A multilayer helmholtz resonator coupled to an acoustic black hole

Abstract

The application discloses a multilayer Helmholtz resonator coupled with an acoustic black hole, which comprises an outer shell, a Helmholtz resonator A and a Helmholtz resonator B, wherein the Helmholtz resonator A and the Helmholtz resonator B are arranged in the outer shell. The application uses a double-layer Helmholtz resonator, and couples an acoustic black hole structure at a joint of the Helmholtz resonator A and the Helmholtz resonator B. First, the acoustic black hole structure reduces the mass of the Helmholtz resonator A, guarantees that the multilayer Helmholtz resonator is light and thin, and provides an access for the neck pipe B due to the opening A generated by the acoustic black hole structure. Moreover, the acoustic black hole structure can effectively make part of sound waves not be reflected any more, and improves a certain sound absorption performance. In addition, the acoustic black hole can absorb sound in a wide frequency domain, and expands the sound absorption frequency band of the Helmholtz cavity.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of acoustic devices, and particularly relates to a multi-layer Helmholtz resonator coupled with an acoustic black hole. BACKGROUND

[0002] The research focus in the field of noise control today is to control the propagation of noise through sound insulation technology. Traditional sound insulation materials follow the mass law and can effectively control the noise in the medium and high frequency part. However, the low frequency noise has a long propagation distance, strong sound transmission ability and high isolation difficulty, so the control effect of traditional sound insulation materials on low frequency noise is poor, and they also have problems such as not being able to be used at low temperature and not having a long enough service life. Since the inertial resistance of the traditional sound insulation material is proportional to its mass and thickness, the mass and thickness are usually increased to improve the sound insulation performance of the low frequency part. The increase of mass and thickness makes the structure not easy to vibrate, so the sound insulation effect can be improved. However, this method will first increase the use cost, and secondly it is not suitable in many cases.

[0003] Helmholtz resonator, its principle is that the air in the neck and the air in the back cavity can be regarded as an elastic system, the sound field in the cavity produces standing wave due to the reflection of the wall, so that the sound of a certain frequency forms resonance. Due to the existence of sound resistance, the sound is quickly dissipated in the cavity, thereby realizing sound elimination.

[0004] Acoustic black hole (ABH) is a passive vibration control technology developed in the field of structural dynamics and vibration noise in the past decade. From the perspective of structure, acoustic black hole effect is achieved by embedding local inhomogeneity in thin-walled structure (usually beam or plate). The characteristic of this inhomogeneity is that the geometric property changes with the change of power-law profile (the material may also change). Due to the change of wall thickness according to power-law, the local stiffness of thin-walled structure is reduced, the local damping is increased, the wave velocity is significantly reduced, and the attenuation characteristic is significantly enhanced. In the ideal case, i.e. when the truncation length of the wedge-shaped tip is zero, the wave number tends to infinity, the wave velocity drops to zero, and the elastic wave is trapped in the tip and is not reflected. In the non-ideal case, i.e. when the truncation length of the acoustic black hole tip is not zero, the wave velocity still decreases smoothly, but it will not disappear. In the non-ideal case, the acoustic black hole is combined with a lossy medium (such as a viscoelastic layer), so as to realize significantly enhanced structural loss factor.

[0005] Acoustic black hole is widely used in noise control field due to its simple structure and wide frequency sound absorption effect. For example, the invention patent application with the application number 2023114259171 proposes an acoustic black hole coil spring structure and a vehicle capable of suppressing structure noise propagation. The periodic distribution of multiple acoustic black hole spring structures can suppress the propagation of wide frequency noise through the suspension system to the vehicle interior. The invention patent application with the application number 2022111983398 proposes a ring spiral acoustic black hole damping structure. Multiple Archimedes spiral acoustic black holes and ring bands are nested on the tubular structure, which can achieve damping and noise reduction of the tubular structure.

[0006] For the traditional noise control problem, the Helmholtz resonator is generally used. For example, the invention patent application with the application number 2018104089934 proposes a honeycomb sandwich sound absorption structure with built-in micro-perforated plate simulating Helmholtz resonator, which can significantly enhance the sound absorption coefficient of the plate. However, due to the structure itself, the noise control structure based on Helmholtz resonator can only work at its resonance frequency and a certain adjacent bandwidth, and cannot achieve wideband sound absorption.

