Imaging damage in steel using a diamond magnetometer

TL;DR

This paper presents a contactless, non-destructive magnetic imaging method using nitrogen vacancy centers in diamond to detect and map structural damage in steel with high spatial resolution, even through non-magnetic coverings.

Contribution

It introduces a novel inhomogeneous magnetic field approach with a fiber-coupled NVC sensor for high-resolution damage detection in steel without magnetic shielding.

Findings

Achieved 1 mm spatial resolution in-plane and 0.1 mm perpendicular.

Successfully detected damage through non-magnetic coverings.

Sensor lift-off distance up to 3 mm from steel surface.

Abstract

We demonstrate a simple, robust and contactless method for non-destructive testing of magnetic materials such as steel. This uses a fiber-coupled magnetic sensor based on nitrogen vacancy centers (NVC) in diamond without magnetic shielding. Previous NVC magnetometry has sought a homogeneous bias magnetic field, but in our design we deliberately applied an inhomogeneous magnetic field. As a consequence of our experimental set-up we achieve a high spatial resolution: 1~mm in the plane parallel and 0.1~mm in the plane perpendicular to the surface of the steel. Structural damage in the steel distorts this inhomogeneous magnetic field and by detecting this distortion we reconstruct the damage profile through quantifying the shifts in the NVC Zeeman splitting. This works even when the steel is covered by a non-magnetic material. The lift-off distance of our sensor head from the surface of 316 stainless steel is up to 3~mm.