Metamaterial unit for low-frequency broadband high-efficiency sound absorption and superstructure module thereof

Abstract

The application discloses a kind of for low frequency broadband high-efficiency sound absorption metamaterial unit and its superstructure module, and the metamaterial unit includes the metamaterial cavity enclosed by multiple blocks of wall and the acoustic waveguide channel being arranged in the metamaterial cavity, acoustic waveguide channel is provided with impedance high-efficiency modulation sound absorption body, impedance high-efficiency modulation sound absorption body includes high porosity sound absorption medium and impedance modulation channel.The introduction of impedance modulation channel can effectively change the acoustic characteristics of high porosity sound absorption medium, by changing the geometric configuration of impedance modulation channel, can be widely modulated acoustic impedance, while producing resonance absorption peak in low frequency band, so as to significantly improve the sound absorption performance in low frequency band.A plurality of metamaterial units with different low-frequency high-efficiency absorption performance are connected in parallel, and through the coupling effect between the metamaterial units, a metamaterial module with low-frequency broadband high-efficiency sound absorption and noise reduction performance can be formed, thereby realizing low-frequency broadband high-efficiency sound absorption performance.

Description

Technical Field

[0001] This invention belongs to the field of new materials and new technologies for noise control, specifically relating to metamaterial units and their metastructure modules for low-frequency broadband high-efficiency sound absorption, which can be applied to the acoustic control of modern transportation vehicles (high-speed rail, airplanes, ships, new energy vehicles), new functional venues / rooms (conference venues, waiting halls, recording / broadcasting studios, anechoic chambers, wind tunnels), etc. Background Technology

[0002] In the field of noise control, materials or structures with sound absorption and noise reduction functions can be divided into two main categories according to their sound absorption principles: porous sound-absorbing materials and resonant sound-absorbing structures. Common porous sound-absorbing materials include organic fiber porous materials, inorganic fiber porous materials, foam porous materials, and metal porous materials. Common resonant sound-absorbing structures include thin film resonant sound-absorbing structures, perforated plate (including micro-perforated plate) resonant sound-absorbing structures, and micro-slit resonant sound-absorbing structures.

[0003] In engineering, traditional porous sound-absorbing materials exhibit excellent sound absorption performance for mid-to-high frequency sound waves above 1000Hz and are widely used in practical engineering. However, their sound absorption performance for low-frequency sound waves (below 1000Hz) is poor. The sound absorption mechanism of porous materials mainly includes: air viscosity and heat exchange in the medium. Currently, the Johnson-Champoux-Allard equivalent model is widely used to describe porous materials, which defines five macroscopic parameters: porosity, flow resistance, tortuosity, viscous characteristic length, and thermal characteristic length. These five macroscopic parameters can be adjusted by changing the equivalent bulk modulus and density of the porous material, thereby affecting the overall sound absorption performance of the porous material. Considering the actual manufacturing process of porous materials, within the processable manufacturing range, the adjustment range of these five macroscopic parameters on acoustic impedance is very limited, making it difficult to achieve wide-bandwidth and large-amplitude adjustment of acoustic impedance, and also difficult to achieve efficient sound absorption in the low-frequency range. Furthermore, the optimal sound absorption frequency of porous materials mainly depends on the overall thickness of the porous material. For every doubling of the thickness, the optimal sound absorption frequency shifts one octave lower. Therefore, using traditional porous materials to improve the sound absorption performance in the low-frequency range often requires a significant increase in the thickness of the porous material, which greatly increases the spatial size and cost of the porous sound-absorbing material, and does not meet the requirements of practical engineering applications.

[0004] To address the challenge of low-frequency sound absorption, existing technologies often employ resonant sound-absorbing structures. For thin-film resonant sound-absorbing structures, research indicates that without a back cavity, the maximum absorption coefficient is generally no more than 0.5. The absorption coefficient can be improved through coherent absorption of multi-layer thin-film structures or hybrid resonance between the thin-film structure and the cavity, achieving perfect sound absorption at low frequencies. Therefore, to achieve efficient low-frequency sound absorption, the overall thickness of the thin-film resonant sound-absorbing structure often needs to be significant. For perforated plate (including micro-perforated plate) and micro-slit resonant sound-absorbing structures, significantly increasing the back cavity thickness is also necessary to improve low-frequency absorption performance. Thus, the resonant absorption frequency range of existing resonant sound-absorbing structures typically depends on the overall structural thickness. Achieving efficient low-frequency sound absorption often requires increasing the thickness of the resonant sound-absorbing structure, greatly increasing its size and cost. This makes it unsuitable for space-constrained applications with low-frequency noise reduction requirements, and the high cost also does not meet practical engineering application requirements. Furthermore, traditional resonant sound-absorbing structures only exhibit good sound absorption performance near their designed resonant frequency. Their sound absorption performance drops sharply when deviating from the designed resonant frequency, resulting in a narrow high-efficiency sound absorption bandwidth that fails to meet the low-frequency broadband sound absorption requirements of practical engineering. Existing research, based on resonant coupling, connects a sufficient number of resonant sound-absorbing structures with different absorption frequencies in parallel to effectively broaden the sound absorption bandwidth. However, as the sound absorption bandwidth widens, its absorption coefficient also decreases, making it difficult to achieve low-frequency broadband high-efficiency sound absorption. In short, existing resonant sound-absorbing structures struggle to achieve a perfect balance between low-frequency, broadband, and high-efficiency sound absorption.

