Velocity induced eddy currents technique to inspect cracks in moving conducting media

This paper presents a new nondestructive testing technique based on velocity induced eddy currents. When a time constant magnetic field moves along a conductive material velocity induced eddy currents are generated in the media. The technique developed within this work uses these eddy currents in the same way as any eddy current testing method where the flow pattern disturbed by the existence of defects creates variations of the secondary magnetic field that can be assessed by a magnetic field sensor. This magnetic field provides the information about the defects. Within this paper the magnetic field parameters are measured using “giant” magnetoresistors (GMR). As far as the authors know this is an original method, that has not yet been reported in the literature, and presents undoubted advantages when the material to be tested is in motion relative to the test sensor (like when inspecting a rail track with a bogie) because the sensitivity of the method increases with speed. To validate the results simulations of the actual testing conditions are also presented using a commercial finite element model.