P. D. Ledger

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The purpose of this paper is to clear up a major mystery in metal detection and confirm that the engineering prediction of H T ¨ pM ind H M q, for the sensitivity of measurements of the perturbed magnetic field to the presence of a general conducting object placed in a low frequency background field, is correct. Explicitly, H T is the background field(More)
Magnetic induction tomography (MIT) is a new electromagnetic imaging modality which has the potential to image changes in the electrical conductivity of the brain due to different pathologies. In this study the feasibility of detecting haemorrhagic cerebral stroke with a 16-channel MIT system operating at 10 MHz was investigated. The finite-element method(More)
This paper proposes a fast and effective method for reconstructing arbitrary defect profiles in steel plates from magnetic flux leakage (MFL) measurements widely used in nondestructive testing (NDT) of oil storage tanks and pipelines. The inverse reconstruction problem is formulated based on a nonlinear forward model using the finite element method (FEM)(More)
For a magnetic induction tomography (MIT) system operating at 10 MHz, the signals produced by a haemorrhagic cerebral stroke were computed using an anatomically realistic, multi-layer, finite element (FE) head model comprising 12 tissues. The eddy-current problem was approximated using the commercial FE package, Comsol Multiphysics, and the numerical(More)
The aim of this paper is to provide new insights into the properties of the rank 2 polarizability tensor M̆ proposed by Ledger and Lionheart for describing the perturbation in the magnetic field caused by the presence of a conducting object in the eddy-current regime. In particular, we explore its connection with the magnetic polarizability tensor(More)
The feasibility of detecting a cerebral haemorrhage with a hemispherical MIT coil array consisting of 56 exciter/sensor coils of 10 mm radius and operating at 1 and 10 MHz was investigated. A finite difference method combined with an anatomically realistic head model comprising 12 tissue types was used to simulate the strokes. Frequency-difference images(More)
This paper considers the numerical simulation of 2D electromagnetic wave scattering problems and describes the construction of a reduced–order approximation which enables the rapid prediction of the scattering width distribution for a range of incident wave directions. Associated certainty bounds ensure confidence in the results of the computed(More)
There is considerable interest in obtaining a low-cost mathematical description, which describes the interaction between a low frequency alternating magnetic field and a conducting object. Electrical engineers have proposed that the voltage perturbation in a coil placed in the field can be described in terms of a tensor that characterises its shape and(More)
This paper presents a few properties of the polarization tensor for conducting and magnetic objects to describe and classify the objects. In order to achieve this, the polarization tensor of the objects are numerically determined by the previous hp-FEM method. We then focus on the polarization tensor for magnetic but non-conducting objects. After that, the(More)
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