Material characterization using a millimeter wave portal-based imaging system for security screening

The following contribution presents two methodologies to obtain geometry and constitutive parameters information about low permittivity lossless dielectric materials using an existing portal-based mm-wave imaging setup. While characterization of high permittivity dielectrics is relatively affordable in SAR images, the low amount of power reflected back by low permittivity bodies makes their characterization a challenging task. The first technique makes use of normal and 45° illumination angles to overcome the permittivity-geometry uncertainty appearing on each independent case. Second method takes advantage of the relationship between reflection coefficient amplitudes between two media, which can be directly extracted from the SAR image to provide an estimation of the dielectric object permittivity. Uncertainty associated to every technique can be reduced by properly combining them. A simulation-based application example is presented for validation purposes.