Novel TOCN/PVOH Dielectric Composite Sheets With Low Ecological Footprint for Microwave Humidity Sensing

Humidity-sensitive dielectric sheets combine easy integration of humidity sensing ability and high sensitivity performance through microwave technologies. However, only a few materials have been investigated so far. This article introduces TEMPO oxidized nanocellulose (TOCN) composite sheets with polyvinyl alcohol (PVOH) as a sensitive material with low ecological footprint for microwave humidity sensing. Preparation and physical characterization of these novel sensitive materials are realized. The humidity sensing performances are studied with a CPW-based serial resonator where the sensitive sheets are deposited. Experimental results validate the sensitivity of TOCN/PVOH sheets both in reflection and transmission. Dynamic range, sensitivity, and the robustness of microwave parameters over the humidity measurement range are analyzed. The best results are reached with the sample with only 4 wt% of PVOH: 1.85 MHz/%RH in the 55–100%RH for the frequency response and 0.46°/%RH in 70–100%RH range for the phase response.