Simulant development of a powder explosive material for a millimeter wave imaging system using a resonant cavity with ensemble averaging and the Houston criterion

This work describes the characterization of a powder threat material and the development of a dielectric simulant for a millimeter wave imaging system. A resonant cavity measurement system was designed and implemented to characterize the permittivity of the powder threat material and the candidate simulant formulation for the frequency range of the millimeter wave imaging system. The Resonant Cavity Measurement System determines the complex permittivity of the material as a function of density. A reflection coefficient is calculated at each frequency from a Fresnel reflection and transmission model developed in the electromagnetic signatures of explosives laboratory. The model allows different backing materials (skin and air) and material thicknesses to be examined. Finally, the Houston Criterion is applied to determine whether the matched simulant material and its paired explosive material can be distinguished from each other by the millimeter wavelength imaging system. The explosive material and the simulant material were found to be a dielectric match for use with the millimeter wavelength imaging system of interest with both backing materials (skin and air). The Houston criterion for resolvability was not exceeded for any thickness for either backing material. Therefore, the two materials are indistinguishable by the millimeter wavelength imaging system of interest.