最近在看Joel T. Johnson的《Third-order small-perturbation method for scattering from dielectric rough surfaces》，具体文章可见附件
在最基础的FORMULATION公式推导阶段，原文如下：
Consider a deterministic periodic surface profile, z=f(x, y), with periods Px and Py in the x and y directions respectively, that separates free space (permittivity , permeability ) for z＞ f(x, y) from a homogeneous nonmagnetic dielectric medium with permittivity for z ＜ f(x, y). This periodic surface can also be expressed in terms of its Fourier series coefficients
3阶SPM.pdf (483.27 KB) 
