Highly Sensitive Bi-Transmission Line-based Sensors for Liquid Characterization

This work presents highly sensitive resonant sensors for liquid characterization. The proposed sensors combine multi-mode coplanar waveguide and microstrip lines in a double-layer PCB, one layer constitutes the feed while the other forms the resonator (sensing element), with a paper superstrate. Equivalent circuit models are derived, which enables the understanding of the behavior of the sensors as lossy transmission lines and, consequently, predicts the changes in the response due to different concentrations of sodium chloride. A prototype was manufactured, and the measurement results are in very good agreement with the EM simulations around the operating frequency (1.6 GHz). The sensor achieves a sensitivity of 4.2 dB between 0.01 and 0.1 mol/L.