Remote concealed weapon detection in millimeter-wave region: active and passive

Sensors used for Security purposes have to cover the non-invasive inspection of persons, baggage and letters with the aim to detect weapons, explosives and chemical or biological threat material. Currently, emphasis is placed on system concepts and technologies for this type of applications, employing millimeterwave-, submillimeterwave- and terahertz sensors. This is based on the capability of these frequency bands to look through textiles and the possibility to achieve a geometric resolution which is sufficient to resolve critical items within the necessary range. Using multiple frequencies promises to give more detailed information about the structure of the observed objects. Furthermore, to overcome the limitations of passive millimeter- and submillimeterwave sensors which depend on indirect illumination, systems using miniaturized mmw-radar modules are applied as well. This paper describes two approaches for the detection of concealed weapons, the first using a millimeterwave radiometer on a scanner and the second employing a miniaturized radar module based on a synthetic aperture method.