Multilayer Helmholtz resonator coupled with acoustic black hole

Abstract

The invention discloses a multilayer Helmholtz resonator coupled with an acoustic black hole. The multilayer Helmholtz resonator comprises a shell, a Helmholtz resonator A and a Helmholtz resonator B. The Helmholtz resonator A and the Helmholtz resonator B are arranged in the shell. A double-layer Helmholtz resonator is used, and an acoustic black hole structure is coupled to the joint of a Helmholtz resonator A and a Helmholtz resonator B. Firstly, the acoustic black hole structure reduces the quality of the Helmholtz resonator A and ensures that the multilayer Helmholtz resonator is light and thin, and the opening A generated by cutting off the multilayer Helmholtz resonator also provides an access port for the neck tube B; moreover, due to the structural characteristics of the acoustic black hole structure, part of sound waves can be effectively prevented from being reflected any more, and certain sound absorption performance is improved. In addition, the acoustic black holes can absorb sound in a wide frequency domain, and the sound absorption frequency band of the Helmholtz cavity is expanded.

Description

Technical Field

[0001] The invention belongs to the technical field of acoustic devices, and in particular relates to a multilayer Helmholtz resonator coupled to an acoustic black hole. Background Art

[0002] The current research hotspot in the field of noise control is to control the propagation of noise through sound insulation technology. Traditional sound insulation materials follow the law of mass and can effectively control the noise in the mid- and high-frequency parts. However, the noise in the low-frequency part has a long propagation distance, strong sound transmission ability, and is difficult to isolate. Therefore, traditional sound insulation materials have poor control effects on low-frequency noise, and also face problems such as being unable to be used at low temperatures and insufficient lifespan. Since the inertial resistance of traditional sound insulation materials is proportional to its mass and thickness, for this reason, the method of increasing its mass and thickness is usually chosen to improve the sound insulation performance of the low-frequency part. The increase in mass and thickness makes the structure less likely to vibrate, thereby improving the sound insulation effect. However, this method will first increase the cost of use, and secondly, it is not applicable in many cases.

[0003] The principle of the Helmholtz resonator 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 generates standing waves due to the reflection of the wall, causing the sound of a specific frequency to resonate. Due to the existence of acoustic resistance, the sound dissipates rapidly in the cavity, thus achieving silencing.

[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 a structural point of view, the acoustic black hole effect is achieved by embedding local inhomogeneities in thin-walled structures (usually beams or plates). The characteristic of this inhomogeneity is that the geometric properties change with the power law profile (the material may also change). Since the wall thickness changes according to the power law, the local stiffness of the thin wall decreases and the local damping increases, resulting in a significant decrease in the wave velocity and a significant enhancement of the attenuation characteristics. In the ideal case, that is, when the truncation length of the wedge tip is zero, the wave number tends to infinity, the wave velocity drops to zero, and the elastic wave is trapped at the tip forever without being reflected. In the non-ideal case, that is, when the truncation length of the acoustic black hole tip is non-zero, the wave velocity still decreases steadily, but it does not disappear. In the non-ideal case, the acoustic black hole is combined with a lossy medium (such as a viscoelastic layer) to achieve a significantly enhanced structural loss factor.

[0005] Since the acoustic black hole has a simple structure and a wide-band sound absorption effect, it is widely used in the field of noise control. For example, the invention patent application with application number 2023114259171 proposes an acoustic black hole spiral spring structure and a vehicle that can suppress the propagation of structural noise. The multiple periodically distributed acoustic black hole spring structures are used to suppress the propagation of broadband noise into the vehicle through the suspension system. The invention patent application with application number 2022111983398 proposes an annular spiral acoustic black hole vibration reduction structure, which nests multiple Archimedean spiral acoustic black holes and annuli on a tubular structure to achieve vibration reduction and noise reduction of the tubular structure.

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

[0007] The problem of insufficient sound absorption bandwidth is currently mainly solved by coupling multiple single resonance systems. The invention patent application with application number 201610366214X proposes a low-frequency composite sound absorption device, which couples multiple Helmholtz resonator arrays to a thin plate. The results show that the sound absorption bandwidth can be increased. However, the above coupling technology ignores the impact of the number and position of the array on the sound absorption performance. The existing method of expanding the bandwidth mainly depends on the number of peaks, but coupling multiple resonators will also make it have multiple troughs, increasing its efficiency loss; at the same time, with multiple Helmholtz resonators with strong sound absorption performance, the main structure must have sufficient thickness, which also makes it impossible to achieve thinner and wider-band sound absorption. Summary of the invention

[0008] In order to solve the above technical problems, the present invention provides a multi-layer Helmholtz resonator coupled with an acoustic black hole, which can solve the problem that the sound absorption bandwidth of a single resonator in the prior art is insufficient and the thickness of the sound absorption structure coupled with multiple resonator arrays is increased, so as to achieve broadband sound absorption and improve its sound absorption capacity.

