A sound-absorbing and sound-insulating suppression type noise reduction phononic crystal, an acoustic metamaterial and a noise reduction device

Abstract

The present application relates to a kind of sound-absorbing and sound-insulating suppression type noise reduction phononic crystal, acoustic metamaterial and noise reduction device, it includes outer frame, resonance body and cavity plate, wherein outer frame is hollow inside, first sound hole and second sound hole are opened in outer frame, resonance body is connected in outer frame, resonance body is used to be excited by the sound wave from first sound hole and be resonated, cavity plate is connected in outer frame, and with the inner wall of outer frame and is enclosed to form independent resonance space, second sound hole is communicated with resonance space to constitute Helmholtz cavity.Compared with prior art, the present application combines local resonance and Helmholtz noise elimination, has the advantages of two ways, has wider sound insulation frequency range, especially for low-frequency noise is particularly effective, at the same time, the geometry design of the present application is relatively unique and simple, small in size, has space advantage, has light weight, easy processing and the like.

Description

Technical Field

[0001] This invention relates to the field of noise reduction technology, and in particular to a sound-absorbing and sound-insulating noise-reducing sub-crystal, acoustic metamaterial, and noise reduction device. Background Technology

[0002] In recent years, the balance between industrial power and major polluters has become increasingly apparent. Low-frequency noise pollution from electrical equipment has caused numerous inconveniences to people's lives and is recognized as one of the environmental problems in today's society, potentially impacting people's health. Therefore, how to eliminate low-frequency noise has become a key focus of research for relevant scholars.

[0003] For a long time, traditional noise reduction materials have been limited in their use in vibration and noise control. Based on the mass law of sound insulation, if the isolation of low-frequency noise with a large wavelength is to be achieved, materials with a large thickness or a very high density are required. This means that existing lightweight sound insulation materials cannot effectively suppress low-frequency noise, while those that can suppress low-frequency noise are large in size and weight, which cannot meet the requirements of space and are difficult to apply to lightweight structures.

[0004] Therefore, there is an urgent need for a lightweight solution that can effectively suppress low-frequency noise. Summary of the Invention

[0005] In view of this, it is necessary to provide a noise reduction sub-crystal, acoustic metamaterial and noise reduction device for sound absorption and suppression, so as to solve the problem that the lightweight noise reduction methods in the prior art cannot suppress low-frequency noise.

[0006] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a sound-absorbing, sound-insulating, and noise-reducing sub-crystal, comprising:

[0008] The outer frame is hollow inside, and a first sound-receiving hole and a second sound-receiving hole are provided on the outer frame;

[0009] A resonator is connected to the outer frame, with the opening of the first sound-receiving hole facing the resonator. The resonator is used to resonate when excited by sound waves incident from the first sound-receiving hole.

[0010] A cavity plate is connected to the outer frame and together with the inner wall of the outer frame, forms an independent resonance space. The second sound-receiving hole is connected to the resonance space to form a Helmholtz cavity.

[0011] Furthermore, the resonator includes a flexible film and a mass block, the edge of the flexible film is connected to the outer frame, the film surface of the flexible film faces the first sound-receiving hole, and the mass block is connected to the flexible film.

[0012] Furthermore, there are multiple cavity plates and multiple second sound receiving holes. The multiple second sound receiving holes and multiple resonance spaces are connected in a one-to-one correspondence. The multiple resonance spaces are equidistantly arranged around the edge of the flexible film. The edge of the flexible film is connected to the inner wall of the outer frame and the cavity plate.

[0013] Furthermore, the outer frame is a multi-prism shaped shell, with multiple edges of the outer frame corresponding one-to-one with multiple cavity plates. Each cavity plate is an arc-shaped plate, comprising two arc-shaped edges and two straight edges. The two straight edges are parallel and respectively connect to two adjacent inner sidewalls of the outer frame. The two arc-shaped edges are respectively connected to two inner end faces of the outer frame. The edge of the flexible film is connected to the inner sidewall of the outer frame and the cavity plate.

