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Electret
Electret
(formed of
elektr-
from "
electricity
" and
-et
from "
magnet
") is a
dielectric
material that has a quasi-permanent
electric charge
or
dipole
polarisation
. An electret generates internal and external
electric fields
, and is the
electrostatic
equivalent of a
permanent magnet
.
Oliver Heaviside
coined this term in 1885. Materials with electret properties were, however, already studied since the early 18th century. One particular 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 and again by
Alessandro Volta
in Italy.
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