Electromagnetic techniques and high sensitivity magnetic sensors in NDT for aeronautical applications

This work is a comparative study of non-destructive testing performed by different sensors: search coil, flux-gate, GMR, HTc-SQUID-based magnetometer, used as eddy-current measuring devices. These sensors have been used for the detection of various artificial defects affecting metallic multi-layered, aluminium-alloy structures and composite materials, without external electromagnetic shielding. The basic concepts of eddy current technique and the working principles of the most useful electromagnetic sensors are reported. In particular, we demonstrate that the higher sensitivity of SQUIDs, in comparison to the other electromagnetic probes, gives a decisive advantage when the structure under inspection are multi-layered or weakly conducting materials such as the new advanced composite materials like CFRP (Carbon Fiber Reinforced Plastic), and Fiber Metallic Laminate (FML).