The current technologies employed to screen both carry-on and checked baggage are based on x-rays. The images produced result from density variations. The shape and size of items in the image are examined visually for carry-on baggage and with a computer for computed tomography images of checked baggage. Suspicious items are then examined manually for identification. A technique to reliably identify the chemical structure of a suspect item remotely would improve baggage throughput by resolving alarms. Mass spectroscopy systems to detect explosives by means of vapor analysis are currently going through field trial investigations.
As discussed in Chapter 2 of this report, there is a significant ongoing effort in examining terahertz time domain spectroscopy (TTDS) to detect spectral features of explosives. There have been numerous reports of TTDS being used for explosives detection in transmission mode. However, for real-field applications, reflection measurements are preferred, since most bulky targets are impossible to measure in a transmission mode, in which the targets will attenuate the incident energy completely. The reflection mode may be used in a standoff detection system, but it is not clear that individuals and vital assets could be outside the zone of severe damage of an explosive detonation.
Conclusion: Millimeter-wavelength/terahertz technology has potential for contributing to overall aviation security, but its limitations need to be recognized. It will be most effective when used in conjunction with sensor technologies that provide detection capabilities in additional frequency regions.