= Electret
An <electret> is a <dielectric> retaining long-lived <electric polarization> or trapped <electric charge> after its preparation field is removed. The retained charge distribution can supply a persistent <electric field> without continuous external <polarization> power.
An electret condenser <microphone> uses this property to bias a variable <capacitor>. Sound moves a diaphragm, changing <capacitance> and producing an electrical signal in the readout circuit. The electret supplies the <polarization> condition; it does not provide unlimited electrical <energy>, and the readout can still require power. Temperature, charge leakage and material history affect long-term stability. https://www.grasacoustics.com/faq[GRAS manufacturer FAQ: electret layer and internally supplied microphone polarization]{ref}
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