Barkhausen spectroscopy: Non-destructive characterization of magnetic materials as a function of depth

Abstract

In this study, we conceptually divided a ferromagnetic specimen into layers along its depth. For each layer, we derived a non-linear integral equation that describes the attenuation with frequency and distance of magnetic Barkhausen emissions coming from that layer. We postulate that the Barkhausen spectrum measured at the surface by an induction coil can be expressed as the sum of the individual layer spectra. We show how a non-linear least squares algorithm can be used to recover the properties in individual layers. These are related to stress using an extension to the theory of ferromagnetic hysteresis. We found that the quality of the fit is influenced by the sensitivity of the ferromagnetic material to strain, as well as by the sensor-specimen coupling. The proposed method can be used for the non-destructive characterization of stress as a function of depth in magnetic materials.