A multi-stage gradient folded side cavity acoustic black hole sound absorption structure and noise reduction device

Abstract

This invention provides an acoustic black hole sound-absorbing structure and silencing device with multi-stage gradient folded side cavities, relating to the field of noise control technology, and solving the problems of large performance fluctuations and insufficient low-frequency sound absorption in existing structures. The acoustic black hole sound-absorbing structure includes a shell and an inclined plate disposed in the shell; the shell is a hollow body with one open end, having a first end and a second end; the inclined plate extends obliquely from the first end to the second end of the shell, forming a sound-absorbing cavity with the shell; the sound-absorbing cavity is divided into multiple side cavities arranged sequentially along the sound wave incident direction by multiple ribs, one or at least two adjacent side cavities forming a side cavity group; along the sound wave incident direction, different numbers of partitions are provided in the side cavities of different side cavity groups, the partitions are arranged perpendicular to the sound wave incident direction, and the number of partitions in each side cavity of the same side cavity group is the same; the partitions in the same side cavity are staggered along the sound wave incident direction, dividing the sound absorption channel into interconnected multi-layer folded side cavities.

Description

Technical Field

[0001] This invention relates to the field of noise control technology, and in particular to an acoustic black hole sound-absorbing structure and silencing device with a multi-stage gradient folded side cavity. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] With rapid societal development, noise pollution has become increasingly prominent, impacting not only human physical and mental health but also hindering the upgrading of machinery and equipment. Low-frequency broadband noise reduction has thus become a key focus of noise control. Currently, noise control is divided into active and passive control. Active control suffers from drawbacks such as narrow bandwidth and high hardware costs, limiting its application; passive control, in order to simultaneously achieve low-frequency broadband noise reduction, often requires larger components.

[0004] In recent years, the concept of acoustic black holes has provided a new solution for achieving low-frequency broadband noise reduction under small-size conditions. Different sound absorption ranges can be achieved by adjusting the internal parameters of the structure. However, traditional acoustic black holes have large performance fluctuations and poor low-frequency sound absorption performance. To address the shortcomings such as insufficient acoustic black hole absorption, the current approach is mainly to add damping inside the acoustic black hole or combine it with acoustic metamaterials. However, this also leads to problems such as complex structure and excessive size, and it has not effectively solved the shortcomings of performance fluctuation and insufficient low-frequency sound absorption. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide an acoustic black hole sound absorption structure and silencing device with a multi-stage gradient folded side cavity that can solve or at least alleviate the above problems, and can ensure stable sound absorption performance while satisfying low-frequency broadband sound absorption.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides an acoustic black hole sound-absorbing structure with multi-stage gradient folded side cavities, comprising a shell and an inclined plate disposed in the shell; the shell is a hollow body with one open end, having a first end forming the open end and a second end opposite to the first end; the inclined plate extends obliquely from the first end to the second end of the shell, forming a sound-absorbing cavity with the shell; the sound-absorbing cavity is divided into multiple side cavities arranged sequentially along the sound wave incident direction by multiple ribs, one or at least two adjacent side cavities forming a side cavity group; along the sound wave incident direction, different numbers of partitions are provided in the side cavities of different side cavity groups, the partitions extending perpendicular to the sound wave incident direction, and the number of partitions in each side cavity of the same side cavity group is the same; the partitions in the same side cavity are staggered along the sound wave incident direction, dividing the sound absorption channel of the same side cavity into multi-layer folded side cavities that are interconnected.

[0007] In some embodiments, the number of folded layers of each side cavity in different side cavity groups As the direction of sound wave incidence gradually increases, the width of each additional layer of folded side cavity increases. Compared to the width of the previous layer Gradually decrease, ,in, n ≥1, This represents the reduction in width.

[0008] In some embodiments, the inclined plate is provided with a plurality of perforations and a sealing portion, the perforations being provided at the inlet end of each side cavity, and the sealing portion being provided on one side of the corresponding perforation.

