A membrane-structured underwater sound-absorbing metamaterial and its preparation method, and an underwater vehicle.

Abstract

This invention discloses an underwater sound-absorbing metamaterial with a membrane structure, its preparation method, and an underwater vehicle, belonging to the field of underwater sound absorption technology. It solves the problems of existing membrane-structured acoustic metamaterials, such as poor strength, insufficient resonant intensity, and impedance mismatch with the water medium, which prevent them from being truly used as underwater sound-absorbing materials. The underwater sound-absorbing metamaterial includes an elastic cover plate, an elastic layer, and a damping layer stacked sequentially. A first through-hole is formed in the elastic layer, and a lead ring is fitted onto the inner wall of the first through-hole. The outer diameter of the lead ring matches the diameter of the through-hole. The above-mentioned underwater sound-absorbing metamaterial with a membrane structure and its preparation method can be used for underwater sound absorption.

Description

Technical Field

[0001] This invention belongs to the field of underwater sound absorption technology, specifically relating to an underwater sound-absorbing metamaterial with a membrane structure and its preparation method, and an underwater vehicle. Background Technology

[0002] With the development of underwater acoustic communication technology, the demand for acoustic signal transmission path control and solving interference between underwater acoustic signals is constantly increasing.

[0003] In existing technologies, the main types of underwater sound-absorbing structures include cavity resonant, impedance-gradient, and localized resonant types. For cavity resonant and impedance-gradient type sound-absorbing structures, since the wavelength of sound waves in water is more than four times that in air at the same frequency, it is impossible to absorb larger wavelength sound waves with a smaller structure. As for localized resonant type sound-absorbing structures, although they have a higher absorption coefficient in the low-frequency range, the absorption coefficient decreases in the mid-frequency range, forming an absorption valley, thus failing to achieve broadband absorption of underwater sound waves.

[0004] Acoustic metamaterials are a relatively new type of artificial periodic composite structure that allows for the control of large-wavelength sound waves with relatively small structural dimensions. Existing acoustic metamaterials mainly include negative dynamic mass density metamaterials and negative dynamic modulus metamaterials that impede sound wave propagation, as well as "double-negative" metamaterials where both dynamic mass density and dynamic modulus are negative. Thin-film structure metamaterials are another type of acoustic metamaterial developed in recent years. By placing a mass block at the center of a tensioned thin film, when sound waves are incident on the surface of the membrane structure metamaterial, the film vibrates. The tension of the film acts as a spring, thus the film and the added mass block form a mass-spring structure, which can create a negative dynamic density phenomenon at low frequencies. However, thin-film structure metamaterials suffer from drawbacks such as poor strength, insufficient resonant intensity, and impedance mismatch with water media. Currently, applications using membrane structure acoustic metamaterials to solve problems are mainly focused on air media, and they cannot be truly used as underwater sound-absorbing materials. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide an underwater sound-absorbing metamaterial with a membrane structure, a preparation method thereof, and an underwater vehicle, which solves the problems of existing membrane structure acoustic metamaterials having poor strength, insufficient resonance intensity, and impedance mismatch with water medium, thus preventing them from being truly used as underwater sound-absorbing materials.

[0006] The objective of this invention is mainly achieved through the following technical solutions:

[0007] This invention provides an underwater sound-absorbing metamaterial with a membrane structure, comprising an elastic cover plate, an elastic layer and a damping layer stacked sequentially, wherein a first through hole is formed in the elastic layer, and a lead ring is fitted on the inner wall of the first through hole, the outer diameter of the lead ring matching the diameter of the through hole.

[0008] Furthermore, the elastic cover, elastic layer, and damping layer are all rubber cylinders.

[0009] Furthermore, the diameter of the aforementioned underwater sound-absorbing metamaterial with a membrane structure is 50–65 mm, and the thickness is 40–100 mm.

[0010] Furthermore, the thickness ratio of the elastic cover plate, the elastic layer, and the damping layer is 0.9–1.2:0.9–1.2:1.9–2.1.

[0011] Furthermore, the thickness ratio of the elastic cover plate, the elastic layer, and the damping layer is 1:1:2.

