Time dependence of electret potential during current limited charging on a small air gap and corona charging

Charge build-up of electret foils (fluoroethylene propylene) at current-limited charging in a small parallel air gap and at corona charging was measured. Calculation of charge build-up is impossible because the effective charging resistance of the air gap depends on the actual electret charge itself. Therefore the effective charging resistance for both charging methods was determined experimentally. The results of these measurements were used to calculate charging time functions. A comparison with the measured results gives an indication of the influence of leakage currents through the foil. It is shown that increasing electret potential reduces the air gap potential and leads to an increasing charging resistance