Multilayer cavity acoustic material

Abstract

To provide a novel structural acoustic material that maintains acoustic performance even under high pressure while reducing manufacturing and maintenance costs.SOLUTION: The acoustic material A comprises a viscoelastic body 100 having a top surface PS and a bottom surface PB, with multiple cavities C, in which the viscoelastic body 100 forms multiple layers A1 to A3 between the top surface PS and the bottom surface PB, and each of the multiple cavities C forms a cylindrical closed space. The cavities C are formed spanning at least two of the multiple layers. The cylindrical closed spaces have a first flat surface on the most surface side and a second flat surface on the most back surface side, with the diameter of the first flat surface being greater than zero and less than or equal to the diameter of the second flat surface.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a structure of an acoustic material that absorbs sound propagating through a medium. [Background technology]

[0002] An underwater sound absorber has been proposed that has many cavities arranged inside a rubber-like elastic body (see Patent Document 1). In particular, by forming the cavities into a cone or frustum shape, the sound absorption effect in a desired frequency range is improved. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 59-200296 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the underwater sound absorber disclosed in Patent Document 1, each cavity is compressed as the water pressure increases. The volume reduction and deformation of the cavities deteriorates acoustic performance, particularly in the low frequency range, resulting in a decrease in the sound absorption effect. Furthermore, the shape of the cavities disclosed in Patent Document 1 is difficult to mold and maintain, resulting in increased manufacturing and maintenance costs.

[0005] The present invention was devised in consideration of the above circumstances, and its object is to provide an acoustic material with a new structure that can maintain acoustic performance even under high pressure and reduce manufacturing and maintenance costs. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, according to one embodiment of the present invention, an acoustic material is provided having a plurality of cavities inside a viscoelastic body having a top surface and a back surface, wherein the viscoelastic body forms a plurality of layers between the top surface and the back surface, and each of the plurality of cavities forms a cylindrical closed space. According to one embodiment of the present invention, the plurality of cavities may be formed across at least two of the plurality of layers. According to one embodiment of the present invention, the cylindrical closed space has a first flat surface on the outermost surface side and a second flat surface on the outermost back surface side, and the diameter of the first flat surface may be greater than zero and less than or equal to the diameter of the second flat surface. According to an embodiment of the present invention, an edge portion of the first flat surface and an edge portion of the second flat surface may be curved. According to an embodiment of the present invention, the cavities may be filled with a gas. According to an embodiment of the present invention, the layer on the outermost surface side of the plurality of layers of the viscoelastic body can have a larger specific gravity than the layer on the innermost surface side. According to an embodiment of the present invention, the plurality of layers of the viscoelastic body may have a specific gravity of 1.0 to 2.0. According to one embodiment of the present invention, the plurality of cavities may be formed of one or more alignment layers, and may have one or more cavities in the thickness direction of the cylindrical closed space. According to one embodiment of the present invention, a viscoelastic material having a thickness of 10 mm or more can be formed between a first flat surface on the side of the outermost surface of the cavity closest to the outermost surface and the outermost surface, and a viscoelastic material having a thickness of 10 mm or more can be formed between a second flat surface on the side of the outermost surface of the cavity closest to the outermost surface and the outermost surface. According to an embodiment of the present invention, the sheet-like member may further include a fiber-reinforced plastic layer provided on at least one of the outermost surface and the outermost back surface. According to an embodiment of the present invention, the fiber reinforced plastic layer may have a thickness of 1 / 16 to 1 / 4 of the wavelength of the highest frequency in the frequency band of sound to be attenuated. [Effects of the Invention]

