Non-destructive methods for space charge distribution measurements: what are the differences?

For more than 25 years, various techniques have been introduced for the nondestructive measurement of the space charge distribution in solid dielectrics. All these techniques can be classified into a set of three methods: (i) the thermal method, (ii) the pressure-wave-propagation method and (iii) the electro-acoustic method. Despite their apparent differences they are based on the same physical idea: the perturbation of the equilibrium between electrostatic and elastic forces in the material induces a response, either electrical or mechanical, which can be analyzed. In this paper, we demonstrate that the information on the material contained in the response is identical whatever the method used. As a consequence the differences between methods stand only in the nature of the perturbation and its physical properties.