An ultrathin pressure-resistant low-frequency broadband underwater sound absorption superstructure and a design method thereof

Abstract

The application provides an ultrathin pressure-resistant low-frequency broadband underwater sound absorption superstructure and a design method thereof, comprising a rubber main body, a water cavity, an air cavity and a bottom steel backing; by integrating quasi-Helmholtz, perforated plate local resonance and Fabry-Perot cavity three mechanisms in a 11 mm thick structure, high sound absorption with a continuous sound absorption coefficient of more than 0.8 from 225 Hz to 10 kHz is realized; the closed topology completely eliminates the risk of pollution and blockage of the open structure, and simultaneously reduces the low-frequency starting point and expands the bandwidth through flexible plate bending dissipation and cavity coupling, overcoming the defects of insufficient low-frequency performance and difficulty in compressing thickness in the conventional technology.

Description

Technical Field

[0001] This invention relates to the field of underwater acoustic control technology, and in particular to an ultrathin, pressure-resistant, low-frequency, broadband underwater sound-absorbing superstructure and its design method. Background Technology

[0002] Existing underwater sound absorption technologies mainly include the following categories, which have been widely used in fields such as shipbuilding, marine engineering, acoustic testing, and underwater noise control: 1. Underwater Quasi-Helmholtz Resonator: Utilizes an acoustic resonance formed by a cavity lined with a rubber layer and a neck opening. Low-frequency sound absorption is achieved through rubber layer compression and cavity volume changes. The cavity structure is often made of metal or composite materials. 2. Flexible Plate Sound Absorption Structure: Achieves low-frequency vibration dissipation by combining a flexible plate (such as rubber or a composite elastic layer) with a backing cavity. Commonly used for underwater coatings or sound insulation panels, but plate thickness and flexibility optimization are necessary. 3. Fabry-Perot Cavity Resonator: Provides high-frequency sound absorption based on the standing wave mode formed by the cavity depth and reflecting interface. Often used in combination with multilayer media to extend the frequency range. 4. Porous Foam Metal Materials: Utilizes the scattering of sound waves and viscous dissipation of sound waves through the internal pore structure of porous foam metals (such as aluminum foam). Commonly used for underwater sound absorption in high-pressure or corrosion-resistant environments, but porosity and material density need to be controlled. 5. Helical cavity slow wave structure: The helical cavity design extends the sound wave propagation path and realizes low-frequency slow wave absorption. It is used as a quasi-Helmholtz structure variant for compact structures, but the helical shape and material combination need to be optimized.

[0003] The aforementioned technologies are widely used in underwater noise control (such as acoustic coverings for submarines, underwater acoustic testing facilities, and noise reduction for marine platforms), but they also have several limitations and defects, especially in terms of low-frequency broadband, thickness control, and adaptability to actual environments.

[0004] 1) Narrow frequency range: Underwater rigid quasi-Helmholtz resonators typically provide high sound absorption only near a single resonant frequency, but have a narrow effective bandwidth. Flexible plates and Fabry-Perot cavity resonators perform well at high frequencies, but have a high low-frequency threshold, which cannot meet the requirements for ultra-low frequency noise control.

[0005] 2) Excessive thickness: Existing structures often require subwavelength thickness to achieve effective sound absorption, especially at low frequencies where the cavity depth requirement is large, resulting in a total thickness exceeding 20 mm, which is not conducive to compact underwater applications, such as ship hulls or portable devices.

[0006] 3) Susceptible to fouling: Open designs, such as underwater quasi-Helmholtz structures, are easily clogged by silt, algae, or organisms in marine environments, leading to a sharp degradation in low-frequency performance.

[0007] 4) Insufficient integration of mechanisms: Although some designs attempt to combine multiple mechanisms, the coupling between mechanisms is weak, which can easily lead to absorption gaps or peak attenuation, making it impossible to achieve seamless high sound absorption continuous coverage.

[0008] 5) Poor scalability in practical applications: Existing solutions are mostly based on single-cell verification and do not consider the coupling effect between cells after arraying, which leads to performance degradation or unevenness when applying coatings on a large scale. Manufacturing complexity (such as the high precision requirements for processing helical cavity slow-wave structures) also limits practical promotion.

[0009] 6) Insufficient pressure-bearing robustness: Existing rubber cavity structures often fail to adequately consider the pressure requirements of underwater environments. In practical applications, performance degradation or structural failure can easily occur due to cavity compression or sheet deformation. Some designs are only suitable for atmospheric pressure conditions and lack systematic protection and assessment for hydrostatic conditions.

