An underwater sound absorbing blanket

Abstract

This invention relates to the field of underwater sound-absorbing material structure design technology, specifically to an underwater sound-absorbing covering layer. The covering layer is composed of multiple sound-absorbing cells arranged periodically and continuously. Each sound-absorbing cell includes a rigid skeleton and a viscoelastic matrix. The rigid skeleton includes a rigid back plate, two rigid vertical plates symmetrically fixed to both sides of the rigid back plate, and multiple rigid horizontal plates symmetrically fixed to the inner walls of the two rigid vertical plates. The viscoelastic matrix is ​​fixed between the two rigid vertical plates, with a fully enclosed cavity spaced between it and the rigid back plate. The multiple rigid horizontal plates are embedded inside the viscoelastic matrix. The viscoelastic matrix contains a micro-slit inlet cavity communicating with the external water environment and a micro-slit spiral cavity communicating with it. The micro-slit spiral cavity is used to fill with water in the underwater working state to form a micro-slit spiral water column structure. This invention achieves excellent performance with a sound absorption coefficient of not less than 0.78 across a wide frequency range from 100Hz to 10000Hz.

Description

Technical Field

[0001] This invention relates to the field of underwater sound-absorbing material structure design technology, specifically to an underwater sound-absorbing covering layer. Background Technology

[0002] For underwater military platforms such as submarines, unmanned underwater vehicles, and autonomous underwater vehicles, the sound-absorbing coatings applied to their surfaces are crucial for resisting active sonar detection and achieving acoustic stealth. Meanwhile, civilian marine engineering fields, such as offshore wind power foundations, offshore oil platforms, and underwater acoustic measurement equipment, are also facing an increasingly urgent need for underwater noise reduction and sound insulation technologies. In recent years, sonar detection technology has developed rapidly, with low-frequency active sonar becoming the mainstream detection method. Its operating frequency has extended from the traditional mid-to-high frequency band down to below 500 Hz, and even as low as 100 Hz in the ultra-low frequency band. Low-frequency sound waves travel long distances and attenuate slowly in water, making them extremely effective at detecting underwater targets. This poses an unprecedented challenge to traditional underwater sound-absorbing coatings.

[0003] Existing underwater sound-absorbing materials and structures mainly face the following technical bottlenecks: First, the low-frequency sound absorption performance is severely inadequate. Traditional underwater sound-absorbing materials are mostly based on the damping dissipation principle of viscoelastic materials, converting sound energy into heat energy through internal friction. However, viscoelastic materials have very limited attenuation capabilities for low-frequency sound waves because the wavelengths of low-frequency sound waves are relatively long, making it difficult to generate sufficient vibration and deformation within a finite-thickness covering layer, resulting in a significant decrease in sound energy dissipation efficiency. Studies have shown that the sound absorption coefficient of existing sound-absorbing structures is generally below 0.5 in the frequency band below 500 Hz, making it difficult to effectively counter the detection threat of low-frequency active sonar.

[0004] Secondly, the effective sound absorption bandwidth is limited. A single sound-absorbing structure often exhibits narrow-band sound absorption characteristics, with its efficient absorption frequency band typically concentrated around a specific resonant frequency. Beyond this frequency, the sound absorption performance drops sharply. However, modern sonar systems often possess broadband detection capabilities, with operating frequencies extending from hundreds of hertz to tens of kilohertz. Narrow-band sound-absorbing structures cannot meet the requirements for full-band stealth. To broaden the sound absorption bandwidth, researchers have attempted to combine multiple sound-absorbing structures in series or parallel, such as using cavity resonant structures, micro-slit structures, and viscoelastic material layers in combination, aiming to achieve frequency band complementarity. However, such multi-structure composite designs often lead to a significant increase in the thickness of the covering layer, a substantial increase in structural complexity, high manufacturing difficulty and cost, and difficulty in ensuring consistency and reliability in mass production.

[0005] Furthermore, structural complexity and manufacturing costs are significant issues. Structures with a single sound absorption mechanism often struggle to meet both low-frequency and wide-bandwidth requirements, while multi-mechanism composite structures face challenges in design complexity and manufacturing difficulties. For example, water column structures based on slit acoustics perform well in low-frequency sound absorption, but the effective absorption bandwidth of a single water column structure is limited; rubber-metal plate structures have good sound absorption in the mid-to-high frequency range, but weak low-frequency sound absorption. To balance the advantages of both, existing technologies typically combine different structural units in series or parallel, resulting in a complex internal structure and increased interfaces in the covering layer. This not only increases the risk of sound wave reflection and scattering but also places extremely high demands on mold design and molding processes, leading to high manufacturing costs and hindering widespread engineering applications.

[0006] In summary, developing an underwater sound-absorbing covering layer that combines low-frequency broadband sound absorption capability with a simple and symmetrical structure suitable for industrial mass production has become a key technological direction for addressing common needs in the fields of national defense equipment and marine engineering. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide an underwater sound-absorbing covering layer. This invention achieves both ultra-low frequency sound absorption and broadband sound absorption.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides an underwater sound-absorbing covering layer, which is composed of multiple sound-absorbing cells arranged periodically and continuously. Each sound-absorbing cell includes a rigid skeleton and a viscoelastic matrix. The rigid skeleton includes a rigid back plate, two rigid vertical plates symmetrically fixed to both sides of the rigid back plate, and multiple rigid horizontal plates symmetrically fixed to the inner sidewalls of the two rigid vertical plates. The viscoelastic matrix is ​​fixed between the two rigid vertical plates, and a fully enclosed cavity is provided between the viscoelastic matrix and the rigid back plate. The multiple rigid horizontal plates are embedded inside the viscoelastic matrix. The viscoelastic matrix has a micro-slit inlet cavity communicating with the external water environment and a micro-slit spiral cavity communicating with the micro-slit inlet cavity. The micro-slit spiral cavity is used to fill water in the underwater working state to form a micro-slit spiral water column structure.