[0012] Furthermore, the thickness of the elastic cover plate is 10–25 mm, the thickness of the elastic layer is 10–25 mm, and the thickness of the damping layer is 20–50 mm.

[0013] Furthermore, the outer diameter of the lead ring is 16–24 mm.

[0014] Furthermore, the inner diameter of the lead ring is 14–22 mm.

[0015] Furthermore, the center-to-center distance between the lead ring and the elastic layer is 8–12 mm.

[0016] Furthermore, the aforementioned underwater sound-absorbing supermaterial also includes an inner lead column disposed within a lead ring.

[0017] Furthermore, the diameter of the lead column inside the ring is 4–8 mm.

[0018] Furthermore, a second through hole is formed on the aforementioned elastic layer, and an outer lead post is disposed within the second through hole.

[0019] Furthermore, the diameter of the outer lead column is 2–8 mm.

[0020] Furthermore, the distance between the center of the outer lead column and the center of the elastic layer is 10–20 mm.

[0021] The present invention also provides an underwater vehicle, including an outer shell (e.g., a steel backing) and a metamaterial covering the surface of the outer shell, the metamaterial being the above-mentioned underwater sound-absorbing metamaterial with a membrane structure.

[0022] This invention also provides a method for preparing an underwater sound-absorbing metamaterial, comprising the following steps:

[0023] Step 1: Process resin-based or metal-based cover plate molds and elastic damping composite molds by machining or 3D printing.

[0024] Step 2: Pour the cover plate material into the cover plate mold to obtain the cover plate. Pour the elastic layer and damping layer materials into the elastic-damping composite mold to obtain the composite structure of the elastic layer and damping layer.

[0025] Step 3: Make the first through hole in the elastic layer and put the lead ring into the first through hole;

[0026] Step 4: Use an adhesive to bond the elastic cover plate and the elastic layer to obtain the underwater sound-absorbing supermaterial.

[0027] Furthermore, when the aforementioned underwater sound-absorbing metamaterial includes a lead ring, step 3 above, after inserting the lead ring into the first through hole, also includes the following steps:

[0028] Place the lead post into the lead ring.

[0029] Furthermore, when the aforementioned underwater sound-absorbing metamaterial includes an outer lead column, step 3 further includes the following steps:

[0030] A second through hole is made in the elastic layer, and the lead column outside the ring is placed into the second through hole.

[0031] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0032] a) The underwater sound-absorbing metamaterial with a membrane structure provided by this invention is a high-efficiency underwater sound-absorbing material. On the one hand, the lead ring in the elastic layer, the part of the elastic cover plate in contact with the air inside the lead ring, and the part of the damping layer in contact with the air inside the lead ring constitute a membrane structure. By introducing a membrane structure that can generate negative mass density into the traditional underwater sound-absorbing structure, the metamaterial effectively improves the low-frequency sound absorption performance and broadens the sound absorption frequency band by utilizing the abnormal effect of sound waves, thus achieving efficient absorption of low-frequency broadband sound waves. On the other hand, the elastic cover plate, the elastic layer, and the damping layer are all elastic materials, which have damping characteristics for underwater sound waves and can also achieve broadband absorption of underwater sound waves.

[0033] b) The underwater sound-absorbing metamaterial with a membrane structure provided by the present invention utilizes the characteristic of acoustic metamaterials that can control large wavelength sound waves with a small size, effectively reducing the structural size and solving the problems of low low-frequency sound absorption performance, narrow sound absorption frequency band and excessive thickness that are common in traditional underwater sound-absorbing structures. The raw materials are readily available, the preparation process is mature, and the implementation is highly feasible.

[0034] c) The underwater sound-absorbing metamaterial with a membrane structure provided by this invention, after testing, shows that its sound absorption coefficient is greater than 0.65 in the 1000Hz-10000Hz range, and greater than 0.7 in the 1000Hz-10000Hz range, except for the 1500-2300Hz range. This indicates that the underwater sound-absorbing metamaterial with a membrane structure has a high sound absorption coefficient and good stealth performance over a very wide frequency range, with good continuity and no sound absorption valleys.

