Recent developments in the pressure wave propagation method

Performing measurements is an essential part of understanding physical phenomena. Hence, numerous measuring techniques have been developed to study space charge build-up in dielectrics. This macroscopic accumulation of charge modifies the electric field and can lead to aging and premature failure of electrical insulation. On the other hand, charge accumulation is essential to the operation of devices such as electret- or piezoelectric-based sensors. It is therefore essential to study charge build-up in order to design insulating materials in which excessive charge does not accumulate, or electrets in which a sufficiently large amount of charge accumulates to ensure adequate device operation, and the stability of that charge in time is sufficient to ensure an acceptable device life-time. This paper focuses on the measurement method using a pressure wave to perturb the charges. That method is commonly called the pressure-wave-propagation (PWP) method. A pressure wave enters the sample through one of its interfaces. As it travels through the material at the velocity of sound, the charges encountered are mechanically displaced.