Signal components selection in multi-frequency eddy current testing

To increase the sensitivity and the robustness of Eddy Current Testing (ECT), deep innovations in probes design, signal processing, and excitation signals optimization have been introduced during the last decade. As far as the excitation signals are concerned, many researchers are engaging the development of eddy current excitations able to provide as much information as possible about the presence, the location, and the geometrical characteristics of defects. To this aim newer signals characterized by a wide spectral content able to penetrate in the different layers of the material under test are substituting the classical sinusoidal excitation approaches. Also the authors are engaged in this field proposing different multi-frequency signals formation and processing in order to improve the defect characterization stage. In this paper, some ECT excitation strategies are experimentally analyzed and compared. They concern with the use of optimized chirp and multi-frequency signals. Fixed the range of the defects depths to be explored, the goal is to define signals that are capable of assuring a quite uniform sensitivity in all the range.