Influence of phase position on the performance of chemical sensors based on SAW device oscillators

Sensor systems for the chemical analysis of organic gases based on mass-sen sitive sensors, i.e,, bulk acoustic wave and surface acoustic wave (SAW) se nsors, are becoming more and more an interesting alternative for highly sop histicated classic instrumentation, Although the use of oscillator-operated SAW resonators as chemical sensors is widely accepted to have the best sen sing properties, some important parameters of influence are not sufficient resolved yet. In general, these are effects arising from the electronic cir cuitry, such as the phase situation on the chemical response of these senso rs. We have found that they can be almost dramatic for several types of sen sitive coatings and, thus, are not negligible, especially their influence o n the sensitivity, We present some exemplary results with SAW resonators, w orking at 433.92 MHz, coated with different polymeric films such as poly(is obutylene), poly(epichlorohydrin), or poly(dimethylsiloxane) and sampled wi th toluene as analyte. Depending on the thickness and homogeneity of the po lymer film; serious influences of the set phase positions on the quality of the chemical response were observed, such as curve shape and signal-to-noi se ratio. Also, a simulation using an equivalent circuit model of the trans ducers including the polymer coating is used to obtain a deeper understandi ng of these phenomena.