[0009] As a preferred embodiment of the present invention, multiple rigid horizontal plates are arranged in parallel at intervals along the height direction of the rigid vertical plate, and the rigid horizontal plates are provided with a width gradient along the incident direction of the sound wave, and the width of the rigid horizontal plates gradually decreases as they approach the rigid back plate.

[0010] As a preferred embodiment of the present invention, the viscoelastic matrix is ​​made of viscoelastic materials including rubber and polyurethane, or a composite material with viscoelastic material as the matrix.

[0011] As a preferred embodiment of the present invention, the rigid back plate, rigid vertical plate and rigid horizontal plate are made of rigid materials, including rigid metal materials or carbon fiber composite materials.

[0012] As a preferred embodiment of the present invention, the fully enclosed cavity is filled with a gaseous medium; the spiral cavity of the micro-slit spiral water column structure is filled with water in the underwater working state, forming a micro-slit spiral water column structure that is connected to the external water environment.

[0013] As a preferred embodiment of the present invention, the main structures of the rigid back plate, rigid vertical plate, rigid horizontal plate, viscoelastic matrix, and closed cavity are all cuboid structures.

[0014] As a preferred embodiment of the present invention, the micro-slit spiral cavity structure is in the shape of an Archimedean spiral, and its cross-sectional width remains constant or varies with gradient along the spiral path.

[0015] As a preferred embodiment of the present invention, the width of the micro-slit inlet cavity is greater than the width of the micro-slit spiral cavity.

[0016] As a preferred embodiment of the present invention, the total thickness of the underwater sound-absorbing covering layer along the direction of sound wave incidence does not exceed 50 mm.

[0017] As a preferred embodiment of the present invention, the underwater sound-absorbing covering layer has a sound absorption coefficient of not less than 0.78 in the frequency range of 100Hz to 10000Hz.

[0018] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. This invention integrates multiple sound absorption mechanisms, such as low-frequency resonant sound absorption, mid-to-high frequency interface damping dissipation, and sound wave mode conversion, through deep coupling of micro-slit spiral water column structure, rigid horizontal plate gradient grid structure, and fully enclosed cavity structure. It achieves excellent performance with a sound absorption coefficient of not less than 0.78 in a wide frequency range of 100Hz to 10000Hz with an ultra-thin thickness of no more than 50mm. In particular, it solves the industry pain point of low sound absorption efficiency in the ultra-low frequency range below 500Hz in the existing technology, and can effectively meet the wideband detection needs of modern low-frequency active sonar.

[0019] 2. The sound-absorbing cells of the present invention adopt a mirror symmetry design, and the main structure is a cuboid structure without complex irregular structure. The mold processing difficulty is low, and integrated industrial production can be achieved through compression molding, which greatly reduces manufacturing costs and process difficulty, and avoids the problems of complex structure, high processing cost and low yield caused by multiple structures connected in series / parallel in the prior art. Attached Figure Description

[0020] Figure 1This is a partial three-dimensional structural diagram of the underwater sound-absorbing covering layer of the present invention.

[0021] Figure 2 This is a partial cross-sectional structural diagram of the underwater sound-absorbing covering layer of the present invention.

[0022] Figure 3 This is a schematic cross-sectional view of a single sound-absorbing cell in this invention.

[0023] Figure 4 These are schematic diagrams of different configurations. Configuration I is a spiral water column structure, configuration II is a rubber-metal plate structure, and configuration III is a novel structure that combines the spiral water column structure and the rubber-metal plate structure.

[0024] Figure 5 for Figure 4 A comparison curve of the sound absorption coefficients of the three configuration structures as a function of frequency.

[0025] In the figure: 1. Sound-absorbing cell; 11. Rigid back plate; 12. Rigid vertical plate; 13. Rigid horizontal plate; 14. Viscoelastic matrix; 15. Fully enclosed cavity; 16. Micro-slit entrance cavity; 17. Micro-slit spiral cavity. Detailed Implementation

[0026] To enable those skilled in the art to better understand the technical solutions of the present invention, preferred embodiments of the present invention are described below in conjunction with specific examples. However, it should be understood that the accompanying drawings are for illustrative purposes only and should not be construed as limiting the present patent. For better illustration of this embodiment, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable that some well-known structures and their descriptions may be omitted in the drawings for those skilled in the art. The positional relationships described in the drawings are for illustrative purposes only and should not be construed as limiting the present patent.

[0027] The present invention will now be described in further detail with reference to the accompanying drawings, illustrating an underwater sound-absorbing covering layer.

