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Article
Publication date: 26 June 2024

Bojana Petkovć, Marek Ziolkowski, Hannes Toepfer and Jens Haueisen

The purpose of this paper is to derive a new stress tensor for calculating the Lorentz force acting on an arbitrarily shaped nonmagnetic conductive specimen moving in the field of…

29

Abstract

Purpose

The purpose of this paper is to derive a new stress tensor for calculating the Lorentz force acting on an arbitrarily shaped nonmagnetic conductive specimen moving in the field of a permanent magnet. The stress tensor allows for a transition from a volume to a surface integral for force calculation.

Design/methodology/approach

This paper derives a new stress tensor which consists of two parts: the first part corresponds to the scaled Poynting vector and the second part corresponds to the velocity term. This paper converts the triple integral over the volume of the conductor to a double integral over its surface, where the subintegral functions are continuous through the different compartments of the model. Numerical results and comparison to the standard volume discretization using the finite element method are given.

Findings

This paper evaluated the performance of the new stress tensor computation on a thick and thin cuboid, a thin disk, a sphere and a thin cuboid containing a surface defect. The integrals are valid for any geometry of the specimen and the position and orientation of the magnet. The normalized root mean square errors are below 0.26% with respect to a reference finite element solution applying volume integration.

Originality/value

Tensor elements are continuous throughout the model, allowing integration directly over the conductor surface.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering , vol. 43 no. 4
Type: Research Article
ISSN: 0332-1649

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Article
Publication date: 1 April 2019

Eva-Maria Dölker, Bojana Petković, Reinhard Schmidt, Marek Ziolkowski, Hartmut Brauer and Jens Haueisen

Lorentz force evaluation is a non-destructive evaluation method for conducting specimens. The movement of a specimen relative to a permanent magnet leads to Lorentz forces that…

128

Abstract

Purpose

Lorentz force evaluation is a non-destructive evaluation method for conducting specimens. The movement of a specimen relative to a permanent magnet leads to Lorentz forces that are perturbed in the presence of a defect. This defect response signal (DRS) is used for defect reconstruction. To solve a linear inverse problem for defect reconstruction, an accurate and fast forward computation method is required. As existing forward methods are either too slow or too inaccurate, the purpose of this paper is to propose the single voxel approach (SVA) as a novel method.

Design/methodology/approach

In SVA, the DRS is computed as a superposition of DRSs from single defect voxels, which are calculated in advance, by applying the boundary element source method. This research uses a setup of an isotropic conducting specimen, a spherical permanent magnet and defects of different shapes at different depths. With the help of simulations, this study compares the SVA to the previously proposed approximate forward solution (AFS) and the extended area approach (EAA) using the normalized root mean square error (NRMSE). Simulated data using the finite element method serve as the reference solution.

Findings

SVA shows across all simulations NRMSE values <2.5 per cent compared to <8 per cent for EAA and <12 per cent for AFS.

Originality/value

The superposition principle of SVA allows for the application of linear inverse methods for defect reconstruction while providing sufficient accuracy of the forward method.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 38 no. 3
Type: Research Article
ISSN: 0332-1649

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Article
Publication date: 18 March 2019

Roland Eichardt, Daniel Strohmeier, Alexander Hunold, René Machts, Jens Haueisen, Gregor Oelsner, Christian B. Schmidt, Volkmar Schultze, Ronny Stolz and Uwe Graichen

The purpose of this paper is to present a simulation study using a model of a new optically pumped magnetometer sensor for application in the field of magnetoencephalography. The…

161

Abstract

Purpose

The purpose of this paper is to present a simulation study using a model of a new optically pumped magnetometer sensor for application in the field of magnetoencephalography. The effects of sensor distance and orientation on the measurement information and the sensitivity to neuronal sources are investigated. Further, this paper uses a combinatorial optimization approach for sensor placement to measure spontaneous activity in the region of the occipital cortex.

Design/methodology/approach

This paper studies the effects of sensor distance and orientation on sensitivity to cortical sources and measurement information. A three-compartment model of the head, using the boundary element method, is applied. For sensor setup optimization, a combinatorial optimization scheme is developed.

