Surface acoustic wave humidity sensor

A new surface acoustic wave humidity sensor has been developed and tested. It is based on the use of a polyphenylacetylene (PPA) membrane which has already been utilized in the I,-doped form for the study of humidity sensors based on electrical conductivity responses. PPA shows physical properties which make it an almost ideal membrane for acoustic wave type sensors. Measurements performed on both Rayleigh and surface transverse waves have shown a high sensitivity of the device over a wide range of relative humidity values, a reversible behaviour together with a fairly fast response time.