NO2 gas-concentration measurement with a SAW-chemosensor

A highly stable and selective SAW-chemosensor has been realized. The sensor system is based upon a dual delay-line oscillator. The difference between the two oscillator frequencies is a measure of the gas concentration. The oscillator is stabilized by means of automatic gain control. The oscillator operates without tuning inductors and with symmetrical driving of the transducers, aiming at a (total) monolithic integration of this sensor in a ZnO-SiO2-Si layered structure. A special feature of the sensor is that the delay lines and the electronic system are constructed in separate modules. The operating frequencies of the sensors are between 30 and 110 MHz. (Author)