Electromagnetic and underwater acoustic wave compatible absorbing material panel

Abstract

The application relates to the field of layered composite materials, and particularly discloses a material plate compatible with electromagnetic waves and underwater acoustic waves, which comprises a composite absorption layer and an underwater acoustic absorption layer; wherein the composite absorption layer comprises an electrically conductive substrate and a plurality of layers of alternately stacked sound absorption material plates and wave absorption functional plates, the wave absorption functional plate is composed of a dielectric substrate and a patterned resistive film; and the underwater acoustic absorption layer is a viscoelastic material matrix embedded with a cavity structure. Wideband resonant absorption and impedance matching of electromagnetic waves are realized through multi-size resistive film patterns, and the sound absorption material plates and the cavity-matrix in the underwater acoustic absorption layer are used in cooperation to preliminarily consume and deeply dissipate underwater acoustic waves. The application improves the impedance mismatching problem of underwater acoustic absorption and electromagnetic absorption, has the advantages of wideband, high efficiency and compact structure, and is suitable for radar and sonar compatible stealth skins of equipment such as ships and cross-medium vehicles.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of layered composite materials, in particular to a material plate capable of absorbing electromagnetic waves and underwater acoustic waves. BACKGROUND

[0002] With the development of modern detection technology, water surface ships, trans-medium vehicles and other equipment are simultaneously threatened by radar and sonar. Electromagnetic waves emitted by radar and underwater acoustic waves emitted by sonar belong to completely different physical fields, and their detection mechanisms and countermeasure technologies have been independent of each other for a long time. In order to improve the stealth capability of equipment, new material structures capable of simultaneously absorbing electromagnetic waves and underwater acoustic waves are needed to be developed.

[0003] In the field of single physical field absorption technology, research has been relatively in-depth. Electromagnetic wave absorbing materials usually adopt impedance gradient structure, magnetic loss material or periodic resonant structure (such as frequency selective surface), and realize energy conversion by introducing dielectric loss or magnetic loss in the microwave frequency band (such as 2-18 GHz). The core of the design is to realize the impedance matching with the free space, and usually requires a small dielectric constant of the electromagnetic wave absorbing material. On the other hand, underwater acoustic absorbing materials mainly rely on viscoelastic polymer materials (such as rubber, polyurethane), which convert the mechanical energy of the acoustic wave into heat energy by using the internal friction mechanism, and the efficiency depends on the matching degree of the material characteristic acoustic impedance and water. However, these two mature technology routes conflict in physical mechanism and material requirements: excellent underwater acoustic absorbing materials require high density and high sound speed to match the extremely high characteristic acoustic impedance of water, which inevitably leads to high dielectric constant of the material, thus deviating from the low dielectric constant characteristics expected by high-efficiency electromagnetic absorbers.

[0004] In recent years, although a few studies have attempted to achieve physical field compatible absorption, most of the work has focused on the joint regulation of electromagnetic waves and air acoustic waves. For example, by combining Helmholtz resonators with metal resonant units, dual absorption of acoustic waves and electromagnetic waves in air can be achieved. However, due to the huge difference in physical properties between air and water (the density of water is more than 800 times that of air, the viscosity coefficient is 59 times that of air, and the characteristic acoustic impedance of water is about 3500 times that of air), these differences make the low-density, low-dielectric-constant porous or resonant structures designed to match air sound completely ineffective underwater, that is, the solutions suitable for air acoustic wave absorption cannot be directly transplanted to the underwater acoustic environment.

