The Investigation Of Asymmetric Wave Propagation Properties In Acoustic Artificial Materials

Recently,the investigation of the characteristics of acoustic wave propagation in acoustic artificial materials has attracted more attention.Acoustic artificial materials are composite materials consisting of artificial structure,which can usually be categorized into phononic crystals and acoustic metamaterials.The distinction between phononic crystals and acoustic metamaterials is that,the variation scale of embedded structure in phononic crystals is comparable with the acoustic wavelength,while the variation scale in acoustic metamaterials is much less than the acoustic wavelength.The main characteristic of the phononic crystals is the acoustic band gaps,so phononic crystals are expected to be utilized to design sound filter,resonating cavity and acoustic waveguide.Because the variation scale in acoustic metamaterials is much less than the acoustic wavelength,acoustic metamaterials can be regarded as a bulk of“effective medium,.Through introducing different kinds of microstructure units,the acoustic metamaterials can render many novel physical properties and some unavailable parameters in nature,such as negative mass density,negative modulus and anisotropic mass density,etc.single-negative-index materials(materials with negative mass density or negative bulk modulus,SNM)and double-negative一index materials(materials with simultaneously negative mass density and bulk modulus,DNM)can be exploited to realize evanescent wave magnification,acoustic super-lenses and acoustic illusions.The material with anisotropic density can be employed to realize arbitrary acoustic waveguide and acoustic cloak.As mentioned above,the investigation of unique characteristics of acoustic wave propagation in phononic crystals and acoustic metamaterials 1s of fundamental scientific significance,which has great application value in practice.This dissertation gives a systematic and indepth theoretical study on the relationship between acoustic wave propagation and the topology of acoustic artificial materials.In Chapter Ⅰ,the background of the research and the progresses of the investigation on acoustic wave propagation in phononic crystals and acoustic metamaterials are introduced respectively,and the development of transformation acoustics and cloaking structures which are based on transformation optics and acoustics are briefly described.In Chapter Ⅱ,the related theories on the acoustic wave propagation in phononic crystals and acoustic metamaterials are introduced respectively.In Chapter Ⅲ,the plane wave expansion(PWE)and the finite element method(FEM)are introduced respectively,and are used to study the influence of topological structure on band structure in periodical Lamb wave phononic crystal.The ’“acoustic band pinning,phenomenon is introduced,in which the dispersive curves are pinned in pairs at the boundary of Brillouin zone.Moreover,acoustic band pinning can lead to something more different,such as quasi-Rayleigh wave,which exhibits very plentiful physical contents.In Chapter IV,the development in the domain of acoustic cloaking is briefly introduced.Then we study the characteristics of the "superlens" cloaking strategy which only consists of a pair of complementary single-negative-index materials by using the acoustic scattering theory.Moreover,a new cloak structure which only consists of a pair of positive-index materials is designed with GA method.Finally,in Chapter V,the main conclusions of the dissertation and the prospect of the future work are presented.The principal contribution of the present study is summarized as below:1.The relationship between the topology of phononic crystals and "band pinning" phenomenon in the anti-symmetric phononic crystal plate is investigated.2.The characteristics of the "superlens" cloaking strategy which only consists of a pair of complementary single-negative-index materials are investigated with the acoustic scattering theory.3.A new design of "acoustic cloak" is proposed,which only consists of a pair of positive-index materials.