A magnetic imaging system for evaluation of material conditions using magnetoresistive devices

A new magnetic imaging system has been developed for nondestructive evaluation of structural and mechanical conditions of magnetic materials. The system produces a multiparameter contour plot of the spatial variations of a variety of magnetic properties such as coercivity, remanence, permeability, and the Barkhausen effect (BE) signal. These can then be used for the detection of material conditions such as residual stress or the presence of cracks, since the magnetic and mechanical properties of materials are closely related via the magnetoelastic coupling. An integrated sensor probe capable of measuring both magnetic hysteresis and Barkhausen effect signals was developed using magnetoresistive devices. Results of experimental studies show that the imaging system can be used to detect surface or subsurface notches, thickness variations in ferrous materials, and stress distribution.