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THz Differential Absorption Radar for Remote Detection of Bioparticles

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Final technical rept. 23 Sep 2002-22 Mar 2003

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This STTR Phase I effort entailed two separate tasks, each focusing on a different aspect of the bioparticle remote detection problem 1 the phenomenology of absorption by Bacillus subtillis BC in the THz region between 300 and 500 GHz and 2 the design, construction, and tabletop demonstration of a differential-absorption radar DAR transceiver suitable as a remote sensor in Phase II. Both tasks met with significant success. The primary objective of the phenomenology effort was to measure the THz transmission through BC with the highest possible accuracy using a vector network analyzer. Previously, measurements made at the University of Virginia displayed two possible absorption resonances in this region centered at 327 and 421 GHz, respectively. In the Phase I measurements, there was no evidence for the 327 GHz resonance. But there was distinct evidence for the 421 GHz resonance that appeared both in vector-network-analyzer and in differential-absorption-radar measurements. Two promising signatures were observed in the Phase 1 effort, one around 425 GHz and the other around 445 CHz. The primary objective of the transceiver development effort was to construct and show the feasibility of a differential absorption radar operating between roughly 420 and 450 GHz. To meet the requirement of field portability, an all-solid-state, cryogen-free, transceiver was assembled using a harmonic multiplier chain for the transmitter and a hot electron bolometer for the receiver. The hot electron bolometer is operated at 4.2 K in a compact, closed-cycle refrigerator. In the first bench-top DAR demonstration, the BC absorption signature centered around 425 GHz was detected and shown to have curvature very close to that obtained by vector network analysis. This is considered to represent a proof-of-concept for the proposed biparticle DAR approach. 15 figures

Subject Categories:

  • Miscellaneous Detection and Detectors
  • Chemical, Biological and Radiological Warfare
  • Electricity and Magnetism

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