Multilayer hollow acoustic material

Abstract

To provide an acoustic material having a new structure that can prevent reduction in sound absorption effect in a low frequency region even at a higher pressure.SOLUTION: A multilayer hollow acoustic material A is provided with a plurality of hollows CU and CL within a viscoelastic body 100 having an outermost surface PS and a rearmost surface PB. Each of the plurality of hollows CU and CL forms a closed space having a predetermined shape. The plurality of hollow CU and CL form a plurality of array layers laminated in a propagation direction of sound waves. The hollows in the array layers are formed in a pattern of a predetermined cycle (Lx).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 pyramidal or frustum shape, the sound absorbing effect in a desired frequency range is improved.

[0003] Patent Document 2 discloses a sound absorbing layer structure in which cavities are provided in a viscoelastic plate and a plurality of layers are laminated so that the cavities are different in each layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 59-200296 [Patent Document 2] Special Publication No. 61-055859 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the underwater sound absorber disclosed in the above-mentioned Patent Document 1, as the water pressure increases, each cavity is compressed and the shape is deformed. The reduction in volume and deformation of the cavities leads to a decrease in the sound absorbing effect, particularly in the low frequency band.

[0006] In the above-mentioned Patent Document 2, the shapes of the cavities in the sound absorbing layers are different, which complicates the manufacturing process and increases the production cost.

[0007] The present invention has been devised in consideration of the above-mentioned circumstances, and an object of the present invention is to provide an acoustic material of a new structure that can suppress a reduction in sound absorption effect in the low frequency range even at high pressure and can be easily manufactured. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, one embodiment of the present invention is characterized in that a plurality of cavities are provided inside a viscoelastic body having a top surface and a back surface, each of the plurality of cavities forms a closed space of a predetermined shape, the plurality of cavities form a plurality of arrangement layers stacked in the direction of propagation of sound waves, and the cavities of the plurality of arrangement layers are formed in a predetermined periodic pattern. Furthermore, according to one embodiment of the present invention, the periodic patterns of at least two of the alignment layers may be aligned to match each other, and at least two cavities may be arranged to spatially overlap with each other in a propagation direction of the sound wave. Furthermore, according to one embodiment of the present invention, the periodic patterns of at least two of the plurality of alignment layers can be arranged to be shifted by half a period in at least one alignment direction. Furthermore, according to one embodiment of the present invention, each of the plurality of cavities can form a cone-shaped closed space whose cross-sectional area decreases from the rear surface to the front surface. Also, according to one embodiment of the present invention, each of the plurality of cavities may be formed in each of the plurality of viscoelastic layers. According to an embodiment of the present invention, each cavity formed in at least one of the plurality of orientation layers may be formed to penetrate one or more of the plurality of viscoelastic layers. Furthermore, according to one embodiment of the present invention, a viscoelastic material having a thickness of 10 mm or more may be provided between the topmost portion of a cavity in an alignment layer among the plurality of alignment layers that is closest to the outermost surface and the outermost surface, and a viscoelastic material having a thickness of 10 mm or more may be provided between the bottommost portion of a cavity in an alignment layer among the plurality of alignment layers that is closest to the backmost surface and the backmost surface. Effect of the Invention

[0009] According to one embodiment of the present invention, multiple cavity arrangement layers are stacked inside a viscoelastic body, each cavity has a predetermined shape, and the cavities in the multiple arrangement layers have a predetermined periodic pattern, so that deformation and blockage of the cavities are suppressed even at high pressure, reduction in sound absorption effect in the low frequency range can be suppressed, and manufacturing is made easier. Furthermore, according to one embodiment of the present invention, by arranging the periodic patterns of the orientation layers to match or to be shifted by half a period, it is possible to suppress a reduction in the sound absorption effect in the low frequency range even at high pressure, and it is possible to facilitate manufacturing. Furthermore, according to one embodiment of the present invention, each cavity forms a closed space having a cone shape, so that reflection of sound waves can be suppressed. Furthermore, according to one embodiment of the present invention, since a cavity is formed in each of the multiple viscoelastic layers, alignment of the cavity during lamination becomes easy, facilitating manufacture. Furthermore, according to one embodiment of the present invention, since the cavities are formed penetrating the viscoelastic layer, cavities of any size and height can be easily formed. 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 in which the cavity alignment layer is formed, deformation and blockage of the cavities can be suppressed even under high pressure. [Brief description of the drawings]

