CHARACTERIZATION OF THE MAGNETIC EASY-AXIS IN PIPELINE STEEL USING MAGNETIC BARKHAUSEN NOISE

The angular dependence of magnetic Barkhausen noise (MBN) on eight surfaces through the thickness of a 2% Mn steel pipeline sample was investigated. The MBN signal was analyzed by integrating the square of the MBN voltage signal with respect to the time axis. The resulting value, referred to as the MBN energy signal, was modeled by considering the irreversible motion of 180-degrees domain walls, under the influence of an oriented magnetic field. An expression for the angular dependence of the MBN energy signal was derived and was given by energy = alpha cos2 theta + beta, where alpha and beta are the fitting parameters and theta is the angle between the maximum MBN signal and the applied sweep field. The a parameter was associated with the irreversible motion of 180-degrees walls that contributed to the net macroscopic easy axis near the surface of the sample, while the beta parameter was associated with the isotropic background MBN signal. The energy equation could be used to fit the data for all sweep field amplitudes in which the MBN spectrum was observed. A dependence of the alpha and beta parameters on the applied sweep field amplitude was observed.