A tunable dual-band acoustic metasurface absorber with nested double helical orbits

Abstract

This invention discloses an adjustable dual-band acoustic metasurface absorber with nested double-helix tracks, comprising an outer cavity, an inner cavity, and a central column arranged coaxially. A sealing cover is provided on the inner cavity, with a through hole and a central hole for avoiding the center. The inner wall of the outer cavity and the outer wall of the inner cavity form an outer large-radius spiral channel, within which outer helical blades are arranged spirally extending along the central axis of the central column. The inner wall of the inner cavity and the outer circumferential surface of the central column form an inner small-radius spiral channel, within which inner helical blades are fixedly connected to the central column. This invention can effectively absorb noise over a wide frequency band (especially in the low-frequency range), exhibits good environmental adaptability and durability, can intelligently adjust sound absorption characteristics, and simultaneously considers environmental friendliness and aesthetics.

Description

Technical Field

[0001] This invention relates to the field of dual-band acoustic metasurface absorbers, and more particularly to an adjustable dual-band acoustic metasurface absorber with nested double helical orbits. Background Technology

[0002] With the acceleration of urbanization, noise pollution has become an increasingly serious environmental problem, severely impacting people's quality of life, physical and mental health, and work efficiency. Long-term exposure to high-intensity noise can not only lead to hearing damage but may also cause irreversible damage to the visual and nervous systems. Currently, noise control technologies mainly include sound absorption technology, vibration isolation and reduction technology, acoustic sound-absorbing materials, sound-absorbing structures, damping treatment, and noise reduction through greening. Among these, sound absorption noise reduction technology is widely used due to its simplicity and effectiveness. This technology converts sound energy into heat energy through sound-absorbing materials or structures, thereby reducing noise intensity.

[0003] However, with the increasing demands for acoustic environment quality, existing sound absorption and noise reduction technologies still face numerous challenges. First, the performance of traditional sound-absorbing materials is easily affected by harsh environments; for example, high temperature, high humidity, or corrosive environments can cause a rapid decline in material performance or even failure, severely limiting their application scenarios. Second, conventional acoustic metamaterials often fall short in dealing with low-frequency noise, struggling to achieve effective absorption while maintaining a small volume. Furthermore, noise in real-world environments typically encompasses multiple frequency bands, while conventional metamaterials often only absorb a specific frequency band with a narrow absorption bandwidth, failing to meet the needs of complex noise environments. More importantly, most existing sound-absorbing materials and structures are passively designed, lacking the ability to adaptively adjust their sound absorption characteristics according to environmental changes. This means that their noise reduction effect may significantly decrease when the noise source or environmental conditions change. Simultaneously, some traditional sound-absorbing materials may generate harmful substances during production, use, and disposal, causing secondary pollution to the environment, which contradicts the growing environmental awareness. Finally, maintaining the aesthetics of the environment while pursuing excellent acoustic effects has also become a significant challenge.

[0004] In view of the above problems, there is an urgent need to develop a dual-band acoustic metasurface absorber to overcome the limitations of existing technologies and meet the growing demand for noise control. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an adjustable dual-band acoustic metasurface absorber with nested double helical tracks, which can effectively absorb noise in a wide frequency band (especially in the low frequency band), has good environmental adaptability and durability, can intelligently adjust sound absorption characteristics, and takes into account both environmental protection and aesthetics.

[0006] The technical solution adopted by this invention to solve its technical problem is as follows: This invention provides an adjustable dual-band acoustic metasurface absorber with nested double helical tracks, which includes an outer cavity, an inner cavity, and a central column arranged coaxially. The inner cavity is provided with a sealing cover, and the sealing cover is provided with a through hole and a central hole for avoiding the center. The inner wall of the outer cavity and the outer wall of the inner cavity form an outer large-radius helical channel. An outer helical blade is provided in the outer large-radius helical channel, which extends helically along the central axis of the central column. The inner wall of the inner cavity and the outer circumferential surface of the central column form an inner small-radius helical channel. An inner helical blade is provided in the inner small-radius helical channel, which is fixedly connected to the central column.

[0007] In a preferred embodiment of the present invention, the radius of the outer helical blade is greater than the radius of the inner helical blade.

[0008] In a preferred embodiment of the present invention, the top of the inner cavity is provided with a plurality of limiting grooves arranged symmetrically along its circumference on its outer side, and the bottom of the sealing cover is provided with limiting teeth for engaging with the limiting grooves.

