In this innovation, a method and associated system have been created to vary a voltage applied to an exposed end of a carbon nanotube for a selected time interval to promote gas discharge, and to estimate a gas component involved in the discharge. Each component of a gas has a first, lower threshold discharge (voltage value, V∞) at which discharge can occur after a long time delay (t(V∞:ho)≈∞), where “ho” refers to a discharge voltage holdoff value. Application of a voltage V above this lower limit V∞ will cause the gas component to undergo a discharge after a discharge holdoff time t(V:ho) that decreases as V increases above V∞.

When the voltage V is ≥ a second (upper) prompt discharge voltage value V0(VV0V), the discharge occurs substantially instantaneously. For some gas components, it may occur that VV0, so that a substantially unique discharge voltage threshold exists; this may occur at low concentrations of that gas component. For other gas components, it may occur that V<V0, and any voltage V in the range V<V<V0 will produce a discharge after a finite, non-zero discharge holdoff time delay (t(V:ho) (>0); in this instance, a single or unique discharge voltage does not exist.

This procedure can be used to distinguish between two or more components (k=1, 2, …,K) present in a gas, if the threshold discharge voltage values V(k)__ for each of the two or more gas components are spaced apart by at least a reasonable amount. As the voltage V is increased, the rate of change of an electrical parameter, such as current or cumulative electrical charge, will change (e.g., become non-zero) as the threshold discharge voltage value V(k) of each distinct gas component is exceeded.

This innovation should be useful, by itself or in combination with other gas discharge methods, to identify the gas or gases that are present in a gaseous medium, at low or moderate concentrations, and to estimate the concentration of one or more of the gases present. This design can be automated, if desired, and used in space exploration — for example, in a planet or satellite flyby, or for a crew exploration vehicle. Also, this design can be used terrestrially, such as for determination of gas composition in a hazardous substance environment.

This work was done by John F. Schipper and Jing Li of Ames Research Center. Contact the Ames Technology Partnership Office at 1-855-627-2249 or This email address is being protected from spambots. You need JavaScript enabled to view it.. Refer to ARC-15506-1.

NASA Tech Briefs Magazine

This article first appeared in the August, 2015 issue of NASA Tech Briefs Magazine.

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