[0009] In some embodiments, the rib is connected between the inclined plate and the inner side of the housing and is arranged perpendicular to the direction of sound wave incidence.

[0010] In some embodiments, multiple ribs in the same set of side cavities are distributed at equal intervals along the direction of sound wave incidence.

[0011] In some embodiments, along the incident direction of the sound wave, the width of the plurality of ribs gradually increases, and the inner ends of the plurality of ribs connected to the inclined plate are distributed along a set power law function.

[0012] In some embodiments, the housing is a hollow square body, and the inclined plate is flat.

[0013] In some embodiments, the second end of the housing forms a closed end, or the second end of the housing has an opening adjacent to the inclined plate, and the opening is located outside the sound-absorbing cavity.

[0014] In some embodiments, the housing is a hollow cylinder with one end open, and the inclined plate is an arc-shaped plate formed by rotating about the axis of the housing.

[0015] Secondly, the present invention provides a noise reduction device, including the above-mentioned acoustic black hole sound absorption structure with multi-stage gradient folded side cavities.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects: 1. The multi-stage gradient folded side cavity acoustic black hole sound absorption structure provided by the present invention can achieve efficient and stable sound absorption performance in the low frequency range, and the structure is relatively simple and the size is controllable.

[0017] 2. This invention sets the side cavity as multiple folded side cavities, increasing the effective depth of the side cavities and shifting the resonant frequency of the side cavities to lower frequencies, thereby enhancing the low-frequency sound absorption performance of the structure. At the same time, the multi-stage progressive folding design of the side cavities makes the effective length of the acoustic black hole change more uniformly, making the resonant peak distribution more uniform and the sound absorption performance more stable. It also ensures sound absorption at both low and mid-high frequencies, solving the problems of poor low-frequency sound absorption performance and poor sound absorption stability of traditional acoustic black holes.

[0018] 3. In this invention, the width of the folded side cavity adopts a gradual design, with the width gradually decreasing, to achieve low-frequency noise reduction without significantly increasing the thickness of the sound-absorbing structure.

[0019] 4. This invention increases the sound energy loss of the sound absorber by setting a perforated part at the side cavity entrance, thereby further improving the sound absorption stability of the structure.

[0020] 5. The multi-stage gradient folded side cavity acoustic black hole sound absorption structure provided by this invention is flexible, simple to design, and easy to process and install. At the same time, it can be designed with rectangular or cylindrical cross-section sound absorbers according to actual requirements, which has strong spatial adaptability and high space utilization. Attached Figure Description

[0021] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0022] Figure 1A A schematic diagram of the acoustic black hole sound-absorbing structure of the multi-stage gradient folded side cavity of Embodiment 1 of the present invention is shown.

[0023] Figure 1B It shows Figure 1A The diagram shows a three-dimensional cross-sectional view of the acoustic black hole sound-absorbing structure with a multi-stage gradient folded side cavity.

[0024] Figure 2 A schematic diagram of the perforated portion at the side cavity entrance in the structure of Embodiment 1 of the present invention is shown.

[0025] Figure 3 A planar schematic diagram of the acoustic black hole sound-absorbing structure of the multi-stage gradient folded side cavity of Embodiment 1 of the present invention is shown.

[0026] Figure 4A A schematic diagram of the first-order side cavity of Embodiment 1 of the present invention is shown.

[0027] Figure 4B A schematic diagram of the second-order side cavity of Embodiment 1 of the present invention is shown.

[0028] Figure 4C A schematic diagram of the third-order side cavity of Embodiment 1 of the present invention is shown.

[0029] Figure 4D A schematic diagram of the fourth-order side cavity of Embodiment 1 of the present invention is shown.

[0030] Figure 5 A schematic diagram of the comparative structure is shown.

[0031] Figure 6 The sound absorption coefficient curves of the sound-absorbing structure and the comparative structure of Embodiment 1 of the present invention are shown.

