Broadband low-frequency sound absorption structure with sub-wavelength thickness

Abstract

The invention discloses a broadband low-frequency sound absorption structure with sub-wavelength thickness, and relates to the technical field of noise control, the broadband low-frequency sound absorption structure with sub-wavelength thickness comprises a box body and fractal members arranged in the box body in a rectangular array mode, and the four adjacent fractal members arranged in the rectangular array mode are combined to form a first cavity; a plurality of fractal components close to the inner side surface of the box body are combined with the inner side surface of the box body to form a second cavity; the fractal component comprises a first plate body and a second plate body, the first plate body is provided with a third cavity, and the second plate body is provided with a fourth cavity; a cover plate is arranged on the top face of the box body, and a plurality of through holes communicated with the first cavity, the second cavity, the third cavity and the fourth cavity respectively are formed in the cover plate. According to the broadband low-frequency sound absorption structure with the sub-wavelength thickness, the technical problems that an existing composite sound absorption structure can only meet the sound wave resonance requirement of a limited frequency band, the sound absorption frequency band range is narrow, and sub-wavelength magnitude light and thin design cannot be achieved are solved.

Description

Technical Field

[0001] This invention relates to the field of noise control technology, and in particular to a broadband low-frequency sound-absorbing structure with subwavelength thickness. Background Technology

[0002] Low-frequency noise, due to its long propagation distance, strong penetration, and slow energy attenuation, is a core challenge in industrial and residential environmental noise control. Traditional porous sound-absorbing materials rely on internal pores to dissipate sound energy, requiring a thickness of 1 / 4 or more of the sound wave wavelength for effective sound absorption in the low-frequency range, which cannot meet the requirements for lightweight and thin engineering. While resonant sound-absorbing structures such as Helmholtz resonators and single-layer perforated plates can enhance low-frequency sound absorption through resonance, their absorption bandwidth is narrow (only 10%-20% of the center frequency), making it difficult to cover the entire wideband absorption range. Cover plate sound-absorbing structures dissipate sound energy through the vibration, friction, and resonance of the air column at the through-holes, offering advantages such as simple structure and strong weather resistance. However, relying solely on the cover plate design makes it difficult to simultaneously achieve a high sound absorption coefficient and subwavelength thickness within the low-frequency wideband.

[0003] Existing composite sound-absorbing structures enhance sound absorption performance through multi-component coupling, but they employ conventional geometric configurations and have a single structural dimension, only capable of matching the sound wave resonance requirements of a limited frequency band. Their sound absorption bandwidth is narrow, and they require increased cavity depth or thickness to enhance low-frequency sound absorption. For low-frequency sound absorption, increasing cavity depth or structural thickness is often necessary, making it impossible to achieve a subwavelength-level thin and lightweight design. Therefore, this paper proposes a broadband low-frequency sound-absorbing structure with subwavelength thickness to address the aforementioned problems. Summary of the Invention

[0004] The purpose of this invention is to provide a broadband low-frequency sound-absorbing structure with subwavelength thickness, which solves the technical problems of existing composite sound-absorbing structures that can only match the sound wave resonance requirements of a limited frequency band, have a narrow sound absorption frequency range, and cannot achieve a lightweight and thin design at the subwavelength level.

[0005] To achieve the above objectives, the present invention provides a broadband low-frequency sound-absorbing structure with subwavelength thickness, comprising: a housing and fractal members arranged in a rectangular array within the housing, two adjacent fractal members being connected, four adjacent fractal members arranged in a rectangular array being combined to form a first cavity, and a plurality of fractal members near the inner side of the housing being combined with the inner side of the housing to form a second cavity. The fractal component includes: a first plate and a second plate disposed on the outer periphery of the first plate, the second plate being a proportionally reduced structure of the first plate, and the first plate having a third cavity and the second plate having a fourth cavity; The top surface of the box is provided with a cover plate for sealing the box. The outer side of the cover plate faces the sound source, and the cover plate is provided with a plurality of through holes that are respectively connected to the first cavity, the second cavity, the third cavity and the fourth cavity.

[0006] Preferably, both the first plate and the second plate are star-shaped, and the first plate is provided with a number of first convex corners and a number of first concave corners alternately along its circumferential direction. The second plate is provided at the positions of the first convex corners and the positions of the first concave corners, and the second plate is provided with a number of second convex corners and a number of second concave corners alternately along its circumferential direction.

[0007] Preferably, on the projection plane in the first direction, the through hole on the cover plate that communicates with the third cavity is located at the second convex corner position; the through hole on the cover plate that communicates with the fourth cavity is located at the second convex corner position.

[0008] Preferably, the size ratio between the second plate and the first plate is 1:6 to 1:2.

[0009] Preferably, the fractal component includes a thick-walled portion and a thin-walled portion, wherein the thickness of the thick-walled portion is between 1 and 2 mm, and the thickness of the thin-walled portion is between 0.25 and 0.5 mm.

