Dual-port asymmetric sound absorption structure based on Helmholtz resonant cavity

Abstract

The invention discloses a dual-port asymmetric sound absorption structure based on a Helmholtz resonant cavity. The structure is formed by connecting a plurality of asymmetric sound absorption units in parallel, wherein the short pipes of the asymmetric sound absorption units are different in radius. The asymmetric sound absorption unit internally comprises two Helmholtz resonant cavities with different cavity lengths, and the two main waveguides and the branch waveguides are used for transmitting sound waves and connecting the two Helmholtz resonant cavities. The two ends of the main waveguide are open, when sound waves are incident from the two ends, the incident sound waves at one end can be almost completely absorbed, the sound waves at the other end can be almost completely reflected, and due to the fact that the reciprocity of the structure is not broken and the transmission coefficients are the same, dual-port sound absorption can be achieved. A plurality of asymmetric sound absorption units with short pipes with different radiuses are connected in parallel, so that the structure has excellent broadband asymmetric sound absorption performance, and the asymmetric sound absorption frequency band can be effectively widened. The broadband sound absorption effect is excellent in the low and medium frequency range, the openings in the two ends of the main waveguide can achieve the good ventilation and heat dissipation effect, the size is small, the structure is compact, and the device is suitable for noise control in multiple fields.

Description

Technical Field

[0001] The invention relates to a dual-port asymmetric sound absorption structure based on a Helmholtz resonance cavity, and belongs to the field of medium and low frequency noise absorption. Background Art

[0002] The Helmholtz resonant cavity is one of the most basic acoustic models, generally composed of a short tube and a cavity. Its operating frequency range can be adjusted by changing the size of the short tube and the cavity. It is often used to suppress medium and low frequency sound waves. Because it has a large equivalent refractive index and a small impedance matching, it can achieve "small size controlling large wavelength" by reasonably designing its own structure, so it is widely used in the field of noise control. With the help of the gradually mature 3D printing technology, a large number of acoustic metamaterials based on the Helmholtz resonant cavity and its variants have emerged.

[0003] Cai et al. constructed a coplanar Helmholtz resonant cavity-type sound-absorbing metamaterial, which only achieved near-perfect sound absorption in deep subwavelength in theory, but did not conduct experimental verification; Huang et al. achieved ultra-wideband sound absorption in the range of 870Hz-3224Hz by coupling weakly sound-absorbing Helmholtz resonant cavity units, providing a method for designing efficient sound absorbers and acoustic impedance matching devices; Chen et al. designed a low-frequency sound-absorbing panel composed of two tubes of different sizes, without considering the high-frequency sound absorption effect; the above examples are all single-port sound-absorbing metamaterials based on the Helmholtz resonant cavity, which can achieve efficient absorption of sound waves by simply eliminating the reflected sound waves as much as possible, but for noise control projects that require ventilation and heat dissipation, the single-port sound-absorbing structure is no longer applicable, so it is necessary to construct a dual-port sound-absorbing system with both the incident and exit ends open.

[0004] Wei et al. theoretically obtained symmetric and antisymmetric coherent perfect sound absorption using Helmholtz resonant cavity and thin film materials, but did not conduct experimental verification; Meng et al. and Zhang et al. experimentally realized coherent perfect sound absorption using membrane materials and coherent channels. However, since coherent perfect sound absorption requires the simultaneous radiation of sound waves with strictly modulated amplitude and phase at both the incident and exit ends of the structure, its overly harsh usage conditions limit its application in noise control engineering and it is often used to make phase sensors.

[0005] Long et al. constructed a ventilated sound absorption system using multi-order Helmholtz resonant cavities, which can realize symmetric or asymmetric sound absorption functions and allow multiple monopole resonance modes in theory and experiment. These modular combinations further create reconfigurable multi-band anomalous absorbers in dual-port waveguides while maintaining ventilation and heat dissipation. In the asymmetric absorption state, through the coupling of artificial acoustic soft boundaries with the preset multi-order resonant cavities, when the sound wave is incident from one side and mostly reflected from the other side, the sound energy is almost completely absorbed in multiple frequency ranges, but no physical object has been designed for verification. Summary of the invention

[0006] Purpose of the invention: In order to solve the problem of medium and low frequency noise in practical engineering, realize broadband asymmetric sound absorption, and solve the problem of ventilation and heat dissipation, the present invention designs a dual-port asymmetric sound absorption structure based on the Helmholtz resonance cavity based on the coupled mode theory and the equivalent boundary theory.

[0007] Technical solution: A dual-port asymmetric sound absorption structure based on the Helmholtz resonant cavity is composed of several asymmetric sound absorption units with different short tube radii in parallel. The asymmetric sound absorption unit contains two Helmholtz resonant cavities with different cavity lengths. Two main waveguides and branch waveguides are used to transmit sound waves and connect the two Helmholtz resonant cavities. The asymmetric sound absorption frequency band is broadened by connecting asymmetric sound absorption units of different sizes in parallel in two-dimensional directions. When the sound wave is incident from one end, the structure realizes broadband and efficient sound absorption of the sound wave; when the sound wave is incident from the other end, the sound wave is almost completely reflected, realizing dual-port sound absorption.

