An acoustic black hole sound-absorbing device

Abstract

This invention belongs to the technical field of noise reduction devices and discloses an acoustic black hole sound-absorbing device. The invention includes a cylindrical substrate, several annular partition plates, sound-absorbing material, a short, thin tube at the tail, and a labyrinthine metasurface. The annular partition plates are arranged in parallel at their centers with equal spacing and fixed to the cylindrical substrate. Each annular partition plate has a hole at its center with gradually increasing or decreasing inner diameter, forming the acoustic black hole substrate. Ribs are coiled inside the labyrinthine metasurface according to a predetermined spiral line, forming a coiled sound channel. The labyrinthine metasurface is closed and connected to the tail of the cylindrical substrate. The short, thin tube at the tail is fixed to the center of the annular partition plate with the smallest hole diameter, located outside the cylindrical substrate, and extends into the labyrinthine metasurface, together forming the sound-absorbing device. This invention has a broadband sound absorption capability from low to high frequencies.

Description

Technical Field

[0001] This utility model belongs to the field of noise reduction device technology, specifically relating to an acoustic black hole sound absorption device. Background Technology

[0002] An acoustic black hole is an acoustic duct consisting of a set of rings whose inner diameter decays according to a power law, such as... Figure 1 As shown. Ideally, as the number of rings approaches infinity, the speed of sound waves reaching the end will drop to 0, thus trapping the sound waves within. An acoustic black hole is a high-performance high-frequency broadband sound absorber, but in practical applications, the limited number of rings prevents effective dissipation of sound waves after they enter it. This results in the prototype acoustic black hole failing to achieve effective sound absorption in the mid-to-low frequencies, such as... Figure 2 As shown. Summary of the Invention

[0003] The purpose of this invention is to address the problem of insufficient low-frequency sound absorption performance in existing acoustic black holes by providing an acoustic black hole sound absorption device. This device incorporates a labyrinth metasurface and sound-absorbing cotton, perfectly combining the high-frequency sound absorption performance of acoustic black holes with the low-frequency sound absorption performance of labyrinth metasurfaces, thereby expanding its application scenarios.

[0004] This utility model provides an acoustic black hole sound absorption device, including a cylindrical base, several annular partition plates, sound-absorbing material, a short tail tube, and a labyrinth metasurface.

[0005] The annular partition plates are arranged in parallel with equal spacing and fixed on the cylindrical base. Each annular partition plate has a hole with an increasing or decreasing inner diameter at its center, forming an acoustic black hole base.

[0006] The labyrinth metasurface has ribs coiled in a set spiral pattern inside, forming a coiled sound channel. The labyrinth metasurface is closed and connected to the tail of the cylindrical base.

[0007] The short, thin tube at the tail end is fixed to the center of the annular partition plate with the smallest aperture, located on the outside of the cylindrical base, and extends into the labyrinth metasurface, together with the labyrinth metasurface forming a sound-absorbing device.

[0008] Furthermore, the inner diameter of the short, thin tube at the tail end is the same as the inner diameter of the annular partition plate with the smallest aperture.

[0009] Furthermore, the inner diameter of each of the aforementioned annular partition plates varies in a power-law manner.

[0010] Furthermore, the formula for calculating the inner diameter of the annular partition plate is as follows:

[0011]

[0012] in, This represents the inner diameter of the i-th annular partition plate. Indicates the inner diameter of the cylindrical base. This represents the inner diameter of the annular separator with the smallest aperture. This indicates the total axial length of the cylindrical base. This represents the distance from the center of the i-th annular separator to the center of the separator with the smallest aperture.

[0013] Furthermore, the labyrinth acoustic metasurface is coiled into an Archimedean spiral.

[0014] Furthermore, the cavity area formed by the adjacent annular partition plate and the cylindrical base is filled with sound-absorbing material; the sound-absorbing material is generally annular, with an inclined inner diameter surface, and the two end faces respectively abut against the annular partition plates on both sides of the sound-absorbing material.

