Dual-band measurement of complex permittivity in a microwave waveguide with a flexible, thin and sensitive metamaterial-based sensor

Abstract

A dual-band metamaterial-based sensor is proposed to determine the complex dielectric constant of ethanol-methanol mixtures. The original sensor structure incorporates one connected dual H-shaped slot resonators at the center and one H-shaped slot resonator at the left and right sides of a rectangular copper patch to provide two distinct resonance frequencies. Polycarbonate is chosen as the substrate material due to its lightness, flexibility, robustness and transparency. Full-wave simulations of electric field distributions reveal that the dual resonances at 3.7 GHz and 4.6 GHz stem from different parts of the metamaterial. Measurements are carried out with a WR-229 microwave waveguide and the electromagnetic simulation results are confirmed with good agreement. A first-order equation that relates the complex dielectric constant to the shift of resonance frequency and peak attenuation is used to determine the complex dielectric constant of ethanol-methanol mixtures in the vicinity of 3.3 GHz and 4.4 GHz frequencies. A good agreement with the literature values is obtained validating the accuracy of the used model. Experimental results revealed that the frequency detection resolution and sensitivity parameter values of the proposed sensor are 25.3 MHz and 0.73% for the lower-frequency band and 9.6 MHz and 0.22% for the higher-frequency band, respectively. In addition to being able to operate at dual frequencies, the proposed metamaterial-based sensor has high sensitivities for the two resonance frequencies. Moreover, the advantages of the proposed sensor, as being electrically-small, flexible, noncontact and reusable, provide a good option for discrimination of binary liquid mixtures at multiple frequencies.