Flexible anisotropic magnetoresistive sensors for novel eddy current testing applications

The standard method for eddy current testing (ET) of conductive materials relies on using rigid coils. In recent years magnetoresistive (MR) sensors in combination with an excitation wire have become a promising candidate for this application since it would increase the spatial resolution. New developments in flexible electronics have enabled the production of flexible sensors with the novel capability of scanning samples in conformal contact with the surface. In this article flexible anisotropic magnetoresistive (AMR) sensors were used in combination with a thin induction wire to perform eddy current testing of a curved aluminum sample with several defects imprinted on its surface. To benchmark the performance of this new method, a flat sample with reference defects of various dimensions was also scanned using flexible AMR sensors, inductive coils and rigid giant magnetoresistive (GMR) sensors. The results show that this new method of using flexible magnetic field sensors coupled with an excitation wire can easily be applied to the scanning of curved samples, while in the benchmark test employing the flat sample, the performance is not far behind more conventional techniques, with defects with depths down to 30 μ m and widths down to 400 μ m being detectable with an SNR of 3 (signal magnitude) and 8 (signal phase shift) at the excitation frequency of 50 kHz, and defects with depths down to 30 μ m and widths down to 600 μ m being detectable with an SNR of 10 (signal magnitude) and 17 (signal phase shift) at 260 kHz. • Flexible magnetic sensors result from recent advancements in the field of flexible electronics. • This article demonstrates the applicatility of such sensors for eddy current testing of aluminum samples. • Scanning can be performed conformal in-contract with the sample surface. • Sensor flexibility allows for the scanning of complex/curved surfaces. • Measurement distance can go down to 20 μ m (corresponding to the flexible substrate thickness).