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