Sensitivity Enhancement Enabled by Strongly Coupled DG-IDC Structure With CSRR for Permittivity Detection

The sensitivity of microwave sensors can be low due to intrinsic factors, such as substrate losses, insufficient field confinement, or weak electromagnetic interaction with the sample. This article introduces a highly sensitive microwave sensor by coupling a defected ground interdigitated capacitor (DG-IDC) structure with a pentagonal complementary split-ring resonator (CSRR) for precise permittivity characterization of chemical samples. The sensor provides a stronger electric-field concentration due to the coupling of the two resonators, enhancing its sensitivity and improving the accuracy of permittivity measurements. The interdigital capacitor (IDC) serves as the primary sensing element, demonstrating a high normalized sensitivity of 3.5%. Eleven chemical liquids were used to validate the sensor’s performance and potential. The extraction of the permittivity of unknown samples is then carried out using curve fitting technique involving the scattering parameters. The comparison of some of the recent works based on sensitivity and other parameters has been further included to validate the performance of the sensor. In comparison with the literature values, the DG-IDC CSRR sensor, when measured with a vector network analyzer (VNA), exhibits errors of 3.2% for $\varepsilon '$ and 3.12% for $\varepsilon "$ , respectively.