[0014] Furthermore, the mass block is connected to the center of the flexible film.

[0015] Furthermore, the first microphone hole and the plurality of second microphone holes are all located on the same end face of the outer frame, with the first microphone hole located at the center of the end face of the outer frame and the plurality of second microphone holes located at the corners of the end face of the outer frame.

[0016] Furthermore, the flexible film has a Poisson's ratio of 0.4 to 0.5 and a Young's modulus of 1.96 to 2.06 × 10⁻⁶. 5 Pa, the density of the flexible film is 980–1030 kg·m³. 3 The Poisson's ratio of the mass block is 0.23 to 0.32, and the Young's modulus of the mass block is 1.1 to 2.0 × 10⁻⁶. 5 Pa, the density of the mass block is 7870~11370 kg·m³. 3 The Poisson's ratio of the outer frame is 0.3 to 0.5, and the Young's modulus of the outer frame is 7.0 to 7.2 × 10⁻⁶. 5 Pa, the density of the outer frame is 2630~2850 kg·m³. 3 .

[0017] Furthermore, the resonant space is filled with a resonant medium.

[0018] Secondly, the present invention also provides an acoustic metamaterial comprising a plurality of sound-absorbing, sound-insulating, and noise-reducing sub-crystals as described in any of the above claims.

[0019] Thirdly, the present invention also provides a noise reduction device comprising the aforementioned acoustic metamaterial.

[0020] This invention provides a sound-absorbing, sound-insulating, and noise-reducing sub-crystal, an acoustic metamaterial, and a noise reduction device, comprising an outer frame, a resonator, and a cavity plate. The outer frame is hollow, and has a first sound-receiving hole and a second sound-receiving hole. The resonator is connected to the outer frame, with the opening of the first sound-receiving hole facing the resonator. The resonator is used to resonate when excited by sound waves incident from the first sound-receiving hole. The cavity plate is connected to the outer frame and, together with the inner wall of the outer frame, forms an independent resonance space. The second sound-receiving hole connects to the resonance space to form a Helmholtz cavity. Sound waves enter the outer frame through the first sound-receiving hole, exciting the resonator to resonate, and then enter the Helmholtz cavity through the second sound-receiving hole, achieving a sound-absorbing effect. Compared to existing technologies, this invention combines local resonance and Helmholtz anechoic silencing, possessing the advantages of both methods. It offers a wider sound insulation frequency range, particularly effective against low-frequency noise. Furthermore, its unique and simple geometric design results in a small size, offering spatial advantages, lightweight construction, ease of processing, and convenient production, achieving "small-size absorption of large wavelengths." Moreover, this invention allows for the adjustment of its acoustic characteristics by modifying parameters such as structure and thickness, thereby achieving sound wave modulation—a capability often difficult to achieve with traditional noise reduction methods. Attached Figure Description

[0021] Figure 1 A schematic diagram of the structure of an embodiment of the sound-absorbing and noise-reducing sub-crystal provided by the present invention;

[0022] Figure 2 for Figure 1 A sectional view;

[0023] Figure 3 for Figure 1 A cross-sectional view from another direction;

[0024] Figure 4 A schematic diagram illustrating the theoretical principle of a sound-absorbing and noise-reducing sub-crystal provided by the present invention;

[0025] Figure 5 A structural simulation diagram of an embodiment of the sound-absorbing and noise-reducing sub-crystal provided by the present invention;

[0026] Figure 6 A schematic diagram of mesh division in an embodiment of the sound-absorbing and noise-reducing sub-crystal provided by the present invention;

[0027] Figure 7 The sound loss curve in an embodiment of the sound-absorbing and noise-reducing sub-crystal provided by the present invention;

[0028] Figure 8 This is a diagram showing the selection of xy boundary conditions in an embodiment of the sound-absorbing and noise-reducing sub-crystal provided by the present invention.

