Certain selected chemicals associated with terrorist activities are too unstable to be prepared in a final form. These selected chemicals are often prepared as precursor components, to be combined at a time immediately preceding a time of application of the selected chemical. An example is a liquid explosive, which usually requires provision of an oxidizer, an energy source and a chemical or physical mechanism to combine the other components at a time immediately preceding detonation. Detection of presence of the oxidizer (e.g., H.sub.2O.sub.2) or the energy source (e.g., nitromethane) is often possible but must be performed in a short time interval (e.g., 5-15 sec) and in an environment with a very small concentration (e.g., 1-100 ppm), because the target chemical(s) is present in a sealed container.
What is needed is a system that allows detection of presence of a target oxidizer and/or a target energizer in small concentrations (as small as 1 ppm) in a relatively small time interval, preferably no more than about 5-15 sec. Preferably, the system should allow detection of at least one oxidizer and of at least one energizer, substantially simultaneously, should operate with a relatively small "footprint" in a real life environment, and should operate with only a small energy expenditure.
These needs are met by NASA scientists Jing Li, Meyya Meyyappan, and Yijiang Lu’s invention of a system and associated method for detecting one or more chemical precursors (components) of a multi-component compound that may become unstable when fully assembled or combined. First and second carbon nanostructures ("CNSs") are loaded (by doping, impregnation, coating or other functionalization process) with different first and second chemical substances that react with first and second chemical precursors, respectively, which may be the same or may be different, if these precursors are present in a gas to which the CNSs are exposed. After exposure to the gas, a measured electrical parameter value (EPV) (e.g., impedance, conductivity, capacitance, inductance, etc.) changes with time in a predictable manner, if a selected chemical precursor is present, and will approach an asymptotic value promptly after exposure to the precursor. The system is detailed in U.S. Patent 7,623,972.
The measured EPVs are compared with one or more sequences of reference EPVs for one or more known target precursor molecules, and a most probable concentration value is estimated for each of one, two or more target molecules. An error value is computed, based on differences for the measured and reference EPVs using the most probable concentration values. Where the error value is less than an error value threshold, the system concludes that the target molecule is likely. Presence of one, two or more target molecules in the gas can be sensed from a single set of measurement.
The system can test for presence of one of different target molecules substantially simultaneously. One advantage of the invention is its flexibility: the presence of any reasonable number of target molecules can be tested for with a single set of EPV measurements.
The system can test for presence of one of different target molecules substantially simultaneously. One advantage of the invention is its flexibility: the presence of any reasonable number of target molecules can be tested for with a single set of EPV measurements.
