A Study Of Sound Insulation Characteristics Of Acoustic Metamaterials

Noise,particularly low frequency noise has tremendous impacts on people's mental health and wellbeing.The effect of low-frequency noise on the community has been under estimated for a long time,and there is a lack of effective and economical methods to control the low-frequency noise due to the mass law governing the sound insulation/attenuation.Locally resonant acoustic metamaterial is a kind of artificial material structure which uses the vibration characteristics of structural units to isolate the propagation of sound waves.It can achieve low frequency sound insulation with a small surface density in a specific frequency domain.Several acoustic metamaterials with different configurations have been proposed in the last two decades.The membrane type acoustic metamaterial has been studied intensively by researchers due to its simple structural configuration and easy fabrication.A membrane type acoustic metamaterial combining with through holes has been proposed recently to achieve low-frequency sound insulation under the air flow condition though the sound insulation bandwidth of the metamaterial is narrow.Further study is therefore required to enable the practical application of such metamaterials which motivates the work presented in this thesis.Firstly,the definition conditions of membrane and thin plate are discussed briefly.The vibration displacement response of circular membrane subjected to uniformly distributed force is derived under fixed boundary condition.By comparing the average displacement response and vibration modes of the membrane with or without mass,and the influence of mass on the vibration of membrane is analyzed,and the sound insulation mechanism of typical membrane type acoustic metamaterials is explained.The lowfrequency vibration characteristics of the membrane and thin plate are compared,and it is pointed out that they have similar vibration response characteristics in low-frequency band.Therefore,it is inferred that they will play similar roles in the application of acoustic metamaterials,and they are verified in the subsequent simulation and experiment.Subsequently,an improved acoustic metamaterial model of membrane(or thin plate)and through-hole combination is proposed,and a theoretical model based on electroacoustic analogy method and a finite element method simulation model are established.Based on an example of membrane through-hole acoustic metamaterial,the mechanism of low-frequency sound insulation of through-hole acoustic metamaterial is explained according to the calculation results of theory and simulation model.Based on the theoretical model,the method of optimizing the sound insulation bandwidth of throughhole acoustic metamaterials is deduced,and the optimization process is designed,which is verified by the finite method.The theory of optimizing the sound insulation bandwidth is further validated by comparing the sound insulation bandwidth of thin plate through-hole acoustic metamaterials with or without additional mass with the same peak frequency of sound insulation.The experimental sample of acoustic metamaterial was designed and manufactured,and the sound insulation of the sample was measured by impedance tube.The accuracy of the simulation results is verified by comparing the measured sound insulation of the sample and the corresponding finite element simulation results.In addition,the experimental results also prove that the improved acoustic metamaterial designed in this paper has good sound insulation performance.Finally,the future and development of acoustic metamaterials are discussed.