Improved Planar Resonant RF Sensor for Retrieval of Permittivity and Permeability of Materials

In this paper, the improved planar resonant sensors based on the generalized split ring resonator (SRR) configuration are proposed for the permittivity and the permeability testing of magneto-dielectric samples. It is observed that the proposed inter-digital capacitor-based SRR and the meandered line-based SRR provide better sensitivity for dielectric and magnetic measurement, respectively, when compared with the standard SRR-based microwave sensors. Both the sensors are first modeled under unloaded condition, using the full wave electromagnetic solver, the CST Microwave Studio, in order to ensure their operating frequency range near 2.45 GHz of industrial, scientific and medical band. In the next step, the numerical simulation of these sensors is carried out by loading them with a number of reference materials in order to develop empirical model for the determination of permittivity and permeability of test samples. Additionally, the equivalent circuit models of these sensors are obtained using the Advanced Design System circuit simulator and results are compared with the numerical simulation. All the sensors are designed and fabricated on 1.27-mm-thick RT/Duroid 6006 substrate, and testing is carried out using the network analyzer. A number of standard dielectric and magneto-dielectric samples are tested using the proposed scheme in order to retrieve their permittivity and permeability values. The measured data of each sample are in good match with the corresponding reference values available in literature having a typical error of less than 6%.