Semi-active pressure-resistant low-frequency sound absorption covering layer containing piezoelectric composite material

Abstract

The invention relates to a semi-active pressure-resistant low-frequency sound absorption covering layer containing a piezoelectric composite material. The semi-active pressure-resistant low-frequency sound-absorbing covering layer containing the piezoelectric composite material structurally comprises a surface protecting layer which is arranged on the outermost side of the covering layer and converts sound energy into heat energy through a damping effect; the piezoelectric composite material layer is arranged on the inner side of the surface protection layer, converts sound energy into electric energy through a direct piezoelectric effect, and dissipates the electric energy through a shunt branch; the cavity layer is arranged on the inner side of the piezoelectric composite material layer and absorbs sound through a cavity resonance effect, waveform conversion and a damping effect; the substrate layer is arranged on the inner side of the cavity layer to seal the cavity layer so as to absorb sound with a damping effect; wherein the composite material layer is electrically connected with an external shunt branch, and the shunt branch is formed by connecting a negative capacitance element, a resistance element and an inductance element in series.

Description

Technical Field

[0001] The invention belongs to the field of underwater sound absorption, and in particular relates to a semi-active pressure-resistant low-frequency sound-absorbing covering layer containing a piezoelectric composite material. Background Art

[0002] With the development of military technology, various combat platforms have become more and more capable of detecting, tracking and attacking underwater vehicles, and the survivability of underwater vehicles is seriously threatened. Good acoustic stealth technology has become an important means to improve the survivability of underwater vehicles.

[0003] Laying acoustic covering layers such as anechoic tiles to absorb sound waves is currently one of the main methods to improve the acoustic stealth capability of underwater vehicles. Traditional sound-absorbing covering layers are generally made of multiple layers of polymer viscoelastic materials, including various structural forms such as homogeneous damping type, cavity resonance type, impedance gradient type and periodic scattering composite type; the sound absorption mechanism includes waveform conversion, sound wave scattering and cavity resonance. However, whether it is a single layer, a multi-layer or a passive sound-absorbing material containing various cavity structures, the sound absorption performance at low frequencies has certain limitations, and the sound absorption characteristics will also decrease with the increase of diving depth (hydrostatic pressure). However, the operating frequency of current active and passive integrated sonars has begun to extend to low frequencies of several hundred hertz, and the operating frequency of long-range detection and target analysis and positioning sonars is even as low as tens of hertz. Therefore, the future sound-absorbing covering layer structure is required to have good sound absorption and vibration reduction and noise reduction effects in a wide frequency range of several hundred hertz (or even lower frequencies) to several thousand hertz, and at the same time, it must have good load-bearing capacity to meet the mechanical properties of underwater vehicles.

[0004] At present, traditional acoustic covering layers are difficult to meet the above requirements at the same time, and there is an urgent need to design new pressure-resistant acoustic covering layers to improve the low-frequency sound absorption capacity. Summary of the invention

[0005] In view of the above technical problems, the purpose of the present invention is to provide a semi-active pressure-resistant low-frequency sound-absorbing covering layer containing piezoelectric composite materials. The acoustic covering layer has multiple energy-consuming sound absorption mechanisms, can improve the low-frequency sound absorption performance and has good pressure resistance to meet the sound absorption requirements of the covering layer of underwater vehicles with great diving depth.

[0006] Specifically, the present invention provides a semi-active pressure-resistant low-frequency sound-absorbing covering layer containing a piezoelectric composite material, wherein the covering layer comprises: A protective layer, which is arranged on the outermost side of the covering layer and converts sound energy into heat energy by means of a damping effect; A piezoelectric composite material layer, which is arranged on the inner side of the face layer and converts acoustic energy into electrical energy by means of a positive piezoelectric effect and dissipates the energy through a shunt branch; A cavity layer, which is arranged inside the piezoelectric composite material layer and absorbs sound by cavity resonance effect, waveform conversion and damping effect; A base layer, wherein the base layer is arranged inside the cavity layer to seal the cavity layer and absorb sound through a damping effect; The composite material layer is electrically connected to an external shunt branch, and the shunt branch is formed by a negative capacitance element, a resistance element and an inductance element connected in series.

