Next-Generation Passive Sensing of Hazardous Liquid Dispersion Events Using Frequency-Selective Surfaces

Timely detection of hazardous liquid releases is critical in high-risk environments, such as research laboratories and industrial facilities, where proactive safety measures are essential to prevent hazardous incidents. This letter introduces a battery-free, passive frequency-selective surface (FSS) structure designed for wireless, real-time detection of liquid spills and evaporation in hazardous environments. The FSS structure comprises an array of 25 × 25 modified ring resonator cells fabricated on a 0.25-mm-thick substrate operating at the resonant frequency of ∼7.2 GHz. The FSS sensor is wirelessly interrogated at a distance of approximately 90 cm, beyond the near-field zone of the horn antenna. Upon interaction with the incident wave from the transceiver antenna, the renormalized reflection coefficient of the sensor is measured, exhibiting a resonant frequency of 7.2 GHz in its unexposed state. The sensor's response to various hazardous liquids, including ethanol, methanol, isopropyl alcohol (IPA), and acetone, was evaluated through both simulation and experimental measurements, revealing significant suppression of the resonant profile in all cases due to the high dielectric loss and permittivity of the materials. Time-resolved measurements conducted over three cycles of liquid exposure and evaporation confirmed the sensor's repeatable and reproducible response. A 200 MHz change of the S₁₁ minimum magnitude's frequency was observed in response to a 4 mL IPA release covering the FSS surface. These findings demonstrate the sensor's potential for effective hazardous liquid monitoring in challenging environments, enabling rapid hazard identification without reliance on active electronics, enhancing safety in laboratory settings.