Characterization Parameter of Material Information in Passive Millimeter-wave Sensing

Passive millimeter-wave (MMW) sensing has been used for several close-range applications such as security checks, military detection, terrain modeling, and so on. By measuring the electromagnetic energy radiated by different materials, it is pos-sible to distinguish them. However, the brightness temperature (TB) can not be directly used for material classification, and those TB-derived material discriminators are not stable charac-terization parameters. In this article, we analyze the multi-polarization brightness temperature model and propose the equivalent permittivity (EP) to characterize the material infor-mation. This parameter, to some extent, is not affected by inci-dent angle and can be derived by multi-polarization measure-ment. The significant advantage of EP is that it reduces the di-mension of parameters in the model. Therefore, it is conducive to extracting object information based on the MMW radiation model. As an application example, we used EP in this article for object classification. Based on EP, we successfully classified four objects with an accuracy of about 99%. Future applications of our method include liquid analysis and scene monitoring.