SIMULATION OF VISCOELASTIC EFFECTS OF POLYMER-COATINGS ON SURFACE-ACOUSTIC-WAVE GAS SENSOR UNDER CONSIDERATION OF FILM THICKNESS

In this paper an analysis of the responses of surface acoustic wave (S AW) sensors coated with polymer films is described. Complex bulk and s hear moduli are utilized to represent viscoelastic properties of the p olymer. Compared with the experimental results, the calculated results strongly suggest that the real part of the shear modulus mostly influ ences the velocity shift and attenuation change in the sensor response s. In addition, using the real parts of the shear modulus, the polymer films can be classified into three types: glassy films, glassy-rubber y films and rubbery films, Simulations of gas sorption for polymer fil ms are performed. For glassy films, the SAW sensor response increases with increasing him thick;;ess, whereas for glassy-rubbery and rubbery films, the relationship between the sensor sensitivity and film thick ness is more complicated. Therefore, an optimization of the properties and thickness of films and the operating frequency is required for de signing SAW gas sensors with polymer coatings.