Medium and low frequency sound absorption metamaterial

Abstract

The utility model discloses a medium and low frequency sound absorption metamaterial which comprises a resonator array, each resonator is enclosed by a housing, the cross section of each resonator is of a concave structure, a through hole is formed in the concave position, and a plurality of resonator units are connected together to form a broadband sound absorption structure. The concave structure enables the resonator units to form a plurality of slits after being connected, the slits and the resonator units form new resonance units together, and the new resonance units are used for enabling air in the resonance structure to generate resonance after sound waves enter and generate heat through friction with the inner walls of the slits, so that sound energy absorption is achieved. The low and medium frequency sound absorption metamaterial is composed of the perforated concave resonant cavity, is thin in thickness, simple in structure, easy to manufacture and flexible to install, and achieves broadband absorption of sound waves at low and medium frequencies.

Description

Technical Field

[0001] The utility model relates to a sound-absorbing metamaterial, in particular to a medium- and low-frequency sound-absorbing metamaterial. Background Art

[0002] The control of mid- and low-frequency noise has always been a major challenge in the field of noise reduction. Traditional acoustic materials, such as porous materials and micro-perforated structures, usually require the structure size to be close to the wavelength of sound to effectively absorb noise. Therefore, processing low-frequency noise often requires a large volume, which is difficult to flexibly adapt to various application scenarios. In recent years, a variety of acoustic metamaterials based on local resonance structures have demonstrated the ability to deal with mid- and low-frequency noise. However, the existing acoustic metamaterial design usually requires the construction of a complex structure inside the cavity to achieve local resonance, which complicates the manufacture of the metamaterial and limits the flexibility of combining multiple units, hindering their potential for large-scale practical application. There is an urgent need to simplify the structure while retaining the mid- and low-frequency sound absorption capabilities to meet the needs of practical applications. Utility Model Content

[0003] Purpose of the utility model: The utility model aims to provide a medium and low frequency sound-absorbing metamaterial with a simple structure, easy manufacturing and high sound absorption efficiency.

[0004] Technical solution: The mid- and low-frequency sound-absorbing metamaterial described in this utility model includes a resonator array, wherein each resonator is surrounded by a cover and has a "concave" cross-section with a perforation provided in the concave portion. Multiple resonator units are connected together to form a broadband sound-absorbing structure. The "concave" structure allows the resonator units to form multiple slits after being connected, and the slits and the resonator units together form a new resonance unit.

[0005] Furthermore, the sound wave incident surface of the resonator is arranged perpendicular to the concave surface, and the sound wave directly hits one side of the incident surface and enters the resonator through the slit. The air resonates and rubs against the slit and the side wall of the cavity to generate heat to achieve sound absorption.

[0006] Furthermore, the cover includes a top cover, a side shell and a bottom plate, and the sound-absorbing metamaterial obtained by connecting multiple resonator units is tightly installed on the flat bottom plate or wall surface.

[0007] Furthermore, the diameter of the perforation of each resonator unit and the vertical distance between the center of the perforation and the top cover of the housing are the same, or not all the same, or are different.

[0008] Furthermore, the aperture of the perforation is 1 mm to 15 mm, the shape of the perforation includes a circle or a rectangle, and the vertical distance between the center of the perforation and the top cover of the housing is required to ensure the integrity of the shape of the perforation.

[0009] Furthermore, the wall thickness of the metamaterial is 0.5-3 mm, the height of the cover is 20-100 mm, the depth of the concave side of the cover is between 1 mm and 3 mm, and the width of the slit naturally generated after welding corresponds to the depth.

[0010] Furthermore, the covers of the plurality of resonator units are connected by ultrasonic welding or epoxy resin adhesive.

[0011] Beneficial Effects: Compared with existing technologies, this invention offers the following significant advantages: The metamaterial utilizes multiple slits, created by combining and connecting concave resonators in parallel. Sound absorption is achieved through the slits and perforations on the side of the resonators. The acoustic impedance of the metamaterial is adjusted by the vertical distance between the perforation center of each resonant unit and the top cover of the housing, achieving broadband sound absorption at low and medium frequencies. Its thickness is only 1 / 20 of the maximum wavelength within the target absorption band, effectively absorbing sound within a frequency range of 390-862 Hz. The raw materials used are inexpensive and safe, and no internal inserts or other structures are required, making it easier to manufacture and saving materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Schematic diagram of a "concave" metamaterial unit;

[0013] Figure 2 Schematic diagram of the connection and combination of sound-absorbing metamaterial units;

[0014] Figure 3 A top view schematic diagram of the connection assembly of the sound-absorbing metamaterial units;

[0015] Figure 4 Schematic diagram of the sound absorption coefficient of the metamaterial in Example 1;

[0016] Figure 5 Schematic diagram of the sound absorption coefficient of the metamaterial in Example 2. DETAILED DESCRIPTION

[0017] The technical solution of the present utility model will be further described below with reference to the accompanying drawings.

[0018] Figure 1-3 The reference numerals in the figures are: 1. resonator unit, 2. slit, 3. additional wall plate, 11. perforation, 12. cover, 13. concave surface, 14. incident surface.