Findings

The sensor distance to sources considerably affects the sensitivity and the retrieved information. A specific arrangement of four sensors for measuring spontaneous activity over the occipital part of the head is optimized by effectively avoiding position conflicts.

Research limitations/implications

Individual head models, as well as more detailed noise and signal models, will increase the significance for specific-use cases in future studies.

Originality/value

Effects of sensor distance and orientation are specifically evaluated for a new optically pumped magnetometer. A discrete optimization scheme for sensor optimization is introduced. The presented methodology is applicable for other sensor characterization and optimization problems. The findings contribute significantly to the development of new sensors.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering , vol. 38 no. 3
Type: Research Article
ISSN: 0332-1649

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Article
Publication date: 11 September 2009

Roland Eichardt, Daniel Baumgarten, Luca Di Rienzo, Sven Linzen, Volkmar Schultze and Jens Haueisen

The purpose of this paper is to examine the localisation of ferromagnetic objects buried in the underground. More specifically, it deals with the reconstruction of the…

242

Abstract

Purpose

The purpose of this paper is to examine the localisation of ferromagnetic objects buried in the underground. More specifically, it deals with the reconstruction of the XY‐positions, the depths (Z‐positions), the number, and the extension of the objects based on geomagnetic measurements. This paper introduces a minimum‐norm reconstruction approach and evaluates its performance in a simulation study.

Design/methodology/approach

A minimum‐L2‐norm estimation based on the truncated singular value decomposition method with lead field weighting is proposed in order to localise geomagnetic sources. The sensor setup and positions are taken from real measurements. The source space is formed by an automatically generated grid. At each grid point, a magneto‐static dipole is assumed.

Findings

Sources with different depths and XY‐positions could be successfully reconstructed. The proposed approach is not overly sensitive to errors/noise in measurement values and sensor positions.

Originality/value

The approach described in this paper can be used for applications like geoprospection, archaeology, mine clearing, and the clean‐up of former waste deposits.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 28 no. 5
Type: Research Article
ISSN: 0332-1649

Keywords

Available. Content available

Abstract

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 28 no. 5
Type: Research Article
ISSN: 0332-1649

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Article
Publication date: 10 April 2007

Luca Di Rienzo and Jens Haueisen

To define a methodology for comparing sensor arrays for solving magnetostatic linear inverse problems.

253

Abstract

Purpose

To define a methodology for comparing sensor arrays for solving magnetostatic linear inverse problems.

Design/methodology/approach

A singular value decomposition related projection method is used for comparing sensor arrays and we applied it to a biomagnetic inverse problem, as an example. Furthermore, a theoretical reference sensor system is introduced and used as a benchmark for the analysed sensor arrays.

Findings

The method has turned out to be effective in comparing three different theoretical sensor arrays, showing the superiority of the two arrays constituted by three‐axial sensors.

Research limitations/implications

The method has been applied only to the case of over‐determined problems. The underdetermined case will be considered in future work.

Practical implications

From the applicative point of view, the illustrated methodology is useful when one has to choose between existing sensor arrays or in the design phase of a new sensor array.

Originality/value

A new methodology is proposed for comparing sensor arrays. The advantage of the methodology are to take into account the regularization in the solution of the inverse problem and to be general, not depending on a particular source configuration.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 26 no. 2
Type: Research Article
ISSN: 0332-1649

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Article
Publication date: 1 June 2001

Hartmut Brauer, Marek Ziolkowski, Uwe Tenner, Jens Haueisen and Hannes Nowak

Applies four different minimum norm estimations with common regularization techniques, often used in biomedical applications to the solution of the biomagnetic inverse field…

224

Abstract

Applies four different minimum norm estimations with common regularization techniques, often used in biomedical applications to the solution of the biomagnetic inverse field problem. Magnetic field data measured with a multi‐channel biomagnetometer sensor system in a magnetically shielded room were used to reconstruct the current density distributions generated by an extended current source which was placed inside a human torso phantom. No one of the tested methods is able to estimate the extension of the source. To improve the results as much as possible a priori information of the source space should be taken into account.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 20 no. 2
Type: Research Article
ISSN: 0332-1649

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Article
Publication date: 11 September 2009

Mehbub‐ur Rahman and René Marklein

The purpose of this paper is to present a time‐domain technique to compute the electromagnetic wave field and to reconstruct the permittivity and electric conductivity profile of…

187

Abstract

Purpose

The purpose of this paper is to present a time‐domain technique to compute the electromagnetic wave field and to reconstruct the permittivity and electric conductivity profile of a one‐dimensional slab of finite length.