[0009] The present invention is achieved through the following technical solutions.

[0010] The present invention provides a multilayer Helmholtz resonator coupled to an acoustic black hole, comprising a shell, a Helmholtz resonator A and a Helmholtz resonator B, wherein the Helmholtz resonator A and the Helmholtz resonator B are arranged in the shell.

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

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

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

[0014] Preferably, the lower end of the acoustic black hole is located on the side close to the opening A, and the thickness of the acoustic black hole is calculated according to the exponential function h(x)=εx m Decreasing, 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 provided at two locations, the neck tube A and the connecting tube are vertically provided, one end of the neck tube A is connected to the opening C, and the other end of the neck tube A is connected to the connecting tube.

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

[0018] Preferably, the volume of the area of ​​the back cavity above the connecting pipe is smaller than the volume of the area of ​​the back cavity below the connecting pipe.

[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 invention are:

[0021] The multilayer Helmholtz resonator coupled to the acoustic black hole of the present application forms an elastic system through a shell, a Helmholtz resonator A and a Helmholtz resonator B. When a sound wave enters it, it is reflected in the Helmholtz resonator A and the neck tube B to generate resonance. The present invention uses a double-layer Helmholtz resonator, and couples the acoustic black hole structure at the point where the Helmholtz resonator A and the Helmholtz resonator B are connected. First, the acoustic black hole structure reduces the mass of the Helmholtz resonator A, ensuring the thinness of the multilayer Helmholtz resonator, because the opening A generated by its truncation also provides an access port for the neck tube B. Moreover, due to its structural characteristics, the acoustic black hole structure can effectively prevent some sound waves from being reflected, and also improves certain sound absorption performance. Not only that, the acoustic black hole can also absorb sound in a wider frequency domain, expanding the sound absorption band of the Helmholtz cavity. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the internal structure of the present invention;

[0023] Figure 2 It is a schematic diagram of the internal structure of the present invention;

[0024] Figure 3 Schematic diagram of the structure of the Helmholtz resonator A of the present invention;

[0025] Figure 4 Schematic diagram of the structure of the Helmholtz resonator A of the present invention;

[0026] Figure 5 It is a schematic structural diagram of the neck tube B of the present invention;

[0027] Figure 6 It is a schematic diagram of the appearance of the present invention;

[0028] Figure 7 It is a schematic diagram of the structure of the acoustic black hole of the present invention;

[0029] Figure 8 It is a schematic diagram of the structure of the acoustic black hole of the present invention;

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

[0031] The technical solution of the present invention is further described below, but the scope of protection claimed is not limited to the description.

[0032] Example:

[0033] like Figures 1 to 8 As shown, a multilayer Helmholtz resonator coupled to an acoustic black hole has an overall shape of a rectangular parallelepiped, including a shell 1, a Helmholtz resonator A2 and a Helmholtz resonator B, wherein the Helmholtz resonator A2 and the Helmholtz resonator B are arranged in the shell 1.

[0034] An opening C11 is provided on the shell 1 . The opening C11 is square and can also be provided in other shapes according to actual needs. Two openings C11 are provided accordingly. A back cavity 12 is provided in the shell 1 . The Helmholtz resonator A2 and the Helmholtz resonator B are provided 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 to the neck tube A4, and the Helmholtz resonator B includes a neck tube B5 and a back cavity 12, and the neck tube B5 is connected to the bottom of the connecting tube 3. Two neck tubes A4 are provided, so that the Helmholtz resonator A2 has a double-neck structure, which can cause friction between the sound wave and the wall surfaces of the two connecting tubes 3, increase the sound energy loss, and broaden the resonance frequency band.

[0036] The connecting tube 3 is provided with an acoustic black hole 6. The thickness of the acoustic black hole 4 decreases with the exponential change. An opening A31 is generated at the truncation point. The acoustic black hole 6 is connected to the neck tube B5 through the opening A31. The acoustic black hole 4 is made of the same material as the bottom of the connecting tube 3, and only the shape changes. The bottom of the connecting tube 3 is symmetrically coupled with two acoustic black holes. The acoustic black holes decrease with the thickness h. b Start decreasing.

[0037] The lower end of the acoustic black hole 6 is located near the opening A31, and the thickness of the acoustic black hole 6 is expressed as an exponential function h(x)=εx m Decreases, where h(x) is the thickness of a point on the acoustic black hole 6, x is the distance from a point on the acoustic black hole 6 to the opening A31, m≥2, and ε is an arbitrary constant.

