Burst Eddy Current Testing with Diamond AC Magnetometry

In this work, a burst eddy current testing technique based on a diamond nitrogen vacancy (NV) center AC magnetometer with the Hahn echo (HE) sequence is proposed. In the confocal experiment apparatus, the NV magnetometer uses the HE sequence to achieve a magnetic sensitivity of $4.3 ~ \mathrm{nT} / \sqrt{\mathrm{Hz}}$ and volume-normalized sensitivity of $3.6 ~ \mathrm{pT} / \sqrt{\mathrm{Hz} \cdot \mathrm{mm}^{-3}}$, 5 times better than the existing method under the same conditions. Based on the magnetometer, a burst eddy current (BEC) testing prototype achieves a minimum detectable sample smaller than ${300~{\mu} \mathrm{m}}$ and a measurement accuracy of $9.85~\mathrm{\mu} \mathrm{m}$., which is used to image different metallic specimens and detect the layered internal structures. With its nanoscale resolution and high sensitivity, it promotes the application in deformation monitoring, security screening, quality control and paves the way for electromagnetic testing in the fields of biomaterials.