Marek Ziolkowski - Academia.edu (original) (raw)

Papers by Marek Ziolkowski

Computer Engineering in Applied Electromagnetism, 2005

Serbian Journal of Electrical Engineering, 2014

ABSTRACT Numerical modeling of commercial ECT equipment requires preparatory work in reverse engi... more ABSTRACT Numerical modeling of commercial ECT equipment requires preparatory work in reverse engineering. The reconstruction of given ECT probes was performed in terms of (i) geometry, (ii) material properties and source parameters, (iii) impedance computation. High-resolution X-ray images were taken in order to build appropriate CAD models of given ECT probes. An optimization strategy was applied in order to estimate the permeability of the magnetic shield as well as the supply current by means of measurement data of the magnetic flux density. Subsequently, normalized impedance calculations were performed and compared to measurements in generic benchmark models containing artificial defects.

Facta universitatis - series: Electronics and Energetics, 2011

During the application of simulation tools of computational electromagnetics it is sometimes diff... more During the application of simulation tools of computational electromagnetics it is sometimes difficult to decide whether the problems can be solved by the computation of electromagnetic fields or circuit simulation tools have to be applied additionally. The paper describes a typical situation in an electromagnetic CAD course, not only for beginners. The modelling and numerical simulation of a simple homopolar motor, similar to that what has been presented by Michael Faraday in 1821 firstly, was used as an example. To simulate the current flow in the permanent magnet the FEM software codes COMSOL Multiphysics including the integrated SPICE module and MAXWELL have been used. The correct simulation of the entire electric circuit as well as the precise modelling of the impressed current and of the electrode contacts turned out to be very important.

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, 2014

Purpose -The purpose of this paper is to present a novel electromagnetic non-destructive evaluati... more Purpose -The purpose of this paper is to present a novel electromagnetic non-destructive evaluation technique, so called Lorentz force eddy current testing (LET). This method can be applied for the detection and reconstruction of defects lying deep inside a non-magnetic conducting material. Design/methodology/approach -In this paper the technique is described in general as well as its experimental realization. Besides that, numerical simulations are performed and compared to experimental data. Using the output data of measurements and simulations, an inverse calculation is performed in order to reconstruct the geometry of a defect by means of sophisticated optimization algorithms. Findings -The results show that measurement data and numerical simulations are in a good agreement. The applied inverse calculation methods allow to reconstruct the dimensions of the defect in a suitable accuracy. Originality/value -LET overcomes the frequency dependent skin-depth of traditional eddy current testing due to the use of permanent magnets and low to moderate magnetic Reynolds numbers (0.1-1). This facilitates the possibility to detect subsurface defects in conductive materials.

2001 Conference Proceedings of the 23rd Annual International Conference of the IEEE Engineering in Medicine and Biology Society (Cat. No.01CH37272), 2001

Measurements of DC near biomagnetic fields are disturbed by low frequency noise, that are not red... more Measurements of DC near biomagnetic fields are disturbed by low frequency noise, that are not reduced sufficiently by most of the magnetically shielded rooms or gradiometers. An effective SQUID based active shielding system has been developed and installed at the magnetically shielded rooms in the Biomagnetic Center of the University Jena to reduce external low frequency disturbances. A reduction of the magnetic noise of about 23 dB could be achieved at 50 mHz.

Measurement Science and Technology, 2004

A novel experiment for characterization of liquid-solid interface deformation by measurement of m... more A novel experiment for characterization of liquid-solid interface deformation by measurement of magnetic flux density has been carried out. A single-axis fluxgate sensor is used to measure the distribution of radial- and z-components of magnetic field around a rotating cylindrical cell containing a solid copper cylinder with a sinusoidal surface and KOH solution above it. The signal from the magnetic

Measurement Science and Technology, 2006

A cylindrical cell containing GaInSn alloy and aqueous solution of KOH, a highly simplified alumi... more A cylindrical cell containing GaInSn alloy and aqueous solution of KOH, a highly simplified aluminium reduction cell, is constructed. A direct current is applied to the cylindrical cell to generate the magnetic field. In a range of amplitude and frequency of vertical vibration, a stable, non-axisymmetric wave pattern is produced, and the displacement of the oscillating interface is measured by

