Thermoconductometric detection of gases and gas flows by means of SAW delay lines

Abstract

Surface acoustic wave (SAW) delay lines without gas-sensitive coatings are used as thermal sensors for the thermoconductometric detection of gases and gas flows. The forced convection of 13 gases is analyzed in the linear approximation without regard for their interaction with the environment. Quartz, LiNbO3, Bi12GeO20, and Bi12SiO20 delay lines are used to detect H2, He, Ar, CH4, NH3, N2, and O2 at frequencies f=21–263 MHz and temperatures T=25–165 °C. The SAW “response” is measured as a function of the gas concentration n, the flow rate U, the temperature coefficient of the SAW velocity (TCV), and the working temperature Tp. The feasibility of controlling the level of the gas “response” and imparting selectivity to the choice of TCV and Tp is demonstrated. The threshold gas concentrations are 0.35% for CH4 and 0.1% for H2 and NH3 in nitrogen. A linear response is obtained in the interval U=20–200 ml/min.