[0005] Currently, the compatible absorption of electromagnetic wave and underwater acoustic wave is still in the initial exploration stage, and the main technical contradiction faced is that: in order to realize the broadband absorption of underwater acoustic wave, the high-density and high-dielectric-constant viscoelastic material must be used, which will cause a serious electromagnetic impedance mismatch with the transmission medium (water or air), resulting in strong reflection of electromagnetic wave at the material interface and unable to enter the material interior to be effectively absorbed. The existing technology lacks effective configuration and design method to coordinate this contradiction, resulting in that most of the compatible design schemes can only work in a single physical field, or although compatible, the performance is low and the bandwidth is narrow, which is difficult to meet the engineering requirements of modern equipment for broadband, high-efficiency and integrated stealth skin. SUMMARY

[0006] In order to solve the problem that the prior art is difficult to realize the broadband compatible absorption of electromagnetic wave and underwater acoustic wave, the application provides an electromagnetic wave and underwater acoustic wave compatible absorption material plate.

[0007] The electromagnetic wave and underwater acoustic wave compatible absorption material plate provided by the application adopts the following technical scheme:

[0008] An electromagnetic wave and underwater acoustic wave compatible absorption material plate comprises:

[0009] An underwater acoustic absorption layer comprising a viscoelastic material base and a cavity structure embedded therein; and

[0010] A composite absorption layer comprising a conductive substrate connected to the viscoelastic material base and an acoustic absorption material plate and a wave-absorbing functional plate alternately arranged on the conductive substrate;

[0011] The top layer of the composite absorption layer is the wave-absorbing functional plate; the wave-absorbing functional plate comprises a dielectric substrate and a patterned resistive film arranged on the dielectric substrate.

[0012] The application can realize the broadband compatible absorption of electromagnetic wave and underwater acoustic wave, specifically:

[0013] In terms of electromagnetic wave absorption, electromagnetic wave first reaches the outermost wave-absorbing functional plate, the equivalent impedance of the patterned resistive film on the wave-absorbing functional plate is designed to match the external medium (such as water), which maximizes the reduction of initial reflection and guides the electromagnetic wave into the interior of the material plate structure; at the same time, the patterned resistive film of this layer will resonate with the electromagnetic wave of a specific frequency band and perform the first round of energy absorption.

[0014] The electromagnetic wave continues to propagate downward and sequentially passes through the multiple layers of the wave-absorbing functional plates and the sound-absorbing material plates alternately stacked, the patterned resistive film on the wave-absorbing functional plates of different layers has different resistances, and can resonantly absorb electromagnetic waves of different frequency bands, and the multiple wave-absorbing functional plates can realize wideband absorption of electromagnetic waves; meanwhile, the equivalent permittivity and equivalent impedance of the multiple wave-absorbing functional plates change layer by layer along the thickness direction, realizing smooth and stepped impedance transition between the external medium and the bottom high-permittivity underwater sound absorption layer, thereby improving the impedance mismatch problem in the prior art.

[0015] The electromagnetic wave that is not completely absorbed finally reaches the conductive substrate at the bottom, the conductive substrate reflects the remaining electromagnetic wave, and the reflected wave passes through the wave-absorbing functional plates again during reverse propagation, and the electromagnetic wave energy is consumed again, thereby improving the overall electromagnetic wave absorption efficiency.

[0016] The alternating stacking structure of the composite absorption layer in the present application forms a three-dimensional impedance gradient network and a distributed energy dissipation network, and the electromagnetic wave energy is not blocked at a single interface, but is consumed layer by layer and dispersed in the depth direction, which effectively widens the absorption bandwidth and improves the absorption efficiency.

[0017] In terms of underwater sound wave absorption, the underwater sound wave enters from the outermost wave-absorbing functional plate, and sequentially passes through the multiple layers of the wave-absorbing functional plates and the sound-absorbing material plates alternately stacked, and since the wave-absorbing functional plates (including the dielectric substrate and the patterned resistive film) and the conductive substrate are acoustically transparent or quasi-transparent to the underwater sound wave, the underwater sound wave passes through the multiple wave-absorbing functional plates and is dissipated in the multiple sound-absorbing material plates to reach the underwater sound absorption layer.

