Design of coplanar dual band resonator sensor for microwave characterization of dispersive liquids

A dual band coplanar resonator sensor for microwave characterization of common dispersive liquids is proposed. The proposed technique provides single step dielectric measurement of dispersive liquids at two designated microwave frequencies. For this purpose, two resonators etched on the central conductor of the coplanar waveguide are designed to resonate at industrial, scientific and medical (ISM) bands of frequency, 2.45 GHz and 5.85 GHz, respectively. For the accurate characterization of the material under test, a numerical model of the proposed sensor is developed which provides the real part of relative permittivity (εr) in terms of the resonant frequency corresponding to each resonator structure. The proposed sensor is fabricated on a 1.6 mm thick FR4 substrate, and its accuracy is experimentally verified by testing a number of standard liquids and comparing the measured data their values available in the literature.