[0010] [Figure 1] 1 is a perspective view illustrating a schematic configuration of a multi-layer hollow acoustic material according to one embodiment of the present invention; [Diagram 2] 1 is a side cross-sectional view showing a schematic configuration of a multi-layered hollow acoustic material according to the present embodiment. [Diagram 3] 3 is a side cross-sectional view showing a schematic diagram of a first example of a layered configuration of a periodic unit in the multilayer hollow acoustic material shown in FIG. 2. [Figure 4] FIG. 3 is a plan view of the multi-layer hollow acoustic material illustrated in FIG. 2. [Diagram 5] 11 is a side cross-sectional view showing a schematic diagram of a second example of a periodic unit lamination configuration in a multi-layer hollow acoustic material according to the present embodiment. FIG. [Figure 6]13 is a side cross-sectional view showing a schematic diagram of a third example of a periodic unit layered configuration in a multi-layer hollow acoustic material according to the present embodiment. FIG. [Figure 7] 1 is a perspective view illustrating a schematic configuration of a multi-layer hollow acoustic material according to another embodiment of the present invention; [Figure 8] 8 is a plan view showing a schematic diagram of a first arrangement example of the multi-layered hollow acoustic material shown in FIG. 7. [Figure 9] 8 is a plan view showing a schematic diagram of a second arrangement example of the multi-layered hollow acoustic material shown in FIG. 7. [Figure 10] 8 is a plan view showing a schematic diagram of a third arrangement example of the multi-layered hollow acoustic material shown in FIG. 7. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the 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 in a liquid that propagates sound, and "underwater" includes underwater environments such as the sea, rivers, lakes, and anechoic tanks.

[0012] 1. One embodiment As shown in Fig. 1, the multi-layered hollow acoustic material A according to this embodiment is attached to a rear structure M, and absorbs and attenuates incident waves propagating through a medium. Here, the rear structure M is an underwater structure, and is made of a strong member such as a metal plate such as iron, concrete, or FRP (Fiber Reinforced Plastics). Hereinafter, for convenience, the directions in which the rear and front surfaces of the multi-layered hollow acoustic material A extend are defined as the X-axis and Y-axis, and the direction perpendicular to these axes is defined as the Z-axis. Here, the incident wave is assumed to be incident in the direction of the Z-axis.

[0013] The multi-layered hollow acoustic material A according to the present embodiment has a plurality of cavities C inside a plate-shaped viscoelastic body 100. U and C L Each of these is arranged in layers (two-layer structure). U and C Lis a closed space within the viscoelastic body 100. The viscoelastic body 100 is made of a material having a sound absorbing effect, such as rubber (for example, chloroprene rubber, nitrile rubber (NBR), or urethane), and has a specific gravity of about 2.0 to 1.0.

[0014] cavity C U and C L has a cone shape, and the sound absorption frequency can be changed by changing its dimensions and the combination of dimensions. Here, the cone shape refers to a shape in which the cross-sectional area gradually decreases from the back surface of the multi-layered hollow acoustic material A to the front surface (i.e., in the positive direction of the Z axis). Examples of cone shapes include a cone shape, a truncated cone shape, and a cone-dome shape with a dome-shaped tip. Below, as an example, a cone-shaped cavity C U and C L shall be illustrated.

[0015] The configuration of the multi-layer hollow acoustic material A according to this embodiment will be described in more detail below with reference to FIGS.

[0016] In FIG. 2 and FIG. 3, the multi-layered hollow acoustic material A has a plurality of cavities C inside a plate-shaped viscoelastic body 100. U and C L Each of these has a layered structure (two-layer structure). L is the thickness t from the back surface PB A1 The viscoelastic body 100 is arranged in a plane and constitutes a first arrangement layer. U is the thickness t from the top surface PS A4 The viscoelastic bodies 100 are arranged in a plane with each other and form a second alignment layer.

[0017] Cavity C of the first alignment layer L are arranged on the XY plane as shown in Fig. 4 in a periodic unit of length Lx, and the cavities C in the second arrangement layer are arranged in the same manner. 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 CL The central axes of each of the vertices coincide with the central axis O and overlap in the Z-axis direction.

