Metamaterial-based sensor with a polycarbonate substrate for sensing the permittivity of alcoholic liquids in a WR-229 waveguide

The design, modeling and experimental confirmation of a metamaterial-based dielectric sensor on a 0.012 lambda(0)-thick (lambda(0) denoting middle free-space excitation wavelength) transparent and flexible substrate is reported at microwave frequencies. A handcrafted hard foam is implemented in front of the meta material inside the WR-229 waveguide to be filled with liquid mixtures in order to predict the complex permittivity. The variation of the volume ratio of the mixture caused a significant shift in the resonance frequencies. A first-order model between the resonance characteristics and complex permittivity is employed to determine the complex permittivity of ethanol-water and methanol-water mixtures at various volume ratios. The remarkable agreement between the predicted complex permittivity values from the measurement and the standardized values from the literature proves the validity of the employed model. The proposed sensor renders a practical, cost-effective and non-contact solution for determining the properties of unknown liquid mixtures. (c) 2020 Elsevier B.V. All rights reserved.