[0028] This invention discloses an underwater sound-absorbing covering layer based on the synergistic effect of a grid structure and a micro-slit structure. It can be widely used in the acoustic stealth installation of underwater military equipment such as military submarines, unmanned underwater vehicles (UUVs), and autonomous underwater vehicles (AUVs). It can also be applied to underwater noise reduction and sound insulation in civilian marine engineering scenarios such as offshore oil platforms, offshore wind power foundations, and underwater acoustic measurement equipment. The core purpose is to solve three major industry pain points of existing underwater sound-absorbing structures: insufficient low-frequency sound absorption performance, limited effective sound absorption bandwidth, and complex structure with high processing difficulty. It achieves high-efficiency underwater sound absorption with ultra-low frequency and wide frequency band in an ultra-thin structural size.

[0029] like Figures 1-3As shown, the underwater sound-absorbing cover layer provided by this invention is composed of multiple sound-absorbing cells 1 arranged periodically and continuously in a two-dimensional plane perpendicular to the direction of sound wave incidence. The core purpose of adopting a periodic array arrangement is to ensure that the overall acoustic impedance is uniform and consistent after the cover layer is laid over a large area, without any local performance blind spots. At the same time, it facilitates standardized production and on-site splicing construction, and can adapt to the needs of different laying interfaces such as planes and low-curvature curved surfaces. The array method can be selected as a square array, rectangular array, or regular hexagonal honeycomb array according to the actual application scenario. Adjacent sound-absorbing cells 1 are tightly fitted without gaps to prevent sound waves from transmitting through splicing gaps, thus ensuring the integrity and acoustic performance stability of the cover layer.

[0030] In this embodiment, each sound-absorbing cell 1 includes three core components: a rigid skeleton, a viscoelastic matrix 14, and a cavity. The rigid skeleton provides structural support and mechanical reinforcement for the entire sound-absorbing cell 1, and also serves as the mounting carrier for the core acoustic functional structure. It includes a rigid back plate 11, two rigid vertical plates 12 symmetrically fixed to both sides of the rigid back plate 11, and multiple rigid horizontal plates 13 symmetrically fixed to the inner walls of the two rigid vertical plates 12. The viscoelastic matrix 14 is the core body for sound energy dissipation, fixed between the two rigid vertical plates 12. A fully enclosed cavity 15 is provided between the viscoelastic matrix 14 and the rigid back plate 11. The multiple rigid horizontal plates 13 are completely embedded inside the viscoelastic matrix 14, forming an interface coupling with the viscoelastic matrix 14. The viscoelastic matrix 14 contains a micro-slit inlet cavity 16 communicating with the external water environment, and a micro-slit spiral cavity 17 communicating with the micro-slit inlet cavity 16. The micro-slit spiral cavity 17 is used to fill with water in underwater operation to form a micro-slit spiral water column structure.

[0031] The core inventive concept of this invention lies in the deep coupling of the ultra-low frequency resonant sound absorption characteristics of the micro-slit spiral water column structure, the mid-to-high frequency broadband sound absorption characteristics of the rigid horizontal plate 13 gradient grid structure, and the low frequency resonant sound absorption characteristics of the fully enclosed cavity 15. Through the synergistic effect of multiple structures, the frequency band limitation of a single sound absorption structure is broken. With an ultra-thin thickness of no more than 50mm, the sound absorption coefficient of no less than 0.78 in a wide frequency band from 100Hz to 10000Hz is achieved, while maintaining a simple and symmetrical structure to meet the needs of industrial mass production.

[0032] In this embodiment, the rigid frame is the core of the mechanical load-bearing structure of the entire sound-absorbing covering layer, and also an important component for realizing the acoustic function. It consists of three parts: a rigid back plate 11, a rigid vertical plate 12, and a rigid horizontal plate 13. All three parts are integrally formed using the same rigid material to ensure the integrity of the structure and the consistency of mechanical properties, and to avoid problems such as deformation, cracking, and falling off caused by differences in thermal expansion coefficients and mismatches in mechanical properties between different materials.

[0033] The rigid backplate 11 serves as the installation reference and load-bearing foundation for the entire sound-absorbing cell 1. Its core functions include three aspects: First, it provides a stable installation and fixing reference for the rigid vertical plate 12 and the viscoelastic matrix 14, ensuring the dimensional accuracy and stability of the entire cell structure. Second, it acts as the connection interface between the sound-absorbing covering layer and the underwater structure to be laid, using adhesives to firmly fix the entire covering layer to the target substrate such as the hull of a submarine, the outer wall of an underwater vehicle, or the surface of a marine engineering structure. Third, it acts as an acoustic hard boundary, blocking the transmission of incompletely absorbed sound waves into the underwater structure, forcing the sound waves to reflect and superimpose multiple times inside the covering layer, extending the sound wave propagation path, and improving the sound energy dissipation efficiency.

[0034] In terms of specific structural design, the rigid backplate 11 is a cuboid plate structure, and its planar dimensions perfectly match the transverse cross-sectional dimensions of a single sound-absorbing cell 1, ensuring that the rigid backplates 11 of adjacent cells can be tightly spliced ​​to form a continuous rigid support layer without splicing gaps. The thickness of the rigid backplate 11 needs to balance structural rigidity and overall thickness control, and is usually set to 1mm~5mm. In the preferred embodiment of the present invention, the thickness of the rigid backplate 11 is set to 2mm. This thickness can ensure structural rigidity in the high hydrostatic pressure environment of the deep sea, avoiding deformation under pressure, and will not occupy too much thickness space, leaving sufficient design margin for the internal sound-absorbing functional structure.

