THz Differential Absorption Radar for Bioparticulate Detection

The Phase-I effort has produced three key results as the foundation for the Phase-II proposal. First, vector network analyzer measurements of a Bacillus subtillis (an Anthrax surrogate) sample has yielded promising absorption signatures around 425 and 445GHz. These are believed to be the most accurate measurements ever made of an Anthrax-like biopaticle in the sub-1.0 THz region. Second, the key components of field-portable differential absorption radar (DAR) have been constructed and demonstratedtogether in the laboratory. The transmitter consists of a solid-state harmonic multiplier chain driven by a W-band tunable synthesizer and solid-state power amplifier. The receiver is based on an InSb hot electron bolometer operating in direct detection.The bolometer is mounted in a field-portable Gifford-McMahon closed-cycle refrigerator requiring no cryogens. The measured NEP of the direct receiver is just under 1x10-12 W/Hz1/2. Third, the transceiver was operated successfully in frequency-hoppeddifferential-absorption mode, and an absorption was detected in a Bacillus subtillis sample around 425 GHz, in agreement with the network analyzer data. In the proposed Phase II effort the DAR approach will be demonstrated on an aerosol bioparticlesample, the DAR components will be integrated in a field-ready sensor, and the sensor will be demonstrated in the field at a site to be determined. If successful this project will produce the first known sensor capable of measuring low densities ofbioparticles at a large stand-off. The commercial applications of such a sensor would be in counter-terrorism and in public health (monitoring the movement of human disease).