[0007] To solve the problem of insufficient sound absorption bandwidth, multiple single resonator systems are currently coupled. The invention patent application with the application number 201610366214X proposes a low-frequency composite sound absorption device, which couples multiple Helmholtz resonators in an array to a thin plate. The results show that the sound absorption bandwidth can be increased. However, the above coupling technology ignores the influence of the number and position of the array on the sound absorption performance. The existing bandwidth expansion method mainly depends on the number of wave peaks, but coupling multiple resonators also has multiple wave troughs, which increases the efficiency loss. At the same time, having multiple Helmholtz resonators with strong sound absorption performance, the main structure must have sufficient thickness, which also leads to the inability to achieve a more lightweight wideband sound absorption. SUMMARY

[0008] To solve the above technical problems, the present application provides a multi-layer Helmholtz resonator coupled with acoustic black holes, which can solve the problems of insufficient sound absorption bandwidth of a single resonator and increased thickness of a sound absorption structure coupled with multiple resonator arrays. It can achieve wideband sound absorption and improve its sound absorption capacity.

[0009] The present application is achieved by the following technical solutions.

[0010] The present application provides a multi-layer Helmholtz resonator coupled with acoustic black holes, which includes an outer shell, a Helmholtz resonator A and a Helmholtz resonator B. The Helmholtz resonator A and the Helmholtz resonator B are arranged in the outer shell.

[0011] Preferably, an opening C is arranged on the shell, the opening C is square, a back cavity is arranged in the shell, and the Helmholtz resonator A and the Helmholtz resonator B are arranged in the back cavity.

[0012] Preferably, the Helmholtz resonator A comprises a connecting tube and a neck tube A, the connecting tube is connected with the neck tube A, the Helmholtz resonator B comprises a neck tube B and a back cavity, and the neck tube B is connected with the bottom of the connecting tube.

[0013] Preferably, an acoustic black hole is arranged in the connecting tube, and the acoustic black hole is communicated with the neck tube B through the opening A.

[0014] Preferably, the low end of the acoustic black hole is located on the side close to the opening A, and the thickness of the acoustic black hole decreases according to an exponential function h(x) = εx m , where h(x) is the thickness, m ≥ 2, and ε is an arbitrary constant.

[0015] Preferably, a damping layer is arranged at the bottom of the acoustic black hole, and the damping layer is arranged around the outer wall of the neck tube B.

[0016] Preferably, the neck tube A is arranged at two places, the neck tube A is arranged vertically with the connecting tube, one end of the neck tube A is communicated with the opening C, and the other end of the neck tube A is communicated with the connecting tube.

[0017] Preferably, the wall thickness of the Helmholtz resonator A is smaller than the wall thickness of the shell, and the volume of the neck tube A is smaller than the volume of the back cavity.

[0018] Preferably, the volume of the region where the back cavity is located above the connecting tube is smaller than the volume of the region where the back cavity is located below the connecting tube.

[0019] Preferably, the cross-sectional area of the opening A is equal to the cross-sectional area of the through hole of the neck tube B.

[0020] The beneficial effects of the present application are as follows:

[0021] The multi-layer Helmholtz resonator coupled with an acoustic black hole of the present application forms an elastic system through the shell, the Helmholtz resonator A and the Helmholtz resonator B. When sound waves enter, they are reflected in the Helmholtz resonator A and the neck tube B to produce resonance. The present application uses a double-layer Helmholtz resonator, and couples an acoustic black hole structure at the connection between the Helmholtz resonator A and the Helmholtz resonator B. First, the acoustic black hole structure reduces the mass of the Helmholtz resonator A, ensuring that the multi-layer Helmholtz resonator is light and thin. In addition, the opening A generated by the acoustic black hole structure also provides an access for the neck tube B. Moreover, due to the structural characteristics of the acoustic black hole structure, part of the sound waves can be effectively prevented from being reflected, and the sound absorption performance is also improved to a certain extent. Furthermore, the acoustic black hole can absorb sound in a relatively wide frequency domain, thereby expanding the sound absorption frequency band of the Helmholtz cavity. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a structural schematic diagram of the inside of the application;