[0010] Preferably, the thickness of the cover plate is between 0.5 and 1.5 mm, and the diameter of the through hole is between 0.8 and 1.5 mm.

[0011] Preferably, the fractal component has a square structure as a whole, and the side length of the fractal component as a whole is between 20-30mm.

[0012] Preferably, a connecting rod for connecting two adjacent fractal components is provided at the second concave corner position, and the distance between the connecting rod and the inner side of the box is between 1 and 5 mm.

[0013] Preferably, the heights of the first plate and the second plate are equal, and the heights of both the first plate and the second plate are between 50-90mm, and the included angle between the first convex angle and the second convex angle is between 40-60°.

[0014] Preferably, the box body, the cover plate, the first plate, the second plate, and the connecting rod are made of one of the following materials: metal, a composite material formed by combining carbon fiber and glass fiber, resin, and plastic.

[0015] Compared to the aforementioned background technology, the broadband low-frequency sound-absorbing structure with subwavelength thickness provided by this invention has the following beneficial effects: In this invention, four adjacent fractal components arranged in a rectangular array combine to form a first cavity; several fractal components near the inner side of the box combine with the inner side of the box to form a second cavity; the first plate and the second plate are also respectively provided with a third cavity and a fourth cavity, enabling the sound-absorbing structure to form a resonant unit matching the resonance requirements of multiple frequency bands, resulting in a wide sound absorption frequency range. Furthermore, each through-hole on the cover plate is connected to any one or two of the first, second, third, and fourth cavities. The larger cavity provides low-frequency acoustic impedance, and the smaller cavity excitation viscous loss, while the differential impedance forms a shear flow within the same through-hole to enhance sound dissipation over a wide frequency range, effectively improving the low-frequency sound absorption performance of the sound-absorbing structure. This enhances the low-frequency sound absorption effect without increasing the depth or thickness of the sound-absorbing structure, achieving a subwavelength-level thin and light design while ensuring a high sound absorption coefficient. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0017] Figure 1 This is a three-dimensional structural diagram of the sound-absorbing structure provided in an embodiment of the present invention; Figure 2 This is a three-dimensional structural diagram of the sound-absorbing structure after the cover plate is hidden, as provided in an embodiment of the present invention. Figure 3 This is an exploded view of the sound-absorbing structure provided in an embodiment of the present invention; Figure 4 This is a planar transparent schematic diagram of the sound-absorbing structure provided in an embodiment of the present invention; Figure 5 This is a side view of the sound-absorbing structure provided in an embodiment of the present invention; Figure 6 This is a three-dimensional structural diagram of the fractal component provided in an embodiment of the present invention; Figure 7 The following is a simulation and experimental curve of the sound absorption coefficient of Embodiment 1 of the present invention; Figure 8 This is a simulation curve of the sound absorption coefficient of Embodiment 2 of the present invention; Figure 9 This is a simulation curve of the sound absorption coefficient of Embodiment 3 of the present invention.

[0018] Specifically, 100 - box body; 110 - cover plate; 111 - through hole; 200 - fractal component; 210 - first plate; 211 - third cavity; 212 - first convex angle; 213 - first concave angle; 220 - second plate; 221 - fourth cavity; 222 - second convex angle; 223 - second concave angle; 230 - connecting rod; 240 - first cavity; 250 - second cavity. Detailed Implementation

[0019] 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 some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] like Figure 1 , Figure 2 and Figure 3 As shown, to achieve the above objectives, the present invention provides a broadband low-frequency sound-absorbing structure with subwavelength thickness, comprising: a housing 100 and fractal components 200 arranged in a rectangular array within the housing 100. One end of each fractal component 200 is sealed to the bottom surface of the housing 100. Adjacent fractal components 200 are connected. Four adjacent fractal components 200 arranged in a rectangular array form a first cavity 240. Each first cavity 240 is independent and not interconnected. Several fractal components 200 near the inner surface of the housing 100 combine with the inner surface of the housing 100 to form a second cavity 250. The second cavity 250 is located circumferentially inside the housing 100, and there is only one second cavity 250 that is integrally closed-loop in shape within the housing 100. It should be noted that the fractal component 200 includes a first plate 210 and a second plate 220 disposed on the outer periphery of the first plate 210. The second plate 220 is a proportionally reduced structure of the first plate 210, that is, the first plate 210 and the second plate 220 are structurally identical, differing only in size. The first plate 210 has a third cavity 211, and the second plate 220 has a fourth cavity 221. Four adjacent fractal components 200 arranged in a rectangular array combine to form the first cavity 240. Several fractal components 200 close to the inner side of the box 100 combine with the inner side of the box 100 to form the second cavity 250. The first plate 210 and the second plate 220 are also respectively provided with the third cavity 211 and the fourth cavity 221, so that the sound absorption structure can form a resonant unit that matches the resonance requirements of multiple frequency bands of sound waves, resulting in a wide sound absorption frequency range.

