Perforated plate structure based on Helmholtz and acoustic black holes

Abstract

The invention discloses a perforated plate structure based on Helmholtz and acoustic black holes, which comprises a perforated plate and a bottom rigid wall which are distributed in parallel, and the perforated plate, the bottom rigid wall and an outer side rigid wall are closed to form a resonant cavity; the bottom rigid wall is provided with a plurality of partition plates distributed in a latticed mode, the resonant cavity is divided into a plurality of sub resonant cavities, the perforated plate is provided with a plurality of acoustic black hole structures, and one acoustic black hole structure is arranged in each sub resonant cavity. A round hole is formed in the perforated plate at the central position of the acoustic black hole structure, and the round hole is used as a neck part of the Helmholtz resonance structure; a gap neck exists between the partition plate and the perforated plate, and an acoustic black hole molded line II is arranged on the partition plate. The perforated plate structure can increase the absorption efficiency of sound waves with specific frequency, dissipation is carried out through the damping sound absorption material, an energy absorption-energy consumption trap is formed, the vibration and noise reduction effect is achieved, and meanwhile the sound waves entering the resonant cavity are dissipated again through the gap type Helmholtz resonance structure between the partition plate and the perforated plate.

Description

Technical Field

[0001] The present invention belongs to the technical field of vibration and noise control, and relates to the design of a broadband noise reduction structure. By superimposing the Helmholtz resonance effect and the acoustic black hole effect, the traditional perforated panel sound absorption structure is improved. Background Technique

[0002] With the development of modern industry and rail transit, the demand for noise control is increasing continuously. There are mainly two kinds of noise control technologies: active control and passive control. Active control collects noise signals and generates reverse waveforms to cancel the noise, so as to achieve the noise reduction effect. Active control requires the use of technologies such as adaptive filters and noise signal acquisition and processing, which is very complex. While passive control reduces noise through physical means, such as various sound-absorbing materials and resonant sound-absorbing structures, and is relatively simple to use. Since the low-frequency sound absorption performance of porous sound-absorbing materials is relatively poor, and for sound waves with longer wavelengths, the thickness requirement of the sound-absorbing materials is very large, the resonance sound-absorption principle is often used to solve the absorption of low-frequency sound waves.

[0003] The perforated panel is a kind of resonant sound-absorbing structure and has a certain sound-absorbing ability. Perforating various thin plates and setting an air layer behind the plate, and adding porous sound-absorbing materials in the cavity when necessary, can form a perforated panel resonant sound-absorbing structure. Due to the viscosity of air, when sound waves pass through the holes, the air generates resistance, consuming part of the sound wave energy. The remaining sound waves enter the porous sound-absorbing materials through the holes, hit its irregular surface, and produce a scattering effect. The holes and the hole walls will also cause multiple reflections and refractions of the sound waves, and propagate and dissipate multiple times inside the material. The sound waves rub against the hole walls and the skeletons inside the material, converting the sound energy into heat energy and consuming the sound wave energy. At the same time, since there is a corresponding cavity behind each opening, this perforated panel structure is a combination of many parallel Helmholtz resonators, so it can be regarded as a resonance system composed of mass and spring. When the frequency of the incident sound wave is consistent with the resonance frequency of the system, the air inside the perforation vibrates violently and rubs, consumes energy through the viscous effect, strengthens the absorption effect, forms an absorption peak, and significantly attenuates the sound energy; when it is far from the resonance frequency, the absorption effect is small. Placing porous sound-absorbing materials behind the perforated panel can increase the acoustic resistance and widen the absorption frequency band of the structure.

[0004] The traditional perforated panel sound absorption structure also has certain problems. For example, its sound absorption performance is limited by the structural size, mainly absorbing the sound waves near its resonance frequency, resulting in a narrow sound absorption frequency band; in actual applications, it is often necessary to add sound absorption materials to meet the sound absorption effect, but it is also restricted by space. The sound absorption coefficient of the traditional perforated panel sound absorption structure is relatively low. When the perforation rate of the perforated panel decreases (the acoustic mass increases) and the aperture decreases from centimeter level to decimillimeter level (the acoustic impedance becomes larger), a micro-perforated panel can be obtained. In theory, the micro-perforated panel sound absorption structure has good broadband sound absorption performance and does not require filling with porous sound absorption materials. However, due to the space limitation (quarter-wavelength limitation) in actual applications, the air back cavity needs to have a relatively large depth to achieve effective sound absorption at low frequencies, which greatly limits the use of micro-perforated panels.

[0005] Therefore, the existing perforated panel and micro-perforated panel sound absorption structures need to be improved to enhance the low-frequency absorption performance and broaden the sound absorption frequency band.