[0007] Preferably, the surface layer, the piezoelectric composite material layer, the cavity layer and the base layer in the cover layer are connected by adhesive bonding, preferably epoxy adhesive bonding.

[0008] Preferably, the material of the armor layer includes at least one of vulcanized rubber, nitrile rubber or carbon black filled rubber; wherein the thickness of the armor layer is 5-30 mm.

[0009] Preferably, the piezoelectric composite material layer includes: electrodes located on the upper and lower surfaces and electrically connected to the shunt branch, a three-dimensionally distributed epoxy resin matrix, a one-dimensionally distributed silicone rubber filled in the epoxy resin matrix, and a piezoelectric material column filled in the silicone rubber.

[0010] Preferably, the piezoelectric material column includes PZT piezoelectric ceramics or PMN-PT single crystal.

[0011] Preferably, the piezoelectric composite material layer has a thickness of 10-40 mm.

[0012] Preferably, the volume fraction of the piezoelectric material columns in the piezoelectric composite material layer is 5-30%.

[0013] Preferably, the capacitance of the negative capacitance element in the shunt branch is -1.125nF, and the resistance of the resistance element is ≤2×10 5 Ω, the inductance of the inductor component is ≤10H.

[0014] Preferably, the material of the cavity layer includes at least one of vulcanized rubber, nitrile rubber, carbon black filled rubber or epoxy resin material filled with hollow glass beads; the thickness of the cavity layer is 10-30mm and has periodically distributed cavities; preferably, the shape of the cavity includes cylindrical, conical and rectangular.

[0015] Preferably, the material of the base layer includes at least one of vulcanized rubber, nitrile rubber, and carbon black filled rubber; and the thickness of the base layer is 10-30 mm.

[0016] Beneficial Effects (1) The present invention combines the protective layer, the piezoelectric composite material and the cavity layer, and utilizes the multiple sound absorption and energy dissipation mechanisms of the damping effect of the viscoelastic material of the protective layer, the piezoelectric shunt damping effect of the piezoelectric material and the shunt circuit, and the cavity resonance effect. The main sound absorption peak is the result of the combined action of multiple energy dissipation mechanisms in the covering layer, which belongs to the overall energy dissipation mode, thereby improving the global sound absorption capacity of the covering layer; (2) The present invention introduces a piezoelectric composite material and a shunt branch. The piezoelectric composite material has a lower acoustic impedance than conventional piezoelectric ceramics and single crystals, which is beneficial to impedance matching. At the same time, the positive piezoelectric effect of the piezoelectric composite material is used to convert acoustic energy into electrical energy, which is consumed through the shunt branch. Moreover, the values ​​of the negative capacitance, inductance and resistance of the shunt path can be adjusted to achieve semi-active control, adjust the number of sound absorption curve peaks and the sound absorption coefficient, reduce the frequency of the sound absorption peak, and improve the low-frequency sound absorption capacity; (3) The present invention introduces a piezoelectric composite material, which improves the structural rigidity compared with the conventional rubber covering layer, which is beneficial to improving the pressure resistance of the covering layer structure, and utilizes the piezoelectric shunt damping effect of the piezoelectric composite material and the shunt circuit to improve the problem of the conventional rubber covering layer having a small sound absorption coefficient under a high hydrostatic pressure environment, which is beneficial to improving the pressure resistance of the covering acoustic performance; (4) The present invention introduces piezoelectric composite materials into viscoelastic rubber to construct intelligent sound-absorbing materials, and proposes a new semi-active pressure-resistant sound-absorbing covering layer structure based on the multiple sound absorption mechanisms of piezoelectric composite materials and rubber materials, providing a new solution for the development of underwater low-frequency sound absorption technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The cross-sectional structure of the semi-active pressure-resistant low-frequency sound-absorbing covering layer containing piezoelectric composite materials and the schematic diagram of its shunt branch are shown in the example of the present invention; Figure 2 It is a schematic structural diagram of a 1-1-3 type piezoelectric composite material layer according to an example of the present invention; Figure 3 This is a curve diagram showing the effect of the hydrostatic pressure outside the covering layer on the sound absorption coefficient of the covering layer in Example 1; Figure 4 is a curve diagram showing the effect of the inductance in the shunt branch on the sound absorption coefficient of the covering layer in Example 2; Figure 5 This is a curve diagram showing the effect of the resistance in the shunt branch on the sound absorption coefficient of the covering layer in Example 3; Figure 6The figure is a schematic diagram of the measured results of the sound absorption coefficient of the cover layer prepared by using piezoelectric composite material structures of different thicknesses based on Example 1; wherein, the thickness of the piezoelectric composite material of the PSC-1 scheme is 40 mm, the thickness of the piezoelectric composite material of the PSC-3 scheme is 30 mm, the thickness of the piezoelectric composite material of the PSC-4 scheme is 20 mm, and the thickness of the piezoelectric composite material of the PSC-5 scheme is 10 mm; Reference numerals: 1. Surface layer; 2. Piezoelectric composite material layer; 3. Cavity layer; 4. Base layer; 5. Shunt branch; 6. Negative capacitance element; 7. Resistance element; 8. Inductance element; 9. Electrode; 10. Epoxy resin matrix; 12. Piezoelectric material column; 13. Silicone rubber. DETAILED DESCRIPTION

