TABLE OF CONTENTS The electric fields generated by lightning flashes can be measured either using a field mill [223] or a flat plate (or a vertical whip) antenna [132,224], each method having its advantages and disadvantages. The conventional method used to measure the magnetic field is the crossed loop antenna [225,226,181]. The following is a brief description of these techniques.
The principle of operation of the field mill is illustrated in Figure 4.38. The plate marked S is the detector which is placed in a background electric field assumed for the moment to be uniform and steady. The plate marked M is a movable electrode which is at ground potential. This electrode can be moved back and forth in front of the sensing plate either exposing it to or screening it from the background electric field. Consider the situation shown in the Figure 4.38 in which the sensing plate is completely exposed to the electric field. The electric field lines end on the plate and the total charge induced on the sensing plate is A e 0E where A is the area of the plate. Assume that the plate M is moved back and forth in front of the sensing plate. This will change the exposed area of the sensing plate as a function of time and since the charge induced on the plate is a function of the exposed area of the sensing...
