Influence of phase position on the chemical response of oscillator driven polymer coated SAW resonators

The use of oscillator operated SAW resonators as chemical sensors is widely accepted to have the best sensing properties. However, some important parameters of influence are not sufficient resolved, yet. In general, these are effects arising from the electronic circuitry such as the phase situation on the chemical response of these sensors. We have found that they can be almost dramatic for several types of sensitive coatings and, thus, are not negligible, especially their influence on the sensitivity. In this work some exemplary results with SAW resonators working at 433,92 MHz coated with different polymeric films such as polyisobutylene (PIB), polyepichlorohydrine (PECH) or polydimethylsiloxane (PDMS) and sampled with toluene as analyte. Depending on thickness and homogeneity of the polymer film serious influences of the set phase positions on the quality of the chemical response were observed such as curve shape, and signal to noise ratio. Also, a simulation using an equivalent circuit model of the transducers including the polymer coating is used for a deeper understanding of these phenomena.