[0035] In terms of material selection, the rigid backplate 11 uses rigid materials with high elastic modulus, resistance to seawater corrosion, and excellent aging resistance, including metallic rigid materials or carbon fiber composite materials. Among them, stainless steel, titanium alloy, and aluminum alloy are preferred metallic rigid materials. Stainless steel is inexpensive, has good processing performance, and excellent resistance to seawater corrosion, making it suitable for conventional marine engineering scenarios and shallow sea application environments. Titanium alloy has high specific strength and extremely strong corrosion resistance, and can maintain stable mechanical properties for a long time in the high pressure and high salt spray environment of the deep sea, making it suitable for high-end equipment such as deep-sea vehicles and deep-sea submarines. Aluminum alloy has low density and light weight, making it suitable for small unmanned underwater vehicles with strict weight control requirements. Carbon fiber composite materials have the characteristics of low density, high rigidity, and excellent damping performance. While ensuring structural rigidity, they can significantly reduce the overall weight of the covering layer. At the same time, their own damping characteristics can help improve the sound energy dissipation effect, making them the preferred material for lightweight high-end equipment.

[0036] Regarding processing and connection methods, the connection process between the rigid backplate 11 and the rigid vertical plate 12 can be selected according to the material: for rigid frames made of metal, welding is preferred for integral connection to ensure the sealing and structural strength of the connection points; integral milling can also be used to further improve the overall structural integrity. For rigid frames made of carbon fiber composite materials, integral molding is preferred, or high-strength seawater-resistant structural adhesive can be used for bonding to ensure connection strength. The side of the rigid backplate 11 that contacts the structure to be laid can be pre-coated with an anti-corrosion coating and an adhesive primer to improve the bonding force with the adhesive and avoid problems such as adhesive layer peeling and interface corrosion during long-term underwater operation; the side that connects to the rigid vertical plate 12 can be equipped with a positioning slot and a welding slot to ensure the positioning accuracy and connection strength of the rigid vertical plate 12 during installation.

[0037] Two rigid vertical plates 12 are symmetrically fixed to both sides of the upper surface of the rigid back plate 11, forming a U-shaped grid frame together with the rigid back plate 11, which is the core load-bearing structure of the rigid skeleton. Its core functions include: first, providing fixed installation points for multiple rigid horizontal plates 13, ensuring that the rigid horizontal plates 13 can be installed accurately and firmly in the designed position; second, providing lateral restraint and enclosure for the viscoelastic matrix 14, ensuring the structural stability of the viscoelastic matrix 14 under underwater high pressure environment and acoustic vibration, and preventing the matrix from deforming or falling off; third, defining the lateral boundary of the fully enclosed cavity 15 and the micro-slit structure, ensuring the spatial dimensional accuracy of the internal functional structure, while maximizing the use of the internal space to design sound-absorbing functional structures and improving space utilization.

[0038] In terms of specific structural design, both rigid vertical plates 12 are cuboid plate structures, vertically fixed to the left and right sides of the upper surface of the rigid back plate 11, forming a 90° vertical angle with the rigid back plate 11. The two rigid vertical plates 12 are parallel to each other and perfectly mirror-symmetrically arranged. The core advantage of the symmetrical design is to ensure that the acoustic performance of the sound-absorbing cell 1 is anisotropic, ensuring that the covering layer maintains a stable and consistent sound absorption effect when sound waves are incident from different angles, avoiding fluctuations in sound absorption performance caused by structural asymmetry.

[0039] In terms of processing and installation details, the top end face of the rigid vertical plate 12 is flush with the incident surface of the viscoelastic matrix 14, forming a flat sound wave incident interface together. This avoids irregular sound wave reflection caused by uneven structure, ensures the uniformity of acoustic impedance of the incident interface, reduces the reflection loss of sound waves at the incident interface, and allows more sound waves to enter the interior of the covering layer and be absorbed.

[0040] Multiple rigid horizontal plates 13 are symmetrically fixed to the inner sidewalls of two rigid vertical plates 12 and are completely embedded in the viscoelastic matrix 14. This is the core structure for achieving mid-to-high frequency broadband sound absorption in this invention. At the same time, it works in conjunction with the micro-slit spiral structure to broaden the overall sound absorption bandwidth. Its core functions are reflected in three aspects: First, through the interface coupling between the rigid horizontal plate 13 and the viscoelastic matrix 14, under the excitation of sound waves, the viscoelastic matrix 14 is induced to generate strong compressive vibration in the interface region, realizing the efficient conversion of longitudinal sound waves to transverse sound waves. The damping and dissipation capacity of the viscoelastic matrix 14 for transverse waves is much higher than that for longitudinal waves, thereby greatly improving the sound energy dissipation efficiency. Second, through the layered parallel arrangement of multiple rigid horizontal plates 13, multiple sets of continuous acoustic impedance gradients are formed in the direction of sound wave incidence, realizing the gradual impedance matching of sound waves inside the covering layer, greatly reducing the reflection of sound waves at the incident interface, and allowing more sound waves to enter the covering layer smoothly and be dissipated. Third, through the width gradient design along the direction of sound wave incidence, the natural frequency and vibration mode of the structure at different depth positions are controlled, so that the rigid horizontal plates 13 of different widths correspond to different sound absorption frequency bands, forming a continuous sound absorption frequency band coverage, and greatly widening the effective sound absorption bandwidth.

