Single-layer spiral cavity labyrinth metasurface structure

Abstract

The invention belongs to the technical field of aviation noise control and low-frequency sound absorption and noise reduction, and particularly relates to a single-layer spiral cavity labyrinth metasurface structure which comprises a front cover plate, a coplanar spiral folding cavity plate and a rear cover plate. The front cover plate, the coplanar spiral folding cavity plate and the rear cover plate are all of cylindrical structures, and the coplanar spiral folding cavity plate is connected between the front cover plate and the rear cover plate; under the action of sound waves, the air column in the hole neck of the center hole of the front cover plate vibrates back and forth like a piston, and in the vibration process, due to the damping effect of the neck wall on the air column, sound energy is converted into heat energy to be dissipated. When sound waves generate local resonance in the spiral cavity of the sound absorption plate, if the frequency of incident waves is equal to the inherent frequency of the resonant cavity, a resonance phenomenon can be generated, at the moment, the vibration amplitude of the air column is maximum, the sound pressure in the spiral cavity is obviously increased, the corresponding sound energy consumption is maximum, and a sound absorption peak is formed, so that the purpose of eliminating noise is achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aviation noise control and low-frequency sound absorption and noise reduction, and particularly relates to a single-layer spiral cavity labyrinth super surface structure. BACKGROUND

[0002] Sound pollution has become one of the main environmental pollutions, which seriously affects people's daily work and life. The influence of noise on people is not only related to the sound pressure level, but also related to the frequency characteristics of the sound waves in the noise.

[0003] The cabin noise of an airplane can reach 140 dB during flight, and the cabin noise can reach 90 dB. The cabin noise of some military aircraft is even higher than 100 dB. Research results show that as long as the noise level is higher than 84 dB, potential damage to hearing will be caused, and the pilots and passengers will have adverse reactions such as fatigue and accelerated heartbeat. Long-term exposure to a noisy environment will also cause different degrees of harm to the nervous system, cardiovascular and cerebrovascular system, and digestive system. In particular, low-frequency vibration and noise are easy to resonate with human organs (including the heart, lungs, stomach, and nervous system), directly causing damage to the human body and affecting normal physiological functions, causing great harm to the human body. In addition, the airborne equipment in the cockpit is exposed to strong vibration and noise for a long time, and the airborne equipment cannot work normally, such as sensitivity failure and inaccurate control.

[0004] Traditional lightweight sound absorption and noise reduction materials, such as porous sound absorption materials and micro-perforated plate structures, have very good sound absorption and noise reduction effects at high frequencies, and are widely used. However, it is very difficult to effectively isolate low-frequency noise. With the continuous development of vibration and noise reduction technology, the requirements for vibration and noise reduction materials for aviation equipment are also increasing. Not only is better vibration and noise reduction required, but also lightweight materials are required. The problem of low-frequency sound absorption and isolation of lightweight materials has always been a bottleneck in the field of acoustics. In recent years, the concept of acoustic metamaterials has provided a new way of thinking for the design of low-frequency sound absorption and isolation materials.

[0005] Acoustic super surface is a unit structure with sub-wavelength thickness designed artificially, which can realize the properties that natural ordinary materials do not have, such as negative equivalent mass density, negative elastic modulus, double negative property, negative refractive index, and near-zero refractive index. Acoustic super surface is mostly arranged periodically in structure, which can realize the reflection sound field control, sound absorption and noise reduction, and sound wave transmission regulation. When sound waves propagate in such a structure, they will be modulated by the structure, thereby affecting the propagation of sound waves. Through the design of such special structures, many new physical properties and phenomena such as reflection, absorption, and invisibility of sound waves can be realized. Its lightweight, sound absorption, vibration isolation, and negative refractive index characteristics provide a new way for low-frequency vibration and noise control. It has broad application prospects in both military and civilian fields.

[0006] Therefore, how to design an effective acoustic metasurface structure is a problem to be solved. SUMMARY

[0007] The purpose of the present application is to provide a single-layer spiral cavity labyrinth metasurface structure to solve the problem that the existing lightweight structure is difficult to ensure sound absorption effect.

[0008] The technical solution of the present application is: a single-layer spiral cavity labyrinth metasurface structure, comprising a front cover plate, a coplanar spiral folded cavity plate and a rear cover plate.

[0009] The front cover plate, the coplanar spiral folded cavity plate and the rear cover plate are all cylindrical structures, and the coplanar spiral folded cavity plate is connected between the front cover plate and the rear cover plate.

[0010] The coplanar spiral folded cavity plate is provided with an inner groove, and the inner groove is in communication with the upper and lower parts; the inner groove in the coplanar spiral folded cavity plate is a bidirectional spiral structure.

