An underwater sound-absorbing metamaterial based on cooperative coupling resonance and its application

Abstract

This invention discloses an underwater sound-absorbing metamaterial based on synergistic coupling resonance and its applications. It comprises M×M subunits arranged periodically along a plane, each subunit consisting of N×N unit cells of uniform geometric dimensions. Each unit cell includes an upper matrix layer, a lower matrix layer, and a coupled resonance intermediate layer embedded between the upper and lower matrix layers. The coupled resonance intermediate layer is symmetrically fastened to the center of an intermediate insert with upper and lower dual harmonic oscillators, respectively, and is embedded between the upper and lower matrix layers. A fluid layer and a backing are sequentially distributed below the lower matrix layer. This underwater sound-absorbing metamaterial can synergistically couple the multi-displacement modes of the intermediate layer, as well as the synergistic coupling resonance excited together with the fluid layer and the backing, thereby forcing the upper and lower matrix layers to dissipate the wave energy in the structure to a great extent using their high loss factors.

Description

Technical Field

[0001] This invention belongs to the field of underwater equipment vibration and noise control technology, specifically an underwater sound-absorbing metamaterial based on cooperative coupling resonance and its application. Background Technology

[0002] Traditional underwater sound-absorbing materials suffer from poor low-frequency sound absorption, necessitating the development of novel low-frequency, broadband underwater sound-absorbing materials or structures. Metamaterials, since their inception, have evolved into a class of artificial composite structures or materials possessing extraordinary physical properties not found in natural media. They represent a breakthrough from traditional materials in terms of "material composition - device assembly - equipment formation - system support," and also a method for achieving superior performance through deep integration of multiple disciplines based on materials or structures. Unlike the background medium of airborne sound, the performance development of underwater acoustic metamaterials integrates underwater acoustics, physics, materials science, mechanics, and engineering. From an application perspective, the design of underwater acoustic metamaterials is a prerequisite for the research, promotion, and deployment of underwater acoustic covering layers. Due to the different underwater acoustic control functions they achieve, numerous types of underwater acoustic metamaterials have emerged in recent years, which can be broadly categorized as: localized resonant, foam metal, gradient exponential, and chiral types.

[0003] Analogous to air-absorbing acoustic metamaterials, locally resonant underwater acoustic metamaterials utilize the low-frequency bandgap generated by the principle of local resonance to achieve low-frequency resonant sound absorption. The absorption bandwidth at the local resonant frequency can be altered by adjusting the different shapes and positions of the local resonant scatterers, potentially achieving high underwater sound absorption performance in the low-frequency band. The matrix material is chosen as a polyurethane polymer elastomer, and through formulation design, it can be flexibly designed for different frequencies and temperatures, thereby maximizing the loss of acoustic energy within the underwater acoustic metamaterial structure.

[0004] Sonar detection is currently the only means of long-range underwater anti-submarine detection. The stealth of underwater equipment is mainly reflected in its acoustic stealth performance in response to underwater sonar detection. The sound absorption mechanism and structural design of underwater sound-absorbing metamaterials can positively support the development of a series of acoustic stealth products for underwater equipment, achieving acoustic stealth in deep-sea operating environments. It can also provide a reference for the development of new sonar transducers, arrays, sonar domes and other underwater acoustic functional devices. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an underwater sound-absorbing metamaterial based on synergistic coupling resonance. By embedding a dual harmonic oscillator structure within a polyurethane polymer elastomer as the matrix material, and by introducing a fluid layer at the bottom of the structure to form a "spring" effect, the matrix material and the backing material are forced to undergo synergistic coupling resonance. This enables the material to achieve high underwater sound absorption performance in the frequency range of 50–5000 Hz, with an average sound absorption coefficient as high as 0.865, and the first sound absorption peak frequency as low as 400 Hz, achieving a subwavelength underwater high sound absorption effect of 1 / 42.135 times.

[0006] The present invention is achieved through the following technical solution.