[0015] Furthermore, the sound absorption coefficient of the acoustic black hole sound-absorbing device for:

[0016] (9)

[0017] In Equation 9, Transfer matrix for acoustic black hole sound absorption device The element in the first row and first column of the middle, For the transfer matrix The element in the second row and first column; the transfer matrix of the acoustic black hole sound-absorbing device. for:

[0018] (1)

[0019] In Equation 1, The acoustic black hole transfer matrix is ​​a nested sound-absorbing material. The acoustic transfer matrix of the short, thin tube at the tail and the labyrinthine metasurface; the acoustic black hole transfer matrix of the nested sound-absorbing material. The specific expression is:

[0020] (2)

[0021] In Equation 2, The wave number of the sound wave. , The resonant sound absorption frequency. The speed of sound in air; The distance between adjacent annular partitions. The characteristic impedance of air, air density; Let be the area of ​​the inner ring of the i-th annular partition plate; The inner surface area of ​​the sound-absorbing material. The wall admittance generated by the sound-absorbing cotton in the i-th annular cavity is expressed as follows:

[0022] (3)

[0023] In Equation 3, J0 is a Bessel function, J1 is a zeroth-order Bessel function, and J1 is a first-order Bessel function. Let N be the von Neumann function, N0 be the zeroth-order von Neumann function, and N1 be the first-order von Neumann function; The inner diameter of the cylindrical base; and The characteristic impedance and complex wavenumber of the sound-absorbing cotton. and The equivalent density and equivalent modulus of sound-absorbing cotton are expressed as follows:

[0024] (4)

[0025] (5)

[0026] In equations 4 and 5, is the dynamic viscosity coefficient of air. The specific heat capacity of air. For tortuosity, Porosity For flow resistance, The viscous characteristic length, For thermal characteristic length, For ambient air pressure, ;

[0027] The acoustic transmission matrix of the tail-end slender tube and the labyrinth metasurface The specific expression is:

[0028] (6)

[0029] In Equation 6, The cross-sectional area of ​​the cylindrical base is... Let be the cross-sectional area of ​​the acoustic channel in the labyrinth metasurface. This represents the curl length of the acoustic channel. For the Archimedean spiral, It can be calculated using Equation 7:

[0030] (7)

[0031] In Equation 7, , which is the total coiling angle. To coil around the outermost diameter of the sound channel, To the innermost diameter of the coiled sound channel, It is a spiral growth ratio, and The number of times it is coiled;

[0032] In Equation 6, The surface acoustic impedance of the short, thin tube at the tail end is expressed as follows:

[0033] (8)

[0034] In Equation 8, Aerodynamic viscosity, The length of the short, thin tube at the tail end. This refers to the inner diameter of the short, thin tube at the tail end, which is also the inner diameter of the rightmost annular partition plate. , .

[0035] Furthermore, the labyrinth metasurface is detachably and closedly connected to the tail of the cylindrical base.

[0036] The beneficial effects of this acoustic black hole sound-absorbing device are as follows:

[0037] The acoustic black hole sound absorption device of this invention solves the problem of low-frequency characteristic frequency noise by nesting a labyrinth metasurface at the tail end to generate an additional sound absorption band in the low-frequency region; by filling it with sound-absorbing cotton to increase the acoustic energy dissipation capacity of the acoustic black hole, it achieves mid-to-high frequency sound absorption, thereby giving this invention a broadband sound absorption capability from low to high frequencies.

[0038] The acoustic black hole sound absorption device of this invention has a detachable labyrinth metasurface nested at the tail. By replacing the metasurface with a spiral with a corresponding curled shape according to the required resonant sound absorption frequency, different resonant sound absorption frequencies can be obtained. Attached Figure Description

[0039] Figure 1 This is a cross-sectional view of an existing acoustic black hole structure;

[0040] Figure 2 yes Figure 1 A schematic diagram of a typical sound absorption frequency band of an acoustic black hole;

[0041] Figure 3 This is a schematic diagram of the structure of an embodiment of the present utility model;

[0042] Figure 4 This is a cross-sectional view of an embodiment of the present utility model;

[0043] Figure 5 This is a schematic diagram of the structure of the labyrinth metasurface according to an embodiment of the present invention;

[0044] Figure 6 for Figure 5 The left view;

[0045] Figure 7 This is a schematic diagram of the sound absorption coefficient of an embodiment of the present invention;

[0046] The diagram shows: 1-cylindrical base, 2-annular partition plate, 3-sound absorbing material, 4-short tail tube, 5-labyrinth metasurface, 51-rib plate. Detailed Implementation

[0047] The present invention will now be described in further detail with reference to the embodiments and accompanying drawings.

