Minkowski-like fractal resonator-based dielectric sensor for estimating the complex permittivity of binary mixtures of ethanol, methanol and water

Abstract

A microwave dielectric sensor with defected ground structure including a Minkowski-like fractal resonator is proposed for estimating the complex permittivity of ethanol-water, methanol-water and ethanol-methanol mixtures. Positioned glass capillary tubes at the center of the metamaterial normal to the sensor surface, it is possible to see the fast impact of the shift of the transmission response for different liquid mixtures. The dimension of the proposed sensor is as small as 0.17λ0 × 0.17λ0 × 0.010λ0, where λ0 indicates the resonance wavelength in free-space. Complex permittivity of the liquid mixtures are estimated based on the shift of the resonance frequency and the magnitude of the S21 values by using a first-order model incorporating in characteristic matrix formulation. Estimated values indicated a very good agreement with the values in the reported studies. The sensitivity of the proposed sensor related to 0.07 μL effective sample volume is obtained to be 0.52 MHz/εr. The attractive features of the sensor, such as being label-free, reusable, easy to fabricate, practical, non-invasive and real-time, assure accurate determination of the complex permittivity of unknown liquid mixtures for applications in chemistry and medicine.