The Transmission Properties Of Acoustic Wave In Acoustic Zero-refractive-index Materials

In recent years,acoustic metamaterials with unusual properties that natural materials do not possess have attracted much attention in the fields of both acoustics and materials.As an artificial fabricated composite structure,acoustic metamaterials may present arbitrary effective mass density and bulk modulus.Acoustic zero-refractive-index materials belong to a special kind of acoustic metamaterials,whose effective mass density and the reciprocal of effective bulk modulus tend to zero individually or simultaneously.Its fantastic ability of manipulating the transmission of acoustic wave is drawing increasing attention from researchers.In acoustic zero-refractive-index materials,acoustic waves possess infinitely large wavelength,no phase change,uniform fields and other properties.Based on these important properties,acoustic zero-refractive-index materials have been used to realize unidirectional transmission,high directional radiation,cloaking,bending and other phenomena of acoustic waves.These novel phenomena have great significance in infrastructure construction,national defense and people's living.Based on acoustical equations in ideal fluid media and the methods of scattering matrix and finite element analysis,this thesis has performed detailed theoretical researches and numerical simulations for total transmission and total reflection of acoustic wave in acoustic zero-refractive-index materials,acoustic energy splitting and squeezing realized by acoustic zero-refractive-index materials waveguides with multiple incoming and outgoing ports.The main jobs are as following:1.The transmission properties of acoustic wave in acoustic zero-refractive-index materials embedded with rectangular defects have been investigated.We embed defects with rectangular geometries into acoustic zero-refractive-index materials for the first time and theoretically derive the expression of transmission coefficient of acoustic wave passing through acoustic zero-refractive-index materials.In addition,we take defects with negative acoustic parameters into consideration and obtain the specific values of mass density and bulk modulus of the embedded defects when total transmission and total reflection occur,respectively.Numerical simulations by finite element software are also carried out to verify our theoretical results.Furthermore,we have discussed the modes and their causes inside defects under the phenomena of total transmission and total reflection in detail.At last,we have made use of two defects with opposite mass density and bulk modulus simultaneously to achieve total transmission,while total reflection occurs when these two defects are embedded into acoustic zero-refractive-index materials individually.This interesting phenomenon has provided a new method to realize acoustic cloaking.2.The transmission properties of acoustic wave through a waveguide with a junction made up of acoustic zero-refractive-index materials and multiple incoming and outgoing ports have been investigated.An analytical form has been derived for the scattering matrix when the junction is made up of anisotropic acoustic zero-refractive-index material for the first time and its detailed deducing process has been given.We further derive the simplified form of the scattering matrix when the junction is made up of isotropic acoustic-zero-refractive-index material.In addition,two different waveguide structures without reflection have been designed theoretically according to the tunneling and squeezing effect of acoustic wave in acoustic zero-refractive-index materials.Based on the derived scattering matrix,theoretical analyses of the realization of acoustic energy splitting and squeezing have been presented.Numerical simulations are also carried out and are consistent with our theoretical results.Our work provides theoretical support for the practical realizations of some acoustical devices experimentally,such as acoustic power splitter and combiner.