[0018] The viscoelastic material matrix of the sound-absorbing material plate and the underwater sound absorption layer converts the mechanical energy of the sound wave into heat energy through a friction mechanism, and this mechanism is particularly effective for medium and high frequency sound waves. The cavity structure embedded in the underwater sound absorption layer resonates at a specific low frequency, and the air vibrates at high speed at the neck of the cavity, rubs against the cavity wall and generates strong viscous loss, thereby efficiently consuming low-frequency sound energy. The above two sound wave dissipation mechanisms cooperate to achieve wideband absorption of underwater sound waves.

[0019] The present application adopts a decoupling design, the sound-absorbing material plate has electromagnetic transparency, and the wave-absorbing functional plate has sound wave transparency. Through the layered structure, the electromagnetic absorption function and the underwater sound absorption function are physically decoupled, and the designer can relatively independently optimize the electromagnetic wave absorption performance or the underwater sound wave absorption performance of each layer, and then perform collaborative fine-tuning.

[0020] Further, the patterned resistive film adopts a pattern composed of multiple different shapes.

[0021] Further, the patterned resistive film includes a rectangular pattern and a circular or elliptical pattern arranged at four corners of the rectangular pattern.

[0022] The patterned resistive film of various shapes can excite diversified electromagnetic resonance modes, thereby effectively widening the electromagnetic wave absorption bandwidth. Compared with a simple geometric pattern such as a square ring, a special pattern composed of a rectangle and a circle has a greater perimeter, thereby enabling absorption of lower frequency electromagnetic waves and helping to expand the working frequency band of the wave absorption structure in the low frequency range.

[0023] Further, the patterned resistive films on the wave absorption functional boards of different layers have different sizes.

[0024] Each layer of the wave absorption functional board can absorb electromagnetic energy of a specific sub-band, and through multi-layer design, each sub-band is continuously covered in the frequency spectrum, thereby expanding the working frequency band to the entire target wide frequency band.

[0025] Further, the patterned resistive films on the wave absorption functional boards of different layers have the same or different shapes.

[0026] The designer can freely combine patterns of different shapes and sizes as needed to accurately regulate the resonance characteristics of each layer, achieve optimal distributed dissipation of electromagnetic waves in the depth direction, and achieve synergistic effects.

[0027] Further, the cavity structure is a cylinder, a cuboid or a cone.

[0028] The cavity structure of regular geometric shapes such as a cylinder, a cuboid or a cone is easy to precisely process and prepare, ensuring the consistency and reliability of product performance. At the same time, the resonance frequency of these shapes is easy to calculate and design through a theoretical model, facilitating accurate regulation of the resonance frequency of the cavity, thereby achieving targeted reinforcement absorption of specific underwater acoustic frequency bands.

[0029] Further, the patterned resistive film includes one or more of a carbon-based conductive ink film, an ITO conductive film and a graphene conductive film.

[0030] Preferably, the surface resistance value of the patterned resistive film is 5-500 Ω / m 2 .

[0031] The above various resistive film materials have suitable resistance, good adhesion and environmental durability. These materials can dissipate electromagnetic energy through Joule heat, and their thin film form is nearly transparent to underwater acoustic waves, meeting the requirement of underwater acoustic wave penetration.

[0032] Further, the viscoelastic material matrix includes one or more of rubber, polyurethane and polydimethylsiloxane.

[0033] Further, the sound absorption material board includes one or more of rubber, polyurethane and polydimethylsiloxane.

[0034] Preferably, the thickness of the sound-absorbing material plate is 0.5-200 mm, the relative dielectric constant is 1.5-20, and the density is 500-2000 kg / m 3 , and the Young's modulus is 5-500 MPa.

[0035] The above various viscoelastic materials have the characteristics of high density and high acoustic loss factor, and the characteristic acoustic impedance can be well matched with water, and the water acoustic wave energy that penetrates can be efficiently converted into heat energy by the significant internal friction effect.

