Surface and Volumetric Scattering by Rough Dielectric Boundary at Terahertz Frequencies

Materials that could be considered as homogeneous and smooth at microwave frequencies may begin to present surface and volumetric scattering behaviors in the terahertz (THz) band. In this paper, theoretical endeavors are presented to explain the surface and volumetric scattering phenomena observed in the experimental data. We first apply the integral equation method (IEM) to fit the measured data of an aluminum plate. Good agreements prove the applicability and superiority of IEM to metallic materials. Nevertheless, for dielectric materials, the inner microstructures or particles, such as the rusty textures or silicon carbide particles whose sizes are comparable to the THz wavelength, need to be taken into account. We found that for dielectric materials, it can only be fit to the experimental data by using the vector radiative transfer theory combined with IEM. The results show that, for metallic materials, we only need to consider the scattering effect due to the surface roughness. While for the materials that present dielectric features, it needs to consider the influence of the inner microstructures or particles. The two modeling methods presented in this paper are suitable to solve the backscattering problems in the THz band, to predict the bistatic scattering coefficients, and can be extended to apply to real-world targets.