A Split-Ring Resonator with Interdigitated Electrodes Aimed at the Dielectric Characterization of Liquid Mixtures (Invited Paper)

This paper is focused on a microwave sensor for the evaluation of the dielectric properties of binary liquid mixtures at RF/microwave frequencies. The sensor consists of a split ring resonator (SRR), built using the microstrip technology. Interdigitated electrodes are integrated into the ring as a sensing element for liquid detection. A proper extraction procedure has been proposed for the accurate evaluation of the resonant frequency of the developed prototype. The resonant extraction procedure is based on the analysis of the frequency-dependent behavior of the complex forward transmission coefficient (S21) that is accurately modeled locally around the resonance by using a fitting function. According to the tests carried out with water-isopropanol liquid mixtures at various volume fractions, the studied device is more sensitive than the more conventional SRR sensor.