4. Electret microphone

4.1 Electrostatic properties of certain insulators

In 1839, following various experimental demonstrations of the electrostatic attraction of certain waxes, Faraday formulated the theory of the remanence of the external electric field applicable to certain permanently polarized dielectric materials (called electrets by Heaviside in 1892).

Various attempts to polarize organic waxes were made in the early 20th century, but it was not until the 1960s that stable effects were achieved using new materials such as polyesters and fluocarbonates.

From 1960 onwards, Sessler and West developed the manufacture of electrets using polymers (Mylar, Teflon, etc.) and adapted them to the manufacture of microphones [26]