[0029] Figure 9 A schematic diagram of the first Brillouin region in an embodiment of the sound-absorbing and noise-reducing sub-crystal provided by the present invention;

[0030] Figure 10 The unit cell energy band curve of a noise reduction sub-crystal of sound absorption and insulation type provided by the present invention;

[0031] Figure 11 The 115Hz vibration mode diagram of a sound-absorbing and noise-reducing sub-crystal provided by the present invention;

[0032] Figure 12 The vibration mode diagram at 117Hz is shown in one embodiment of the sound-absorbing and noise-reducing sub-crystal provided by the present invention.

[0033] Figure 13 The 126Hz vibration mode diagram is shown in one embodiment of the sound-absorbing and noise-reducing sub-crystal provided by the present invention.

[0034] Figure 14 The 120Hz sound pressure distribution diagram is shown in one embodiment of the sound-absorbing and noise-reducing sub-crystal provided by the present invention. Detailed Implementation

[0035] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0036] First, let's explain the technical terms that appear in the text:

[0037] A Helmholtz cavity, also known as a Helmholtz resonator, is a traditional acoustic sound-absorbing device. It is a fundamental acoustic structure used for sound absorption, proposed by the renowned German physicist Hermann von Helmholtz in the 1850s. It was initially used to identify the frequency components of sound. During measurement, the sound source is placed at the bottom opening, and the top fine opening is placed near the ear.

[0038] MFH: an abbreviation for Mass Film and Helmholtz, meaning a combination of a flexible thin film, a mass ring, and a Helmholtz cavity. In this article, the sound-absorbing and noise-reducing sub-crystal can be simply referred to as an MFH phonon crystal (or MFH unit cell, etc.), and acoustic metamaterials can be simply referred to as MFH materials.

[0039] In the description of this application, "multiple" means two or more, unless otherwise expressly and specifically defined.

[0040] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0041] This invention, based on local resonance and Helmholtz sound absorption theory, breaks through many limitations of traditional materials in low-frequency noise suppression. Through ingenious design, it exhibits unique acoustic properties, such as negative equivalent modulus and negative refraction—qualities contrary to natural laws. These properties also give it excellent low-frequency sound absorption and insulation performance while maintaining light weight and small volume. Furthermore, as a subwavelength structure that can be artificially controlled, proposed in the research of artificial periodic structures, by adjusting various geometric and material parameters of the acoustic metamaterial, the propagation direction and intensity of sound waves can be changed when passing through the acoustic metamaterial. This invention can be used to reduce low-frequency noise generated during the operation of power equipment, while simultaneously achieving lightweight and small volume, providing a reference for the low-frequency and broadband design of sound insulation and noise reduction structures.

[0042] The problems that this invention can solve are as follows:

[0043] 1. It overcomes many limitations of traditional materials in low-frequency noise suppression and has a better low-frequency sound insulation effect;

[0044] 2. The structure is relatively lightweight and small in size, offering good economy and convenience;

[0045] 3. The material is thin, which meets the space requirements;

[0046] 4. Lightweight, making it suitable for lightweight structures;

[0047] 5. Low cost, which facilitates widespread application.

[0048] This invention provides a sound-absorbing and noise-reducing sub-crystal, an acoustic metamaterial, and a noise reduction device, which are described below.

[0049] Combination Figures 1-3As shown in the figure, a specific embodiment of the present invention discloses a sound-absorbing and noise-reducing sub-crystal, including an outer frame 1, a resonator 2, and a cavity plate 3. The outer frame 1 is hollow inside, and a first sound-receiving hole 11 and a second sound-receiving hole 12 are provided on the outer frame 1. The resonator 2 is connected inside the outer frame 1, and the opening direction of the first sound-receiving hole 11 faces the resonator 2. The resonator 2 is used to resonate when excited by the sound wave incident from the first sound-receiving hole 11. The cavity plate 3 is connected inside the outer frame 1 and together with the inner wall of the outer frame 1, forms an independent resonance space. The second sound-receiving hole 12 communicates with the resonance space to form a Helmholtz cavity.