[0048] One embodiment of this utility model is an acoustic black hole sound-absorbing device, such as... Figures 3-6 As shown, it includes a cylindrical base 1, several annular partition plates 2, sound-absorbing material 3, a short tail tube 4, and a labyrinth metasurface 5.

[0049] The annular partition plates 2 are arranged in parallel with equal spacing and fixed to the cylindrical base 1. Each annular partition plate 2 has a hole with an increasing or decreasing inner diameter at its center, forming an acoustic black hole matrix. Ribs 51 are coiled inside the labyrinth metasurface 5 according to a predetermined spiral, forming a coiled sound channel. The labyrinth metasurface 5 is closed and connected to the tail end of the cylindrical base 1. The tail end thin tube 4 is fixed to the center of the annular partition plate 2 with the smallest aperture, located outside the cylindrical base, and extends into the labyrinth metasurface 5, forming a sound-absorbing device together with the labyrinth metasurface 5. Preferably, in another embodiment, the inner diameter of the tail end thin tube 4 is the same as the inner diameter of the annular partition plate 2 with the smallest aperture.

[0050] The inner diameter of each annular partition 2 varies according to a power law. Preferably, in another embodiment, the formula for calculating the inner diameter of each annular partition 2 is as follows:

[0051]

[0052] in, This represents the inner diameter of the i-th annular partition plate 2. This indicates the inner diameter of the cylindrical base 1. This represents the inner diameter of the annular partition plate with the smallest inner diameter. This represents the total axial length of the cylindrical base 1. This represents the distance from the center of the i-th annular partition 2 to the center of the partition with the smallest inner diameter.

[0053] Each annular partition plate 2 has a thickness of not less than 1 mm, and the cylindrical base 1 has a thickness of not less than 2 mm.

[0054] Preferably, in another embodiment, the cavity area formed by the adjacent annular partition plate 2 and the cylindrical base 1 is filled with sound-absorbing material 3 (e.g., melamine sound-absorbing cotton). The sound-absorbing material 3 is generally annular, with an inclined inner diameter surface, and its two end faces respectively abut against the annular partition plate 2 on both sides of the sound-absorbing material 3. The sound-absorbing material 3 can be fixed to the annular partition plate 2 by adhesive or other adhesive materials.

[0055] The labyrinth metasurface 5 and the cylindrical substrate 1 can be fixedly connected by means of adhesive bonding or welding. For example... Figure 6 As shown, the labyrinthine acoustic metasurface elongates the acoustic channel in a folded labyrinth shape, thereby significantly reducing the structural thickness of the acoustic metasurface. In fact, after entering the folded labyrinth, sound waves propagate along the path of the labyrinthine channel; therefore, with the same structural thickness, the folded labyrinth shape is equivalent to extending the length of sound wave propagation. Acoustic metasurfaces can generate effective sound absorption near the resonant absorption frequency. Using a labyrinthine acoustic metasurface, the structural thickness can be only one-hundredth of the wavelength of the sound wave at its effective absorption frequency. This allows the labyrinthine metasurface to achieve low-frequency sound absorption with extremely low structural thickness, significantly reducing the thickness requirements of traditional Helmholtz resonators.

[0056] Preferably, in another embodiment, the labyrinth acoustic metasurface is coiled into an Archimedean spiral. This invention has a simple structure, low cost, and exhibits wideband sound absorption performance as well as low-frequency sound absorption.