[0019] Example 1

[0020] like Figure 1-3As shown, the medium and low frequency sound absorbing metamaterial includes a resonator array, wherein each resonator is surrounded by a cover 12 and has a "concave" structure in cross section, with a perforation 11 provided in the concave portion, and multiple resonator units 1 are connected together to form a broadband sound absorbing structure. The metamaterial wall thickness is 1 mm, the cover 12 height is 40 mm, the concave surface 13 depth is 2 mm, the center distance of each unit perforation 11 from the upper surface ranges from 6 mm to 34 mm, and the diameter of the perforation 11 is 10 mm. A slit 2 is formed between two adjacent units, and the rightmost row of units needs to be equipped with a wall panel 3 to form a slit. The sound wave incident surface 14 is perpendicular to the concave surface 13. After the sound wave is incident, the slit 2 resonates with the air in the resonance cavity and generates heat by friction with the inner wall of the slit to achieve sound absorption. As shown Figure 4 As shown in the figure, the sound absorption coefficient in the range of 390-862Hz is around 0.8 or above.

[0021] The corresponding sound absorption coefficient can be obtained by calculating the acoustic impedance of the sound-absorbing metamaterial. The acoustic impedance calculation method of each unit of the sound-absorbing metamaterial is as follows:

[0022] (1) Calculate the equivalent medium complex parameters at each position, so that the acoustic resistance caused by the thermal viscosity of the air can be effectively calculated. The equivalent density and bulk modulus in the slit are: and in and is the corresponding viscous wave number and thermal wave number, t is the slit width, η and κ are the dynamic viscosity coefficient and thermal conductivity, C p is the specific heat capacity at constant pressure. The equivalent density and bulk modulus of the circular perforated area are: and where J0 and J1 are the zero-order and first-order Bessel functions of the first kind, respectively, and r is the radius of the perforation. Since the thermoviscous effect within the cavity is small, the original density and bulk modulus can be used directly.

[0023] (2) The acoustic impedance of the unit is calculated using the transfer matrix method. The relationship between the unit surface acoustic impedance and the bottom acoustic impedance is: T is the transfer matrix, p and v are the sound pressure and particle velocity at the corresponding positions, and S is the cross-sectional area of ​​the slit. The transfer matrix of the slit is Among them, k f With Z f The equivalent complex wave number and complex characteristic acoustic impedance in the slit are calculated using the above equivalent parameters. This transfer matrix is ​​used in both the areas above and below the center of the perforation. The transfer matrix at the perforation position is where Z His the acoustic impedance of the combination of the perforation and the cavity. This acoustic impedance can be calculated using the acoustic impedance calculation method of the classical Helmholtz resonator, where equivalent parameters are required for the calculation of the perforation. The final total transfer matrix is ​​obtained by multiplying the three regional transfer matrices. The acoustic impedance of the unit is A is the total area of ​​the metamaterial after multiple units are spliced ​​together.

[0024] (3) The acoustic impedance of the spliced ​​metamaterial is Z n Represents the acoustic impedance of the nth unit. According to the above design method, the interior point method is used to optimize the structural parameters of each unit to obtain the optimal sound absorption capacity in the target frequency band.

[0025] Example 2

[0026] The structure of the mid- and low-frequency sound-absorbing metamaterial is the same as that of Example 1, except that the height of the housing 12 is 60 mm, and the distance between the center of each unit perforation 11 and the upper surface varies from 6 mm to 54 mm. Figure 5 Shown is a schematic diagram of the sound absorption coefficient of the metamaterial in Example 2.

Claims

1. A medium and low frequency sound absorbing metamaterial, characterized in that: The invention comprises a resonator array, wherein each resonator unit (1) is surrounded by a cover (12) and has a "concave" structure in cross section, a perforation (11) is provided at the concave part, and a plurality of resonator units (1) are connected together to form a broadband sound absorption structure. The "concave" structure enables the resonator units (1) to form a plurality of slits (2) after being connected. The outermost row of units needs to be equipped with a wall panel (3) to form the slits (2), and the slits (2) and the resonator units (1) together form a new resonance unit.

2. The medium and low frequency sound absorbing metamaterial according to claim 1, characterized in that: The sound wave incident surface (14) of the resonator is arranged perpendicular to the concave surface (13), and the sound wave directly hits one side of the incident surface and enters the resonator through the slit (2), and the air resonates and rubs against the slit (2) and the side wall of the cavity to generate heat and achieve sound absorption.

3. The medium and low frequency sound absorbing metamaterial according to claim 1, characterized in that: The housing (12) comprises a top cover, a side shell and a bottom plate, and the sound-absorbing metamaterial obtained by connecting a plurality of resonator units (1) is tightly mounted on a flat bottom plate or wall surface.

4. The low- to medium-frequency sound-absorbing metamaterial according to claim 1, characterized in that: The aperture of the through hole (11) of each resonator unit (1) and the vertical distance between the center of the through hole (11) and the top cover of the housing (12) are the same or not completely the same or are different.

5. The medium and low frequency sound absorbing metamaterial according to claim 1, characterized in that: The diameter of the perforation (11) is 1 mm-15 mm.

6. The medium and low frequency sound absorbing metamaterial according to claim 1, characterized in that: The shape of the perforation (11) includes a circle or a rectangle.

7. The medium and low frequency sound absorbing metamaterial according to claim 1, characterized in that: The covers of the plurality of resonator units (1) are connected by ultrasonic welding or epoxy resin adhesive.

8. The medium and low frequency sound absorbing metamaterial according to claim 1, characterized in that: The depth of the concave portion of the side surface of the housing (12) is between 1 mm and 3 mm, and the width of the slit naturally generated after welding corresponds to the depth.

9. The medium and low frequency sound absorbing metamaterial according to claim 1, characterized in that: The wall thickness of the metamaterial is 0.5-3 mm, the height of the cover (12) is 20-100 mm, and the vertical distance between the center of the perforation (11) and the top cover of the cover (12) meets the requirement of complete perforation.

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