[0008] Preferably, the present invention is prepared by 3D printing. Since the sample has a cavity structure inside, a step-by-step printing and final assembly method is selected to ensure that there is no extra residue in the cavity of the final sample.

[0009] Beneficial effects: The present invention is a dual-port asymmetric sound-absorbing structure based on the Helmholtz resonance cavity, which has the following advantages compared with existing acoustic metamaterials:

[0010] (1) Compared with other devices, the present invention is light and thin, and the openings at both ends of the main waveguide realize the ventilation function. It has certain development prospects in the field of noise control and is expected to be used in projects requiring ventilation and heat dissipation. It also has good application prospects in noise control projects of airflow and heat exchange.

[0011] (2) The processing and preparation process is simple and can be prepared by 3D printing technology. Compared with the traditional production and preparation method of local resonance acoustic metamaterials, it has the advantages of simple processing technology, low preparation cost, energy-saving and environmentally friendly process, and suitable for mass production.

[0012] (3) The dual-port asymmetric sound absorption structure designed by the present invention, which is composed of multiple asymmetric sound absorption units connected in parallel, can produce broadband and efficient asymmetric sound absorption for medium and low frequency noise.

[0013] (4) Compared with other acoustic materials, the present invention is small in size and is convenient for installation and use in actual noise reduction projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of a dual-port asymmetric sound absorption structure based on the Helmholtz resonance cavity.

[0015] Figure 2 Schematic diagram of an asymmetric sound absorbing unit.

[0016] Figure 3 Label the geometric parameters of the asymmetric sound absorbing unit.

[0017] Figure 4 is the sound absorption coefficient when the sound wave is incident from the left onto the dual-port asymmetric sound absorption structure.

[0018] Figure 5 is the sound absorption coefficient when the sound wave is incident from the right onto the dual-port asymmetric sound absorbing structure.

[0019] Figure 6 is the relative impedance corresponding to the sound wave incident from the left to the dual-port asymmetric sound absorbing structure.

[0020] Figure 7 is the relative impedance corresponding to the sound wave incident from the right to the dual-port asymmetric sound absorbing structure.

[0021] Figure 8 This is a sample picture of a dual-port asymmetric sound absorption structure.

[0022] Fig. 9 This is a comparison chart of the sound absorption coefficient test and simulation results when the sound wave is incident on the sample from the left.

[0023] Fig.10 This is a comparison chart of the sound absorption coefficient test and simulation results when the sound wave is incident on the sample from the right. DETAILED DESCRIPTION

[0024] The present invention is further described below in conjunction with the accompanying drawings. In the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or structure referred to must have a specified direction, be constructed or operate in a specific direction, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0025] The present invention provides a dual-port asymmetric sound absorption structure based on a Helmholtz resonance cavity, which is composed of a plurality of asymmetric sound absorption units with different short tube radii connected in parallel, such as Figure 2 The asymmetric sound absorbing unit includes two Helmholtz resonant cavities 3 with different cavity lengths, and the upper and lower main waveguides 2 and the branch waveguide 1 are used to transmit sound waves and connect the two Helmholtz resonant cavities.

[0026] Both ends of the upper and lower main waveguides are open. When sound waves are incident from the left and right ends, they enter through the upper and lower main waveguides at the left and right ends respectively. The left end can achieve nearly perfect sound absorption, and the sound waves at the right end are almost completely reflected. Since the structure does not break the reciprocity, the transmission coefficients are the same, and asymmetric absorption can be achieved.

[0027] Here is a specific example:

[0028] Figure 3 The geometric parameters of the asymmetric sound absorbing unit are as follows: the length L of the asymmetric sound absorbing unit is 44 mm, the height W is 27 mm, and the thickness D is 12 mm. The cross-sectional width t of the main waveguide is 10 mm, the height b is 2.5 mm, the width a of the branch waveguide is 5 mm, and the two internal Helmholtz resonance cavities have the same geometric parameters except for the length of the cavity. The short tube length l is 2 mm, the short tube radius r is 1 mm, the cavity height h is 13 mm, the width t is 10 mm, and the cavity lengths w1 and w2 of the two Helmholtz resonance cavities are 15 mm and 17 mm respectively. Different asymmetric sound absorbing units only have different short tube radii of the two internal Helmholtz resonance cavities, and the other geometric parameters are the same. Therefore, only the short tube radius inside each asymmetric sound absorbing unit is given in Table 1.