[0050] The present invention employs a combination of local resonance and Helmholtz cavity. Sound waves enter the outer frame 1 from the first sound receiving hole 11 and excite the resonator 2 to resonate (i.e., the local resonance), and enter the Helmholtz cavity from the second sound receiving hole 12, thereby achieving the effect of sound absorption.

[0051] Specifically, in a preferred embodiment, the outer frame 1 is a polyhedral shell, such as a cube or hexagonal prism. This structure facilitates assembly and internal molding.

[0052] Furthermore, in a preferred embodiment, the first sound receiving hole 11 and the plurality of second sound receiving holes 12 are all located on the same end face of the outer frame 1. The first sound receiving hole 11 is located at the center of the end face of the outer frame 1, and the plurality of second sound receiving holes 12 are respectively located at the corners of the end face of the outer frame 1. Both the first sound receiving hole 11 and the second sound receiving hole 12 are used to receive incident sound waves. It is understood that, in practice, the relative positional relationship between the two can be flexibly adjusted according to different specific application conditions.

[0053] In a preferred embodiment, the resonator 2 includes a flexible film 21 and a mass block 22. The edge of the flexible film 21 is connected to the inner frame 1, and the film surface of the flexible film 21 faces the first sound receiving hole 11. The mass block 22 is connected to the flexible film 21. It is understood that other existing structures capable of resonating with sound waves can also be used as the resonator 2 in practice.

[0054] In a preferred embodiment, the mass block 22 is connected to the center of the flexible film 21. This allows the flexible film 21 to achieve the best resonance effect.

[0055] The aforementioned resonator 2 is mainly used for local resonance noise reduction. In terms of local resonance, the equivalent "spring-oscillator" model formed by the flexible film 21 and the mass block 22 interacts with the traveling wave in the resonance mode under the incident sound wave at a specific frequency, thereby suppressing the wave propagation. The wavelength of the controlled sound can be much larger than its structural size. The sound absorption effect of local resonance depends on the selection of its material parameters, such as the tension, thickness, and density of the flexible film 21, and the position, size, density, and acoustic impedance of the mass block 22. By adjusting these parameters, effective noise control can be achieved.

[0056] Furthermore, in a preferred embodiment, there are multiple cavity plates 3 and multiple second sound receiving holes 12, and the multiple second sound receiving holes 12 and multiple resonance spaces are connected in a one-to-one correspondence. The multiple resonance spaces are arranged equidistantly around the edge of the flexible film 21, and the edge of the flexible film 21 is connected to the inner wall of the outer frame 1 and the cavity plate 3.

[0057] In a preferred embodiment, the multiple edges of the outer frame 1 correspond one-to-one with the multiple cavity plates 3. The cavity plate 3 is an arc-shaped plate, and the cavity plate 3 includes two arc-shaped edges and two straight edges. The two straight edges are parallel and respectively connect to two adjacent inner sidewalls in the outer frame 1. The two arc-shaped edges are respectively connected to two inner end faces of the outer frame 1. The edge of the flexible film 21 is connected to the inner sidewall of the outer frame 1 and the cavity plate 3.

[0058] This layout makes the structure of the entire unit easy to form and manufacture, while also ensuring the effectiveness of both local resonance and Helmholtz anechoic silencing.

[0059] In a preferred embodiment, the resonant space is filled with a resonant medium to improve the resonance noise reduction effect. In this embodiment, the resonant medium is air.

[0060] The aforementioned structure is primarily used for Helmholtz silencing. An air-filled Helmholtz cavity utilizes the principle of resonance silencing. When sound waves enter the cavity through the second sound-receiving hole 12, they excite the air within the cavity to resonate. This resonance converts a portion of the sound wave energy into the thermal and kinetic energy of the gas inside the cavity, thus achieving sound absorption. The resonance effect is strongest when the sound wave frequency matches the cavity's natural frequency, allowing the cavity to absorb more sound energy. The sound absorption effect of the Helmholtz cavity depends on factors such as the cavity's geometry, the density and viscosity of the gas inside, and the type and density of the filling material. During implementation, these parameters are adjusted to absorb sound waves of different frequencies.