[0006] Object of the Invention

[0007] Aiming at the deficiencies of the traditional perforated panel resonance sound absorption structure, the object of the present invention is to provide a perforated panel structure based on Helmholtz and acoustic black hole. By introducing a Helmholtz resonance structure at the center of the acoustic black hole, the sound absorption ability of sound waves is greatly enhanced, realizing the absorption of sound waves with different frequencies by the perforated panel sound absorption structure, broadening the sound absorption frequency band, and improving the sound absorption performance.

[0008] To achieve the foregoing object, the technical solution adopted by the present invention is as follows:

[0009] A perforated panel structure based on Helmholtz and acoustic black hole, comprising a perforated panel 1 and a bottom rigid wall 5 distributed in parallel. The cavity between the perforated panel and the bottom rigid wall is enclosed by an outer rigid wall 4 extending circumferentially to form a resonance cavity 8 of the Helmholtz resonance structure; a plurality of partitions 7 distributed in a grid pattern are provided on the wall surface of the bottom rigid wall 5 facing the perforated panel, and the resonance cavity 8 is divided into a plurality of sub-resonance cavities. A plurality of acoustic black hole structures are provided on the wall surface of the perforated panel 1 facing the bottom rigid wall, and one acoustic black hole structure is arranged in each sub-resonance cavity; the thickness of the acoustic black hole profile Ⅰ 101 of the acoustic black hole structure decreases in a power function from outside to inside. A round hole is provided on the perforated panel 1 at the central position of the acoustic black hole structure, and this round hole serves as the neck 102 of the Helmholtz resonance structure; there is a gap neck 9 with a distance of 0.1 mm - 10 mm between the partition 7 and the perforated panel 1, and an acoustic black hole profile Ⅱ is provided on the side of the partition 7 close to the perforated panel, and the thickness of the acoustic black hole profile Ⅱ decreases in a power function from outside to inside.

[0010] In one embodiment, a round hole with a diameter of 0.1 mm - 10 mm is provided on the perforated panel 1 at the central position of the acoustic black hole structure.

[0011] In one embodiment, a damping material layer I2 is provided inside the acoustic black hole structure, and a through hole coaxial with and having the same size as the neck 102 is provided through the damping material layer I.

[0012] In one embodiment, an acoustic absorption material layer 3 is provided between the damping material layer I and the bottom rigid wall.

[0013] In one embodiment, a damping material layer II6 is provided outside the acoustic black hole profile II701.

[0014] In one embodiment, the materials of the damping material layer I2 and the damping material layer II6 are rubber, polyurethane or polymer resin.

[0015] In one embodiment, round holes with a size less than millimeters are provided on the perforated plate 1 at the center of the acoustic black hole structure.

[0016] In one embodiment, the power exponent of the power function is not less than 2.

[0017] By means of the above technical solutions, the technical effects of the present invention are as follows:

[0018] The perforated plate structure proposed by the present invention includes a Helmholtz resonance structure and an acoustic black hole structure. When sound waves enter the resonance cavity from the neck, the air at the neck opening moves back and forth, and the air in the resonance cavity is compressed and expanded, forming a vibration system similar to a mass spring. When the frequency of the incident sound wave is consistent with the natural frequency of the resonator structure, the resonance amplitude is the largest and the energy consumption is the most. At the same time, the sound wave excites the perforated plate to generate vibration waves, which are transmitted along the acoustic black hole structure to the vicinity of the neck. The phase velocity of the vibration wave gradually decreases as the thickness of the perforated plate decreases, and the reflection coefficient approaches zero. The energy of the vibration wave continuously accumulates inward, causing the neck to vibrate, greatly strengthening the air vibration near the neck opening, and being dissipated by converting into heat energy through viscous friction with the cavity wall surface. In this way, the absorption efficiency of sound waves at specific frequencies can be increased. The sound waves that cannot be dissipated and the energy of the captured vibration waves are transmitted to the damping and sound-absorbing materials connected thereto, and are dissipated through the damping and sound-absorbing materials, forming an "energy absorption - energy dissipation trap" to achieve the effect of vibration reduction and noise reduction.

[0019] The sound waves entering the Helmholtz resonance cavity pass through the series slit-type Helmholtz resonance structure formed by the partition plate and the perforated plate, and are dissipated again. The partition plate is provided with an acoustic black hole structure, a damping material layer and an acoustic absorption material layer, which can effectively absorb the vibration waves generated by the excitation of sound waves, superimpose the Helmholtz resonance effect and the acoustic black hole effect, broaden the sound absorption frequency band, and improve the sound absorption performance.

