On-the-move detection of security threats using 3D mm-wave radar imaging

Abstract

There is a critical need to develop new imaging systems capable of detecting security threats, both at near-field ranges (1-5m) and standoff ranges (10-40 meters). Millimeter wave (mm-wave) radar possesses unique features that makes it well-suited for addressing such a need; these include but are not limited to the following: (i) ability to penetrate through clothing, thus revealing potential threats that may be concealed under clothing; (ii) ability to provide depth information and complex scattering signatures, so it can detect and differentiate between weak dielectric and strong metallic threats, like TNT or metallic pipes and shrapnel. The current mm-wave portal imaging systems used in airport security checkpoints present several drawbacks, being of particular relevance the following: (i) slow-throughput, resulting from passenger's divestment and recollection of their belongings; (ii) frequent false alarms and successive pat-downs, resulting from image artifacts like dihedral effects intrinsic in monostatic radar imaging systems; and (iii) need of expensive, power-hungry, and bulky complex hardware architectures, resulting from the electromechanical scanning of dense mm-wave arrays. The overarching goal of this thesis is the design, fabrication, and experimental validation of the first fully-electronic 3D mm-wave Multiple Input Multiple Output (MIMO) imaging system that has the potential to detect security threats while they are on-the-move. This goal is achieved through the following contributions: (1) development of fast forward models capable of predicting the interaction of electromagnetic waves with complex structures, like lossy and penetrable multilayered dielectrics; (2) design and implementation of new distributed algorithms capable of performing compressive sensing and real-time imaging of security threats; (3) experimental validation of a novel 3D calibration technique needed for coherent imaging of multi-static radar configurations; and (4) integration of the algorithms, hardware, and fundamental science in a fully-electronic, mm-wave MIMO testbed, showing that 3D images can be created as the target under test moves in front of the radar system. This paves the way towards new mm-wave imaging systems that can potentially be used in airport checkpoints for on-the-move detection of potential security threats, resulting in high scanning throughput and enhancing passengers' experience.