The term electret was coined by Oliver Heaviside[1] for a (typically dielectric) material which has electrical charges of opposite sign at its extremities.
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.
Although electrets are only in a metastable state, those fashioned from very low leakage materials can retain excess charge or polarisation for many years.
Bulk electrets can be prepared by heating or melting the material, then cooling it in the presence of a strong electric field.
[citation needed] Most commercially produced electrets are based on fluoropolymers (e.g. amorphous Teflon) machined to thin films.