[0007] This invention provides an underwater sound-absorbing metamaterial based on cooperative coupling resonance, comprising M×M subunits arranged periodically along a plane, each subunit consisting of N×N unit cells with consistent geometric dimensions;

[0008] Each unit cell includes an upper matrix layer, a lower matrix layer, and a coupled resonance intermediate layer embedded between the upper matrix layer and the lower matrix layer. The coupled resonance intermediate layer is symmetrically fastened to the center of the intermediate insert by the upper dual harmonic oscillator and the lower dual harmonic oscillator, respectively, and is embedded between the upper matrix layer and the lower matrix layer. A fluid layer and a backing are distributed sequentially below the lower matrix layer.

[0009] Preferably, the upper and lower dual harmonic oscillators of each unit cell are fixed to the middle insert and rotate sequentially at a 90° angle to each other.

[0010] Preferably, the middle insert is a rectangular plate with an unclosed groove cut out in the center, and the groove is arranged with the middle insert rotated 90° relative to the middle insert.

[0011] Preferably, the center of the groove is a docking platform, and the bottom surfaces of the upper and lower dual resonators are arranged opposite each other on the docking platform in the center of the middle insert; the fixing method is welding, riveting or threaded connection.

[0012] Preferably, the upper-layer dual harmonic oscillator and the lower-layer dual harmonic oscillator are wedge-shaped blocks, with the inclined surfaces of each wedge-shaped block facing each other and the right-angled surface of the wedge-shaped block facing the diagonal of the sub-unit.

[0013] Preferably, the upper and lower substrate layers have the same geometric dimensions, and the thickness of the coupling resonance intermediate layer is less than the thickness of the upper and lower substrate layers.

[0014] Preferably, the fluid layer and the backing have the same geometry.

[0015] Preferably, the upper matrix layer, the lower matrix layer, and the backing are made of polyurethane polymer elastomer.

[0016] Preferably, the material of the coupling resonance intermediate layer is Q235A3 steel; the material of the fluid layer is air or water.

[0017] The underwater sound-absorbing metamaterial based on synergistic coupling resonance of the present invention can be applied in the acoustic concealment of underwater equipment.

[0018] The present invention, by adopting the above technical solution, has the following beneficial effects:

[0019] This invention is based on underwater sound-absorbing metamaterials with synergistic resonance. It utilizes the waveform transformation mechanism and high loss factor characteristics of sound wave transmission within the matrix material to embed a synergistic coupling resonance intermediate layer and a fluid layer, forming a synergistic coupling resonance phenomenon under the action of incident sound waves. This maximizes the excitation of displacement deformation of the matrix material, thereby greatly enhancing the loss of incident sound energy.

[0020] This invention achieves an average sound absorption coefficient of 0.865 within a wide frequency range of 50–5000 Hz, with the first absorption peak occurring as low as 400 Hz, corresponding to a sound absorption coefficient as high as 0.98. This represents a subwavelength underwater high sound absorption performance that is 1 / 42.135 times better. Furthermore, within the frequency range of 307–5000 Hz, the sound absorption coefficient remains above 0.6, with an average echo reduction of 10.31 dB and an average insertion loss of 64.9 dB, demonstrating wideband and highly efficient underwater sound absorption performance. This invention overcomes the key problem of poor low-frequency sound absorption performance in traditional underwater acoustic materials, providing new ideas and guidance for the development of underwater acoustic materials or structures and underwater covering layers. It can also effectively target underwater equipment, enhancing its anti-detection capabilities and acoustic stealth, and has broad application prospects in the development of underwater acoustic covering layers and the silent design of underwater equipment. Attached Figure Description

[0021] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, do not constitute an undue limitation of the invention. In the drawings:

[0022] Figure 1 This is a schematic diagram of a three-dimensional underwater sound-absorbing metamaterial structure based on synergistic coupling resonance according to the present invention;

[0023] Figure 2 This is a schematic diagram of the subunit three-dimensional structure of an underwater sound-absorbing metamaterial based on cooperative coupling resonance according to the present invention;

[0024] Figure 3 This is a schematic diagram of the structure of an underwater sound-absorbing metamaterial based on cooperative coupling resonance according to the present invention;

[0025] Figure 4 This is a schematic diagram of the intermediate layer structure of the scatterer in this invention;

[0026] Figure 5 This is a schematic diagram of the upper and lower dual harmonic oscillators of the scatterer in this invention;

[0027] Figure 6 This is a finite element simulation mesh diagram of an underwater sound-absorbing metamaterial based on synergistic coupling resonance according to the present invention.

