Microphones

Condenser Microphones 

The first condense  microphones were developed at Bell Labs in early 1916.  The condenser microphones is build up by   air gap capacitors with a back-plate and a flexible diaphragm. When the diaphragm moves in response to sound, the capacitance changes and the resulting voltage is amplified.

MEMS Mircrophones 

Modern capacitive MEMS microphones operate on the same principle and are basically miniaturized condenser microphones manufactured in a silicon wafer process.  Capacitive microphones use two or three plates, a diaphragm and one or two back-plates, that form an air gap capacitor that has a high bias charge.