What is an Electret ?

An electret is an interesting material which is analogous to a magnet. An Electret generates a permanent electrical Field.  It can be called an "Electrostatic Magnet".

Just as  a magnet is able to generate a magnetic field because of dipole polarization, the Electret is able to generate a permanent electric field. The Electret was first described by Oliver Heaviside in 1885.

The name Electret is a combination of the words Electron and Magnet. 

The Electret is made of special materials such as Quartz, PolyethyleneTerephthalate (PET) and polypropylene.  Modern electrets are made using Polytetrafluoroethylene material.

An Electret is made by melting the electret material, then placing the molten material in an electric field and then allowing the material to solidify.  The solidified material, retains the electric charge as the dipoles are polarized.  

Electrets are used in applications such as printing where a uniform electrostatic field is necessary.  They are also used in microphones, gas filters and even in the pharmaceutical industry.