Transient voltage and injection in insulators

The authors discuss `local´ models applicable to thin samples in which the injected charge density exceeds the intrinsic one. Experimental results are presented on such `electrically inhomogeneous´ samples. The experiment was performed on a Kapton sample in a space simulation chamber. The constant mobility hypothesis is valid provided that the initial field across the sample does not exceed some critical value. Comparison of the decay curves for bulk and surface charges permits an evaluation of the injection coefficient and its evolution. This in turn may help to improve the understanding of injection processes in dielectric materials, and to assess the effects of surface treatments