[0032] Figure 7 A planar schematic diagram of the acoustic black hole sound-absorbing structure of the multi-stage gradient folded side cavity of Embodiment 2 of the present invention is shown.

[0033] Explanation of reference numerals in the attached drawings: 1-shell; 11-first side plate; 12-second side plate; 13-third side plate; 15-opening; 2-perforated part; 3-rib plate; 4-closed part; 5-first-order side cavity; 6-second-order side cavity; 7-third-order side cavity; 8-fourth-order side cavity; 9-partition plate. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0035] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0036] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0037] In this invention, terms such as "upper," "lower," "left," "right," "front," "back," "vertical," "horizontal," "side," and "bottom" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used only to facilitate the description of the structural relationships of the various components or elements of this invention and do not specifically refer to any component or element in this invention. They should not be construed as limiting the invention.

[0038] In this invention, terms such as "fixed connection," "connected," and "linked" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can determine the specific meaning of these terms in this invention based on the specific circumstances, and they should not be construed as limitations on the invention.

[0039] Example 1 like Figures 1A to 3 As shown, the multi-stage gradient folded side cavity acoustic black hole sound-absorbing structure (hereinafter referred to as the acoustic black hole sound-absorbing structure) provided in this embodiment includes a shell 1 and an inclined plate disposed in the shell 1. The shell 1 is generally a hollow body with one open end, having a first end forming the open end and a second end opposite to the first end. In this embodiment, the open end (i.e., the first end) of the shell 1 is used to receive incident sound waves, and the second end is set as a closed end. Preferably, the shell 1 is a hollow square body with one open end, including a bottom plate forming the closed end, and a first side plate 11, a second side plate 12, a third side plate 13 and a fourth side plate disposed on the bottom plate. The bottom plate and the multiple side plates enclose a receiving space with one open end, and the inclined plate is inclinedly disposed in the receiving space, dividing the receiving space into two parts. The first side plate 11 is connected between the second side plate 12 and the third side plate 13, and the fourth side plate is disposed opposite to the first side plate 11. The inclined plate extends obliquely from one side of the open end of the housing 1 towards the closed end; in other words, the distance between the inclined plate and the first side plate 11 gradually increases along the direction of sound wave incidence. The inclined plate, the bottom plate, the first side plate 11, the second side plate 12, and the third side plate 13 together form a sound-absorbing cavity. The sound-absorbing cavity is divided into multiple side cavities arranged sequentially along the direction of sound wave incidence by multiple ribs 3, each side cavity forming an independent sound-absorbing channel. One or at least two adjacent side cavities constitute a side cavity group. Preferably, every three adjacent side cavities form a group, and the sound-absorbing cavity has multiple groups of side cavities. The ribs 3 connect the inclined plate and the inner side of the housing 1 and are arranged perpendicular to the direction of sound wave incidence. Preferably, the ribs 3 are perpendicularly fixed to the inner side of the housing 1. Multiple ribs 3 in the same group of side cavities are evenly distributed along the direction of sound wave incidence. Along the direction of sound wave incidence, the width of the multiple ribs 3 gradually increases, and the inner ends of the multiple ribs 3 connected to the inclined plate are distributed along a set power law function.

[0040] In this embodiment, as Figure 3 As shown, the origin of the coordinate system containing the power-law function is the point at the end of the shell 1 furthest from the rib, along the direction of sound wave incidence. Axis, perpendicular to The coordinate axis along the width direction of rib 3 is... axis.

[0041] Specifically, the power-law function is defined as follows: , in, The distance between the incident sound wave and the origin of the coordinate system is... The point in the coordinate system value, The length of the incident surface of the sound wave at the open end. The total length of the structure. for time The value is the residual height at the end of the channel (the position adjacent to the inner closed end of the inclined plate and housing 1). To control the order of the cross-section, in this embodiment, it is preferred that... The set power law function is a first-order power law function, and at this time the distribution surface of the inner ends of the multiple ribs 3 is a plane.