[0028] Figure 7 The sound absorption coefficient of an underwater sound-absorbing metamaterial based on synergistic coupling resonance of the present invention is in the frequency range of 50 to 5000 Hz when the fluid layers are air and water respectively.

[0029] Figure 8 The present invention relates to an underwater sound-absorbing metamaterial based on synergistic coupling resonance for reducing echoes when the fluid layers are air and water, with a frequency range of 50 to 5000 Hz.

[0030] Figure 9 The insertion loss of an underwater sound-absorbing metamaterial based on synergistic coupling resonance in the fluid layers is air and water, with a frequency range of 50 to 5000 Hz.

[0031] Figure 10 This is a displacement mode cloud diagram of an underwater sound-absorbing metamaterial based on synergistic coupling resonance at the first sound absorption peak (400Hz) according to the present invention.

[0032] Figure 11 The displacement mode cloud diagram of an underwater sound-absorbing metamaterial based on cooperative coupling resonance according to the present invention is shown at the first sound absorption valley (870Hz).

[0033] Figure 12 The displacement mode cloud diagram of an underwater sound-absorbing metamaterial based on synergistic coupling resonance according to the present invention is shown at the second sound absorption peak (1500Hz).

[0034] Figure 13 This is a sound pressure cloud map at the first sound absorption peak (400Hz) of an underwater sound-absorbing metamaterial based on synergistic coupling resonance according to the present invention.

[0035] Figure 14 This is a sound pressure cloud map at the first sound absorption valley (870Hz) of an underwater sound-absorbing metamaterial based on synergistic coupling resonance according to the present invention.

[0036] Figure 15 This is a sound pressure cloud map at the second sound absorption peak (1500Hz) of an underwater sound-absorbing metamaterial based on synergistic coupling resonance according to the present invention.

[0037] The labels in the attached figures are as follows: 1-upper substrate layer; 2-lower substrate layer; 3-coupled resonance intermediate layer; 3-1-upper dual harmonic oscillator; 3-2-intermediate insert; 3-3-lower dual harmonic oscillator; 4-fluid layer; 5-backing; 6-sound wave incident and reflection domain; 7-sound wave transmission domain. Detailed Implementation

[0038] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The illustrative embodiments and descriptions herein are used to explain the invention but are not intended to limit it. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0039] like Figure 1 As shown, this embodiment of the invention provides an underwater sound-absorbing metamaterial based on cooperative coupling resonance, comprising M×M subunits arranged periodically along a plane, each subunit consisting of N×N unit cells with consistent geometric dimensions; in this embodiment, the subunit of the underwater sound-absorbing metamaterial consists of four underwater sound-absorbing metamaterial unit cells arranged in a 2×2 manner towards the center.

[0040] like Figure 2 As shown, each unit cell includes an upper matrix layer 1, a lower matrix layer 2, a coupled resonance intermediate layer 3, a fluid layer 4, and a backing 5. The coupled resonance intermediate layer 3 is disposed between the upper matrix layer 1 and the lower matrix layer 2. The fluid layer 4 and the backing 5 are sequentially disposed below the lower matrix layer 2. The coupled resonance intermediate layer 3 is completely enclosed within the upper matrix layer 1 and the lower matrix layer 2, and its thickness is less than that of the upper matrix layer 1 and the lower matrix layer 2. A fluid layer 4 and a backing 5 are embedded at the bottom of the lower matrix layer 2, and the thickness of the fluid layer 4 and the backing 5 is less than that of the upper matrix layer 1 and the lower matrix layer 2.