[0018] The present invention is further described below by the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention, but not to limit the present invention.

[0019] The following, combined Figure 1 , exemplarily illustrating the structural composition of the semi-active pressure-resistant low-frequency sound-absorbing covering layer containing piezoelectric composite materials provided by the present invention. Wherein, the structural composition of the semi-active pressure-resistant low-frequency sound-absorbing covering layer containing piezoelectric composite materials may include: A protective layer 1, which is arranged on the outermost side of the covering layer to convert sound energy into heat energy by means of a damping effect; A piezoelectric composite material layer 2, which is arranged inside the face layer 1 and converts acoustic energy into electrical energy by a positive piezoelectric effect and dissipates it through a shunt branch 5; The cavity layer 3 is arranged inside the piezoelectric composite material layer 2 to absorb sound by cavity resonance effect, waveform conversion and damping effect; A base layer 4, wherein the base layer 4 is arranged inside the cavity layer 3 to seal the cavity layer 3 and absorb sound through a damping effect; The composite material layer 2 is electrically connected to an external shunt branch 5 , and the shunt branch 5 is formed by a negative capacitor element 6 , a resistor element 7 and an inductor element 8 connected in series.

[0020] In some embodiments, the connection between the face layer 1, the piezoelectric composite material layer 2, the cavity layer 3, and the base layer 4 in the cover layer may be adhesive connection, preferably epoxy adhesive connection.

[0021] In some embodiments, the material of the armor layer 1 can be a rubber material having an acoustic impedance close to that of water and a high sound absorption coefficient, preferably at least one of vulcanized rubber, nitrile rubber or carbon black filled rubber; wherein the thickness of the armor layer 1 can be 5-30 mm.

[0022] If the thickness of the protective layer 1 is too thin, the pressure resistance effect will be weakened and the sound absorption coefficient will also be reduced; if the protective layer 1 is too thick, the overall thickness of the covering layer will be too large, which is not conducive to the laying of the target surface with large curvature. At the same time, the overall mass of the covering layer will also increase, and it will not be applicable in some cases where the mass of underwater targets is restricted. The protective layer 1 used in the present invention is arranged at the outermost layer of the covering layer to achieve the impedance transition of seawater and piezoelectric composite materials, etc., to avoid a large amount of sound waves being reflected; at the same time, the viscosity of the protective layer 1 material, that is, the damping effect, is used to convert part of the sound energy into heat energy, thereby improving the sound absorption capacity.

[0023] In some embodiments, the piezoelectric composite material layer 2 may be a 1-1-3 type piezoelectric composite material, such as Figure 2 The piezoelectric composite material layer 2 may include: electrodes 9 located on the upper and lower surfaces and electrically connected to the shunt branch 5, a three-dimensionally distributed epoxy resin matrix 10, a one-dimensionally distributed silicone rubber 13 filled in the epoxy resin matrix 10, and a piezoelectric material column 12 filled in the silicone rubber 13.

