Development of an analytical microsystem for organic gas detection based on surface acoustic wave resonators

Abstract

Modified Surface Acoustic Wave (SAW) devices can be used as highly sensitive detectors for gases: coated with a selective sorptive layer, they serve as a frequency determining element of an oscillator circuit. To perform a quantitative analysis of organic gas mixtures with polymer coatings as sensitive membranes, it is necessary to use an array of several SAW sensors with sensitivities towards various gaseous components and a subsequent pattern recognition of the sensor responses. An automatic working, self purging and compact analytical microsystem has been developed for organic gas detection. As the central component it contains an array of nine commercially available SAW resonators working at frequency of 433.92 MHz. Eight sensor oscillators, one common reference oscillator for temperature compensation and circuits for frequency mixing are mounted within a compact radial housing (diameter 108 mm). A selection of polymers has been made to detect a broad variety of gaseous organic analytes. Of particular interest have been hydrocarbons, halogenated hydrocarbons and aromatic compounds. Initial experiments with these analytes have been carried out to proof the selection and to optimize the combination of polymer coatings. With the compact sensor configuration a very fast response time in the range of seconds is obtained for qualitative determination of the analytes.