Investigating a Microwave Waveguide Sensor with an Organic PEDOT:PSS Boundary for Humidity Detection

Biodegradable organic conductive polymers are seeing ever-increasing attention for the development of future generation electronic devices. This paper investigates the integration of PEDOT: PSS - an organic nanomaterial - with a microwave waveguide resonator for humidity detection. A microwave resonant cavity was developed by terminating an open-ended waveguiding structure with a conductive PEDOT: PSS thin film boundary. Variations in relative humidity affect the conductivity of the PEDOT: PSS thin film, which impact the reflection coefficient seen at the waveguide input. Therefore, by monitoring the S11 (dB) reflection coefficient parameter, changes in relative humidity can be detected. The resonators sensitivity to humidity was validated by observing strong humidity variations in an enclosed container. Varying humidity from 0% to 85% RH in 20% RH intervals resulted in an increase in resonant amplitude of 5.54 dB and a decrease in resonant frequency of 18.5 MHz. Five extreme humidity cycle measurements ranging between 0% and 85% RH were conducted to successfully verify the stability and repeatability of amplitude variation. Offering a robust structure, shielded from EMI, and featuring a biodegradable, organic component, the proposed device demonstrated a potential for humidity sensing applications in harsh environments (i.e. oil-sand industry), and paves the way for novel developments into the future integration of waveguides and organic materials.