Design and development of a microwave sensor for the selective detection of hydroxyl organic compounds

Abstract This research presents the design and development of a microwave sensor capable of detecting and distinguishing hydroxylated organic compounds (HOCs), namely water, methanol, ethanol, and propanol. The work analyzes the physical mechanisms that govern the sensitivity and detectability of these liquids in the microwave range. Differences in sensor response are linked to variations in molecular characteristics such as dipole moment, microwave absorption, and refractive index. Unlike approaches that rely solely on experimentation, this study connects microwave behavior to fundamental molecular properties, enabling a predictive, physics-based understanding of HOC detection. Molecular polarization and relaxation models were combined with experimental observations to explain how these compounds interact with microwave fields. A metamaterial-based sensing cell was designed, simulated, and experimentally validated. Results demonstrate that the sensor effectively identifies hydroxyl compounds with high sensitivity. Water produced the highest resonance-frequency shift (0.76 GHz), followed by methanol (0.7 GHz), while ethanol and propanol showed similar shifts around 0.35–0.37 GHz. Propanol achieved a quality factor of 10.82 in the 12–17 GHz range. The sensor also reached a frequency detection resolution of 6.75 MHz and showed strong amplitude sensitivity, highest for water at 10.66 dB.