[0035] d) The underwater sound-absorbing metamaterial with a membrane structure provided by the present invention, through the setting of the lead pillar inside the ring, can effectively support the part of the elastic cover plate and part of the damping layer corresponding to the cavity inside the lead ring, so as to prevent the cavity inside the lead ring from collapsing inward when the hydrostatic pressure is too high, thereby ensuring the stability of the sound absorption coefficient; on the other hand, after the sound wave enters the underwater sound-absorbing metamaterial, the lead pillar can generate reciprocating vibration, which acts as a spring, thereby adjusting the overall impedance of the underwater sound-absorbing metamaterial, so that the sound wave can more easily propagate into the interior of the underwater sound-absorbing metamaterial.

[0036] e) The underwater sound-absorbing metamaterial with a membrane structure provided by the present invention, on the one hand, can effectively support the elastic layer, elastic cover plate and damping layer outside the lead ring through the lead pillar outside the lead ring, thereby further avoiding the deformation of the elastic layer when the hydrostatic pressure is too high, thus ensuring the stability of the sound absorption coefficient; on the other hand, after the sound wave enters the underwater sound-absorbing metamaterial, the lead pillar outside the ring can also adjust the overall impedance of the underwater sound-absorbing metamaterial, so that the sound wave can more easily propagate into the interior of the underwater sound-absorbing metamaterial.

[0037] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings. Attached Figure Description

[0038] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0039] Figure 1 This is a schematic diagram of the underwater sound-absorbing metamaterial of Embodiment 1 of the present invention;

[0040] Figure 2 The sound absorption coefficient curve and equivalent density curve generated by the structure in Embodiment 1 of the present invention;

[0041] Figure 3 This is a schematic diagram of the underwater sound-absorbing metamaterial of Embodiment 2 of the present invention;

[0042] Figure 4 This is the sound absorption coefficient curve generated by the structure in Embodiment 1 of the present invention.

[0043] Figure label:

[0044] 1-Elastic cover plate; 2-Inner lead column of the ring; 3-Lead ring; 4-Outer lead column of the ring; 5-Elastic layer; 6-Damping layer. Detailed Implementation

[0045] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of the present invention and, together with the embodiments of the present invention, serve to illustrate the principles of the present invention.

[0046] This invention provides an underwater sound-absorbing metamaterial with a membrane structure, based on a negative mass density mechanism. (See also...) Figures 1 to 4 It includes an elastic cover plate 1, an elastic layer 5 and a damping layer 6 stacked in sequence. The elastic layer 5 has a first through hole, and a lead ring 3 is fitted on the inner wall of the first through hole. The outer diameter of the lead ring 3 matches the diameter of the through hole.

[0047] For example, the elastic cover plate 1, the elastic layer 5, and the damping layer 6 are all rubber cylinders.

[0048] During implementation, the damping layer 6 is connected to the mounting surface (e.g., the steel backing of an underwater vehicle). When sound waves are incident on the underwater sound-absorbing metamaterial, at low frequencies, the metamaterial and the mounting surface produce a spring-oscillator-like effect, generating a sound absorption peak at low frequencies. At mid-frequency frequencies, the sound waves cause relative motion between the upper and lower interfaces of the lead ring 3, generating a negative dynamic mass density effect under frequency loading in specific frequency bands. When the dynamic mass density is negative, sound waves cannot propagate, and combined with the damping effect of the rubber, a large amount of sound energy is dissipated. At high frequencies, the sound wave wavelength is shorter, and the damping of the rubber material itself has a natural dissipation effect on high-frequency sound waves.

[0049] Compared with existing technologies, the underwater sound-absorbing metamaterial with a membrane structure provided by this invention is a highly efficient underwater sound-absorbing material. On the one hand, the lead ring 3 in the elastic layer 5, the part of the elastic cover plate 1 in contact with the air inside the lead ring 3, and the part of the damping layer 6 in contact with the air inside the lead ring 3 constitute a membrane structure. By introducing a membrane structure that can generate negative mass density into the traditional underwater sound-absorbing structure, the metamaterial effectively improves the low-frequency sound absorption performance and broadens the sound absorption frequency band by utilizing the abnormal effect of sound waves, thus achieving efficient absorption of low-frequency broadband sound waves. On the other hand, the elastic cover plate 1, the elastic layer 5, and the damping layer 6 are all elastic materials, which have damping characteristics for underwater sound waves and can also achieve broadband absorption of underwater sound waves.