Journal of Applied Physics, 2012

The present communication reports a new technique for the contactless measurement of the specific... more The present communication reports a new technique for the contactless measurement of the specific electrical conductivity of a solid body or an electrically conducting fluid. We term the technique "Lorentz force sigmometry" where the neologism "sigmometry" is derived from the Greek letter sigma, often used to denote the electrical conductivity. Lorentz force sigmometry (LoFoS) is based on similar principles as the traditional eddy current testing but allows a larger penetration depth and is less sensitive to variations in the distance between the sensor and the sample. We formulate the theory of LoFoS and compute the calibration function which is necessary for determining the unknown electrical conductivity from measurements of the Lorentz force. We conduct a series of experiments which demonstrate that the measured Lorentz forces are in excellent agreement with the numerical predictions. Applying this technique to an aluminum sample with a known electrical conductivity of r Al ¼ 20:4 MS=m and to a copper sample with r Cu ¼ 57:92 MS=m we obtain r Al ¼ 21:59 MS=m and r Cu ¼ 60:08 MS=m, respectively. This demonstrates that LoFoS is a convenient and accurate technique that may find application in process control and thermo-physical property measurements for solid and liquid conductors. V C 2012 American Institute of Physics.

IEEE Transactions on Magnetics, 1996

The paper deals with techniques used for creation of realistically shaped models applied in solut... more The paper deals with techniques used for creation of realistically shaped models applied in solution of forward and inverse biomagnetic problems. An application of parametric Fourier representation of closed polygons to generation of boundary element meshes is described. It enables to reduce the number of generated elements with preserving the essential information about an object shape. A simple 2D-finite element mesh generator is also presented. Finally, an example of calculations of electric and magnetic fields generated by a current dipole placed in a human brain is given.

IEEE Transactions on Magnetics, 2000

The paper presents an equivalent ellipsoid approach for interpretation and visualization of exten... more The paper presents an equivalent ellipsoid approach for interpretation and visualization of extended current distributions in biomagnetic inverse problems. The example of simulations performed with physical thorax phantom is also given.

IEEE Transactions on Magnetics, 2004

The identification of characteristics or shape reconstruction of boundary surfaces are inverse pr... more The identification of characteristics or shape reconstruction of boundary surfaces are inverse problems arising in industrial applications, e.g., in magnetic fluid dynamics. We have investigated the identification of the interface between two conducting fluids using multichannel magnetic field measurements (magnetic field tomography). We considered a highly simplified model of an aluminum electrolysis cell consisting of a cylinder containing two compartments with different conductivities. Numerical simulations using the finite element method (FEM) have been evaluated. Additionally, magnetic field measurements taken from an experimental setup of this cylindrical object have been used as a reference for comparison. We propose a new test problem for the evaluation of inverse methods which consists in the estimation of the interface shape characteristics based on the current density distribution in the vicinity of the deformed interface using magnetic field measurements.

IEEE Transactions on Magnetics, 2000

Abstract We have prepared a human body phantom for experimental verification of inverse solution ... more Abstract We have prepared a human body phantom for experimental verification of inverse solution techniques which are applied to magnetic (and electric) measuring data. Physical models of extended primary current sources were used to generate these fields. Magnetic ...

IEEE Transactions on Magnetics, 2000

Relative movement of permanent magnet and conductor evokes forces acting on both objects (Lorentz... more Relative movement of permanent magnet and conductor evokes forces acting on both objects (Lorentz forces). These forces can be used for studying material characteristics of the conducting object (nondestructive testing). The paper compares various modeling techniques (transient, quasi-static, fast-quasi-static) of a moving permanent magnet above conducting plate using 2-D and 3-D finite-element method (FEM). The proposed approaches are applied to calculations of force profiles which enable to identify defects in conductor. The comparison of simulations with measurements performed on a long aluminum bar is also presented.

