In the early 1960’s, James West and Gerhard Sessler developed the foil electret transducer, a technology present in 90 percent of all microphones built today. Electret circuits, derived from the words electrostatic and magnet, permanently charge an electrical insulator in response to an electrostatic field. In essence, this process allows electret microphones to operate with little reliance on external power, and modern electrets are remarkably durable. In fact, most of us carry these microphones everywhere we go via our cell phones.