The Barkhausen effect is the noise in the magnetic output of a ferromagnet when the magnetizing force applied to it is changed. When an external magnetizing field through a piece of ferromagnetic material is changed, for example by moving a magnet toward or away from an iron bar, the magnetization of the material changes in a series of discontinuous changes, causing „jumps“ in the magnetic flux through the iron. These can be detected by winding a coil of wire around the bar, attached to an amplifier and loudspeaker. The sudden transitions in the magnetization of the material produce current pulses in the coil , which when amplified produce a sound in the loudspeaker.
Barkhausen noise analysis is a non-destructive method involving the measurement of a noise-like signal induced in a ferromagnetic material by an applied magnetic field. There are two main material characteristics that will directly affect the intensity of the Barkhausen noise signal: hardness and stress.