[0050] Meanwhile, by utilizing acoustic metamaterials, which can control sound waves of larger wavelengths with smaller dimensions, the structural size can be effectively reduced. This solves the problems commonly found in traditional underwater sound-absorbing structures, such as low low-frequency sound absorption performance, narrow sound absorption bandwidth, excessive thickness, poor strength, insufficient resonance intensity, and impedance mismatch with the water medium, which prevent them from being truly used as underwater sound-absorbing materials. Furthermore, the raw materials are readily available, the preparation process is mature, and the feasibility of implementation is high.

[0051] Specifically, the functions of each layer in the aforementioned underwater sound-absorbing metamaterial with a membrane structure are as follows:

[0052] The elastic cover plate 1 is a cover layer that can seal the air inside the lead ring 3 and provide the upper interface of the membrane structure.

[0053] The elastic layer 5 is a structural layer that can provide a resonant environment for the lead ring 3.

[0054] Damping layer 6 is a material layer composed of pure rubber, which can not only effectively absorb high-frequency sound waves, but also provide the lower interface of the membrane structure.

[0055] The sound absorption coefficient is an important indicator for evaluating the stealth performance of sound-absorbing coatings. At specific frequencies, a higher sound absorption coefficient indicates better stealth performance. Tests showed that the aforementioned underwater sound-absorbing metamaterial with a membrane structure has a sound absorption coefficient greater than 0.65 in the 1000Hz-10000Hz range, and a sound absorption coefficient greater than 0.7 in the 1000Hz-10000Hz range, except for the 1500-2300Hz range. This indicates that the aforementioned underwater sound-absorbing metamaterial with a membrane structure exhibits a high sound absorption coefficient and good stealth performance over a very wide frequency range, with good continuity and no sound absorption valleys.

[0056] For example, the diameter of the aforementioned underwater sound-absorbing metamaterial with a membrane structure is 50-65 mm, and the thickness is 40-100 mm. This is because, in practical applications, the aforementioned underwater sound-absorbing metamaterial needs to be mounted on the surface of an underwater vehicle. Due to the load-bearing capacity and manufacturing limitations of the underwater vehicle, it should not be too thick. If the underwater sound-absorbing metamaterial is too thin, its overall sound absorption effect will be reduced.

[0057] Considering that the thickness of the elastic cover plate 1, the elastic layer 5, and the damping layer 6 all directly affect the overall sound absorption effect of the aforementioned underwater sound-absorbing metamaterial, the thickness ratio of the elastic cover plate 1, the elastic layer 5, and the damping layer 6 is 0.9–1.2:0.9–1.2:1.9–2.1 (e.g., 1:1:2). For example, the thickness of the elastic cover plate 1 is 10–25 mm, the thickness of the elastic layer 5 is 10–25 mm, and the thickness of the damping layer 6 is 20–50 mm. It should be noted that the main function of the elastic layer 5 is to dissipate sound waves by generating a negative mass density through the lead ring 3 and the upper and lower interfaces; therefore, resonance is crucial, and the elastic layer 5 cannot be too thick. The damping layer 6 is a material layer mainly for absorbing higher frequency sound waves; therefore, it is thicker than the elastic cover plate 1 and the elastic layer 5.

[0058] To ensure a sufficiently large cavity for resonance, the diameter of the lead ring 3 is greater than the thickness of the elastic layer 5. For example, the outer diameter of the lead ring 3 is 16–24 mm. Since the outer diameter of the lead ring 3 matches the diameter of the first through hole, the diameter of the first through hole is also the outer diameter of the lead ring 3. The inner wall of the lead ring 3 is a rigid wall. Because it needs to provide a sufficiently large cavity for resonance, the outer diameter of the lead ring 3 needs to be greater than the thickness of the elastic layer 5. On the other hand, from the perspective of sound wave propagation, the impedance mismatch between air and water is severe. Therefore, the cavity cannot be too large to prevent obstructing high-frequency sound waves from entering the damping layer 6.