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

[0039] The neck tube A4 is set at two places, and the interface and cavity cross-section of the neck tube A4 are square, and can also be set to other shapes according to actual needs. The neck tube A4 is vertically set to the connecting tube 3, one end of the neck tube A4 is connected to the opening C11, and the other end of the neck tube A4 is connected to the connecting tube 3. The neck tube A4 is embedded and extends into the back cavity 12. The neck tube A4 does not contact the back cavity 12 to avoid a large number of reflections, and the two neck tubes A4 can adjust the distance according to the sound absorbing belt.

[0040] The wall thickness of the Helmholtz resonator A2 is smaller than the wall thickness of the housing 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 resonance cavity; 3. The walls of the resonance cavity are all rigid walls, which will not deform when affected by external sound pressure, and will not cause the fluid medium to be transmitted outside the resonance cavity.

[0041] The volume of the area of ​​the back cavity 12 located above the connecting pipe 3 is smaller than the volume of the area of ​​the back cavity 12 located below the connecting pipe 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 tube B5. The cross-sectional area of ​​the inner hole 51 can be square, but the shape varies with the shape of the opening A31 generated by the truncation of the upper acoustic black hole 6, and must be closely connected to the opening. The wall thickness of the neck tube B5 needs to be as small as possible, otherwise it will affect the position of the acoustic damping layer 7, resulting in reduced performance of the acoustic black hole 6.

[0043] like Figure 7 , 8 As mentioned above, the acoustic black hole 6 can theoretically make the wave speed 0, but because truncation is inevitable, a damping layer 7 with a thickness of h is required to be attached to the bottom. The material of the damping layer is butyl rubber to enhance its dissipation performance as much as possible. The attachment position of the damping layer 7 leaves a position for setting the neck tube B5. Figure 8 Here o is the cut-off position of the acoustic black hole 6, which is the opening A31, and o to labh is the length of the acoustic black hole 6.

Claims

1. A multilayer Helmholtz resonator coupled to an acoustic black hole, characterized in that: The invention comprises a housing (1), a Helmholtz resonator A (2) and a Helmholtz resonator B, wherein the Helmholtz resonator A (2) and the Helmholtz resonator B are arranged in the housing (1).

2. A multilayer Helmholtz resonator coupled to an acoustic black hole as claimed in claim 1, characterized in that: An opening C (11) is provided on the housing (1), and the opening C (11) is in a square shape. A back cavity (12) is provided in the housing (1), and the Helmholtz resonator A (2) and the Helmholtz resonator B are provided in the back cavity (12).

3. A multilayer Helmholtz resonator coupled to an acoustic black hole as claimed in claim 2, characterized in that: The Helmholtz resonator A (2) comprises a connecting tube (3) and a neck tube A (4), wherein the connecting tube (3) is connected to the neck tube A (4), and the Helmholtz resonator B comprises a neck tube B (5) and a back cavity (12), wherein the neck tube B (5) is connected to the bottom of the connecting tube (3).

4. A multilayer Helmholtz resonator coupled to an acoustic black hole as claimed in claim 3, characterized in that: An acoustic black hole (6) is arranged in the connecting tube (3), and the acoustic black hole (6) is connected to the neck tube B (5) through the opening A (31).

5. A multilayer Helmholtz resonator coupled to an acoustic black hole as claimed in claim 4, characterized in that: The lower end of the acoustic black hole (6) is located on the side close to the opening A (31), and the thickness of the acoustic black hole (6) is calculated according to an exponential function h(x)=εx m Decreasing, where h(x) is the thickness, m ≥ 2, and ε is an arbitrary constant.

6. A multilayer Helmholtz resonator coupled to an acoustic black hole as claimed in claim 5, characterized in that: A damping layer (7) is arranged at the bottom of the acoustic black hole (6), and the damping layer (7) is arranged around the outer wall of the neck tube B (5).

7. A multilayer Helmholtz resonator coupled to an acoustic black hole as claimed in claim 3, characterized in that: The neck tube A (4) is arranged at two locations, the neck tube A (4) and the connecting tube (3) are arranged vertically, one end of the neck tube A (4) is connected to the opening C (11), and the other end of the neck tube A (4) is connected to the connecting tube (3).

8. The multilayer Helmholtz resonator coupled to an acoustic black hole as claimed in claim 3, characterized in that: The wall thickness of the Helmholtz resonator A (2) is smaller than the wall thickness of the housing (1), and the volume of the neck tube A (4) is smaller than the volume of the back cavity (12).

9. The multilayer Helmholtz resonator coupled to an acoustic black hole according to claim 3, characterized in that: The volume of the area of ​​the back cavity (12) located above the connecting pipe (3) is smaller than the volume of the area of ​​the back cavity (12) located below the connecting pipe (3).

10. The multilayer Helmholtz resonator coupled to an acoustic black hole according to claim 1, characterized in that: 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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