[0020] In this way, the energy absorption efficiency of the perforated plate resonance sound absorption structure can be greatly improved, and the absorption frequency band will also be greatly broadened, thus achieving the purpose of the present invention.

[0021] The further effects of the above optional methods will be described below in conjunction with specific embodiments. Brief Description of the Drawings

[0022] Figure 1 This is a three-dimensional sectional view of Embodiment 1 of a perforated plate structure based on Helmholtz and acoustic black holes of the present invention.

[0023] Figure 2 For Figure 1 a top view schematic diagram of the illustrated embodiment.

[0024] Figure 3 For Figure 1 a sectional view schematic diagram of a single Helmholtz and acoustic black hole perforated resonance structure in the illustrated embodiment.

[0025] Figure 4 is an absorption effect diagram of a traditional perforated plate structure.

[0026] Figure 5 is an absorption effect diagram of the perforated plate structure based on Helmholtz and acoustic black holes shown in Embodiment 1 of the present invention.

[0027] Figure 6 This is a three-dimensional sectional view of Embodiment 2 of a perforated plate structure based on Helmholtz and acoustic black holes of the present invention.

[0028] In the figure: 1, perforated plate; 101, acoustic black hole profile I; 102, neck; 2, damping material layer I; 3, sound absorption material layer; 4, outer rigid wall; 5, bottom rigid wall; 6, damping material layer II; 7, partition, 701, acoustic black hole profile II; 8, resonance cavity; 9, gap neck. Specific Embodiments

[0029] The technical solutions of the present invention will be described in detail below in conjunction with the embodiments shown in the accompanying drawings.

[0030] The present invention proposes a perforated plate structure based on Helmholtz and acoustic black holes. By optimizing the structure, the Helmholtz resonance effect and the acoustic black hole effect are superimposed to increase the absorption of sound waves at specific frequencies, effectively capture the vibration waves caused by sound waves, and dissipate them, improving the energy absorption efficiency of the perforated plate resonance absorption structure, broadening the absorption frequency range, and achieving the effect of vibration reduction and noise reduction.

[0031] Embodiment 1

[0032] Please refer to Figures 1 - 3, which is Embodiment 1 of a perforated plate structure based on Helmholtz and acoustic black holes of the present invention. This embodiment includes a perforated plate 1 and a bottom rigid wall 5 that are distributed in parallel. The cavity between the perforated plate and the bottom rigid wall is enclosed by an outer rigid wall 4 that extends circumferentially to form a resonance cavity 8 of a Helmholtz resonance structure; a number of partitions 7 distributed in a grid pattern are provided on the wall surface of the bottom rigid wall 5 facing the perforated plate, and the resonance cavity 8 is divided into several sub-resonance cavities. A number of acoustic black hole structures are provided on the wall surface of the perforated plate 1 facing the bottom rigid wall (at this time, the other wall surface of the perforated plate facing away from the bottom rigid wall serves as the sound-absorbing surface of the perforated plate structure), and one acoustic black hole structure is arranged in each sub-resonance cavity; the thickness of the acoustic black hole profile I 101 of the acoustic black hole structure decreases in a power function from the outside to the inside, and the power exponent of the power function is not less than 2. This acoustic black hole structure is used to absorb the vibration waves generated by the perforated plate excited by sound waves; a circular hole with a diameter of 0.1 mm - 10 mm (i.e., from decimillimeter level to centimeter level) is provided on the perforated plate 1 at the central position of the acoustic black hole structure (i.e., the thinnest part of the thickness). This circular hole serves as the neck 102 of the Helmholtz resonance structure. The aforementioned neck 102 and the corresponding sub-resonance cavity constitute an independent Helmholtz resonance structure, which can absorb sound waves of certain specific frequencies. When the frequency of the incident sound wave is consistent with the natural frequency in the cavity, the air in the cavity will vibrate violently, thereby generating friction with the cavity wall surface and generating heat energy, realizing the conversion from sound energy to mechanical energy and then to internal energy.

[0033] Further, please refer to Figure 3 , there is a gap with a distance of 0.1 mm - 10 mm (i.e., from decimillimeter level to centimeter level) between the partition 7 and the perforated plate 1. This gap serves as the gap neck 9 of the gap-type Helmholtz resonance structure. At the same time, any two adjacent Helmholtz resonance structures are in a connected state through the gap neck. In addition, an acoustic black hole profile II is provided on the side of the partition 7 close to the perforated plate. The thickness of the acoustic black hole profile II decreases in a power function from the outside to the inside, and the power exponent of the power function is not less than 2, which is used to absorb the vibration waves generated by the bottom rigid wall excited by sound waves.

