C-curve feature of complex permittivity estimation based on multi-polarization measurements in passive millimeter-wave sensing

Passive millimeter-wave (PMMW) sensing has been used for several close-range applications such as scene monitoring and security check. Aiming to sense man-made or natural dielectrics, we report the estimation characteristics of complex permittivity by multi-polarization measurements. According to the polarization brightness temperature (TB) model, the complex permittivities of dielectric materials are estimated by using the TB data of multiple linear polarizations. By Monte Carlo simulations, we found that the estimated complex permittivities can form a special cluster. All estimation values of each dielectric spread around a special nonlinear curve (called the "C-curve"). Then the "C-curve" distribution characteristics of different parameter conditions such as polarization number, incident angle, roughness, and measurement noise, have been analyzed. The 94 GHz multi-polarization measurements have been conducted to prove the existence of "C-curve" feature. The results suggest that this invariant feature can be possibly used for material classification and image segmentation in PMMW sensing. (c) 2019 Optical Society of America