结构各向异性对传输平均自由程的影响研究

Influence of Structural Anisotropy on Transport Mean Free Path

本文研究了由定向排布的椭球形粒子组成的无序介质中微纳结构的各向异性对辐射传输平均自由程的影响机理。采用离散偶极子算法(DDA)计算单个椭球形粒子的各向异性辐射特性,为了得到多重散射下的各向异性介质的辐射特性,采用随机行走方法研究了传输平均自由程随粒子浓度、长径比、分布角度的变化关系,并与各向同性理论的计算结果进行了对比,证明了现有理论的不足。最后,利用辐射传递方程的扩散理论得到了椭球形粒子各向异性介质的表面反射能量分布图。结果表明,微纳结构的各向异性对辐射传输平均自由程和表面辐射能量分布有较大影响,对于各向异性较强的介质,在理论计算中必须加以考虑。

In this study,the impact of structural anisotropy of random media composed of prolate ellipsoids oriented in the same direction on the radiative transport mean free path is investigated.Optical properties of single ellipsoids with different aspect ratio were calculated from Discrete Dipole Approximation(DDA)method.In order to obtain the radiative characteristics of anisotropic media which experience multiple scattering effect,the random walk method was applied to study relations of transport mean free path with concentration,aspect ratio and orientation of ellipsoids,which were also compared with results deduced from isotropic theory,proving the shortcomings of the existing theory.Furthermore,the diffusion theory based on radiative transfer equation was employed to derive two-dimensional spatially resolved reflectance from turbid slabs consisting of different aligned ellipsoids.The results show that structural anisotropy has a great impact on transport mean free path and distribution of radiative energy and should be taken into consideration,especially for highly scattering media.