Dynamic models of certain DC and low frequency electric field sensors

The covering fieldmill is used for measuring electrical DC field, and its theoretical treatment in the literature is not detailed. The authors have developed an unusual model that enables a comprehensive treatment of the sensor. It is based on a viewpoint borrowed from antenna theory. The authors regard the sensor as a very small antenna coupled to the field sources by a small series capacitance. They show, however, that the actual coupling of the sensing system to the sources of the measured field is due to the variation in time of the latter capacitance. One method for evaluating the system is to use a steady state approach that enables the output voltage of the sensor to be related to the field. Another approach uses the system differential equation to simulate the performance via MATLAB. The results of both methods are in complete agreement. Furthermore, the authors show that the results conform with those obtained by the approaches of other authors, regarding the system as periodically chopping the displacement-vector-flux. An interesting outcome of the approach is the proof that the output power of the device is due to the mechanical mover of the fieldmill, and is not supplied by the sources of the measured field