[0005] In summary, in engineering applications, existing sound-absorbing materials and structures are limited by structural dimensions, manufacturing processes, and costs, making it difficult to achieve efficient low-frequency broadband sound absorption. Low-frequency broadband efficient sound absorption is a technically critical issue of great interest to those in the field of noise control, and currently, no literature discloses the method described in this invention, which utilizes a metamaterial unit comprised of a high-porosity sound-absorbing medium and an impedance modulation channel, and a metastructure module based thereon to achieve efficient low-frequency broadband sound absorption and noise reduction. Summary of the Invention

[0006] In view of the defects and shortcomings of the existing technology, the purpose of this invention is to provide a metamaterial unit and its metastructure module for low-frequency broadband high-efficiency sound absorption and noise reduction.

[0007] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0008] On one hand, the present invention provides a metamaterial unit for low-frequency broadband high-efficiency sound absorption, comprising a metamaterial cavity formed by multiple surrounding walls and an acoustic waveguide channel disposed within the metamaterial cavity, wherein an impedance-efficient modulation sound absorber is disposed within the acoustic waveguide channel.

[0009] Furthermore, the metamaterial unit of the present invention may also include a high acoustic transmittance cover plate, which is disposed on the metamaterial cavity, and the acoustic waveguide channel in the metamaterial cavity is connected to the outside through the opening or slit on the high acoustic transmittance cover plate.

[0010] Furthermore, the impedance-efficient modulation sound absorber of the present invention includes a high-porosity sound-absorbing medium and an impedance modulation channel. The high-porosity sound-absorbing medium covers the inner wall of the acoustic waveguide channel, and one or more impedance modulation channels are provided in the high-porosity sound-absorbing medium.

[0011] Furthermore, the axial direction of the impedance modulation channel described in this invention is consistent with the waveguide direction of the acoustic waveguide channel in which it is located.

[0012] Furthermore, by changing the geometric configuration of the impedance modulation channel, the present invention can achieve wideband amplitude modulation of acoustic impedance and generate a resonant absorption peak in the low-frequency range, thereby improving the sound absorption performance in the low-frequency range.

[0013] Furthermore, the impedance modulation channel of the present invention has a cross-sectional shape in the waveguide direction parallel to its acoustic waveguide channel as a rectangle, cone, trapezoid, rhombus, or axisymmetric regular polygon.

[0014] Furthermore, the acoustic waveguide channel of the present invention is a straight channel or a tortuous channel, and the width of the acoustic waveguide channel is constant, gradually changing, or gradient-changing along its waveguide direction.

[0015] Furthermore, the high-porosity sound-absorbing medium of the present invention fills the entire acoustic waveguide channel; or the high-porosity sound-absorbing medium fills a portion of the acoustic waveguide channel from the bottom of the acoustic waveguide channel.

[0016] Furthermore, the metamaterial cavity of the present invention is made of metal plate, plastic plate, hard fiberboard, plywood, gypsum board, resin board or tempered glass plate.

[0017] Furthermore, the metamaterial cavity of the present invention is formed by riveting, welding or gluing, or the metamaterial cavity is integrally formed by casting or additive processing.

[0018] Furthermore, the high-porosity sound-absorbing medium of the present invention is an organic fiber-type porous material, an inorganic fiber-type porous material, a foam-type porous material, or a metal-type porous material;

[0019] On the other hand, the present invention provides a metastructure module, comprising a plurality of metamaterial units for low-frequency broadband high-efficiency sound absorption, wherein each metamaterial unit is connected in parallel.

[0020] Furthermore, in the superstructure module, the metamaterial units are arranged in a one-dimensional periodic pattern or a two-dimensional periodic pattern.

[0021] The beneficial technical effects that this invention can produce are as follows:

[0022] This invention provides a metamaterial unit and its metastructure module for low-frequency broadband high-efficiency sound absorption with a simpler and more reasonable structure.

[0023] This invention introduces an impedance-efficient modulation sound absorber into the acoustic waveguide channel. The impedance-efficient modulation sound absorber includes a high-porosity sound-absorbing medium and an impedance modulation channel, thus designing a simpler and more reasonable metamaterial unit and its metastructure module for low-frequency broadband high-efficiency sound absorption.

