Surface acoustic wave (SAW) devices are very attractive as gases and vapours sensors due to their high sensitivity. The SAW chemical sensors have been implemented onto 128° YX-LiNbO_3 piezoelectric substrates and configurated as SAW delay lines, which have been equipped by a pair of input and output interdigital transducers operating at a frequency of 42 MHz and have been coated along the SAW propagation path by different sorbent layers of organic films such as polypyrrole, polyvinyl-alcohol. These chemically sensitive coatings have been used to detect, under ambient conditions, ammonia and relative humidity, respectively. Reversible SAW acoustic responses towards the analytes under test have showed high sensitivity. The calibration curves, detection limits and ageing phenomena of the organic coatings have been investigated.
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