[0041] like Figure 3 , Figure 4 and Figure 5 As shown, the coupled resonance intermediate layer 3 in the unit cell of the underwater sound-absorbing metamaterial includes an upper dual resonator 3-1, an intermediate insert 3-2, and a lower dual resonator 3-3. The upper dual resonator 3-1 and the lower dual resonator 3-3 are distributed in a fastened manner at the center of the intermediate insert 3-2. The upper dual resonator 3-1 and the lower dual resonator 3-3 are wedge-shaped block structures. The intermediate insert 3-2 is a rectangular plate with an unclosed groove cut out in the center. The groove is arranged with a 90° rotation relative to the intermediate insert 3-2. The middle part of the groove is a docking platform. The bottom surfaces of the wedge-shaped blocks of the upper dual resonator 3-1 and the lower dual resonator 3-3 are arranged opposite each other on the docking platform in the middle of the intermediate insert 3-2.

[0042] like Figure 1As shown, the inclined surfaces of the wedge blocks of the dual harmonic oscillator 3-1 and the lower dual harmonic oscillator 3-3 in each unit cell are arranged opposite each other, and the right angle surface of the wedge block faces the diagonal of the 2×2 sub-units.

[0043] Each unit cell has the same geometric dimensions, and wedge blocks are arranged in a 90° rotational arrangement in the direction of each unit cell to form a sub-unit.

[0044] The multimodal nature of the coupled resonant intermediate layer over a wide frequency range can excite different displacements and deformations in the upper and lower substrate layers. The introduction of the fluid layer breaks the displacement continuity in the upper, lower, and backing layers, exhibiting a "spring" effect without damping. The weak connection, similar to the "spring" effect, can excite a synergistic coupled resonance effect at a specific, designable frequency, thereby increasing the loss of acoustic energy.

[0045] The design aims to increase the resonant displacement of the dual harmonic oscillator, thereby maximizing the dissipation of ground acoustic energy immersed in the underwater sound-absorbing metamaterial.

[0046] When the incident sound wave is located at the top of the underwater sound-absorbing metamaterial, a reflected sound wave will be generated on the surface of the underwater sound-absorbing metamaterial in the opposite direction to the incident sound wave, and a transmitted sound wave will be generated at the bottom of the underwater sound-absorbing metamaterial in the opposite direction to the incident sound wave.

[0047] In this embodiment, the upper and lower substrate layers are spatial geometric bodies formed by stretching a square in the XY plane in the Z direction, with a side length r = 60 mm and a stretching thickness w = 30 mm. The fluid layer and backing have the same dimensions as the upper and lower substrate layers in the XY plane, with stretching thicknesses z = 12 mm and q = 12 mm in the Z direction, respectively. The intermediate insert 3-2 is formed by cutting an unclosed groove in the middle of a spatial geometric body with a side length a = 60 mm and a thickness t = 5 mm in the XY plane. The geometric dimensions of the groove include: outer frame width b = 30 mm, inner platform width c = 26 mm, groove width d = 2 mm; length from outer frame to inner platform rib m = 12 mm and length from outer frame to inner platform rib n = 10 mm. The upper and lower dual harmonic oscillators are geometrically wedge-shaped blocks, formed by stretching right triangles with legs k = 15 mm and e = 26 mm by a distance v = 26 mm. The upper dual harmonic oscillator 3-1 and the lower dual harmonic oscillator 3-3 are separated by a distance s = 5 mm.

[0048] The upper substrate layer 1, the lower substrate layer 2, and the backing 5 are all made of polyurethane polymer elastomer, with the following material properties: density of 4500 kg / m³. 3 Young's modulus is 5×10 7 Pa, Poisson's ratio is 0.46, and loss factor is 0.46.

