weight of the hydrophone. Polyvinylidene fluoride (PVDF) film is a flexible piezoelectric polymer. It has a low sound velocity and density, an acoustic impedance close to that of water, and a high hydrostatic piezoelectric constant gh, making it a suitable piezoelectric material for hydrophones. Its flexibility makes it easy to manufacture hydrophones of different shapes, such as planar, cylindrical, needle-shaped, or other shapes conforming to the overall shape of the device. However, existing PVDF hydrophones all use a rigid substrate, making their shape unchangeable after processing, requiring specialized design for each specific application.

[0004] Therefore, it is necessary to invent a small, lightweight, and overall flexible underwater acoustic testing device to address the shortcomings of existing hydrophones in terms of size, weight, and applicability. However, the overall flexibility of the testing device means that materials such as the watertight cladding layer also need to be flexible. This flexible cladding layer significantly affects the stress distribution within the device, negatively impacting its sensitivity and the flatness of its frequency response curve. Therefore, how to achieve good flexibility while mitigating the negative impact of flexible materials on acoustic testing performance remains a challenging problem. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a flexible underwater acoustic detection skin and an underwater acoustic sensor.

[0006] According to the present invention, a flexible underwater acoustic detection skin includes an upper electrode signal line, a lower electrode signal line, and a top flexible waterproof layer, an upper electrode layer, a PVDF piezoelectric layer, a lower electrode layer, a high Young's modulus thin film backing, and a flexible substrate layer arranged sequentially from top to bottom.

[0007] The upper electrode signal line is connected to the upper electrode layer, and the lower electrode signal line is connected to the lower electrode layer;

[0008] The bottom areas of the upper electrode layer, PVDF piezoelectric layer, lower electrode layer, and high Young's modulus film backing are all the same; the multilayer structure formed by the upper electrode layer, PVDF piezoelectric layer, lower electrode layer, and high Young's modulus film backing completely covers the flexible substrate layer and the top flexible waterproof layer.

[0009] The top flexible waterproof layer, upper electrode layer, PVDF piezoelectric layer, lower electrode layer, high Young's modulus film backing, and flexible substrate layer all possess flexibility.

[0010] Preferably, the flexible substrate layer is made of a material with a Young's modulus of less than or equal to 2e6 N / m2, and is waterproof and corrosion resistant, and the thickness of the flexible substrate layer is between 1 mm and 10 mm.

[0011] Preferably, the high Young's modulus film backing is made of aluminum foil, copper foil, or stainless steel foil; the thickness of the high Young's modulus film backing is 40-60 μm.

[0012] Preferably, the upper electrode layer and the lower electrode layer are made of metallic materials such as silver, copper, and gold.

[0013] Preferably, the upper electrode signal line is bonded to the upper electrode layer, and the lower electrode signal line is bonded to the lower electrode layer using conductive silver paste or conductive copper foil.

[0014] Preferably, through holes or U-shaped grooves for fixed installation can be formed on the flexible substrate.

[0015] Preferably, the Young's modulus of the high Young's modulus film backing is between 7e10 and 2e11 N / m2, and the product of Young's modulus and thickness is between 3.5e6 and 1.1e7 N / m.

[0016] Preferably, both the flexible base layer and the top flexible waterproof layer are made of polydimethylsiloxane.

[0017] Preferably, the watertightness of the flexible underwater acoustic testing skin is achieved using any of the following methods:

[0018] Method 1: After injecting polydimethylsiloxane into a mold, heat it at 60°C for 1 hour to obtain a partially cured but not fully cured flexible substrate layer; place the multilayer structure consisting of the upper electrode layer, PVDF piezoelectric layer, lower electrode layer, and high Young's modulus film backing onto the flexible substrate layer, inject polydimethylsiloxane again to form a top flexible waterproof layer, and heat the entire structure again at 60°C for 1.5 hours to fully cure.