[0036] The sound-absorbing material plate and the viscoelastic material base can be made of the same material, thereby ensuring the uniformity and consistency of the composite absorption layer and the water acoustic absorption layer in acoustic performance, so that the water acoustic wave will not be unnecessarily reflected and scattered due to material discontinuity during penetration through the entire composite absorption layer, and smooth transition of the water acoustic wave from the multiple composite absorption layers to the water acoustic absorption layer is achieved.

[0037] Preferably, the thickness of the viscoelastic material base is 1-500 mm, the thickness of the conductive substrate is 0.5-200 mm, the thickness of the sound-absorbing material plate is 0.5-200 mm, and the thickness of the wave-absorbing functional plate is 0.5-200 mm.

[0038] Preferably, the thickness of the viscoelastic material base is 10-200 mm, the thickness of the conductive substrate is 1-50 mm, the thickness of the sound-absorbing material plate is 1-50 mm, and the thickness of the wave-absorbing functional plate is 1-50 mm.

[0039] The application also provides an equipment skin prepared from the above electromagnetic wave and water acoustic wave compatible absorption material plate, which is used for surface ships or trans-medium vehicles.

[0040] In summary, the application has the following beneficial technical effects:

[0041] The application realizes wide-frequency compatible absorption of electromagnetic waves and water acoustic waves through the up-down integrated design of the composite absorption layer and the water acoustic absorption layer: the upper composite absorption layer not only realizes wide-frequency absorption of electromagnetic waves (2-18 GHz) by using the patterned resistive film stacked alternately in multiple layers, but also preliminarily consumes water acoustic waves, especially medium-high frequency water acoustic waves, through the viscoelastic internal friction of the sound-absorbing material plate between the layers; and the lower water acoustic absorption layer strengthens the absorption of medium-low frequency water acoustic waves through the resonance of the viscoelastic material base and the multiple-size cavities.

[0042] The application can improve the cross-medium impedance mismatch problem in the compatible absorption of electromagnetic waves and underwater acoustic waves: the wave-absorbing functional plate of the outermost layer of the composite absorption layer guides electromagnetic waves into the structure, and through multi-size resonance and impedance gradient design, bridges the impedance gap between the external medium (such as water) and the internal high dielectric constant material, ensuring efficient incidence of electromagnetic waves. At the same time, the sound-absorbing material plate has electromagnetic transparency, and the wave-absorbing functional plate has acoustic transparency, and through the layered structure, the physical field is decoupled in space and the functions are coordinated. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 is a perspective view of an electromagnetic wave and underwater acoustic wave compatible absorption material plate according to an embodiment of the application;

[0044] Figure 2 is a cross-sectional view of an electromagnetic wave and underwater acoustic wave compatible absorption material plate according to an embodiment of the application;

[0045] Figure 3 is a structural schematic diagram of a wave-absorbing functional plate according to an embodiment of the application;

[0046] Figure 4 is an electromagnetic wave absorption characteristic diagram of an electromagnetic wave and underwater acoustic wave compatible absorption material plate according to an embodiment of the application;

[0047] Figure 5 is an underwater acoustic wave absorption characteristic diagram of an electromagnetic wave and underwater acoustic wave compatible absorption material plate according to an embodiment of the application.

[0048] Reference signs: 1, composite absorption layer; 2, underwater acoustic absorption layer; 3, cavity structure; 4, viscoelastic material matrix; 5, wave-absorbing functional plate; 6, sound-absorbing material plate; 7, conductive substrate; 8, dielectric substrate; 9, patterned resistive film. DETAILED DESCRIPTION

[0049] The following will be described in detail below Figures 1-5 The application will be further described in detail.

[0050] An electromagnetic wave and underwater acoustic wave compatible absorption material plate is disclosed according to an embodiment of the application. Referring to Figure 1 , the electromagnetic wave and underwater acoustic wave compatible absorption material plate comprises a composite absorption layer 1 and an underwater acoustic absorption layer 2, the underwater acoustic absorption layer 2 is located below the composite absorption layer 1, and the two can be bonded by glue or connected by screws. In this embodiment, the cross sections of the composite absorption layer 1 and the underwater acoustic absorption layer 2 are both square, so as to facilitate the array arrangement and splicing of multiple material plates in the plane, and the size of the square is not limited and can be adjusted according to actual needs. In other feasible embodiments, the cross sections of the composite absorption layer 1 and the underwater acoustic absorption layer 2 can also adopt other shapes such as regular hexagons.