[0049] The polyurethane polymer elastomer in this invention, as a type of viscoelastic damping material, possesses a very high loss factor and its characteristic impedance is close to that of water. The selection of the polyurethane polymer elastomer is based on the fact that the characteristic impedance of polyurethane polymer materials is similar to that of water, thus allowing as many sound waves in water as possible to enter the underwater sound-absorbing metamaterial. Many material properties and physical and mechanical performance indicators, such as hardness and strength, can be adjusted within a certain range by selecting raw materials and formulating the material. Under working conditions in an aquatic environment, the wear resistance of the polyurethane polymer elastomer is often several to tens of times that of ordinary rubber materials. The loss factor of polyurethane polymer materials can be improved by adjusting the formula, resulting in excellent vibration reduction effects. The processing and molding of polyurethane polymer elastomers are flexible and reliable, and they can be molded using plasticizing, mixing, vulcanization processes, casting, compression molding, spraying, potting, centrifugal molding, injection molding, extrusion, calendering, blow molding, and other processes. Therefore, the selection of polyurethane polymer elastomer materials combines impedance matching, adjustable formula and performance, unique characteristics, wear resistance, vibration reduction, and flexible processing, while also possessing a large loss factor capable of dissipating incident sound wave energy; therefore, this material is used.

[0050] In this embodiment, the material of the coupled resonance intermediate layer 3 is Q235A3 steel, and the density of Q235A3 steel is 7850 kg / m³. 3 The Young's modulus is 210 GPa and the Poisson's ratio is 0.29.

[0051] In this embodiment, the fluid layer 4 is made of a non-solid medium such as air, with a density of 1.29 kg / m³. 3 The speed of sound is 343 m / s.

[0052] In this embodiment, the underwater sound-absorbing metamaterial is used in an environment where the material has a density of 998 kg / m³. 3 The speed of sound is 1500 m / s.

[0053] In this embodiment, the underwater sound-absorbing metamaterial subunits can be combined in an n×n (n≧2) arrangement on the XY plane, where the value of n is determined according to the actual surface area of ​​the application.

[0054] In this embodiment, the upper dual resonator 3-1, the middle insert 3-2, and the lower dual resonator 3-3 are fastened by welding.

[0055] The geometric design and combination of the dual harmonic oscillator and intermediate insert can excite the polyurethane polymer elastomer, which serves as the matrix material, to undergo greater displacement and deformation, thereby maximizing the dissipation of acoustic energy entering the structure by utilizing its high loss factor. The backing material, also a polyurethane polymer elastomer, is consistent with the matrix material. The introduction of the fluid layer enables a "spring-like" physical connection, forcing the matrix material and backing material to more easily achieve synergistic coupling resonance, thus further maximizing the dissipation of acoustic energy.

[0056] The working principle of this invention is as follows: When incident sound waves in the water medium enter the surface of the underwater sound-absorbing metamaterial, because the surface impedance of the polyurethane polymer elastomer is very close to that of water, most of the sound waves will carry wave energy into the underwater sound-absorbing metamaterial structure, and no obvious reflection phenomenon will occur at the interface in contact with water. The sound waves entering the underwater sound-absorbing metamaterial structure initially propagate in the form of longitudinal waves. Due to the resonance effect of the co-coupled resonance intermediate layer 3, the polyurethane polymer elastomer, which is the matrix material, is forced to undergo displacement deformation, thereby causing the wave energy propagating in the longitudinal wave to be converted into shear wave propagation. The high loss factor of the polyurethane polymer elastomer is equivalent to high shear loss, thus enabling the sound energy inside the structure to be dissipated. Since only air exists in the fluid layer 4, and the air medium can only allow longitudinal waves to propagate in it, and due to the characteristic impedance mismatch between the matrix material and air, all the shear waves and part of the longitudinal waves in the wave energy passing through the lower matrix layer will be reflected back into the matrix material for secondary loss, while the remaining longitudinal waves can enter the backing 5 through the fluid layer 4. Since the material of the backing 5 is also polyurethane polymer elastomer, and the fluid layer plays the role of a "spring" without damping effect in the overall structure of the underwater sound-absorbing metamaterial, the vibration mode of the backing as a thin plate will have a synergistic coupling resonance with the upper matrix layer 1, the lower matrix layer 2 and the synergistic coupling resonance intermediate layer 3 at certain specific frequencies, which can further increase the displacement deformation in the matrix material and further consume the wave energy in the underwater sound-absorbing metamaterial.

