Surface acoustic wave humidity sensors based on poly (p-diethynylbenzene) and sodium poly sulfone sulfonate

Surface acoustic wave (SAW) humidity sensors have been constructed by using poly(p-diethynylbenzene) (PDEB) and sodium polysulfone-sulfonate (NaSPF) as the sensitive film. The 138 MHz SAW sensors were configured as a delay line onto a 128 degrees YX-LiNbO3 substrate with the SAW path covered by the LB membrane of PDEB and the spin-coated NaSPF film. The frequency responses of the SAW sensors have been investigated over the range of relative humidity (RH) of 20-85% at different temperatures. It is found that the temperature has a great influence on the frequency shift of the SAW sensors. The PDEB and NaSPF based SAW sensors exhibit a decreased frequency with an increase in humidity, and the sensitivity is found to be -0.4 and -1.1 kHz/%RH, respectively. The effect of chemical structure on the sensing characteristics has also been discussed. (c) 2006 Elsevier B.V. All rights reserved.