[0007] According to one embodiment of the present invention, a viscoelastic body having multiple layers between the top surface and the back surface is provided with multiple cavities, and each cavity forms a cylindrical closed space, thereby achieving the effects of maintaining acoustic performance even under high pressure and reducing manufacturing and maintenance costs. Furthermore, according to one embodiment of the present invention, multiple cavities are formed across at least two of the multiple layers, which provides the advantage that cavities of any size and height can be easily formed. Furthermore, according to one embodiment of the present invention, the diameter of the first flat surface of the cylindrical closed space is greater than zero and less than or equal to the diameter of the second flat surface, thereby reducing top blockage under high water pressure due to the first flat surface, thereby suppressing performance degradation and further reducing maintenance costs.Furthermore, by making the diameter of the first flat surface smaller than the diameter of the second flat surface, it is possible to create a gradient in the acoustic impedance. Furthermore, according to one embodiment of the present invention, by forming the edge portions of the first flat surface and the second flat surface into curved surfaces, it is possible to achieve the effect of facilitating manufacturing and maintenance. Furthermore, according to one embodiment of the present invention, by filling a plurality of cavities with gas, it is possible to obtain an effect of improving the sound absorbing effect in a desired frequency range. Furthermore, according to one embodiment of the present invention, the layer on the outermost surface of the multiple layers of viscoelastic material has a higher specific gravity than the layer on the outermost back surface, thereby achieving the effect of maintaining acoustic performance even under high pressure. Furthermore, according to one embodiment of the present invention, the multiple layers of the viscoelastic material have a specific gravity of 1.0 to 2.0, which provides the effect of maintaining acoustic performance even under high pressure. Furthermore, according to one embodiment of the present invention, by providing a viscoelastic layer of 10 mm or more on the front and back sides of the area where the cavity alignment layer is formed, deformation and blockage of the cavities can be suppressed even under high pressure. Furthermore, according to one embodiment of the present invention, by further including a fiber-reinforced plastic layer, deformation and blockage of the cavity are suppressed even under high pressure, and a reduction in the sound absorption effect in the low frequency range can be suppressed. According to one embodiment of the present invention, the sound absorbing effect can be improved by making the thickness of the fiber reinforced plastic layer 1 / 16 to 1 / 4 of the wavelength of the highest frequency in the frequency band of sound to be attenuated. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a perspective view illustrating a schematic configuration of a multi-layer hollow acoustic material according to a first embodiment of the present invention. [Figure 2] 1 is a side cross-sectional view showing a schematic configuration of a multi-layered cavity acoustic material according to a first embodiment. [Figure 3] 1A is a longitudinal cross-sectional view showing a first example of a cavity shape in a multi-layered cavity acoustic material, and FIG. 1B is a longitudinal cross-sectional view showing a second example of the cavity shape. [Figure 4] 3A is a vertical cross-sectional view showing a modified example of FIG. 3A, and FIG. 3B is a vertical cross-sectional view showing a modified example of FIG. 3B. [Figure 5] 1 is a schematic side cross-sectional view showing an example of the multilayer structure of a multilayer cavity acoustic material. FIG. [Figure 6] FIG. 10 is a cross-sectional side view schematically showing a first example of a periodic unit layer configuration in a multi-layer hollow acoustic material according to a second embodiment of the present invention. [Figure 7] 10 is a cross-sectional side view schematically showing a second example of a periodic unit layer configuration in a multi-layer hollow acoustic material according to a second embodiment. FIG. [Figure 8] FIG. 10 is a cross-sectional side view schematically showing the configuration of a multi-layer cavity acoustic material according to a third embodiment of the present invention. [Figure 9] FIG. 10 is a cross-sectional side view schematically showing a first example of a periodic unit layer configuration in a multi-layer hollow acoustic material according to a fourth embodiment of the present invention. [Figure 10] FIG. 10 is a cross-sectional side view schematically showing a second example of a periodic unit layer configuration in a multi-layer hollow acoustic material according to the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the components described in the following embodiments are merely examples and are not intended to limit the technical scope of the present invention to those. For example, the environment in which the multi-layered cavity acoustic material of the present invention is used may be any medium that propagates sound, and in the following description, "underwater" includes underwater environments such as the sea, rivers, lakes, and anechoic tanks.