IEEE Transactions on Magnetics, 2000

There are several applications in magnetic fluid dynamics where it is important to know the behav... more There are several applications in magnetic fluid dynamics where it is important to know the behaviour of separation surfaces between fluids. Our magnetic field tomography system enables to reconstruct interface shapes between two conducting fluids on the basis of magnetic field measurements. A simple direct searching strategy for an identification of dominant modes of the interface in a cylindrical two-fluid system is presented.

IEEE Transactions on Biomedical Engineering, 2002

A method of postprocessing and visualizing three-dimensional vector fields, such as current densi... more A method of postprocessing and visualizing three-dimensional vector fields, such as current density reconstruction results, is presented. This method is based on equivalent ellipsoids fitted to the vector fields. The technique has been tested with simulated data and current density reconstructions based on bioelectromagnetic data obtained from a physical thorax phantom. Three different approaches based on: 1) longest distance; 2) dominant direction; and 3) principal component analysis, for fitting the equivalent ellipsoids are proposed. Multiple foci in vector fields are extracted by multiple ellipsoids which are fitted iteratively. The method enables statistical postprocessing for the sake of comparisons of different source reconstructions algorithms or comparisons of groups of patients or volunteers.

COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering, 2003

In many industrial applications of magnetic fluid dynamics it is important to control the motion ... more In many industrial applications of magnetic fluid dynamics it is important to control the motion of the surface of liquids. In aluminium electrolysis cells, large surface deformations of the molten aluminium are undesired, and it would be useful to have the possibility to recognize the surface deviation. This includes the problem of reconstructing a free boundary between the conducting fluids. We have investigated how the interface between two fluids of different conductivity assumed in a highly simplified model of an aluminium electrolysis cell could be reconstructed by means of external magnetic field measurements. Forward simulations of the magnetic field generated by the impressed current are done by applying the FEM software code FEMLAB. Several interface shapes which can be realized in experiments are investigated and a strategy for identifying the main interface characteristics using magnetic field measurements as an initial guess to the solution of the inverse problem is proposed.

COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering, 1994

ABSTRACT

COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering, 2005

Purpose – To provide a new semi-analytical procedure which is much faster than FEM and for this r... more Purpose – To provide a new semi-analytical procedure which is much faster than FEM and for this reason can be applied in a reconstruction of an interface between two conducting fluids (magnetic fluid dynamics problem) by means of magnetic field tomography. Design/methodology/approach – Three approaches are compared: a simple analytical solution (AS1), a modified semi-analytical solution (AS2), and the finite

COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering, 2005

Purpose – The interface between two conducting fluids in a magnetic fluid dynamics (MFD) problem ... more Purpose – The interface between two conducting fluids in a magnetic fluid dynamics (MFD) problem was identified by means of external magnetic field measurements. Genetic algorithms (GA) were applied to solve the inverse problem.The principal component analysis (PCA) was used to speed up the process of interface reconstruction. Design/methodology/approach – With respect to the experimental results we have designed a general technique for mode identification and/or interface reconstruction. Two main procedures are available to solve the inverse problem, the full interface reconstruction and the principle component analysis (PCA) mode. In the case of full reconstruction, it can be decided whether an algorithm for fast identification of the dominant modes applying a FFT module should be performed or not. The full interface reconstruction applies stochastic optimization methods ((GA) or evolution strategies (ES)) for the estimation of the interface shape characteristics. The main goal of the PCA mode is to find the dominant mode of the interface shape and its amplitude. The PCA mode is realized by means of stochastic optimization methods (GA, ES) and a simple direct searching (DS) using the golden section technique. Findings – PCA with GA procedure enables the identification of the dominant mode of the interface shape between two conducting fluids with sufficient accuracy for simulated magnetic fields. Time of identification is strongly reduced due to a redefinition of the genotype representations in the PCA mode. Accuracy of reconstruction depends on the noise level, i.e. signal to noise ratio and a geometrical model used in the reconstruction phase. The correlation between the noise level and values of cost function for identified modes has been found if a proper geometry modelling is applied. Originality/value – The paper describes a new, fast technique for solving an inverse field problem of a MFD problem where the interface between two conducting fluids has to be identified using a magnetic field tomography measuring system.

