High-Sensitivity Microwave Sensor Based on Slot Structures for Permittivity Characterization

Planar microwave sensors, known for their low cost and simple fabrication, are widely employed for characterizing the permittivity of materials. In this study, we propose two high-sensitivity sensors for planar material permittivity characterization based on improved single-ring complementary split-ring resonator (CSRR) structures. The first sensor incorporates a spiral-shaped slot structure (SS-SS), while the second sensor employs an interdigital-capacitor-shaped slot structure (IDCS-SS). Each sensor designs significantly enhance the electric field in the sensing region, maximizing the interaction between the tested sample and the sensor’s coupling field at the resonance frequency. The proposed sensors, along with the traditional circular dual-ring complementary split ring resonator (DR-CSRR), were loaded with identical material under test (MUT) spanning a permittivity range of 1 to 10. The sensitivity of the sensors was quantitatively compared by experimentally measuring the resonance frequency along with the variation rate of permittivity. The results indicate that compared to the traditional circular DR-CSRR sensor, both proposed sensor structures exhibit higher sensitivity, with the IDCS-SS sensor achieving the greatest improvement at 1.57 times.