Accurate extraction method and analysis of the resonance parameters of a differential SRR-based RF sensor

This paper presents a differential split-ring resonator sensor, designed for the analysis of small volumes around 20 µl of liquid. One resonator is filled with a reference liquid while the other contains the liquid under test. Although the differential configuration reduces the influence of environmental parameters, it can lead to resonance overlap when the dielectric properties of the two liquids are close to each other. To overcome this limitation, a post-processing method based on Lorentzian fitting is used to accurately extract resonance parameters such as frequency and width, even when the resonances strongly overlap. The method is validated through experiments with water–ethanol mixtures of different concentrations. This shows excellent agreement between measured and calculated values. Eigenmode simulations are also performed to analyze field distributions, providing additional insight into resonance behavior. The proposed approach offers a reliable and general methodology for the analysis of differential resonant sensors.