[0010] These shortcomings limit the practical application of existing technologies, especially in deep-sea noise control and marine engineering. Summary of the Invention

[0011] In view of this, the purpose of the present invention is to provide an ultrathin, pressure-resistant, low-frequency, broadband underwater sound-absorbing superstructure and its design method, which achieves a high sound absorption coefficient of more than 0.8 from 225 Hz to 10 kHz.

[0012] To achieve the above objectives, the present invention adopts the following technical solution: an ultra-thin, pressure-resistant, low-frequency, broadband underwater sound-absorbing superstructure, comprising a rubber body 1, a water cavity 2, an air cavity 3, and a bottom steel backing 4; the rubber body 1 is composed of a top sealing plate 1.1, a perforated plate 1.2, a partition plate 1.3, and an outer substrate 1.4; the water cavity 2 is composed of an upper cylindrical water cavity 2.1, a cylindrical perforation 2.2, and a lower cylindrical water cavity 2.3, wherein the upper cylindrical water cavity 2.1 and the cylindrical perforation 2.2... 2 and the lower cylindrical water cavity 2.3 are interconnected; the partition 1.3 separates the water cavity 2 from the air cavity 3; the air cavity 3 is a bottom cylindrical cavity that is tightly attached to the steel backing 4; the rubber body 1 is bonded and fixed to the steel backing 4; the top sealing plate 1.1, perforated plate 1.2, partition 1.3, outer substrate 1.4, upper cylindrical water cavity 2.1, cylindrical perforated plate 2.2, lower cylindrical water cavity 2.3, air cavity 3 and bottom steel backing 4 are arranged coaxially and have a completely closed topology design.

[0013] In a preferred embodiment, the top sealing plate 1.1, the partition plate 1.3 and the air cavity 3 are combined to form a quasi-Helmholtz resonance, which, combined with the mass effect of water inside the cylindrical perforation 2.2, achieves low-frequency sound absorption below 1 kHz.

[0014] In a preferred embodiment, the perforated plate 1.2 undergoes local resonance under water load, forming a perforated plate local resonance and creating a mid-frequency sound-absorbing band of 1 kHz to 3 kHz.

[0015] In a preferred embodiment, the air cavity 3 and the partition 1.3 form a standing wave mode to generate a Fabry-Perot cavity resonance, achieving high-frequency sound absorption from 4 kHz to 10 kHz.

[0016] In a preferred embodiment, wideband high sound absorption is achieved through the synergistic effect of three mechanisms—quasi-Helmholtz resonance, perforated plate local resonance, and Fabry-Perot cavity resonance—within a single enclosed unit.

[0017] In a preferred embodiment, the sound absorption coefficient is ≥0.8 in the 225 Hz to 10 kHz frequency band under normal pressure; and ≥0.74 in the 312 Hz to 10 kHz frequency band under 1 MPa static water pressure.

[0018] In a preferred embodiment, under a static water pressure of 1 MPa, the top sealing plate 1.1 is concave inward, and the pressure is transmitted to the partition 1.3 to continue to compress the bottom air cavity 3; before the pressure causes the partition 1.3 to come into contact with the steel backing 4, the superstructure maintains its sound absorption performance while bearing the load.

[0019] In a preferred embodiment, the superstructure geometry parameters are specifically as follows: H 1 indicates that the total height of the rubber body 1, water cavity 2, and air cavity 3 is 11mm. H 2 indicates that the thickness of the steel backing 4 is 5mm. W The steel backing 4 of the superstructure has a side length of 30mm. h 1 indicates that the height of air cavity 3 is 2mm. h 2 indicates that the thickness of the partition 1.3 is 1mm, and h3 indicates that the height of the lower cylindrical water cavity 2.3 is 3mm. h 4 indicates that the thickness of the perforated plate 1.2 is 2mm. h 5 indicates that the height of the upper cylindrical water cavity 2.1 is 2mm. h 6 indicates that the height of the top-level enclosure panel 1.1 is 1mm. d 1 indicates that the diameters of the air cavity 3, the upper cylindrical water cavity 2.1, and the lower cylindrical water cavity 2.3 are 18 mm. d 2 indicates that the diameter of the cylindrical perforation 2.2 is 3mm.

