The EL2 Electret Transmitter: Technology Development

The first electrets were made by the Japanese physicist Eguchi in 1919 using carnauba wax.1 Subsequently, other thick organic waxes were used in early electret microphones such as the World War II Japanese field equipment and the commercially offered "No-voltage Velotron."2 However, these electrets suffered from poor electrical stability. Fluoroplastic polymer materials such as Teflon* have excellent electrical characteristics even after exposure to high temperature and high humidity conditions. The availability of such materials, along with a better understanding of the technology, has given rise to reliable transducers based on electrets. Polymer film electret transducers, developed by G. M. Sessler and J. E. West of Bell Laboratories in the early 1960s, ' have many technical advantages. For a given acoustic input, electret microphones generate the highest electrical signal of any type of microphone except the carbon transmitter. The flatter response of an electret microphone * Registered trademark of E. I. DuPont de Nemours. 745