[0009] In a preferred embodiment of the present invention, the radius of the sealing cap corresponds to the radius of the inner cavity.

[0010] In a preferred embodiment of the present invention, the central post extends through the central hole of the sealing cover and is rotatable about its own axis.

[0011] In a preferred embodiment of the present invention, the axial length of the inner helical blade is less than the distance between the bottom surface of the sealing cover and the bottom surface of the outer cavity.

[0012] In a preferred embodiment of the present invention, the outer helical blade is made of resin.

[0013] In a preferred embodiment of the present invention, the inner helical blade is made of resin.

[0014] In a preferred embodiment of the present invention, an external drive plate is mounted on the lower end of the outer helical blade.

[0015] In a preferred embodiment of the present invention, an inner drive plate is mounted on the upper end of the inner helical blade.

[0016] The nested double-helix track adjustable dual-band acoustic metasurface absorber provided by this invention not only effectively solves many shortcomings of existing technologies but also brings significant technological advancements. Through an innovative nested double-helix structure design, this invention cleverly extends the sound wave propagation path, greatly enhancing the absorption effect of low-frequency noise while effectively saving space. This unique three-dimensional helical design not only achieves miniaturization but also maintains good airflow, greatly expanding its application scenarios.

[0017] Furthermore, this invention introduces a rotatable cap structure, allowing for flexible adjustment of the absorption peak frequency by adjusting the effective length of the inner spiral channel. This adjustability enables the device to adapt to noise in different frequency bands, exhibiting excellent broadband bimodal absorption characteristics. The spiral blades, made of resin, are not only environmentally friendly and safe but also possess a deep subwavelength thickness, significantly reducing sound wave transmission while ensuring that the absorber's acoustic impedance remains well-matched to the background air.

[0018] Most importantly, this invention achieves perfect low-frequency noise control within a limited volume by integrating different resonant structures into a single cell and combining this with an adjustable cover design. This innovative design not only reduces the surface thickness of the acoustic metamaterial but also cleverly balances noise reduction performance with airflow, enabling the device to perform excellently in various complex environments and significantly extending its service life. In summary, this invention represents a breakthrough in the field of noise control technology, providing an efficient, flexible, and environmentally friendly solution to the increasingly serious problem of noise pollution. Attached Figure Description

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0020] Figure 1 This is a schematic diagram of the structure of the present invention;

[0021] Figure 2 This is a schematic diagram of the structure of the internal helical blade of the present invention;

[0022] Figure 3 This is a schematic diagram of the limiting groove of the present invention;

[0023] Figure 4 This is a schematic diagram of the structure when the outer helical blade and the inner helical blade of the present invention are engaged;

[0024] Figure 5 This is a cross-sectional view of the present invention;

[0025] In the diagram: 1. Outer cavity; 2. Inner cavity; 3. Outer helical blade; 4. Sealing cap; 5. Through hole; 6. Central column; 7. Limiting groove; 8. Limiting tooth; 9. Inner helical blade; 10. Inner drive plate; 11. Outer drive plate. Detailed Implementation

[0026] The technical solutions (including preferred technical solutions) of the present invention will be further described in detail below with reference to the accompanying drawings and by way of listing some optional embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0027] like Figure 1-5 The present invention provides a technical solution: an adjustable dual-band acoustic metasurface absorber with nested double helical tracks, comprising: an outer cavity 1 being a circular cavity with an opening at the top; an inner cavity 2 fixedly connected to the middle of the outer cavity 1, with an outer helical blade 3 rotatably fitted on the outer side of the inner cavity 2, the outer helical blade 3 dividing the space between the outer cavity 1 and the inner cavity 2 into an outer large-radius helical channel; a central column 6 fixedly connected to the middle of the inner cavity 2, with an inner helical blade 9 rotatably fitted on the outer side of the central column 6, the inner helical blade 9 dividing the space between the central column 6 and the inner cavity 2 into an inner small-radius helical channel; a sealing cover 4 installed on the top of the inner cavity 2, the top of the sealing cover 4 having a through hole 5; sound continuously reflects and consumes energy through the inner and outer helical tracks, while the through hole 5 induces a velocity field that triggers nontrivial relative motion within the viscous boundary layer, converting sound energy into heat dissipation through friction, resulting in energy loss.

[0028] It should be noted that the radius of the outer spiral blade 3 of this invention is larger than that of the inner spiral blade 9. By extending the sound propagation path in a three-dimensional spiral manner, the space occupied by the device is saved. The noise reduction method of extending the sound propagation path without sealing improves the airflow of the acoustic metamaterial, achieving miniaturization and breathability, and is suitable for a variety of application scenarios.

