Broadband Permittivity Characterization of Polyvinyl-Alcohol Film for Humidity Sensing Applications

This paper presents broadband complex permittivity characterization of polyvinyl-alcohol (PVA) film at different relative humidities (RHs) from 13.7% to 94.3% for sensing applications. Interdigital capacitor is employed as a basic component to characterize the permittivity in a microwave range between 1.5 and 15 GHz. The investigated PVA film shows low hysteresis and stable long interval performance, making it a good candidate for humidity sensing applications. The extracted complex permittivities at different RHs show properties of dielectric relaxation, which is described by the Cole-Cole equation. The coefficients in the Cole-Cole equation are calculated at different RHs. The functions of the coefficients over RH are found, by which the complex permittivity can be obtained at an arbitrary RH. This comprehensive model of the PVA film provides for the first time an accurate mathematical model for RH sensing applications.