[0024] The 1-1-3 interconnection method is adopted, that is, the piezoelectric phase is distributed in one dimension in space and is wrapped by the silicone rubber distributed in one dimension in space, and the silicone rubber phase is wrapped by the epoxy resin phase distributed in three dimensions in space. Compared with conventional piezoelectric ceramic blocks, this structure can use the longitudinal vibration mode of the one-dimensionally distributed piezoelectric ceramic column to realize the thickness vibration of the composite material, and its electromechanical coupling coefficient is close to the k of the ceramic material. 33 , which is much larger than the thickness vibration electromechanical coupling coefficient k of the ceramic block t , so it has a stronger electroacoustic conversion efficiency, thereby enhancing the sound absorption ability; at the same time, the introduction of low-density epoxy resin and silicone rubber makes the piezoelectric composite material have a lower acoustic impedance, which is conducive to the impedance matching between the covering layers.

[0025] The piezoelectric material column 12 may include PZT piezoelectric ceramics or PMN-PT single crystal.

[0026] In some embodiments, the thickness of the piezoelectric composite material layer 2 can be 10-40 mm. The resonant frequency of the piezoelectric composite material is inversely proportional to the thickness, and the electroacoustic conversion efficiency is higher near the resonant frequency. If the thickness is too low, it is not conducive to low-frequency sound absorption; if the thickness is too large, the overall thickness of the covering layer is large, which is not conducive to laying on the surface of a target with a large curvature, and the overall mass of the covering layer will also increase, which will not be applicable in some cases where there are restrictions on the mass of underwater targets.

[0027] In some embodiments, the volume fraction of the piezoelectric material column in the piezoelectric composite material layer 2 may be 5-30%. If the volume fraction of the piezoelectric phase is too large, the density of the composite material will be too large, the acoustic impedance will be too high, and it will be unfavorable for the acoustic impedance matching between the layers of the sound-absorbing cover layer; if the volume fraction of the piezoelectric phase is too small, the piezoelectric coefficient of the composite material will be low, and the electroacoustic conversion ability will be weak, thereby reducing the sound absorption coefficient.

[0028] In some embodiments, the capacitance of the negative capacitance element 6 in the shunt branch 5 may be -1.125 nF, and the resistance of the resistance element 7 may be ≤2×10 5 Ω, the inductance of the inductor element 8 can be ≤10H.

[0029] The piezoelectric composite material layer used in the present invention is arranged below the protective layer 1, which can improve the stiffness and pressure resistance of the covering layer, and utilize the positive piezoelectric effect to convert part of the mechanical energy of the sound wave into electrical energy, and convert it into heat energy consumption through the shunt branch 5, thereby improving the low-frequency sound absorption capacity; in addition, the shunt branch 5 is connected in series between the upper and lower electrodes of the piezoelectric composite material layer 2, and semi-active sound absorption regulation can be achieved by changing the impedance value of the shunt branch.

[0030] It should be noted that the present invention introduces piezoelectric composite materials and shunt branches. The piezoelectric composite materials have lower acoustic impedance than conventional piezoelectric ceramics and single crystals, which is beneficial to impedance matching. At the same time, the positive piezoelectric effect of the piezoelectric composite materials is used to convert acoustic energy into electrical energy, and it is consumed through the shunt branch. Moreover, by adjusting the values ​​of the negative capacitance, inductance and resistance of the shunt path, semi-active control can be achieved, the number of peaks of the sound absorption curve and the sound absorption coefficient can be adjusted, the frequency of the sound absorption peak can be reduced, and the low-frequency sound absorption capacity can be improved. Moreover, the introduction of the piezoelectric composite material improves the structural rigidity compared with the conventional rubber covering layer, which is beneficial to improving the pressure resistance of the covering layer structure, and the piezoelectric shunt damping effect of the piezoelectric composite material and the shunt circuit is used to improve the problem of the conventional rubber covering layer having a small sound absorption coefficient in a high hydrostatic pressure environment, which is beneficial to improving the pressure resistance of the covering acoustic performance.

[0031] In some embodiments, the material of the cavity layer 3 can be a rubber material with a higher sound absorption coefficient (such as vulcanized rubber, nitrile rubber or carbon black filled rubber) or an epoxy resin material filled with hollow glass microspheres, preferably an epoxy resin material filled with hollow glass microspheres with high rigidity to improve the pressure resistance of the covering layer.