[0061] Furthermore, in a preferred embodiment, the flexible film 21 has a Poisson's ratio of 0.49 and a Young's modulus of 2 × 10⁻⁶. 5Pa, the density of the flexible film 21 is 980 kg·m³. 3 The Poisson's ratio of the mass block 22 is 0.49, and the Young's modulus of the mass block 22 is 2 × 10⁻⁶. 5 Pa, the density of the mass block 22 is 980 kg·m³. 3 The Poisson's ratio of the outer frame 1 is 0.49, and the Young's modulus of the outer frame 1 is 2 × 10⁻⁶. 5 Pa, the density of the outer frame 1 is 980 kg·m³. 3 .

[0062] The sound-absorbing and noise-reducing sub-crystals manufactured within the above-mentioned range can have a good low-frequency noise reduction effect.

[0063] The present invention also provides a more detailed embodiment to more clearly illustrate the above-described sound-absorbing and noise-reducing sub-crystal:

[0064] In this embodiment, the straight edge length of the cavity plate 3 is 30.5 mm, the radius of the arc edge is 14 mm, the thickness of the cavity plate 3 is 1 mm, and the radius of the second sound hole 12 is 0.4 mm; the outer side length of the outer frame 1 is 37 mm, the side thickness is 1 mm, and the end thickness is 2 mm; the mass block 22 is cylindrical with a radius of 2.5 mm and a height of 1 mm; the radius of the arc of the notch at the connection between the edge of the flexible film 21 and the cavity plate 3 is 14 mm, and the thickness of the flexible film 21 is 0.5 mm.

[0065] In this embodiment, the material parameters of the flexible film 21, the mass block 22, and the outer frame 1 are as follows: the Poisson's ratio of the flexible film is 0.4 to 0.5, and the Young's modulus of the flexible film is 1.96 to 2.06 × 10⁻⁶. 5 Pa, the density of the flexible film is 980–1030 kg·m³. 3 The Poisson's ratio of the mass block is 0.23 to 0.32, and the Young's modulus of the mass block is 1.1 to 2.0 × 10⁻⁶. 5 Pa, the density of the mass block is 7870~11370 kg·m³. 3 The Poisson's ratio of the outer frame is 0.3 to 0.5, and the Young's modulus of the outer frame is 7.0 to 7.2 × 10⁻⁶. 5 Pa, the density of the outer frame is 2630~2850 kg·m³. 3 .

[0066] The following section will simulate the sound-absorbing and noise-reducing sub-crystal in the above embodiments to demonstrate its effectiveness. Before describing the specific simulation process, the noise reduction theory on which this invention is based will be introduced:

[0067] According to the mass law, sound is transmitted to varying degrees when passing through different types of sound insulation structures due to factors such as the material properties and shape of the structure. The transmission coefficient directly determines the sound insulation effect of the structure, which is usually evaluated using parameters such as insertion loss and transmission loss. In this calculation, a plane wave is used as the incident sound field, and the transmission loss calculation method for a comprehensive acoustic metamaterial structure is derived using the sound wave propagation equation.

[0068] Figure 4 A simplified model of plane wave propagation and conversion in a medium is presented. The model includes perfectly matched layers (PMLs) on both sides, an air cavity, and an acoustic metamaterial structure (such as the sound-absorbing and noise-reducing sub-crystal in this invention) at the gray area OD in the figure. The acoustic impedance of the air on both sides is assumed to be ρ0c0. The perfectly matched layers, acting as non-reflective absorbing boundaries, minimize the influence of the boundaries on the sound field. The plane wave equation of the simplified model can be written as:

[0069]

[0070] Where, p i0 For the incident sound pressure, p r0 For the reflected sound pressure, p t0 S1 represents the transmitted sound pressure. S2 is the area of ​​the incident plane, and S1 is the area of ​​the exit plane.

