A novel electret rotational speed sensor

In this paper, a novel rotational speed sensor based on electrostatic field variation is designed, fabricated and tested. Unlike traditional magnetic and optical rotational speed sensors, the presented sensor has the merit of simple configuration, small size, and low cost. The principle of the device is introduced through the equivalent circuit and the finite element model of electrostatic field. A demo sensor is fabricated by typical micro fabrication processes. Inexpensive PTFE film is corona charged as electret material to form the sensing electrostatic field. Experiment results show that the resolution of sensor is better than 6 rpm when the gear is with module of 3 and teeth number of 15. The rotation direction of gear is denoted by the sign of phase difference between the signals from two parallel output electrodes.