[0042] Preferably, the multiple sets of side cavities include at least two sets of side cavities arranged sequentially along the incident direction of the sound wave, namely, a first set of side cavities, a second set of side cavities, and so on up to the third set of side cavities. n Side cavity groups. More preferably, at least two side cavities include a first side cavity group, a second side cavity group, a third side cavity group, and a fourth side cavity group arranged sequentially in the direction of sound wave incident. In the case of multiple side cavity groups comprising four side cavity groups, the number of side cavities is 12. The inclined plate is provided with multiple perforated portions 2 and closed portions 4. The perforated portions 2 are provided corresponding to the inlet end of each side cavity, and the closed portions 4 are provided on one side of the corresponding perforated portion. The following description uses four side cavity groups (each side cavity group includes three side cavities, i.e., the number of side cavities is 12) as an example.

[0043] Along the incident direction of the sound wave, different numbers of partitions 9 are provided in the side cavities of different side cavity groups. The partitions 9 extend perpendicular to the incident direction of the sound wave, and the number of partitions 9 in each side cavity of the same side cavity group is the same. (See also...) Figures 3 to 4DEach side cavity in the first side cavity group is a first-order side cavity 5. The sound absorption channel of the first-order side cavity 5 is a single channel disposed between the inclined plate and the side plate of the housing 1, which is a folded side cavity (i.e., the folding order is 1), preferably a straight channel. Each side cavity in the second side cavity group is a second-order side cavity 6. The sound absorption channel of the second-order side cavity 6 is provided with a partition 9 connected to the inclined plate and disposed perpendicular to the sound wave incident direction. The partition 9 is spaced apart from the first side plate 11. The partition 9 divides the sound absorption channel of the second-order side cavity 6 into two connected folded side cavities (i.e., the folding order is 2) along the sound wave incident direction, namely the first folded side cavity and the second folded side cavity, wherein the first folded side cavity is adjacent to the perforated part 2. Preferably, the distance between the partition 9 and the first side plate 11 is equal to the distance between the partition 9 and the rib 3 of the second folded side cavity. Each side cavity in the third side cavity group is a third-order side cavity 7. The sound absorption channel of the third-order side cavity 7 is provided with two partitions 9. The two partitions 9 are respectively connected to the inclined plate and the housing 1 and are arranged perpendicular to the sound wave incident direction, and are staggered in the sound wave incident direction, dividing the sound absorption channel of the third-order side cavity 7 into three interconnected folded side cavities (i.e., the folding order is 3) along the sound wave incident direction. These are the first folded side cavity, the second folded side cavity, and the third folded side cavity. The first folded side cavity is adjacent to the perforated part 2, and the second folded side cavity connects the first folded side cavity and the third folded side cavity. Preferably, the distance between the partition 9 connected to the first side plate 11 and the inclined plate is equal to the distance between the partition 9 of the third folded side cavity and the rib plate 3. Each side cavity in the fourth side cavity group is a fourth-order side cavity 8. The sound absorption channel of each fourth-order side cavity 8 has three partitions 9, all perpendicular to the sound wave incident direction and staggered along the sound wave incident direction, dividing the sound absorption channel of the fourth-order side cavity 8 into four interconnected folded side cavities (i.e., a folding order of 4) along the sound wave incident direction. Based on this, the highest folding order of the side cavity... Set to order 4 (or, the highest number of folds in the side cavity) (Set to order 4), the number of side cavities in each group with the same number of folds is 3, and the total number of side cavities is 12. The order of the side cavities from the sound wave incident surface to the end of the channel is denoted as follows: .

[0044] The number of folds in each lateral cavity of different lateral cavity groups As the direction of sound wave incidence gradually increases, the width of each additional layer of folded side cavity increases. Compared to the width of the previous layer Gradually decrease, , This represents the reduction in width.