[0059] Similarly, the inner diameter of the lead ring 3 needs to ensure a sufficiently large cavity for resonance; for example, the inner diameter of the lead ring 3 is 14–22 mm.

[0060] Considering that inner lead pillars 2 and outer lead pillars 4 will be added to the elastic layer 5 later, from the perspective of spatial distribution and processing technology, the distance between the center of the lead ring 3 and the center of the elastic layer 5 is 8-12mm. In practical applications, considering that the above-mentioned underwater sound-absorbing metamaterials are usually arranged in periodic units, the distance between the lead ring 3 and the center of the elastic layer 5 is due to the process considerations of manufacturing the outer lead pillars 4. Generally, the inner lead pillars 2 and outer lead pillars 4 are better evenly distributed. When the lead ring 3 is placed in the center of the elastic layer 5, if we want to keep the distance between each inner lead pillar 2 and outer lead pillar 4 consistent, the position of the outer lead pillar 4 will be placed at the interface of two underwater sound-absorbing metamaterial units, which will increase the processing difficulty and is not conducive to the testing and analysis of individual units. The lead ring 3 is offset from the center of the elastic layer 5 by a certain distance to leave space for the outer lead pillars 4, which simplifies the manufacturing process and does not change the overall sound absorption effect.

[0061] Considering the high hydrostatic pressure in the underwater environment, which may cause the cavity inside the lead ring 3 to collapse inward, resulting in an unstable sound absorption coefficient, the aforementioned underwater sound-absorbing metamaterial also includes an inner lead column 2 within the lead ring 3. In this way, the inner lead column 2 effectively supports the portion of the elastic cover plate 1 and the portion of the damping layer 6 corresponding to the cavity inside the lead ring 3, preventing the cavity from collapsing inward under excessive hydrostatic pressure, thus ensuring the stability of the sound absorption coefficient. Furthermore, after sound waves enter the underwater sound-absorbing metamaterial, the lead column can reciprocate, acting as a spring, thereby adjusting the overall impedance of the underwater sound-absorbing metamaterial and allowing sound waves to propagate more easily into its interior.

[0062] To minimize the impact of the inner lead pillar 2 on the cavity inside the lead ring 3, the diameter of the inner lead pillar 2 is 4–8 mm. This is because the placement of the inner lead pillar 2 will affect the resonance of the cavity inside the lead ring 3. To reduce this impact, the size of the inner lead pillar 2 needs to be limited. Limiting the diameter of the inner lead pillar 2 to the above-mentioned range ensures that the lead pillar has sufficient mechanical strength to support the elastic cover plate 1 and the damping layer 6, while minimizing the impact of the inner lead pillar 2 on the resonance space.

[0063] To further ensure the structural strength of the elastic layer 5 and thus the stability of the sound absorption coefficient, a second through hole is opened on the elastic layer 5, and the outer lead column 4 is placed in the second through hole. In this way, on the one hand, the outer lead column 4 can effectively support the part of the elastic layer 5, part of the elastic cover plate 1, and part of the damping layer 6 outside the lead ring 3, thereby further preventing the deformation of the elastic layer 5 when the hydrostatic pressure is too high, thus ensuring the stability of the sound absorption coefficient; on the other hand, after the sound wave enters the underwater sound-absorbing metamaterial, the outer lead column 4 can also adjust the overall impedance of the underwater sound-absorbing metamaterial, so that the sound wave can more easily propagate into the interior of the underwater sound-absorbing metamaterial.

