A Novel Microwave Sensor Based on Coupled Step Impedance Line and Complementary Split Ring Resonator Structure for Liquid Characterization

This letter presents a microwave sensor for characterizing the dielectric constant and loss tangent of liquid samples. The proposed microwave sensor consists of a coupled step impedance line (CSIL) loaded on a complementary split ring resonator (CSRR). The CSIL-CSRR sensor has a simple fabrication process and is etched on a low-cost substrate (FR4) with a size of 40 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $</tex-math> </inline-formula> 20 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $</tex-math> </inline-formula> 0.8 mm. A linear polydimethylsiloxane (PDMS) microfluidic channel is placed at the maximum electric field of CSRR, and the sensor has achieved a high average sensitivity of 1.13%. The polynomial fitting determines the dielectric constant and the loss tangent of liquid samples. The experimental results demonstrate that the designed sensor has the advantages of low cost, high sensitivity, and accuracy.