[0051] Referring to Figure 1 andFigure 2 The underwater acoustic absorption layer 2 includes a viscoelastic material matrix 4 and a cavity structure 3 embedded therein; wherein, the viscoelastic material matrix 4 is made of rubber, polyurethane or polydimethylsiloxane, and the cavity structure 3 is a cylinder, cuboid or cone, and is located at the center of the viscoelastic material matrix 4.

[0052] Reference Figure 2 The composite absorption layer 1 includes a conductive substrate 7 connected to the upper surface of a viscoelastic material matrix 4. The conductive substrate 7 is made of a metal plate such as an aluminum plate. Multiple layers of sound-absorbing material plates 6 and wave-absorbing functional plates 5 are alternately stacked on the upper surface of the conductive substrate 7, with the outermost layer of the composite absorption layer 1 being the wave-absorbing functional plate 5. The sound-absorbing material plates 6 are made of viscoelastic materials such as rubber, polyurethane, or polydimethylsiloxane. The conductive substrate 7 and the sound-absorbing material plates 6, as well as the sound-absorbing material plates 6 and the wave-absorbing functional plates 5, can be connected by adhesive or screws.

[0053] Reference Figure 2 and Figure 3 The microwave absorbing functional board 5 includes a dielectric substrate 8 and a patterned resistive film 9 disposed on the dielectric substrate 8. The dielectric substrate 8 is an organic polymer material board such as an epoxy resin board or a polyimide board. The patterned resistive film 9 is a carbon-based conductive ink film, an ITO (Indium Tin Oxide) conductive film, or a graphene conductive film printed on the dielectric substrate 8.

[0054] Multiple electromagnetic wave and underwater acoustic wave compatible absorbing material plates are arrayed on the surface of the equipment and can be used as the equipment skin of surface ships or cross-medium vehicles.

[0055] In this embodiment, the preparation steps of an electromagnetic wave and underwater acoustic wave compatible absorbing material plate are as follows:

[0056] S1. Preparation of composite absorber layer 1, including:

[0057] Prepare conductive substrate 7: Take a square aluminum plate with a thickness of 1.0 mm and a flat shape as conductive substrate 7.

[0058] Prepare sound-absorbing material board 6: 2.0 mm thick, with a density of 1200 kg / m³. 3 Square polyurethane rubber sheets are used as sound-absorbing material panels 6.

[0059] Fabrication of the microwave absorbing functional board 5: A 1.0 mm thick square polyimide board is used as the dielectric substrate 8. An ITO thin film is prepared on the surface of this polyimide board as a patterned resistive film 9 using magnetron sputtering. Laser etching technology is then used to process the ITO thin film into a specific pattern. (Refer to...) Figure 3The pattern of the patterned resistive film 9 is a square pattern with a side length of 12 mm, and four circular patterns with a radius of 5 mm are integrated at the four corners of the square pattern (the top corner of the square pattern is taken as the center of the circular pattern). A plurality of wave-absorbing functional plates 5 are prepared by the same method, and the resistive film patterns on the wave-absorbing functional plates 5 have the same shape and different sizes.

[0060] Stacking and curing: using an epoxy adhesive, the stacking and curing are performed in the following order: first, the first layer of sound-absorbing material plate is bonded to the conductive substrate 7; then, the first layer of wave-absorbing functional plate (ITO face up) is bonded to the first layer of sound-absorbing material plate; then, the sound-absorbing material plates 6 and the wave-absorbing functional plates 5 are alternately bonded in sequence thereon, and the top layer is the wave-absorbing functional plate 5. The number of sound-absorbing material plates 6 and wave-absorbing functional plates 5 is at least two layers respectively; the sizes of the patterned resistive film 9 on the plurality of wave-absorbing functional plates 5 gradually change along the thickness direction of the composite absorbing layer 1. The layers are tightly bonded by a hot pressing process to form a complete composite absorbing layer 1.

