Michael Chakinis, Brianna Undzis, Swan Htun, Barrett Neath Electret Microphones Michael Chakinis, Brianna Undzis, Swan Htun, Barrett Neath
How Regular Microphones Work Sound propagates through air in the form of waves A thin, flexible diaphragm is contacted by waves Moving diaphragm creates varying current Dynamic Induction Condenser Capacitance Ribbon Crystal Piezoelectricity effect
How the Electret Microphone Works The electret condenser microphone works on the principle of variable capacitance Use a parallel plate capacitor with a fixed and moveable plate When sound waves hit the moveable plate, it changes the capacitance and electric flow They’re made by melting a dielectric material then solidifying it to a strong electrostatic field Being chemically stable and having high resistance embeds a permanent electric dipole moment It can be connected to a JFET (Junction Field Effect Transistor) to increase the generated electric current
Different Types of Electret Microphones There are three main types of electret microphones: front electret, back electret, and foil-type. Front Electret Newer Back plate eliminated Capacitor formed by diaphragm and inside surface of capsule Electret, inside front cover Any conductive film may be used for diaphragm Back Electret Electret film applied to back plate of microphone capsule Diaphragm, uncharged materials Transducer design Physical quantity -> electrical signal Foil-Type Film of electret used for diaphragm Most common Lowest quality
Relevant Equations Variations in air pressure is detected by the diaphragm. The voltage change is induced by the varying distance between the diaphragm and the back plate due to voltage fluctuations across the capacitor. Thus, across the the diaphragm and the back plates, the voltage varies accordingly with the vibrations in the air given by the capacitance equation: C = Q/V
Sources https://en.wikipedia.org/wiki/Electret_microphone https://www.mediacollege.com/audio/microphones/h ow-microphones-work.html https://www.engineersgarage.com/insight/how- electret-condenser-microphone-works http://hades.mech.northwestern.edu/index.php/Micro phones https://www.cui.com/product-spotlight/electret- condenser-microphones