Electret - definition
Electret - definition
An Electrite is a dielectric material that permanently maintains an ordered electrical polarity, analogous to how a permanent magnet maintains magnetisation. It is created by placing a dielectric in a strong electric field, usually at an elevated temperature, and then rapidly cooling it to 'freeze' the orientation of the electric dipoles or surface charges. This allows the electret to generate its own electric field for a very long time, even for many years, without the need for an external power supply.
Typical materials used to make electrets are plastics such as polytetrafluoroethylene (PTFE), fluoropolymers, aromatic polymers or mixtures containing conductive particles. There are two basic mechanisms for the formation of permanent polarisation: dipole orientation and trapping of free charges in the dielectric matrix. In both cases, the effect leads to a quasi-permanent distribution of the electric potential.
Electrets are widely used in electroacoustic technology, particularly as active elements in electret microphones, where they provide a source of a constant electric field in the capacitor transducer circuit. Their presence eliminates the need for an external polarising voltage, which simplifies the design and reduces energy requirements. In addition, they are used in Pressure Sensors, electrostatic filters and electrostatic transducers, where permanent polarisation enables effective interaction with external charges or fields.
The stability of electret properties depends on factors such as temperature, humidity, ionising radiation and the chemical composition of the material. Their use requires careful selection of manufacturing technology and protection against degradation that could lead to the disappearance of the established electrostatic field.
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