Lightweight asymmetric thin film metamaterial for low frequency sound isolation

Abstract

The application relates to a low-frequency sound insulation and noise reduction technology, in particular to a light-weight asymmetric film metamaterial for low-frequency sound insulation, which comprises a film, asymmetric annular masses acting as acoustic metamaterial masses and pasted on the same side surface of the film, and frames pasted on the two side surfaces of the film; wherein four same asymmetric annular masses are symmetrically distributed in a cross shape on the same side surface of the film, the directions are consistent, and the film is tightly pasted between two same frames; the above structure constitutes a cell of the acoustic metamaterial, and the acoustic metamaterial is formed by uniformly and closely periodically arranging the cells in the horizontal and vertical directions on a plane. The structure generates a reverse resonance mode through the local resonance characteristics of the whole system of the film and the mass, and generates a new asymmetric reverse resonance mode through the structure of the asymmetric mass, so that the sound insulation peaks increase, the effective sound insulation frequency band can be widened, and the position and density of the sound insulation peaks can be effectively adjusted by changing the size parameters of the mass and the film to meet different working scene requirements.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of low-frequency sound insulation noise reduction technology, and in particular to a lightweight asymmetric film metamaterial for low-frequency sound insulation. BACKGROUND

[0002] For many years, due to the rapid development of industrial technology, many industrial fields have produced noise problems, and this problem has also disturbed people's life, and because noise has serious harm to people's physical and mental health, the control of noise has also become an important indicator of environmental protection. Sound insulation as an important noise reduction method has been widely used in life and industry. By adding sound insulation materials, the propagation of noise can be blocked, so that noise cannot be transmitted into the ear. However, there are still many problems in the field of sound insulation, for example, low-frequency noise has very strong propagation ability, and ordinary sound insulation materials have weak blocking ability, and in order to block low-frequency noise, a very thick and heavy sound insulation structure is often designed, so how to realize high-performance sound insulation under the premise of lightweight has become a difficult problem.

[0003] In recent years, the emergence of acoustic metamaterials has opened up a new way for sound insulation. Acoustic metamaterials are a kind of periodic structure constructed artificially, which is different from traditional materials in nature and can break the law of mass to produce special physical properties. Thin film metamaterials, as typical sound insulation metamaterials, can exhibit negative equivalent mass characteristics under the excitation of specific frequency sound waves by constructing local resonance structures, and exhibit good sound insulation effect in the low frequency band, and almost completely block sound waves in a specific frequency band, and its mass is light and the volume is small, which has become a research object that has attracted much attention in recent years. However, the traditional thin film acoustic metamaterial also has obvious shortcomings: the frequency range with outstanding sound insulation effect is narrow, and the effect is poor in the remaining frequency range; the anti-resonance mode is single and can only work in a specific frequency band. SUMMARY

[0004] In order to solve the problems in the prior art, the present application provides a lightweight asymmetric film metamaterial for low-frequency sound insulation, which is configured in an asymmetric circular ring form, produces multiple sound insulation peaks, widens the sound insulation frequency band, overcomes the narrow sound insulation frequency domain of traditional thin film metamaterials, and meets the requirements of lightweight and small volume.

[0005] In order to solve the technical problems proposed in the present application, the technical scheme adopted by the present application is:

[0006] A light-weight asymmetric thin film metamaterial for low-frequency sound insulation, comprising a thin film, asymmetric annular masses as the quality blocks of the acoustic metamaterial pasted on the same side surface of the thin film, and frames pasted on the two side surfaces of the thin film; wherein four identical asymmetric annular masses are symmetrically distributed in a cross shape on the same side surface of the thin film, and the directions are consistent; the thin film is tightly pasted between two identical frames; the above structure constitutes a unit cell of the metamaterial, and the metamaterial is formed by uniformly and closely periodically arranging the unit cells in the horizontal and vertical directions on a plane.

[0007] In the above scheme, the thin film is square in shape, with a side length of L and a thickness of d = 0.02-0.03 mm; the thin film is connected and fixed by being tightly pasted around the frame, and the internal uniform tension of the thin film is T due to the tightness.