[0045] Within the acoustic black hole sound-absorbing structure, the inclined surface at the entrance of each side cavity is fixedly connected to the perforated part 2. The perforated part 2 is a plate distributed along a predetermined power-law function. Because a first-order power-law function is used, the perforated part 2 is flat, as shown below. Figure 2 As shown, the perforated part 2 is provided with multiple sets of through holes.

[0046] The working principle of the acoustic black hole sound-absorbing structure in this embodiment is as follows: After the noise sound wave enters the sound absorption channel through the opening end of the shell 1, it passes through the rib 3 whose width varies according to a set power law function, causing the incident sound wave to generate a slow wave effect inside the structure. The phase velocity of the sound wave gradually decreases and the wavelength is compressed. The sound energy continuously converges and accumulates towards the end of the black hole, greatly extending the interaction time between the sound wave and the structure. At the same time, the embedded perforated part 2 and the side cavity form a Helmholtz resonance system. Under the excitation of the sound wave, the air column inside the hole vibrates strongly. With the help of the air viscosity friction and heat conduction effect at the micropore boundary, the accumulated sound energy is efficiently converted into heat energy dissipation.

[0047] The sound absorption frequency range of the perforated section 2 is significantly affected by the depth of the back cavity. As the depth of the back cavity increases, the sound absorption frequency range of the perforated section 2 gradually shifts towards lower frequencies. Therefore, this embodiment effectively increases the depth of the back cavity of the perforated section 2 by folding the acoustic black hole side cavity, thereby reducing the resonant frequency of the side cavity and widening the low-frequency sound absorption range of the structure. Simultaneously, the design increases the width of each additional folded side cavity layer. Compared to the width of the previous layer The gradual reduction method effectively increases the low-frequency sound absorption performance of the structure without significantly increasing the thickness, while making the structure more compact and achieving low-frequency broadband sound absorption in a smaller size.

[0048] The housing 1 in this embodiment adopts a cuboid structure, which can be applied to large-area noise absorption. Multiple acoustic black hole sound-absorbing structures can be installed in parallel to achieve large-area sound absorption, realize high space utilization, and avoid space waste.

[0049] The sound absorption coefficient of the structure proposed in this embodiment is calculated using the transfer matrix method. The structure is discretized based on the number of independent side cavities. The unit, for the first The relationship between sound pressure and acoustic volume at the input and output terminals of each unit can be represented by a transfer matrix as follows:

[0050] , in, The transfer matrix is ​​the conical cavity formed by the thickness of the rib plate. The transfer matrix connecting the conical cavities of the two sound-absorbing units. The transfer matrix for the side cavity. air characteristic impedance, air density, To account for the speed of sound in damped air, , , For complex wave number, Angular frequency, For frequency, For rib thickness, The thickness of the sound-absorbing unit. For the first Cross-sectional area of ​​the inlet end of each unit Let be the width of the incident surface of the sound wave. For the first Area of ​​the perforated portion at the entrance of each unit's side cavity For the first The impedance of each side cavity The surface resistance of the perforated part 2 is given.

[0051] For the first The impedance of each side cavity, superscript The folding order (i.e., the number of folds) of the lateral cavity is expressed as follows: The calculation method when the folding order is... When the value is arbitrary, the following calculation rules also apply: , ; in, , Indicates the first The first lateral cavity The cross-sectional area of ​​the folded side cavity Indicates the first The effective length within each side cavity.

[0052] For perforated section 2, its surface impedance is calculated using the Beranek Ingard model: , , ; in, Indicates surface acoustic resistance. Indicates the corrected length. This indicates the thickness of the perforated portion 2. Indicates the diameter of the perforated part 2. This indicates the perforation rate of the perforated portion 2. Indicates dynamic viscosity.

