GMR second order electronic gradiometer for NDE applications

With the aim to improve the spatial resolution and the sensitivity of Eddy Current (EC) technique on metallic structures used in aircraft industry, a probe based on a Giant Magnetoresistive (GMR) sensors has been designed. To reduce the environmental noise that deteriorates the magnetic field sensitivity of the GMR sensors, a second order electronic gradiometer configuration has been realized. The electromagnetic characterization of the GMR gradiometer in terms of magnetic noise density spectrum and magnetic field sensitivity has been carried out to demonstrate the advantage of the GMR sensors gradiometric configuration. The EC measurements of defects and rivets in multi-layers non-magnetic Al-Ti alloy, applied in aircraft structures, by using the GMR gradiometer will be discussed and a comparison of the spatial resolution of the commercially available search coil probe and the GMR based prototype has been reported.