Researches On Sound Transmission Of Acoustic Waveguide With Asymmetric Coupling Acoustic Structures

In this thesis,we mainly study the transmission characteristics of asymmetric coupling structure.This thesis consists of four chapters,in addition to the first chapter based on the introduction and the last chapter which is about summary and outlook,our main work includes two parts:(1)the finite element simulation of the asymmetric coupling structure;(2)the theoretical modeling of the asymmetric coupling structure and the analysis of acoustic impedance.The detailed descriptions on two main chapters are given as follows:The second chapter is about the introduction of the finite element simulation of the asymmetric coupling structure.Recently,Researchers have shown great interest in EAT(Extraordinary Acoustic Transmission)in the traditional acoustic grating and done many excellent research achievements about this due to the appearance of EOT(Extraordinary Optical Transmission).Besides,the research on the acoustic metamaterials,where researchers realize some special acoustic properties by designing periodic sub-wavelength structures,emerge one after another.In our study,in order to break through the limitation of structure size and realize the extraordinary transmission in low frequencies,we combine the traditional acoustic waveguide with the Helmholtz cavity-like collateral structure.We find that new transmission modes appear on the transmission spectrum in the symmetrical collateral structure.Meanwhile,another transmission mode appears by breaking the symmetry of collateral structure.That is to say,we realize multi-mode transmission by breaking the symmetry of the structure,which gives the composite structure more application possibilities in sound regulation with low frequencies.The third chapter mainly introduces the theoretical modeling of the asymmetric coupling structure and the analysis of acoustic impedance.Based on the results of finite element simulation,we use nonlocal description theory,combined with acoustic continuity equation to model the coupling acoustic waveguide and can obtain the formula of acoustic transmission and the acoustic impedance of structure.In the theoretical analysis,we regard the acoustic impedance of collateral structure as the breakthrough point and we find that the reason for extraordinary transmission in low frequencies is the zero point of acoustic impedance of the main waveguide caused by the acoustic impedance of the whole collateral structure.Based on the theoretical investigations,we conclude that the acoustic resonance and the coupling resonance in the waveguide and asymmetric collateral structures are the main reasons for the appearance of EAT.