Electret microphone is a type of condenser microphone. The basic principle of a condenser microphone is to use a capacitor as the transducer for sound signals - electrical signals. One of the electrodes of this capacitor can sense changes in sound pressure, playing a role in the intake of sound signals. Usually, this pole is composed of a metallized polymer membrane, which forms a variable capacitance with adjustable distance between the poles. When there is sound pressure, the diaphragm vibrates, and the vibration intensity and frequency are determined by the immediate sound pressure. The capacitance also changes accordingly with the sound signal. If a constant voltage has already been applied to the capacitor at this point, the change in capacitor capacity will cause a change in the amount of polarized charge on the capacitor, thereby generating an electrical signal at both ends of the capacitor, achieving acoustic electrical signal conversion. Some materials can permanently retain these charges after adding them, which is commonly referred to as electret materials. Mics using these materials are called electret condenser microphones. The pickup unit of a condenser microphone has two poles, one of which is a metal diaphragm that can vibrate, and the other pole is a metal plate.
