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 S
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(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.