[0010] 1. First embodiment As shown in Figure 1, the multilayer cavity acoustic material A according to this embodiment is attached to a rear structure M, and absorbs and attenuates incident waves propagating through the medium. Here, the rear structure M is, for example, an underwater structure, and can be made of a strong material such as a metal plate such as iron, concrete, or FRP (Fiber Reinforced Plastics). For convenience, the directions in which the rear and front surfaces of the multilayer cavity acoustic material A extend are represented by the X-axis and Y-axis, and the direction perpendicular to these axes is represented by the Z-axis. Here, the incident wave is assumed to be incident in the direction of the Z-axis.

[0011] The multilayer hollow acoustic material A according to this embodiment has a configuration in which multiple cavities C are arranged in layers inside a plate-shaped viscoelastic body 100. As will be described later, the viscoelastic body 100 is made up of multiple layers and can be made of a material with sound-absorbing properties, such as rubber (for example, chloroprene rubber, nitrile rubber (NBR), or urethane). The viscoelastic body 100 has a specific gravity of approximately 1.0 to 2.0, and is configured so that the specific gravity of the multiple layers increases in the positive direction of the Z axis. The cavities C are cylindrical closed spaces inside the viscoelastic body 100, and are filled with gas (air in this case). The shape of the cavities C will be described later.

[0012] In Figure 2, the multilayer cavity acoustic material A has a configuration in which multiple layers of viscoelastic material are laminated, with multiple cavities C formed across the multiple layers of viscoelastic material. Each of the multiple cavities C has a cylindrical shape extending in the thickness direction (Z direction) and is arranged in the XY direction in a periodic pattern with a length Lx. Figure 2 shows an example of a multilayer cavity acoustic material A in which three layers (back layer A1, middle layer A2, surface layer A3) are laminated in the Z direction, with cylindrical cavities C arranged across the three layers A1 to A3. The back layer A1, middle layer A2, and surface layer A3 may be integrally molded from viscoelastic materials with successively increasing specific gravities, or may be formed by sequentially attaching separate plate-shaped viscoelastic materials (viscoelastic layers).

[0013] The thickness of each of the layers and the cavity C in the multilayer cavity acoustic material A in the Z direction is not limited, but the thickness t between the bottom surface of the cavity C on the rearmost PB side and the rearmost PB A1and the thickness t between the upper surface of the outermost PS side and the outermost PS A3 It is necessary to determine this in consideration of the pressure resistance performance. In this embodiment, in order to prevent the destruction of the internal structure due to water pressure, the inflow of water into the cavity C, etc., for example, the thickness t A1 and t A3 are both desirably set to 10 mm or more.

[0014] Regarding the specifications such as the thickness of each layer shown in FIG. 2 and the period Lx, etc., it is possible to set them so that the sound absorption effect in the low frequency band is better or does not decrease compared to the conventional case. For example, a combination that shows a good solution in the low frequency band with the specifications as parameters can be found by Bayesian optimization.

[0015] <Cylindrical closed space> As described above, the cavity C in this embodiment is a cylindrical closed space formed in the viscoelastic body. Here, the cylindrical closed space may have a shape in which the diameter of the upper surface of the cavity is smaller than the diameter of the bottom surface, but it is desirable to have a larger space volume than the conical closed space. In particular, by making the upper surface on the outermost PS side of the cavity C a flat surface of sufficient size, the blockage at the top can be alleviated under high water pressure, and a performance degradation can be suppressed. Also, when the cavity C is molded by a mold, the tip of a mold with a sharp conical top is likely to wear and the maintenance cost increases, but by flattening the top, the wear can be suppressed and the maintenance cost can be reduced.

[0016] The shape of the cavity C in this embodiment will be described with reference to FIGS. 3 and 4. Hereinafter, let the diameter of the upper surface (first flat surface) of the cavity C, which is a cylindrical closed space, in the Z direction be D1, the diameter of the bottom surface (second flat surface) be D2, and the thickness be L.