[0008] In the above scheme, the asymmetric annular mass is a circular ring formed by removing a non-concentric inner cylinder from a middle of an outer cylinder, and the outer cylinder and the inner cylinder have a certain eccentric distance; the outer cylinder has a radius of R, the inner cylinder has a radius of r, the eccentric distance between the large cylinder and the small cylinder is l0, and the overall height of the circular ring is h. k The mass of the asymmetric annular mass is 0.15-0.25 g.

[0009] In the above scheme, the four identical asymmetric annular masses have consistent eccentric directions, and the distance between adjacent two asymmetric annular masses in the horizontal and vertical directions is equal, and the distance is x0; the four identical asymmetric annular masses are placed in the middle of the thin film.

[0010] In the above scheme, the frame is square, with an outer side length of L = 19-34 mm, an inner side length of l = 15-30 mm, a difference between the outer and inner side lengths of 4 mm, and a thickness of h; the outer side length of the frame is equal to the side length of the thin film, and the two frames are respectively pasted on the two side surfaces of the thin film and can completely coincide when pasted.

[0011] In the above scheme, the thin film, the asymmetric annular mass, and the frame are all pasted and connected by glue.

[0012] In the above scheme, the thin film is one of a polyetherimide film and a polyethylene film.

[0013] In the above scheme, the asymmetric annular mass is one of a steel asymmetric annular mass and a copper asymmetric annular mass.

[0014] In the above scheme, the frame is one of an aluminum frame and an aluminum alloy frame.

[0015] Preferably, the cell structure has strong adjustability, the length, thickness of the film and the size of the asymmetric circular ring can be adjusted according to the specific sound insulation frequency band requirements to meet the sound insulation requirements of different frequency noise conditions.

[0016] Compared with the prior art, the beneficial effects of the present application are:

[0017] (1) The low-frequency sound insulation light asymmetric film metamaterial provided by the present application adopts a film and a mass block as a sound insulation main body, adopts a frame to meet the strength and rigidity requirements, and the prepared metamaterial has small overall structure surface density, and can produce good sound insulation effect under the premise of light weight and small volume.

[0018] (2) The mass block in the present application achieves the effect of asymmetry by being configured as an asymmetric circular ring, and the degree of asymmetry of the structure is convenient to adjust, and this configuration makes the overall structure of the metamaterial produce new asymmetric modes in the low-frequency band, increases the anti-resonance mode, thereby increasing the number of sound insulation peaks, widening the low-frequency sound insulation frequency band, and making the sound insulation applicable conditions wider.

[0019] (3) The film and the asymmetric mass block in the present application together constitute a spring oscillator system, by adjusting the parameters of the mass block and the film, the anti-resonance mode frequency of the spring oscillator system can be changed, the sound insulation peak size and position can be tuned, and different use requirements can be met. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 It is a schematic diagram of the cell structure of the low-frequency sound insulation light asymmetric film metamaterial of embodiment 1;

[0021] Figure 2 It is a top view of the cell structure of the low-frequency sound insulation light asymmetric film metamaterial of embodiment 1;

[0022] Figure 3 It is a side view of the film, the asymmetric circular ring and the frame in the cell structure of the low-frequency sound insulation light asymmetric film metamaterial of embodiment 1;

[0023] Figure 4 It is a comparison diagram of the theoretical calculation sound insulation amount and the simulation calculation sound insulation amount of the cell structure of the low-frequency sound insulation light asymmetric film metamaterial of embodiment 1;

[0024] Figure 5 It is five eigenmode diagrams of the cell structure of the low-frequency sound insulation light asymmetric film metamaterial of embodiment 1;

[0025] Figure 6 It is a comparison diagram of the sound insulation amount of the cell structure and the mass law of the low-frequency sound insulation light asymmetric film metamaterial of embodiment 1;

[0026] Figure 7This is a comparison diagram of the sound insulation properties of the cell structure of the lightweight asymmetric thin-film metamaterial for low-frequency sound insulation in Example 1 and the structure of a traditional thin-film metamaterial.

