Effects of temperature and humidity on the performance of polymer-coated surface acoustic wave vapor sensor arrays

The influences of temperature and atmospheric humidity on the performance of an array of eight polymer-coated 158-MHz surface acoustic wave vapor sensors were investigated. Sensitivities to the seven organic vapors examined all exhibited negative Arrhenius temperature dependencies, with responses increasing by factors of 1.5-4.4 on going from 38 to 18 degrees C. The magnitudes of the temperature effects, while generally similar, differed sufficiently among certain sensor-vapor combinations to cause marked changes in vapor response patterns. In addition, it was found that operating identically coated sensors at different temperatures could provide a means for discriminating certain vapors. The changes in sensor responses with temperature agreed reasonably well with those expected assuming ideal vapor sorption behavior and indicated that changes in the moduli of the sensor coatings were not important mediating factors. Responses to relative humidity (RH) from 0 to 85% RH were important even for the nonpolar sensor coatings. Significant changes in the sensitivities to the organic vapors were observed as a function of atmospheric humidity for several sensor-vapor combinations, which, in turn, affected the patterns of responses obtained from the sensor array. Results indicate that small changes in temperature or humidity have a larger effect on baseline stabilities than on the responses to the vapors. Monte Carlo simulations of sensor responses show that the ability to discriminate vapors in binary and ternary mixtures using a four-sensor array remains high regardless of the operating temperature and ambient humidity, provided that temperature-or humidity-induced changes in the response patterns are taken into account.