[0019] Method 2: The flexible substrate layer and the top flexible waterproof layer are obtained by separately injecting polydimethylsiloxane. A polydimethylsiloxane film is then spin-coated around the multilayer structure consisting of the upper electrode layer, the PVDF piezoelectric layer, the lower electrode layer, and the high Young's modulus film backing. All three layers are then plasma-treated for 10 seconds using a plasma treatment machine to activate the polydimethylsiloxane molecules on the surface. Finally, the three layers are quickly pressed together.

[0020] According to the present invention, an underwater acoustic sensor employs a flexible underwater acoustic detection skin, which covers the main body of the underwater acoustic sensor.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. In this invention, the top flexible waterproof layer, the upper electrode layer, the PVDF piezoelectric layer, the lower electrode layer, the high Young's modulus film backing, and the flexible base layer all have flexibility, which makes the skin as a whole have good flexibility and can be conformally installed on surfaces with different radii of curvature.

[0023] 2. In this invention, the high Young's modulus thin film backing simultaneously possesses both high Young's modulus and thin thickness. On one hand, the high Young's modulus allows the backing to regulate the stress distribution within the PVDF piezoelectric layer. On the other hand, the thin thickness ensures that the backing still maintains good flexibility.

[0024] 3. Through the rational arrangement of each layer structure and the design and specification of the material, thickness, Young's modulus, etc. of the layer structure, the present invention verifies that the present invention reduces the negative impact on acoustic detection performance by using parameters such as signal-to-noise ratio and flatness of response curves through experiments. Attached Figure Description

[0025] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0026] Figure 1 This is an exploded three-dimensional view of the flexible underwater acoustic testing skin according to an embodiment of the present invention.

[0027] Figure 2 This is a side view of the flexible underwater acoustic detection skin according to an embodiment of the present invention;

[0028] Figure 3 This is a top view of the flexible underwater acoustic detection skin according to an embodiment of the present invention;

[0029] Figure 4 This is a comparison chart of the frequency domain response curves with and without a backing in an embodiment of the present invention;

[0030] Figure 5 This is a comparison diagram of the stress distribution within the PVDF piezoelectric layer with and without a backing in an embodiment of the present invention;

[0031] Figure 6 The figures show the simulation and measured results of the frequency domain response curves corresponding to different radii of curvature in this embodiment of the invention.

[0032] The diagram shows:

[0033] Detailed Implementation

[0034] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0035] This invention provides a flexible underwater acoustic detection skin, such as... Figure 1-3 As shown, it includes an upper electrode signal line 8, a lower electrode signal line 7, and, arranged from top to bottom, a top flexible waterproof layer 1, an upper electrode layer 2, a PVDF piezoelectric layer 3, a lower electrode layer 4, a high Young's modulus thin film backing 5, and a flexible substrate layer 6. Figure 2 In this diagram, t1 represents the thickness of the flexible waterproof layer 1, t2 represents the thickness of the flexible substrate layer 6, tp represents the thickness of the PVDF piezoelectric layer 3, and ta represents the thickness of the high Young's modulus film backing 5. The upper electrode signal line 8 is connected to the upper electrode layer 2, and the lower electrode signal line 7 is connected to the lower electrode layer 4.

[0036] Specifically, the upper electrode layer 2 is located on the PVDF piezoelectric layer 3, the upper PVDF piezoelectric layer 3 is located on the lower electrode layer 4, the lower electrode layer 4 is located on the high Young's modulus film backing 5, and the upper electrode signal line 8 is bonded to the upper electrode layer 2 and the lower electrode signal line 7 is bonded to the lower electrode layer 4 by conductive silver paste or conductive copper foil, preferably, conductive copper foil bonding.

