Differential Microwave Resonator Sensor for Real-Time Monitoring of Volatile Organic Compounds

In this work, a noninvasive microwave gas sensor suitable for accurate and real-time tracking of volatile organic compounds concentration is presented. The proposed differential sensor was comprised of two independent split-ring resonators in power splitter/combiner configuration to enhance the robustness of the sensor to changes in environmental parameters. The design was fabricated on a Rogers RT/duroid 5880 high-frequency substrate and operated at f
_s
= 5.12 GHz and f
_r
= 5.65 GHz, referring to the sensing and reference resonant frequencies, respectively. A thin layer of polydimethylsiloxane was used as an interface layer in the sensing resonator region with the strongest electric field to enable gas sensing with high sensitivity. The performance of the sensor was validated by introducing different volatile organic compounds, such as acetone, methanol, ethanol, and isopropyl alcohol. Time-based responses of the sensor demonstrated the capability of the sensor to monitor different concentrations of acetone vapor ranging from low, 387 to 1935 ppm, with the sensitivity of 0.02 mdB/ppm and high concentrations, 3878 to 62048 ppm, with sensitivity of 0.0125 mdB/ppm.