[0020] In a preferred embodiment, the parameters of the rubber body 1 are as follows: density 1100 kg*m -3 Young's modulus 140 MPa, Poisson's ratio 0.49, isotropic loss factor 0.6.

[0021] This invention also provides a design method for an ultrathin, pressure-resistant, low-frequency, broadband underwater sound-absorbing superstructure. The method includes: filling and sealing the water cavity 2 with water; arranging and fixing multiple rubber bodies 1 to a steel backing 4 by adhesive bonding or mechanical means; attaching the superstructure to the surface of a ship's hull or underwater structure; and adjusting the height of the air cavity 3. h 1. Control the Fabry-Perot resonant frequency to optimize the high-frequency sound absorption bandwidth.

[0022] Compared with the prior art, the present invention has the following beneficial effects: (1) Strong ultra-low frequency broadband sound absorption capability With a thickness of only 11 mm, it achieves a high sound absorption coefficient of over 0.8 from 225 Hz to 10 kHz, which is far superior to the narrow-band or inefficient performance of traditional Helmholtz or perforated plate structures in the low-frequency range, making it suitable for underwater low-frequency noise control needs.

[0023] (2) The closed topology has strong anti-fouling ability. The fully enclosed design completely eliminates the defects of open Helmholtz or perforated structures that are susceptible to clogging by silt, algae, and biological attachments, maintaining stable sound absorption performance in long-term marine environments and significantly improving reliability in actual use.

[0024] (3) It has moderate pressure-bearing capacity and simple structure. The enclosed structure itself can withstand a hydrostatic pressure of 1 MPa (approximately 100 m water depth) without failure, and the performance degradation caused by compression of the cavity is controllable; the structure is compact and can meet the needs of shallow and medium water projects without complex reinforcement.

[0025] (4) Achieving seamless broadband through multi-mechanism collaboration The three mechanisms of quasi-Helmholtz resonance, perforated plate local resonance, and Fabry-Perot cavity resonance are effectively coupled within a single unit. The dissipation peaks overlap and are dominated by rubber viscoelastic damping, avoiding absorption gaps and achieving continuous near-perfect sound absorption.

[0026] (5) Extremely thin and easy to integrate into engineering With a total thickness of only 11 mm and a strict subwavelength scale, it is easy to attach to curved or confined space structures such as ship hulls, submarine surfaces, or underwater platforms, enabling large-scale array deployment.

[0027] This product is suitable for various underwater noise control scenarios and can be applied to: Applications include sound-absorbing coatings for ship and submarine hulls, noise reduction for underwater acoustic testing facilities, noise suppression for offshore platforms and subsea pipelines, stealth design for underwater robots or unmanned submersibles, and sound insulation for port terminals and underwater acoustic monitoring equipment. It is particularly suitable for engineering applications with comprehensive requirements for low-frequency broadband sound absorption, thickness limitations, fouling resistance, and pressure resistance in shallow to medium water. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the overall structure of the superstructure of the present invention; Figure 2 This is a side sectional view of the superstructure of the present invention; Figure 3 This is a top view of the superstructure of the present invention; Figure 4 This is a geometric dimensioning diagram of the superstructure of the present invention; Figure 5 This is a cross-sectional view of the displacement field of the superstructure bearing 1 MPa in this invention; Figure 6 This is a comparison chart of the sound absorption coefficients of the superstructure of this invention under normal pressure and at 1 MPa. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0030] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0031] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application; as used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise; furthermore, it should be understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0032] As attached Figure 1-3 As shown, this invention provides a design method for an ultrathin, pressure-resistant, low-frequency, broadband underwater sound-absorbing superstructure. The superstructure consists of a rubber body 1, a water cavity 2, an air cavity 3, and a bottom steel backing 4. The sound-absorbing layer is formed by embedding the water cavity 2 and the air cavity 3 within the rubber body 1. The rubber body 1 is composed of a top sealing plate 1.1, a perforated plate 1.2, a partition plate 1.3, and an outer substrate 1.4. The rubber body 1, consisting of the top sealing plate 1.1, perforated plate 1.2, partition plate 1.3, and outer substrate 1.4, is considered a whole; detailed regional divisions are only used for illustrating the sound absorption mechanism. The water cavity 2 is formed by connecting the upper cylindrical water cavity 2.1 and the lower cylindrical water cavity 2.3 through cylindrical perforations 2.2, allowing them to communicate with each other. The partition plate 1.3 separates the water cavity 2 from the air cavity 3. The bottom cylindrical air cavity 3 is tightly attached to the steel backing 4. All cylindrical cavities are coaxially arranged with the center of the square unit. The rubber body 1 is bonded and fastened to the steel backing 4 to form a complete underwater sound-absorbing superstructure.

