Simultaneous measurement of thickness and permittivity using microwave resonator-based planar sensor

This article presents a microwave sensor for dielectric characterization and thickness measurement of solid materials. The proposed sensor incorporates an interdigital capacitor (IDC) and a split-ring resonator to create an intense electric field, allowing it to efficiently interact with a sensing material. IDC parameters such as width and gap of the finger and length and gap of the electrode are optimized to enhance the material characterization sensitivity. The microwave resonant sensor structure is designed to operate at 1.8 GHz, making it applicable to measure permittivity and thickness of solid materials. The proximity of the material to be sensed influences the field distribution of the developed sensor, which, in turn, enables the simultaneous measurement of permittivity and thickness based on variations in a resonant frequency. Experimental results reveal that the highest sensitivity value reaches 113.4 MHz/mm and 47.6 MHz/∆ε_r for permittivity of the solids, when the thickness is between 0 and 1 mm. Furthermore, the developed sensor demonstrates a high accuracy (99.6%) and adequate accuracy (87.6%) for both real and imaginary permittivity, respectively. The developed microwave resonant sensor also shows excellent resolution for permittivity (0.04716) and thickness (0.1314), validating its high-performance for measuring permittivity and thickness for various solids.