[0064] The outer lead pillar 4 not only effectively supports part of the elastic layer 5, part of the elastic cover plate 1, and part of the damping layer 6, but also adjusts the overall impedance of the elastic layer 5 and the underwater sound-absorbing metamaterial. For example, the diameter of the outer lead pillar 4 is 2–8 mm, and the center distance between the outer lead pillar 4 and the elastic layer 5 is 10–20 mm. This is because the elastic layer 5 is made of different materials (air, elastic material, and lead), and the impedance of different materials is also different. When sound waves enter the elastic layer 5 from the interface between the elastic cover plate 1 and the elastic layer 5, the impedance of the elastic layer 5 is close to the impedance of the interface between the elastic cover plate 1 and the elastic layer 5. This is more conducive to the sound waves entering the metamaterial. The diameter of the outer lead pillar 4 is 4–8 mm, and the center distance between the outer lead pillar 4 and the elastic layer 5 is 10–20 mm, which allows for better adjustment of the impedance of the elastic layer 5 while ensuring sufficient mechanical strength of the outer lead pillar 4.

[0065] The present invention also provides an underwater vehicle comprising an outer shell (e.g., a steel backing) and a metamaterial covering the surface of the outer shell, the metamaterial being the aforementioned underwater sound-absorbing metamaterial with a membrane structure. The metamaterial can act as a unit cell, periodically covering the surface of the underwater vehicle as a sound-absorbing covering layer to counteract active sonar and improve the stealth of the underwater vehicle.

[0066] Compared with the prior art, the beneficial effects of the underwater vehicle provided by the present invention are basically the same as those of the underwater sound-absorbing metamaterials provided above, and will not be elaborated here.

[0067] This invention also provides a method for preparing an underwater sound-absorbing metamaterial, comprising the following steps:

[0068] Step 1: Process resin-based or metal-based cover plate molds and elastic damping composite molds by machining or 3D printing.

[0069] Step 2: Pour the cover plate material into the cover plate mold to obtain the cover plate. Pour the elastic layer 5 and damping layer 6 materials into the elastic-damping composite mold to obtain the composite structure of elastic layer 5 and damping layer 6.

[0070] Step 3: Make a first through hole in the elastic layer 5 and put the lead ring 3 into the first through hole;

[0071] Step 4: Use an adhesive to bond the elastic cover plate 1 and the elastic layer 5 to obtain the underwater sound-absorbing supermaterial.

[0072] Compared with the prior art, the beneficial effects of the underwater sound-absorbing metamaterial preparation method provided by the present invention are basically the same as those of the underwater sound-absorbing metamaterial provided above, and will not be elaborated here.

[0073] It is understandable that when the aforementioned underwater sound-absorbing metamaterial includes the inner lead pillar 2, step 3 above, after inserting the lead ring 3 into the first through hole, also includes the following steps:

[0074] Place the lead post 2 inside the ring into the lead ring 3.

[0075] Similarly, when the aforementioned underwater sound-absorbing metamaterial includes the outer lead column 4, step 3 further includes the following steps:

[0076] A second through hole is made in the elastic layer 5, and the outer lead post 4 is placed into the second through hole.

[0077] Specific embodiments of the present invention are given below.

[0078] Example 1

[0079] Material properties used in Example 1:

[0080] Rubber: Density 1000~1200kg / m³ 3 Young's modulus is 10 MPa.

[0081] Water: density 1000 kg / m³ 3 The sound velocity is 1500 m / s, and the dynamic viscosity coefficient is 0.00101 Pa·s.

[0082] Lead: density 11600 kg / m³ 3 Young's modulus is 17 GPa and Poisson's ratio is 0.42.

[0083] See the complete structure. Figure 1The structure consists of a cylinder with a diameter of 56 mm. Specifically, the elastic cover plate 1 has a thickness of 10 mm, the elastic layer 5 has a thickness of 10 mm, and the damping layer has a thickness of 20 mm. In the elastic layer 5, the diameter of the first through-hole is 20 mm, the diameter of the second through-hole is 4 mm, the distance from the center of the lead ring 3 to the center of the elastic layer 5 is 10 mm, and the distance from the center of the second through-hole to the center of the elastic layer 5 is 15 mm. The outer diameter of the lead ring 3 is 20 mm, and the inner diameter is 18 mm. An inner lead pillar 2 and an outer lead pillar 4, each with a diameter of 4 mm, are placed in the center of the first through-hole and the second through-hole, respectively. The underwater sound-absorbing structure is fabricated by first machining a metal-based mold. One mold is used for the cover plate, while the elastic layer 5 and the damping layer 6 share a common mold. Next, modified rubber is poured into the mold to obtain a mixed layer of the elastic cover plate 1, the elastic layer 5, and the damping layer 6. Secondly, lead rings 3, inner lead pillars 2, and outer lead pillars 4 are embedded in the elastic layer 5, and finally the desired superstructure is obtained.