[0057] The following simulation model is established using the acoustic-structure interaction module in Comsol Mutiphysics 6.0 finite element simulation software to calculate the sound absorption coefficient, echo reduction, insertion loss, displacement mode contour map, and sound pressure distribution in the fluid domain of the underwater sound-absorbing metamaterial based on synergistic coupling resonance.

[0058] like Figure 6 As shown, in the finite element simulation mesh model of the underwater sound-absorbing metamaterial, an incident sound domain 6 and a transmission sound domain 7 were added to calculate the sound absorption coefficient, echo reduction, and insertion loss. In the finite element simulation settings, the incident sound pressure amplitude is 1 Pa. The top surface of the incident sound domain 6 is selected as the incident surface, and the bottom surface of the transmission sound domain 7 is selected as the transmission surface. Here, the incident sound wave is set to p.i The reflected sound wave is p r The transmitted sound wave is p t Then the sound pressure reflection coefficient R p and sound pressure transmission coefficient T p for

[0059]

[0060] When the incident sound wave is a plane wave, the absorption coefficient α, echo reduction ER, and insertion loss IL are:

[0061]

[0062]

[0063] like Figure 7 As shown, the solid line represents the sound absorption coefficient curve of the underwater sound-absorbing metamaterial in this embodiment within the frequency range of 50–5000 Hz, and the dashed line represents the corresponding sound absorption coefficient curve when the material of fluid layer 4 in this embodiment becomes water. It can be clearly seen that in this embodiment, the average sound absorption coefficient in the frequency range of 50–5000 Hz is as high as 0.865. Here, a sound absorption coefficient of 0.6 is set as an indicator for evaluating the high and low sound absorption performance of the underwater material. It can be found that in this embodiment, the underwater sound-absorbing metamaterial can enter the high sound absorption region at a frequency of 308 Hz. The underwater sound-absorbing metamaterial in this embodiment has a distinct first sound absorption peak at a frequency of 400 Hz, corresponding to a sound absorption coefficient as high as 0.98; a first sound absorption valley at a frequency of 870 Hz, corresponding to a sound absorption coefficient of 0.63; and a second sound absorption peak at a frequency of 1500 Hz, corresponding to a sound absorption coefficient as high as 0.97. There is a large bandwidth between the sound absorption peaks and valleys, which can form a broadband sound absorption effect. When the material of fluid layer 4 is changed to water, the overall sound absorption coefficient curve in the frequency range of 50 to 5000 Hz decreases. The main reason is that the characteristic impedance of water is very close to that of the lower substrate layer 2, which allows the wave energy propagating in the substrate material to continue to propagate forward and reach the backing 5 through fluid layer 4. Since the material of backing 5 cannot form an effective reflection condition for the forward-propagating wave energy, some sound energy is transmitted out of backing 5, resulting in energy leakage. Therefore, from the perspective of sound absorption performance, air is the preferred material for fluid layer.

[0064] like Figure 8 As shown, the solid and dashed lines represent the echo reduction curves when the fluid layers are air and water, respectively, with a frequency range of 50–5000 Hz. Assuming the underwater equipment in the water environment is a passive target, echo detection is currently the only effective method. When the frequency is below 500 Hz,

