Measuring the Magnetic Polarizability Tensor of Nonsymmetrical Metallic Objects

Özdeğer, Toykan; Davidson, Jennifer L.; Ledger, P.D.; Conniffe, Daniel; Lionheart, William R B; Peyton, A. J.

doi:10.1109/jsen.2023.3296439

Cited by 3 publications

(3 citation statements)

References 32 publications

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“…Accurate apparatus for measuring MPT spectral signatures has been developed for symmetrical (Özdeğer et al. , 2021) and non-symmetrical objects (Özdeğer et al. , 2023) and the measured MPT coefficients have been found to be in excellent agreement with the simulated MPT coefficients for the same object geometry and for material parameters chosen according to the metal in the samples.…”

Section: Introductionmentioning

confidence: 76%

“…Subsequent signal averaging of the acquired measurements were performed in the control software prior to MPT inversion. Full details of the coil arrangement, bespoke electronics and data acquisition are detailed in Özdeğer et al. (2021).…”

Section: Measurement Proceduresmentioning

confidence: 99%

“…This ensures control of the horizontal position of the target and thereby keeps rotation around the vertical axis fixed for consistency. The use of the tI method has been fully described in Özdeğer et al. (2023) and enables non-symmetrical target objects to be characterised.…”

Section: Measurement Proceduresmentioning

confidence: 99%

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Computations and measurements of the magnetic polarizability tensor characterisation of highly conducting and magnetic objects

Elgy,

Ledger,

Davidson

et al. 2023

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PurposeThe ability to characterise highly conducting objects, that may also be highly magnetic, by the complex symmetric rank–2 magnetic polarizability tensor (MPT) is important for metal detection applications including discriminating between threat and non-threat objects in security screening, identifying unexploded anti-personnel landmines and ordnance and identifying metals of high commercial value in scrap sorting. Many everyday non-threat items have both a large electrical conductivity and a magnetic behaviour, which, for sufficiently weak fields and the frequencies of interest, can be modelled by a high relative magnetic permeability. This paper aims to discuss the aforementioned idea.Design/methodology/approachThe numerical simulation of the MPT for everyday non-threat highly conducting magnetic objects over a broad range of frequencies is challenging due to the resulting thin skin depths. The authors address this by employing higher order edge finite element discretisations based on unstructured meshes of tetrahedral elements with the addition of thin layers of prismatic elements. Furthermore, computer aided design (CAD) geometrical models of the non-threat and threat object are often not available and, instead, the authors extract the geometrical features of an object from an imaging procedure.FindingsThe authors obtain accurate numerical MPT characterisations that are in close agreement with experimental measurements for realistic physical objects. The assessment of uncertainty shows the impact of geometrical and material parameter uncertainties on the computational results.Originality/valueThe authors present novel computations and measurements of MPT characterisations of realistic objects made of magnetic materials. A novel assessment of uncertainty in the numerical predictions of MPT characterisations for uncertain geometry and material parameters is included.

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Section: Introductionmentioning

confidence: 76%

Section: Measurement Proceduresmentioning

confidence: 99%