THERMOCONDUCTOMETRIC DETECTION OF GASES AND GAS-FLOWS BY MEANS OF SAWDELAY-LINES

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 far their interaction with th e environment. Quartz, LiNbO3, Bi12GeO20, and Bi12SiO20 delay lines ar e used to detect H-2, He, Ar, CH4, NH3, N-2, acid O-2 at frequencies f = 21-263 MHz and temperatures T=25-165 degrees 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 work ing temperature T-p. The feasibility of controlling the level of the g as ''response'' and imparting selectivity to the choice of TCV and T-p is demonstrated. The threshold gas concentrations are 0.35% for CH4 a nd 0.1% for H-2 and NH3 in nitrogen. A linear response is obtained in the interval U=20-200 ml/min. (C) 1997 American Institute of Physics. [S1063-7842(97)01705-4].