[0022] The top surface of the housing 100 is provided with a cover plate 110 for sealing the housing 100. The end of the fractal member 200 abuts against the inner side of the cover plate 110. The outer side of the cover plate 110 faces the sound source. The cover plate 110 is provided with a plurality of through holes 111 that are respectively connected to the first cavity 240, the second cavity 250, the third cavity 211 and the fourth cavity 221. Each through hole 111 on the cover plate 110 is respectively connected to any one or two of the first cavity 240, the second cavity 250, the third cavity 211 and the fourth cavity 221. Among them, a portion of the through holes 111 on the cover plate 110 are only connected to the second cavity 250, serving as a resonant unit for conventionally matching the resonance requirements of a certain frequency band of sound waves. The other part of the through holes 111 on the cover plate 110 are connected to any one or two of the first cavity 240, the third cavity 211 and the fourth cavity 221. The larger cavity provides low-frequency acoustic impedance and the smaller cavity excitation viscous loss. At the same time, the differential impedance is used to form a shear flow in the same through hole 111 to enhance the sound wave dissipation in a wide frequency range, effectively improving the sound absorption performance of the sound absorption structure at low frequencies. The low-frequency sound absorption effect can be enhanced without increasing the depth or thickness of the sound absorption structure. While ensuring a high sound absorption coefficient, a subwavelength-level thin and light design is achieved.

[0023] It should be noted that the fractal components 200 are arranged in a periodic pattern of n×n within the box 100 to form a sound-absorbing structure, such that the overall sound-absorbing structure includes n² third cavities 211, n-1² first cavities 240, one second cavity 250, and 8n² fourth cavities 221, where n represents the number of fractal components 200.

[0024] In some embodiments of the present invention, the first plate 210 and the second plate 220 are both star-shaped. The first plate 210 is provided with a plurality of first convex corners 212 and a plurality of first concave corners 213 alternately along its circumferential direction. The second plate 220 is provided at each position of the first convex corner 212 and at each position of the first concave corner 213 of the first plate 210. The second plate 220 is also provided with a plurality of second convex corners 222 and a plurality of second concave corners 223 alternately along its circumferential direction. By cooperating with the star-shaped first plate 210 and the first convex angle 212 and the first concave angle 213 on the first plate 210, and the second plate 220 and the second convex angle 222 and the second concave angle 223 on the second plate 220, multiple fractal components 200 can be assembled and spliced ​​within the box 100 to form cavity structures of various sizes and specifications, such as the first cavity 240, the second cavity 250, the third cavity 211, and the fourth cavity 221. This gives the overall sound absorption structure a richer structural scale hierarchy, which can accurately match the resonance requirements of sound waves in different frequency bands, thereby effectively widening the sound absorption frequency band range. Through multi-scale cavities, full coverage resonance of multi-frequency sound waves is achieved. Each cavity and the corresponding through hole 111 form a precise acoustic coupling, improving the uniformity and effectiveness of broadband sound absorption.

[0025] It should be noted that by combining the first plate 210 and the second plate 220 to form the fractal component 200, while having the diversity of cavity structure dimensions and adapting to the resonance requirements of multi-frequency sound waves, the complexity of splicing the fractal component 200 and forming the cavity structure is not increased, which facilitates subsequent processing, manufacturing and assembly, and effectively improves the sound absorption performance of the overall sound absorption structure as well as the manufacturing and maintenance costs.

[0026] In some embodiments of the present invention, on the projection plane in the first direction, the through hole 111 on the cover plate 110 that communicates with the third cavity 211 is located at the second convex angle 222; the through hole 111 on the cover plate 110 that communicates with the fourth cavity 221 is located at the second convex angle 222, to ensure that the through hole 111 communicating with the third cavity 211 can simultaneously connect to the fourth cavity 221, and the through hole 111 communicating with the first cavity 240 can also simultaneously connect to the fourth cavity 221, ensuring that the shear flow is formed in the same through hole 111 by utilizing the differential impedance to enhance the sound wave dissipation in a wide frequency range and improve the sound absorption performance of the sound absorption structure at low frequencies. Moreover, by forming a stable communication relationship between a portion of the through holes 111 on the cover plate 110 and the corresponding third cavity 211 and fourth cavity 221, the problem of poor sound energy conduction caused by misalignment of the through holes 111 with the third cavity 211 or the fourth cavity 221 is avoided, thereby ensuring the sound absorption effect of the sound absorption structure.