[0029] The inner cavity 2 has multiple limiting grooves 7 evenly distributed on the outer side of its top. The bottom of the sealing cover 4 has limiting teeth 8 that cooperate with the limiting grooves 7. The sealing cover 4 and the inner cavity 2 have the same radius. The central column 6 passes through the center of the sealing cover 4 and the two are rotatably connected. The length of the inner spiral channel path can be changed by rotation. The outer spiral blade 3 is equipped with an outer drive plate 11 at its lower end, and the inner spiral blade 9 is equipped with an inner drive plate 10 at its upper end.

[0030] It should be noted that the limiting groove 7 and the sealing cover 4 of this invention are installed together by the cooperation of the limiting groove 7 and the limiting tooth 8. The position of the through hole 5 is adjusted by rotating the sealing cover 4, and the length of the inner spiral path is changed to change the absorption peak frequency. The space occupied by the equipment is saved by extending the sound propagation path in a three-dimensional spiral manner. The continuous rebound of sound propagation through the double spiral structure embedded inside and outside consumes energy, and the energy loss caused by the local resonance at the cover opening through friction converting sound energy into heat dissipation is completed, thus effectively treating low-frequency noise.

[0031] Both the outer spiral blade 3 and the inner spiral blade 9 are made of resin material. The resin surface thickness is a deep subwavelength thickness. The thickness of the material is smaller than the wavelength of the sound, which significantly reduces the transmission of sound waves and reduces the impact of noise. Through this effect, the acoustic impedance of the absorber is always roughly matched with the background air, so that the absorption area can move flexibly in a wide frequency range.

[0032] It should be noted that this invention uses resin material, which is non-toxic, safe, and easy to use. It is reusable. Compared to traditional foam and asbestos materials, it is more environmentally friendly and more efficient. As a wall sandwich structure or steel plate sandwich structure, it is easy to install and requires no replacement for its entire lifespan. The surface thickness is a deep subwavelength thickness. By integrating different resonant structures into a single cell, the effective length of the three-dimensional spiral track is adjusted by rolling up the space. Combined with an adjustable cap, adjustable broadband bi-peak absorption is achieved, making it more flexible in use.

[0033] In the experimental verification of the above-mentioned sound absorber scheme, two three-dimensional spiral sound absorber structures with different track widths and different pitches were nested in a single unit structure;

[0034] The nested three-dimensional helical structure can be viewed as two tubes with rigid back walls and gradually changing bottom cross-sections. The impedance of the tube opening with a constant cross-section can be expressed as...

[0035]

[0036] The surface impedance of the nested spiral structure here can be considered as the impedance of two straight rectangular tubes connected in parallel. If the viscous loss of air is taken into account, the air density, sound velocity, and wave vector in the above equation are all complex numbers.

[0037] The slit region model in the multiphysics simulation software COMSOL can be used to simulate thermal and viscous losses within narrow tubes, where the length of the tube's cross-section is on the order of the thermal or viscous boundary layer thickness (boundary layer absorption). Considering these losses is necessary and important to obtain accurate sound absorption results.

[0038] Based on a simplified low-frequency model, impedance approximations for slits, circular tubes, rectangular tubes, and equilateral triangular tubes can be obtained. This model describes the propagation of sound waves in small waveguides and considers viscosity and heat loss in the waveguide. The model covers a range from completely isothermal conditions (very low frequencies or very narrow tubes) to large pipe sizes (where the boundary layer represents only a portion of the pipe size). The model is applicable when the cross-sectional dimension of the tube is smaller than the wavelength of the sound wave (i.e., at the cutoff frequency).

[0039] In narrow waveguides, the complex wave number kc and complex impedance can be expressed by the following formula:

[0040]

[0041]

[0042] Here, ψv and ψh are the viscosity and thermal wave functions, respectively, both related to the material and pipe geometry. γ is Poisson's ratio, the ratio of isobaric specific heat capacity to isochoric specific heat capacity. ρ0 and c0 are the fluid density and the speed of sound in the fluid, respectively, with the corresponding Z0 being the acoustic impedance in air. ω is the angular frequency of the incident sound wave, and k0 is the wave vector of the free sound field in space. The subscript 0 indicates a physical quantity in free space, without considering losses. The subscripts h and v represent physical quantities related to heat and viscosity, respectively.

