SAW gas sensing using reflectors and multistrip couplers

In this paper we present a new technique for chemical sensing with surface acoustic waves. This technique makes use of the fact that the acoustic impedance of a SAW changes when a sensor film on the device absorbs the analyte. If the sensor film is structured as a reflecting array, the amplitude of the reflected wave varies with the mechanical or electrical properties of the film. The advantage is, that the amplitude is much less sensitive to temperature fluctuations of the device. High stability and sensitivity of the sensor can therefore be reached. We have built a NO₂ sensor based on this principle using copper-phthalocyanine as sensitive film. Similar properties are obtained if a multistrip coupler is used instead of a reflector array