Electro acoustical probing of space charge and dipole polarization profiles in polymer dielectrics for electret and electrical insulation applications Electrets are dielectrics with quasi permanent electric charge and or dipoles sometimes can be regarded as an electric analogy to a magnet. Since the discovery of the excellent charge retention capacity of poly(tetrafluoro ethylene) and the invention of the electret microphone electrets have grown out of a scientific curiosity to an important application both in science and technology. The history of electret research goes hand in hand with the quest for new materials with better capacity at charge and or dipole retention. To be useful electrets normally have to be charged poled to render them electro active. This process involves electric charge deposition and or electric dipole orientation within the dielectrics ` surfaces and bulk. Knowledge of the spatial distribution of electric charge and or dipole polarization after their deposition and subsequent decay is crucial in the task to improve their stability in the dielectrics. Likewise for dielectrics used in electrical insulation applications there are also needs for ...