Dielectric measurements of plastic explosives using a loaded waveguide technique via vector network analyzer and banded millimeter wave extender modules operating at V-band (50 to 75 GHz) are performed. A portion of an explosive sample is inserted into a waveguide shim 2 mm in length and trimmed flush with the faces of the shim. Two-port S-parameter measurements are conducted on the explosive; the empty shim is similarly characterized. Using standard waveguide equations and the measured length of the shim, the complex S-parameter data obtained with the filled shim is optimized to four free parameters—complex permittivity and distance offsets for the two sample faces relative to the calibration planes. Permittivity data obtained from measurements of the plastic explosives C-4, Primasheet 1000, Primasheet 2000 and Semtex 10 are presented. Results obtained for C-4 and Primasheet 1000 are comparable to other data in the literature, and the data on Primasheet 2000 and Semtex 10 are the first known published permittivity values in this range. Excellent agreement between the experiment and the fit is obtained using a constant permittivity across the waveguide band, indicating that dispersion is not significant for these materials.
Dielectric measurements of plastic explosives using a loaded waveguide technique via vector network analyzer and banded MMW extender modules operating at V-band (50 – 75 GHz) are performed. A portion of explosive sample is inserted into a waveguide shim 2mm in length and trimmed flush with the faces of the shim. Two-port S-parameter measurements were conducted on the explosive; the empty shim is similarly characterized. Using standard waveguide equations and the measured length of the shim, the complex S-parameter data obtained with the filled shim is optimized to four free parameters — complex permittivity and distance offsets for the two sample faces relative to the calibration planes. Permittivity data obtained from measurements of the plastic explosives C-4, Primasheet 1000, Primasheet 2000 and Semtex 10 are presented. Results obtained for C-4 are comparable to other data in open literature. Excellent agreement between the experiment and the fit is obtained using a constant permittivity across the waveguide band, indicating that dispersion is not significant for these materials.
Active mode standoff measurement using infrared spectroscopy were carried out in which the angle between target and the source was varied from 0-70° with respect to the surface normal of substrates containing traces of highly energetic materials (explosives). The experiments were made using three infrared sources: a modulated source (Mod-FTIR), an unmodulated source (UnMod-FTIR) and a scanning quantum cascade laser (QCL), part of a dispersive mid infrared (MIR) spectrometer. The targets consisted of PENT 200 μg/cm2 deposited on aluminum plates placed at 1 m from the sources. The evaluation of the three modalities was aimed at verifying the influence of the highly collimated laser beam in the detection in comparison with the other sources. The Mod-FTIR performed better than QCL source in terms of the MIR signal intensity decrease with increasing angle.
A standoff multivariate calibration for detection of highly energetic materials (HEM) using Fourier transform infrared
spectroscopy is presented in this report. The procedure consists in standoff sensing at 1 m distance and the variation of
three parameters of detection. The first variable considered was the angular dependence: 0° to 45‡ from source-target with respect to alignment of target-detector. The second variable consisted on the use of several surfaces on which the material was deposited. The substrates used were polished aluminum and anodized aluminum. The third variable studied was the dependence on some specific analyte loading surface concentration: from 10 μg/cm2 to200 μg/cm2. The HEM
used in this work was PETN, synthesized in our lab. Calibration curves were based on the use of chemometrics routines
such as partial least squares (PLS) regression analysis. This algorithm was used to evaluate the impact of the angular
dependence about the limits of detection of different HME loadings on aluminum substrates.
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