Design/methodology/approach

The forward scattering problem is solved by a Green's function formulation to generate synthetic data that are used as a testbed for the inversion scheme. The inverse scattering problem is solved by reconstructing the unknown permittivity and electric conductivity profile of the medium with the help of an invariant embedding method.

Findings

The Green's operator maps the incident field on either side of the medium to the field at an arbitrary observation point inside the slab and hence, the internal fields can be computed directly without computing the wave field throughout the entire medium. The invariant embedding method requires a finite time trace of reflection data and therefore it is suitable for reconstructing the material parameters in real‐time.

Practical implications

The implemented methods have been validated against synthetic and measured time domain reflectometry data.

Originality/value

This paper fulfils an identified need to determine unknown one‐dimensional profiles and thus plays an important role in electromagnetics, non‐destructive testing, and geophysics.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 28 no. 5
Type: Research Article
ISSN: 0332-1649

Keywords

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Article
Publication date: 11 September 2009

P. Di Barba and M.E. Mognaschi

The purpose of the paper is to show that the a posteriori analysis of the Pareto front associated with a given design problem facilitates the task of the decision maker and…

642

Abstract

Purpose

The purpose of the paper is to show that the a posteriori analysis of the Pareto front associated with a given design problem facilitates the task of the decision maker and possibly helps to identify innovative solutions. The idea is to investigate the similarities existing among non‐dominated solutions.

Design/methodology/approach

A permanent‐magnet alternator for automotive applications is considered as case study. The design problem exhibits six design variables and two energy‐related objective functions. A suitable sampling of the objective space is made and non‐dominated solutions, located along an L‐shaped front, are approximated. Results are assessed by means of a successive optimization using NSGA‐II algorithm.

Findings

From the approximated Pareto front, three optimal devices have been selected and remapped in the design space in order to compare their performance. This is done in terms of iron and copper losses, material costs, rated voltage, and air‐gap induction. Moreover, making the NSGA‐II start from the knee‐point of the front, it is shown that a direct approximation of the two sub‐fronts is possible.

Originality/value

In this paper, a method to sort out the optimal solutions located along the Pareto front is proposed as a possible criterion of decision making; so doing, previously unpredicted solutions might be identified.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 28 no. 5
Type: Research Article
ISSN: 0332-1649

Keywords

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Article
Publication date: 1 September 2005

Luca Di Rienzo, Jens Haueisen and Cesare Mario Arturi

To demonstrate the improvement of three‐axial magnetic sensors systems for magnetocardiography when using minimum norm solutions (MNS).

342

Abstract

Purpose

To demonstrate the improvement of three‐axial magnetic sensors systems for magnetocardiography when using minimum norm solutions (MNS).

Design/methodology/approach

The thesis is proved by using figures of merit and by means of repeated numerical simulations, starting from a BEM model for forward calculations.

Findings

We found out that both for under‐determined and over‐determined problems two figures of merit show better performance of a three‐axial sensor system when compared with two mono‐axial sensor systems. We also showed the positive impact of three component magnetic field data on MNS by means of repeated simulations.

Research limitations/implications

The analysis is limited to theoretical sensor systems and can be applied also to realistic measurement set‐ups. Noise is considered uncorrelated. The analysis could be carried out with the help of other figures of merit. More refined models for the human body could be adopted.

Practical implications

The use of three axial sensor systems is encouraged in the field of magnetocardiography.

Originality/value

Numerical analysis of inversion algorithms using three‐dimensional magnetic field data in magnetocardiography have been never carried out.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 24 no. 3
Type: Research Article
ISSN: 0332-1649

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