[0041] In terms of specific structural design, multiple rigid horizontal plates 13 are arranged in parallel at equal intervals along the height direction (i.e., the direction of sound wave incident) of the rigid vertical plate 12. The rigid horizontal plates 13 on the inner sidewalls of the two rigid vertical plates 12 are arranged in a one-to-one correspondence and mirror symmetry. The two rigid horizontal plates 13 at the same height position are on the same horizontal plane and do not contact each other. The reserved central space is used to fill the viscoelastic matrix 14 and set the micro-slit structure to ensure that the viscoelastic matrix 14 can completely wrap each rigid horizontal plate 13, forming a gapless interface fit and maximizing the interface vibration coupling effect.

[0042] Regarding the quantity and spacing design, the number of rigid horizontal plates 13 can be flexibly adjusted according to the target sound absorption frequency band requirements, typically set to 4 to 20 pairs. In the preferred embodiment of the present invention, it is set to 9 pairs of rigid horizontal plates 13. The more rigid horizontal plates 13 there are, the denser the acoustic impedance gradient is formed, and the better the broadband sound absorption effect. However, it will also increase the processing difficulty and structural weight. Therefore, a balanced design is required based on the sound absorption requirements, weight limitations, and processing costs of the actual application scenario. The vertical spacing between two adjacent rigid horizontal plates 13 is kept consistent, forming an equidistant layered structure. The spacing is typically set to 1mm to 5mm, and in the preferred embodiment, it is set to 2mm. The equidistant design can ensure the formation of a uniform and continuous impedance gradient over a wide frequency range, avoiding blind spots in the sound absorption frequency band, and facilitating mold processing and mass production.

[0043] The rigid horizontal plate 13 has a width gradient along the direction of sound wave incidence. The width of the rigid horizontal plate 13 gradually decreases as it approaches the rigid back plate 11. This design is key to achieving broadband sound absorption. The core principle of this width gradient design is as follows: First, the rigid horizontal plate 13 is wider near the water surface, which can form a better acoustic impedance matching at the incident interface, allowing more mid-to-high frequency sound waves to enter the covering layer. At the same time, the larger contact area between the wide rigid horizontal plate 13 and the viscoelastic matrix 14 can induce stronger interface vibrations under mid-to-high frequency sound wave excitation, enhance the mode conversion from longitudinal wave to transverse wave, and significantly improve the sound energy dissipation efficiency in the mid-to-high frequency range. Second, the gradually decreasing width of the rigid horizontal plate 13 near the rigid back plate 11 can gradually reduce the structural density. The local rigidity of the structure regulates the natural frequency of the structure to extend to the low frequency band. At the same time, the gradual space formed by the decreasing width allows the viscoelastic matrix 14 to produce greater deformation under the excitation of low frequency sound waves, improving the dissipation of vibration energy in the low frequency band and making up for the sound absorption shortcomings of the rigid horizontal plate 13 structure in the low frequency band. Thirdly, the rigid horizontal plates 13 of different widths correspond to different resonant sound absorption frequency bands. Multiple sets of rigid horizontal plates 13 with gradient widths can form a continuous resonant sound absorption frequency band, avoiding the problem of narrowing the sound absorption frequency band caused by a single-width rigid horizontal plate 13, and greatly widening the effective sound absorption bandwidth.

[0044] In terms of materials and processing methods, the rigid horizontal plate 13 uses the same rigid material as the rigid back plate 11 and the rigid vertical plate 12 to ensure the material consistency and vibration mode controllability of the entire rigid frame. The rigid horizontal plate 13 and the rigid vertical plate 12 made of metal are connected by welding to ensure connection strength and prevent loosening or falling off under the action of acoustic vibration and underwater high pressure. The rigid horizontal plate 13 and the rigid vertical plate 12 made of carbon fiber composite material are preferably integrally molded to ensure the integrity of the structure. The surface of the rigid horizontal plate 13 needs to be roughened to improve the interfacial bonding force with the viscoelastic matrix 14 and prevent interfacial debonding under long-term vibration, which would lead to a decrease in sound absorption performance.

[0045] In this embodiment, the viscoelastic matrix 14 is the core sound energy dissipation body of the sound-absorbing covering layer of the present invention. At the same time, it serves as the carrier of the rigid horizontal plate 13, the micro-slit structure, and the fully enclosed cavity 15. It works in synergy with the rigid frame to achieve the coupling of multiple sound absorption mechanisms such as impedance matching, mode conversion, and resonant sound absorption. It is the core foundation for achieving high-efficiency sound absorption.

[0046] In terms of specific structural design, the viscoelastic matrix 14 is a cuboid structure, filled within the grid space enclosed by two rigid vertical plates 12 and multiple layers of rigid horizontal plates 13. Its lateral dimension perfectly matches the spacing between the two rigid vertical plates 12, and its height dimension is less than the height of the rigid vertical plates 12. All rigid horizontal plates 13 are completely embedded inside the viscoelastic matrix 14, and the upper and lower surfaces and left and right end faces of the matrix and rigid horizontal plates 13 are completely fitted without gaps, ensuring maximum vibration coupling effect at the interface and avoiding vibration transmission loss caused by interface gaps.

