Characterization of the Electromagnetic Field Generated by Eddy Current Probes

Considerable inspection efforts are required to achieve quality requirements for mechanical parts during manufacturing and maintenance operational safety for aging power stations, fleets of civil and military aircraft, trains and offshore structures. Problems arising from parts made of metallic materials are mainly due to corrosion and fatigue crack propagation. Currently many of these inspections are carried out using Eddy Current methods. The detection and the quantification (sizing) of defects in metallic materials with Eddy Current (EC) techniques are based on the performances of the EC equipment and probes. The EC probes, which get all the information from the materials to be inspected, need to be well characterized to ensure the quality of the Eddy Current inspection. Their characterization has to take into account their geometry, their electrical and electromagnetic characteristics as well as their behavior in relation to materials and defects. The usual method for characterizing an Eddy Current probe is to measure its response to reference blocks and reference defects in terms of the resulting impedance or induced voltage in the receiving coil. Few papers [1,2] describe the characterization of the electromagnetic field generated by EC probes. The knowledge of this electromagnetic field is very important for a better understanding of the field repartition and its influence on defects but also to compare probes between them and to follow their evolution. This measurement system could also be a good method to validate electromagnetic model and to design EC probes. We describe in this paper an instrumentation for a direct measurement of the electromagnetic field of EC probes in emitting in air and in transmission through materials