A Wideband Reflector-based Mm-Wave/THz Nearfield Line Scanner for Rapidly Sensing Materials in Envelopes

For non-invasive detection of illicit materials arriving at postal facilities, it is important to be able to rapidly scan envelopes. Illegal drugs, shipped in thin packages, can be identified based on form factor (pills) or wideband sub-terahertz frequency signature. To image efficiently the contents of an envelope, a millimeter-wave or sub-terahertz signal can be focused to a small spot on the surface of the package. This provides sufficient intensity and resolution to both penetrate and distinguish the shapes of the contents. To be practical, the beam would have to scan the entire envelope surface on the fly. A flying beam scanner is developed that makes use of a wideband focusing reflector with a small physically rotating feed. The novel shaped reflector scans focal spots along a straight line at the surface of the envelope, sensing in one dimension. It is assumed that the envelope moves on a conveyer belt in the perpendicular direction. The line scanning time is limited by the mechanical rotation speed of the small feed, which does not have to reverse direction or accelerate. Thus, a line scan can be accomplished in ∼0.01 sec., and the entire envelope could be scanned in less than 1/5
^th
second (or 18,000 per hour).