[0034] Further, please refer to Figure 3 , a damping material layer I 2 is provided inside the acoustic black hole structure. A through hole coaxial with and having the same size as the neck 102 is provided through the damping material layer I. The damping material layer I is made of known materials, such as rubber, polyurethane, polymer resin, etc., and is connected to the perforated plate through bonding or vulcanization processes.

[0035] Further, please refer to Figure 3 , an acoustic absorption material layer 3 is provided between the damping material layer and the bottom rigid wall. The acoustic absorption material layer is made of known materials, such as porous acoustic absorption materials.

[0036] Further, please refer to Figure 3, a damping material layer II 6 is provided on the outer side of the acoustic black hole profile II 701. The damping material layer II is made of known materials, such as rubber, polyurethane, polymer resin, etc., and is connected to the partition by bonding or vulcanization process.

[0037] The working process of a perforated plate structure based on Helmholtz and acoustic black hole in this embodiment is as follows:

[0038] When sound waves propagate to the circular holes of the perforated plate 1, they will cause the vibration of the air inside the neck 102 and near the orifice. This part of the air can be analogized to a sound mass element; the air vibrates and rubs on the opening wall surface, and due to the effects of viscous damping and heat conduction, the sound energy will be lost, and its effect on acoustics is equivalent to a sound resistance element. The air pressure in the resonance cavity 8 changes with the expansion and contraction of the air, generating a restoring force, which can be analogized to a sound compliance element. The air in the resonance cavity vibrates with the sound waves to a certain extent and also has a certain sound mass. In the case where the sound wave wavelength is much larger than the geometric scale of the resonator, it can be considered that the kinetic energy of the air vibration in the resonator is concentrated in the movement of the air in the neck, and the potential energy is only related to the elastic deformation of the air in the resonance cavity 8. At this time, the effective mass of the air in the neck and the air spring in the resonance cavity form a vibration system. When the frequency of the incident sound wave approaches the natural frequency of the resonator, the air column in the neck generates strong vibration. During the vibration process, the sound energy is consumed due to overcoming the frictional resistance. When the frequency of the incident sound wave is far from the natural frequency of the resonator, the vibration of the resonator is very weak, and the sound absorption effect is very small. At this time, a damping material layer 2 and a sound absorption material layer 3 located under the damping material layer are added near the neck 102 in the cavity to increase the sound resistance, which will broaden the absorption frequency band of the structure. Since there is a corresponding sub-resonance cavity behind each through hole, many parallel Helmholtz resonance structures can be formed.

[0039] When sound waves propagate to the other wall surface of the perforated plate 1 away from the bottom rigid wall, they will cause the perforated plate 1 to vibrate and generate vibration waves. An acoustic black hole structure is provided on the wall surface of the perforated plate 1 facing the bottom rigid wall. The vibration waves will be transmitted along the acoustic black hole profile 101 to near the neck 102. The phase velocity of the vibration waves gradually decreases as the thickness of the perforated plate decreases, and the reflection coefficient approaches zero. The energy of the vibration waves continuously accumulates inward and is transmitted to the connected damping material layer 2, and is dissipated as heat through the damping material, forming an "energy absorption - energy dissipation trap" to achieve the purpose of vibration reduction and noise reduction.

[0040] Since the Helmholtz resonance structure is arranged at the center of the acoustic black hole structure, the Helmholtz resonance effect and the acoustic black hole effect are superimposed, which will greatly strengthen the air vibration at the neck 102, increase the loss of the incident sound wave at a specific frequency, and the sound wave and vibration wave energy that cannot be dissipated can be transmitted to the damping material layer and the sound absorption material layer for dissipation, and the absorption frequency band will also be greatly broadened.

[0041] When the sound wave enters the Helmholtz resonance cavity 8 and passes through the slit neck 9 formed by the partition plate 7 and the perforated plate 1, the Helmholtz resonance effect is generated again. With the help of a plurality of vertically and horizontally arranged partition plates 7, a plurality of Helmholtz resonance structures are in a connected state. At the same time, an acoustic black hole profile II is provided on one side of the partition plate 7 close to the perforated plate 1, which can be used to absorb the vibration wave generated by the excitation of the bottom rigid wall 5 by the sound wave, and can also superimpose the Helmholtz resonance effect and the acoustic black hole effect to strengthen the air vibration at the slit neck 9, broaden the sound absorption frequency band, and improve the sound absorption performance. In addition, the damping material layer II 6 pasted on the surface of one side of the partition plate 7 close to the perforated plate 1 also forms an "energy absorption - energy dissipation trap" to achieve the purpose of vibration reduction and noise reduction.

