GAS-DETECTION USING SURFACE ACOUSTIC-WAVE DELAY-LINES

Experimental results are presented for a gas detector employing surface acoustic waves (SAW). The SAW piezoelectric gas (SAWPG) detector consists of twin SAW delay lines fabricated on a single piezoelectric substrate and each connected in an oscillator configuration. The propagation path of one delay line oscillator is coated with a selectively sorbent film, while the other is uncoated and used as a stable reference. Phase delay changes due to mass loading or stress effects induced by gases sorbed on the delay line containing the film result in corresponding frequency shifts relative to the reference oscillator; these shifts are proportional to gas concentration. Since SAW energy is concentrated near the film, the detector is found to be highly sensitive. For demonstration purposes both SO//2 and H//2S detectors have been fabricated that are capable of measuring concentrations in air of 10 ppb of SO//2 and 10 ppm of H//2S.