[0023] Figure 2 is a structural schematic diagram of the inside of the application;

[0024] Figure 3 is a structural schematic diagram of the Helmholtz resonator A of the application;

[0025] Figure 4 is a structural schematic diagram of the Helmholtz resonator A of the application;

[0026] Figure 5 is a structural schematic diagram of the neck pipe B of the application;

[0027] Figure 6 is a structural schematic diagram of the outside of the application;

[0028] Figure 7 is a structural schematic diagram of the acoustic black hole of the application;

[0029] Figure 8 is a structural schematic diagram of the acoustic black hole of the application;

[0030] In the figure: 1 - shell, 11 - opening C, 12 - back cavity, 2 - Helmholtz resonator A, 3 - connecting pipe, 31 - opening A, 4 - neck pipe A, 5 - neck pipe B, 51 - through hole, 6 - acoustic black hole, 7 - damping layer. DETAILED DESCRIPTION

[0031] The technical solutions of the application are described further below, but the scope of protection is not limited to the description.

[0032] Embodiment:

[0033] As shown in Figures 1 to 8 A multi-layer Helmholtz resonator coupled with an acoustic black hole, the overall shape of the multi-layer Helmholtz resonator is a cuboid, which comprises a shell 1, a Helmholtz resonator A 2 and a Helmholtz resonator B, the Helmholtz resonator A 2 and the Helmholtz resonator B are arranged in the shell 1.

[0034] The shell 1 is provided with an opening C 11, which is square, and can also be provided with other shapes according to actual needs, and two openings C 11 are arranged correspondingly, a back cavity 12 is arranged in the shell 1, and the Helmholtz resonator A 2 and the Helmholtz resonator B are arranged in the back cavity 12.

[0035] The Helmholtz resonator A2 includes a connecting tube 3 and a neck tube A4, the connecting tube 3 is connected with the neck tube A4, the Helmholtz resonator B includes a neck tube B5 and a back cavity 12, the neck tube B5 is connected with the bottom of the connecting tube 3. The neck tube A4 is provided with two, so that the Helmholtz resonator A2 is a double-neck structure, which can make the sound wave rub with the wall of the two connecting tubes 3, increase the sound energy loss, and broaden the resonance frequency band.

[0036] The acoustic black hole 6 is arranged in the connecting tube 3, the thickness of the acoustic black hole 4 decreases with the exponential change, an opening A31 is generated at the truncation, and the acoustic black hole 6 communicates with the neck tube B5 through the opening A31. The same material is used at the acoustic black hole 4 and the bottom of the connecting tube 3, only the shape is changed. The bottom of the connecting tube 3 is symmetrically coupled with two acoustic black holes, and the acoustic black hole decreases with the thickness h b Start decreasing.

[0037] The low end of the acoustic black hole 6 is located on the side of the opening A31, and the thickness of the acoustic black hole 6 is according to the exponential function h(x) = εx m Decreasing, wherein h(x) is the thickness of a certain point on the acoustic black hole 6, x is the distance from a certain point on the acoustic black hole 6 to the opening A31, m≥2, and ε is an arbitrary constant.

[0038] The bottom of the acoustic black hole 6 is provided with a damping layer 7, the damping layer 7 is arranged around the outer wall of the neck tube B5, and the damping layer 7 is used to alleviate the influence generated by the truncation of the acoustic black hole 6.

[0039] The neck tube A4 is provided with two, the interface of the neck tube A4 and the cross section of the cavity are square, and other shapes can also be provided according to actual needs, the neck tube A4 is vertically arranged with the connecting tube 3, one end of the neck tube A4 communicates with the opening C11, the other end of the neck tube A4 communicates with the connecting tube 3, the neck tube A4 is embedded, extends into the back cavity 12, the neck tube A4 does not contact the back cavity 12, avoids generating a large amount of reflection, and the two neck tubes A4 can adjust the distance according to the sound absorption band.

