Terahertz imaging of concealed objects by acoustic phase detection

Abstract

We present a novel technique for detecting objects that are concealed by textiles. Items of virtually all materials can be sensed, which includes metals as well as dielectrics. Our technique detects the acoustic phase lag of objects when they follow a driven oscillation. The acoustic phase is measured interferometrically with continuous wave radiation at about 77 GHz. Typical oscillation amplitudes are about 1 µm, which is close to the human perception level. The technique provides no insight into the concealed item's material properties. It exclusively shows whether or not an object is hidden, which is the most relevant information for many sensing applications.