[0024] Specifically, this invention introduces an impedance-modulated sound absorber into the acoustic waveguide channel. Due to its coupling resonance effect in the low-frequency range, it can generate a highly efficient resonant absorption peak in the low-frequency range, thereby improving the sound absorption performance in the low-frequency range while maintaining efficient sound absorption performance in the mid-to-high frequency range. Considering the actual manufacturing process, simply using a high-porosity sound-absorbing medium to modulate acoustic impedance has a very limited modulation range. Furthermore, this invention introduces an impedance modulation channel into the high-porosity sound-absorbing medium, forming an impedance-modulated sound absorber. Due to the introduction of the impedance modulation channel, without changing the material parameters of the high-porosity sound-absorbing medium, a wide-range modulation of acoustic impedance can be achieved simply by changing the geometric configuration of the impedance modulation channel. This significantly improves the sound absorption performance in the low-frequency range without increasing the thickness of the high-porosity sound-absorbing medium, while maintaining efficient sound absorption performance in the mid-to-high frequency range.

[0025] Furthermore, by utilizing the tortuous arrangement of the acoustic waveguide channels, the present invention significantly increases the equivalent path of sound wave propagation to a certain extent while maintaining the overall thickness of the structure, thereby improving the sound absorption performance in the low-frequency range to a certain extent.

[0026] Furthermore, by designing the geometric configuration of the impedance modulation channel in the metamaterial unit, metamaterial units with different low-frequency high-efficiency absorption properties can be obtained. Multiple metamaterial units with different low-frequency high-efficiency absorption properties are connected in parallel to form a superstructure module. Through the coupling and superposition between the metamaterial units, the superstructure module can not only achieve efficient absorption of low-frequency sound waves, but also efficiently absorb sound in the mid-to-high frequency range, thus achieving broadband and efficient absorption of sound waves at low frequencies.

[0027] In summary, this invention has excellent low-frequency, wide-bandwidth, and high-efficiency sound absorption performance, as well as advantages such as simple structure, easy processing and manufacturing, and low cost. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of a structure according to an embodiment of the present invention;

[0029] Figure 2 This is a schematic diagram of the acoustic waveguide channel in one embodiment of the present invention;

[0030] Figure 3 This is a cross-sectional view of an embodiment of the present invention;

[0031] Figure 4 This is a schematic diagram of the structure of a metamaterial unit in one embodiment of the present invention;

[0032] Figure 5 This is a schematic diagram of the structure of a metamaterial unit in one embodiment of the present invention;

[0033] Figure 6 This is a schematic diagram of the structure of a metamaterial unit in one embodiment of the present invention;

[0034] Figure 7 This is a schematic diagram of the structure of a metamaterial unit in one embodiment of the present invention;

[0035] Figure 8 This is a schematic diagram of the acoustic waveguide channel in one embodiment of the present invention;

[0036] Figure 9 This is a schematic diagram of the acoustic waveguide channel in one embodiment of the present invention;

[0037] Figure 10 This is a schematic diagram of the acoustic waveguide channel in one embodiment of the present invention;

[0038] Figure 11 This is a schematic diagram of the filling form of a high-porosity sound-absorbing medium in one embodiment of the present invention;

[0039] Figure 12 This is a schematic diagram of the filling form of a high-porosity sound-absorbing medium in one embodiment of the present invention;

[0040] Figure 13 This is a schematic diagram of a structure according to an embodiment of the present invention (with a cover plate that has high acoustic transmittance);

[0041] Figure 14 This is a schematic diagram of a structure according to an embodiment of the present invention (with a cover plate that has high acoustic transmittance);

[0042] Figure 15 This is a schematic diagram of a structure according to an embodiment of the present invention (with a cover plate that has high acoustic transmittance);

[0043] Figure 16 This is a schematic diagram of a structure according to an embodiment of the present invention (without a high acoustic transmittance cover plate);

[0044] Figure 17 This is a cross-sectional view of an embodiment of the present invention;

[0045] Figure 18 This is a cross-sectional view of an embodiment of the present invention;

[0046] Figure 19 This is a cross-sectional view of an embodiment of the present invention;

[0047] Figure 20 A schematic diagram of the structure of a superstructure module (one-dimensional periodic arrangement) provided in an embodiment of the present invention;

[0048] Figure 21 This is a schematic diagram of the structure of a superstructure module (two-dimensional periodic arrangement) provided in an embodiment of the present invention;

[0049] Figure 22 This is a schematic diagram of the structure of a superstructure module provided in an embodiment of the present invention;

[0050] Figure 23 A sound absorption coefficient curve of a superstructure module provided in an embodiment of the present invention;

[0051] Figure 24 This is a schematic diagram of the structure of a superstructure module provided in an embodiment of the present invention;

[0052] Figure 25 A sound absorption coefficient curve of a superstructure module provided in an embodiment of the present invention;

[0053] Numbering on the map:

[0054] 1. Acoustic waveguide channel; 1.1. Inner wall of acoustic waveguide channel; 2. Metamaterial cavity; 2.1. Enclosure; 3. Impedance-efficient modulation sound absorber; 3a. High porosity sound-absorbing medium; 3b. Impedance modulation channel; 4. High sound wave transmittance cover plate; 4.1. Opening.

