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Standoff Detection of Concealed Weapons using a Terahertz Illuminator With an Uncooled Imager

NCJ Number
Date Published
Lothar Moeller
This project investigated and developed the fundamentals of a handheld THz imager for detecting concealed weapons.
Although a final product solution will require more years of development, the experience gained through the current project is essential in the next design phase for handheld THz imagers; and the results indicate that they will be available in the near future. The current project developed for such THz imagers two kinds of optics, an active illumination scheme and detector technology. Both refractive and reflective lens systems were simulated, manufactured, lab tested, and characterized. The project experimentally confirmed that both designs approach well the theoretical limit for best performance in terms of spatial resolution. All phases of the lens and illuminator development have produced valuable experience, not only by determining performance limits, but also by exploring manufacturing feasibility. Technical challenges during component prototyping delayed the project; however, the challenges were overcome by innovative vendor solutions. The project characterized and integrated into the imager optics a THz detector based on microbolometer technology. The project’s THz testbed found that the bolometer performance was significantly poorer than expected and therefore unsuitable for THz imaging under real or lab conditions. The main reasons for the low coupling efficiency between the bolometer antenna and the THz optics were identified, but in order to achieve improvement, a redesign of the bolometer hardware is necessary. The project characterized and integrated in its testbed a THz source. Although its performance is within specification, its output power was known to be too low for imaging experiments at video rate; however, during the project period, no other source with more suitable parameters was commercially available. Extensive figures
Date Created: February 15, 2011