[0027] like Figure 4As shown, it should be noted that the through hole 111 on the cover plate 110 that connects to the third cavity 211 is not exactly located at the second convex angle 222; the through hole 111 on the cover plate 110 that connects to the fourth cavity 221 is not exactly located at the second convex angle 222, but is finely adjusted according to different needs to adapt to different low-frequency sound waves. Assuming the geometric center of the third cavity 211 is the first coordinate origin, the through holes 111 at the four second convex corners 222 of the third cavity 211 (upper left, upper right, lower left, lower right) are obtained by moving the through holes 111 at the first coordinate origin 8.15-8.65mm to the upper left, lower right, and upper right, and lower left along the first and second directions, respectively. Assuming the geometric center of the fourth cavity 221 is the second coordinate origin, the through holes 111 at the four second convex corners 222 of the fourth cavity 221 (upper left, upper right, lower left, lower right) are obtained by moving the through holes 111 at the second coordinate origin 211 to the upper left, lower right, upper right, and lower left along the first and second directions, respectively, 2.9-3.9mm. The first direction is referenced in the attached diagram. Figure 4 For the direction of X, please refer to the attached second direction. Figure 4 In the Y direction, the first direction is perpendicular to the second direction, together forming a planar coordinate system. It should be further explained that the distribution of the through holes 111 on the cover plate 110 allows the same through hole 111 to be simultaneously distributed above the third cavity 211 and the fourth cavity 221. The moving distance of the through hole 111, i.e., its distribution position, directly affects its contact ratio with the third cavity 211 and the fourth cavity 221, thereby controlling the sound absorption performance. This allows the sound absorption structure to be parametrically designed for the sound absorption needs of different noise environments, thus flexibly adapting to diverse noise reduction scenarios.

[0028] In some embodiments of the present invention, the size ratio between the second plate 220 and the first plate 210 is 1:6 to 1:2. Preferably, the size ratio between the second plate 220 and the first plate 210 is 1:4, wherein the size ratio between the second plate 220 and the first plate 210 is also 1:4. Reasonably setting the ratio between the second plate 220 and the first plate 210 ensures the tightness of the splicing and fitting between the second plate 220 and the first plate 210, avoiding problems such as misalignment of the first plate 210 and the second plate 220 and irregular cavity forming due to proportional imbalance, thus ensuring the integrity and stability of the overall structure of the fractal component 200. Simultaneously, the first plate 210 and the second plate 220 can accurately match their respective acoustic functions, allowing the third cavity 211 and the fourth cavity 221 to form a size gradient adapted to multi-frequency sound waves. The third cavity 211 and the fourth cavity 221 can respectively adapt to low-frequency sound waves of different frequencies, further enriching the structural scale hierarchy of the sound-absorbing structure.

[0029] like Figure 6As shown, in some embodiments of the present invention, the fractal component 200 includes a thick-walled portion and a thin-walled portion. The thickness of the thick-walled portion is between 1-2 mm, and the thickness of the thin-walled portion is between 0.25-0.5 mm. The thick-walled portion and the thin-walled portion are combined to form a complete star-shaped fractal component 200. The first plate 210 is provided with the thick-walled portion and the thin-walled portion, and the second plate 220 is the thin-walled portion, located at the position of the thin-walled portion on the first plate 210. By limiting the thickness of the thick-walled portion to between 1-2 mm and the thickness of the thin-walled portion to between 0.25-0.5 mm, the lightweight design of the thin-walled portion is used to meet the lightweight requirements of the fractal component 200, avoiding the overall sound absorption structure from being too heavy due to excessive overall wall thickness, thus meeting the core design goals of subwavelength thickness and lightweight of the sound absorption structure. Moreover, relying on the structural strength of the thick-walled part, it provides a stable support for the fractal component 200, thereby enhancing the overall structural rigidity of the fractal component 200 and avoiding problems such as deformation and breakage during use, so as to ensure the structural stability of the fractal component 200. In other words, the overall sound-absorbing structure has a certain mechanical strength and can be integrated into the carrier such as walls and equipment shells, thus taking into account both noise reduction function and structural support requirements.

[0030] In some embodiments, the thickness of the cover plate 110 is between 0.5 and 1.5 mm, that is, the length of the through hole 111 is between 0.5 and 1.5 mm, and the length of the through hole 111 matches the thickness of the cover plate 110. In addition, the diameter of the through hole 111 is between 0.8 and 1.5 mm. This design is able to adapt to the conduction characteristics of sound energy within the through hole 111. The key to these two size ranges is that the through hole 111 will not cause sound energy to penetrate too quickly due to excessively large diameter or short length, nor will it cause sound energy conduction to be obstructed due to excessively small diameter or long length. This allows sound waves to smoothly pass through the through hole 111 into the first cavity 240, the second cavity 250, the third cavity 211, and the fourth cavity 221, effectively enhancing the shear flow effect brought about by the differential impedance, thereby causing the air to form a stable shear motion within the through hole 111 and amplifying the frictional dissipation effect of sound energy.

