During the last decade, the safety regulations of the airports have been set to a new level. As the number of
passengers is constantly increasing, yet effective but quick security control at checkpoints sets great requirements
to the 21st century security systems. In this paper, we shall introduce a novel metal detector concept that
enables not only to detect but also to classify hidden items, though their orientation and accurate location
are unknown. Our new prototype walk-through metal detector generates mutually orthogonal homogeneous
magnetic fields so that the measured dipole moments allow classification of even the smallest of the items with
high degree of accuracy in real-time. Invariant to different rotations of an object, the classification is based
on eigenvalues of the polarizability tensor that incorporate information about the item (size, shape, orientation
etc.); as a further novelty, we treat the eigenvalues as time series. In our laboratory settings, no assumptions
concerning the typical place, where an item is likely situated, are made. In that case, 90 % of the dangerous and
harmless items, including knives, guns, gun parts, belts etc. according to a security organisation, are correctly
classified. Made misclassifications are explained by too similar electromagnetic properties of the items in question.
The theoretical treatment and simulations are verified via empirical tests conducted using a robotic arm and our
prototype system. In the future, the state-of-the-art system is likely to speed-up the security controls significantly
with improved safety.