Modeling Of Effective Radiation Characteristic Parameter Of Composite Medium With Different Shapes Of Dispersed Nanoparticles

The composite medium with dispersed nanoparticles is associated with many fields,such as energy materials,atmospheric science and military,and analyzing its radiation characteristics plays a very important role in its application process.However,the absorption and scattering of incident light by the nanoparticles in the composite medium make it complicated to calculate the radiation characteristic parameters of composite medium.One way to simplify the calculation is by viewing the composite medium as an effective homogeneous medium.Obtaining the radiation characteristic parameters of the effective medium(such as the effective dielectric constant)is the prerequisite for the success of process.In this paper,the effective radiation characteristic parameters of composite media are studied,and the following work is completed:(1)The Comsol is employed to construct model for S-parameter retrieval and reflection,transmittance calculations.The randomly distributed spheres,core-shell structures or ellipsoid nanoparticles are also constructed in Comsol to simulate the disordered distribution of nanoparticles in the medium under considered situations.Moreover,the accuracy of calculated results of constructed model is verified.(2)The Maxwell-Garnett theory and S-parameter retrieval are employed to calculate the effective dielectric constant of composite medium with sphere,core-shell structure or ellipsoidal dispersed nanoparticles.Various influence factors,such as volume fraction,size,core-shell ratio,aspect ratio and absorbent substrate media,are considered to analyze the applicability of the two methods.Results show that the error of the S-parameter retrieval mainly appears in the resonant region,and S-parameter retrieval has good applicability in the long wavelength region.At the same time,the S-parameter retrieval is greatly affected by the thickness of the composite medium,and smaller doped nanoparticles can reduce its error.Maxwell-Ganette theory is applicable to lower volume fraction,smaller size or smaller coreshell ratio of nanoparticles.When the absorption of the base medium is high,the resonant intensity of the nanoparticles is reduced,and the electric field disturbance in the composite medium is reduced,so the error of the two models can be reduced to some extent.(3)Considering a structural unit in the composite medium,the Comsol is employed to calculate the effective dielectric constant of composite medium with different shapes of doped nanoparticles by using a weighted average method.Taking the spherical doped nanoparticles as an example,the applicability of the three weighting methods is analyzed by considering threeinfluence factors,like the volume fraction,size and material of nanoparticles.Results show that the weighting factor,which uses the product of the local electric field and incident electric field conjugate vector(M2),is the most applicable.Then the applicability of M2 method is compared with Maxwell-Garnett theory and S-parameter retrieval.Two influence factors,like volume fraction and size of spherical nanoparticles,are considered.Results show that the M2 method has better applicability under the considered wavelength region.Finally,three different shapes,like ellipsoid,cylinder and cuboid,are considered.The applicability of M2 under different AR is also analyzed.It is found that for the three shapes,the more the AR deviates from 1,the worse the applicability of M2 in the long wavelength region.While in the short wavelength region,M2 will have some improvement under some situations,and keep consistent under the other situations.