Velocity and attenuation effects in acoustic wave chemical sensors

A variety of chemical sensors have been developed using surface acoustic wave (SAW) devices coated with sorptive films. Chemical uptake into the coating results in a change in the coating´s physical properties. Typically, only the velocity response is used and responses are interpreted gravimetrically. Polymers are commonly used as the sorptive coatings due to the ease of forming thin films and to the wide range of chemical affinities that can be obtained. We have shown that viscoelastic properties play a significant role in polymer-coated SAW sensors, especially due to the onset of a film resonance when the inertial phase lag across the film approaches π/2. This film resonance causes enhanced absorption of acoustic energy from the wave and a dramatic effect on device response. Based on understanding these acoustic wave/polymer film interactions and the resulting changes in both wave velocity and attenuation, device sensitivity can be significantly increased and the ability to utilize both responses to discriminate between isolated chemical species with a single SAW device can be improved