[0057] The cylindrical substrate 1, the annular partition plate 2, the sound-absorbing material 3, and the labyrinth metasurface 5 can be tightly connected by means of adhesive bonding or welding. The specific fixing sequence is as follows: First, the cylindrical substrate 1 is connected to the annular partition plate with the smallest aperture ( Figure 4 The rightmost annular partition plate is fixedly connected, and then the sound-absorbing material 3 and the remaining annular partition plates 2 are inserted into the cylindrical base 1 one by one and fixedly connected. Finally, the labyrinth metasurface 5 is fixedly connected to the tail of the cylindrical base 1.

[0058] The acoustic black hole sound-absorbing device of this utility model is set up according to the following steps:

[0059] The first step is to construct a transfer matrix model for an acoustic black hole sound-absorbing device. :

[0060] (1)

[0061] in, The acoustic black hole transfer matrix is ​​a nested sound-absorbing material. The acoustic transfer matrix is ​​the short, thin tube at the tail and the labyrinth metasurface.

[0062] The second step is to construct the acoustic black hole transfer matrix of the nested sound-absorbing cotton in Formula 1. The specific expression is:

[0063] (2)

[0064] In Equation 2, The wave number of the sound wave. , The resonant sound absorption frequency. The speed of sound in air; The distance between adjacent annular partitions. The characteristic impedance of air, air density; Let be the area of ​​the inner ring of the i-th annular partition plate; The inner surface area of ​​the sound-absorbing material. The wall admittance generated by the sound-absorbing cotton in the i-th annular cavity is expressed as follows:

[0065] (3)

[0066] In Equation 3, J0 is a Bessel function, J1 is a zeroth-order Bessel function, and J1 is a first-order Bessel function. Let N be the von Neumann function, N0 be the zeroth-order von Neumann function, and N1 be the first-order von Neumann function; The inner diameter of the cylindrical base; and The characteristic impedance and complex wavenumber of the sound-absorbing cotton. and The equivalent density and equivalent modulus of sound-absorbing cotton are expressed as follows:

[0067] (4) (5)

[0068] In equations 4 and 5, is the dynamic viscosity coefficient of air. The specific heat capacity of air. For tortuosity, Porosity For flow resistance, The viscous characteristic length, For thermal characteristic length, For ambient air pressure, .

[0069] The third step is to construct the acoustic transfer matrix between the short, thin tube at the tail and the labyrinth metasurface in Formula 1. The specific expression is:

[0070] (6)

[0071] In Equation 6, The surface acoustic impedance of the short, thin tube at the tail end. The cross-sectional area of ​​the cylindrical base is... Let be the cross-sectional area of ​​the acoustic channel in the labyrinth metasurface. This represents the curl length of the acoustic channel. For the Archimedean spiral, It can be calculated using the following formula:

[0072] (7)

[0073] In Equation 7, , which is the total coiling angle. To coil around the outermost diameter of the sound channel, To the innermost diameter of the coiled sound channel, It is a spiral growth ratio, and The number of times the coil is wound.

[0074] In Equation 6, the surface acoustic impedance of the short, thin tube at the tail end... The specific expression is:

[0075] (8)

[0076] In Equation 8, Aerodynamic viscosity, The length of the short, thin tube at the tail end. This refers to the inner diameter of the short, thin tube at the tail end, which is also the inner diameter of the rightmost annular partition plate. , .

[0077] As can be seen from Equation 8, the length of the short, thin tube 4 at the tail end should not be less than the set value (e.g., 2mm) in order to increase acoustic resistance and enhance sound energy loss.

[0078] Ultimately, the sound absorption coefficient of the acoustic black hole sound-absorbing device with nested labyrinth metasurface and sound-absorbing cotton in this invention is... It can be calculated using the following formula:

[0079] (9)

[0080] In Equation 9, It is the transfer matrix model of the acoustic black hole sound absorption device in Formula 1, which is a 2×2 matrix; For the transfer matrix The element in the first row and first column of the middle, For the transfer matrix The element in the second row and first column.

