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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.
The term electret was coined by Oliver Heaviside[1] for a (typically dielectric) material which has electrical charges of opposite sign at its extremities.[2] Some materials with electret properties were already known to science and had been studied since the early 1700s. One example is the electrophorus, a device consisting of a slab with electret properties and a separate metal plate. The electrophorus was originally invented by Johan Carl Wilcke in Sweden in 1762[3] and improved by Alessandro Volta in Italy in 1775.[4] The first documented case of production was by Mototarô Eguchi in 1925[5] who melting a suitable dielectric material such as a polymer or wax that contains polar molecules, and then allowing it to solidify in a powerful electric field. The polar molecules of the dielectric align themselves to the direction of the electric field, producing a dipole electret with a permanent polarization. Modern electrets are sometimes made by embedding excess charges into a highly insulating dielectric, e.g. using an electron beam, corona discharge, injection from an electron gun, electric breakdown across a gap, or a dielectric barrier.[6][7]
^Heaviside, Oliver (1894). Electrical Papers. Macmillan and Company. pp. 488–493.
^Gutmann, F. (1948). "The Electret". Reviews of Modern Physics. 20 (3): 457–472. Bibcode:1948RvMP...20..457G. doi:10.1103/RevModPhys.20.457. ISSN 0034-6861.
^Vetenskapsakademien (Stockholm), Kungliga Svenska (1762). Kungliga Svenska Vetenskapsakademiens handlingar (in Swedish). Almqvist & Wiksell.
^Pancaldi, Giuliano (2005). Volta: Science and Culture in the Age of Enlightenment. Princeton University Press. pp. Chapter 3. ISBN 978-0-691-12226-7.
^Eguchi, Mototarô (1925). "XX. On the permanent electret". The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science. 49 (289): 178–192. doi:10.1080/14786442508634594. ISSN 1941-5982.
^Gross, B. (1980), Sessler, Gerhard M. (ed.), "Radiation-induced charge storage and polarization effects", Electrets, Topics in Applied Physics, vol. 33, Berlin, Heidelberg: Springer Berlin Heidelberg, pp. 217–284, doi:10.1007/3540173358_12, ISBN 978-3-540-17335-9, retrieved 2024-01-22
^Tsai, Peter P.; Schreuder-Gibson, Heidi; Gibson, Phillip (2002). "Different electrostatic methods for making electret filters". Journal of Electrostatics. 54 (3–4): 333–341. doi:10.1016/S0304-3886(01)00160-7.
An electret (formed as a portmanteau of electr- from "electricity" and -et from "magnet") is a dielectric material that has a quasi-permanent electrical...
electret microphone is a microphone whose diaphragm forms a capacitor (historically-termed a condenser) that incorporates an electret. The electret's...
condenser microphone is replaced by a permanent charge in an electret material. An electret is a ferroelectric material that has been permanently electrically...
case of fault. An electret driver functions along the same electromechanical means as an electrostatic driver. However, the electret driver has a permanent...
can also be stand-alone devices. The integrated preamplifier in a foil electret microphone. The first stages of an instrument amplifier, which is then...
some typically small distance. (A permanent electric dipole is called an electret.) A magnetic dipole is the closed circulation of an electric current system...
cathode. Initial velocity bias is used only for small input signal voltages. Electret microphone elements typically include a junction field-effect transistor...
Textbooks Phenomena Electrostatics Charge density Conductor Coulomb law Electret Electric charge Electric dipole Electric field Electric flux Electric potential...
Textbooks Phenomena Electrostatics Charge density Conductor Coulomb law Electret Electric charge Electric dipole Electric field Electric flux Electric potential...
from subsequent audio frequency circuits. It is often used for powering electret microphones, which will not function without power. It is suitable only...
bulk resistivity makes it an ideal material for fabricating long-life electrets, the electrostatic analogues of permanent magnets. PTFE film is also widely...
Textbooks Phenomena Electrostatics Charge density Conductor Coulomb law Electret Electric charge Electric dipole Electric field Electric flux Electric potential...
microfibers with an electrostatic charge; that is, the fibers are electrets. An electret filter increases the chances that smaller particles will veer and...
Textbooks Phenomena Electrostatics Charge density Conductor Coulomb law Electret Electric charge Electric dipole Electric field Electric flux Electric potential...
Textbooks Phenomena Electrostatics Charge density Conductor Coulomb law Electret Electric charge Electric dipole Electric field Electric flux Electric potential...
Textbooks Phenomena Electrostatics Charge density Conductor Coulomb law Electret Electric charge Electric dipole Electric field Electric flux Electric potential...
Francis, G. W., "Electrostatic Experiments" Oleg D. Jefimenko, Editor, Electret Scientific Company, Star City, 2005 Aplin, K. L.; Harrison, R. G. (September...
Textbooks Phenomena Electrostatics Charge density Conductor Coulomb law Electret Electric charge Electric dipole Electric field Electric flux Electric potential...
and crystals; however, soft pyroelectricity can be achieved by using electrets. Pyroelectricity is measured as the change in net polarization (a vector)...
Textbooks Phenomena Electrostatics Charge density Conductor Coulomb law Electret Electric charge Electric dipole Electric field Electric flux Electric potential...
Textbooks Phenomena Electrostatics Charge density Conductor Coulomb law Electret Electric charge Electric dipole Electric field Electric flux Electric potential...
Textbooks Phenomena Electrostatics Charge density Conductor Coulomb law Electret Electric charge Electric dipole Electric field Electric flux Electric potential...
seen in the case of an object with a "frozen in" polarization like a bar electret, the electric analogue to a bar magnet. There is no free charge in such...