[0027] Explanation of reference numerals in the attached figures

[0028] 1. Thin film; 2. Asymmetric ring; 3. Framework. Detailed Implementation

[0029] To better understand the present invention, the following description, in conjunction with the accompanying drawings and embodiments, further clarifies the content of the present invention, but the present invention is not limited to the following embodiments.

[0030] Example 1

[0031] A lightweight asymmetric thin-film metamaterial for low-frequency sound insulation includes a polyetherimide membrane 1, four identical steel asymmetric rings 2 glued to the same side surface of the polyetherimide membrane 1, and two identical aluminum square frames 3 glued to both sides of the polyetherimide membrane 1. Figures 1-3 As shown, four asymmetric steel rings 2 are symmetrically distributed in a cross shape on the same side surface of the polyetherimide film 1, with the eccentricity direction being consistent. The polyetherimide film 1 is tensioned and adhered between two aluminum square frames 3. The polyetherimide film 1 is square in shape, with a side length of L = 24 mm, a thickness of d = 0.025 mm, and an internal tension force of T = 120 N / m. The asymmetric steel rings 2 are formed by subtracting a non-concentric inner cylinder from an outer cylinder. There is a certain eccentricity distance l0 = 0.5 mm between the outer and inner cylinders. Each asymmetric steel ring has a mass of 0.2 g. The radius of the outer cylinder is R = 2.5 mm, the radius of the inner cylinder is r = 1.5 mm, and the overall height of the ring is h. k =2mm, the four steel asymmetric rings 2 are aligned in the same direction, and the horizontal and vertical distances between two adjacent steel asymmetric rings 2 are equal, with a distance of x0 = 10mm; the outer side length of the aluminum square frame 3 is L = 24mm, the inner side length is l = 20mm, and the thickness is h = 2mm; the outer side length of the aluminum square frame 3 is equal to the side length of the polyetherimide film 1, and the two aluminum square frames 3 are glued to the two sides of the polyetherimide film 1, and can completely overlap during the glued surface; it can be seen that the single cell structure of the lightweight asymmetric thin film metamaterial for low-frequency sound insulation in Example 1 is asymmetric.

[0032] The material parameters for this embodiment are shown in Table 1:

[0033] Table 1. Materials and parameters used in lightweight asymmetric thin-film metamaterials for low-frequency sound insulation.

[0034]

[0035] For further understanding of the present application, theoretical calculation is made on the single-cell structure of the lightweight asymmetric thin film metamaterial for low-frequency sound insulation described in Example 1 by using MATLAB software, and simulation calculation is made by using COMSOL Multiphysics software for comparison and verification, and the calculation frequency range is 50-1000Hz.

[0036] The sound insulation amount calculation formula obtained from the mass law is:

[0037]

[0038] Wherein, ρ0 and c0 are the density and sound speed of air respectively; m' is the equivalent mass density of the metamaterial, which can be calculated by the following formula:

[0039]

[0040] Wherein, b is the membrane excitation vector; B is a matrix in the standard eigenvalue equation Ax=k 2 Bx obtained from the vibration equation set of this mass-loaded membrane; the standard eigenvalue problem can be solved by using Arnoldi method and the eigenvalues and eigenvectors of the coupled system are obtained; Λ is a diagonal matrix composed of the eigenvalues, and X is a matrix in which the eigenvectors are arranged; I is the unit matrix.

[0041] Figure 4 The comparison chart of the theoretical calculation sound insulation amount and the simulation calculation sound insulation amount of the cell structure of the lightweight asymmetric thin film metamaterial for low-frequency sound insulation of Example 1 is shown in the figure, wherein the solid line is the theoretical calculation sound insulation amount curve, and the dotted line is the simulation calculation sound insulation amount curve. It can be seen from Figure 4 that the theoretical curve and the simulation curve are relatively consistent in most ranges, and the trend is very close, indicating that the calculation results of the theoretical formula are reliable. The structure has three sound insulation peaks, which are located at frequencies of about 500Hz, 617Hz and 674Hz, and the peak values are 72.3dB, 74dB and 69.2dB respectively. The first sound insulation peak is the main peak, and the reason for its occurrence is the anti-resonance mode generated by the spring oscillator system of the metamaterial itself, and two sound insulation sub-peaks also appear, which are due to the four new anti-resonance modes generated by the asymmetry of the structure.