[0081] Preferably, in another embodiment, the labyrinth metasurface 5 is detachably and enclosedly connected to the tail of the cylindrical base 1, and can be adjusted according to the desired resonant sound absorption frequency. By replacing the ribs 51 with spirals of different curl shapes, the ribs 51 form an acoustic channel inside the labyrinth metasurface 5. The length of the curled acoustic channel inside the labyrinth metasurface 5 is related to the resonant absorption frequency. It can be calculated using formulas 6, 7, and 8. Figure 7 The first peak value in the spectrum corresponds to the resonant absorption frequency. Different winding parameters can be selected during the design process according to the required resonant sound absorption frequency.

[0082] Preferably, in another embodiment, the cylindrical substrate 1, the annular partition plate 2, the tail-end slender tube 4, and the labyrinth metasurface 5 are fabricated by 3D printing. The annular partition plate 2, with the smallest inner diameter, is integrally printed with the tail-end slender tube 4. The cylindrical substrate 1 has a thickness of 2mm, an inner diameter of 30mm, and a length of 90mm; the annular partition plate 2 has a thickness of 1mm; the tail-end slender tube 4 has a thickness of 1mm and an inner diameter of 2mm; the labyrinth metasurface 5 has an outer diameter of 2mm, and the ribs 51 forming the internal acoustic channels have a thickness of 1mm. The axial thickness of the labyrinth metasurface 5 is 10mm, and the total length of the entire acoustic black hole sound-absorbing device is 100mm. The sound absorption coefficient was measured using the standard acoustic impedance tube method. The experiment simultaneously tested the sound absorption performance of the acoustic black hole sound-absorbing device of this embodiment and the prototype acoustic black hole. The results are as follows: Figure 7 As shown.

[0083] The experimental results show that the prototype acoustic black hole exhibits unsatisfactory sound absorption performance in the low-to-mid frequency range, mainly due to its weak sound energy dissipation and lack of low-frequency sound absorption. The acoustic black hole sound-absorbing device of this invention, by filling it with sound-absorbing material (such as melamine sound-absorbing cotton), significantly improves its overall mid-to-high frequency sound absorption performance, achieving a near-perfect sound absorption coefficient of 0.9 with a cutoff frequency of 510Hz. Furthermore, the nested labyrinth metasurface enables an additional absorption peak at 264Hz despite its extremely low thickness. The experimental results demonstrate that the acoustic black hole sound-absorbing device of this invention possesses broadband sound absorption capabilities from low to high frequencies.

[0084] The acoustic black hole sound absorption device of this invention solves the problem of low-frequency characteristic frequency noise by nesting a labyrinth metasurface at the tail end to generate an additional sound absorption band in the low-frequency region; by filling it with sound-absorbing cotton to increase the acoustic energy dissipation capacity of the acoustic black hole, it achieves mid-to-high frequency sound absorption, thereby giving this invention a broadband sound absorption capability from low to high frequencies.

[0085] The acoustic black hole sound absorption device of this invention has a detachable labyrinth metasurface nested at the tail. By replacing the metasurface with a spiral with a corresponding curled shape according to the required resonant sound absorption frequency, different resonant sound absorption frequencies can be obtained.

[0086] The above description is merely a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. An acoustic black hole sound-absorbing device, characterized in that, It includes a cylindrical base, several annular partition plates, sound-absorbing material, a short, thin tube at the tail, and a labyrinth metasurface; The annular partition plates are arranged in parallel with equal spacing and fixed on the cylindrical base. Each annular partition plate has a hole with an increasing or decreasing inner diameter at its center, forming an acoustic black hole base. The labyrinth metasurface has ribs coiled in a set spiral pattern inside, forming a coiled sound channel. The labyrinth metasurface is closed and connected to the tail of the cylindrical base. The short, thin tube at the tail end is fixed to the center of the annular partition plate with the smallest aperture, located on the outside of the cylindrical base, and extends into the labyrinth metasurface, together with the labyrinth metasurface forming a sound-absorbing device.

