Study On Noise Reduction Based On Metamaterial With Negative Modulus

Noise has been one of the most serious environment pollution.It is urgent for improving people's life quality and keeping health to control noise and vibration.Traditional materials with noise reduction are limited by the mass law,whose height has to be added to improve effect of the noise reduction,while it is very difficult to be realized.Acoustic metamaterials can achieve acoustic wave attenuation at sub-wavelength size and provide a new technical idea for noise reduction in the range of low-frequency.Based on the acoustic metamaterial of SHS unit with negative modulus and the theory of noise reduction,an acoustic metamaterial with negative modulus is established.The parameters of the split hollow sphere,the environment parameters and the influence of composite medium on transmission was investigated.In addition,the calculation formula has been proposed and compared with the simulation results,and the mechanism of noise reduction has been revealed.Furthermore,an array model of the acoustic metamaterial had been designed based on SHS with the composite medium,and the noise reduction with multiband and broadband was achieved.The thesis mainly involves the following aspects:1.Based on the local resonance of SHS,the transmission properties of single-media acoustic metamaterial with structural unit of negative modulus were simulated by COMSOL multiphysics software with finite element method.The influence of mechanical parameters,environment parameters and the hole radius of SHS on transmission properties has been discussed,and.The calculation formula based on electro-force-sound analogy method has been compared and analyzed with simulation results.The results show that the density,Young's modulus and Poisson's ratio of SHS have little effect on the resonant frequency of transmission property,and have a small effect on the transmission coefficient.The temperature,the density of the gas medium and the hole radius of SHS have a great influence on the resonant frequency of transmission property.Furthermore,the simulation frequency isconsistent with the calculated frequency,and it reveals the mechanism of noise reduction.2.Based on SHS with air medium,transmission properties has been controlled by changing composite medium with COMSOL,and its resonant frequency was compared with the calculation formula based on electro-force-sound analogy method.The transmission behavior of multiple units with composite medium was discussed.The results show that the resonant frequency of transmission properties was greatly adjusted by changing the ratio of water to air in the composite medium,and it is consistent with the calculation frequency,which reveals the mechanism of noise reduction with the composite medium.Multiple resonant frequencies can be realized by multiple structural units with the composite medium.The transmission coefficient can be further reduced by adding the number of the same structual unit,that is,multi-frequency noise reduction and absorption can be realized by using multiple units with different composite medium.3.Due to the unsaticfactory noise reduction of traditional materials,this thesis aims at broadband and low transmission noise reduction,and designs acoustic metamaterial arrays based on SHS structural units with composite medium.In addition,the transmission properties of single-layer,double-layer,three-layer and six-layer combination structures have been investigated,and the effects of the position and the number of layers on the transmission properties were analyzed.The results show that every layer structure obtains an independent band of the noise reduction,and the number of layers can increase the bandwidth and improve noise reduction.Finally,a broadband with a width of 400 Hz and the sound absorption rate over 99% is realized by a six-layer combination structure.