[0042] Figure 5 The five eigenmodes of the cell structure of the lightweight asymmetric thin film metamaterial for low-frequency sound insulation of Example 1 (the aluminum square frame is assumed to be a rigid body, so its mode is ignored), the frequencies are 192.72Hz, 571.13Hz, 575.69Hz, 632.59Hz and 644.25Hz, which are consistent with Figure 4The frequencies of the sound insulation valleys in the sound insulation curve correspond well. The anti-resonance modes of thin-film metamaterials are a linear superposition of intrinsic modes; therefore, the intrinsic modes can reflect the characteristics of the anti-resonance modes. From Figure 5 It can be seen that the intrinsic modes (b) and (c), (d) and (e) have orthogonal symmetry. This is because the arrangement of the two sets of mass blocks has orthogonal symmetry. Therefore, although the two sets of modes are different, their modal frequencies are similar. The result is that the sound insulation peaks and valleys at similar positions are enhanced. Thus, there are two obvious secondary sound insulation peaks, and the total number of sound insulation peaks and valleys is three.

[0043] Figure 6 This is a comparison of the sound insulation properties of the cell structure and the mass law for the lightweight asymmetric thin-film metamaterial used for low-frequency sound insulation in Example 1. The solid line represents the sound insulation curve of the cell structure of the lightweight asymmetric thin-film metamaterial, and the dashed line represents the sound insulation curve of the mass law. The areal density of this lightweight asymmetric thin-film metamaterial for low-frequency sound insulation, calculated based on the selected material density and structural dimensions, is 3.539 kg / m³. 2 It is only comparable to an aluminum plate with a thickness of 1.31mm, making it extremely lightweight. The sound insulation value according to the mass law can be calculated by substituting the surface density into the mass law formula. From Figure 6 It can be seen that the low-frequency sound insulation performance of traditional homogeneous materials with the same surface density is very poor, with no frequency band exceeding 30dB. This also illustrates the necessity of using metamaterials in the field of low-frequency sound insulation and noise reduction. The lightweight asymmetric thin-film metamaterial for low-frequency sound insulation designed in this invention can break the mass law and achieve a maximum sound insulation peak of over 70dB. Therefore, it has extremely high application value as a lightweight low-frequency sound insulation material.

[0044] Figure 7 This is a comparison of the sound insulation properties of the cell structure of the lightweight asymmetric thin-film metamaterial for low-frequency sound insulation in Example 1 with those of a conventional thin-film metamaterial. The solid line represents the sound insulation curve of the cell structure of the lightweight asymmetric thin-film metamaterial, and the dashed line represents the sound insulation curve of the conventional thin-film metamaterial. The mass block of the conventional thin-film metamaterial is a typical cylinder. For comparison, the cylindrical mass block is set to have the same material, thickness, and weight as the asymmetric toroidal mass block, thus also having the same weight, number, and position. Figure 7It can be seen that the traditional thin film metamaterial does not show more sound insulation peaks compared with the asymmetric metamaterial, only one large main peak and one small secondary peak, which is just because of the limitation of the symmetric structure. Under the condition of consistent total weight, the sound insulation of the asymmetric model is obviously higher than that of the traditional model in more frequency bands, the average sound insulation of the asymmetric model in the shown frequency band reaches 23.334dB, which is more than 1dB higher than that of the traditional model 21.904dB, the effect is very obvious. And the frequency band of the sound insulation of the asymmetric model higher than 30dB is 422-536Hz, 587-644Hz, 660-827Hz, the total bandwidth is 338Hz, the frequency band higher than 40dB is 479-516Hz, 605-632Hz, 668-692Hz, 699-709Hz, the total bandwidth is 98Hz; the frequency band of the sound insulation of the traditional model higher than 30dB is 398-605Hz, 625-668Hz, the total bandwidth is 250Hz, the frequency band higher than 40dB is 461-533Hz, 625-629Hz, the total bandwidth is 76Hz; the low-frequency sound insulation bandwidth of the asymmetric model is obviously larger than that of the traditional model, the bandwidth above 30dB and 40dB is increased by about 35.2% and 28.9% respectively, which proves that the performance has significant superiority.