2. The acoustic black hole sound-absorbing device according to claim 1, characterized in that, The inner diameter of the short, thin tube at the tail end is the same as the inner diameter of the annular partition plate with the smallest aperture.

3. The acoustic black hole sound-absorbing device according to claim 2, characterized in that, The inner diameter of each of the aforementioned annular partition plates varies in a power-law manner.

4. The acoustic black hole sound-absorbing device according to claim 3, characterized in that, The formula for calculating the inner diameter of the annular partition plate is as follows: in, This represents the inner diameter of the i-th annular partition plate. Indicates the inner diameter of the cylindrical base. This represents the inner diameter of the annular separator with the smallest aperture. This indicates the total axial length of the cylindrical base. This represents the distance from the center of the i-th annular separator to the center of the separator with the smallest aperture.

5. The acoustic black hole sound-absorbing device according to claim 1, characterized in that, The labyrinth acoustic metasurface is coiled in an Archimedean spiral.

6. The acoustic black hole sound-absorbing device according to claim 1, characterized in that, The cavity area formed by the adjacent annular partition plate and the cylindrical base is filled with sound-absorbing material; the sound-absorbing material is generally annular, with an inclined inner diameter surface, and the two end faces respectively abut against the annular partition plates on both sides of the sound-absorbing material.

7. The acoustic black hole sound-absorbing device according to claim 6, characterized in that, The sound absorption coefficient of the acoustic black hole sound absorption device for: （9） In Equation 9, Transfer matrix for acoustic black hole sound absorption device The element in the first row and first column of the middle, For the transfer matrix The element in the second row and first column; the transfer matrix of the acoustic black hole sound-absorbing device. for: （1） In Equation 1, The acoustic black hole transfer matrix is ​​a nested sound-absorbing material. The acoustic transfer matrix of the short, thin tube at the tail and the labyrinth metasurface; Acoustic black hole transfer matrix with nested sound-absorbing materials The specific expression is: （2） In Equation 2, The wave number of the sound wave. , The resonant sound absorption frequency. The speed of sound in air; The distance between adjacent annular partitions. The characteristic impedance of air, air density; Let be the area of ​​the inner ring of the i-th annular partition plate; The inner surface area of ​​the sound-absorbing material. The wall admittance generated by the sound-absorbing cotton in the i-th annular cavity is expressed as follows: （3） In Equation 3, J0 is a Bessel function, J1 is a zeroth-order Bessel function, and J1 is a first-order Bessel function. Let N be the von Neumann function, N0 be the zeroth-order von Neumann function, and N1 be the first-order von Neumann function; The inner diameter of the cylindrical base; and The characteristic impedance and complex wavenumber of the sound-absorbing cotton. and The equivalent density and equivalent modulus of sound-absorbing cotton are expressed as follows: （4） （5） In equations 4 and 5, is the dynamic viscosity coefficient of air. The specific heat capacity of air. For tortuosity, Porosity For flow resistance, The viscous characteristic length, For thermal characteristic length, For ambient air pressure, ; The acoustic transmission matrix of the tail-end slender tube and the labyrinth metasurface The specific expression is: （6） In Equation 6, The cross-sectional area of ​​the cylindrical base is... Let be the cross-sectional area of ​​the acoustic channel in the labyrinth metasurface. This represents the curl length of the acoustic channel. For the Archimedean spiral, It can be calculated using Equation 7: （7） In Equation 7, , which is the total coiling angle. To coil around the outermost diameter of the sound channel, To the innermost diameter of the coiled sound channel, It is a spiral growth ratio, and The number of times it is coiled; In Equation 6, The surface acoustic impedance of the short, thin tube at the tail end is expressed as follows: （8） In Equation 8, Aerodynamic viscosity, The length of the short, thin tube at the tail end. This refers to the inner diameter of the short, thin tube at the tail end, which is also the inner diameter of the rightmost annular partition plate. , .

8. The acoustic black hole sound-absorbing device according to any one of claims 1-7, characterized in that, The labyrinth metasurface is detachably and closedly connected to the tail of the cylindrical base.

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