Investigation of cocaine plumes using surface acoustic wave immunoassay sensors.
Vapor sensors, aka electronic noses, are becoming an increasingly popular analytical tool for detection and identification of small molecules in the gas phase. In this paper, we present the results of a series of experiments demonstrating real-time vapor phase detection of cocaine molecules. A distinctive response or signature was observed under laboratory conditions in which the cocaine vapors were presented using an INEL vapor generator and under "field" conditions facilitated by the Georgia Bureau of Investigation (GBI) Crime Lab. For these experiments, the sensor component was a two-port resonator on ST-X quartz with a center frequency of approximately 250 MHz. On this cut of quartz, a temperature-compensated surface acoustic wave is generated via an interdigital transducer. Antibenzoylecgonine (anti-BZE) antibodies are attached to the electrodes on the device surface via a protein-A cross linker. We observed a large transient frequency shift accompanied by baseline shift with the anti-BZE coated sensor. After repeated experiments and the use of numerous controls, we believe that we have achieved real time molecular recognition of cocaine molecules.
A comparison of temperature performance of SAW filters made on ST- and LST-cut quartz
The authors built several narrowband SAW (surface acoustic wave) bandpass filters centered at 200, 250, and 740 MHz on several orientations of LST-cut quartz. Devices were also made on ST-cut quartz for direct comparison. The authors report the performance of these devices with emphasis on temperature stability of frequency, transmission phase, and insertion loss. The LST-cut of quartz demonstrates superior frequency and phase stability over a wide temperature range when compared with the ST-cut devices. It is also demonstrated that the quasilongitudinal plate modes of LST-cut SAW filters are more attenuated than those of the ST-cut devices. The LST-cut is also a singly-rotated T-cut with X-propagation; hence the energy power flow angle on the XZ plane remains zero for all temperatures. LST-cut devices exhibit a greater increase in insertion loss as temperature rises as comprised to the ST-cut devices.<<ETX>>
Far-field dispersal modeling for fuel-air-explosive devices
A computer model for simulating the explosive dispersal of a fuel agent in the far-field regime is described and is applied to a wide variety of initial conditions to judge their effect upon the resulting fuel/air cloud. This work was directed toward modeling the dispersal process associated with Fuel-Air-Explosives devices. The far-field dispersal regime is taken to be that time after the initial burster charge detonation in which the shock forces no longer dominate the flow field and initial canister and fuel mass breakup has occurred. The model was applied to a low vapor pressure fuel, a high vapor pressure fuel and a solid fuel. A strong dependence of the final cloud characteristics upon the initial droplet size distribution was demonstrated. The predicted fuel-air clouds were highly non-uniform in concentration. 18 refs., 86 figs., 4 tabs.