[0037] The bottom areas of the upper electrode layer 2, PVDF piezoelectric layer 3, lower electrode layer 4, and high Young's modulus film backing 5 are all the same; the multilayer structure formed by the upper electrode layer 2, PVDF piezoelectric layer 3, lower electrode layer 4, and high Young's modulus film backing 5 completely covers the space between the flexible substrate layer 6 and the top flexible waterproof layer 1; the bottom area of ​​the top flexible waterproof layer 1 is larger than that of the upper electrode layer 2 and smaller than or equal to that of the flexible substrate layer 6.

[0038] The top flexible waterproof layer 1, upper electrode layer 2, PVDF piezoelectric layer 3, lower electrode layer 4, high Young's modulus film backing 5, and flexible base layer 6 all possess flexibility, further enhancing the overall flexibility of the skin and enabling conformal installation on surfaces with different radii of curvature. The high Young's modulus film backing 5 weakens the lateral stress within the PVDF piezoelectric layer 3, thereby improving the sensitivity and usable working bandwidth of the flexible underwater acoustic detection skin.

[0039] In a preferred embodiment, the flexible substrate 6 is made of a material with a Young's modulus less than or equal to 2e6 N / m², possessing waterproof and corrosion-resistant properties, and the thickness of the flexible substrate 6 is between 1 mm and 10 mm. The high Young's modulus film backing 5 has a Young's modulus between 7e10 and 2e11 N / m², and the product of Young's modulus and thickness is between 3.5e6 and 1.1e7 N / m. The high Young's modulus film backing 5 is made of aluminum foil, copper foil, or stainless steel foil, and its thickness is 40-60 μm. Preferably, the high Young's modulus film backing 5 is made of 50 μm thick aluminum foil, and its Young's modulus-thickness product is 3.5e6 N / m. The upper electrode layer 2 and the lower electrode layer 4 are made of metal materials such as silver, copper, and gold, and are prepared by magnetron sputtering or chemical plating. Through holes or U-shaped grooves for fixed installation can be formed on the flexible substrate 6. The PVDF piezoelectric layer 3 has a thickness of 110 μm and is polarized along its thickness direction. Figure 2 In the x3 direction. The upper electrode layer 2 and the lower electrode layer 4 are made of silver electrodes and are magnetron sputtered on both sides of the PVDF piezoelectric layer 3, each with a thickness of 200 nm.

[0040] In this invention, the high Young's modulus thin film backing 5 possesses both high Young's modulus and thin thickness. On one hand, the high Young's modulus allows the backing to regulate the stress distribution within the PVDF piezoelectric layer 3. On the other hand, the thin thickness ensures that the backing still maintains good flexibility.

[0041] In a preferred embodiment, the flexible substrate layer 6 is made of polydimethylsiloxane (PDMS) and prepared by a mold casting method. The top flexible waterproof layer 1 can be prepared using PDMS via a mold casting method, with a thickness of 4 mm, or using Parylene C material via a vacuum phase deposition coating process. If Parylene C material is used, the thickness of the top flexible waterproof layer 1 is not less than 5 μm, preferably 10 μm.

[0042] In a preferred embodiment where both the flexible substrate layer 6 and the top flexible waterproof layer 1 are made of polydimethylsiloxane, the watertightness of the flexible underwater acoustic detection skin is achieved using any of the following methods: Method 1: After injecting polydimethylsiloxane into a mold, heat it at 60°C for 1 hour to obtain a partially cured but not fully cured flexible substrate layer 6; place the multilayer structure of the upper electrode layer 2, PVDF piezoelectric layer 3, lower electrode layer 4, and high Young's modulus film backing 5 on the flexible substrate layer 6, and inject polydimethylsiloxane again to form the top flexible waterproof layer 1; heat the entire structure again at 60°C for 1.5 hours to fully cure. Method 2: Use polydimethylsiloxane to separately inject the flexible substrate layer 6 and the top flexible waterproof layer 1. Then, spin-coat a polydimethylsiloxane film around the multilayer structure composed of the upper electrode layer 2, PVDF piezoelectric layer 3, lower electrode layer 4, and high Young's modulus film backing 5. The three components were plasma-treated for 10 seconds using a plasma treatment machine to activate the polydimethylsiloxane molecules on the surface, and then the three components were quickly pressed together.

