Planar Microwave Sensor Using Interleaved Cascaded Symmetric SRR for Fluidic Analysis

This article presents a planar microwave sensor utilizing interleaved cascaded symmetric split-ring resonators (Sym-SRRs) to accurately detect liquid mixtures, such as water–ethanol and water–methanol, with high sensitivity. The proposed sensor employs highly localized split-ring resonator (SRR) structures that confine strong electric fields, allowing for the precise monitoring of liquid mixture samples through observed frequency shifts. The Sym-SRRs resonate at frequencies of 2.4 and 3.32 GHz, facilitating dual-mode sensing and improving the detection of minute variations in fluidic samples. In addition, the design incorporates a tapered transmission line to optimize impedance transition from the microstrip feed to the resonator, thereby enhancing sensitivity and minimizing signal losses. The tapered transmission line enhances power transfer, minimizes reflections, and interacts optimally with the material under test (MUT), resulting in sharper resonance peaks and more precise frequency shifts. The geometric design of the sensor is optimized to generate a uniform electric field, ensuring effective interaction with the MUT for accurate detection. By loading the sensor with various test samples, the resulting measured shifts in the resonant frequency yield high sensitivity for methanol (4.81 MHz/ $\varepsilon _{r}$ ) and ethanol (3.96 MHz/ $\varepsilon _{r}$ ). Through experimental validation, a fabricated prototype of the bare sensor has shown a good correlation with theoretical predictions. The findings validate the sensor’s performance in accurately characterizing the dielectric properties of fluidic media. By loading the sensor with various test samples, we observed significant shifts in the resonant frequency, demonstrating high sensitivity for methanol and ethanol. These findings confirm the sensor’s effectiveness in accurately characterizing the dielectric properties of fluidic media.