A Novel Microwave Sensor with Enhanced Coupling to Measure Dielectric Constants of Solid Materials

A Complementary Split-Ring Resonators (CSRR) planar microwave sensor loaded with Interdigital Electrode (IDE) is proposed to measure complex dielectric constants of solid materials. The sensor consists of a CSRR-IDE structure etched on the bottom layer of a 1 mm F4B substrate with a metal through-hole between a microstrip line and the resonant structure. The IDE structure enhances electric fields to achieve high-sensitivity measurement. The metal through hole enhances the coupling and weakens the relationship between |S21| and the real part of the complex dielectric constant, improving the accuracy of the imaginary part measurement. The experimental results show that the proposed sensor has a high sensitivity of 9.6%, and the measurement errors of the real and imaginary parts of the complex dielectric constant are 1.3% and 3.0%, respectively. The microwave sensor proposed in this paper achieves better results than most conventional sensors with similar structures.