Michael D. Janezic, Jolene D. Splett, Kevin J. Coakley, James R. Baker-Jarvis
The primary objective of this study is to determine the feasibility of using low-power microwaves to distinguish between hazardous and non-hazardous liquids at security checkpoints. According to the 2008 High-Priority Technology Needs, a report published by the Department of Homeland Security's Science and Technology Directorate, system solutions are currently needed for identifying hazardous materials, including liquids, in checked and carry-on baggage at airports and other security checkpoints. Our approach to liquid identification is based on the fact that the propagation of microwaves through liquids is substantially different than microwaves traveling in air. In general, both the frequency-dependent velocity and attenuation of microwaves will vary from liquid to liquid, depending on the liquid's molecular composition, leading to the possibility of using this property to uniquely identify various liquids. However, instead of directly measuring the change in velocity and attenuation in this study, we measure a more fundamental quantity, the liquid's complex permittivity, which we use as a basis for identifying one liquid from another. In this report, we describe how we obtained accurate, broadband complex permittivity data, using the shielded-open coaxial measurement technique, for a number of hazardous and non-hazardous liquids, and then summarize the classification of these liquids using the complex permittivity as a basis for comparison. We conclude with a summary of this feasibility study and make some recommendations for the future research necessary to develop a screening method that can both quickly and accurately distinguish between hazardous and non-hazardous liquids.
IEEE Transactions on Instrumentation and Measurement
permittivity, loss tangent, liquid, shielded open, transmission line, broadband