Analysis of the different contributions to the response of SAW gas sensors

Numerical estimations of the mass and elastic loadings are performed for different possible material combinations. In order to do this, the density and elastic constants of the film are changed consequently and one by one for each of the combination selected in accordance with Farnell-Adler's theory. In addition, the perturbation approach is applied to analyse the SAW gas response in analytical form. On considering, as an example, Pd coated SAW delay lines exposed to hydrogen, the relative changes in Pd parameters are measured, the mass and elastic loadings are estimated and the SAW hydrogen responses are theoretically predicted and experimentally verified. An increase of a factor 10 in the SAW gas response is demonstrated for Pd film deposited on different substrate materials and/or crystallographic orientations.