[0055] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0056] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0057] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0058] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0059] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection, an electrical connection, a physical connection, or a wireless communication connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two elements or the interaction between two elements, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0060] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0061] like Figure 1 As shown, in one embodiment, a superstructure module for low-frequency broadband high-efficiency sound absorption is provided, which is composed of three different metamaterial units connected in parallel. It includes a metamaterial cavity 2 enclosed by multiple walls 2.1 and three acoustic waveguide channels 1 disposed in the metamaterial cavity 2. The acoustic waveguide channels 1 are provided with impedance high-efficiency modulation sound absorbers. Figure 1 In the design, the metamaterial cavity 2 is a cuboid with a high acoustic transmittance cover 4 on top. Each acoustic waveguide channel 1 inside the metamaterial cavity 2 is connected to the outside through an opening 4.1 on the high acoustic transmittance cover 4. The specific shape of the opening on the high acoustic transmittance cover 4 is not limited; it can be rectangular, circular, triangular, rhomboid, or polygonal. Figure 1 The opening 4.1 on the high transmittance cover plate 4 is a rectangular opening. The three rectangular openings on the high transmittance cover plate 4 correspond to the three acoustic waveguide channels 1 in the metamaterial cavity 2.

[0062] use Figure 1 In some embodiments of the illustrated structure, the enclosure is made of a high-reflectivity acoustic plate, which can be a metal plate, plastic plate, hard fiberboard, plywood, gypsum board, synthetic resin board, or tempered glass plate. Similarly, the inner wall 1.1 of the acoustic waveguide channel is made of a high-reflectivity acoustic plate structure, which can be a metal plate, plastic plate, hard fiberboard, plywood, gypsum board, synthetic resin board, or tempered glass plate. The high-transmittance acoustic cover 4 is made of a high-reflectivity acoustic plate structure, which can be a metal plate, plastic plate, hard fiberboard, plywood, gypsum board, synthetic resin board, or tempered glass plate. When the enclosure and the high-transmittance acoustic cover are made of high-rigidity plates such as tempered glass plates or metal plates, the metamaterial unit can have good load-bearing capacity.

[0063] In some embodiments, each enclosure wall, each inner wall 1.1 of the acoustic waveguide channel, and the high-transmittance cover plate can be manufactured separately and then connected to form a whole by riveting, welding, or gluing. This facilitates separate manufacturing and assembly, and also makes it easy to adjust and assemble acoustic waveguide channels with different geometric configurations as needed.

[0064] In some embodiments, the enclosure walls, the inner walls 1.1 of each acoustic waveguide channel, and the high-transmittance acoustic cover plate can also be integrally formed by casting, 3D printing, or additive manufacturing. Integral forming can ensure the integrity of the product and also enable the metamaterial unit to have good load-bearing capacity.

[0065] The shape of the acoustic waveguide channel 1 in this invention is not limited. The acoustic waveguide channel 1 can be a straight channel or a tortuous channel, such as an L-shaped tortuous channel. A tortuous channel can significantly extend the propagation path of the sound wave while maintaining a constant overall thickness, thereby shifting its sound absorption frequency band to lower frequencies. The width of the acoustic waveguide channel 1 is not limited; it can be set at a constant width along its waveguide direction, or it can gradually change along its waveguide direction according to a certain pattern, or it can change with a gradient along its waveguide direction. (Refer to...) Figure 2 In one embodiment, the acoustic waveguide channel 1 is an L-shaped tortuous channel, and the width of the acoustic waveguide channel 1 is set at a constant width along its waveguide direction.

[0066] Reference Figure 3In one embodiment, the metamaterial cavity 2 contains three acoustic waveguide channels 1, each equipped with an impedance-modulated sound absorber 3. The impedance-modulated sound absorber 3 comprises a high-porosity sound-absorbing medium 3a and an impedance modulation channel 3b. The high-porosity sound-absorbing medium 3a covers the inner wall 1.1 of the acoustic waveguide channel, and one or more impedance modulation channels 3b are provided within the high-porosity sound-absorbing medium 3a. Specifically, of the three acoustic waveguide channels 1 within the metamaterial cavity 2, one acoustic waveguide channel 1 is straight, and the other two are L-shaped tortuous channels. The L-shaped tortuous channels can significantly extend the propagation path of sound waves while maintaining the overall thickness, thereby shifting the sound absorption frequency band to lower frequencies. The high-porosity sound-absorbing medium 3a in all three acoustic waveguide channels 1 fills the entire length of the acoustic waveguide channel. Each of the three acoustic waveguide channels has an impedance modulation channel 3b, and the axial direction of each impedance modulation channel 3b is consistent with the waveguide direction of the acoustic waveguide channel 1 in which it is located. Figure 3 The super material cavity 2 is equipped with a high acoustic transmittance cover plate 4. The high acoustic transmittance cover plate 4 has three rectangular openings 4.1 at the positions corresponding to the three impedance modulation channels 3b. The three impedance modulation channels 3b are connected to the outside through the corresponding openings 4.1 on the high acoustic transmittance cover plate 4.

