Although the principles of signal generation in these detectors are very well known, the detailed simulation of detector processes like e.g. space charge effects and rate effects in RPCs requires the explicit knowledge of the Green's Functions for the given detector geometry. We will review open questions in this area and show some analytical models and techniques that can be used to answer them. In particular, a quasi-static theory for weakly conducting media is presented; this is used to discuss the relevant time constants and to show the influence of the conductivity on the generation and the shape of the signal.