A. Pirani

Galois sequences in the non-destructive evaluation of metallic materials

A new eddy currents non-destructive evaluation technique for the investigation of deep defects is presented. The method joins the favourable features of the pulsed eddy currents approach with the peculiar properties of the Galois sequences to extend the detection area down to large depths. The proposed method has been successfully tested on a benchmark; the experimental results have been compared with the standard pulsed method and with numerical simulations. The comparisons confirmed the accuracy of the method and its effectiveness in allowing a significant improvement in deep defect detection.

Multi-frequency identification of defects in conducting media

An eddy currents based procedure for the 3D image reconstruction of defects in metallic plates from multi-frequency data is presented. In particular, we exploit the collection of data at different probe positions as well as at different excitation frequencies in order to improve the amount of information content, the accuracy of the inverse methodology and its robustness against the experimental noise. The identification tool we developed, exploits the geometric A − χ formulation for the solution of the eddy-current forward problem together with a full nonlinear iterative inversion algorithm based on the total variation regularization.

Time domain deconvolution approach relying on Galois sequences

Purpose – The paper seeks to present a novel pulsed eddy currents (PEC) non‐destructive technique to investigate deep cracks in metallic structures.Design/methodology/approach – The method is based on the time‐domain analysis of the “defect response” and joins the PEC approach with the exploitation of the peculiar auto‐correlation properties of the Galois sequences. The procedure, relying on the deconvolution of Galois sequences, greatly improves the signal to noise ratio (SNR) and thus the operating depth. De‐convolving even short Galois sequences allows one to investigate at depth ranges larger than those allowed by the conventional pulsed excitation techniques.Findings – The technique has been tested on a benchmark and compared with numerical simulations. The experimental results showed that the SNR and the detection depth range have been significantly improved.Research limitations/implications – Some limitations of the measuring set up were evidenced requiring a new measuring apparatus if explorations...

Nonferromagnetic Open Shields at Industrial Frequency Rate

We have investigated some innovative geometric configurations for shielding extremely low-frequency (ELF) magnetic fields through nonferromagnetic materials. We define proper 2-D and 3-D finite-element (FE) models for the numerical computation of the shielding effectiveness of open conducting shields, in order to assess the mitigation of the magnetic field generated by a single-wire transmission line, two-wire t.l., or three-phase current excitation at industrial frequency rates. For the case of current conductors in air (i.e., in absence of the metallic shield) we validate our numerical model using the Biot-Savart law, while for the case of an infinite plane shield we exploit an analytical validation by means of a direct solution of the Maxwells equations, with properly defined boundary conditions. We compare our experimental results with those found in literature and prove the accuracy of the computed shielding efficiency. After this preliminary validation of the numerical tool, we study the behavior of several nonplane open shields, characterized by different transversal profiles: by means of the FE model, we directly compare these innovative configurations to the plane one, thus showing that they can guarantee an increase of the shielding effectiveness at constant weight of the shield just by a simultaneous mitigation of both the two components of the magnetic field in the transversal plane. This feature is verified by means of experimental results, in which we have considered a finite shield with a current source constituted by a single long wire.