[0067] In this invention, the cross-sectional shape of the impedance modulation channel 3b in the waveguide direction parallel to its acoustic waveguide channel 1 is not limited, and can be rectangular, conical, trapezoidal, rhomboid, or other polygonal. The introduction of the impedance modulation channel can effectively change the acoustic characteristics of the high-porosity sound-absorbing medium. By changing the geometric configuration of the impedance modulation channel, the acoustic impedance can be wide-bandwidth modulation, and a resonant absorption peak is generated in the low-frequency range, thereby significantly improving the sound absorption performance in the low-frequency range.

[0068] Reference Figure 4 , Figure 4 This is a schematic diagram of the structure of a metamaterial unit in one embodiment of the present invention, including a metamaterial cavity formed by multiple walls 2.1 and an acoustic waveguide channel 1 disposed in the metamaterial cavity, wherein an impedance-efficient modulation sound absorber 3 is disposed in the acoustic waveguide channel 1. Figure 4The acoustic waveguide channel is an L-shaped acoustic waveguide channel 1. An impedance-efficient modulation (EEM) sound absorber 3 is installed within the acoustic waveguide channel 1, and the EEM sound absorber 3 completely fills the entire acoustic waveguide channel 1. The EEM sound absorber 3 includes a high-porosity sound-absorbing medium 3a and an impedance modulation channel 3b. The high-porosity sound-absorbing medium 3a covers the inner wall 1.1 of the acoustic waveguide channel, and one or more impedance modulation channels 3b are provided within the high-porosity sound-absorbing medium 3a. The high-porosity sound-absorbing medium 3a covers the inner wall 1.1 of the acoustic waveguide channel. The high-porosity sound-absorbing medium 3a and the inner wall 1.1 of the acoustic waveguide channel can be fixedly connected by adhesive bonding, or by using ribs, grids, or meshes. The high-porosity sound-absorbing medium 3a can also be covered with a high-transmittance acoustic fabric and fixedly connected to the inner wall 1.1 of the acoustic waveguide channel. This improves the durability of the high-porosity sound-absorbing medium while ensuring sound wave transmission and absorption. An impedance modulation channel 3b is provided in the high-porosity sound-absorbing medium 3a. The axial direction of the impedance modulation channel 3b is consistent with the waveguide direction of the acoustic waveguide channel 1 it is in, and the cross-sectional shape of the impedance modulation channel 3b in the waveguide direction parallel to its acoustic waveguide channel 1 is rectangular. By changing the geometric configuration (such as length and width) of the impedance modulation channel 3b, wide-band amplitude modulation of the acoustic impedance can be achieved, while generating a resonant absorption peak in the low-frequency range, thereby improving the sound absorption performance in the low-frequency range.

[0069] Reference Figure 5 , Figure 5 This is a schematic diagram of the metamaterial unit in one embodiment of the present invention; an impedance-efficient modulation sound absorber 3 is disposed within the L-shaped acoustic waveguide channel 1, and the impedance-efficient modulation sound absorber 3 completely fills the entire acoustic waveguide channel 1. A high-porosity sound-absorbing medium 3a is fixed to the inner wall 1.1 of the acoustic waveguide channel. Figure 4 The difference in the illustrated embodiment is that, Figure 5 The illustrated embodiment includes two impedance modulation channels 3b within the high-porosity sound-absorbing medium 3a. One impedance modulation channel 3b is rectangular, while the other is parallel to the L-shaped acoustic waveguide channel 1, forming an L-shaped broken line. The axial direction of each impedance modulation channel 3b is consistent with the waveguide direction of its corresponding acoustic waveguide channel 1. By altering the geometric configuration of the impedance modulation channels 3b (such as the length, width, and spacing between adjacent channels 3b), wideband amplitude modulation of the acoustic impedance can be achieved, while simultaneously generating resonant absorption peaks in the low-frequency range, thereby improving the sound absorption performance in the low-frequency range.

[0070] Reference Figure 6 , Figure 6This is a schematic diagram of the metamaterial unit in one embodiment of the present invention. An impedance-modulated high-efficiency sound absorber 3 is disposed within the L-shaped acoustic waveguide channel 1, and the impedance-modulated high-efficiency sound absorber 3 completely fills the entire acoustic waveguide channel 1. A high-porosity sound-absorbing medium 3a is fixed to the inner wall 1.1 of the acoustic waveguide channel. A conical impedance modulation channel 3b is disposed within the high-porosity sound-absorbing medium 3a, meaning that the cross-sectional shape of the impedance modulation channel 3b in the waveguide direction parallel to its acoustic waveguide channel is conical. By changing the geometric configuration of the impedance modulation channel 3b (such as the length of the impedance modulation channel 3b, the size of the top channel opening, and the included angle of the bottom channel), wideband amplitude modulation of the acoustic impedance can be achieved, while generating a resonant absorption peak in the low-frequency range, thereby improving the sound absorption performance in the low-frequency range.

