超材料中的非线性布里渊散射特性研究

【作者】 杨波；

【导师】 李力；

【作者基本信息】 南京理工大学 ， 光学工程， 2021， 硕士

【摘要】 利用超材料技术可实现对非线性布里渊散射的特性调控,本论文据此构建了具备简单立方晶格结构的超材料,其基本单元为镶嵌小球的立方基体,然后对其布里渊散射参数及调控特性开展了相关研究。主要内容如下:首先介绍了布里渊散射和超材料的基本理论。包括介绍了受激布里渊散射声光耦合方程及其增益因子;并介绍了超材料中的波为布洛赫波。然后利用有效介质理论,对超材料中的布里渊增益因子峰值进行数值计算和分析。包括利用COMSOL Multiphysics软件仿真筛选合适的有效介质理论,验证了Maxwell Garnett(MG)理论的正确性;基于体积平均方法计算超材料的质量密度与布里渊线宽,再利用有效介质理论将超材料中的纵向声速转化成与组成材料体积占比、体积模量和剪切模量有关的解析表达式;基于MG理论推导了超材料的声光耦合参数表达式。通过与已有研究结果对比,验证了本文理论的合理性与准确性。最后,利用本文理论基础,设计和构建了若干新型超材料,分别可增强或抑制非线性布里渊散射,并进而设计了理论上可实现零布里渊散射的新型超材料。本文研究发现,首先,超材料结构本身对电致伸缩常数的调控在抑制布里渊散射中起着关键的作用;其次,通过研究合成声光耦合参数对超材料电致伸缩常数的影响,发现两种电致伸缩常数符号相同的材料组合也能得到具有零或符号相反电致伸缩常数的超材料,这或可为超材料中非线性布里渊散射的调控特性研究提供一种新思路。更多还原

【Abstract】 The metamaterials can be used to control the characteristics of nonlinear Brillouin scattering.Based on this,this thesis constructs metamaterials with a simple cubic lattice structure,the basic unit of which is a cubic matrix inlaid with a small sphere,and then conducts theoretical researches on Brillouin scattering parameters and characteristics regulations in the metamaterials.The main contents are as follows:Firstly,the basic theories of Brillouin scattering and metamaterials are introduced.Including introducing the stimulated Brillouin scattering acousto-optic coupling equation and its gain factor;and introducing that the wave in metamaterials is Bloch wave.Then the effective medium theories are utilized for numerical calculation and analysis of the peak value of the Brillouin gain factor in the metamaterials.The COMSOL Multiphysics software is employed for simulating and screening the appropriate effective medium theory,which verifies the correction of Maxwell Garnett(MG)theory.The calculations of mass density and Brillouin linewidth of the metamaterials based on the volume average method.Then the effective medium theory is adopted to convert the longitudinal sound velocity in the metamaterials into an analytical expression related to the volume ratio,bulk modulus and shear modulus of the constituent materials.Finally,the acousto-optic coupling parameter expression of metamaterials is derived based on the MG theory.By comparing with the existing research results,the rationality and accuracy of the theories in this thesis are verified.Finally,using the theoretical basis of this thesis,several new metamaterials are designed and constructed,which can respectively enhance or suppress nonlinear Brillouin scattering,and then new metamaterials that can theoretically achieve zero Brillouin scattering are designed.This thesis finds that,firstly,the regulation of the metamaterial structure itself on the electrostriction constant plays a key role in suppressing Brillouin scattering;secondly,by studying the influence of synthetic acousto-optic coupling parameter on the metamaterial’s electrostriction constant,it is found the combination of two materials with the same sign of the electrostriction constant can also acquire a metamaterial with zero or opposite sign of electrostriction constant,which may provide a new idea for the study of the characteristics regulations of nonlinear Brillouin scattering in metamaterials.更多还原