A Microwave Sensor Based on Split Ring Resonators for Differential Measuring Permittivity

In this paper, a microwave sensor with the dual three-layer electrically small resonators based on split ring resonators (SRRs) is proposed to measure the permittivity of the small sample of unknown materials. By virtue of SRRs, the single resonator has merits of the compact size $(0.052 \lambda_{0} $$ \times 0.052 \lambda_{0} $), high quality factor (Q) value and ultra-low radiation. And combined with the design of the differential measurement structure, this sensor can greatly compensate the interference from the environment. Different from the sensor with single resonator using reflection coefficients, the measurement process is greatly simplified with transmission coefficients by the proposed sensor.