[0033] As attached Figure 4 As shown, the specific geometric parameters of the superstructure are: H 1 indicates that the total height of the rubber body 1, water cavity 2, and air cavity 3 is 11mm. H 2 indicates that the thickness of the steel backing 4 is 5mm. W The steel backing 4 of the superstructure has a side length of 30mm. h 1 indicates that the height of air cavity 3 is 2mm. h 2 indicates that the thickness of the partition 1.3 is 1mm, and h3 indicates that the height of the lower cylindrical water cavity 2.3 is 3mm. h 4 indicates that the thickness of the perforated plate 1.2 is 2mm. h 5 indicates that the height of the upper cylindrical water cavity 2.1 is 2mm. h 6 indicates that the height of the top-level enclosure panel 1.1 is 1mm. d 1 indicates that the diameters of the air cavity 3, the upper cylindrical water cavity 2.1, and the lower cylindrical water cavity 2.3 are 18 mm. d 2 indicates that the diameter of the cylindrical perforation 2.2 is 3mm.

[0034] The parameters of the superstructured rubber material are as follows: density 1100 kg*m -3 The Young's modulus is 140 MPa, Poisson's ratio is 0.49, and isotropic loss factor is 0.6. The three mechanisms are coupled and overlapped within a single closed unit, with dissipation peaks continuously distributed. The performance is dominated by rubber viscoelastic damping, achieving wideband high sound absorption.

[0035] Three-mechanism synergy principle I. Low-Frequency Quasi-Helmholtz Resonance: In the frequency range below 1kHz, a quasi-Helmholtz resonance mode is formed through the top sealing plate 1.1, partition 1.3, and air cavity 3. The combination of the top sealing plate 1.1, partition 1.3, and air cavity 3 is a flexible component that increases the compressibility of the internal structure, generating system acoustic capacitance and acoustic damping; the mass of water within the cylindrical perforation 2.2 generates equivalent acoustic mass, thereby forming a quasi-Helmholtz resonance and achieving efficient energy dissipation. Combined with rubber viscoelastic damping, efficient low-frequency dissipation is achieved, and the cutoff frequency of the 0.8 absorption coefficient is reduced to 225 Hz.

[0036] (2) Local resonance of the perforated plate in the mid-frequency range: The superstructure achieves near-perfect matching of surface acoustic impedance in a wide mid-frequency range. In the range of about 1kHz-3kHz, the perforated plate 1.2 resonates locally under water load, producing an approximately rigid translational motion. At this time, the gradient of the normal displacement within the plate is approximately parallel, and there are almost no bending waves within the plate. At this resonant frequency, a strong loss zone is formed in the area of ​​the perforated plate 1.2 near the inner edge of the cylindrical perforation 2.2, which at the same time drives the adjacent outer substrate 1.4 to undergo strong coupling dissipation, ultimately forming a relatively wide sound-absorbing band.

[0037] (3) High-frequency air cavity Fabry-Perot resonance (FP resonance): In the 4kHz-10kHz frequency band, air cavity 3 and the outer substrate 1.4 exhibit air cavity FP resonance. When the acoustic energy reaches the structural partition 1.3, a standing wave mode is formed at the reflection interface between partition 1.3 and air cavity 3. At this time, the sound pressure inside air cavity 3 exhibits an approximately axial gradient distribution, and the absolute value of the sound pressure reaches its maximum at the interface between air cavity 3 and steel backing 4. FP resonance represents the simultaneous strong vibration dissipation of partition 1.3 and outer substrate 1.4. The air cavity FP resonance frequency is roughly calculated without correction term as follows: ,in It is the speed of sound in water. It is a scaling factor, and the resonant frequency is inversely proportional to the air cavity height h1. Therefore, the FP resonant frequency can be controlled by adjusting the parameter h1, that is, adjusting the frequency of the high-frequency absorption peak, thereby achieving a more perfect sound absorption bandwidth coverage.

