Passive Terahertz Multi-Polarization Imaging Experiments for Personnel Screening Application

Abstract

Passive millimeter and terahertz wave imaging systems have been demonstrated to detect a wide variety of concealed contrabands including explosives, handguns, and knifes <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1, 2</sup> . Although a variety of security systems have been developed, it is still difficult to reach the level of large-scale commercial application. The reason is not only the lack of radiometer performance, but also the insufficiency of obtained information (e.g., single or dual polarization and single frequency band data). When the radiometer hardware performance is given, how to improve detectivity is an important problem to be resolved. Multi-polarization imaging might contribute to improve the imaging performance. In this paper, we have constructed a novel experiment system of W-band passive imaging, which can generate multiple polarization images. The imaging system mainly contains a W-band radiometer, a focal plane lens, an arc-shaped orbit for horizontal pixel, a plane reflector for vertical pixel, and a control computer. The radiometer is placed on a rotating base of the arc-shaped orbit. When the radiometer has a linear polarized antenna, rotating the base around the observation direction can obtain arbitrary linear polarization. By replacing with left-hand or right-land circularly polarized antenna, we can acquire the corresponding circular polarization image. Scanning imaging time is about 20s. The temperature sensitivity is better than 1K. The equivalent spatial resolution is about 1cm. Multi-polarization imaging experiments have been conducted and the polarization characteristics have been analyzed. The experimental results indicate that multi-polarization imaging can obtain more information of human body and concealed objects and is helpful to improve image quality.