Charge density limits in polymer film electrets

Corona charging process is widely used to produce the electret state in materials that include polymers. Polymer films may be charged in air by sweeping the surface with a linear array of corona triode electrodes. We report the development of a constant current total area charging system and our production of electrets on polymers films of ETFE (Ethylenetetrafluoroethylene), PFA (Tetrafluoropropylene-per-fluoromethoxethylene) and FEP (Tetrafluoroethylene-hexa-fluoropropylene). The corona charging and charge reading experimental setups are described. We have also produced electrets in these materials with MeV ion beams and consider for the first time important phenomena that occur in the high fields that are produced near surface of charged films especially near the rear surface that may be close to a ground plane.