There are three primary types of microphones electret, carbon, and dynamic. Electret microphones are the most popular for aviation use. They are smaller and lighter than other microphone elements and work by placing a charged, flexible diaphragm a given distance from a fixed plate. Sound waves created by speaking into the microphone cause the diaphragm to vibrate, changing the distance between the diaphragm and the plate. Those changes are translated into electrical signals and transmitted.
Carbon microphones are the simplest and least expensive.
In carbon mics, the movement of a diaphragm is transmitted to carbon granules inside a small container connected to the diaphragm. As sound waves strike the diaphragm, the carbon granules move. The resulting fluctuations in the current running through the system are then amplified and transmitted. Dynamic microphones form a middle ground in terms of cost and sophistication. In these microphones, a coil of wire is connected to the diaphragm, which is in a strong magnetic field.