A Transmission Mode Dielectric Resonator as a Displacement Sensor
A. V. Praveen Kumar, Premsai Regalla
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 (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> -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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">011+δ</sub> 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 S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> -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.