[0031] It should be noted that the design of the two size ranges mentioned above allows the through-hole 111 to form an acoustic fit with the first cavity 240, the second cavity 250, the third cavity 211, and the fourth cavity 221 of the fractal component 200, respectively. This better coordinates the low-frequency acoustic impedance of the larger cavity with the viscous loss of the smaller cavity. The coupling effect of a single through-hole 111 with different cavities is more efficient, and the synergistic effect of multiple through-holes 111 is more significant, further improving the acoustic energy dissipation efficiency in the low-frequency wideband. Furthermore, limiting the thickness of the cover plate 110 to between 0.5-1.5mm achieves a lightweight design for the cover plate 110, aligning with the design goal of subwavelength thickness of the sound-absorbing structure and avoiding an increase in the overall thickness of the sound-absorbing structure due to an excessively thick cover plate 110.

[0032] In some embodiments of the present invention, the fractal component 200 is generally square in shape, and the side length of the overall fractal component 200 is between 20-30 mm. Preferably, the side length of the overall fractal component 200 is 25 mm. The fractal components 200 are arranged in a rectangular array inside the box 100, with one end sealed to the bottom surface of the box 100. Adjacent fractal components 200 are interconnected, and four adjacent square fractal components 200 enclose each other to form a first cavity 240. The square structure makes the connection and fit of adjacent fractal components 200 higher, so as to ensure the consistency of the shape of each first cavity 240, thereby ensuring the uniformity of the sound absorption effect of the first cavity 240 in the sound absorption structure.

[0033] In some embodiments of the present invention, a connecting rod 230 for connecting two adjacent fractal components 200 is provided at the second concave angle 223. The connecting rod 230 serves as a connection structure between adjacent fractal components 200, realizing a stable connection between two adjacent fractal components 200 within the housing 100. The end face of the connecting rod 230 in one fractal component 200 is in contact with the end face of the connecting rod 230 in another fractal component 200, so that a seamless and stable connection relationship is formed between adjacent fractal components 200. This can block the spatial communication between the first cavities 240 formed by four adjacent fractal components 200 within the same housing 100, ensuring that all first cavities 240 remain independent and unconnected to each other. This avoids problems such as acoustic impedance disorder and acoustic crosstalk caused by communication between first cavities 240, effectively ensuring that each first cavity 240 can stably perform its acoustic function as an independent acoustic unit. On the other hand, all the first cavities 240 remain independent of each other and are not connected to each other, which can ensure that the volume and acoustic characteristics of the first cavity 240 are consistent, thereby enabling the overall sound absorption structure to achieve a more efficient and uniform sound absorption effect in the low-frequency wide frequency range.

[0034] In addition, the distance between the connecting rod 230 and the inner side of the box 100 is between 1 and 5 mm, so that the second cavity 250 formed by the fractal components 200 close to the inner side of the box 100 and the inner side of the box 100 is an interconnected, closed annular cavity. This distance range will not cause the effective volume of the second cavity 250 to be dispersed due to excessive distance, nor will it cause structural interference between the connecting rod 230 and the inner side of the box 100 due to excessive distance. This ensures that the second cavity 250 always maintains complete connectivity and a regular annular structure, so that low-frequency sound waves can fully propagate in the second cavity 250 and form a strong resonance effect, so as to better exert the low-frequency acoustic impedance.

[0035] like Figure 5 and Figure 6 As shown, in some embodiments of the present invention, the first plate 210 and the second plate 220 are of equal height, such that the two end faces of the first plate 210 and the second plate 220 are respectively attached to the inner bottom surface of the box 100 and the inner side surface of the cover plate 110. The first cavity 240, the second cavity 250, the third cavity 211 and the fourth cavity 221 are all independent of each other and not connected to each other, ensuring that the volume and acoustic characteristics of the first cavity 240, the second cavity 250, the third cavity 211 and the fourth cavity 221 are consistent. Optionally, the heights of both the first plate 210 and the second plate 220 are between 50-90mm, and the included angle between the first convex angle 212 and the second convex angle 222 is between 40-60°. This ensures that the fractal component 200 has sufficient structural rigidity to resist external deformation during processing or use, ensuring the structural strength of the overall sound-absorbing structure. Simultaneously, it ensures that each cavity formed by the fractal component 200 maintains a reasonable spatial volume and shape to meet the requirements of low-frequency sound wave propagation and resonance. Furthermore, it can adapt to the molding characteristics of manufacturing processes such as 3D printing, preventing defects such as excessive overhang or warping during printing due to excessive height or steep angles, and avoiding structural redundancy and increased material consumption due to insufficient height or gentle angles. This effectively improves the printing yield of the fractal component 200 and reduces processing difficulty and manufacturing costs.

