Electret microphone
 | This article needs additional citations for verification. (September 2012) |
DC blocking capacitor
.An electret microphone is a
condenser microphones, though a preamplifier is typically incorporated to boost the audio voltage signal
.
Electret material
An electret is a stable
electrostatic field
. The polar molecules of the dielectric align themselves to the direction of the electrostatic field, producing a permanent electrostatic "bias".
History
Electret materials have been known since the 1920s and were proposed as
PTFE
plastic, either in film or solute form, to form the electret.
Types
There are three major types of electret microphones, differing in the way the electret material is used:
- Foil-type or diaphragm-type
- A film of electret material is used as the diaphragm itself. This is the most common construction. It is often considered the lowest quality, as the electret material used sometimes does not make a particularly good diaphragm. Modern materials have enabled very comparable performance to other designs.
- Back electret
- An electret film is applied to the back plate of the microphone capsule and the diaphragm is made of an uncharged material, which may be mechanically more suitable for the transducer design being realized.
- Front electret
- This design features no back plate, and the capacitor is formed by the diaphragm and the inside surface of the capsule. The electret film is adhered to the inside front cover and the metalized diaphragm is connected to the input of the FET (field-effect transistor). It is equivalent to the back electret in that any conductive film may be used for the diaphragm.
Electret microphones require no polarizing voltage unlike other
condenser microphones, but normally contain an integrated preamplifier which requires a small amount of power (often incorrectly called polarizing power or bias). This preamp is frequently phantom powered
in sound reinforcement and studio applications. Other types include a 1.5 V battery in the microphone housing, which is often left permanently connected as the current drain is usually very small.
Notes
- ^ Rose, Bruce (2019-01-08). "Comparing MEMS and Electret Condenser (ECM) Microphones". CUI Devices. Archived from the original on 2024-02-07. Retrieved 2024-05-17.
- ^ Ainissa Ramirez (2022-02-07). "Jim West's marvellous microphone". Chemistry World. Royal Society of Chemistry. Retrieved 2022-02-24.
- ^ "Patent US3118979: Electrostatic transducer" (PDF). www.freepatentsonline.com. United States Patent Office. Retrieved 12 April 2016.
- ^ Juang, Lynn. "Foil Electret Microphone: Sessler & West (1960)". Bell Labs, Multimedia Communications Research Laboratory. Archived from the original on February 4, 2012. Retrieved 19 January 2009.
References
- Sessler, G.M.; West, J.E. (1962). "Self-biased condenser microphone with high capacitance". Journal of the Acoustical Society of America. 34 (11): 1787–1788. .
External links
- Powering microphones
- Explanation of construction
- Integrated Circuits for High Performance Electret Microphones — Audio Engineering Society Convention Paper
- Apply Electret Microphones to Voice Input Designs App Note Archived 2018-04-17 at the Wayback Machine.
- Electret Microphone Amplifier Circuit with Arduino code and tutorial