Residual fields characterization with a virtual space charge model

The purpose of this work is to adopt a new procedure which consists in choosing a simple virtual charge distribution model. We have developed this model in association with an evolution of the LIMM method, called FLIMM (Focused Laser Intensity Modulation Method). The model has been applied to study the residual field after the application of an incident field to three polyethylene-based dielectrics samples. Analytical analysis shows that the pyroelectric current I(f) records a maximum I/sub M/ at the frequency f/sub M/. This frequency varies with the sample thickness but the IM value is independent of this one. I. was estimated from the set of data measured with an incident beam on each side of the sample. With these two IM values one can calculate the space charge profile and then the corresponding residual internal field level. In LDPE materials the residual field is approximately 1 kV/mm, whereas for XLPE and LDPE with antioxidant samples it is four and ten times, respectively, more important. Therefore, it was estimated that in this case, the LDPE sample seems to be more insensitive to the aging process linked to space charge characteristics.