Surface Acoustic Waves In Phononic Crystal Of Laminated Pillars On A Semi-infinite Substrate

Phononic crystal is a kind of high frequency dispersive elastic material,which is generally composed of two or more media with periodic distribution.When the elastic wave propagates in the phononic crystal,due to the action of the internal periodic structure,the elastic wave in some frequency range can not propagate.This property of phononic crystals has been widely used in filtering,waveguides,sensing,acoustic focusing and topological phonology.In this paper,a model of phononic crystals of laminated pillar based on semi-infinite substrate is proposed.Based on the advantages of finite element simulation software COMSOL in processing partial differential equations in scientific research and engineering applications,the surface acoustic wave(SAW)band gap characteristics of phononic crystals of laminated pillars are studied.The main research work of this paper is as follows:In the first chapter,the introduction part summarizes the research background and current research status of phononic crystals,and introduces the basic concepts and theoretical basis of phononic crystals in detail.In the second chapter,the characteristics and application fields of finite element package COMSOL Multiphysics are described in detail.The process and method of solving the energy band structure of phononic crystals are introduced in detail.In addition,the excitation principle of Inter Digital transducer(IDT)is described in detail.Combined with the excellent absorption characteristics of perfectly matched layer(PML),the transmission spectrum of SAW propagating on the coupled surface of pillar-based phononic crystals is simulated.In chapter 3 and chapter 4,two models of phononic crystals of laminated pillar on semiinfinite Zn O substrates — longitudinal and radial laminated columns are proposed respectively.By introducing the concept of volume fraction,the band gap characteristics of onedimensional and two-dimensional phononic crystals are studied respectively,and the effects of the proportion of sandwich materials and the types of contact materials on the band structure of phononic crystals are analyzed.In addition,through the analysis of the modal displacement field and the calculated transmission spectrum of SAW,the band gap characteristics and local resonance mechanism of the two structures of phononic crystals of laminated pillar are studied deeply.In the fifth chapter,the defect mode of phononic crystal is analyzed,and the effects of different material volume fraction and defect position on the defect state in the supercell structure laminated pillars are studied by introducing line defects.In addition,the effects of structural damping caused by internal friction and relative slip between connecting interfaces on the energy band structure and transmission spectrum of phononic crystals of laminated pillar are studied.