Computer Engineering in Applied Electromagnetism, 2005

Serbian Journal of Electrical Engineering, 2014

ABSTRACT Numerical modeling of commercial ECT equipment requires preparatory work in reverse engi... more ABSTRACT Numerical modeling of commercial ECT equipment requires preparatory work in reverse engineering. The reconstruction of given ECT probes was performed in terms of (i) geometry, (ii) material properties and source parameters, (iii) impedance computation. High-resolution X-ray images were taken in order to build appropriate CAD models of given ECT probes. An optimization strategy was applied in order to estimate the permeability of the magnetic shield as well as the supply current by means of measurement data of the magnetic flux density. Subsequently, normalized impedance calculations were performed and compared to measurements in generic benchmark models containing artificial defects.

Facta universitatis - series: Electronics and Energetics, 2011

During the application of simulation tools of computational electromagnetics it is sometimes diff... more During the application of simulation tools of computational electromagnetics it is sometimes difficult to decide whether the problems can be solved by the computation of electromagnetic fields or circuit simulation tools have to be applied additionally. The paper describes a typical situation in an electromagnetic CAD course, not only for beginners. The modelling and numerical simulation of a simple homopolar motor, similar to that what has been presented by Michael Faraday in 1821 firstly, was used as an example. To simulate the current flow in the permanent magnet the FEM software codes COMSOL Multiphysics including the integrated SPICE module and MAXWELL have been used. The correct simulation of the entire electric circuit as well as the precise modelling of the impressed current and of the electrode contacts turned out to be very important.

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, 2014

Purpose -The purpose of this paper is to present a novel electromagnetic non-destructive evaluati... more Purpose -The purpose of this paper is to present a novel electromagnetic non-destructive evaluation technique, so called Lorentz force eddy current testing (LET). This method can be applied for the detection and reconstruction of defects lying deep inside a non-magnetic conducting material. Design/methodology/approach -In this paper the technique is described in general as well as its experimental realization. Besides that, numerical simulations are performed and compared to experimental data. Using the output data of measurements and simulations, an inverse calculation is performed in order to reconstruct the geometry of a defect by means of sophisticated optimization algorithms. Findings -The results show that measurement data and numerical simulations are in a good agreement. The applied inverse calculation methods allow to reconstruct the dimensions of the defect in a suitable accuracy. Originality/value -LET overcomes the frequency dependent skin-depth of traditional eddy current testing due to the use of permanent magnets and low to moderate magnetic Reynolds numbers (0.1-1). This facilitates the possibility to detect subsurface defects in conductive materials.

2001 Conference Proceedings of the 23rd Annual International Conference of the IEEE Engineering in Medicine and Biology Society (Cat. No.01CH37272), 2001

Measurements of DC near biomagnetic fields are disturbed by low frequency noise, that are not red... more Measurements of DC near biomagnetic fields are disturbed by low frequency noise, that are not reduced sufficiently by most of the magnetically shielded rooms or gradiometers. An effective SQUID based active shielding system has been developed and installed at the magnetically shielded rooms in the Biomagnetic Center of the University Jena to reduce external low frequency disturbances. A reduction of the magnetic noise of about 23 dB could be achieved at 50 mHz.

Measurement Science and Technology, 2004

A novel experiment for characterization of liquid-solid interface deformation by measurement of m... more A novel experiment for characterization of liquid-solid interface deformation by measurement of magnetic flux density has been carried out. A single-axis fluxgate sensor is used to measure the distribution of radial- and z-components of magnetic field around a rotating cylindrical cell containing a solid copper cylinder with a sinusoidal surface and KOH solution above it. The signal from the magnetic

Measurement Science and Technology, 2006

A cylindrical cell containing GaInSn alloy and aqueous solution of KOH, a highly simplified alumi... more A cylindrical cell containing GaInSn alloy and aqueous solution of KOH, a highly simplified aluminium reduction cell, is constructed. A direct current is applied to the cylindrical cell to generate the magnetic field. In a range of amplitude and frequency of vertical vibration, a stable, non-axisymmetric wave pattern is produced, and the displacement of the oscillating interface is measured by