[0038] The pressure-bearing sound absorption mechanism is as follows: When the superstructure is subjected to a pressure of 1 MPa, the static displacement of the structure is as shown in the attached figure. Figure 5 As shown (scale factor 1). The top sealing plate 1.1 is concave inward, and because the water is nearly incompressible, the pressure is transmitted to the inner partition 1.3, which continues to compress the bottom air cavity 3. Before the pressure causes the inner partition 1.3 to contact the steel backing 4, the superstructure can maintain good sound absorption performance while bearing the load. A comparison of the initial sound absorption performance and the sound absorption performance under 1MPa pressure is attached. Figure 6 As shown, the sound absorption coefficient reaches above 0.8 in the range of 225Hz-10kHz under normal pressure; and above 0.74 in the range of 312Hz-10kHz under pressure, with controllable performance degradation.

[0039] The product is used in practical applications as follows: (I) Structural water filling and unit assembly The superstructure unit water cavity 2 is pre-filled with an appropriate amount of water, and the water filling and sealing are completed through vacuum-assisted or low-pressure injection. Then, multiple sound-absorbing layer units are periodically arranged on the steel backing 4 using adhesives or mechanical fixing methods to form an array coating structure. The bonding process must ensure seamless connection between the units to avoid the risk of leakage in underwater applications.

[0040] (II) Enclosed installation The arrayed superstructure coating is attached to the surface of the ship's hull using specialized adhesives or mechanical clamping. During installation, it is ensured that the coating adheres completely to the substrate without cavities or warping, and the surface coating thickness is maintained at approximately 11 mm.

[0041] (III) Operation under normal pressure Under normal pressure or low hydrostatic pressure conditions, the unit achieves wideband high sound absorption through the synergistic effect of three mechanisms: quasi-Helmholtz resonance, perforated plate local resonance, and Fabry-Perot cavity. The closed topology ensures the integrity of each cavity.

[0042] (Ⅳ) Absorption state under 1 MPa pressure conditions When the ambient hydrostatic pressure rises to 1 MPa, the compression of the three air chambers causes a slight rightward shift in each resonant frequency, while the overall sound absorption performance remains stable. The enclosed structure effectively resists water pressure deformation, the damping characteristics of the rubber layer maintain dissipation capacity, and the absorption bandwidth remains essentially unchanged, making it suitable for long-term noise control in shallow to medium-water environments.

[0043] (V) Atmospheric pressure deformation recovery and continuous operation When the hydrostatic pressure returns to normal or the external load is removed, the volume of air cavity 3 and the deformation of the top sealing plate 1.1 and partition 1.3 automatically recover, and the resonant frequency returns to its initial state. The superstructure maintains structural integrity and sound absorption stability under repeated water pressure cycles, achieving long-term reliable operation.

[0044] This invention addresses the problem of low-frequency noise control underwater by designing an ultrathin, pressure-resistant, low-frequency, broadband underwater sound-absorbing superstructure. Within a thickness of only 11 mm, this structure integrates three mechanisms: quasi-Helmholtz resonance, perforated plate local resonance, and Fabry-Perot cavity. Continuous high sound absorption is achieved through the synergistic effect of flexible plate bending dissipation, perforation edge viscosity heat loss, and cavity standing waves. Simultaneously, the closed topology completely eliminates the drawbacks of open structures, such as susceptibility to silt and algae blockage. It is suitable for practical marine environments such as ship hull coatings and underwater platform noise reduction, providing a comprehensive solution with an extremely low low-frequency threshold, seamless broadband coverage, and robust anti-fouling properties.

Claims

1. A thin, pressure-resistant, low-frequency, broadband underwater sound-absorbing superstructure, characterized in that, It includes a rubber body (1), a water cavity (2), an air cavity (3), and a bottom steel backing (4); the rubber body (1) is composed of a top sealing plate (1.1), a perforated plate (1.2), a partition plate (1.3), and an outer substrate (1.4); the water cavity (2) is composed of an upper cylindrical water cavity (2.1), a cylindrical perforation (2.2), and a lower cylindrical water cavity (2.3), which are interconnected; A partition (1.3) separates the water cavity (2) from the air cavity (3); the air cavity (3) is a bottom cylindrical cavity that is closely attached to the steel backing (4); the rubber body (1) is bonded and fixed to the steel backing (4); the top sealing plate (1.1), perforated plate (1.2), partition (1.3), outer substrate (1.4), upper cylindrical water cavity (2.1), cylindrical perforation (2.2), lower cylindrical water cavity (2.3), air cavity (3) and bottom steel backing (4) are arranged coaxially and have a completely closed topology design.