[0047] The surface of the viscoelastic matrix 14 facing the water is completely flush with the top end face of the rigid vertical plate 12, forming a smooth and flat sound wave incident interface. This avoids irregular scattering of sound waves caused by uneven structures, ensures the uniformity of acoustic impedance at the incident interface, reduces sound wave reflection at the incident interface, and allows more sound waves to enter the matrix smoothly and be dissipated. The bottom end of the viscoelastic matrix 14 (the side closest to the rigid back plate 11) does not contact the rigid back plate 11. A fully enclosed cavity 15 is provided between the two. That is, the bottom end of the viscoelastic matrix 14, the inner sidewalls of the two rigid vertical plates 12, and the upper surface of the rigid back plate 11 together form a fully enclosed cavity structure. The matrix serves as the upper boundary of the cavity and together with the cavity, constitutes a resonant sound absorption structure.

[0048] The viscoelastic matrix 14 has a micro-slit inlet cavity 16 and a micro-slit spiral cavity 17 pre-reserved in the central area. The cavity structure is integrally processed during the matrix molding process, which ensures the dimensional accuracy and inner wall smoothness of the cavity, avoids the increase of sound wave scattering and water flow resistance caused by processing defects, and ensures that it can be quickly filled with water during underwater operation to form a stable spiral water column structure.

[0049] The viscoelastic matrix 14 is made of viscoelastic materials including rubber and polyurethane, or composite materials with viscoelastic materials as the matrix. Different materials can be adapted to different application scenarios and performance requirements. In a preferred embodiment of the present invention, the viscoelastic matrix 14 is made of butyl rubber. The core advantages of butyl rubber are: high damping loss factor, which can efficiently convert the mechanical energy of sound wave vibration into heat energy dissipation; excellent resistance to seawater corrosion, hydrolysis, and aging, which can maintain stable mechanical and acoustic properties in long-term underwater immersion environment and have a long service life; good adhesion to the metal skeleton, which can form a stable interface bond with the rigid cross plate 13 and avoid interface debonding; and good acoustic impedance matching with water, which can significantly reduce the reflection of sound waves at the incident interface and improve the sound wave incident efficiency.

[0050] The fully enclosed cavity 15 is filled with a gaseous medium, preferably air, but inert gases such as nitrogen or argon can also be used as needed to prevent oxidation and corrosion of the cavity wall. The density and acoustic impedance of the gaseous medium are much lower than those of water and the viscoelastic matrix 14, creating a significant difference in acoustic impedance between them, which is the core of achieving resonant sound absorption and sound wave reflection. The fully enclosed cavity 15 is an important auxiliary structure for achieving low-frequency sound absorption in this invention. Together with the viscoelastic matrix 14, it forms a resonant sound absorption system, further broadening the low-frequency sound absorption bandwidth and enhancing the dissipation of sound waves through multiple reflections.

[0051] The microslit structure, comprising a microslit inlet cavity 16 and a microslit spiral cavity 17, is the core innovative structure for achieving ultra-low frequency sound absorption in this invention. Based on slit acoustics theory, it achieves efficient sound absorption in the 100Hz~500Hz ultra-low frequency range within a limited structural size through a spiral ultra-long microslit design. Simultaneously, it works in conjunction with the rigid horizontal plate 13 structure to achieve broadband sound absorption across the entire frequency range. The microslit inlet cavity 16 is located in the central region of the viscoelastic matrix 14, with its top opening onto the sound wave incident surface of the viscoelastic matrix 14, directly communicating with the external water environment. Its bottom end communicates with the inlet of the microslit spiral cavity 17. It is a cuboid cavity structure, serving as the channel for external water and sound waves to enter the microslit spiral cavity 17.

[0052] In terms of size design, the width of the micro-slit inlet cavity 16 is greater than the width of the micro-slit spiral cavity 17. This large inlet design significantly reduces the resistance to sound waves and water flow entering the micro-slit structure, allowing more low-frequency sound waves to smoothly enter the micro-slit spiral cavity 17. Simultaneously, the inlet cavity rectifies the incident sound waves, preventing irregular scattering at the inlet and ensuring efficient entry of sound waves into the spiral cavity, thus improving low-frequency sound absorption efficiency. One end of the micro-slit spiral cavity 17 is connected to the bottom of the micro-slit inlet cavity 16, while the other end is closed. Extending along an Archimedean spiral shape, it is located inside the viscoelastic matrix 14 below the micro-slit inlet cavity 16, in the central region between the multiple rigid horizontal plates 13. It does not contact the rigid horizontal plates 13 or the fully enclosed cavity 15, and is completely enclosed by the viscoelastic matrix 14, ensuring the structure's independence and stability.

[0053] Regarding the cross-sectional width design, the cross-sectional width of the micro-slit spiral cavity 17 can remain constant along the spiral path or exhibit a gradient change. The advantage of the constant width design lies in its simple processing and molding, uniform water flow resistance, and rapid filling with water during underwater operation to form a stable spiral water column, making it suitable for mass production. The gradient width design prioritizes a decreasing gradient with a wide inlet and a narrow end, which can further control the resonance mode of the water column, broaden the low-frequency sound absorption bandwidth, and simultaneously allow the sound waves to generate continuous impedance changes within the spiral cavity, reducing sound wave reflection and improving energy dissipation efficiency. It can be flexibly designed according to customized sound absorption requirements.

