Imaging of material defects with a radio-frequency atomic magnetometer

Non-destructive inductive testing of defects in metal plates using the magnetic resonance signal of a radio-frequency atomic magnetometer is demonstrated. The shape and amplitude of the spatial profile of the signal features, which represent structural defects, are explored. By comparing numerical and experimental results on a series of benchmark aluminium plates, we show correspondence between the properties of the secondary field and those of the magnetometer signal. In particular, we show that two components of the secondary field are mapped onto the amplitude and phase of the atomic magnetometer signal. Hence, a magnetic field measurement with the atomic magnetometer, although scalar in its nature, provides semi-vectorial information on the secondary field. Moreover, we demonstrate a robust process for determining defect dimensions, which is not limited by the size of the sensor. We prove that the amplitude and phase contrast of the observed profiles enables us to reliably measure defect depth.