[0011] The front cover plate is provided with a center hole at the middle position, and the rear cover plate is a fully enclosed structure.

[0012] Preferably, the coplanar spiral folded cavity plate is composed of an S shape at the center position, and the inner grooves of the bidirectional spiral structure are symmetrical to each other through the coplanar spiral folded cavity plate.

[0013] Preferably, the outer wall thickness of the coplanar spiral folded cavity plate gradually decreases along the path direction of the bidirectional spiral structure of the outermost inner groove.

[0014] Preferably, the front cover plate and the rear cover plate are both hard plates, and the front cover plate, the coplanar spiral folded cavity plate and the rear cover plate are all made of photosensitive resin; the front cover plate, the coplanar spiral folded cavity plate and the rear cover plate are all made by 3D printing.

[0015] Preferably, the center hole has a diameter of 3.5mm, the spiral tube length of the coplanar spiral folded cavity plate is 103.5mm, the tube groove width is 4mm, and the front cover plate thickness is 10mm.

[0016] Preferably, the structure thickness of the front cover plate, the coplanar spiral folded cavity plate and the rear cover plate is less than 1% of the working wavelength.

[0017] The single-layer spiral cavity labyrinth super surface structure of the application forms a single-layer bidirectional spiral sound absorption structure. Under the action of sound waves, the air column in the neck of the center hole of the front cover plate vibrates back and forth like a "piston". In the vibration process, due to the damping effect of the neck wall on the air column, sound energy is converted into heat energy and dissipated. When sound waves occur local resonance in the spiral cavity of the sound absorption plate, if the frequency of the incident wave is equal to the natural frequency of the resonance cavity, resonance phenomenon will occur. At this time, the amplitude of the air column vibration is the largest, the sound pressure in the spiral cavity increases obviously, the corresponding sound energy dissipation is also the largest, forming a sound absorption peak, thereby achieving the purpose of eliminating noise. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions provided by the application, the following will briefly introduce the drawings. Obviously, the drawings described below are only some embodiments of the application.

[0019] Figure 1 It is an overall structural explosion diagram of the application.

[0020] Figure 2 It is a schematic diagram of the internal sound absorption principle of the single-layer spiral cavity labyrinth super surface of the application.

[0021] Figure 3 It is a schematic diagram of the coplanar spiral folded cavity plate structure of the application.

[0022] Figure 4 It is a schematic diagram of the sound absorption calculation model of the single-layer spiral cavity labyrinth super surface of the application.

[0023] Figure 5(a) is a schematic diagram of the influence of the diameter of the small hole of the front cover plate on the sound absorption coefficient of the application.

[0024] Figure 5(b) is a schematic diagram of the influence of the length of the spiral tube on the sound absorption coefficient of the application.

[0025] Figure 5(c) is a schematic diagram of the influence of the width of the spiral tube slot on the sound absorption coefficient of the application.

[0026] Figure 5(d) is a schematic diagram of the influence of the thickness of the front cover plate on the sound absorption coefficient of the application.

[0027] Figure 6 It is a schematic diagram of the sound absorption coefficient of the comprehensive design and optimization structure of the application.

[0028] 1, front cover plate; 2, coplanar spiral folded cavity plate; 3, rear cover plate; 4, inner groove; 5, center hole. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0030] A single-layer spiral cavity labyrinth metasurface structure is designed based on Helmholtz resonance theory and space folding principle, and includes a front cover plate 1, a coplanar spiral folded cavity plate 2 and a rear cover plate 3. Figures 1-2 The front cover plate 1, the coplanar spiral folded cavity plate 2 and the rear cover plate 3 are all cylindrical structures, and the coplanar spiral folded cavity plate 2 is connected between the front cover plate 1 and the rear cover plate 3, and can be fixed by adhesion.

[0031] The front cover plate 1, the coplanar spiral folded cavity plate 2 and the rear cover plate 3 are all cylindrical structures, and the coplanar spiral folded cavity plate 2 is connected between the front cover plate 1 and the rear cover plate 3, and can be fixed by adhesion.

[0032] The coplanar spiral folded cavity plate 2 is provided with an inner groove 4, and the inner groove 4 is in communication with the upper and lower portions of the coplanar spiral folded cavity plate 2. The inner groove 4 is a bidirectional spiral structure in the coplanar spiral folded cavity plate 2.

[0033] The front cover plate 1 is provided with a central hole 5 at the middle portion, and the rear cover plate 3 is a fully closed structure.