[0054] In underwater operation, water from the external aquatic environment enters the micro-slit spiral cavity 17 through the micro-slit inlet cavity 16, completely filling the spiral cavity and forming a micro-slit spiral water column structure that communicates with the external aquatic environment. This structure is the core of achieving ultra-low frequency sound absorption, and its sound absorption mechanism is mainly reflected in three aspects: First, the ultra-low frequency resonant sound absorption mechanism based on slit acoustics. A water-filled spiral cavity forms a continuous water column structure. The density and acoustic impedance of the water column are completely consistent with the external water environment, allowing low-frequency sound waves to enter the water column structure with almost no reflection. A significant acoustic impedance difference exists between the water column and the surrounding viscoelastic matrix 14. Under the excitation of low-frequency sound waves, the water column generates strong longitudinal vibrations along the spiral path, producing strong shear forces with the surrounding viscoelastic matrix 14. This induces strong damped vibrations in the matrix, efficiently dissipating the mechanical energy of the sound waves into heat energy, thus achieving resonant absorption of ultra-low frequency sound waves.

[0055] Second, the multi-mode conversion and dissipation mechanism of acoustic energy. The spiral water column structure can continuously change the propagation direction of sound waves, causing the incident longitudinal waves to be reflected and refracted repeatedly within the spiral path, resulting in efficient mode conversion from longitudinal waves to transverse waves and surface waves. The viscoelastic matrix 14 has a much higher damping and dissipation capacity for transverse waves and surface waves than for longitudinal waves, thus the mode conversion can significantly improve the dissipation efficiency of acoustic energy. At the same time, the multiple reflections of sound waves within the spiral cavity significantly increase the propagation path length of the sound waves, allowing the sound waves to have more contact opportunities with the viscoelastic matrix 14, further enhancing the damping and dissipation effect.

[0056] Third, the broadband sound absorption mechanism of multi-structure synergistic coupling. The micro-slit spiral water column structure is mainly for efficient sound absorption in the ultra-low frequency band of 100Hz~500Hz, the rigid horizontal plate 13-viscoelastic matrix 14 structure is mainly for efficient sound absorption in the mid-high frequency band of 500Hz~10000Hz, and the fully enclosed cavity 15 structure further broadens the low-frequency sound absorption bandwidth. The sound absorption frequency bands of the three sound absorption structures are interconnected and complementary, forming a broadband sound absorption effect across the entire frequency band of 100Hz~10000Hz, avoiding the problem of narrow sound absorption bandwidth of a single structure. At the same time, the design of the micro-slit structure does not affect the entry of mid-high frequency sound waves into the viscoelastic matrix 14, ensuring that the mid-high frequency sound absorption performance of the rigid horizontal plate 13 structure is not affected, thus achieving the design goal of low-frequency enhancement and broadband coverage.

[0057] To clearly illustrate the technical solution and beneficial effects of the present invention, this section provides a complete set of preferred embodiment parameters and verifies its sound absorption performance through finite element simulation. All parameters are illustrative and not intended to limit the scope of protection of the present invention. Those skilled in the art can adjust the parameters according to actual application scenarios, and all such adjustments fall within the scope of protection of the present invention.

[0058] Complete parameters of the preferred embodiment 1. Overall dimensions of the sound-absorbing cell Each sound-absorbing cell has a cuboid structure with a total thickness of 50 mm along the direction of sound wave incidence (Z direction). In the plane perpendicular to the direction of sound wave incidence, the cell has a width of 40 mm in the X direction and a height of 50 mm in the Z direction. Multiple sound-absorbing cells are arranged in a square periodic array in the XY plane, with adjacent cells closely attached.

[0059] 2. Rigid frame parameters (1) Rigid back plate: made of stainless steel, 50mm wide in the X direction, 2mm thick in the Z direction, elastic modulus ,density Poisson's ratio .

[0060] (2) Rigid vertical plate: The same stainless steel material as the rigid back plate is used. There are two plates in total, which are symmetrically welded to the upper surface of the rigid back plate on both sides in the X direction. The height of each rigid vertical plate in the Z direction is 48mm, the thickness in the X direction is 2mm, and the distance between the two vertical plates in the X direction is 46mm.

[0061] (3) Rigid horizontal plates: Made of the same stainless steel as the rigid vertical plates, there are 9 pairs (18 pieces in total), symmetrically welded to the inner walls of two rigid vertical plates, arranged parallel at equal intervals along the Z direction, with a Z-direction spacing of 2mm between adjacent horizontal plates and a Z-direction thickness of 2mm. The width of the horizontal plates decreases linearly along the Z direction, with the first layer of horizontal plates having a width of 9.75mm, and subsequent layers decreasing according to formula l. i =9.75-i×9.75 / 10mm decreasing, where i is the layer number from 1 to 9.

[0062] 3. Viscoelastic matrix parameters Made of butyl rubber, it fills the grid space between two rigid vertical plates, with a width of 46mm in the X direction and a height of 45mm in the Z direction. All rigid horizontal plates are completely embedded inside the substrate. Material performance parameters: elastic modulus ,density Poisson's ratio Loss factor .

[0063] 4. Parameters of a fully enclosed cavity A rectangular parallelepiped structure, 46mm wide in the X direction and 3mm high in the Z direction, completely enclosed, filled with air, with an air density of [missing information]. speed of sound .

[0064] 5. Microslit structure parameters (1) Micro-slit entrance cavity: cuboid structure, 1.6 mm wide in the X direction, 19.6 mm high in the Z direction, with the top opening on the incident surface of the substrate and the bottom communicating with the spiral cavity.

[0065] (2) Micro-slit helical cavity: Archimedean spiral shape, Archimedean spiral formula , where the initial r 0 is 0.5 mm. β =0.5 mm, θ =6π rad. Cross-sectional width 0.5mm, total unfolded length 99mm, filled with water when working underwater, density of water... speed of sound .

