Measuring the Magnetic Polarizability Tensor of Nonsymmetrical Metallic Objects

The magnetic polarizability tensor (MPT) is a representative electromagnetic property of a metallic object, which depends on the size, material, shape, and excitation frequency of the object. The MPT can be used to describe the response of metal detector systems and improve target classification performance in applications utilizing electromagnetic induction spectroscopy. However, for target characterization, a library of possible target objects needs to be created, which can be used for training machine learning classifiers. To supplement and benchmark our existing library of simulated and measured MPT object characterizations, it is necessary to be able to measure object characterizations accurately and efficiently. This article describes a novel method utilizing a truncated icosahedron-shaped manipulator and procedure to measure MPT characterizations of nonsymmetrical, irregular objects. This new method allows the measurement of the MPT of any appropriately sized object. The method also ensures that the MPT characterizations are measured quickly and are well posed, without sacrificing accuracy. The performance of the method is validated by comparing the experiment results acquired using the new method with experiment results acquired using a slower method for symmetrical objects as well as synthetic results generated using a commercial finite element package and an optimized dedicated open-source MPT-calculator package, which offers high accuracy and considerable computational advantages. Good agreement between the new method and the other three methods is seen. For all objects that have been characterized, MPT loss-peak magnitude and horizontal positions from all described methods are within 5% of each other at worst.