[0043] The expressions for complex velocity and complex density are respectively

[0044] and

[0045] The j-function can be derived from the linear Navier-Stokes equations. The overall equation can be separated into three parts: isentropic (adiabatic), viscous, and thermal. Through this separation, the viscosity and thermal wavenumber of the system can be obtained.

[0046]

[0047] Based on the following assumptions, analytical solutions for thermal or viscous wave functions can be obtained using the LRF (low reduced frequency) model.

[0048] (1) The wavenumbers of viscosity and heat must be much greater than the wavenumbers of sound waves (the wavelength of sound waves must be much greater than the thickness of the boundary layer). That is... It is much greater than one, or λ0 is much greater than δj.

[0049] (2) The cross-sectional area of ​​the waveguide must be constant or vary slowly in its propagation direction.

[0050] (3) In the direction of sound propagation, the length of the waveguide must be longer than the thickness of the boundary layer.

[0051] The viscous and thermal wave functions differ significantly for cross-sections with different geometries. The main tube types include slit tubes, circular tubes, square tubes, and equilateral triangular tubes. The aforementioned three-dimensional helical structure can be considered as a rectangular tube with a constant cross-sectional area plus a rectangular tube with a gradually changing cross-sectional area at the tail. For a rectangular tube with height H and width W, its viscous and thermal wave functions can be expressed by the following formula:

[0052]

[0053]

[0054] in,

[0055]

[0056] The impedance of the rigid tube at the bottom was obtained by measuring the input impedance through the tube. The impedance at the tube opening can be expressed as:

[0057]

[0058] Where S and L are the cross-sectional area and length of the tube, respectively, and ρ and c are the effective mass density and effective particle velocity, respectively. k is the effective propagation constant considering viscosity. At the surface of the structure, the boundary conditions can be simply expressed as zero air particle velocity and zero temperature gradient. This causes relative air motion within the viscous boundary layer, resulting in heat exchange with the outside environment and disrupting adiabatic transport.

[0059] The sound absorption spectrum shows that the simulation results agree well with the experimental results. Experimentally, the sound absorption coefficient is measured using a commercial impedance tube (…). A pair of condenser microphones (diameter-100mm) were obtained. A 1 / 4-inch (pole) is used at a designated location to extract the amplitude and phase of the sound pressure field. The measurement principle has been explained in Chapter 2. The white noise source is controlled by an amplifier. The perfect sound absorption occurs at 162Hz and 189Hz. The blue hollow circles represent experimental measurements, and the black lines represent simulated data. The impedance diagram shows the measured and simulated acoustic impedance (xs) and acoustic reactance (ys) near the resonant frequencies of the inner and outer spiral structures. Experiments demonstrate that perfect sound absorption corresponds to xs = 1 and ys = 0. Discrete blue circles and lines represent the measured and simulated acoustic reactance, respectively. Discrete black circles and lines represent the measured and simulated acoustic impedance, respectively. At the resonant frequency, the surface impedance of the absorbing structure exhibits pure acoustic impedance characteristics, and the acoustic reactance is completely suppressed. It can be seen that the sound absorption range of the nested spiral structure in this chapter is much wider than that of the single spiral structure in the previous chapter. This is essentially because the unit spiral absorber has two resonant frequencies, and these two resonant frequencies are close, which to some extent broadens the sound absorption range.

[0060] To reveal the physical mechanism of sound absorption in this unit metamaterial structure, the particle velocity field of the unit absorber was further calculated. Simulated particle velocity fields were performed at frequencies of 162 Hz, 179 Hz, and 189 Hz. The simulation results show that local resonance plays a major role in perfect sound absorption. Within the viscous boundary layer, resonance excites a nontrivial, relatively large relative motion at the tube opening, indicating the resonance of the outer and inner spiral structures. The maximum particle velocity at the resonance point is more than 10 times that at the non-resonance point. Therefore, sound energy is converted into heat energy through friction of the air within the boundary layer. At the resonant frequencies of 162 Hz and 189 Hz, we observed that the high-speed particle motion mainly occurs at the tube openings of the inner and outer spiral orbits.

[0061] Rotating the cap with a fan-shaped opening on the inner spiral structure adjusts its resonant frequency. Periodic slots on the cap seal the air within the inner spiral structure and minimize air leakage. They also fix the rotation angle of the cap, facilitating experimental measurements and ensuring perfect acoustic absorption at resonance. Rotating the cap on the structural unit alters the equivalent length of the inner spiral structure, allowing for flexible movement of the absorption spectrum over a wide frequency range. Specifically, rotating the cap 270° increases the effective length of the structure by approximately 70 mm, resulting in a significant redshift in the acoustic absorption band. In this proof-of-concept experiment, we shifted only the absorption spectrum of the inner spiral structure while keeping the outer spiral absorption spectrum unchanged. This demonstrates that the absorption peak frequency of the dual-band absorber can be independently adjusted.