[0032] In some embodiments, the cavity layer 3 may have a thickness of 10-30 mm and have periodically distributed cavities; preferably, the shape of the cavity may include cylindrical, conical, or rectangular.

[0033] If the thickness of the cavity layer is too small, it is not conducive to weakening the cavity resonance effect and reducing the low-frequency sound absorption capacity; if the thickness of the cavity layer is too large, the overall thickness of the covering layer is large, which is not conducive to laying on the surface of the target with large curvature, and the overall mass of the covering layer will also increase, which will not be applicable in some cases where there are restrictions on the mass of underwater targets. The present invention arranges the cavity layer 3 below the piezoelectric composite material layer 2, and can utilize the resonance effect of the cavity, waveform conversion and the damping effect of the cavity layer material itself to improve the sound absorption capacity.

[0034] In some embodiments, the material of the base layer 4 may be a rubber material having an acoustic impedance close to that of water and a high sound absorption coefficient, preferably at least one of vulcanized rubber, nitrile rubber, and carbon black filled rubber; the thickness of the base layer 4 may be 10-30 mm.

[0035] In the present invention, the base layer 4 is arranged below the cavity layer 3, so as to seal the cavity layer 3 and prevent seawater from entering the cavity, and the damping effect of the base layer material can be utilized to improve the sound absorption capability.

[0036] In the covering layer provided by the present invention, a uniform protective layer, a piezoelectric composite material and a cavity layer are compounded, and multiple sound absorption and energy dissipation mechanisms of the damping effect of the viscoelastic material of the uniform protective layer, the piezoelectric shunt damping effect of the piezoelectric material and the shunt circuit, and the cavity resonance effect are utilized. The main sound absorption peak is the result of the combined action of multiple energy dissipation mechanisms in the covering layer, which belongs to an overall energy dissipation mode, thereby improving the global sound absorption capacity of the covering layer.

[0037] In some embodiments, the sound absorption coefficient of the semi-active pressure-resistant low-frequency sound-absorbing covering layer containing the piezoelectric composite material may be ≥0.2, preferably ≥0.5.

[0038] The sound-absorbing covering layer structure provided by the present invention has good pressure resistance and semi-active sound absorption capacity that is easy to modulate. At the same time, a 1-1-3 type piezoelectric composite material with a high electromechanical coupling coefficient, low density and low acoustic impedance is used as a piezoelectric layer. While improving the structural rigidity, the damping effect of the piezoelectric layer shunt branch is also utilized to improve the low-frequency pressure resistance and sound absorption capacity.

[0039] The following further examples are given to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention all belong to the scope of protection of the present invention. The specific process parameters of the following examples are also only examples within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description of this article, and are not limited to the specific values ​​​​exemplified below. If not specifically stated, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0040] Example 1

[0041] like Figure 1 In the semi-active composite covering layer shown, the piezoelectric composite material 2 uses PZT-5H ceramic as the material used for the piezoelectric column. The material parameters of PZT-5H ceramic, epoxy resin and silicone rubber in the piezoelectric composite material are shown in Table 1. The volume fraction of PZT-5H ceramic in the piezoelectric composite material 2 is 24.45%, the volume fraction of silicone rubber is 25%, and the volume fraction of epoxy resin is 50.55%. The thickness h2 of the piezoelectric composite material 2 is 40mm, of which the side length of the PZT-5H ceramic column 12 is 4.95mm, and the side length of the silicone rubber 13 is 7.03mm. According to the dielectric parameters and volume fractions of each material, based on the series-parallel model, the capacitance C of the piezoelectric composite material 2 p =1.875nF. Table 1 Material parameters of piezoelectric composite materials The value of negative capacitance 6 in shunt branch 5 is C s =-0.6C p =-1.125nF, the value of resistor 7 is R s =0Ω, the value of inductor 8 is L s =0H, that is, at this time the shunt branch only contains negative capacitance. The materials of the armour layer 1, the cavity layer 3 and the base layer 4 are all carbon black filled rubber NR100N550; in terms of geometric characteristics, the outer diameter of the covering layer is 114 mm, the thickness h1 of the armour layer 1 is 10 mm, the thickness h3 of the cavity layer 3 is 20 mm, the thickness h4 of the base layer 4 is 20 mm, and the cavity in the cavity layer 3 is cylindrical with a diameter d of 20 mm.