[0071] Reference Figure 7 , Figure 7 This is a schematic diagram of the metamaterial unit in one embodiment of the present invention. An impedance-modulated sound absorber 3 is disposed within the L-shaped acoustic waveguide channel 1, and the impedance-modulated sound absorber 3 completely fills the entire acoustic waveguide channel 1. A high-porosity sound-absorbing medium 3a is fixed to the inner wall 1.1 of the acoustic waveguide channel. An impedance modulation channel 3b is disposed within the high-porosity sound-absorbing medium 3a, which first contracts and then expands along the waveguide direction of the acoustic waveguide channel. The cross-sectional shape of the impedance modulation channel 3b in the waveguide direction parallel to its acoustic waveguide channel is similar to a rhombus. By changing the geometric configuration of the impedance modulation channel 3b (such as the length of the impedance modulation channel 3b, the size of the top channel opening, the size of the middle channel portion, and the size of the bottom channel), wideband amplitude modulation of the acoustic impedance can be achieved, while generating a resonant absorption peak in the low-frequency range, thereby improving the sound absorption performance in the low-frequency range.

[0072] It is understood that the geometric configuration of the impedance modulation channel 3b of the present invention is not limited to... Figure 3 , Figure 4 , Figure 5 , Figure 6 and Figure 7 The examples shown can be reasonably designed and adjusted by those skilled in the art.

[0073] In the superstructure module of the present invention, one or more acoustic waveguide channels 1 are provided in the metamaterial cavity 2. The arrangement of the acoustic waveguide channels 1 is not limited, and the shape of each acoustic waveguide channel 1 is not limited. Various combinations of acoustic waveguide channels 1 can be used.

[0074] The shape of the acoustic waveguide channel is not limited; it can be a straight channel or a tortuous channel. (Refer to...) Figure 8 , Figure 9 and Figure 10The invention provides three different types of acoustic waveguide channels: a straight acoustic waveguide channel, an L-shaped acoustic waveguide channel with one bend, and a hook-shaped acoustic waveguide channel with two bends. It is understood that the geometric configuration of the acoustic waveguide channel of this invention is not limited to... Figure 8 , Figure 9 and Figure 10 The examples shown can be reasonably designed and adjusted by those skilled in the art.

[0075] The high-porosity sound-absorbing medium 3a described in this invention can completely fill the entire acoustic waveguide channel, or it can fill a portion of the acoustic waveguide channel starting from the bottom. (See reference...) Figure 11 , Figure 11 In the embodiment described, each acoustic waveguide channel 1 within the metamaterial cavity 2 is filled with a high-porosity sound-absorbing medium 3a along its entire length, meaning the high-porosity sound-absorbing medium 3a completely fills each acoustic waveguide channel. (Refer to...) Figure 12 , Figure 12 In the embodiment shown, in each acoustic waveguide channel 1 provided in the metamaterial cavity 2, a high porosity sound-absorbing medium 3a fills a portion of the length of the acoustic waveguide channel from the bottom of the acoustic waveguide channel. Figure 12 The heights of the high-porosity sound-absorbing medium 3a filling the three acoustic waveguide channels are different.

[0076] In this invention, the metamaterial cavity 2 may or may not be equipped with a high-transmittance acoustic wave cover plate. If the metamaterial cavity 2 is equipped with a high-transmittance acoustic wave cover plate 4, the shape and distribution of the openings or slits on the cover plate 4 are not limited. The high-transmittance acoustic wave cover plate 4 can be a slit plate, a fully perforated plate, or a semi-perforated plate. Figure 13 , Figure 14 , Figure 15 As shown, several different cases of high acoustic transmittance cover plates 4 are illustrated. Figure 13 In the middle, the high-transmittance cover plate 4 on the metamaterial cavity 2 has 3 rectangular openings. Figure 14 In the metamaterial cavity 2, the high-transmittance cover plate 4 is provided with three long strip-shaped perforated bands, and each perforated band has multiple round or square holes. Figure 15 In the metamaterial cavity 2, the high-transmittance acoustic cover plate 4 is a fully perforated plate. The openings on the high-transmittance acoustic cover plate 4 are arranged in a matrix, and the shape of the openings is not limited; they can be circular or square. (See reference...) Figure 16 , Figure 16 The high-transmittance cover plate 4 is not installed on the cavity 2 of the super material.

