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Coil noise
Coil noise or coil whine is a phenomenon in electronics which produces undesirable audible sound. In magnetic resonance imaging "coil noise" is that part of total system noise attributed to the receiving coil, due to its non-zero temperature.
== Description ==
Coil noise is, as its name suggests, caused by electromagnetic coils. These coils, which may act as inductors or transformers, have a certain resonant frequency when coupled with the rest of the electric circuit, as well as a resonance at which it will tend to physically vibrate.
As the wire that makes up the coil passes a variable current, a varying magnetic field exists around the coil. Forces due to this magnetic field can cause vibration of the coil wires or the core of the coil. For some magnetic core materials, a (strong) varying field can cause vibration of the core due to magnetostriction. If the frequency of the current in the coil falls within the audible range, the resulting vibration may produce sounds audible at a distance from the coil, especially if magnified by a mechanical resonance in the components or in the equipment enclosure.
Coil noise can occur when the coil is poorly secured to the circuit board or is poorly damped. The effect is more pronounced as the signal passing through the coil increases in strength or nears the (mechanical) resonant frequency of the coil.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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