In search of a material in which Dipoles are created easily and rapidly with a high ability of dipole formation beside it should be an excellent insulator to be used near high voltage/ electric fields without any hazard?
Hello Khola Azhar ,
The following explanation was taken directly from a footnote in my MS thesis, Research Coherers, A Review
.Most technical people are, no doubt, familiar with some type of electromagnetic sound transducer (speakers, microphones, telephone receivers, etc.), but the term ‘electret microphone’ probably does not have as wide an acquaintance. Briefly, an electret is a dielectric able to exhibit a permanent external macroscopic electric field. The constituent molecules of most normal dielectrics, while they may have, individually, a significant dipole moment, do not produce collectively any macroscopic electric fields because the dipole moments are oriented randomly to one another. In an electret, the individual molecules with their dipole moments can be made to exhibit large scale organization, i.e., all the molecule can be made to line up facing the same direction (homocharge). In addition, the conducted charge can be frozen in place temporarily (heterocharge); it is this heterocharge which is responsible for the short term transient variations in the sign of the electret field. Consider carnauba wax, if it is brought to the melting point, then placed in an electric field - say, between the plates of an air capacitor - and then allowed to cool and solidify in the presence of the imposed field, the constituent dipole molecules will be oriented and frozen in position. A similar process is used to create magnets. In fact, the name ‘electret’ was originally chosen by Oliver Heaviside to suggest the idea of an ELECTRical magnET. Note, at the time Heaviside conjured up this name, electrets were just an idea as no one had actually made any. It was not until 1919, that the Japanese physicist, Mototarô Eguchi, while investigating electrical conduction in waxes, had the idea of trying to freeze these charges in place. Although he first published in 1919 in the Proceedings of the Physico-Mathematical Society of Japan, this journal is not generally available so the following citation is offered,
M. Eguchi; On the Permanent Electret; Philosophical Magazine [and Journal of Science]; Vol. 49 (6th Series); January-June 1925; pp. 178-192.
A good review article on the subject is,
A. Gemant; Recent Investigations on Electrets; Philosophical Magazine [and Journal of Science]; Vol. 20 (7th Series); November 1935; pp. 929-952.
Regards,
Tom Cuff
Hi Khola Azhar ,
For further discussion of ferroelectrics, see [1]. For a discussion of the practical problems of measuring whether or not a dieectric material is actually an electret, see [2].
[1] John R. Reitz, Frederick J. Milford; Foundations of Electromagnetic Theory, Second Edition; Addison-Wesley Publishing Company; 1967; pp. 101-103.
[2] R.N. Varney, H.T. Hahn; Electrets and electrostatic measurements; American Journal of Physics; Vol. 43; No.6; June 1975; pp. 509-513.
Regards,
Tom Cuff
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