Open Complementary Split-Ring Resonator Sensor for Dropping-Based Liquid Dielectric Characterization

Abstract

A microwave sensor with a coplanar waveguide semilumped meander open complementary split-ring resonator (MOCSRR) is proposed to analyze the dielectric properties of liquid. The proposed method operates at subgigahertz frequencies and uses a small volume of liquid (>0.08 mL) on a substrate-integrated slot container. A resonance reflection coefficient notch frequency and its magnitude in decibels are observed for complex permittivity ( $\varepsilon'+j \varepsilon $ ”) characterization. A strong electric field distributed on the edge of the designed MOCSRR slot provides a sensitive compact area to detect small variations in the liquid sample or concentration. Operations need not be constrained to micropipette operations or microfluidic channel fabrication. A specific volume of the sample liquid must be dropped in the detection zone to analyze complex permittivity. To test the proposed methods, binary mixtures of ethanol and water were loaded, and a 58.7 MHz shift in resonant frequency and a variation of 6.77 dB were attributed to a complex permittivity perturbation phenomenon when ethanol concentration was varied from 0% to 100%. Different concentrations of ethanol and liquid were evaluated and analyzed. The proposed sensor exhibited repeatability and easy operation in detecting liquids with high relative permittivity, such as water and lossy liquids.