不连续金属膜的介电性能计算

Calculations of dielectric properties of discontinuous metal films

采用Bruggeman有效媒质理论、基于HFSS软件的S参数法和谐振腔微扰法对不连续金属膜的介电常数进行计算.计算结果表明,在满足长波准静态近似条件下,通过对金属的介电常数进行重整化处理,将涡流效应和局域场增强效应纳入到重整化介电常数中,可以将金属等效为均匀极化的介质,并利用有效媒质理论解析的计算出不连续金属膜的介电常数.且在不连续金属膜中,由于涡流效应的影响,不连续金属膜单元尺寸的大小将显著影响到不连续金属膜的有效介电常数.另外,Bruggeman理论在计算填充浓度小于阈值的样品时才可以获得准确结果.该文结论对研究不连续金属膜的介电性质具有积极的指导意义.

In the paper ,the complex permittivity of discontinuous films was calculated using Bruggeman effective medium theory （EM T ） ,moreover ,an S parameter retrieved method based on HFSS software and a cavity perturbation method were also used for comparison to verify the EMT results .The calculation results indicate that the effective permittivity of discontinuous films can be analytically calculated using Bruggeman effective medium theory when the condition of long wave approximation is met ,which gives a convenient routine to get the permittivity of discontinuous films .The metal permittivity based on Drude equation has been renormalized to be used in Bruggeman theory ,and the renormalized metal permittivity effectively reflects the influence of eddy effect and enhanced effect of local electric field ,so that the metal unit can be considered as a homogenously polarized medium in the discontinuous films .Due to eddy effect ,the size of metal unit would remarkably influence the effective permittivity of discontinuous films ,which means that the larger unit size will result in the higher renormalized metal permittivity .The effective permittivity could be tuned by controlling the metal unit size in the discontinuous metal films .Additionally ,another key result is that the Bruggeman theory is effective only when the metal unit concentration is below the percolation threshold ,because the effective medium theory is based on the assumption that the fields are the same in all metal units ,which is the base to renormalize metal permittivity .This assumption does＆amp;nbsp;not hold when a metal concentration approaches the percolation threshold because the multipole scattering will take effect .All the results concluded in the paper give a rule to use EM T to handle the discontinuous metal films ,and are very valuable in studying their dielectric properties .