Abstract
A surface acoustic wave (SAW) sensor utilizing the acoustoelectric effect has been designed for measurement of humidity in sensing ambient atmosphere. Most of the studies reported on sensors utilize the effect of mass loading. In this paper, we propose a somewhat different SAW humidity sensor that uses the changes in the film conductivity rather than the mass. A 30 MHz dual SAW delay line fabricated on 128° YX LiNbO3 was coated with the sodium salt of poly(styrene) sulfonate. This hygroscopic polymer coating caused the SAW velocity change of 10 m/s per 10% relative humidity. The response was quite linear in the range from 20 to 70%RH.
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