Magnetic induction tomography of structural defects with alkali–metal spin maser

Abstract

Implementation of an alkali-metal spin maser in magnetic induction tomography is explored. While the spin maser vastly improves the detection speed and solves the problem of imperfect bias magnetic field stabilization in non-destructive testing, it provides only partial information about the spatial extent of the defect. We demonstrate two ways in which the whole image of the defect can be reconstructed and experimentally demonstrate that the amplitude of the spin maser signal can be used as an indicator of defect depth. Additionally, the spatial extent of the imaging of the defect is increased by the application of a spin maser operating at two frequencies. A significant benefit of operating in the spin maser mode is that the system follows any fluctuations in the Larmor frequency due to changes in the bias magnetic field strength. This removes the need for active stabilization of the bias magnetic field, greatly reducing the complexity of the system.