[0036] In some embodiments of the present invention, the housing 100, cover plate 110, first plate 210, second plate 220, and connecting rod 230 are made of one of the following materials: metal, composite material formed by combining carbon fiber and glass fiber, resin, and plastic. Each of these materials can be individually adapted to the processing and manufacturing of all structural components, ensuring good structural adaptability and connection fit after molding. This guarantees a sealed fit between the housing 100 and cover plate 110, a sealed connection between the fractal component 200 and the bottom surface of the housing 100, and a close fit between the end faces of the connecting rods 230. Consequently, the fractal component 200, after being assembled within the housing 100, forms a structurally stable sound-absorbing structure.

[0037] It's important to note that the diverse material selection is primarily designed to meet the needs of various application scenarios. The properties of different materials are precisely tailored to the environmental requirements of different environments. For example, metal materials possess excellent high-temperature resistance, corrosion resistance, and structural strength, making them suitable for harsh environments such as industrial high-temperature workshops and engine compartments. Composite materials formed from carbon fiber and glass fiber combine the advantages of lightweight and high rigidity, ensuring the overall structural strength of the sound-absorbing structure while meeting the requirements of lightweight design. Resin and plastic materials offer convenient processing and molding, low cost, and good sound and heat insulation properties, making them suitable for conventional low-frequency noise reduction scenarios. Furthermore, the diverse material selection is highly compatible with different manufacturing processes such as 3D printing, injection molding, and sheet metal processing. Metal materials are compatible with sheet metal and metal 3D printing processes, while composite materials, resins, and plastics are compatible with fused deposition modeling (FDM), photopolymerization, and other 3D printing processes, as well as injection molding. Flexible selection of processing methods based on production needs and scenario requirements facilitates small-batch customized production and also meets the needs of large-scale engineering applications, effectively reducing manufacturing costs and improving production efficiency.

[0038] Example 1

[0039] Simulation Test: The overall height of the sound-absorbing structure was set to 60.8 mm, consisting of fractal components 200 arranged in a 3×3 periodic array, including nine third cavities 211, four first cavities 240, one second cavity 250, and 72 fourth cavities 221. The thick-walled portion of each fractal component 200 is 1 mm, and the thin-walled portion is 0.5 mm. The angles of the first convex angle 212 and the second convex angle 222 are both 50°. The side length of a single fractal component 200 is 25 mm. The dimensional ratio between the second plate 220 and the first plate 210 is 1:4. The distance between the inner side of the box 100 and the outermost connecting rod 230 of the fractal component 200 is 2.5 mm. The thickness of the bottom surface and each side surface of the box 100 is 2 mm. A cover plate 110 with a thickness of 0.8 mm and a through hole 111 with a diameter of 1 mm are selected. A portion of the through holes 111 on the cover plate 110 are connected only to the second cavity 250, and the other portion of the through holes 111 on the cover plate 110 are connected to any one or two of the first cavity 240, the third cavity 211, and the fourth cavity 221. The through hole 111 on the cover plate 110 connected to the third cavity 211 is located at the second convex angle 222. The through hole 111 on the cover plate 110 connected to the fourth cavity 221 is located at the second convex angle 222, that is, it is set by translating 8.4 mm from the geometric center of the third cavity 211 along the first direction and the second direction. The through hole 111 at the second convex angle 222 is set by translating 3.2 mm from the geometric center of the fourth cavity 221 along the first direction and the second direction. The through hole 111 connected to the second cavity 250 is located in the central region of the second cavity 250. Based on the above geometric parameters, a three-dimensional simulation model is established in simulation software. Preferably, the simulation software is COMSOL Multiphysics. The simulation results are obtained by calculating the sound pressure distribution and sound absorption coefficient curves.

[0040] Experimental Testing: To verify the accuracy of the finite element simulation calculations, the sound absorption coefficient of the sound-absorbing structure was measured using an impedance tube measurement system according to the GB / T18696.2-2002 standard. Preferably, the impedance tube was a BOACH Test-HW-SIT square impedance tube with a cavity diameter of 100mm. The test frequency range was 100-1200Hz, and the sampling interval was 1Hz. The sound absorption coefficient of the sound-absorbing structure was calculated using software.

[0041] Results Analysis: Comparison of sound absorption coefficient curves obtained from simulation and experiments (e.g.) Figure 7As shown, the two have a high degree of agreement in the 250-1050Hz frequency band. The overall sound absorption structure has a wide sound absorption bandwidth and high amplitude. In this embodiment, the sound absorption structure has an average sound absorption coefficient of 0.8 in the 250-800Hz bandwidth (550Hz) and an average sound absorption coefficient of 0.9 in the 305-695Hz bandwidth (390Hz). At the same time, the total thickness of the structure is only 61.75mm (including the cover plate 110 with a thickness of 0.75mm), which is about 1 / 22 of the wavelength of 250Hz sound wave (about 1.37m), realizing subwavelength design, thereby meeting the needs of modern engineering for lightweight and compact structures.