2. The ultrathin, pressure-resistant, low-frequency, broadband underwater sound-absorbing superstructure according to claim 1, characterized in that, The top-level sealing plate (1.1), partition plate (1.3) and air cavity (3) are combined to form a quasi-Helmholtz resonance. Combined with the mass effect of water in the cylindrical perforation (2.2), low-frequency sound absorption below 1 kHz is achieved.

3. The ultrathin, pressure-resistant, low-frequency, broadband underwater sound-absorbing superstructure according to claim 2, characterized in that, The perforated plate (1.2) undergoes local resonance under water load, forming a perforated plate local resonance and creating a mid-frequency sound-absorbing band of 1 kHz to 3 kHz.

4. The ultrathin, pressure-resistant, low-frequency, broadband underwater sound-absorbing superstructure according to claim 3, characterized in that, The air cavity (3) and the partition (1.3) form a standing wave mode to generate Fabry-Perot cavity resonance, achieving high-frequency sound absorption from 4 kHz to 10 kHz.

5. The ultrathin, pressure-resistant, low-frequency, broadband underwater sound-absorbing superstructure according to claim 4, characterized in that, Wideband high sound absorption is achieved by the synergistic effect of three mechanisms—quasi-Helmholtz resonance, perforated plate local resonance, and Fabry-Perot cavity resonance—within a single enclosed unit.

6. The ultrathin, pressure-resistant, low-frequency, broadband underwater sound-absorbing superstructure according to claim 1, characterized in that, Under normal pressure, the sound absorption coefficient is ≥0.8 in the frequency band from 225 Hz to 10 kHz; under 1 MPa static water pressure, the sound absorption coefficient is ≥0.74 in the frequency band from 312 Hz to 10 kHz.

7. The ultrathin, pressure-resistant, low-frequency, broadband underwater sound-absorbing superstructure according to claim 6, characterized in that, Under 1MPa hydrostatic pressure, the top sealing plate (1.1) is concave inward, and the pressure is transmitted to the partition (1.3) to continue to compress the bottom air cavity (3); before the pressure causes the partition (1.3) to come into contact with the steel backing (4), the superstructure maintains its sound absorption performance while bearing the load.

8. The ultrathin, pressure-resistant, low-frequency, broadband underwater sound-absorbing superstructure according to claim 1, characterized in that, The specific geometric parameters of the superstructure are: H 1 indicates that the total height of the rubber body (1), water cavity (2), and air cavity (3) is 11mm. H 2 indicates that the thickness of the steel backing (4) is 5mm. W The side length of the steel backing (4) of the superstructure is 30mm. h 1 indicates that the height of the air cavity (3) is 2mm. h 2 indicates that the thickness of the partition (1.3) is 1mm, and h3 indicates that the height of the lower cylindrical water cavity (2.3) is 3mm. h 4 indicates that the thickness of the perforated plate (1.2) is 2mm. h 5 indicates that the height of the upper cylindrical water cavity (2.1) is 2mm. h 6 indicates that the height of the top sealing panel (1.1) is 1mm. d 1 indicates that the diameters of the air cavity (3), the upper cylindrical water cavity (2.1), and the lower cylindrical water cavity (2.3) are 18 mm. d 2 indicates that the diameter of the cylindrical perforation (2.2) is 3mm.

9. The ultrathin, pressure-resistant, low-frequency, broadband underwater sound-absorbing superstructure according to claim 1, characterized in that, The parameters of the rubber body (1) are as follows: density 1100 kg*m -3 Young's modulus 140 MPa, Poisson's ratio 0.49, isotropic loss factor 0.

6.

10. A design method for an ultrathin, pressure-resistant, low-frequency, broadband underwater sound-absorbing metastructure, characterized in that, An ultrathin, pressure-resistant, low-frequency, broadband underwater sound-absorbing superstructure as described in any one of claims 1-9 is designed, comprising: filling and sealing the water cavity (2) with water; arranging and fixing multiple rubber bodies (1) onto a steel backing (4) by adhesive bonding or mechanical means; attaching the superstructure to the hull of a ship or the surface of an underwater structure; and adjusting the height of the air cavity (3). h 1. Control the Fabry-Perot resonant frequency to optimize the high-frequency sound absorption bandwidth.

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