[0017] The cavity C shown in FIG. 3(A) is a cylindrical closed space and D1 = D2. However, the cavity C is not limited to a cylindrical shape, and as shown in FIG. 3(B), it can also be set such that D1 < D2 and D1 ≠ 0 in order to give a gradient to the acoustic impedance. In either case, by making the upper surface of the cavity C a flat surface of sufficient size, the blockage at the top can be alleviated under high water pressure, and a performance degradation can be suppressed.

[0018] Furthermore, as shown in Figures 4(A) and 4(B), by making the edges of the top surface (first flat surface) and bottom surface (second flat surface) of the cylindrical cavity C curved, it is possible to further reduce maintenance costs while maintaining acoustic performance.

[0019] <Specific gravity composition of viscoelastic body> 2 above illustrates a multi-layer hollow acoustic material A in which three layers (a back layer A1, a middle layer A2, and a surface layer A3) are stacked in the Z direction, but the present invention is not limited to this. The viscoelastic body 100 of the multi-layer hollow acoustic material A can also be configured from N layers (N is an integer of 2 or more) of viscoelastic bodies as shown in FIG.

[0020] In Figure 5, the multilayer acoustic cavity material A has a structure in which the first layer, the second layer, ..., the Nth layer are stacked in the Z direction, that is, from the back surface PB to the top surface PS. Furthermore, the viscoelastic material of each layer i (i = 1, 2, ... N) has a specific gravity ρ i It is desirable that the specific gravity of the adjacent layers be set so that the specific gravity of the top surface side is equal to or greater than the specific gravity of the back surface side. j ≧ρ j-1 The specific gravity ρ i is in the range of about 1.0 to 2.0.

[0021] Cylindrical cavities C are arranged in a predetermined periodic pattern within the viscoelastic body 100 of the multilayer hollow acoustic material A having such a specific gravity configuration. The cavities C may be formed within a single layer, or may be formed across multiple layers as described above.

[0022] 2. Second embodiment According to the above-described embodiment, a plurality of cavities C form one alignment layer, but this is not limited to this, and a configuration in which alignment layers of a plurality of cavities are stacked in the Z direction may also be used.

[0023] <Example 1> In FIG. 6, the multi-layer cavity acoustic material A has a plurality of cavities C inside the viscoelastic body 100. U and C LEach cavity has a structure in which the cavities are arranged in layers (two-layer structure). L is the thickness t from the back surface PB A1 The cavities C are arranged in a plane with the viscoelastic layer in between, forming the first arrangement layer. U is the thickness t from the outermost surface PS A3 The viscoelastic layer is separated by a plane arrangement, forming the second arrangement layer. As mentioned above, the internal structure is destroyed by water pressure, and the cavity C U and C L To prevent water from entering the A1 and t A3 It is desirable that both be 10 mm or more.

[0024] Cavity C in the first alignment layer L are arranged in the XY plane in a periodic unit of length Lx as described above, and the cavities C in the second arrangement layer are U The cavities C in the first alignment layer are also arranged in the XY plane in a periodic unit of the same length Lx. L The periodic pattern of the second alignment layer and the cavity C U The phase of the periodic pattern of cavity C is the same as that of cavity C. U and C L The central axes of each of the elements coincide with the central axis O, and they overlap in the Z-axis direction.

[0025] Each cavity C L and each cavity C U has a cylindrical closed space having a shape as shown in FIG. 3 or FIG. 4. L is formed in a single layer A2, and a cavity C U is formed across the layers A2 and A3. The specific gravities of the back layer A1, the intermediate layer A2 and the surface layer A3 are set to increase in this order within a range of 2.0 to 1.0.

[0026] The cavities in each layer are cylindrical closed spaces of the same size, but the sizes of the cavities differ between different layers. Here, the cavity C in the first layer L The thickness of the cavity C of the second alignment layer U The thickness of the cavity C is shorter than that of the cavity C. Uand C L By providing the first and second alignment layers with the same central axis, it is possible to disperse the deformation of the cavity due to high water pressure and suppress the rate of volume reduction. U and C L By reducing deformation and shrinkage, the sound absorption effect in the low frequency range can be maintained even under high water pressure.

