Circuit level modelling of a capacitive electric field sensor.

Abstract

This work addresses the problem of modelling an electric field detection device. The modelling of the device was approached from two different perspectives. The first approach entailed using the physics principles which describe the operation of the electric field sensor, the contemporary theory which is used to analyze electric field sensors and its limitations. The second approach used the theory which describes the capacitive interaction of a four-bodied system. A robust circuit model was derived using both cases and shown to be interchangeable under the assumptions that the electrodes generating the electric field are sufficiently large and far enough from the sensor. An experimental apparatus was designed which could verify this model. This apparatus was composed of two major parts, namely the field generation device, and the field detection system. Considerations in the construction of the field generation device involved uniformity of the generated field and a ground reference of the supply. This influenced the design of the sensor system. The sensor system had to operate as a free-body system with no ground reference connection in order for the uniformity of the generated field to remain intact. The differences between the model prediction for the expected measurements and the actual physical measurements are small. Reasons for this difference are presented and they include non-uniformities in the generated field and non-ideal characteristics of the components and devices used for the experiment. Possible improvements to the model and sensor device are discussed and they include installation of an attachment which allows maneuverability of the sensor, such as an insulated handle and a further derivation which would result in a more geometrically independent model.