[0042] Example 2

[0043] Simulation Test: The overall height of the sound-absorbing structure was set to 85mm, consisting of fractal components 200 arranged in a 3×3 periodic array, including nine third cavities 211, four first cavities 240, one second cavity 250, and 72 fourth cavities 221. The thick-walled portion of each fractal component 200 is 1.2mm, and the thin-walled portion is 0.3mm. The angles of the first convex angle 212 and the second convex angle 222 are both 50°. The side length of a single fractal component 200 is 25mm. The dimensional ratio between the second plate 220 and the first plate 210 is 1:4. The distance between the inner side of the box 100 and the outermost connecting rod 230 of the fractal component 200 is 2.5mm. The thickness of the bottom surface and each side surface of the box 100 is 1mm. A cover plate 110 with a thickness of 0.6 mm and a through hole 111 with a diameter of 1.2 mm are selected. A portion of the through holes 111 on the cover plate 110 are connected only to the second cavity 250, while the other portion of the through holes 111 on the cover plate 110 are connected to any one or two of the first cavity 240, the third cavity 211, and the fourth cavity 221. The through hole 111 on the cover plate 110 connected to the third cavity 211 is located at the second convex angle 222. The through hole 111 on the cover plate 110 connected to the fourth cavity 221 is located at the second convex angle 222, that is, it is set by translating 8 mm from the geometric center of the third cavity 211 along the first and second directions. The through hole 111 at the second convex angle 222 is set by translating 3.82 mm from the geometric center of the fourth cavity 221 along the first and second directions. The through hole 111 connected to the second cavity 250 is located in the central region of the second cavity 250. Based on the above geometric parameters, a three-dimensional simulation model is established in the simulation software, and the simulation results are obtained by calculating the sound pressure distribution and sound absorption coefficient curves.

[0044] Results Analysis: The sound absorption coefficient curve obtained from the simulation is as follows: Figure 8 As shown, in this embodiment, the sound-absorbing structure has an average sound absorption coefficient of 0.8 in the 270-730Hz wideband and an average sound absorption coefficient of 0.9 in the 310-650Hz wideband.

[0045] Example 3

[0046] Simulation Test: The overall height of the sound-absorbing structure is set to 75mm, consisting of fractal components 200 arranged in a 3×3 periodic array, including nine third cavities 211, four first cavities 240, one second cavity 250, and 72 fourth cavities 221. The thick-walled portion of each fractal component 200 is 1mm, and the thin-walled portion is 0.25mm; the angles of the first convex angle 212 and the second convex angle 222 are both 50°; the side length of a single fractal component 200 is 25mm; the dimensional ratio between the second plate 220 and the first plate 210 is 1:4; the distance between the inner side of the box 100 and the outermost connecting rod 230 of the fractal component 200 is 2.5mm; the thickness of the bottom surface of the box 100 is 1mm; and the thickness of each side surface of the box 100 is 2mm. A cover plate 110 with a thickness of 0.9 mm and a through hole 111 with a diameter of 1 mm are selected. A portion of the through holes 111 on the cover plate 110 are connected only to the second cavity 250, and the other portion of the through holes 111 on the cover plate 110 are connected to any one or two of the first cavity 240, the third cavity 211, and the fourth cavity 221. The through hole 111 on the cover plate 110 connected to the third cavity 211 is located at the second convex angle 222. The through hole 111 on the cover plate 110 connected to the fourth cavity 221 is located at the second convex angle 222, that is, it is set by translating 8.4 mm from the geometric center of the third cavity 211 along the first direction and the second direction. The through hole 111 at the second convex angle 222 is set by translating 3.2 mm from the geometric center of the fourth cavity 221 along the first direction and the second direction. The through hole 111 connected to the second cavity 250 is located in the central region of the second cavity 250. Based on the above geometric parameters, a three-dimensional simulation model was established, and the simulation results were obtained by calculating the sound pressure distribution and sound absorption coefficient curves.

[0047] Results Analysis: The sound absorption coefficient curve obtained from the simulation is as follows: Figure 9 As shown, in this embodiment, the sound-absorbing structure has an average sound absorption coefficient of 0.8 in the 240-680Hz wideband and an average sound absorption coefficient of 0.9 in the 270-580Hz wideband.

[0048] The above embodiments 1-3, by adjusting the parameters of the box 100, cover plate 110, through hole 111, first plate 210, and second plate 220, flexibly control the sound absorption performance according to actual needs. This allows the sound absorption structure to be parametrically designed for the sound absorption requirements of different noise environments, thus adapting to diverse noise reduction scenarios. Furthermore, simulation and experimental results in the above embodiments show that within a wide frequency band of 250-800Hz, the average sound absorption coefficient of the sound absorption structure reaches over 0.8, meeting the requirements for low-frequency broadband and high-efficiency sound absorption. Compared to traditional conventional geometric configurations, composite sound absorption structures with a single structural dimension offer better sound absorption performance, not only broadening the sound absorption frequency band but also increasing the overall sound absorption coefficient amplitude.

