Noninvasive Reflective Microwave Sensor for Accurate Dielectric Material Characterization

This article presents the compact design of a reflective-type noninvasive microwave sensor using an omega-type slot in the ground plane for accurate unknown dielectric material (UDM) characterization. The sensor has one-port and operates in a reflective mode in microwave frequencies from 1.35 to 2.43 GHz. The sensing element is an omega-type slot in the ground plane. The electric field distribution around this slot interacts with the dielectric material (DM), and this interaction is utilized to characterize the unknown dielectric material (UDM). We have developed simple, computationally efficient analytical expressions by accounting for the air gap that provide accurate characterizations of unknown dielectric materials, achieving high accuracy with less than 2.57% error in predicting the real part of permittivity and 2.86% in predicting the imaginary part. By fabricating the sensor, its measured results verify the performance of the proposed sensor. The proposed sensor is suitable for characterizing both very thin and thick DMs, with potential applications in material science, industrial quality control, and biomedical sensing.