A novel surface acoustic wave-impedance humidity sensor based on the composite of polyaniline and poly(vinyl alcohol) with a capability of detecting low humidity

This paper presents a novel humidity sensor composed of a 433 MHz surface acoustic wave (SAW) resonator and an interdigitated gold electrode connected in series. The gold electrode was covered with a sensitive film of a composite of processable conductive polyaniline and polyvinyl alcohol. The frequency response of the novel SAW-impedance humidity sensor toward relative humidity (RH) was investigated at room temperature. The sensitivity of the SAW-impedance humidity sensors increased with the increase in the conductivity of the sensitive film. The sensor showed a sensitivity of ∼7.4 kHz/%RH at 30%RH, which was increased to 60 kHz/%RH at 47%RH. Moreover, such sensors exhibited short response and recovery times and good repeatability. It is worth noting that the sensor showed a linear frequency response to humidity over the range of 0.4–20%RH with a good sensitivity of ∼2 kHz/%RH, which reveals its potentials for detecting low humidity.