[0077] Reference Figures 1 to 19The number, shape, and arrangement of acoustic waveguide channels 1 within the metamaterial cavity 2 are not limited. When the metamaterial cavity 2 can have multiple acoustic waveguide channels 1, the filling height of the high-porosity sound-absorbing medium 3a within each acoustic waveguide channel can be the same, partially the same, or different, and can be arbitrarily combined. The length, shape, and width of each acoustic waveguide channel can be the same, partially the same, or different, and can be arbitrarily combined. The number, geometric configuration, and distribution of impedance modulation channels 3b within the high-porosity sound-absorbing medium 3a of each acoustic waveguide channel can be the same, partially the same, or different, and can be arbitrarily combined. By designing these features differently, metamaterial units with different low-frequency high-efficiency absorption performance can be obtained.

[0078] The metamaterial unit provided by this invention introduces an impedance-modulated sound absorber into the acoustic waveguide channel. On the one hand, by utilizing its coupling resonance effect in the low-frequency band, an efficient resonance absorption peak can be generated in the low-frequency band, thereby improving the sound absorption performance in the low-frequency band. On the other hand, by changing the geometric configuration of the impedance modulation channel, wideband amplitude modulation of the acoustic impedance in the low-frequency band can be achieved, significantly improving the sound absorption performance in the low-frequency band.

[0079] The metastructure module provided by the present invention is composed of multiple metamaterial units for low-frequency broadband high-efficiency sound absorption provided in any one or more of the above embodiments, and the metamaterial units are connected in parallel.

[0080] The metamaterial units used in the metastructure module can be completely identical, partially identical, or completely different. Different metamaterial units have different low-frequency high-efficiency absorption properties. The methods for obtaining metamaterial units with different low-frequency high-efficiency absorption properties have been described in detail in the foregoing embodiments concerning metamaterial units, and will not be repeated here.

[0081] In one embodiment, multiple metamaterial units with different low-frequency high-efficiency absorption properties are connected in parallel. Through the coupling effect between the metamaterial units, a superstructure module with low-frequency broadband high-efficiency sound absorption and noise reduction performance is formed, thereby achieving low-frequency broadband high-efficiency sound absorption performance.

[0082] The superstructure module utilizes the wideband amplitude modulation of acoustic impedance by its metamaterial units and its low-frequency coupling resonance effect to significantly improve the sound absorption performance of low-frequency sound waves, while maintaining excellent sound absorption performance in the mid-to-high frequency range. It has the advantages of good low-frequency, wideband, and high-efficiency sound absorption performance, as well as simple structure, easy processing and manufacturing, and low cost.

[0083] Reference Figure 20This is a schematic diagram of a superstructure module provided in an embodiment of the present invention. The metamaterial units in the superstructure module are arranged in a one-dimensional periodic pattern. The length of the metamaterial units in the superstructure module along the x-axis is unlimited and can extend infinitely. The metamaterial units in the superstructure module are arranged periodically along the y-axis.

[0084] Reference Figure 21 This is a schematic diagram of a superstructure module provided in an embodiment of the present invention. The metamaterial units in the superstructure module are arranged in a two-dimensional periodic pattern. The metamaterial units in the superstructure module are arranged periodically along the x-axis and also periodically along the y-axis.

[0085] In a preferred embodiment of the present invention, the superstructure module is composed of two different metamaterial units connected in parallel, arranged in a two-dimensional periodic pattern. For example... Figure 22 As shown, a structural schematic diagram of the superstructure module is presented. Its structural dimensions are 80mm along the x-axis, 80mm along the y-axis, and 100mm along the z-axis. The superstructure module includes two acoustic waveguide channels 1: a straight channel and an L-shaped tortuous channel, with equal and gradient widths. Each impedance-modulated sound absorber 3 includes an impedance modulation channel 3b, with a rectangular cross-section parallel to the waveguide direction. The impedance-modulated sound absorber 3 completely fills the acoustic waveguide channel 1. The enclosure 2 is made of steel metal plates, connected by welding, providing good load-bearing capacity. The high-porosity sound-absorbing medium 3a is a foam-type porous material. The high-porosity sound-absorbing medium 3a is fixedly connected to the enclosure 2 by adhesive bonding. The metamaterial unit includes a high-transmittance sound wave cover plate 4, a slotted plate with rectangular slots, made of steel metal plates. Combined with the high-rigidity enclosure 2, this gives the superstructure module good overall load-bearing capacity. Figure 23 The figure shows the sound absorption coefficient curves corresponding to this embodiment. It can be seen that in the low-frequency broadband range of 273 to 1000 Hz, the sound absorption coefficient is above 0.9, with an average of 0.965; in the low-frequency broadband range of 294 to 779 Hz, the sound absorption coefficient is above 0.96, with an average of 0.984.

