ANALYSIS OF CAPACITANCE AND LINEARITY OF GAUGE CHARACTERISTIC OF COPLANAR MICRO-DISPLACEMENT SENSOR

Abstract- Capacitive sensors can be applied for measuring different kind of non-electrical quantities, such as geometrical dimensions of subjects, thickness of films, displacement and vibration of grounded surfaces, position of the object and others. Existing three-electrode micro-displacement sensors, made in the shape of flat capacitor geometry, do have high values of sensitivity, but they also have notable non-linear behaviour over their whole gauge characteristics. A three-electrode coplanar sensor, subject of this paper, can be designed by calculation in such a way, that its gauge characteristic does have relatively large section with relative error of the non-linearity of its gauge characteristic equals 0,051 % within certain ratio of sensor dimensions. The method of direct field-strength determination, in combination with the method of conformal mapping, is used for a precise analytical calculation of the sensor capacitance. Analysis of the capacitance and special cases of sensor design has been discussed