Sensing mechanism of an ionization gas temperature sensor based on a carbon nanotube film

Abstract

In this paper, we propose a novel ionized gas temperature sensor which has a triple-electrode structure and carbon nanotubes (CNTs) as a field emission cathode. The measurement current, as part of the non-self-sustaining discharge current, changes with the changing of initial emission current I₀ and Townsend's first ionization coefficient α according to the theory of Townsend discharge. The ionization coefficient α increases with increasing gas temperature for a given gas at a certain electric field because the mean free path is proportional to the gas temperature. In addition, the initial current increases with increasing gas temperature. Experimental results showed that the collecting current exhibited an exponential increase with the gas temperature rising from 20 °C to 110 °C and the sensitivity is 4.74 μA °C⁻¹ to air and 22.72 μA °C⁻¹ to nitrogen at 110 °C. The difference in the effective work function after nitrogen and oxygen adsorption is the response for the different sensitivities. The triple-electrode ionization sensor is a new mechanism of gas temperature measurement and has the merit of facilitating the fabrication of CNTs compared with the existing CNT-based resistive or thermal expansion temperature sensors.