Wave Characterization Of Acoustic Metamaterials In Time-Domain

Recently,the stationary analyses upon metamaterial-based wave controlling are mainly concerned.However in practical environments,the short pulse excitations are commonly used for example in medical focused imaging and underwater sonar detection.There are nontrivial differences between stationary and temporal responses of metamaterials due to their inherent dispersion characteristics.Thereby,the research of time-domain acoustic metamaterials is the objective demand of their potential application in practical engineering.This thesis studies the time-domain wave dynamics of anisotropic metamaterials that follow either Drude or Lorentz dispersions by using finite-difference-time-domain(FDTD)method.Negative refraction and super-resolution acoustic focusing by a single metamaterial,and extraordinary acoustic transmission by a metamaterial conjugate pair are studied in details.The research results are as follows:1.Finite-difference formulations are given for anisotropic metamaterials that follow either the Drude or Lorentz dispersions.The FDTD algorithms are coded based on MATLAB for non-dispersive acoustic medium,perfectly matched layers and dispersive metamaterials.2.Wave propagation nature of anisotropic acoustic metamaterials is analyzed in a general manner.The time-domain characteristics of negative refraction and super-resolution focusing adhered to acoustic metamaterials are analyzed by use of the developed FDTD.3.A metamaterial conjugate pair that permits wave propagation in only selected angles of incidence is theoretically proposed.FDTD simulation has verified that the selected angle of complete transmission is monotonically related to the frequency of operation.The feature can be used to realize an acoustic antenna whose radiation angle can be modulated by the source frequency.