[0071] The transmission loss TL is defined as follows:

[0072]

[0073] Among them W in With W out These are incident sound energy and emitted sound energy, respectively.

[0074] The vibration equation of the flexible film 21 in this embodiment is:

[0075]

[0076] in, T is the tension of the flexible film 21, and σ is the areal density of the film; It is a Laplace operator for two-dimensional rectangular coordinates.

[0077] For a typical Helmholtz cavity, when the sound pressure at its cavity opening (i.e., the second sound receiving hole 12 in this embodiment) is p = p a e jωt When subjected to sound waves, it can be simplified as a damped forced vibration spring oscillator system, where the oscillator is the gas at the opening and the spring is the gas inside the cavity. Its vibration equation can be expressed as:

[0078]

[0079] Among them, M a For sound quality, R a For acoustic impedance, C a Let v be the acoustic volume, v be the air velocity at the opening, S be the opening area, and U be the volumetric velocity.

[0080] Based on the above noise reduction theory, the simulation process of this invention is as follows:

[0081] like Figure 5 As shown, the designed sound-absorbing and noise-reducing sub-crystal was calculated using the pressure acoustics module and the structural mechanics module in COMSOL Multiphysics 5.6. When the flexible film 21 is calculated as a thin plate, it can be calculated using the three-dimensional solid mechanics module in the structural mechanics module, using its own stiffness to replace the prestressing effect. Since the difference between the film's flat area and its thickness is too large, this calculation method usually requires dividing a large number of finite element meshes to ensure calculation accuracy. Finally, to consider that a large number of iterative calculations would slow down the calculation speed, a linear geometry method was introduced.

[0082] A finite element model of a sound-absorbing, sound-insulating, and noise-reducing sub-crystal was established. Figure 6 This is a schematic diagram of the mesh generation for an acoustic metamaterial. The medium is air. Plane wave radiation and corresponding incident and exit surfaces are set. The acoustic-structure interaction physics module in the software is used to simulate the acoustic performance and solve the transmission loss curve of the model by combining the finite element method and the boundary element method.

[0083] Two air layers (with a set sound velocity of 343 m / s) are defined on the upper and lower surfaces of the flexible film 21: the upper air layer is defined as the incident sound pressure surface, with a sound pressure amplitude p0 = 1.0 Pa, and a plane wave is incident on the flexible film 21 from the normal direction; the lower air layer is defined as the transmission sound pressure surface; the periphery of both the upper and lower air layers is defined as a completely reflective surface to simulate an impedance tube test. Through simulation analysis, the average sound pressure amplitude p0 of the incident and transmission sound pressure surfaces is obtained respectively. i and p t The sound absorption coefficient is calculated using the following formula:

[0084]

[0085] Its corresponding transmission curve in COMSOL Multiphysics 5.6a is as follows: Figure 7 As shown:

[0086] The sound transmission loss curve is the result obtained by measuring the sound insulation performance of the material. Generally, the horizontal axis represents frequency and the vertical axis represents sound transmission loss. From the curve, it can be determined that the overall sound transmission loss is good in the 10-1000Hz frequency range, and the sound energy intensity is significantly reduced. This sound-absorbing and noise-reducing sub-crystal has a wide sound insulation frequency range and good low-frequency noise reduction effect.

[0087] When noise propagates and its frequency coincides with the natural frequency of an acoustic metamaterial, suppression or inhibition occurs on the surface of the metamaterial; this is known as the acoustic band gap phenomenon. Acoustic metamaterials possess unique acoustic band gaps to suppress noise propagation, and one of the main aspects of research on acoustic metamaterials is the existence and location of these gaps. In locally resonant acoustic metamaterial structures, the scatterers of individual elementary cells primarily play a decisive role in the structure's resonance characteristics; their inherent structural periodicity and symmetry have little impact on sound suppression characteristics. Modal vibration simulations of the MFH phonon crystal were performed using COMSOL Multiphysics 5.6a software, establishing... Figure 8 The model shown has Floquet periodic boundary conditions set for the xy edges. After setting the parameters, a parametric scan is performed using the set parameter k. x k y The range is from 0 to π / a (where a is the lattice constant), enabling wavenumber scanning over the edges of the irreducible Brillouin zone. The principle is as follows: Figure 9 As shown, the calculation of the frequency response of phononic crystals mainly focuses on the periodic cell expansion and periodic structural conditions. For the irreducible Brillouin zone (IBZ), within the constrained range covered by the wave vector and in planar two-dimensional characteristics, the IBZ begins in the initial region Γ, undergoes a lateral translation to X, then a vertical translation from X to M, and finally returns to its initial position Γ; this is called a Brillouin zone.

