The Barkhausen effect is the noise in the magnetic output of a ferromagnet when the magnetising 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 magnetisation 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.