A SAW resonator sensor system employed in humidity measurements

The present paper describes a sensor system based on Surface Acoustic Wave (SAW) resonators, used both as the frequency control component and the sensor device. The system makes use of two 303 MHz oscillators, specifically designed by the authors for this application, thus accounting for the proper gain in the feedback path. The oscillators are frequency controlled by two identical SAW resonators, one sealed and used as a reference, whereas the of her had its surface coated with a cellulose acetate film, thus allowing the system to operate as a humidity detector. Although the system has been tested to sense humidity, it can be easily adapted to detect other gaseous materials, provided an adequate film is deposited on the SAW device. The sensor system built is described and the achieved performance of the humidity detector is presented.