SAW delay lines for thermal detection of gases and gas flows

Uncoated SAW delay lines performing as thermal probes are applied for detection of gases and gas flows. Analysis of the forced convection is performed for 13 analytes in linear approximation by neglecting their chemical interaction with the ambient. Experimental detection is performed for H₂, He, Ar, CH₄, NH₃, N ₂, O₂, dry air, using SAW delay lines on SiO₂ , LiNbO₃, Bi₁₂GeO₂₀, Bi₁₂ SiO₂₀, at operating temperatures T=25-165°C and frequencies f=21-263 MHz. SAW responses are measured as a function of concentration n, flow rate u, temperature coefficient of velocity (TCV) and temperature T. Efficient selectivity and monitoring of the responses are demonstrated by a proper selection of TCV and T. Detection of 0.35% CH₄, 0.25% H₂ and 0.1% NH₃ in N₂ is performed. Linear output for u=50-2000 ml/min is obtained