[0043] The effectiveness of this invention is demonstrated as follows:

[0044] Figure 4 This is a comparison chart of the frequency domain response curves with and without a backing in embodiments of the present invention. From Figure 4 As can be seen, the embodiment with a 50µm aluminum foil backing (i.e., high Young's modulus film backing 5) has a sensitivity of -212.3dB (ref 1V / μPa) at 20Hz, which is 14dB higher than that without the aluminum foil backing. Meanwhile, with a sensitivity fluctuation of no more than 3dB as the standard, the embodiment with the 50µm aluminum foil backing maintained constant sensitivity in the 20-500Hz range, while the embodiment without the aluminum foil backing only maintained constant sensitivity in the 20-125Hz range.

[0045] Figure 5 This is a comparison diagram of the internal stress distribution of PVDF films with and without aluminum foil backing according to embodiments of the present invention, where x1, x2, and x3 directions are as follows: Figure 2 and Figure 3 As shown in the figure. The average stress in the xi direction of the PVDF piezoelectric layer 3 is shown in Equation 1. Figure 5 As shown in (a), the average stress in the x1, x2 and x3 directions of the PVDF piezoelectric layer 3 when there is no aluminum foil backing and the incident sound wave frequency is 100Hz is... and The piezoelectric coefficients are 1.93 N / m², 2.56 N / m², and 1.00 N / m², respectively. The calculation formula for the output voltage signal of the PVDF piezoelectric layer 3 is shown in Formula 2. Due to the piezoelectric coefficient d of the PVDF piezoelectric layer 3... 33 Numerically, it is d 31 It is 2.5 times that, and the sign is opposite. Therefore To a large extent The cancellation results in a smaller output voltage signal.

[0046] from Figure 5 As can be seen in (b), the 50µm aluminum foil backing causes transverse stress within the layer. Reduced to 1.12 N / m², The offsetting effect is weakened, and at the same time, the normal stress The output voltage signal of PVDF piezoelectric layer 3 remains unchanged. Therefore, the output voltage signal of PVDF piezoelectric layer 3 increases compared to when there is no aluminum foil backing, and the signal-to-noise ratio is improved.

[0047]

[0048]

[0049] In the formula, V is the volume of the PVDF piezoelectric layer 3, and U p It is the output voltage signal of PVDF piezoelectric layer 3, d 3i It is the piezoelectric coefficient of PVDF piezoelectric layer 3 along the xi direction, t p is the thickness of PVDF piezoelectric layer 3, and ∈ is the dielectric constant of PVDF piezoelectric layer 3.

[0050] Figure 6 The figures show the simulation and measured results of the frequency domain response curves corresponding to different radii of curvature in embodiments of the present invention. Figure 6 As can be seen, within the operating frequency range of 100-500Hz, the frequency domain response curves of the flexible underwater acoustic detection skin of this embodiment exhibit good flatness in both planar and curved surface states with a curvature radius of 200mm. Furthermore, the sensitivity values ​​in the planar and curved surface states with a curvature radius of 200mm are similar, with a measured difference of approximately 1.5dB. This demonstrates that the flexible underwater acoustic detection skin of this embodiment can effectively detect underwater acoustic signals. Moreover, the flexible underwater acoustic detection skin of this embodiment is lightweight and flexible. The measured curvature radius can be as low as 20mm, adapting to conformal installation requirements in various application scenarios, demonstrating its advanced technology.

[0051] The present invention also provides an underwater acoustic sensor, which employs the flexible underwater acoustic detection skin, which covers the main body of the underwater acoustic sensor.

[0052] In summary, this invention provides an underwater acoustic detection skin that is flexible, compact, and lightweight. Its overall flexibility allows it to be easily attached to the surface of various small underwater vehicles such as UUVs and divers for acoustic sensing.