[0042] Using the dynamic material parameters of carbon black filled rubber NR100N550 in a static pressure environment, combined with the finite deformation prediction method of the cavity cover layer based on phenomenological theory and the transfer matrix method, the global sound absorption characteristics of the cover layer in this embodiment at the diving depths of 0m, 300m and 600m, that is, when the static water pressure outside the boat is 0MPa, 3MPa and 6MPa respectively, are calculated as follows: Figure 3As shown in the figure, it can be seen that the sound absorption curve of the semi-active covering layer in this embodiment moves toward the high frequency direction with the increase of the hydrostatic pressure outside the boat. In the frequency band below the first sound absorption peak frequency, the amplitude of the sound absorption coefficient decreases slightly. In the frequency band above the first sound absorption peak, the sound absorption coefficient changes little with the increase of the hydrostatic pressure, indicating that the structural covering layer has good pressure resistance. The movement of the sound absorption peak to high frequency is mainly due to the increase of the hydrostatic pressure outside the boat, which will also cause the compression deformation of the covering layer to increase and the overall thickness to become thinner, making the sound propagation path shorter, the overall resonance frequency increase, and the volume of the embedded cavity decreases, and the corresponding resonance frequency increases.

[0043] Example 2

[0044] Based on the structure and material parameters of the covering layer in Example 1, the peak number and frequency of the sound absorption curve are adjusted by changing the value of the inductor 8 in the shunt branch 5. The negative capacitor 6 and the resistor 7 in the shunt branch 5 are C s =-0.6C p =-1.125nF, R s =0Ω, and change the size of inductor 8 to make it 0H, 1H and 10H respectively.

[0045] The variation of the sound absorption coefficient of the covering layer with inductance is obtained by theoretical analysis, such as Figure 4 As shown in the figure, when the inductance in the shunt path is not zero, that is, the introduction of the inductor element can make the sound absorption of the cover layer appear a new sound absorption peak, which is conducive to achieving broadband high-performance sound absorption, and increasing the value of the inductor can make the sound absorption peak move to low frequency, which is conducive to low-frequency sound absorption. This is due to the introduction of the inductor, and the internal capacitance C of the piezoelectric composite material. p and negative capacitance C s =-0.6C p The shunt circuit resonance is formed, which adds a resonant energy consumption mode to the cover layer. The resonant frequency is inversely proportional to the product of inductance and capacitance. If the physical parameters of the piezoelectric composite material are fixed, the resonant frequency moves toward the low frequency direction as the inductance increases.

[0046] Example 3

[0047] On the basis of Example 2, the inductance 8 in the shunt branch 5 is kept at 1H and the negative capacitance 6 is kept at C s =-0.6C p = -1.125nF, change the value of resistor 7 to 0Ω, 1×10 5 Ω and 2×10 5 Ω.

[0048] The variation of the sound absorption coefficient of the covering layer with the resistance is obtained by theoretical analysis, such as Figure 5As shown in the figure, when the resistance in the shunt path is not zero, that is, the resistance element is introduced, the peak amplitude of the sound absorption of the covering layer caused by the resonance of the shunt circuit decreases, and gradually decreases with the increase of the resistance value, which inhibits the effect of the shunt damping dissipation mechanism to a certain extent. This can be attributed to the fact that the resistance element in the shunt circuit has a damping characteristic similar to that in the mechanical vibration system. Therefore, when designing and preparing the shunt branch, the size of the resistance in the shunt circuit should be minimized.

[0049] According to the above embodiments, the semi-active pressure-resistant low-frequency sound-absorbing covering layer containing piezoelectric composite materials proposed in the present invention has good pressure resistance, and the sound absorption coefficient changes little with the increase of hydrostatic pressure within a certain frequency band. The amplitude and frequency of the sound absorption peak can be controlled by changing the value of the inductance element in the shunt branch, thereby realizing semi-active control and improving the low-frequency sound absorption performance.

