An electromagnetic diaphragm is a form of
capacitive
A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals.
The effect of a c ...
sensor used on an
electronic stethoscope. The diaphragm is coated with a
conductive material. A conductive plate is positioned behind and parallel to the diaphragm, so that the two conductive elements form a
capacitor
A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passivity (engineering), passive electronic component with two termi ...
. Capacitance is a function of plate area,
dielectric properties of the space between the conductors, and the distance between the conductors. It is this latter parameter which is modulated by vibration such that the capacitance varies with the distance between the
electromagnetic diaphragm and the plate, forming an acoustic sensor.
The electromagnetic diaphragm is a form of capacitive sensor, and shares properties with
condenser microphone
A microphone, colloquially called a mic or mike (), is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and public ...
s. The difference between the electromagnetic diaphragm and a condenser microphone is that a condenser microphone operates on the basis of air transmission, has a very thin membrane instead of a diaphragm, and cannot be placed against a body to sense sounds within the body.
The electromagnetic diaphragm for stethoscopes was patented by Clive Smith in 2002 and is used on
Thinklabs electronic stethoscopes.
Photography
Electromagnetic diaphragm mechanisms are also used in photography lens barrels for providing highly accurate
aperture
In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane.
An opti ...
blade control when using
auto exposure during continuous shooting.
See also
*
Microphone
References
{{reflist
Medical equipment
Audio engineering