[0088] The band structure of a sound-absorbing and noise-reducing sub-crystal can characterize the propagation properties of sound waves in a material by describing the dispersion relation of the sound waves, i.e., the relationship between the sound wave frequency and the wave vector. Its corresponding vibrational band structure in COMSOL Multiphysics 5.6a is shown below. Figure 10 As shown, a vocal tract gap exists between 115Hz and 126Hz. Specifically, as... Figures 11-13 As shown, at 115Hz, the film exhibits two deformation directions aligned with the sound wave propagation direction, and two other deformation directions opposite to the sound wave propagation direction; however, at 117Hz, all deformation directions are opposite to the sound wave propagation direction; furthermore, in the bandgap frequency band, i.e., at 120Hz, Figure 14 The sound pressure distribution in the MFH unit cell shows that sound propagation is significantly impeded; however, at 126 Hz, the inhibitory deformation returns to half.

[0089] The present invention also provides an acoustic metamaterial comprising a plurality of sound-absorbing, sound-insulating, and noise-reducing sub-crystals as described in any of the above embodiments. It is understood that the acoustic metamaterial in this embodiment may be composed entirely of the aforementioned sound-absorbing, sound-insulating, and noise-reducing sub-crystals, or it may be composed of the aforementioned sound-absorbing, sound-insulating, and noise-reducing sub-crystals combined with other materials.

[0090] The present invention also provides a noise reduction device comprising the aforementioned acoustic metamaterial. It is understood that the noise reduction device in this embodiment can be any facility or device containing the aforementioned acoustic metamaterial, such as a wall covered with the aforementioned acoustic metamaterial, or a vehicle (such as a vehicle, ship, or train) with the aforementioned acoustic metamaterial as its outer layer.

[0091] This invention provides a sound-absorbing, sound-insulating, and noise-reducing sub-crystal, an acoustic metamaterial, and a noise reduction device, comprising an outer frame 1, a resonator 2, and a cavity plate 3. The outer frame 1 is hollow, and has a first sound-receiving hole 11 and a second sound-receiving hole 12. The resonator 2 is connected inside the outer frame 1, with the opening of the first sound-receiving hole 11 facing the resonator 2. The resonator 2 is used to resonate when excited by sound waves incident from the first sound-receiving hole 11. The cavity plate 3 is connected inside the outer frame 1 and, together with the inner wall of the outer frame 1, forms an independent resonance space. The second sound-receiving hole 12 communicates with the resonance space to form a Helmholtz cavity. Sound waves enter the outer frame 1 through the first sound-receiving hole 11, exciting the resonator 2 to resonate, and then enter the Helmholtz cavity through the second sound-receiving hole 12, achieving a sound-absorbing effect. Compared to existing technologies, this invention combines local resonance and Helmholtz anechoic silencing, possessing the advantages of both methods. It offers a wider sound insulation frequency range, particularly effective against low-frequency noise. Furthermore, its unique and simple geometric design results in a small size, offering spatial advantages, lightweight construction, ease of processing, and convenient production, achieving "small-size absorption of large wavelengths." In addition, this invention allows for the adjustment of its acoustic characteristics by modifying parameters such as structure and thickness, thereby achieving sound wave manipulation—a capability often difficult to achieve with traditional noise reduction methods.

