Through-Barrier Sub-mm Electromagnetic Induction Imaging With Atomic Magnetometers

Eddy-current nondestructive testing is widely used for the detection of cracks and fatigue in metallic structures. This is usually done by sweeping an inductor coil over the sample of interest while monitoring changes in the coil response. While this may allow for the detection of sub-mm cracks and defects, the technique lacks penetrating power through barriers. This work addresses such capability gaps. We demonstrate a mechanically translatable system based on an atomic magnetometer (AM) that allows for sub-mm resolution while simultaneously allowing also for penetration through shields. The adoption of a radio frequency (RF) AM as a sensor allows for the operation of the system at low frequency, with high sensitivity achieved by introducing several technical solutions, which lead to enhanced performances, with respect to existing systems, and improved stability of the instrument while scanning over the target object. The obtained enhanced performances are highlighted by the demonstrated ability to detect and image gaps as small as 0.27 mm concealed behind a shield consisting of a 1.50-mm rubber sheet and a 0.42-mm aluminum sheet.