Double Split-Ring Resonator for Dielectric Constant Measurement of Solids and Liquids

This study proposes a 2.45-GHz double split-ring resonator for measuring the dielectric constant in both solids and liquids. Two concentric rectangular rings with asymmetric splits are used in the proposed resonator to achieve a high-quality factor for increasing the sensitivity to resonant frequency changes. The dielectric constants of solids and liquids are obtained based on quadratic polynomial equations with different coefficients, obtained by measuring the frequency shift of reference materials through the maximum return loss of the resonator, which is implemented on an FR4 PCB. The experimental results for the dielectric constants of silicon and rubber obtained using the resonator show errors of 5.92% and 6.81%, respectively, compared with the reference values from certified equipment. The measurement results for liquid samples with different concentrations of ethanol diluted in deionized water indicate a 2.59% error in the estimated dielectric constant. The sensitivities of the proposed resonator were measured to be 2.58% in solids and 0.30% in liquids.