[0061] S2, preparing a water sound absorbing layer 2:

[0062] The viscoelastic material matrix 4 with a cuboid cavity inside is prepared by 3D printing. The viscoelastic material matrix 4 is made of rubber material and has a thickness of 20 mm. The bottom surface of the cuboid cavity has a side length of 5 mm and a height of 15 mm.

[0063] S3, overall compounding:

[0064] Using an epoxy adhesive, the prepared aluminum plate of the composite absorbing layer 1 is bonded to the viscoelastic material matrix 4 of the water sound absorbing layer 2 under a certain pressure to obtain an electromagnetic wave and water sound wave compatible absorbing material plate.

[0065] Referring to Figure 4 The electromagnetic wave and water sound wave compatible absorbing material plate prepared in this embodiment has an electromagnetic wave absorption rate of 93.7% or more in the continuous frequency band of 2-18 GHz, which exceeds the engineering allowable value of 90%. The converted reflectivity value is better than -12 dB, which meets the requirements of high-performance electromagnetic wave absorbing materials. Referring to Figure 5 The sound absorption coefficient of the electromagnetic wave and water sound wave compatible absorbing material plate prepared in this embodiment reaches about 0.5 or more in the water sound wave frequency range of 3.64-20 kHz, and the sound absorption frequency range covers most of the working frequency range of medium frequency sonar.

[0066] The above are preferred embodiments of the present application, which do not limit the protection scope of the present application. Therefore, any equivalent changes made on the basis of the structure, shape and principle of the present application should be covered by the protection scope of the present application.

Claims

1. A panel of electromagnetic and underwater acoustic wave compatible absorbing material, characterized in that: Comprise: a water sound absorbing layer, comprising a viscoelastic material matrix and a cavity structure embedded therein; and a composite absorbing layer, comprising a conductive substrate connected to the viscoelastic material matrix and sound absorbing material plates and wave absorbing functional plates arranged alternately on the conductive substrate; the sound absorbing material plates have electromagnetic transparency, and the wave absorbing functional plates have sound wave transparency; wherein the top layer of the composite absorbing layer is a wave absorbing functional plate; the wave absorbing functional plate comprises a dielectric substrate and a patterned resistive film arranged on the dielectric substrate, and the patterned resistive film adopts a pattern composed of multiple different shapes, including a rectangular pattern and a circular or elliptical pattern arranged at four corners of the rectangular pattern; the patterned resistive films on the wave absorbing functional plates of different layers have different sizes.

2. A panel of electromagnetic and underwater acoustic wave compatible absorbing material according to claim 1, characterized in that: The patterned resistive films on the wave absorbing functional plates of different layers have the same or different shapes.

3. A panel of electromagnetic and underwater acoustic wave compatible absorbing material according to claim 1, characterized in that: The cavity structure is a cylinder, a cuboid or a cone.

4. A panel of electromagnetic and underwater acoustic wave compatible absorbing material according to claim 1, characterized in that: The patterned resistive film comprises one or more of carbon-based conductive ink film, ITO conductive film and graphene conductive film.

5. A panel of electromagnetic and underwater acoustic wave compatible absorbing material according to claim 1, characterized in that: The viscoelastic material matrix comprises one or more of rubber, polyurethane and polydimethylsiloxane.

6. A panel of electromagnetic and underwater acoustic wave compatible absorbing material according to claim 1, characterized in that: The sound absorbing material plate comprises one or more of rubber, polyurethane and polydimethylsiloxane.

7. An equipment skin, characterized by: Prepared from the electromagnetic wave and water sound wave compatible absorbing material plate according to any one of claims 1-6, used for water surface ships or trans-medium vehicles.

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