Towards Material Characterization and Thickness Measurements using Pulsed Eddy Currents implemented with an Improved Giant Magneto Resistance Magnetometer

摘要

Standard Pulsed Eddy Current Systems, as RTD-INCOTEST equipment, use receiver coils to measure eddy current decay in conducting objects. Advantages of full coils, as sensor for the eddy current, are its simple construction and the possibility of eddy current focusing. But, some disadvantages are the high induction voltage due to a large pulsed signal, the large sensor area and the low coil's sensitivity especially at large times. Some of these disadvantages can be avoided by using a magnetic-field sensor instead of a coil and some advantages also appear. Recent developments in Improved GMR Magnetometer open a new possibility to measure the decay by means of magnetic-field measurement. The present paper focuses on recent theoretical and practical investigations made by RTD and his partners. The measurement method is presented and discussed in comparison with the theoretical signal behaviour. Experimental features are investigated and the practical feasibility of the technique is shown. Furthermore, an analysis is presented enabling the simultaneous determination of both material properties and thickness with an optimal fitted function. For several types of Carbon steel materials, a good accuracy of their properties (permeability, conductivity, and thickness) can be achieved. Recommendations for further development are also given.