Electromagnetically induced acoustic noise

Equivalent electromagnetic forces due to the presence of an electrical field can involve electrostatic, electrostrictive and reverse piezoelectric effects.

Vibration level is increased in case of a mechanical resonance, when electromagnetic forces match with a structural mode natural frequency of the active component (magnetic circuit, electromagnetic coil or electrical circuit) or of its enclosure.

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.

This force can excite the bending mode of the rotor and create additional vibration and noise.

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).

It corresponds to an ideal one pole pair permanent magnet synchronous machine with a slotless stator.

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.