Electronic Military & Defense magazine was developed for engineers, program managers, project managers, and those involved in the design and development of electronic and electro-optic systems for military, defense, and aerospace applications.
Issue link: https://electronicsmilitarydefense.epubxp.com/i/146848
Techniques A "Smoke And Mirrors" Approach To Remote Explosives Detection A new technique based on cavity ring-down spectroscopy can detect NO2 from explosives at sub-ppb levels — and send the results to a smartphone. By James Hargrove and David Szpunar I magine that a U.S. soldier or marine could remotely determine whether a suspect package, garbage pile, or patch of disturbed earth contained a deadly improvised explosive device (IED). And imagine that they would receive the verdict instantly via a go/no-go indication on a standard smartphone. This scenario may soon become a reality, thanks to a project known as FEROS. The technology behind the FEROS project is the Ferret Optical Sensor, an analyzer that has been laboratory proven to detect sub-ppb (parts per billion) levels of explosives with no known interferences. ALTI LLC uses this patent-pending method to selectively generate nitrogen dioxide (NO2) from explosives. It then uses a sensitive cavity ring-down spectrometer tuned specifically for NO2 with patented gated integrated detection (TD-CARDS-GID) to achieve sensitivity levels limited primarily by the photon noise limit. A scrubber passes the explosive odor while blocking even the most difficult to eliminate interferences such as auto exhaust and cigarette smoke. The technology is being further developed and tested in collaboration with Roosevelt University in Chicago. The analyzers have been reduced to the size of a large lunch box and can be further reduced to the size of a laptop computer (Figure 1). The TD-CARDSGID is literally accomplished by "smoke and mirrors," only in this case, instead of fooling people, the method actually makes incredibly precise measurements of explosives. How It Works First, the odor is collected by suction and drawn through a special filter that blocks regular organic nitrates and nitrogen dioxide and other species that could show 22 Electronic Military & Defense ■ a false signal. Then, a heater converts the explosives to air pollution (or "smoke"). This pollution contains NO2, a gas that absorbs violet to green light, leaving the red, orange, and yellow colors of visible light, which give a brown appearance that for levels of explosive vapor would be invisible to the human eye. (This color is the primary cause of the brown appearance of the air in polluted cities.) Suction continues to draw the sample through a light cavity formed by two concave mirrors. A violet laser is turned on and off at one end of the cavity to ring up and ring down the light levels within the cavity. The light also follows an exponential decay when its source is turned off (ring down) and an exponential decay when the light is turned on (ring up), giving a pair of signals that can be combined to give the total laser intensity of the cavity. Dividing a series of decays by this total gives a normalized decay curve that can be directly converted into a decay rate. The decay rate Figure 1: The Ferret TD-CARDS-GID prototype www.vertmarkets.com/electronics