Simultaneous space charge and TSDC measurements on polarized polymer

The present work is concerned with the development of an experimental device for simultaneous measurements of space charge profiles and thermally stimulated depolarization currents (TSDC) on polymer sheets. Space charge measurements are nowadays realized by nondestructive methods but TSDC are still a destructive one. However coupling the results from the two techniques allows to watch the evolution of the charges and finally their disappearance. The space charge measurement is based on the current response to a low frequency thermal wave applied on the sample by using the alternating thermal wave method (ATWM). Basically the TSDC require to heat the sample slowly and linearly. So, a controlled thermo-electrical module is used to generate the appropriate thermal profile and a temperature cycle including both the linear temperature rises and low frequency thermal waves around a chosen temperature level is generated. Both measurements are made on one and the same sample without handling it during the procedure. The space charge measurement accuracy is improved by varying the thermal wave frequencies from large to short wavelengths. The purpose is to scan successively the different layers in the sample. The use of an adapted mathematical model for the electric field representation and space charge distribution is helpful for the signal processing. Experimental results obtained on polymer materials are given and discussed to illustrate the change in density and position of the remaining space charge due to the TSDC effect