Showing papers by "Michael G. Pollack published in 1997"

MEMS-based explosive particle detection and remote particle stimulation

Abstract: We report on a new methodology for chemical detection of explosive particles associated with anti-personnel mines. Traceparticle detection can be used to complement vapor detection of explosives with an electronic nose. Our approach is toremotely stimulate a target area with a high intensity, focused air ultrasonic beam whose energy can megasomcally clean thetarget area of particles above a designed-for size. We have designed a MEMS electrostatic transducer to test the concept.Nanogram particle detection will occur by collecting particles on an array of temperature sensitive MEMS sensors andirradiating the particles with 3-5 im wavelength infrared light. Explosive particles will selectively absorb the infrared energyat approximately 1600 cnf', decompose, and give offheat which can be detected.Keywords: explosive particle detection, ultrasound, land mines, nanogram particles, decomposition, MEMS, cantileverbeams 1. INTRODUCTION Recently, the idea ofusing chemical detection for finding land mines has gained attention as a result of successes achieved inthe use of trained dogs. Dogs have proven to be the most effective land mine detectors, although the dogs have limitedattention spans measured in tens of minutes. An electronic nose can work 24 hours a day! Since the land mine detectionproblem is huge, it will require full time noses in the search process.Dogs search by placing their noses close to the ground, inhaling vapors as well as solid particles of material. There have beenrecent successes in mimicking the vapor detection aspects of the smell sense in the "nose-on-a-chip" at Cal Tech, which candifferentiate among various vapors. 1 A complementary approach to obtaining increased chemical sensitivity is beingexplored at Duke University. One issue in vapor detection ofexplosives is that sampling at ambient temperatures may limitdetectability. An alternative is to collect particles as samples. Since plastic explosives are fabricated by creating a mixture ofground RDX or TNT with a binder substance, the putty-like material which is formed tends to capture particles to its surfacewhen contact is made. Additionally, because particles are distributed further by handling, the surface of the device and itssurrounding area are often heavily contaminated with particles ofexplosives. During diurnal temperature cycles the explosiveparticles attached to a buried mine diffuse their y to the surface of the ground. By sampling fine particles on the ground'ssurface in addition to vapors, it is possible that analysis and detectability may be enhanced. 2Significant success has been reported using trace explosive particles for substance identification.2 Indeed, both RDX and TNThave been detected at higher levels than expected when the vapor sampling system was augmented with a trace particle