Inversion-Based Magnetic Polarizability Tensor Measurement From Time-Domain EMI Data

The magnetic polarizability tensor (MPT) provides a means of quantifying the perturbation of a time-varying magnetic field due to the presence of a metallic object and is highly correlated with the object’s geometrical and material properties. As such, MPT is an essential tool for metallic object characterization using electromagnetic induction (EMI) sensing. This article demonstrates inversion-based MPT measurement using a mono-coil pulse induction metal detector (MD) in combination with an electromagnetic (EM) tracking system. Experimental evaluation was conducted under laboratory conditions on a dataset of nonferrous metallic objects of various sizes, shapes, and materials. A methodology for comparison between frequency-domain (FD) and time-domain (TD) MPTs was developed to validate the measurement performance. The results showed a very good agreement with the simulations, as evidenced by a normalized root-mean-square error (NRMSE) of under 13.5%. Furthermore, the excellent repeatability of measurements with an NRMSE of
$ < 5.5$
% indicates that the proposed system has great potential for hidden metallic object detection.