[0034] Through the above design, a single-layer bidirectional spiral sound absorption structure is formed. Under the action of sound waves, the air column in the hole neck of the central hole 5 of the front cover plate 1 vibrates back and forth like a “piston”. In the vibration process, due to the damping effect of the neck wall on the air column, the sound energy is converted into heat energy and dissipated. When the sound wave occurs in the local resonance in the spiral cavity of the sound absorption plate, if the frequency of the incident wave is equal to the natural frequency of the resonance cavity, resonance phenomenon will occur. At this time, the amplitude of the air column vibration is the largest, the sound pressure in the spiral cavity is obviously increased, the corresponding sound energy dissipation is the largest, the sound absorption peak is formed, and the purpose of eliminating noise is achieved.

[0035] Moreover, the structure is relatively simple in composition, convenient in manufacturing and processing, and strong in structural stability, realizes the absorption of low-frequency sound waves in a small size (ultra-thin structure), and the structural thickness of the front cover plate 1, the coplanar spiral folded cavity plate 2 and the rear cover plate 3 is less than 1% of the working wavelength in the propagation direction. There is a high sound absorption peak in the low-frequency range, and it has a good application prospect.

[0036] Preferably, the coplanar spiral folded cavity plate 2 is composed of an S shape at the central position, and the inner grooves 4 of the bidirectional spiral structure are symmetrical to each other through the coplanar spiral folded cavity plate 2, so that the structure is stable.

[0037] As shown in Figure 3Preferably, the outer wall thickness of the coplanar spiral folded cavity panel 2 gradually decreases along the path direction of the bidirectional spiral structure of the outermost inner groove 4. Through the design of variable thickness, the bidirectional spiral structure can effectively absorb sound waves of different frequencies.

[0038] Preferably, the front cover plate 1 and the rear cover plate 3 are both hard plates, and the front cover plate 1, the coplanar spiral folded cavity panel 2 and the rear cover plate 3 are all made of photosensitive resin to ensure the structural strength. The front cover plate 1, the coplanar spiral folded cavity panel 2 and the rear cover plate 3 can all be made by 3D printing.

[0039] Preferably, the diameter of the front cover plate center hole, the length of the spiral tube, the width of the spiral tube groove and the thickness of the sound absorption panel all have certain influence on the sound absorption performance.

[0040] The spiral tube length, the center hole diameter, the front cover plate thickness and the tube groove width are optimized as a whole, specifically:

[0041] The sound absorption coefficient of the single-layer spiral cavity labyrinth metasurface structure in the application is calculated by using the commercial finite element software COMSOL Multiphysics. As shown in Figure 4 , the acoustic hard boundary is used as the boundary condition, the perfect matched layer (PML) is set in the far field to simulate the infinite domain of pressure wave, and the influence of false reflected wave is eliminated. The plane wave is used as the background sound field, the sound wave impacts the upper surface of the whole structure, the temperature in the model input condition is 293.15K, the air density is 1.25kg / m 3 , the sound velocity is 343m / s, and the dynamic viscosity is 17.9μPa·s.

[0042] From the comparison of the four curves in Fig. 5(a), it is found that the diameter of the hole in the front cover plate has a great influence on the sound absorption performance of the structure. With the increase of the diameter of the hole, the resonance frequency of the structure increases from 415 Hz to 575 Hz, and the peak value of the sound absorption coefficient increases from 0.73 to 0.99. At the same time, through the correction formula of the acoustic impedance of the hole, it is found that the main reason for the increase of the peak value of the sound absorption coefficient with the increase of the diameter of the hole in the front cover plate is that the diameter of the hole is inversely proportional to the sound attenuation coefficient. The smaller the diameter, the more obvious the effect of viscous effect, so that the dissipation of sound energy of the whole system is more sufficient. However, the decrease of the cross-sectional area of the hole increases the acoustic resistance, which has a smaller influence on the dissipation of sound energy compared with the influence of viscous effect. Therefore, in general, the sound absorption coefficient increases with the increase of the hole neck. From the comparison of the four curves in Fig. 5(b), it is found that with the increase of the length of the spiral tube, the resonance peak frequency of the structure decreases from 1600 Hz to 920 Hz, and the peak value of the sound absorption coefficient increases from 0.90 to 0.98. The resonance frequency corresponding to the peak value of the sound absorption coefficient moves to low frequency, and the peak value also increases. This is mainly because the length of the spiral tube increases, the volume of the spiral tube increases, and the resonance frequency decreases. At the same time, the increase of the peak value of the sound absorption coefficient is due to the increase of the length of the tube, the volume of the air cavity increases, and the acoustic impedance of the air cavity in the spiral cavity decreases, so the sound absorption coefficient increases. From the comparison of the four curves in Fig. 5(c), it is found that with the increase of the width of the spiral tube slot, the resonance frequency decreases from 1240 Hz to 900 Hz, and the peak value of the sound absorption coefficient decreases slightly, but the change is not obvious, from 0.99 to 0.97. This is mainly because the increase of the width of the coplanar spiral tube slot increases the overall volume of the spiral cavity, so that the resonance frequency decreases accordingly. The main reason for the decrease of the peak value of the sound absorption coefficient is that the increase of the width of the coplanar spiral tube increases the characteristic acoustic impedance of the coplanar spiral tube and the corresponding effective length. From the comparison of the four curves in Fig. 5(d), it is found that with the increase of the thickness of the front cover plate of the sound absorption plate, the resonance peak frequency of the structure decreases from 930 Hz to 892 Hz, and the resonance frequency corresponding to the peak value of the sound absorption coefficient moves to low frequency, but the peak value is almost unchanged. This is mainly because with the increase of the thickness of the front cover plate of the sound absorption plate, the resonance frequency decreases, and the increase of the thickness of the hole makes the viscosity per unit area of the hole smaller, so the peak value of the sound absorption coefficient should decrease. Because the influence of viscous effect is too small, the peak value of the sound absorption coefficient is almost unchanged.