[0092] Therefore, compared with existing technologies, the advantages of this invention are:

[0093] 1. It has several sound insulation peaks in the 10-1000Hz low frequency range, and overall it also has a good low frequency sound insulation effect;

[0094] 2. Wide range of adjustable properties: Its acoustic characteristics can be adjusted by changing parameters such as its structure and thickness, thereby achieving the control of sound waves. This adjustable property is often difficult to achieve in traditional materials.

[0095] 3. High controllability: The preparation and processing technology is relatively mature, and its structure and performance can be precisely controlled through methods such as electron beam exposure and photolithography, thereby achieving a high degree of control and optimization of sound waves.

[0096] 4. Lightweight and easy to process: It can be made of a variety of materials, thus achieving lightweight. At the same time, its structure also has a certain degree of processability, which facilitates large-scale manufacturing and application.

[0097] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A noise-reducing sub-crystal for sound absorption, insulation, and suppression, characterized in that, include: The outer frame is hollow inside, and a first sound-receiving hole and a second sound-receiving hole are provided on the outer frame; A resonator is connected to the outer frame, with the opening of the first sound-receiving hole facing the resonator. The resonator is used to resonate when excited by sound waves incident from the first sound-receiving hole. The resonator includes a flexible film and a mass block. The edge of the flexible film is connected to the outer frame, and the film surface of the flexible film faces the first sound-receiving hole. The mass block is connected to the flexible film. A cavity plate is connected to the outer frame and together with the inner wall of the outer frame, forms an independent resonance space. The second sound receiving hole is connected to the resonance space to form a Helmholtz cavity. There are multiple cavity plates and multiple second sound receiving holes. The multiple second sound receiving holes and multiple resonance spaces are connected in a one-to-one correspondence. The multiple resonance spaces are arranged equidistantly around the edge of the flexible film. The edge of the flexible film is connected to the inner wall of the outer frame and the cavity plate.

2. The sound-absorbing and noise-reducing sub-crystal according to claim 1, characterized in that, The outer frame is a multi-prism shaped shell, with multiple edges of the outer frame corresponding to multiple cavity plates. Each cavity plate is an arc-shaped plate, comprising two arc-shaped edges and two straight edges. The two straight edges are parallel and respectively connect to two adjacent inner sidewalls of the outer frame. The two arc-shaped edges are respectively connected to two inner end faces of the outer frame. The edge of the flexible film is connected to the inner sidewall of the outer frame and the cavity plate.

3. The sound-absorbing, sound-insulating, and noise-reducing sub-crystal according to claim 2, characterized in that, The mass block is connected to the center of the flexible film.

4. The sound-absorbing, sound-insulating, and noise-reducing sub-crystal according to claim 3, characterized in that, The first microphone hole and the plurality of second microphone holes are all located on the same end face of the outer frame. The first microphone hole is located at the center of the end face of the outer frame, and the plurality of second microphone holes are located at the corners of the end face of the outer frame.

5. The sound-absorbing and noise-reducing sub-crystal according to claim 4, characterized in that, The flexible film has a Poisson's ratio of 0.4 to 0.5 and a Young's modulus of 1.96 to 2.06 × 10⁻⁶. 5 Pa, the density of the flexible film is 980~1030 kg·m³. 3 The Poisson's ratio of the mass block is 0.23~0.32, and the Young's modulus of the mass block is 1.1~2.0×10⁻⁶. 5 Pa, the density of the mass block is 7870~11370 kg·m³. 3 The Poisson's ratio of the outer frame is 0.3~0.5, and the Young's modulus of the outer frame is 7.0~7.2×10⁻⁶. 5 Pa, the density of the outer frame is 2630~2850 kg·m³. 3 .

6. The sound-absorbing and noise-reducing sub-crystal according to claim 1, characterized in that, The resonant space is filled with a resonant medium.

7. An acoustic metamaterial, characterized in that, It includes multiple sound-absorbing and noise-reducing sub-crystals as described in any one of claims 1 to 5.

8. A noise reduction device, characterized in that, Including the acoustic metamaterials as described in claim 7.

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