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The gas sensing properties of organic polypyrrole (PPS) film, deposited onto LiNbO/sub 3/ substrate by Langmuir-Blodgett (LB) technique, have been monitored by surface acoustic wave (SAW) delay lines and studied with respect to sensitivity, selectivity, response time, stability, repeatability, and aging. The SAW PPy elements demonstrate high sensitivity toward NH/sub 3/ gas with high selectivity against CH/sub 4/, CO, H/sub 2/, and O/sub 2/. The detectable threshold concentration has been estimated as 20 ppm NH/sub 3/ in air; the response time is in the 10s range, and the recovery time is about 15 min; the repeatability of the SAW response toward eight sequential NH/sub 3/ gas exposures is within 6%; the aging of the PPy film is within 4% over a month; and the effect of humidity on SAW NH/sub 3/ gas response is negligible for the typical conditions at room ambient air. Partially reversible SAW response recognizing NH/sub 3/ gas as one component of an interfering gases-mixture has been observed. Simultaneous chemoresponses of SAW phase and insertion loss have been performed in order to investigate the sensing mechanisms. By merging with electrical conductivity gas response, the dominant SAW sensing effects for NH/sub 3/ gas detection are defined as elastic loading.
Ultrasonics, Ferroelectrics and Frequency Control, IEEE Transactions on (Volume:45 , Issue: 5 )
Date of Publication: Sept. 1998