Influence of divergent electric fields on space-charge distribution measurements by elastic methods

Abstract

Elastic methods are presently being used to study the space charge distributions in insulators. They are limited in their interpretation to simple geometries whereas real systems often involve complex structures such as the case for divergent electric field regions. The authors propose a general theory for the interpretation of the data obtained by the pressure-wave-propagation method and the electro-acoustic method. This model makes it possible to study crystals, isotropic solids, or fluid samples of any geometry, containing charge and dipole distributions and also submitted to divergent electric fields such as produced by treeing or defects. A comparison is made with existing models in the case of simple geometries, such as planar or coaxial. It is shown that classical results are justified in the case of a planar sample. However, a correction has to be introduced in more complex geometries, even in coaxial ones. Indeed, some experiments show the associated difference. The model also emphasizes the similarities of the two elastic methods of measurement both for the analytical and experimental point of view.