Sound Absorption Characteristics Based On Planar Acoustic Metamaterials

The traditional sound absorbing structure usually has many disadvantages such as large structural size,polluted environment,narrow sound absorption band,poor sound absorption effect,etc.so a light structure,environmentally friendly,sound absorption frequency bandwidth,sound absorption effect is good artificial composite structure-acoustic metamaterial comes into being.The folded space-based acoustic sound absorber proposed in this paper is an acoustic metamaterial structure.Because of its small size,environmental friendliness,and wide-band low frequency sound absorption,this structure has great advantages over traditional sound absorbing materials.In this paper,we first studied the sound absorption effect of the porous sound absorbing material structure,and combined the porous sound absorbing material structure and the perforated plate resonance sound absorbing structure to form a composite perforated plate structure,the improved composite perforated plate structure can absorb sound efficiently in a certain low frequency range,but its low frequency sound absorption bandwidth is still relatively narrow.Therefore,an improved structure based on the structure of a porous sound absorbing material with air backing layer is proposed,which is a composite structure of porous sound absorbing structure based on a folded space,and it can absorb noise well in the low-frequency broadband range,and even perfectly sound absorption at some frequency points.The main research contents of this paper can be divided into the following aspects:First,research and analysis on the structure of porous sound absorbing materials with or without air backing layer.From the simulation results of the two structures,it is found that the sound absorbing effect of the porous sound absorbing material structure with the air backing layer is better than that of the porous sound absorbing material structure without the air backing layer,which is manifested in:In the mid-low frequency range,the sound absorbing performance of the porous sound absorbing material structure with the air backing layer is significantly better than that of the porous sound absorbing material structure without the air backing layer.In addition,increasing the thickness of the air backing layer of porous sound absorbing material is equivalent to increasing the thickness of porous sound absorbing material,which can improve the absorption effect of low-frequency sound waves of the material.In this way,the material can be saved and the cost is much smaller than that of increasing the thickness of porous sound absorbing material.Second,we attached the porous sound absorbing material to the end of the perforated plate to form a composite perforated plate structure.After analyzing the simulation results of this structure,we determined that the sound absorption effect of this structure at low frequency is better than the traditional resonant structure of perforated plate and the structure of porous sound absorption material with air backing layer.At the same time,as the radius of the hole decreases,the resonant frequency of the composite perforated plate moves to the high frequency,and the maximum sound absorption coefficient of the structure will increase first and then decrease,the sound absorption effect reaches 96%.As the thickness of the porous sound absorbing material increases within a certain range,the resonance frequency moves to the low frequency,and the sound absorption bandwidth gradually increases.The maximum sound absorption coefficient of the structure will first increase and then slow down,and finally maintain the sound absorption coefficient at 95%.Third,in the analysis of the above several structures,we have found that the composite perforated structure has significantly better sound absorption performance in the low frequency range than the other two structures.Although the composite perforated plate structure has certain advantages in low frequency sound absorption,the frequency band is still narrow and the average sound absorption coefficient at low frequencies is low.In order to perform broadband sound absorption on low frequency sound waves,we propose an optimization scheme that combines the porous sound absorbing material structure with the folded space structure to form a combined structure.We compare the sound absorption coefficient of this combined structure with several structures mentioned above,and verify that the absorption coefficient of this composite structure can reach more than 80% in the range of 400Hz~1600Hz,a high-efficiency sound absorption band width of 1200 Hz at low frequencies,and even perfect sound absorption at a frequency of 1160 Hz.