High-Sensitivity Accurate Characterization of Complex Permittivity Using Inter-digital Capacitor-Based Planar Microwave Sensor

An interdigital capacitor (IDC)-based planar microwave sensor is developed for characterizing the complex permittivity of solid materials with an enhanced sensitivity. To implement the proposed microwave permittivity sensor, a parallel combination of an IDC and a wide dual gap split-ring resonator (SRR) was etched on the ground layer and coupled with a transmission line on the opposite conductive layer of a RF-35 substrate. The main advantage of the proposed sensor layout lies in the generation of a high-intensity coupled E-field, which enables an effective interaction between the sensing field and the sensed material, thereby generating a high-sensitivity. The experimental results revealed that our developed sensor exhibits an improvement in the field of resolution (0.13 GHz) and sensitivity (3.39^%). In addition, the developed sensor indicated a high-accuracy (up to 99.6^%) and an acceptable accuracy (87.6^%) for the real and imaginary parts of the permittivity, respectively. Besides, the numerically modelled and the measured values of permittivity were compared and analyzed to validate our proposed microwave complex permittivity characterization method.