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Faraday Induction Effect Applied to the Detection of Defects in a Moving Plate

Ramos, H. ; Rocha, T. ; Pasadas, D. ; Ribeiro, A. L.

Faraday Induction Effect Applied to the Detection of Defects in a Moving Plate, Proc Review of Progress in Quantitative Nondestructive Evaluation - QNDE, Denver, United States, Vol. 2, pp. 00 - 00, July, 2012.

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Abstract
Nowadays the importance of railways in surface transportation is rising again. This is partly due to the high quality service of trains, its convenience and also to some external factors. Safety in the railway network became a paramount issue and in addition maintenance costs must be kept at the lowest value. Therefore, railway operators want to increase the rail inspection speed in order not to adversely affect the normal transportation service.
In order to increase the testing speed, this paper presents a new approach by exploiting the velocity of the object under test to produce the detector signal. The technique is a modified eddy current method. Surface eddy currents will result from the induction phenomena due to the relative movement between the rail and the transducer imposing the DC magnetic field. A giant magnetoresistor (GMR) will be used to detect the magnetic field perturbations produced by the surface currents when a defect exists. In this way an eddy current testing system (ECT) with a sensitivity that increases with the inspection speed is obtained.
Besides the theoretical study of the electromagnetic system composed by the DC magnetic field applied to the moving conductive media and the sensing transducer, the paper describes the experiments that have been carried out to support the theory and results are presented for different materials at different testing speeds.