Miniature Gas Sensor and Sensor Array With Single- and Dual-Mode RF Dielectric Resonators

RF resonant polymer-coated sensors are a proven effective approach to enhance the sensitivity of polymeric sensing materials. However, the level of sensitivity improvement offered by an RF resonant sensor is directly proportional to the quality factor (Q) of the resonator—the larger the Q-factor, the higher the sensitivity enhancement is. This paper first presents a miniature polymer-based dielectric resonant (DR) sensor design operated at its fundamental mode (TEH) at 24 GHz demonstrating a measured Q-factor of 3820. The sensor is coated with a (per)nigraniline-based conductive sensing material for detections of acetone and isopropanol volatile organic compounds and has a small footprint of $4.5\,\,\text {mm} \times 4.5$ mm. The sensor has demonstrated a low-ppm detection capability for acetone and isopropanol gases with a response onset time less than 15 s. This paper further demonstrates a novel airborne carcinogenic agent sensor array implemented with a single dielectric resonator operating in dual mode (HEH) at 27 GHz. It is functionalized by placing two carcinogen sensing materials—polyhydroxyethyl-methacrylate (PHM) and fluoroalcohol polysiloxanes (FAPS)—at the optimal geometrical locations on the DR, such that the polymers would independently affect the resonant frequencies of the two orthogonal HEH degenerate modes. By monitoring $\Delta f_{0}$ and $\Delta S_{11}$ near $f_{0,\mathrm {HEH1}}$ and $f_{0,\mathrm {HEH2}}$ , both the concentrations and the response signatures of the airborne carcinogenic agents can be detected. The measurement results indicate that the HEH-mode two-sensor array carrying PHM and FAPS is successful in identifying and differentiating two carcinogenic agents—dioxane and benzene—and their respective concentrations.