[0043] In summary of the above four parts, the length of the spiral tube, the diameter of the hole, the thickness of the front cover plate, and the width of the tube slot can be optimized as a whole to obtain the best parameter values: the diameter of the center hole is 3.5 mm, the length of the spiral tube is 103.5 mm, the width of the tube slot is 4 mm, and the thickness of the front cover plate is 10 mm. The sound absorption coefficient curve corresponding to the frequency change is shown in Fig. 6. Figure 6

[0044] ​Through theoretical analysis and simulation verification on the structural parameters, the sound absorption coefficient under the optimal condition is close to 1 at the resonance frequency of about 560 Hz, and the sound wave is approximately completely absorbed. It can be seen that this structure still has very good sound absorption performance in the narrow low frequency band near 560 Hz, and the sound absorption frequency band can be adjusted by adjusting the structural parameters. However, due to the limited width of the sound absorption frequency band, this structure is only suitable for narrow-band sound absorption in the middle and low frequency range, and is not suitable for reducing low-frequency random noise.

[0045] Finally, it should be noted that the present application discloses the structure involved in the embodiment, and other structures can be referred to the general design. In the case of no conflict, the same embodiment and different embodiments of the present application can be combined with each other.

[0046] Finally, the above-mentioned is only the preferred embodiment of the present application, and is not used to limit the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A single-layer helical cavity labyrinth metasurface structure, characterized in that: It includes a front cover plate (1), a coplanar spiral folding cavity plate (2), and a rear cover plate (3); The front cover plate (1), the coplanar spiral folding cavity plate (2) and the rear cover plate (3) are all cylindrical structures, and the coplanar spiral folding cavity plate (2) is connected between the front cover plate (1) and the rear cover plate (3); The coplanar spiral folded cavity plate (2) has an inner groove (4) which is connected vertically; the inner groove (4) has a bidirectional spiral structure within the coplanar spiral folded cavity plate (2). The front cover plate (1) has a central hole (5) in the middle, and the rear cover plate (3) is a fully enclosed structure.

2. The single-layer helical cavity labyrinth metasurface structure as described in claim 1, characterized in that: The coplanar spiral folded cavity plate (2) forms an S-shape at the center position, and the inner groove (4) of the bidirectional spiral structure is symmetrical to each other through the coplanar spiral folded cavity plate (2).

3. The single-layer helical cavity labyrinth metasurface structure as described in claim 1, characterized in that: The outer wall thickness of the coplanar helical folded cavity plate (2) gradually decreases following the path direction of the bidirectional helical structure of the outermost inner groove (4).

4. The single-layer helical cavity labyrinth metasurface structure as described in claim 1, characterized in that: The front cover plate (1) and the rear cover plate (3) are both rigid plates. The front cover plate (1), the coplanar spiral folded cavity plate (2) and the rear cover plate (3) are all made of photosensitive resin. The front cover plate (1), the coplanar spiral folded cavity plate (2) and the rear cover plate (3) are all made by 3D printing.

5. The single-layer helical cavity labyrinth metasurface structure as described in claim 1, characterized in that: The diameter of the central hole (5) is 3.5 mm, the length of the spiral tube of the coplanar spiral folded cavity plate (2) is 103.5 mm, the width of the tube groove is 4 mm, and the thickness of the front cover plate (1) is 10 mm.

6. The single-layer helical cavity labyrinth metasurface structure as described in claim 1, characterized in that: The structural thickness of the front cover plate (1), the coplanar spiral folded cavity plate (2), and the rear cover plate (3) is less than 1% of the working wavelength.

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