Effect of surface mechanical changes on magnetic Barkhausen emissions

Magnetic Barkhausen emissions are sensitive to changes in the surface mechanical condition in magnetic materials. This sensitivity arises because magnetic properties of the material are closely linked to stress via the magnetoelastic coupling. Barkhausen signals in steels which are typically in the frequency range 20-200 KHz, are detected predominantly from a surface layer up to 0.5 mm in depth. Signals from deeper layers are attenuated by eddy currents in the material. The depth sensitivity can be controlled to analyze material condition at different depths by an adjustment of the frequency bandwidth of the detected signal.