Sar Processing for Profile Reconstruction and Characterization of Dielectric Objects on the Human Body Surface

Abstract

Abstract-Contour reconstruction and accurate identification of dielectric objects placed on a conducting surface are the aims of the millimeter-wave Synthetic Aperture Radar (SAR) imaging processing system presented in this paper. The method uses multiple frequencies, multiple receivers and one transmitter in a portal-based configuration in order to generate the SAR image. Then, the information in the image is used to estimate the contour of the body under test together with the permittivity of the dielectric region. The results presented in this paper are based on synthetic scattered electromagnetic field data generated using an accurate Finite-Difference Frequency-Domain (FDFD)-based model and inversion based on a fast SAR inversion algorithm. Representative examples showing the good behavior of the method in terms of detection accuracy are provided.

SAR imaging-based techniques for Low Permittivity Lossless Dielectric Bodies Characterization

“…That is, a SAR image is formed when coherently combining the backpropagated field for multiple frequencies [14]. Moreover, phase shift values can be corrupted with noise and uncertainties associated to the imaging system accuracy; hence, the measured phase shift cannot be reliable.…”

“…Equation (10) is specialized for the case in which both media have a negligible permittivity imaginary part, as it is the case for lossless dielectric-related threats in the 60-GHz frequency band [14].…”

“…That is why this antenna allows illuminating individual slices of the human body, as shown in Figure 1. Thus, every illuminated two-dimensional (2-D) slice can be processed individually, using 2-D SAR image formation [9], [14].…”

“…The capability of detecting and characterizing relatively high permittivity (or high contrast) lossless dielectric bodies detection on skin from SAR image processing is demonstrated in [14]. In this high-contrast case, the dielectric-air interface reflection is clearly visible since part of the incident power is reflected back to the receiver.…”

“…If the power transmitted inside the dielectric is sufficient, a second delayed reflection corresponding to the dielectric-human body skin interface will follow. As described in [14], knowledge of the position of both echoes univocally gives the dielectric thickness and permittivity. It must be pointed out that neither the thickness nor the permittivity of the skin (the background material) do not play a role in the SAR imaging, avoiding the need for accurate skin characterization.…”