Terahertz (THZ) Imaging

Previously, the problem of Concealed Weapon Detection, CWD, was addressed in the context of detecting weapons concealed under clothing. Infrared and millimeter wave images were considered for the purpose. Infrared detection depends on the concealed weapons temperature being significantly different from that of its surroundings. Millimeter wave detection relies on reflection from the object of interest. Passive detection is possible in many instances since MMW is present naturally and can penetrate various types of clothing. Active devices can also be used to provide MMW illumination. It was found that IR images are less reliable since one can easily defeat or mask the objects response. MMW detector technology has only now advanced to the point where real time images are possible. Imaging in the Terahertz THz wavelengths was an avenue that suggested itself as worthy of exploration. Like MMW it penetrates clothing. However, with wavelengths ranging from 1 micron to 1 mm, it provides superior resolution. Furthermore, it offers spectroscopic capability that enables object identification not only by shape attributes but also by material composition. This opens up applications such as standoff detection of explosives. The range of 300 GHz to 3 THz has been explored by many researchers. Standoff ranges of up to 50 meters can be achieved at these frequencies. The main limitation is water vapor absorption. A considerable amount of work has been done in developing THz generators and detectors. However, there is much work that needs to be done in the area of signal and image processing algorithms for making THz technology useful in applications such as CWD and explosives detection.