Terahertz detection of substances for security related purposes

Terahertz (THz) radiation has many far reaching applications—of specific interest is that many non-metallic and non-polar substances are transparent in the THz frequency range. This provides many practical uses for security purposes, where it is possible to detect and determine various substances that may be hidden or undetectable via conventional methods such as X-rays. In addition to this property, terahertz radiation can either be used in reflection or transmission modes. This paper will look into the use of transmission techniques to detect various substances using a terahertz system. Common materials used in bags and suitcases such as nylon, polycarbonate (PC), and polyethylene (PE) are tested for transparency. These materials then sandwich various illicit substances, and are scanned by the terahertz system to obtain spectral data, simulating the probing of a suitcase. The sample materials are then subtracted from the obtained data, which is then compared with previously obtained data of known substances, and an examination of features in the sample is carried out to determine if a particular substance is present in the sample.