[0027] Furthermore, when setting the cavity ratio (void ratio) to achieve the desired sound absorption effect in the low-frequency range, forming multiple cavities rather than a single cavity allows for a smaller volume per cavity, reducing the rate at which the cavity volume decreases due to water pressure. While an example of a two-layer cavity arrangement is shown here, multi-layer cavity acoustic material A can also have three or more cavity arrangement layers. Furthermore, instead of a three-layer structure consisting of a back layer A1, a middle layer A2, and a surface layer A3, multiple cavity arrangement layers can be formed in a viscoelastic body with any laminated structure, as shown in Figure 5.

[0028] <Example 2> In the first example described above, a multi-layered acoustic material was illustrated in which the phases of the periodic patterns of the cavities in each arrangement layer were aligned, but the present invention is not limited to this. For example, even if the periodic patterns in the upper and lower arrangement layers are shifted by half a period, the same sound absorption effect as in the above-mentioned embodiment can be obtained in a high water pressure environment.

[0029] As shown in Fig. 7, an intermediate layer A2 and a surface layer A3 are laminated on a back surface layer A1 in the same manner as in the second embodiment. L are formed in a first periodic pattern, and the surface layer A3 has a cavity C U is formed by the second periodic pattern. The first periodic pattern and the second periodic pattern have the same period Lx, but the phase is shifted by Lx / 2. Therefore, when viewed from the incident direction of the incident wave, the cavity C L and Cavity C U If the diameters D1 and D2 of the cavity are less than half of the periodic unit Lx, the cavity C L and Cavity C U It is separate from.

[0030] The first periodic pattern and the second periodic pattern may be misaligned by Lx / 2 in the X direction, by Lx / 2 in each of the X and Y directions, or by Lx / 2 in both the X and Y directions. L The number of cavities C U The number may be set to be greater than the number of

[0031] 3. Third embodiment The multilayer cavity acoustic material according to the third embodiment of the present invention has a structure in which a fiber reinforced plastics (hereinafter referred to as FRP) layer is laminated on the backmost surface PB and / or the topmost surface PS of the multilayer cavity acoustic material according to the first embodiment described above. By providing an FRP layer, it is possible to further suppress volumetric contraction and deformation of the cavities due to water pressure, and to prevent deterioration of acoustic performance, especially a decrease in sound absorption effect in the low frequency range.

[0032] Hereinafter, a multilayer hollow acoustic material in which FRP layers are laminated on both the back surface PB and the top surface PS will be described with reference to Fig. 8. Since the configuration other than the FRP layers is the same as that of the first embodiment shown in Figs. 2 to 5, the same reference numbers or symbols are used and the description will be omitted.

[0033] 8, an example of a multi-layer hollow acoustic material according to this embodiment has an FRP layer 101 on the back surface PB side of a back layer A1, and an FRP layer 102 on the front surface PS side of a surface layer A3. The thickness d of each FRP layer is preferably about 1 / 16 to 1 / 4 of the wavelength of the highest frequency in the frequency band of sound waves to be attenuated.

[0034] The fiber reinforced plastic of the FRP layers 101 and 102 is a reinforced plastic whose strength is improved by compounding fibers such as glass fiber, resin fiber, and carbon fiber with epoxy resin, phenolic resin, etc. Fiber reinforced plastic has a higher specific strength than metal materials and can be made lighter than metal materials with the same strength.

[0035] 4. Fourth embodiment The multi-layer cavity acoustic material according to the fourth embodiment of the present invention has a structure in which an FRP layer is laminated on the backmost surface PB and / or the topmost surface PS of the multi-layer cavity acoustic material according to the second embodiment described above. By providing an FRP layer, it is possible to further suppress volumetric contraction and deformation of the cavities due to water pressure, and to prevent deterioration of acoustic performance, especially a decrease in sound absorption effect in the low frequency range.

[0036] <Example 1> A first example of a multilayer hollow acoustic material in which FRP layers are laminated on both the back surface PB and the top surface PS will be described with reference to Figure 9. Since the configuration other than the FRP layers is the same as the first example of the second embodiment shown in Figure 6, the same reference numbers or characters are used and the description will be omitted.