[0045] The light asymmetric thin film metamaterial for low-frequency sound insulation designed in the application can be applied to sound insulation structures with high requirements for lightweight structure. The mass block of the acoustic metamaterial is constructed in the form of an asymmetric circular ring, breaking through the limitation of narrow sound insulation frequency band in the traditional acoustic metamaterial structure; and the structure parameters of the film and the mass block can also be used to realize the tuning effect on the sound insulation frequency band.

[0046] The above only describes the preferred embodiments of the application, and it should be noted that for ordinary skilled persons in the art, some improvements and changes can be made without departing from the inventive concept, and these all belong to the protection scope of the application.

Claims

1. A lightweight asymmetric thin-film metamaterial for low-frequency sound insulation, characterized in that: The metamaterial includes a thin film (1), an asymmetric ring (2) attached to the same side surface of the thin film (1) as the mass block of this acoustic metamaterial, and frames (3) attached to both sides of the thin film (1); wherein four identical asymmetric rings (2) are symmetrically distributed in a cross shape on the same side surface of the thin film (1) in the same direction, and the thin film (1) is tautly attached between two identical frames (3); the above structure constitutes a cell of the metamaterial, and the metamaterial is formed by uniformly and tightly periodically arranging the cells in the horizontal and vertical directions on a plane; The asymmetric ring (2) is a ring formed by subtracting a non-concentric inner cylinder from the middle of an outer cylinder, and there is a certain eccentric distance between the outer cylinder and the inner cylinder.

2. The lightweight asymmetric thin-film metamaterial for low-frequency sound insulation according to claim 1, characterized in that: The film (1) is square in shape and has a thickness of 0.02-0.03 mm. It is connected to the frame (3) by tensioning to form a fixed constraint. The film (1) has a uniform tension force inside due to tension.

3. The lightweight asymmetric thin-film metamaterial for low-frequency sound insulation according to claim 1, characterized in that: The mass of the asymmetric ring (2) is 0.15-0.25g.

4. The lightweight asymmetric thin-film metamaterial for low-frequency sound insulation according to claim 1, characterized in that: The four identical asymmetric rings (2) are eccentric in the same direction, and the lateral and longitudinal distances between two adjacent asymmetric rings (2) are equal. The four identical asymmetric rings (2) are placed in the center of the film (1).

5. The lightweight asymmetric thin-film metamaterial for low-frequency sound insulation according to claim 1, characterized in that: The frame (3) is square, with an outer side length of 19-34mm, an inner side length of 15-30mm, and a difference of 4mm between the inner and outer side lengths. The outer side length of the frame (3) is equal to the side length of the film (1). The two frames (3) are respectively pasted onto the two sides of the film (1) and can completely overlap when pasted.

6. The lightweight asymmetric thin-film metamaterial for low-frequency sound insulation according to claim 1, characterized in that: The film (1) is bonded to the asymmetric ring (2) and the frame (3) by adhesive.

7. The lightweight asymmetric thin-film metamaterial for low-frequency sound insulation according to claim 1, characterized in that: The film (1) is either a polyetherimide film or a polyethylene film.

8. The lightweight asymmetric thin-film metamaterial for low-frequency sound insulation according to claim 1, characterized in that: The asymmetric ring (2) is one of a steel asymmetric ring and a copper asymmetric ring.

9. The lightweight asymmetric thin-film metamaterial for low-frequency sound insulation according to claim 1, characterized in that: The frame (3) is either an aluminum frame or an aluminum alloy frame.

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