Gas-detecting properties of surface acoustic wave ammonia sensors

The detecting properties of l-glutamic acid hydrochloride that is deposited on 128° YX-LiNbO3 surface acoustic wave (SAW) delay lines are studied in this work. SAW gas sensors that were based on l-glutamic acid hydrochloride had good sensitivity, selectivity, reversibility, and repeatability to ammonia gas. A detection limit of 0.56 ppm for gaseous ammonia was observed when using l-glutamic acid hydrochloride for the sensing film at room temperature. The response degraded at a rate of −0.01 ppm per day at room temperature, and it means that the long-term stability of l-glutamic acid hydrochloride is quite enough. The cross-sensitivity from humidity interference was approximately 0.011. Therefore, the interference from water molecules is slight in room ambient air, so the effect of humidity on SAW response is negligible.