[0040] The wall thickness of the Helmholtz resonator A2 is smaller than the wall thickness of the shell 1, and the volume of the neck tube A4 is smaller than the volume of the back cavity 12. Because the size parameters of the Helmholtz resonator generally need to meet the following conditions: 1, the wavelength is much larger than the linear size of the overall structure; 2, the volume of the neck tube is much smaller than the volume of the resonant cavity; 3, the wall of the resonant cavity is a rigid wall, which will not be deformed when affected by external sound pressure, and will not make the fluid medium pass out of the resonant cavity.

[0041] The volume of the region where the back cavity 12 is located above the connecting tube 3 is smaller than the volume of the region where the back cavity 12 is located below the connecting tube 3.

[0042] The cross-sectional area of the opening A31 is equal to the cross-sectional area of the inner hole 51 of the neck pipe B5, which can be square, but the shape varies with the shape of the opening A31 produced by the truncation of the upper end acoustic black hole 6 and must be closely connected with the opening. The wall thickness of the neck pipe B5 needs to be as small as possible, otherwise it will affect the position of the sound damping layer 7, resulting in a decrease in the performance of the acoustic black hole 6 point.

[0043] As Figure 7 , 8 The acoustic black hole 6 can theoretically make the wave speed 0, but due to the truncation, it is necessary to use a damping layer 7 with a thickness of h attached to the bottom, and the material of the damping layer is butyl rubber, which enhances its dissipation performance as much as possible. The attachment position of the damping layer 7 leaves a position for the neck pipe B5. Figure 8 The o is the truncation position of the acoustic black hole 6, which is the opening A31, and the o to labh is the length of the acoustic black hole 6.

Claims

1. A multilayered Helmholtz resonator coupled to an acoustic black hole, characterized by: It comprises a shell (1), a Helmholtz resonator A (2) and a Helmholtz resonator B, the Helmholtz resonator A (2) and the Helmholtz resonator B are arranged in the shell (1); An opening C (11) is arranged on the shell (1), the opening C (11) is square, a back cavity (12) is arranged in the shell (1), the Helmholtz resonator A (2) and the Helmholtz resonator B are arranged in the back cavity (12); The Helmholtz resonator A (2) comprises a connecting tube (3) and a neck tube A (4), the connecting tube (3) is connected with the neck tube A (4), the Helmholtz resonator B comprises a neck tube B (5) and the back cavity (12), the neck tube B (5) is connected with the bottom of the connecting tube (3); An acoustic black hole (6) is arranged in the connecting tube (3), the acoustic black hole (6) is communicated with the neck tube B (5) through an opening A (31); The low end of the acoustic black hole (6) is located on the side of the opening A (31), the thickness of the acoustic black hole (6) decreases according to an exponential function where h(x) is the thickness, m≥2, is an arbitrary constant.

2. A multi-layered Helmholtz resonator coupled to an acoustic black hole as defined in claim 1, wherein: A damping layer (7) is arranged at the bottom of the acoustic black hole (6), the damping layer (7) is arranged around the outer wall of the neck tube B (5).

3. A multi-layered Helmholtz resonator coupled to an acoustic black hole as defined in claim 1, wherein: The neck tube A (4) is arranged in two places, the neck tube A (4) is arranged vertically with the connecting tube (3), one end of the neck tube A (4) is communicated with the opening C (11), the other end of the neck tube A (4) is communicated with the connecting tube (3).

4. A multi-layered Helmholtz resonator coupled to an acoustic black hole of claim 1, wherein: The wall thickness of the Helmholtz resonator A (2) is smaller than the wall thickness of the shell (1), the volume of the neck tube A (4) is smaller than the volume of the back cavity (12).

5. A multilayered Helmholtz resonator coupled to an acoustic black hole of claim 1, wherein: The volume of the area above the connecting tube (3) of the back cavity (12) is smaller than the volume of the area below the connecting tube (3) of the back cavity (12).

6. A multilayer Helmholtz resonator coupled to an acoustic black hole of claim 1, wherein: The cross-sectional area of the opening A (31) is equal to the cross-sectional area of the through hole (51) of the neck tube B (5).

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