Production and Charge Decay of Film Electrets

The object of this work has been to obtain charged dielectric films, electrets, that retain their charge over periods of years when left open circuited. Such films are receiving increasing attention because of their potential use in practical devices such as condenser microphones, electrostatic recorders, air filters, etc. Procedures have been devised to form highly charged thin films and to measure their decay rates. Charge decay comparisons are made among different materials at various temperatures, charged in different ways. A procedure is developed that enables long lifetimes of electrets at room temperature to be predicted by extrapolating short charge decay times at elevated temperatures. A number of materials are identified as suitable for very longlived electrets.