[0086] In another preferred embodiment of the invention, the superstructure module is composed of four different metamaterial units connected in parallel, arranged in a one-dimensional periodic pattern. For example... Figure 24The diagram shows the structural schematic of the superstructure module. Its structural dimension along the x-axis is 20mm, the structural dimension along the y-axis can be any preset size (chosen here as 60mm), and the structural dimension along the z-axis is 100mm. This superstructure module includes four acoustic waveguide channels 1: one straight channel and three L-shaped meandering channels, with equal and gradient widths. Each impedance-modulated sound absorber 3 consists of only one impedance-modulated channel 3b, and its cross-sectional shape parallel to the waveguide direction is conical. The impedance-modulated sound absorber 3 completely fills the acoustic waveguide channels 1. The enclosure 2 is made of tempered glass and formed by adhesive bonding. The high-porosity sound-absorbing medium 3a is a foam-type porous material. The high-porosity sound-absorbing medium 3a is fixedly connected to the enclosure 2 by adhesive bonding. Calculation results are available in the [reference needed]. Figure 25 In the frequency range of 271 to 20000 Hz, the sound absorption coefficient is above 0.928, with an average of 0.993; in the low-frequency broadband range of 260 to 1000 Hz, the sound absorption coefficient is above 0.9, with an average of 0.943.

[0087] The results of the above embodiments show that the present invention can significantly improve the sound absorption performance of low-frequency sound waves by utilizing its wideband amplitude modulation of acoustic impedance and its low-frequency coupling resonance effect, while maintaining excellent sound absorption performance in the mid-to-high frequency range, and has good low-frequency, wideband, and high-efficiency sound absorption performance.

[0088] All features disclosed in this specification, or steps in all disclosed methods or processes, may be combined in any manner, except for mutually exclusive features and / or steps. Any feature disclosed in this specification (including any appended claims, abstract, and drawings) may be replaced by other equivalent or similar features, unless specifically stated otherwise. That is, unless specifically stated otherwise, each feature is merely one example of a series of equivalent or similar features.

[0089] The above description is merely one preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Various modifications or other equivalent embodiments easily obtained by those skilled in the art based on or drawing upon the concept of the present invention are all within the scope of protection of the present invention.

Claims

1. A metamaterial unit for low-frequency broadband high-efficiency sound absorption, characterized in that, The device comprises a metamaterial cavity enclosed by multiple walls and an acoustic waveguide channel disposed within the metamaterial cavity. An impedance-modulated sound absorber is disposed within the acoustic waveguide channel. The impedance-modulated sound absorber includes a high-porosity sound-absorbing medium and an impedance modulation channel. The high-porosity sound-absorbing medium covers the inner wall of the acoustic waveguide channel, and one or more impedance modulation channels are disposed within the high-porosity sound-absorbing medium. The axial direction of the impedance modulation channel is consistent with the waveguide direction of the acoustic waveguide channel in which it is located. The cross-sectional shape of the impedance modulation channel in the waveguide direction parallel to its acoustic waveguide channel is rectangular, conical, trapezoidal, or rhomboid. The high-porosity sound-absorbing medium fills the entire acoustic waveguide channel or fills a portion of the acoustic waveguide channel from the bottom.

2. The metamaterial unit for low-frequency broadband high-efficiency sound absorption according to claim 1, characterized in that, The metamaterial unit also includes a high-transmittance acoustic cover plate, which is disposed on the metamaterial cavity. The acoustic waveguide channel inside the metamaterial cavity is connected to the outside through openings or slits on the high-transmittance acoustic cover plate.

3. The metamaterial unit for low-frequency broadband high-efficiency sound absorption according to claim 2, characterized in that, By changing the geometry of the impedance modulation channel, wideband amplitude modulation of acoustic impedance can be achieved, while generating resonant absorption peaks in the low-frequency range, thereby improving the sound absorption performance in the low-frequency range.

4. The metamaterial unit for low-frequency broadband high-efficiency sound absorption according to claim 2 or 3, characterized in that, The acoustic waveguide channel is a straight channel or a tortuous channel, and the width of the acoustic waveguide channel is constant, gradually changes, or varies with a gradient along its waveguide direction.

5. The metamaterial unit for low-frequency broadband high-efficiency sound absorption according to claim 1, characterized in that, The metamaterial cavity is made of metal plate, plastic plate, hard fiberboard, plywood, gypsum board, synthetic resin board or tempered glass plate. The metamaterial cavity is formed by riveting, welding or gluing, or the metamaterial cavity is formed as a single piece by casting or additive manufacturing.

6. The metamaterial unit for low-frequency broadband high-efficiency sound absorption according to claim 1, 2, 3, or 5, characterized in that, High-porosity sound-absorbing media can be organic fiber-type porous materials, inorganic fiber-type porous materials, foam-type porous materials, or metal-type porous materials.

7. A superstructure module, characterized in that, It includes multiple metamaterial units for low-frequency broadband high-efficiency sound absorption as described in claim 1, with each metamaterial unit connected in parallel.

8. The superstructure module according to claim 7, characterized in that, The metamaterial units are arranged in a one-dimensional periodic pattern or a two-dimensional periodic pattern.

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