Practical criteria for the separability of eddy-current testing signals on multiple defects

Practical quantities have been introduced by the authors to characterize the interaction among multiple defects located in a specimen under eddy-current testing (ECT). If these quantities indicate that the interaction between the pairs of defects is negligible, the signal of an ECT probe for multiple defects can be calculated as the superposition of those signals, which are obtained for each defect as if it would be a single one. Conversely, if the criteria holds, the measured ECT signal can be decomposed into signals associated with the individual defects, which essentially simplifies the solution of the inverse problem of defect reconstruction. As an application of the criteria, the design of a novel barcoding system is presented, which is developed for marking metallic parts by laser treating, and where the applicability of linear signal processing methods for the reading out of the barcode is a requirement.