Electromagnetically induced acoustic noise

Equivalent electromagnetic forces due to the presence of an electrical field can involve electrostatic, electrostrictive and reverse piezoelectric effects.Some tangential magnetic force harmonics can directly create magnetic vibrations and acoustic noise when applied to the stator teeth: tangential forces create a bending moment of the stator teeth, resulting in radial vibrations of the yoke.NVH mitigation techniques in electrical machines include Electromagnetic noise and vibration mitigation techniques in electrical machines include: Coil noise mitigation actions include: A varying electromagnetic force can be produced either by a moving source of DC magnetic field (e.g. rotating permanent magnet or rotating coil supplied with DC current), or by a steady source of AC magnetic field (e.g. a coil fed by a variable current).The resonance effect of magnetic vibration with a structural mode can be illustrated using a tuning fork made of iron.A prong of the tuning fork is wound with a coil fed by a variable frequency power supply.When the exciting force frequency matches the fundamental mode of the tuning fork close to 400 Hz, a strong acoustic resonance occurs.
Example of modal shape number 2 of a stator; movements have been exaggerated for presentation purposes
Deflection of a ferromagnetic cylinder due to a rotating permanent magnet excitation field
Set-up of the electromagnetically excited tuning fork
Example of magnetic noise coming from a subway electric motor
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