1. An insulator carrying a permanent charge similar to a permanent magnet.
2. A solid dielectric with a permanent electric polarization.

This is the electric equivalent of a permanent magnet.

3. A permanently polarized piece of dielectric material produced by heating the material and placing it in a strong electric field during cooling.

Some barium titanate ceramics can carnauba waxes. The electric field of an electret corresponds somewhat to the magnetic field of a permanent magnet.

4. A special plastic piezoelectric element, polarized during manufacture to become the equivalent of a permanently charged capacitor.

It generates an amplitude-responsive output voltage, like a ceramic element, but it requires less energy from the stylus system.

1. An earphone; such as, those used in sound-powered phones, which has a diaphragm of dielectrically (very poor conductor of electric current) charged material including polarized plastic, thereby eliminating the need for an external power source.
2. A headphone consisting of an electret transducer, usually in the form of a push-pull transducer or an instrument; such as, a microphone or electric motor, which converts one form of energy into another form.

1. A microphone that has an electret transducer capable of converting audio waves into electromagnetic waves.
2. A microphone consisting of an electret transducer in which the foil electret diaphragm is placed next to a perforated, ridged, metal or metal-coated backplate, and output voltage, taken between diaphragm and backplate.

It is proportional to the displacement of the diaphragm or a thin, flexible sheet that can be moved by sound waves, as in a microphone, or which can produce sound waves when moved, as in a loudspeaker.

A tool that is actuated by electric waves from one system and which supplies power in the form of electric waves to a second network.