Sub-Terahertz Dielectric Measurement and Its Application to Concealed Object Detection

This paper reports on complex permittivity values of different natural and synthetic materials at J-band (220-325 GHz). The materials considered in this study include different types of fabrics (wool, polyester, acrylic, jeans, vinyl, and cow leather), in addition to human skin. For the wool and jeans materials, we consider both dry and wet conditions. The knowledge of dielectric constant of these materials is needed for evaluation of radar based concealed object detection methods. The measurement setup used consists mainly of a vector network analyzer (VNA) combined with two -band frequency extenders. A free space transmission only measurement technique is used to obtain both the complex dielectric constant and the effective thickness of all the fabric materials. Such approach is adequate for fabric materials as they do not have a well-defined thickness. The major factors affecting the uncertainty in the measurements are shown to be related to the sample thickness inhomogeneity, and to the unrepeatability of the network analyzer measurement itself. For the human skin case, a reflection measurement method from a terminated waveguide is adapted.