[0084] The acoustic performance of the superstructure under steel backing with perpendicular acoustic wave incidence was analyzed using the finite element method. Figure 2 The figures show the dynamic curves of the sound absorption coefficient and equivalent mass density of the underwater sound-absorbing metamaterial in the embodiment from 1Hz to 10000Hz. It can be seen that in the frequency range where the equivalent density is negative, the sound absorption coefficient curve of the underwater sound-absorbing metamaterial with a membrane structure based on the negative mass mechanism exhibits an absorption peak, fully demonstrating the effect of the negative mass mechanism. The sound absorption coefficient curves show that the underwater sound-absorbing metamaterial with a membrane structure based on the negative mass mechanism has a sound absorption coefficient greater than 0.65 in the 1000Hz-10000Hz range, and except for 1500-2300Hz, the sound absorption coefficient is greater than 0.7 in the 1000Hz-10000Hz range, exhibiting excellent underwater sound absorption performance.

[0085] Example 2

[0086] Material properties used in the examples:

[0087] Rubber: Density 1000-1200 kg / m³ 3 Young's modulus is 10 MPa.

[0088] Water: density 1000 kg / m³ 3 The sound velocity is 1500 m / s, and the dynamic viscosity coefficient is 0.00101 Pa·s.

[0089] Lead: density 11600 kg / m³ 3 Young's modulus is 17 GPa and Poisson's ratio is 0.42.

[0090] See the complete structure. Figure 3A cylinder with a diameter of 56mm is used. Specifically, the thickness of the elastic cover plate 1 is 10mm, the thickness of the elastic layer 5 is 10mm, and the thickness of the damping layer 6 is 20mm. In the elastic layer 5, the diameter of the first through hole is 20mm, the diameter of the second through hole is 4mm, the distance from the first through hole to the center of the elastic layer 5 is 10mm, and the distance from the second through hole to the center of the elastic layer 5 is 15mm. The outer diameter of the lead ring 3 is 20mm, and the inner diameter is 18mm. A second lead cylinder with a diameter of 4mm is placed in the second through hole.

[0091] In this embodiment, the underwater sound-absorbing structure is fabricated by first machining a metal-based mold, with the cover plate sharing one mold and the elastic layer 5 and damping layer 6 sharing the same mold. Next, modified rubber is poured into the mold to obtain the elastic cover plate 1, the elastic layer 5, and the damping layer 6 mixed layer. Then, lead rings 3 and lead pillars are embedded in the elastic layer 5, finally yielding the desired superstructure.

[0092] The acoustic performance of the superstructure under steel backing with perpendicular acoustic wave incidence was analyzed using the finite element method. Figure 4 The values ​​represent the sound absorption coefficients of the underwater sound-absorbing metamaterials in the embodiment within the 1Hz-10000Hz range. It can be seen that the underwater sound-absorbing metamaterial structure with a negative mass mechanism and containing a membrane exhibits a sound absorption coefficient greater than 0.65 within the 1000Hz-10000Hz range. Except for the 1800-2200Hz range, the sound absorption coefficients within this range are all greater than 0.7, demonstrating excellent underwater sound absorption performance.

[0093] Example 3

[0094] Material properties used in Example 3:

[0095] Rubber: Density 1000~1200kg / m³ 3 Young's modulus is 10 MPa.

[0096] Water: density 1000 kg / m³ 3 The sound velocity is 1500 m / s, and the dynamic viscosity coefficient is 0.00101 Pa·s.

[0097] Lead: density 11600 kg / m³ 3 Young's modulus is 17 GPa and Poisson's ratio is 0.42.

