Design and experimental validation of a hexagonal split-ring resonator sensor formicrowave dielectric characterization of liquids

Abstract

This research work has presented a compact microwave sensor based on a hexagonal split-ring resonator (H-SRR) useful for dielectric (ε) characterization of liquid samples. The proposed microwave sensor has consisted of three concentric hexagonal rings, which are etched on a low-cost FR4 substrate with a two-port resonant structure. The sensing principle depends upon the perturbation of the resonant characteristics when a liquid sample has been introduced into the high electric-field region made of H-SRR of the resonator. The sensor has been designed using 3D full-wave electromagnetic simulation and has been fabricated on a single-layer FR4 substrate. Experimental validation has been carried out using a low-cost LibreVNA and a commercial Rohde & Schwarz vector network analyzer. In the measurement results, noticeable shifts in the resonant frequency of the measured S-parameter responses have been observed for different liquid samples. A MATLAB-based matrix method has been used to estimate the complex permittivity (ε′−jε′′) from measured S-parameters data. The extracted dielectric properties have shown good agreement with reported literature values, thereby demonstrating the effectiveness of the proposed sensing approach.