[0065] When the fluid layer 4 is made of water and air, the peak values ​​of the first echo reduction peak differ by nearly 10 dB. The echo reduction of the underwater sound-absorbing metamaterial with fluid layer 4 being water is much higher than that in this embodiment. This is mainly because the low-frequency wavelength of sound waves in water is much larger than the overall thickness of the underwater sound-absorbing metamaterial. When low-frequency sound waves pass through the matrix material and encounter the water-based fluid layer 4, due to characteristic impedance matching, a large portion of the wave energy in the structure will propagate forward, while very little of the reflected echo will pass through the surface of the underwater sound-absorbing metamaterial and enter the incident water area. When the fluid layer 4 is made of air, the reflected echo in the low-frequency range will increase. Therefore, the echo reduction in this embodiment is lower than when the fluid layer 4 is made of water. When the frequency range is in the mid-to-high frequency range, due to the relatively shortened wavelength in the water medium and the displacement deformation of the co-coupled resonance intermediate layer 3 exciting more modes in the matrix material, the wave energy entering the matrix material is greatly dissipated. Because the fluid layer 4 acts as a "spring" for weak connections, when the material of the fluid layer 4 is air, the weak connection effect is continuously strengthened, and the synergistic coupling effect between the upper substrate layer 1, the lower substrate layer 2, and the backing 5 is further enhanced. Therefore, the echo reduction of the underwater sound-absorbing metamaterial in this embodiment is improved in the mid-to-high frequency range. The average echo reduction in the frequency range of 50 to 5000 Hz is 10.31 dB, and when the fluid layer material is water, the average echo reduction in the frequency range of 50 to 5000 Hz is 10.56 dB.

[0066] like Figure 9 As shown, the underwater sound-absorbing metamaterial in this embodiment exhibits a high insertion loss in the 50–5000 Hz frequency range, with an average insertion loss as high as 64.9 dB. When the fluid layer 4 is made of water, the average insertion loss in the 50–5000 Hz frequency range is only 13.25 dB. When the fluid layer 4 is made of water, the wave energy in the underwater sound-absorbing metamaterial structure can propagate further forward because the characteristic impedances of the upper substrate layer 1, lower substrate layer 2, fluid layer 4, and backing 5 are close, failing to meet the mismatch condition. Therefore, more sound energy is transmitted through the backing, resulting in a lower insertion loss. However, in this embodiment, due to impedance mismatch at the interface, the sound energy transmitted through the backing of the fluid layer 4 is greatly reduced, resulting in a higher insertion loss.

[0067] like Figure 10-12As shown, the post-processing function of the finite element simulation software provides displacement mode cloud diagrams at the corresponding frequencies of the first absorption peak, the first absorption valley, and the second absorption peak. The arrows indicate the magnitude and direction of the displacement deformation. Through the XYZ view space, the XY plane, and the XZ space, it can be seen that at the first absorption peak, the locations with larger displacement deformations are mainly concentrated around the perimeter and center of the underwater sound-absorbing metamaterial, and are located on the surface of the upper substrate layer 1. From the arrows distributed on the surface of the co-coupled resonance intermediate layer 3, it can be seen that the upper dual harmonic oscillator 3-1 and the lower dual harmonic oscillator 3-3 drive the intermediate insert 3-2 to produce large displacement deformations. At the first absorption valley, the larger displacement deformations are mainly distributed at the corners of the underwater sound-absorbing metamaterial structure, while there is no obvious displacement deformation at the center. At the second absorption peak, the distribution of larger displacement deformations is similar to that at the first absorption peak. Therefore, the strength of the sound absorption performance is strongly correlated with the displacement deformation modes of the co-coupled resonance intermediate layer 3.

[0068] like Figure 13-15 As shown, the post-processing function of the finite element simulation software provides sound pressure cloud maps at the frequencies corresponding to the first absorption peak, the first absorption valley, and the second absorption peak. The arrows indicate the magnitude and direction of the sound intensity. The sound pressure is stronger in the sound wave incident domain 6 and weaker in the sound wave transmission domain 7 and the fluid layer 4. This is mainly because the matrix material has consumed most of the acoustic energy in the underwater sound-absorbing metamaterial. The magnitude and direction of the sound intensity correspond to the magnitude and direction of sound energy propagation, reflecting the average sound power per unit mass point and also showing the influence of the displacement deformation of the cooperative coupling resonance intermediate layer 3 on the propagation of sound energy. Figure 13-15 In the sound wave incident domain 6, the arrow directions are relatively consistent and are consistent with the direction of the incident sound wave, indicating that the characteristic impedance of the upper substrate layer 1 and the water medium is approximately consistent; the arrow directions in the fluid layer 4 are significantly different from the direction of the incident sound wave, mainly because the material of the fluid layer 4 in this embodiment is air, and the directionality of the sound intensity reflects that the characteristic impedance at the interface between the fluid layer 4 and the lower substrate layer 2 is mismatched.

