The gas sensing properties of organic polypyrrole (PPy) Him, deposited onto LiNhOg 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 NHa gas with high selectivity against CH4, CO, Hs, and O-2. The detectable threshold concentration has been estimated as 20 ppm NHa in air; the response time is in the 10s seconds range, and the recovery time is about 15 min; the repeatability of the SAW response toward eight sequential NHa gas exposures is within 6%; the aging of the PPy Him is within 4% over a month; and the effect of humidity on SAW NHs gas response is negligible for the typical conditions at room ambient air. Partially reversible SAW response recognizing NHg gas as one component of an interfering gases-mixture has been observed. Simultaneous chemoreiîponses 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 NHs gas detection are denned as elastic loading. © 1998 IEEE.

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