Research On Eletromagnetic Scattering Characteristics Of Composite Spheroidal Particles

Composite media have wide applications in areas such as optics,biology,medicine,and nanoscience,and electromagnetic(light)scattering by composite media have always been the research topics in electromagnetic(EM)area.The thesis investigates the analytical solutions for the EM scattering properties of radially multilayered gyroelectric(gyromagnetic)spheres,radially multilayered gyrotropic spheres,and metal nanospheroids,and also presents the analytical formulations and methods in computing the eigenfrequencies of metal spheroidal cavities.The primary work has been summarized as follows:1.Based on the separation of variables method(SVM)and the theory of spherical vector wave functions,the T-matrix formulations of plane waves scattered by a radially multilayered gyroelectric or gyromagnetic anisotropic sphere are derived.First,the vector wave functions characterising the gyroelectric or gyromagnetic media are solved by applying the orthogonality and completness of the spherical vector wave functions,and the set of basis functions for the vector wave functions are constructed.Second,based on the Mie scattering theory,the incident,scattered and the internal fields are expanded as an infinite series summations of the spherical wave functions.Third,the T-matrix formulations in computing the scattering and internal expansion coefficients are obtained by matching the boundary conditions on the discontinuous surfaces.The derived formulations are implemented by Mathematica codes to compute the radar cross sections(RCS),and the correctness and effectiveness of the obtained formulas are verified.Then the scattering properties are analyzed in details based on the effects caused by uniaxial anisotropy,electric(magnetic)gyrotropy and the electrical dimensions.2.The characteristics of plane wave scattered by a radially multilayered gyrotropic sphere(characterized by both gyroelectric and gryomagneic tensors)are investigated.The T-matrix formulations for computing the scattering fields of the radially multilayered gyrotropic sphere are derived.The convergence rules of the electric and magnetic fields series expanded by spherical vector wave functions are verified and discussed by investigating the convergence properties of scattering efficiency factors.The effects for the scattering fields caused by the electric/magnetic gyrotropy,electrical dimensions are analyzed by computing the radar cross sections.The backscattering cross sections are investigated by properly configuring the EM parameters.3.The SVM in spheroidal coordinate is applied to solve the Maxwell's equations.The analytical solutions for the far-and near-field light scattering by metal nanospheroids are derived based on the smart method proposed by Asano et al for matching the boundary conditions.Computations for the eigenvalues of spheroidal wave functions with complex parameters and the corresponding spheroidal radial functions of the second kind in computing the near-fields are investigated in details.The RCS of oblique incidence TE and TM plane waves scattered by prolate nanospheroids and the near-fields of axial incidence plane waves scattered by prolate/oblate gold/silver nanospheroids are computed.The effects for the localized surface plasmon resonance(LSPR)caused by the major to minor axial ratios and the size of spheroids are analyzed by computing the extinction efficiencies.The near-fields distributions for prolate and oblate silver nanospheroids under the condition of LSPR are presented.4.Analytical solutions for computing the eigenfrequencies of metallic spheroidal cavities are presented based on the spheroidal vector wave functions.A semi-analytical method is proposed to compute the eigenfrequencies of spheroidal cavities with arbitrary major to minor axial ratios.Eigenfrequencies from lower to higher modes of the spheroidal cavities with different major to minor ratios are computed,and different eigenmodes are analyzed.The EM fields vector patterns of dominant mode,the diagram of eigenfrequencies of dominant mode vary with major to minor axial ratios,and the electric fields distributions of the first six eigenmodes are presented in terms of prolate spheroidal cavities.