A Highly Sensitive Planar Microwave Sensor for Detecting Direction and Angle of Rotation

This article presents a technique based on a modified complementary split-ring resonator (CSRR) to detect angular displacement and direction of rotation with high resolution and sensitivity over a wide dynamic range. The proposed microwave planar sensor takes advantage of the asymmetry of the sensor geometry and measures the angle of rotation in terms of the change in the relative phase of the reflection coefficients. The sensor consists of a movable modified CSRR (the rotor) and a microstrip line with a circular defect in the ground plane (the stator). By selecting the substrate material and the rotor thickness, the sensor can be designed to work at different operating frequencies. A theoretical model of the sensor is proposed and is followed by a detailed numerical analysis involving equivalent circuit simulations, full-wave computations, and measurement results. Using positioning error estimation and air-gap analysis, a technique based on phase-change measurements is found to be better than those based on magnitude measurements alone. The maximum sensitivity for measuring the angular rotation is found to be a 4.3° change in the relative phase of the reflection coefficient per 1° of rotation. The sensor has an angular measurement range from -90° to +90°. The sensor - a stator fabricated on a 0.5-mm-thick Rogers RT5880 substrate and three rotors fabricated on a 1.5-mm-thick Rogers RT5880, a 1-mm-thick FR4, and a 0.5-mm-thick Rogers RT5880 - can effectively detect the direction of rotation, measure the angle of rotation and angular velocity with reasonable accuracy.