[0042] Figure 4 shows the sound absorption effect diagram of the traditional perforated plate structure, Figure 5 is the sound absorption effect diagram of the perforated plate structure based on Helmholtz and acoustic black hole in this embodiment. By comparing Figure 4 and Figure 5 it can be seen that the perforated plate structure based on Helmholtz and acoustic black hole in this embodiment can effectively absorb the energy of sound waves in a wide frequency range.

[0043] Embodiment 2

[0044] Please refer to Figure 6 , which is Embodiment 2 of a perforated plate structure based on Helmholtz and acoustic black hole of the present invention. In this embodiment, the diameter of the circular hole opened on the perforated plate 1 at the center position of the acoustic black hole structure (i.e., the thinnest part) is less than millimeters, and the perforated plate forms a micro-perforated plate, and the ratio of acoustic resistance to acoustic mass is greatly improved. At this time, the damping material layer I 2, the sound absorption material layer 3, and the damping material layer II 6 in Embodiment 1 can be omitted. Under the Helmholtz resonance effect and the acoustic black hole effect, it can become a good sound absorption structure, which can reduce the space, facilitate the actual layout, has a simple and environmentally friendly structure, and is suitable for special environments such as high-speed air flow, high temperature, and humidity. Except for the aforementioned differences, the structures of the perforated plate 1, the bottom rigid wall 5, the outer rigid wall 4, and the partition plate 7 and the connection manners between them in Embodiment 2 are exactly the same as those in Embodiment 1 and will not be repeated.

[0045] It should be noted that the above are only the preferred embodiments of the present invention, and do not limit the patent protection scope of the present invention. The present invention can also be replaced by equivalent technologies. Therefore, any equivalent changes made by using the description and illustration content of the present invention, or directly or indirectly applied to other related technical fields, are included in the scope covered by the present invention.

Claims

1. A perforated plate structure based on Helmholtz and acoustic black hole, characterized in that The invention comprises a perforated plate and a bottom rigid wall which are distributed in parallel, wherein the cavity between the perforated plate and the bottom rigid wall is closed by an outer rigid wall which extends in a circumferential direction, so as to form a resonance cavity of a Helmholtz resonance structure; a plurality of partitions which are distributed in a grid are arranged on the wall surface of the bottom rigid wall which faces the perforated plate, and the resonance cavity is divided into a plurality of sub-resonance cavities; a plurality of acoustic black hole structures are arranged on the wall surface of the perforated plate which faces the bottom rigid wall, and an acoustic black hole structure is arranged in each sub-resonance cavity; the thickness of an acoustic black hole profile line I of the acoustic black hole structure decreases from the outside to the inside in a power function, a circular hole is arranged on the perforated plate which is located at the center of the acoustic black hole structure, and the circular hole serves as the neck of the Helmholtz resonance structure; a gap neck with a distance of 0.1 mm to 10 mm is provided between the partition and the perforated plate, and an acoustic black hole profile line II is arranged on the side of the partition which is close to the perforated plate, and the thickness of the acoustic black hole profile line II decreases from the outside to the inside in a power function.

2. A perforated plate structure based on Helmholtz and acoustic black hole according to claim 1, characterized in that A circular hole with a diameter of 0.1 mm to 10 mm is provided on the perforated plate located at the center of the acoustic black hole structure.

3. A perforated plate structure based on Helmholtz and acoustic black hole according to claim 2, characterized in that A damping material layer I is provided inside the acoustic black hole structure, and a through hole coaxial with the neck and having the same size as that of the neck is penetrated through the damping material layer I.

4. A perforated plate structure based on Helmholtz and acoustic black hole according to claim 3, characterized in that A sound absorbing material layer is provided between the damping material layer I and the bottom rigid wall.

5. A perforated plate structure based on Helmholtz and acoustic black hole according to claim 4, characterized in that A damping material layer II is provided on the outer side of the acoustic black hole profile II.

6. A perforated plate structure based on Helmholtz and acoustic black hole according to claim 5, characterized in that The damping material layer I and the damping material layer II are made of rubber, polyurethane or high molecular resin.

7. The perforated plate structure based on Helmholtz and acoustic black hole according to claim 1, characterized in that The perforated plate located at the center of the acoustic black hole structure is equipped with circular holes below the millimeter level.

8. A perforated plate structure based on Helmholtz and acoustic black hole according to any one of claims 1 to 7, characterized in that The power exponent of the power function is not less than 2.

Images