[0069] This invention provides an underwater sound-absorbing metamaterial based on synergistic coupling resonance, which effectively solves the problem of broadband and efficient underwater sound absorption in the frequency range of 50-5000Hz. The structure of this invention has a thickness of 89mm. Relative to the wavelength of underwater sound waves at the first sound absorption peak frequency, the underwater sound-absorbing metamaterial can achieve efficient subwavelength sound absorption performance. It also has the technical advantages of simple geometric structure, adjustable material formula and excellent underwater sound absorption effect. It has broad application prospects in the development and research of underwater acoustic covering products and in realizing the acoustic concealment of underwater equipment.

[0070] This invention is not limited to the above embodiments. Based on the technical solutions disclosed in this invention, those skilled in the art can make some substitutions and modifications to some of the technical features without creative effort, and all such substitutions and modifications are within the protection scope of this invention.

Claims

1. An underwater sound-absorbing metamaterial based on cooperative coupling resonance, characterized in that, It includes M×M sub-units arranged periodically along the plane, and each sub-unit consists of N×N unit cells with the same geometric dimensions; Each unit cell includes an upper matrix layer, a lower matrix layer, and a coupled resonance intermediate layer embedded between the upper and lower matrix layers. The coupled resonance intermediate layer is symmetrically fastened to the center of the intermediate insert by the upper dual harmonic oscillator and the lower dual harmonic oscillator, respectively, and is embedded between the upper and lower matrix layers. A fluid layer and a backing are distributed sequentially below the lower matrix layer. Each unit cell has its upper and lower dual harmonic oscillators fastened to the intermediate insert in a direction that is mutually oriented. The angles rotate sequentially; The upper-layer dual harmonic oscillator and the lower-layer dual harmonic oscillator are wedge-shaped blocks, with the inclined surfaces of each wedge-shaped block facing each other, and the right-angled surfaces of the wedge-shaped blocks facing the diagonal of the sub-unit.

2. The underwater sound-absorbing metamaterial based on cooperative coupling resonance according to claim 1, characterized in that, A rectangular plate with an unclosed groove cut out from the center of the middle insert, the groove being arranged with the center insert rotated 90° relative to the middle insert.

3. The underwater sound-absorbing metamaterial based on synergistic coupling resonance according to claim 2, characterized in that, The center of the groove is a docking platform, and the bottom surfaces of the upper and lower dual resonators are fixed relative to each other on the docking platform in the center of the middle insert; the fixing method is welding, riveting or threaded connection.

4. The underwater sound-absorbing metamaterial based on cooperative coupling resonance according to claim 1, characterized in that, The upper and lower matrix layers have the same geometric dimensions, and the thickness of the coupled resonance intermediate layer is less than the thickness of the upper and lower matrix layers.

5. The underwater sound-absorbing metamaterial based on cooperative coupling resonance according to claim 1, characterized in that, The fluid layer and the backing have the same geometry.

6. The underwater sound-absorbing metamaterial based on cooperative coupling resonance according to claim 1, characterized in that, The upper substrate layer, lower substrate layer and backing are made of polyurethane polymer elastomer.

7. The underwater sound-absorbing metamaterial based on cooperative coupling resonance according to claim 1, characterized in that, The material of the coupling resonance intermediate layer is Q235A3 steel; the material of the fluid layer is air or water.

8. The application of an underwater sound-absorbing metamaterial based on synergistic coupling resonance as described in any one of claims 1-7 in the acoustic concealment of underwater equipment.

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