[0053] For the entire acoustic black hole sound-absorbing structure, its transfer matrix is ​​a continuous product of the transfer matrices of all its elements:

[0054] The impedance at the entrance of the acoustic black hole sound-absorbing structure's sound wave incident surface is:

[0055] The reflection coefficient of the acoustic black hole sound-absorbing structure is:

[0056] The sound absorption coefficient is:

[0057] This embodiment is compared with a traditional rectangular acoustic black hole sound-absorbing structure, such as... Figure 5 As shown, the comparative structure also includes a shell, the size of which is the same as that of the shell in this embodiment. Multiple ribs are evenly distributed along the length direction inside the shell. The outer side of the multiple ribs is fixed to the inner side of one side of the shell, and the length of the ribs is distributed along a set power law function.

[0058] The dimensions of the housing are .

[0059] in, The length of shell 1, Let be the width of the incident surface of the sound wave. is the length of the incident surface of the sound wave.

[0060] The specific remaining structural parameters of this embodiment are shown in Table 1: Table 1. Sound Absorber Parameters

[0061] The comparison structure has the same shell size as this embodiment, and the rib length variation pattern is the same.

[0062] Using the above parameters, the sound absorption coefficients of the two structures were calculated using the transfer matrix method. The sound absorption coefficients of the two structures were plotted on a two-dimensional plane. For ease of calculation, the shell thickness and ribs were ignored. Thickness. Four comparative indicators were also designed: 1) the absorption frequency at which the absorption coefficient of each sound-absorbing structure reaches 0.6, and the frequency and magnitude of the absorption coefficient at which the first absorption peak appears; 2) low-frequency sound absorption performance below 500Hz; 3) the average absorption coefficient in the frequency range of 270Hz-2400Hz; 4) the quality of the absorption peaks produced by the two structures and the fluctuation of their sound absorption performance.

[0063] like Figure 6As shown, the sound absorption performance of this embodiment is significantly better than that of the comparative structure. Specifically, this embodiment achieves a sound absorption coefficient of 0.6 at 270Hz, and the sound absorption coefficient remains greater than 0.6 throughout the subsequent wide frequency range. This frequency wavelength is 9.4 times the structural scale, achieving low-frequency broadband sound absorption at a subwavelength scale. Its first sound absorption peak appears at 317Hz, corresponding to a sound absorption coefficient of 0.99, achieving near-perfect sound absorption. There are three sound absorption peaks in the low-frequency range below 500Hz, exhibiting good low-frequency sound absorption performance. The embodiment achieves an average sound absorption coefficient of 0.97 in the 270-2400Hz range. The embodiment has a greater number of sound absorption peaks and higher peak values, with peak values ​​generally above 0.95, resulting in less fluctuation in sound absorption performance.

[0064] The comparative structure only reached a sound absorption coefficient of 0.6 at 770Hz, 500Hz later than Example 1. The first sound absorption peak appeared at 640Hz, with a sound absorption coefficient of only 0.56. No sound absorption peak appeared in the low-frequency range below 500Hz, indicating poor sound absorption performance. Its average sound absorption coefficient in the 270-2400Hz range was 0.75, which was also significantly lower than that of Example 1.

[0065] This invention designs the side cavities of different side cavity groups with a progressive folding pattern of 1 to n steps along the incident direction of the sound wave. That is, the number of folding layers (folding order) increases gradually along the incident direction of the sound wave, while the folding width gradually decreases, reducing the axial width and significantly increasing the effective cavity depth. By folding the side cavities to extend the sound wave path, the resonant frequency is actively shifted to lower frequencies, achieving small-size, subwavelength, low-frequency broadband sound absorption. Furthermore, broadband coverage is achieved using only a single-cavity side cavity grouping method, resulting in a simpler structure, easier manufacturing, and a wider range of applications.

[0066] It can be seen that the sound absorption performance of the structure described in Embodiment 1 is greatly improved compared with the traditional structure in terms of low frequency, wide frequency range, and sound absorption stability.

