Analysis of dc and ac properties of humidity sensor based on polypyrrole materials

Polypyrrole (PPY) materials were prepared by using chemical polymerization at room temperature for 96 h. A resistive-type humidity sensor was fabricated on a ceramic substrate with Ag–Pd interdigital electrodes. The humidity-sensing mechanism of the polypyrrole materials was discussed in terms of capacitance, direct current, complex impedance and dielectric loss properties. The discussion on the sensing mechanism indicated that not only electrons or ions but also dipoles contributed to the conduction in the whole relative humidity range.