This simple experimental setup illustrates the phenomenon of electromagnetic acoustic noise and vibrations - also called electromagnetically-excited noise, e-NVH or electrical noise - occurring in electrical systems such as rotating machines (e.g. permanent magnet synchronous machine, induction machines) or passive components (e.g. inductors).
<p>A coil powered by a fixed frequency AC current is put around a Tuning Fork prong. The current source create an AC flux density flowing in the magnetic circuit and the airgap created by the two iron prongs. Maxwell forces attract the two fork tips (equivalent magnetic dipole) similarly to what happens between the opposite polarities of North and South magnets. This magnetic force creates a vibration of the tuning fork prongs at twice the current frequency because magnetic force is proportional to the square of the flux density. The fork tips behave like an acoustic linear quadrupole. A strong tonal noise is created without any mechanical contact between excitation coil and tuning fork, illustrating the origin of the whining noise of electric motors.
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