Condenser microphones use a change in the size of a capacitor to convert a sound signal into an electrical signal. This type of microphone is most common.
The condenser microphone has two metal plates, one of which is coated with an electret film (mostly polytetrafluoroethylene) and grounded, and the other plate is connected to the gate of the field effect transistor, gate and source. There is a diode connected between the poles. When the electret diaphragm itself has a charge, the surface charge is Q, and the interlayer capacitance is C, the ground voltage U=Q/C is generated on the pole, when subjected to vibration or friction by the airflow. Because the vibration changes the distance between the two plates, that is, the capacitance C changes, and the electric quantity Q does not change, it will cause a voltage change. The magnitude of the voltage change reflects the strength of the external sound pressure. This voltage change frequency reflects The frequency of the external sound, this is the working principle of the electret microphone.
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