Transducers are devices which convert energy from one form to other. A microphone is a transducer which converts sound energy to electrical signals. It works opposite to a speaker (see how speaker works). Microphones are available in different shape and sizes. Depending on the application, a microphone may use different technologies to convert sound to electrical signals. Here we are going to discuss about the Electret Condenser Microphone which is widely used in mobile phones, laptops, etc.
Electret Condenser Microphone, as the name suggests is a parallel plate capacitor and works on the principle of a variable capacitance. It consists of two plates, one fixed (called the back plate) and the other moveable (called Diaphragm) with a small gap between them. An electric potential charges the plate. When sound strikes the diaphragm it starts moving, thereby changing the capacitance between the plates which in turn results in a variable electric current to flow.
The above image shows an Electret microphone. These microphones are widely used in electronic circuits to detect minor sounds or air vibrations which in turn are converted to electrical signals for further use. The two legs as shown in the image above are used to make electrical connection with the circuit.
A solid conducting metal body encapsulates the various parts of the microphone. The top face is covered with a porous material with the help of glue. It acts as a filter for the dust particles. The sound signals/air vibrations passes through the porous material and falls on the diaphragm through the hole shown in the image above.