High-frequency One-port Colpitts SAW Oscillator for Chemical Sensing

Abstract

Abstract—This paper reports upon the design and development of a low cost, high sensitivity, high frequency surface acoustic wave resonator (SAWR) based system for gas sensing applications. The 262 MHz one-port SAWR operates in a grounded-base Colpitts oscillator arrangement that was developed based on an equivalent circuit model. Electrical characteristics of the fabricated SAWR show good agreement with its equivalent device model at the resonant frequencies, and it was found to have good stability and sensitivity with a Q-factor in air of about 2,870 at its fundamental resonant frequency. The sensor system is designed to operate in a dual configuration in which one resonator is coated with a gas- sensitive polymer (polyethylene) coating, whilst the second one is used as a reference channel; thereby eliminating common mode interferences on the baseline signal. Mass sensitivity was found to be ca. 1 Hz/ng, which corresponds to sub-ppm sensitivity to gas/odour concentration.