Electromagnetic SQUID Based NDE: a Comparison Between Experimental Data and Numerical FEM Modeling
Over the existing electromagnetic sensors used in eddy-current Non-Destructive Evaluation (NDE), SQUID (Superconducting QUantum Interference Device) magnetometers are very attractive as multi-mode instruments capable of obtaining very high magnetic field sensitivity (detection of sub-pT signals) even in unshielded environments, high resolution imaging of low frequency eddy current distributions, large bandwidth (up to MHz) and high spatial resolution [1,2,3]. Moreover, a well optimized flux-locked-loop electronics allows SQUID systems to operate with large dynamic range and high linearity. These characteristics are extremely important in order to perform quantitative measurements of magnetic field distributions produced by induced currents in test samples. Of course, the need to operate the SQUID at cryogenic temperatures limits its use in many practical applications. The advent of High Temperature Superconductors (HTS) and the development of HTS SQUIDs has renewed the interest for NDE with these superconducting sensors .