Condenser microphones convert sound signals into electrical signals by taking advantage of changes in capacitance. This type of microphone is the most common, as is the case with built-in microphones in common recorders. Because it is cheap, compact, and the effect is not bad. Sometimes it is also called a microphone.
The condenser microphone has two metal plates, one of which is coated with an electret film (mostly perfluoroethylene propylene) and grounded, the other plate is connected to the grid of the field effect transistor, and a diode is connected between the grid and the source. When the electret film itself is charged, the surface charge is Q, and the ground capacitance between the plates is C, the ground voltage U=Q/C is generated on the electrode tip, When subjected to vibration or air flow friction, the distance between the two plates changes due to vibration, that is, the capacitance C changes, while the electric quantity Q remains unchanged, which will cause the voltage change. The magnitude of the voltage change reflects the strength of the external sound pressure. The frequency of the voltage change reflects the frequency of the external sound, which is the working principle of the electret microphone.
