A Transmission Mode Dielectric Resonator as a Displacement Sensor

Abstract

This paper proposes a displacement sensor using a cylindrical dielectric resonator (DR) coupled to a pair of parallel, open-ended microstrip lines. This circuit enables displacement sensing through the measurement of the transmission coefficient ( $\text{S}_{{21}}$ -parameter) between the microstrip lines. The sensor operates at a fixed frequency of ~ 3.7 GHz, which is the resonant frequency of the DR, excited in the TE $_{{{011}+\delta }}$ mode, by the coupling circuit. The displacement of the DR relative to the open ends of the microstrip lines changes the coupling coefficient ( ${k}$ ) between the DR and the lines, resulting a change in the measured $\text{S}_{{21}}$ -parameter. In simulations, the variation of ${k}$ with displacement is found to be nearly linear in the range of 1–10 mm. To demonstrate the sensor operation, a laboratory prototype of the sensor is fabricated and experimentally characterized using two different setups. The first setup uses a standard vector network analyzer (VNA), while the second setup has a less costly system comprising a signal generator and a power meter. Sensitivity plots ( ${k}$ vs displacement) generated from both the methods show good agreement with the simulated plot, demonstrating a linear range of 2–8 mm.