[0018] As shown in FIG. 3, each cavity C L has a conical shape, and the diameter of its base is D A2 , height H A2 In addition, each cavity C U Also has a conical shape, and the diameter of its base is D A3 , height H A3 The viscoelastic body 100 is composed of a plurality of viscoelastic layers, specifically, from the back surface PB to the front surface PS, the back surface layer A1, the intermediate layer A2, and the surface layer A3 are arranged in this order. The thicknesses of the back surface layer A1, the intermediate layer A2, and the surface layer A3 are respectively t A1 , t A2 and t A3 Let us assume that.

[0019] The back layer A1, the intermediate layer A2 and the surface layer A3 may be integrally molded with a viscoelastic material, or may be formed by sequentially attaching separate plate-like viscoelastic bodies (viscoelastic layers). For example, a cavity C is formed on the plate-like back layer A1. L The intermediate layer A2 is attached on which recesses in the shape of a side of a cone are formed in a predetermined periodic pattern. U The surface layer A3, which has the same periodic pattern of recesses in the shape of a cone on the side, is attached to the intermediate layer A2 while aligning the central axis O. L The first alignment layer is formed, and the cavity C is formed in the surface layer A3. U The cavities in each layer have the same pyramidal shape but different sizes, but are formed in the same periodic pattern, which makes manufacturing easier and reduces production costs.

[0020] cavity C L Distance t from the bottom surface of the A1 is the thickness of the back side of the viscoelastic body 100. U Distance t from the apex to the top surface PS A4 is the thickness of the front surface side of the viscoelastic body 100. Therefore, the thickness of the rear surface side t A1 and surface thickness t A4It is necessary to determine the pressure resistance performance. In this embodiment, the internal structure is destroyed by water pressure, and the cavity C U and C L For example, thickness t A1 and t A4 It is desirable to set both to 10 mm or more.

[0021] cavity C U and C L By providing the first and second alignment layers with the central axes of the layers aligned, the deformation of the cavity caused by high water pressure can be dispersed, and the rate of volume reduction can be suppressed. U and C L By mitigating deformation and shrinkage, it is possible to maintain the sound absorbing effect in the low frequency range even under high water pressure.

[0022] In addition, when the ratio of cavities (porosity) is set to obtain a desired sound absorbing effect in the low frequency range, forming multiple cavities rather than one cavity allows the volume of each cavity to be smaller, and the rate of reduction in cavity volume due to water pressure can be reduced. The specific gravity of the laminated viscoelastic body 100 is about 2.0 to 1.0, but it is desirable to form it so that the specific gravity gradually increases from the back surface PB to the front surface PS.

[0023] The parameters shown in Fig. 3 can be set so that the sound absorption effect, especially in the low frequency band, is better than before or does not decrease. For example, a combination that shows a good solution in the low frequency band with the parameters of the parameters can be found by Bayesian optimization. For example, it can be configured with the following ratios.

[0024] If the length of the periodic unit is Lx, then Thickness of the middle layer A2 t A2 =0.4Lx~0.6Lx approx. Thickness of surface layer A3 t A3 =0.75Lx approx. Thickness of the middle layer A2 t A2 Cavity C L Height H A2 Ratio of: H A2 / t A2 = 0.2 Thickness of surface layer A3 t A3 Cavity C U Height H A3 Ratio of: H A3 / t A3 =0.1~0.2 ·Cavity C for periodic unit length Lx L Diameter D A2 Ratio of: D A2 / Lx=0.5 approx. ·Cavity C for periodic unit length Lx U Diameter D A3 Ratio of: D A3 / Lx=0.5 approx. In addition, the thickness t A1 and t A4 The above parameters, especially t A2 , H A2 / t A2 , H A3 / t A3 , D A2 / Lx and D A3 It is desirable to determine the internal structure of the multilayer hollow acoustic material A within the range of / Lx.

[0025] <Layer configuration example> Although the above description has been given based on the two-layer hollow structure shown in Fig. 3, the present invention is not limited to this structure. Other structure examples will be described below.

