Abstract
A gas sensor 39 comprises a control circuit 34; a first surface acoustic wave (SAW) device including, a piezoelectric substrate 3, a transducer pair 381, 382 spaced apart across the piezoelectric substrate, and a control circuit connection 32; and at least one further surface acoustic wave device the same as the first but with a sensing porous thin film 361 located between the transducer pair. In operation a surface acoustic wave is generated on the substrate by the first transducer 381 and subsequently detected by the second transducer 382. Analyte gas molecules can be absorbed by the thin film resulting in a variation in the characteristics of this surface acoustic wave. The first sensor has no thin film and acts as a reference sensor to eliminate environmental interference while the control circuit controls operation such that only one of the SAW devices is activated at any time. The transducer pair may be inter-digital transducers (IDT) and the invention can be employed, for example, as a breathalyser to sense alcohol.