The proposed technology is based on the micro-fabrication of electrodes in order to generate surface acoustic waves (SAW) with well-defined frequencies, on piezoelectric substrates. The operating principle of a surface acoustic wave sensor is linked to the variation of the characteristics of the acoustic wave that propagates on the device (e.g. wave velocity on the substrate, etc.) caused by the interaction with the environment (e.g. interaction of an analyte on the surface of the device, deformation of the substrate, etc.). This variation produces a change in the frequency of the wave, which can be detected with great accuracy thanks to an electronic oscillator that uses the SAW device as a control element. This technology allows to manufacture very small devices (in the order of a few mm2) and obtain sensors with high sensitivity.
The described technology has allowed the development of some prototypes of sensors systems tested in the laboratory with excellent results. In particular, in a first application called “Electronic Nose” a system equipped with SAW sensor arrays capable of detecting small concentrations of volatile substances has been developed. In a first version, polymers were used as sensitive materials for the detection of vapours of different analytes, while in a second version proteins (odorant-binding proteins) were used for the detection of odorant molecules in the air. In a second application has been developed an absolute pressure SAW sensor, capable of measuring pressures in the range of 0-3 bar with excellent resolution. In this application, the surface acoustic wave device exploits the deformation of a piezoelectric membrane exposed to the difference between the external pressure and the internal reference pressure. In both cases, the fabrication costs were very low.