Existing terahertz THz systems for detecting concealed explosives are not capable of identifying explosive type
which leads to higher false alarm rates. Moreover, some of those systems are imaging systems that invade personal
privacy, and require more processing and computational resources. Other systems have no polarization preference
which makes them incapable of capturing the geometric features of an explosive.
In this study a non-imaging polarized THz passive system for detecting and identifying concealed explosives
overcoming the forgoing shortcomings is developed. The system employs a polarized passive THz sensor in
acquiring emitted data from a scene that may have concealed explosives. The acquired data are decomposed into
their natural resonance frequencies, and the number of those frequencies is used as criteria in detecting the explosive
presence. If the presence of an explosive is confirmed, a set of physically based retrieval algorithms is used in
extracting the explosive dielectric constant/refractive index value from natural resonance frequencies and amplitudes
of associated signals. Comparing the refractive index value against a database of refractive indexes of known
explosives identifies the explosive type.
As an application, a system having a dual polarized radiometer operating within the frequency band of 0.62- 0.82
THz is presented and used in detecting and identifying person borne C-4 explosive concealed under a cotton
garment. The system showed higher efficiencies in detecting and identifying the explosive.