[0098] See the complete structure. Figure 1The structure consists of a cylinder with a diameter of 63mm. Specifically, the thickness of the elastic cover plate 1 is 15mm, the thickness of the elastic layer 5 is 33mm, and the thickness of the damping layer is 15mm. In the elastic layer 5, the diameter of the first through hole is 24mm, the diameter of the second through hole is 6mm, the distance from the center of the lead ring 3 to the center of the elastic layer 5 is 12mm, and the distance from the center of the second through hole to the center of the elastic layer 5 is 15mm. The outer diameter of the lead ring 3 is 24mm, and the inner diameter is 20mm. An inner lead pillar 2 and an outer lead pillar 4, each with a diameter of 6mm, are placed in the center of the first through hole and in the second through hole, respectively. The underwater sound-absorbing structure is fabricated by first machining a metal-based mold. One mold is used for the cover plate, while the elastic layer 5 and the damping layer 6 share a common mold. Next, modified rubber is poured into the mold to obtain a mixed layer of the elastic cover plate 1, the elastic layer 5, and the damping layer 6. Secondly, lead rings 3, inner lead pillars 2, and outer lead pillars 4 are embedded in the elastic layer 5, and finally the desired superstructure is obtained.

[0099] The acoustic performance of the metastructure under perpendicular sound wave incidence with a steel backing was analyzed using the finite element method. Within the frequency range where the equivalent density is negative, the sound absorption coefficient curve of the underwater sound-absorbing metastructure with a membrane structure based on the negative mass mechanism exhibits an absorption peak. The sound absorption coefficient is greater than 0.65 in the 1000Hz-10000Hz range, and except for the 1500-2300Hz range, the sound absorption coefficient is greater than 0.7 in the 1000Hz-10000Hz range, demonstrating excellent underwater sound absorption performance.

[0100] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. An underwater sound-absorbing metamaterial with a membrane structure, characterized in that, It includes an elastic cover plate, an elastic layer and a damping layer stacked in sequence. A first through hole is formed in the elastic layer. A lead ring is fitted on the inner wall of the first through hole. The outer diameter of the lead ring matches the diameter of the through hole. The underwater sound-absorbing metamaterial also includes an inner lead column disposed within the lead ring; A second through hole is formed on the elastic layer, and an outer lead post is disposed in the second through hole; The lead ring in the elastic layer, the portion of the elastic cover plate in contact with the air inside the lead ring, and the portion of the damping layer in contact with the air inside the lead ring constitute a membrane structure. The lead ring is offset from the center of the elastic layer.

2. The underwater sound-absorbing metamaterial with a membrane structure according to claim 1, characterized in that, The underwater sound-absorbing metamaterial has a diameter of 50–65 mm and a thickness of 40–100 mm.

3. The underwater sound-absorbing metamaterial with a membrane structure according to claim 1, characterized in that, The thickness ratio of the elastic cover plate, the elastic layer and the damping layer is 0.9-1.2:0.9-1.2:1.9-2.

1.

4. The underwater sound-absorbing metamaterial with a membrane structure according to claim 1, characterized in that, The thickness of the elastic cover plate is 10-25 mm, the thickness of the elastic layer is 10-25 mm, and the thickness of the damping layer is 20-50 mm.

5. The underwater sound-absorbing metamaterial with a membrane structure according to claim 1, characterized in that, The diameter of the lead column inside the ring is 4 to 8 mm.

6. The underwater sound-absorbing metamaterial with a membrane structure according to claim 1, characterized in that, The diameter of the outer lead column is 2-8 mm.

7. An underwater vehicle, characterized in that, It includes an outer shell and a metamaterial covering the surface of the outer shell, said metamaterial being an underwater sound-absorbing metamaterial with a membrane structure as described in any one of claims 1 to 6.

8. A method for preparing an underwater sound-absorbing metamaterial, characterized in that, Includes the following steps: Step 1: Prepare the cover plate mold and the elastic damping composite mold; Step 2: Pour the cover plate material into the cover plate mold to obtain the cover plate; The raw materials for the elastic layer and the damping layer are poured into an elastic-damping composite mold to obtain a composite structure of the elastic layer and the damping layer. Step 3: Make the first through hole in the elastic layer and put the lead ring into the first through hole; Step 4: Bond the elastic cover plate to the elastic layer to obtain the underwater sound-absorbing supermaterial.

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