The Researches On The Control Of Scattering Characteristics For Sub-wavelength Particle

The scattering characteristics of small particles have very actual application in the field of antenna,sensor and light emitting devices.In recent years,the effective control of the scattering characteristics of small particle has become an important research direction.This thesis mainly investigates the scattering characteristics of spherical and ellipsoidal particles with the similar size of the wavelength.This thesis uses Mie theory to-calculate and analyze the scattering characteristics of spherical particles.And the combined method of finite element method and multiple dipole theory has been used to calculate and analyze the scattering characteristics of ellipsoidal particles.In this thesis,two schemes are proposed to realize the control of the scattering characteristics of particles.The main work is as follows:1?Propose a scheme to control the scattering characteristics of particles by adjusting the geometrical parameters.For a spherical particle,it is found that the resonant wavelength of intrinsic mode is far away from the wavelength satisfying the first Kerker condition where the particle can obtain zero backward scattering,but the forward scattering intensity is small.In order to suppress the backward scattering and get strong forward scattering,the influence of the geometric parameters of ellipsoidal particle on its scattering characteristics is analyzed in this thesis.It is found that both oblate ellipsoid and prolate ellipsoid particles can achieve the suppression of the backscattering with the enhanced forward scattering.For the oblate ellipsoid dielectric particle,when the longitudinal and transverse ratio is reach to 1.6,zero backscattering with the enhanced forward scattering can be realized.For the prolate ellipsoid dielectric particle,when the transverse and longitudinal ratio is close to 4.2,the backscattering is suppressed and the forward scattering can be greatly enhanced.2?Propose a scheme to control the scattering characteristics of particles by adjusting the material composition.The previous studies have shown that the complete suppression of forward scattering cannot be achieved for the lossy and lossless particles.In order to achieve zero forward scattering,the coated spherical core-shell particle,which is composed of gold core and gain-doped dielectric shell,is designed in this thesis.The results show that the perfect control of forward scattering can be achieved by adjusting the doping concentration,and the strong enhancement and complete suppression of forward scattering can be obtained.In addition,this thesis uses a theoretical model,which is different from the second Kerker condition,to explain the reason of the suppressed forward scattering.The electromagnetic simulation results verify the correctness of this interpretation.