As people enter secure areas, it is important that they be scanned to ensure that they are not entering with weapons or explosives. In addition, airport departure gates, office buildings, stadiums and similar venues must have fast, accurate and non-intrusive means of detecting threats concealed against a highly conducting background (such as human skin).
Portal-based screening systems at security check points typically use millimeter wave technology to image objects concealed beneath clothing on a human body. Specific characterization of weak dielectric threat objects, however, is a challenge for millimeter-wave scanning systems. Currently deployed focused mm-wave systems do not specifically address dielectric materials. Dielectric slabs appear as anomalies on the body, but are uncharacterized. The inability to accurately characterize dielectric materials with millimeter-wave scanning systems may result in an unacceptable number of false alarms.
To speed up the scanning process, Northeastern university inventors present an efficient algorithm to determine the size and electric properties of concealed objects via the radar signal processing in order to distinguish threat objects from non-explosive dielectrics.
A system for characterizing a dielectric object situated adjacent to an electrically conductive surface comprises a radiation source configured to radiate electromagnetic energy toward the dielectric object, and a receiver configured to receive scattered electromagnetic energy scattered by the dielectric object and the electrically conductive surface. The system may further comprise a control subsystem, coupled to the radiation source and the receiver, that determines an apparent focal point within the object, determines a phase shift associated with the scattered electromagnetic energy with respect to the electromagnetic energy radiated by the radiation source, and determine a thickness and an index of refraction of the object based, on the apparent focal point and the phase shift. The system can determine the apparent focal point by scanning a calculated focus point of the radiated energy through different depths of the object, and searching for a peak in an amplitude of the scattered energy.