[0053] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0054] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A flexible underwater acoustic detection skin, characterized in that, It includes an upper electrode signal line (8), a lower electrode signal line (7), and a top flexible waterproof layer (1), an upper electrode layer (2), a PVDF piezoelectric layer (3), a lower electrode layer (4), a high Young's modulus film backing (5), and a flexible substrate layer (6) arranged from top to bottom. The upper electrode signal line (8) is connected to the upper electrode layer (2), and the lower electrode signal line (7) is connected to the lower electrode layer (4); The bottom areas of the upper electrode layer (2), PVDF piezoelectric layer (3), lower electrode layer (4), and high Young's modulus film backing (5) are all the same; the multilayer structure formed by the upper electrode layer (2), PVDF piezoelectric layer (3), lower electrode layer (4), and high Young's modulus film backing (5) completely covers the flexible substrate layer (6) and the top flexible waterproof layer (1); The top flexible waterproof layer (1), upper electrode layer (2), PVDF piezoelectric layer (3), lower electrode layer (4), high Young's modulus film backing (5), and flexible substrate layer (6) all have flexibility; The high Young's modulus film backing (5) is made of aluminum foil, copper foil or stainless steel foil; the thickness of the high Young's modulus film backing (5) is 40-60 μm. The Young's modulus of the high Young's modulus film backing (5) is between 7e10 and 2e11 N / m2, and the product of Young's modulus and thickness is between 3.5e6 and 1.1e7 N / m.

2. The flexible underwater acoustic detection skin according to claim 1, characterized in that, The flexible substrate (6) is made of a material with a Young's modulus of less than or equal to 2e6 N / m2, and is waterproof and corrosion resistant. The thickness of the flexible substrate (6) is between 1 mm and 10 mm.

3. The flexible underwater acoustic detection skin according to claim 1, characterized in that, The upper electrode layer (2) and the lower electrode layer (4) are made of silver, copper and gold metal materials.

4. The flexible underwater acoustic detection skin according to claim 1, characterized in that, The upper electrode signal line (8) is bonded to the upper electrode layer (2), and the lower electrode signal line (7) is bonded to the lower electrode layer (4) by conductive silver paste or conductive copper foil.

5. The flexible underwater acoustic detection skin according to claim 1, characterized in that, Through holes or U-shaped grooves for fixed installation are opened on the flexible base layer (6).

6. The flexible underwater acoustic detection skin according to claim 1, characterized in that, Both the flexible base layer (6) and the top flexible waterproof layer (1) are made of polydimethylsiloxane.

7. The flexible underwater acoustic detection skin according to claim 6, characterized in that, The watertightness of the flexible underwater acoustic testing skin is achieved using any of the following methods: Method 1: After injecting polydimethylsiloxane into the mold, heat it at 60°C for 1 hour to obtain the partially cured but not fully cured flexible substrate layer (6); place the multilayer structure consisting of the upper electrode layer (2), PVDF piezoelectric layer (3), lower electrode layer (4), and high Young's modulus film backing (5) on the flexible substrate layer (6), inject polydimethylsiloxane again to form the top flexible waterproof layer (1), and heat the whole structure again at 60°C for 1.5 hours to fully cure. Method 2: Polydimethylsiloxane is used to inject the flexible base layer (6) and the top flexible waterproof layer (1) respectively. Polydimethylsiloxane film is spin-coated around the multilayer structure consisting of the upper electrode layer (2), PVDF piezoelectric layer (3), lower electrode layer (4), and high Young's modulus film backing (5). The three are plasma-treated for 10 seconds to activate the polydimethylsiloxane molecules on the surface. Then the three are quickly pressed and bonded together.

8. An underwater acoustic sensor, characterized in that, The flexible underwater acoustic detection skin according to any one of claims 1-7 is used, wherein the flexible underwater acoustic detection skin covers the main body of the underwater acoustic sensor.

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