[0067] Example 2 Figure 7 This paper illustrates a second embodiment of the acoustic black hole sound-absorbing structure with a multi-stage gradient folded side cavity provided by the present invention. The difference between this embodiment and the first embodiment is that the second end of the housing 1 has an opening 15 adjacent to the inclined plate (that is, the upper edge of the opening 15 is the boundary line between the inclined plate and the second end of the housing 1), and the opening 15 is located outside the sound-absorbing cavity. The remaining structure is the same as in embodiment 1 and will not be repeated here. Preferably, the second end is a bottom plate opposite to the opening end of the housing 1, and the opening 15 is located between the inclined plate and the fourth side plate.

[0068] Example 3 This embodiment provides an acoustic black hole sound-absorbing structure with a multi-stage gradient folded side cavity and a circular cross-section. The shell of this structure is cylindrical, and it is achieved through... Figure 3 The plane shown is around The shaft (the axis of the housing) is rotated to form a muffler and can be used in cylindrical spaces where structural requirements exist. The inclined plate is an arc-shaped plate rotated about the axis of the housing.

[0069] Example 4 This embodiment provides a noise reduction device, which is equipped with an acoustic black hole sound absorption structure with a multi-stage gradient folded side cavity as described in Embodiment 1, Embodiment 2 or Embodiment 3. The remaining structure of the noise reduction device can adopt existing structures in the prior art, and will not be described in detail here.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An acoustic black hole sound-absorbing structure with a multi-stage gradient folded side cavity, characterized in that, The device includes a housing and an inclined plate disposed within the housing. The housing is a hollow body with one open end, having a first end forming the open end and a second end opposite to the first end. The inclined plate extends obliquely from the first end to the second end of the housing, forming a sound-absorbing cavity with the housing. The sound-absorbing cavity is divided into multiple side cavities arranged sequentially along the sound wave incident direction by multiple ribs, with one or at least two adjacent side cavities forming a side cavity group. Along the sound wave incident direction, different numbers of partitions are provided in the side cavities within different side cavity groups. The partitions extend perpendicular to the sound wave incident direction, and the number of partitions in each side cavity within the same side cavity group is the same. The partitions in the same side cavity are staggered along the sound wave incident direction, dividing the sound absorption channel of the same side cavity into interconnected multi-layered folded side cavities. The number of folds in each lateral cavity of different lateral cavity groups As the direction of sound wave incidence gradually increases, the width of each additional layer of folded side cavity increases. Compared to the width of the previous layer Gradually decrease, ,in, This represents the value at which the width is reduced. The inclined plate is provided with multiple perforated sections and closed sections. The perforated sections are provided at the entrance end of each side cavity, and the closed sections are provided on one side of the corresponding perforated section. Along the direction of sound wave incidence, the width of multiple ribs gradually increases, and the inner ends of the multiple ribs connected to the inclined plate are distributed along a set power law function.

2. The acoustic black hole sound-absorbing structure with multi-stage gradient folded side cavities according to claim 1, characterized in that, The rib is connected between the inclined plate and the inner side of the shell, and is set perpendicular to the direction of sound wave incident.

3. The acoustic black hole sound-absorbing structure with multi-stage gradient folded side cavities according to claim 2, characterized in that, Multiple ribs in the same set of side cavities are distributed at equal intervals along the direction of sound wave incidence.

4. The acoustic black hole sound-absorbing structure with multi-stage gradient folded side cavities according to claim 1, characterized in that, The shell is a hollow square, and the inclined plate is flat.

5. The acoustic black hole sound-absorbing structure with multi-stage gradient folded side cavities according to claim 4, characterized in that, The second end of the housing forms a closed end, or the second end of the housing has an opening adjacent to the inclined plate, and the opening is located outside the sound-absorbing cavity.

6. The acoustic black hole sound-absorbing structure with multi-stage gradient folded side cavities according to claim 1, characterized in that, The shell is a hollow cylinder with one end open, and the inclined plate is an arc-shaped plate formed by rotating around the axis of the shell.

7. A noise reduction device, characterized in that, Acoustic black hole sound-absorbing structure including the multi-stage gradient folded side cavity as described in any one of claims 1 to 6.

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