[0049] In summary, the first cavity 240, the second cavity 250, the third cavity 211, and the fourth cavity 221 in this invention enable the sound-absorbing structure to form a resonant unit that matches the resonance requirements of multiple frequency bands of sound waves, resulting in a wide sound absorption frequency range. Furthermore, a portion of the through holes 111 on the cover plate 110 are connected to any one or two of the first cavity 240, the third cavity 211, and the fourth cavity 221. The larger cavity provides low-frequency acoustic impedance, and the smaller cavity excitation viscous loss, while the differential impedance creates shear flow within the same through hole 111 to enhance sound wave dissipation over a wide frequency range, improving the sound absorption performance of the sound-absorbing structure at low frequencies. This achieves a subwavelength-level thin and light design while maintaining a high sound absorption coefficient.

[0050] It should be noted that in this specification, relational terms such as first and second are used only to distinguish one entity from several other entities, and do not necessarily require or imply any such actual relationship or order between these entities.

[0051] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the present invention.

Claims

1. A broadband low-frequency sound-absorbing structure with subwavelength thickness, characterized in that, include: The box (100) and the fractal components (200) arranged in a rectangular array within the box (100) are connected to each other. Four fractal components (200) arranged in a rectangular array and adjacent to each other form a first cavity (240). A plurality of fractal components (200) near the inner side of the box (100) and the inner side of the box (100) are combined to form a second cavity (250). The fractal component (200) includes: a first plate (210) and a second plate (220) disposed on the outer periphery of the first plate (210), the second plate (220) being a proportionally reduced structure of the first plate (210), and the first plate (210) having a third cavity (211) and the second plate (220) having a fourth cavity (221). The top surface of the box (100) is provided with a cover plate (110) for sealing the box (100). The outer side of the cover plate (110) faces the sound source, and the cover plate (110) is provided with a plurality of through holes (111) that are respectively connected to the first cavity (240), the second cavity (250), the third cavity (211) and the fourth cavity (221).

2. The broadband low-frequency sound-absorbing structure with subwavelength thickness according to claim 1, characterized in that, Both the first plate (210) and the second plate (220) are star-shaped. The first plate (210) has several first convex corners (212) and several first concave corners (213) alternately arranged along its circumferential direction. The second plate (220) is respectively arranged at the positions of the first convex corners (212) and the first concave corners (213). The second plate (220) has several second convex corners (222) and several second concave corners (223) alternately arranged along its circumferential direction.

3. The broadband low-frequency sound-absorbing structure with subwavelength thickness according to claim 2, characterized in that, On the projection plane in the first direction, the through hole (111) on the cover plate (110) that communicates with the third cavity (211) is located at the second convex angle (222); the through hole (111) on the cover plate (110) that communicates with the fourth cavity (221) is located at the second convex angle (222).

4. The broadband low-frequency sound-absorbing structure with subwavelength thickness according to any one of claims 1-3, characterized in that, The size ratio between the second plate (220) and the first plate (210) is 1:6 to 1:

2.

5. The broadband low-frequency sound-absorbing structure with subwavelength thickness according to any one of claims 1-3, characterized in that, The fractal component (200) includes a thick-walled portion and a thin-walled portion, wherein the thickness of the thick-walled portion is between 1 and 2 mm, and the thickness of the thin-walled portion is between 0.25 and 0.5 mm.

6. The broadband low-frequency sound-absorbing structure with subwavelength thickness according to claim 5, characterized in that, The thickness of the cover plate (110) is between 0.5 and 1.5 mm, and the diameter of the through hole (111) is between 0.8 and 1.5 mm.

7. The broadband low-frequency sound-absorbing structure with subwavelength thickness according to claim 2 or 3, characterized in that, The fractal component (200) has a square structure as a whole, and the side length of the fractal component (200) is between 20-30mm.

8. The broadband low-frequency sound-absorbing structure with subwavelength thickness according to claim 7, characterized in that, A connecting rod (230) for connecting two adjacent fractal components (200) is provided at the second concave corner (223) position, and the distance between the connecting rod (230) and the inner side of the box body (100) is between 1-5mm.

9. The broadband low-frequency sound-absorbing structure with subwavelength thickness according to claim 2 or 3, characterized in that, The first plate (210) and the second plate (220) have the same height, and the height of the first plate (210) and the second plate (220) is between 50-90mm. The included angle between the first convex angle (212) and the second convex angle (222) is between 40-60°.

10. The broadband low-frequency sound-absorbing structure with subwavelength thickness according to claim 8, characterized in that, The box body (100), the cover plate (110), the first plate (210), the second plate (220) and the connecting rod (230) are made of one of the following materials: metal, composite material formed by a combination of carbon fiber and glass fiber, resin and plastic.

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