Journal of Applied Physics, 2012

The present communication reports a new technique for the contactless measurement of the specific... more The present communication reports a new technique for the contactless measurement of the specific electrical conductivity of a solid body or an electrically conducting fluid. We term the technique "Lorentz force sigmometry" where the neologism "sigmometry" is derived from the Greek letter sigma, often used to denote the electrical conductivity. Lorentz force sigmometry (LoFoS) is based on similar principles as the traditional eddy current testing but allows a larger penetration depth and is less sensitive to variations in the distance between the sensor and the sample. We formulate the theory of LoFoS and compute the calibration function which is necessary for determining the unknown electrical conductivity from measurements of the Lorentz force. We conduct a series of experiments which demonstrate that the measured Lorentz forces are in excellent agreement with the numerical predictions. Applying this technique to an aluminum sample with a known electrical conductivity of r Al ¼ 20:4 MS=m and to a copper sample with r Cu ¼ 57:92 MS=m we obtain r Al ¼ 21:59 MS=m and r Cu ¼ 60:08 MS=m, respectively. This demonstrates that LoFoS is a convenient and accurate technique that may find application in process control and thermo-physical property measurements for solid and liquid conductors. V C 2012 American Institute of Physics.

IEEE Transactions on Magnetics, 1996

The paper deals with techniques used for creation of realistically shaped models applied in solut... more The paper deals with techniques used for creation of realistically shaped models applied in solution of forward and inverse biomagnetic problems. An application of parametric Fourier representation of closed polygons to generation of boundary element meshes is described. It enables to reduce the number of generated elements with preserving the essential information about an object shape. A simple 2D-finite element mesh generator is also presented. Finally, an example of calculations of electric and magnetic fields generated by a current dipole placed in a human brain is given.

IEEE Transactions on Magnetics, 2000

The paper presents an equivalent ellipsoid approach for interpretation and visualization of exten... more The paper presents an equivalent ellipsoid approach for interpretation and visualization of extended current distributions in biomagnetic inverse problems. The example of simulations performed with physical thorax phantom is also given.

IEEE Transactions on Magnetics, 2004

The identification of characteristics or shape reconstruction of boundary surfaces are inverse pr... more The identification of characteristics or shape reconstruction of boundary surfaces are inverse problems arising in industrial applications, e.g., in magnetic fluid dynamics. We have investigated the identification of the interface between two conducting fluids using multichannel magnetic field measurements (magnetic field tomography). We considered a highly simplified model of an aluminum electrolysis cell consisting of a cylinder containing two compartments with different conductivities. Numerical simulations using the finite element method (FEM) have been evaluated. Additionally, magnetic field measurements taken from an experimental setup of this cylindrical object have been used as a reference for comparison. We propose a new test problem for the evaluation of inverse methods which consists in the estimation of the interface shape characteristics based on the current density distribution in the vicinity of the deformed interface using magnetic field measurements.

IEEE Transactions on Magnetics, 2000

Abstract We have prepared a human body phantom for experimental verification of inverse solution ... more Abstract We have prepared a human body phantom for experimental verification of inverse solution techniques which are applied to magnetic (and electric) measuring data. Physical models of extended primary current sources were used to generate these fields. Magnetic ...

IEEE Transactions on Magnetics, 2000

Relative movement of permanent magnet and conductor evokes forces acting on both objects (Lorentz... more Relative movement of permanent magnet and conductor evokes forces acting on both objects (Lorentz forces). These forces can be used for studying material characteristics of the conducting object (nondestructive testing). The paper compares various modeling techniques (transient, quasi-static, fast-quasi-static) of a moving permanent magnet above conducting plate using 2-D and 3-D finite-element method (FEM). The proposed approaches are applied to calculations of force profiles which enable to identify defects in conductor. The comparison of simulations with measurements performed on a long aluminum bar is also presented.

