/spl Sscr/tudy of the dynamic response of QCM sensors by means of a fast and accurate all-digital frequency detector

Abstract

In this paper an innovative measurement system for odor classification, based on Quartz Crystal Microbalances (QCHs), is presented. In particular, the problem of detecting typical wine aroma components in mixtures where ethanol is present is taken into account. In QCM sensors the sensitive layer is a polymeric layer deposited on a quartz surface. Chemical mixtures are adsorbed by the polymeric layer, inducing a change in the quantz mass and therefore in its resonance frequency. The frequency shift is measured by a dedicated fully digital front-end hardware implementing a technique proposed by Cantoni (2000). This approach allows reducing the measurement time while maintaining a high frequency resolution. The developed system allows measuring variations of the QCM resonance frequency shifts during chemical transients obtained with abrupt changes in odor concentration. Hence the reaction kinetics can be exploited to differentiate among different compounds. In this study some measurements obtained with an array of 4 sensors with different sensitive layers are presented. An exponential fitting of the transient responses is used for feature extraction. Principal Component Analysis (PCA) to reduce data dimensionality is used.