[0026] As shown in FIG. 5, the multi-layered hollow acoustic material A may have three hollow arrangement layers in the viscoelastic body 100. That is, two intermediate layers A2(1) and A2(2) are provided between the back layer A1 and the surface layer A3, and a hollow C is provided in the intermediate layer A2(1). L1 The first arrangement layer has a cavity C in the intermediate layer A2(2). L2 The second arrangement layer has a cavity C in the surface layer A3. U The arrangement of the cavities in each alignment layer and the method of manufacturing the same are shown in FIG. 2. L1 , C L2 and CU have their central axes coinciding with the central axis O. In the same manner, a multi-layered hollow acoustic material can be constructed having five or more viscoelastic layers and four or more alignment layers.

[0027] As illustrated in FIG. 6, the cavity may be formed through a plurality of layers. When the multi-layered cavity acoustic material A has two intermediate layers A2(1) and A2(2) between the back layer A1 and the surface layer A3, the cavity C of the first arrangement layer L is formed in the intermediate layer A2(1), and the cavity C of the second alignment layer U is formed penetrating the surface layer A3 and the intermediate layer A2(2). In this manner, any cavity can be formed penetrating multiple viscoelastic layers.

[0028] 2. Other embodiments In the above embodiment, a multi-layered hollow acoustic material in which the phases of the periodic patterns of the cavities in each arrangement layer are in phase with each other is exemplified, 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 absorbing effect as in the above embodiment can be obtained in a high water pressure environment.

[0029] As shown in FIG. 7, the internal structure of the multi-layered hollow acoustic material A according to this embodiment is as follows. As in the above embodiment, an intermediate layer A2 and a surface layer A3 are laminated on a back layer A1. The intermediate layer A2 has a cavity C. 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 are out of phase with each other by Lx / 2. Therefore, when viewed from the incident direction of the incident wave, the cavity C L and Cavity C U The diameter of the cavity D A2 and D. A3 If is less than half the period unit Lx, the cavity C is L and Cavity C U It is separate from.

[0030] 8 illustrates a case where the first periodic pattern and the second periodic pattern are offset by Lx / 2 in the X direction, FIG. 9 illustrates a case where the first periodic pattern and the second periodic pattern are offset by Lx / 2 in the X direction and the Y direction, respectively, and FIG. 10 illustrates a case where the first periodic pattern and the second periodic pattern are offset by Lx / 2 in both the X direction and the Y direction. In the pattern illustrated in FIG. 9, the cavities C arranged in the intermediate layer A2 L The number of cavities C in the surface layer A3 U It is set to be greater than the number of [Explanation of symbols]

[0031] 100 Viscoelastic body A Multilayer cavity acoustic material A1 back layer A2, A2(1), A2(2) Middle layer A3 surface layer C, C U , C L cavity 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 a top surface and a bottom surface, Each of the plurality of cavities forms a closed space of a predetermined shape, The plurality of cavities form a plurality of arrangement layers stacked in the propagation direction of the sound wave, and the cavities of each arrangement layer are formed in a predetermined periodic pattern. A multilayer hollow acoustic material characterized by:

2. The multilayer cavity acoustic material described in claim 1, characterized in that, in the multiple arrangement layers, the phases of the periodic patterns of at least two arrangement layers are consistent, and at least two cavities are arranged to spatially overlap with respect to the propagation direction of the sound wave.

3. 2. The multi-layer hollow acoustic material according to claim 1, wherein the periodic patterns of at least two of the plurality of orientation layers are shifted by half a period in at least one orientation direction.

4. A multi-layer hollow acoustic material as described in any one of claims 1 to 3, characterized in that each of the multiple cavities forms a cone-shaped closed space whose cross-sectional area decreases from the back surface to the front surface.

5. 4. A multi-layer hollow acoustic material according to claim 1, wherein each of the plurality of cavities is formed within each of the plurality of viscoelastic layers.

6. A multilayer hollow acoustic material as described in any one of claims 1 to 3, characterized in that each cavity formed in at least one of the multiple alignment layers is formed by penetrating one or more of the multiple viscoelastic layers.

7. a gap between the outermost surface and the uppermost portion of a cavity in the orientation layer closest to the outermost surface among the plurality of orientation layers is 10 mm or more and is made of a viscoelastic material; a gap between the rear surface and a lowest portion of a cavity in the alignment layer closest to the rear surface among the plurality of alignment layers is 10 mm or more and is made of a viscoelastic material; A multi-layer hollow acoustic material according to any one of claims 1 to 3.

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