[0062] In simulation result (a), the lid was rotated from 0° to 315°. During the rotation, the upper absorption band was redshifted, and its center frequency could be adjusted from 192Hz to 176Hz. During this adjustment, we observed that the upper absorption band maintained good sound absorption performance. This indicates that the acoustic impedance of the structure surface consistently matches the impedance of the background air medium, maintaining high-quality sound absorption. The relative positions of the fan-shaped opening and the inner spiral structure were changed during lid rotation, resulting in experimental measurements. In the experiment, each 45° rotation was a measurement interval, showing good agreement between the experimental and simulation results. Furthermore, the two separate absorption bands merged into a single, wider absorption band after a 315° rotation. The simulated particle velocity fields obtained when the lid was rotated 90°, 180°, and 270° had resonant frequencies of 191Hz, 184Hz, and 176Hz, respectively. These results reveal the vibration at the three resonant frequencies, with localized resonance occurring within the fan-shaped opening, indicating high-speed particle velocities within the opening. This resulted in perfect sound absorption in the experiment.

[0063] This invention enhances the absorption of low-frequency noise by increasing the length of the viscous boundary layer through an elongated spiral path, saving space and perfectly handling low-frequency noise within a limited volume. A rotatable through-hole structure is designed, integrating different resonant structures into a single cell. Rolling up the space adjusts the effective length of the three-dimensional spiral track, achieving a wide range of absorption band variations. This results in adjustable bi-peak broadband absorption, reduces the surface thickness of the acoustic metamaterial, and balances noise reduction with airflow, expanding its application scenarios and extending its service life.

[0064] It will be readily understood by those skilled in the art that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, combinations, substitutions, improvements, etc., made under the spirit and principles of the present invention are included within the protection scope of the present invention.

Claims

1. A tunable dual-band acoustic metasurface absorber with nested double helical orbits, characterized in that, The system includes an outer cavity (1), an inner cavity (2), and a central column (6) arranged coaxially. The inner cavity (2) is provided with a sealing cap (4), which has a through hole (5) and a central hole for avoiding the central column (6). The inner wall of the outer cavity (1) and the outer wall of the inner cavity (2) form an outer large-radius spiral channel. An outer spiral blade (3) is arranged spirally extending along the central axis of the central column (6) within the outer large-radius spiral channel. The outer circumferential surface of the central column (6) forms an inner small-radius spiral channel, and an inner spiral blade (9) fixed to the central column (6) is provided in the inner small-radius spiral channel; the top of the inner cavity (2) is provided with a plurality of limiting grooves (7) arranged symmetrically around its circumference on its outer side surface, and the bottom of the sealing cover (4) is provided with limiting teeth (8) for engaging with the limiting grooves (7); the central column (6) passes through the central hole of the sealing cover (4), and the central column (6) can rotate around its own axis.

2. The tunable dual-band acoustic metasurface absorber with nested double-helix orbits according to claim 1, characterized in that: The radius of the outer helical blade (3) is greater than the radius of the inner helical blade (9).

3. The adjustable dual-band acoustic metasurface absorber with nested double-helix orbits according to claim 1, characterized in that, The radius of the sealing cap (4) corresponds to the radius of the inner cavity (2).

4. The tunable dual-band acoustic metasurface absorber with nested double-helix orbits according to claim 1, characterized in that, The axial length of the inner spiral blade (9) is less than the distance between the bottom surface of the sealing cover (4) and the bottom surface of the outer cavity (1).

5. The tunable dual-band acoustic metasurface absorber with nested double helical orbits according to claim 1, characterized in that: The outer helical blade (3) is made of resin.

6. The tunable dual-band acoustic metasurface absorber with nested double-helix orbits according to claim 1, characterized in that, The inner helical blade (9) is made of resin.

7. The adjustable dual-band acoustic metasurface absorber with nested double-helix orbits according to claim 1, characterized in that, An external drive plate (11) is installed at the lower end of the outer helical blade (3).

8. The tunable dual-band acoustic metasurface absorber with nested double-helix orbits according to claim 1, characterized in that, An inner drive plate (10) is mounted on the upper end of the inner helical blade (9).

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