A Highly Sensitive Liquid Sensor Based on CSRR-SS and Interdigitated Structure

In this letter, a high-sensitivity microwave sensor based on a complementary split-ring resonator (CSRR) is proposed. The dual interdigital electrodes (IDEs) are loaded in the CSRR, and the serrated structure (SS) is inserted into the IDE, which can further improve the electric field aggregation ability and generate strong electric field constraints. Sample containers made of acrylonitrile-butadiene–styrene (ABS) plastic are placed throughout the CSRR to capture the largest electric field changes. The equivalent circuit model is established and analyzed. The curves of complex permittivity versus resonant frequency and peak attenuation are fit. The fit curve is tested using an ethanol-water solution and verified using the methanol-water solution. The results show that the measured complex permittivity values are highly consistent with the complex permittivity values given in the literature. The average sensitivity of the proposed sensor is as high as 2.28%. The average errors of the real and imaginary parts of the complex permittivity are 1.45% and 2.16%, respectively.