[0029] First, three asymmetric sound absorbing units are connected in parallel, and then six groups are connected in parallel vertically. The size of the sample is 67mm×67mm×44mm. Figure 8 As shown, it includes 18 asymmetric sound absorbing units and the material used is 9400 resin.

[0030] Table 1 Short tube radius inside the dual-port asymmetric sound absorption structure (mm)

[0031]

[0032] When the sound wave is incident from the left end, the sound absorption coefficient of the dual-port asymmetric sound absorption structure exceeds 70% in the wide frequency range of 970Hz to 1655Hz, and the average sound absorption coefficient in the range of 1100Hz to 1630Hz exceeds 84%, achieving broadband and efficient sound absorption when the sound wave is incident from the left end. Figure 6 It can be observed from the relative impedance results that within the calculated frequency range, the real part of the relative impedance approaches 1 and the imaginary part approaches 0, indicating that the surface impedance of the absorber matches the air impedance well within a wide frequency range. When the sound wave is incident from the right end, it can be seen that the highest sound absorption coefficient of the absorber within the calculated frequency range does not exceed 60%, and the average sound absorption coefficient in the entire frequency band is less than 40%. Figure 7 It can be seen from the impedance results that the surface impedance of the absorber is mismatched with the air impedance, so the sound wave is mainly reflected back to the incident end by the right end surface of the absorber. Therefore, the asymmetric sound absorption structure based on the Helmholtz resonant cavity double port designed by the present invention can achieve asymmetric sound absorption in a wide frequency range.

[0033] Fig. 9 This is a comparison chart of the sound absorption coefficient test and simulation results when the sound wave is incident on the sample from the left. Fig.10 This is a comparison chart of the sound absorption coefficient test and simulation results when the sound wave is incident on the sample from the right. Overall, the test and simulation results are in good consistency. The sound absorber designed by the present invention, which uses multiple asymmetric sound absorption units in parallel, can produce broadband and efficient asymmetric sound absorption for medium and low frequency noise, and has good application prospects in noise control projects requiring airflow and heat exchange.

[0034] In practical applications, the structural dimensions, the number of structural units, etc. in the present invention can be adjusted according to engineering requirements to achieve the purpose of on-demand production.

[0035] The specific preparation process of the present invention is as follows:

[0036] 1. Using UG and COMSOL software, starting from actual engineering use, determine the size of each structure of the present invention, select the base material, and generate a structural model suitable for 3D printing.

[0037] 2. Import the designed acoustic metamaterial physical model into the 3D printer. To ensure that there is no printing residue in the Helmholtz resonance cavity, a step-by-step printing and final assembly method is adopted to ensure that there is no excess residue in the cavity of the final sample. The printed samples are bonded together, such as Figure 8 shown.

[0038] It should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the technical solution. Although the applicant has described the present invention in detail with reference to the preferred embodiments, ordinary technicians in this field should understand that those modifications or equivalent substitutions made to the technical solution of the present invention cannot depart from the purpose and scope of the technical solution of the present invention and should be included in the scope of the claims of the present invention.

Claims

1. A dual-port asymmetric sound absorption structure based on a Helmholtz resonance cavity, characterized in that: The asymmetric sound absorption structure is composed of a plurality of asymmetric sound absorption units with different short tube radii connected in parallel. The asymmetric sound absorption unit contains two Helmholtz resonant cavities with different cavity lengths, and two main waveguides and branch waveguides are used to transmit sound waves and connect the two Helmholtz resonant cavity units.

2. The dual-port asymmetric sound absorption structure based on the Helmholtz resonance cavity according to claim 1, characterized in that: The two Helmholtz resonant cavities in the asymmetric sound absorbing unit have slightly detuned resonant frequencies and have almost the same leakage factor and loss factor.

3. According to the dual-port asymmetric sound absorption structure based on the Helmholtz resonance cavity according to claim 1, the main waveguide is open at both ends. When sound waves are incident from both ends, the incident sound waves at one end can be almost completely absorbed, and the sound waves at the other end are almost completely reflected. The transmission coefficients are the same, and dual-port sound absorption can be achieved.

4. The dual-port asymmetric sound absorbing structure based on the Helmholtz resonance cavity according to claim 1, characterized in that: The main waveguide is open at both ends to achieve better ventilation.

5. The dual-port asymmetric sound absorption structure based on the Helmholtz resonance cavity according to claim 1, characterized in that: The asymmetric sound absorption frequency band can be widened by connecting multiple asymmetric sound absorption units with different short tube radii in parallel.

6. The dual-port asymmetric sound absorption structure based on the Helmholtz resonance cavity according to claim 1, characterized in that: The asymmetric sound-absorbing structure is made of the same material and prepared by 3D printing.

7. The dual-port asymmetric sound absorption structure based on the Helmholtz resonance cavity according to claim 1, characterized in that: Since both ends of the waveguide are open, the unit main waveguides form a structural waveguide after parallel connection.

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