High-Sensitivity CPW Microwave Sensor Based on OCSRR and IDE Structure for Permittivity Characterization

This article presents a high sensitivity microwave sensor based on coplanar waveguide (CPW) for measuring the permittivity of solid materials. It is developed from the open complementary split ring resonator (OCSRR), which is sensitive to the dielectric characteristics of the material under test (MUT). To further improve the sensitivity, interdigital electrodes (IDEs) are added on both sides of the resonator. By analyzing the equivalent circuit, the IDE increases the equivalent capacitance inside the resonator, the positive effect of IDE on the sensitivity is proved. Different MUTs with known permittivity are loaded into the sensing region, the resonance frequency is extracted, and the fitting equation is constructed to retrieve the permittivity. The proposed sensor is fabricated and tested, and the consistency between measurement and simulation results is good, the maximum error and the sensitivity are 1.35% and 5.51%, respectively, which ensures accurate and effective detection in the practical application.