Surface acoustic wave humidity sensor using polyvinyl-alcohol film

A surface acoustic wave (SAW) sensor has been fabricated and used to study the hygroscopic properties of the polyvinyl-alcohol (PVA) polymer film as layer chemically sensitive to relative humidity (RH). A 42 MHz SAW device has been configured as delay Line onto 128 degrees YX-LiNbO3 substrate with the SAW path totally covered by the spin-coated PVA film. The SAW phase response of the sensor shows high sensitivity toward RH, excellent repeatability of the response, quite good water-resistance of the PVA film, low hysteresis, at room temperature. The SAW PVA sensor shows negligible cross sensitivity toward gases (NH3, NO2, CO, H-2) and seems to be sensitive toward organic vapours molecules (ethanol, methanol) containing OH groups. (C) 1999 Elsevier Science S.A. All rights reserved.