GMR versus differential coils in velocity induced eddy current testing

This paper presents a development on a new nondestructive testing method using eddy currents induced by velocity. This new method uses a constant magnetic field that attached to a moving media induces eddy currents in the conductive material to be tested. By measuring the opposing magnetic field generated by the eddy currents it is possible to obtain information regarding the presence of defects. Two different magnetic field sensors, GMR and differential pick-up coils, were used and compared in the detection of perpendicular components of the magnetic field created by disrupted eddy currents due to linear defects machined on an aluminum plate.