[0050] Figure 6 The diagram is a schematic diagram of the measured results of the sound absorption coefficient of the covering layer prepared by using piezoelectric composite material structures of different thicknesses based on Example 1; wherein, the thickness of the piezoelectric composite material of the PSC-1 scheme is 40 mm, the thickness of the piezoelectric composite material of the PSC-3 scheme is 30 mm, the thickness of the piezoelectric composite material of the PSC-4 scheme is 20 mm, and the thickness of the piezoelectric composite material of the PSC-5 scheme is 10 mm. It can be seen from the figure that the composite material scheme PSC-5 still has a relatively high low-frequency sound absorption coefficient (>0.7) when the hydrostatic pressure is 0.3 MPa, which is relatively better than other schemes.

[0051] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. A semi-active pressure-resistant low-frequency sound-absorbing covering layer containing a piezoelectric composite material, characterized in that: The structural composition of the covering layer includes: A protective layer, which is arranged on the outermost side of the covering layer and converts sound energy into heat energy by means of a damping effect; A piezoelectric composite material layer, which is arranged on the inner side of the face layer and converts acoustic energy into electrical energy by means of a positive piezoelectric effect and dissipates the energy through a shunt branch; A cavity layer, which is arranged inside the piezoelectric composite material layer and absorbs sound by cavity resonance effect, waveform conversion and damping effect; A base layer, wherein the base layer is arranged inside the cavity layer to seal the cavity layer and absorb sound through a damping effect; The composite material layer is electrically connected to an external shunt branch, and the shunt branch is formed by a negative capacitance element, a resistance element and an inductance element connected in series.

2. The semi-active pressure-resistant low-frequency sound-absorbing covering layer containing piezoelectric composite materials according to claim 1 is characterized in that: The surface layer, the piezoelectric composite material layer, the cavity layer and the base layer in the cover layer are connected by adhesive bonding, preferably epoxy adhesive bonding.

3. The semi-active pressure-resistant low-frequency sound-absorbing covering layer containing piezoelectric composite materials according to claim 1 or 2, characterized in that: The material of the armor layer includes at least one of vulcanized rubber, nitrile rubber or carbon black filled rubber; wherein the thickness of the armor layer is 5-30 mm.

4. The semi-active pressure-resistant low-frequency sound-absorbing covering layer containing piezoelectric composite materials according to any one of claims 1 to 3, characterized in that: The piezoelectric composite material layer includes: electrodes located on the upper and lower surfaces and electrically connected to the shunt branch, a three-dimensionally distributed epoxy resin matrix, a one-dimensionally distributed silicone rubber filled in the epoxy resin matrix, and a piezoelectric material column filled in the silicone rubber.

5. The semi-active pressure-resistant low-frequency sound-absorbing covering layer containing piezoelectric composite materials according to any one of claims 1 to 4, characterized in that: The piezoelectric material column includes PZT piezoelectric ceramics and PMN-PT single crystal.

6. The semi-active pressure-resistant low-frequency sound-absorbing covering layer containing piezoelectric composite materials according to any one of claims 1 to 5, characterized in that: The thickness of the piezoelectric composite material layer is 10-40 mm.

7. The semi-active pressure-resistant low-frequency sound-absorbing covering layer containing piezoelectric composite materials according to any one of claims 1 to 6, characterized in that: The volume fraction of the piezoelectric material columns in the piezoelectric composite material layer is 5-30%.

8. The semi-active pressure-resistant low-frequency sound-absorbing covering layer containing piezoelectric composite materials according to any one of claims 1 to 7, characterized in that: The capacitance of the negative capacitance element in the shunt branch is -1.125nF, and the resistance of the resistance element is ≤2×10 5 Ω, the inductance of the inductor component is ≤10H.

9. The semi-active pressure-resistant low-frequency sound-absorbing covering layer containing piezoelectric composite materials according to any one of claims 1 to 8, characterized in that: The material of the cavity layer includes at least one of vulcanized rubber, nitrile rubber, carbon black filled rubber or epoxy resin material filled with hollow glass beads; the thickness of the cavity layer is 10-30mm and has periodically distributed cavities; preferably, the shape of the cavity includes cylindrical, conical, and rectangular.

10. The semi-active pressure-resistant low-frequency sound-absorbing covering layer containing piezoelectric composite materials according to any one of claims 1 to 9, characterized in that: The material of the base layer includes at least one of vulcanized rubber, nitrile rubber, and carbon black filled rubber; the thickness of the base layer is 10-30 mm.

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