[0037] 9, an example of a multi-layer hollow acoustic material according to this embodiment has an FRP layer 101 on the rearmost side PB of a rear layer A1, and an FRP layer 102 on the frontmost side PS of a surface layer A3. The thickness d of each FRP layer is preferably about 1 / 16 to 1 / 4 of the wavelength of the highest frequency in the frequency band of sound waves to be attenuated. The other configurations and functions of the FRP layers are as described in the third embodiment.

[0038] <Example 2> A second example of a multilayer hollow acoustic material in which FRP layers are laminated on both the back surface PB and the top surface PS will be described with reference to Figure 10. Since the configuration other than the FRP layers is the same as the second example of the second embodiment shown in Figure 7, the same reference numbers or characters are used and the description will be omitted.

[0039] As shown in Figure 10, an example of a multi-layer hollow acoustic material according to this embodiment has an FRP layer 101 on the rearmost side PB of a back layer A1, and an FRP layer 102 on the frontmost side PS of a surface layer A3. The thickness d of each FRP layer is preferably about 1 / 16 to 1 / 4 of the wavelength of the highest frequency in the frequency band of sound waves to be attenuated. The other configurations and functions of the FRP layers are as described in the third embodiment. [Explanation of symbols]

[0040] 100 Viscoelastic body 101, 102 Fiber reinforced plastic (FRP) layer A Multilayer cavity acoustic material C, C U , C L cavity A1 back layer A2 middle layer A3 surface layer Lx period unit O center axis PB backmost PS Top surface

Claims

1. An acoustic material having a plurality of cavities provided inside a viscoelastic body having an outermost surface and an outermost back surface, A multilayer cavity acoustic material characterized in that the viscoelastic body forms a plurality of layers between the outermost surface and the outermost back surface, and each of the plurality of cavities forms a cylindrical closed space.

2. 2. A multi-layer cavity acoustic material according to claim 1, wherein the plurality of cavities are formed across at least two of the plurality of layers.

3. The multilayer cavity acoustic material described in claim 1, characterized in that the cylindrical closed space has a first flat surface on the outermost surface side and a second flat surface on the outermost back surface side, and the diameter of the first flat surface is greater than zero and less than or equal to the diameter of the second flat surface.

4. 4. The multilayer hollow acoustic material according to claim 1, wherein the edge portion of the first flat surface and the edge portion of the second flat surface are curved surfaces.

5. 4. The multi-layer hollow acoustic material according to claim 1, wherein the plurality of cavities are filled with a gas.

6. A multilayer hollow acoustic material according to any one of claims 1 to 3, characterized in that the layer on the outermost surface side of the plurality of layers of viscoelastic material has a higher specific gravity than the layer on the outermost back side.

7. 7. The multi-layer hollow acoustic material according to claim 6, wherein the plurality of layers of the viscoelastic material have a specific gravity of 1.0 to 2.

0.

8. A multilayer cavity acoustic material as described in any one of claims 1 to 3, characterized in that the multiple cavities consist of one or more arrangement layers and have one or more cavities in the thickness direction of the cylindrical closed space.

9. a viscoelastic body having a width of 10 mm or more between a first flat surface on the outermost surface side of the cavity closest to the outermost surface and the outermost surface; a space between the rear surface and a second flat surface on the rear surface side of the cavity closest to the rear surface, the space being made of a viscoelastic material with a thickness of 10 mm or more; A multilayer hollow acoustic material according to any one of claims 1 to 3.

10. A multilayer hollow acoustic material according to any one of claims 1 to 3, further comprising a fiber-reinforced plastic layer provided on at least one of the outermost surface and the outermost back surface.

11. 11. The multilayer hollow acoustic material according to claim 10, wherein the thickness of the fiber reinforced plastic layer is 1 / 16 to 1 / 4 of the wavelength of the highest frequency in the frequency band of sound to be attenuated.

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