IEEE Transactions on Magnetics, 2000

There are several applications in magnetic fluid dynamics where it is important to know the behav... more There are several applications in magnetic fluid dynamics where it is important to know the behaviour of separation surfaces between fluids. Our magnetic field tomography system enables to reconstruct interface shapes between two conducting fluids on the basis of magnetic field measurements. A simple direct searching strategy for an identification of dominant modes of the interface in a cylindrical two-fluid system is presented.

IEEE Transactions on Biomedical Engineering, 2002

A method of postprocessing and visualizing three-dimensional vector fields, such as current densi... more A method of postprocessing and visualizing three-dimensional vector fields, such as current density reconstruction results, is presented. This method is based on equivalent ellipsoids fitted to the vector fields. The technique has been tested with simulated data and current density reconstructions based on bioelectromagnetic data obtained from a physical thorax phantom. Three different approaches based on: 1) longest distance; 2) dominant direction; and 3) principal component analysis, for fitting the equivalent ellipsoids are proposed. Multiple foci in vector fields are extracted by multiple ellipsoids which are fitted iteratively. The method enables statistical postprocessing for the sake of comparisons of different source reconstructions algorithms or comparisons of groups of patients or volunteers.

COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering, 2003

In many industrial applications of magnetic fluid dynamics it is important to control the motion ... more In many industrial applications of magnetic fluid dynamics it is important to control the motion of the surface of liquids. In aluminium electrolysis cells, large surface deformations of the molten aluminium are undesired, and it would be useful to have the possibility to recognize the surface deviation. This includes the problem of reconstructing a free boundary between the conducting fluids. We have investigated how the interface between two fluids of different conductivity assumed in a highly simplified model of an aluminium electrolysis cell could be reconstructed by means of external magnetic field measurements. Forward simulations of the magnetic field generated by the impressed current are done by applying the FEM software code FEMLAB. Several interface shapes which can be realized in experiments are investigated and a strategy for identifying the main interface characteristics using magnetic field measurements as an initial guess to the solution of the inverse problem is proposed.

COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering, 1994

ABSTRACT

COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering, 2005

Purpose – To provide a new semi-analytical procedure which is much faster than FEM and for this r... more Purpose – To provide a new semi-analytical procedure which is much faster than FEM and for this reason can be applied in a reconstruction of an interface between two conducting fluids (magnetic fluid dynamics problem) by means of magnetic field tomography. Design/methodology/approach – Three approaches are compared: a simple analytical solution (AS1), a modified semi-analytical solution (AS2), and the finite

COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering, 2005

Purpose – The interface between two conducting fluids in a magnetic fluid dynamics (MFD) problem ... more Purpose – The interface between two conducting fluids in a magnetic fluid dynamics (MFD) problem was identified by means of external magnetic field measurements. Genetic algorithms (GA) were applied to solve the inverse problem.The principal component analysis (PCA) was used to speed up the process of interface reconstruction. Design/methodology/approach – With respect to the experimental results we have designed a general technique for mode identification and/or interface reconstruction. Two main procedures are available to solve the inverse problem, the full interface reconstruction and the principle component analysis (PCA) mode. In the case of full reconstruction, it can be decided whether an algorithm for fast identification of the dominant modes applying a FFT module should be performed or not. The full interface reconstruction applies stochastic optimization methods ((GA) or evolution strategies (ES)) for the estimation of the interface shape characteristics. The main goal of the PCA mode is to find the dominant mode of the interface shape and its amplitude. The PCA mode is realized by means of stochastic optimization methods (GA, ES) and a simple direct searching (DS) using the golden section technique. Findings – PCA with GA procedure enables the identification of the dominant mode of the interface shape between two conducting fluids with sufficient accuracy for simulated magnetic fields. Time of identification is strongly reduced due to a redefinition of the genotype representations in the PCA mode. Accuracy of reconstruction depends on the noise level, i.e. signal to noise ratio and a geometrical model used in the reconstruction phase. The correlation between the noise level and values of cost function for identified modes has been found if a proper geometry modelling is applied. Originality/value – The paper describes a new, fast technique for solving an inverse field problem of a MFD problem where the interface between two conducting fluids has to be identified using a magnetic field tomography measuring system.