[0066] Performance Verification and Comparative Analysis like Figure 4 As shown, the finite element model of the above embodiment was established using COMSOL Multiphysics simulation software, and its underwater sound absorption performance was numerically simulated and calculated. Two control groups were also set up for comparative verification. Control group 1 (configuration I): Only the micro-slit spiral water column structure is retained, all rigid cross plates are removed, and the remaining parameters are consistent with the preferred embodiment; Control group 2 (configuration II): Only the rigid cross plate-viscoelastic matrix structure is retained, and the micro-slit inlet cavity and micro-slit spiral cavity are removed. The remaining parameters are the same as those of the preferred embodiment. Example group (configuration III): The complete cooperative structure of the present invention, namely the above preferred embodiment.

[0067] like Figure 5 As shown, the simulation results indicate that: Control group 2 (rubber-metal plate structure only) has a certain sound absorption effect in the mid-to-high frequency range, but its sound absorption performance drops significantly in the low-frequency range below 500Hz, with the sound absorption coefficient below 0.78 in most frequency ranges, failing to meet the low-frequency sound absorption requirements; Control group 1 (spiral water column structure only) has excellent sound absorption effect in the low-frequency range, but its sound absorption performance fluctuates significantly in the mid-to-high frequency range, with a narrow effective sound absorption bandwidth, failing to cover the high-frequency range of 10000Hz; while the embodiment group of the present invention has a sound absorption coefficient of no less than 0.78 in the entire frequency range from 100Hz to 10000Hz, with the highest sound absorption coefficient reaching above 0.95 in the ultra-low frequency range of 100Hz to 500Hz, and the sound absorption coefficient remaining stable above 0.85 in the mid-to-high frequency range of 500Hz to 10000Hz, achieving efficient sound absorption in the ultra-low frequency and wide frequency range, fully verifying the performance leap brought about by the multi-structure collaborative design.

[0068] In summary, this invention fully combines and amplifies the advantages of the micro-slit spiral water column structure and the rubber rigid plate structure, resulting in excellent low-frequency broadband sound absorption performance.

[0069] The above are merely specific embodiments of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features of the invention herein.

Claims

1. An underwater sound-absorbing covering layer, wherein the underwater sound-absorbing covering layer is composed of a plurality of sound-absorbing cells (1) arranged periodically and continuously, each of the sound-absorbing cells (1) comprising a rigid skeleton and a viscoelastic matrix (14); characterized in that, The rigid frame includes a rigid back plate (11), two rigid vertical plates (12) symmetrically fixed on both sides of the rigid back plate (11), and multiple rigid horizontal plates (13) symmetrically fixed on the inner sidewalls of the two rigid vertical plates (12); the viscoelastic matrix (14) is fixed between the two rigid vertical plates (12), and a fully enclosed cavity (15) is provided between the viscoelastic matrix (14) and the rigid back plate (11); the multiple rigid horizontal plates (13) are embedded inside the viscoelastic matrix (14); the viscoelastic matrix (14) is provided with a micro-slit inlet cavity (16) communicating with the external water environment, and a micro-slit spiral cavity (17) communicating with the micro-slit inlet cavity (16), and the micro-slit spiral cavity (17) is used to fill water in the underwater working state to form a micro-slit spiral water column structure.

2. The underwater sound-absorbing covering layer according to claim 1, characterized in that, Multiple rigid horizontal plates (13) are arranged in parallel at intervals along the height direction of the rigid vertical plate (12). The rigid horizontal plates (13) are provided with a width gradient along the incident direction of the sound wave. The width of the rigid horizontal plates (13) gradually decreases as they approach the rigid back plate (11).

3. The underwater sound-absorbing covering layer according to claim 1, characterized in that, The viscoelastic matrix (14) is made of viscoelastic materials including rubber and polyurethane, or a composite material with viscoelastic material as the matrix.

4. The underwater sound-absorbing covering layer according to claim 1, characterized in that, The rigid back plate (11), rigid vertical plate (12) and rigid horizontal plate (13) are made of rigid materials, including rigid metal materials or carbon fiber composite materials.

5. The underwater sound-absorbing covering layer according to claim 1, characterized in that, The fully enclosed cavity (15) is filled with a gaseous medium; the spiral cavity of the micro-slit spiral water column structure is filled with water when working underwater, forming a micro-slit spiral water column structure that is connected to the external water environment.

6. The underwater sound-absorbing covering layer according to claim 1, characterized in that, The rigid back plate (11), rigid vertical plate (12), rigid horizontal plate (13), viscoelastic matrix (14), and the main structure of the closed cavity are all cuboid structures.

7. The underwater sound-absorbing covering layer according to claim 1, characterized in that, The micro-slit helical cavity (17) has an Archimedean spiral shape, and its cross-sectional width remains constant or varies with gradient along the helical path.

8. The underwater sound-absorbing covering layer according to claim 1, characterized in that, The width of the micro-slit inlet cavity (16) is greater than the width of the micro-slit spiral cavity (17).

9. The underwater sound-absorbing covering layer according to claim 1, characterized in that, The total thickness of the underwater sound-absorbing covering layer along the direction of sound wave incidence does not exceed 50 mm.

10. The underwater sound-absorbing covering layer according to claim 1, characterized in that, The underwater sound-absorbing covering layer has a sound absorption coefficient of not less than 0.78 in the frequency range of 100Hz to 10000Hz.

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