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Electret materials have been known since the 1920s and were proposed as condenser microphone elements several times, but they were considered impractical until the foil electret type was invented at Bell Laboratories in 1961 by Gerhard Sessler and James West, using a thin metallized Teflon foil.
First patent on foil electret microphone by G. M. Sessler et al. (pages 1 to 3) An electret microphone is a type of condenser microphone invented by Gerhard Sessler and Jim West at Bell laboratories in 1962. [24] The externally applied charge used for a conventional condenser microphone is replaced by a permanent charge in an electret material.
Along with Gerhard Sessler, West invented the foil electret microphone in 1962 while developing instruments for human hearing research. [7] [8] Compared to the previous condenser microphones, the electret microphone has higher capacitance and does not require a DC bias. [9]
An electret (formed as a portmanteau of electr-from "electricity" and -et from "magnet") is a dielectric material that has a quasi-permanent electrical polarisation. An electret has internal and external electric fields , and is the electrostatic equivalent of a permanent magnet .
Some condenser microphones can be powered with a 1.5-volt cell contained in a small compartment in the microphone or in an external housing. Phantom power is sometimes used by workers in avionics to describe the DC bias voltage used to power aviation microphones, which use a lower voltage than professional audio microphones.
Pages in category "Condenser microphones" ... Electret microphone; U. Neumann U 47; Neumann U47 FET; Neumann U48; Neumann U67; Neumann U 87; V. Valve microphone