Mihai Vasiliu | Universitatea Politehnica din Bucuresti (original) (raw)

Papers by Mihai Vasiliu

IEEE Transactions on Magnetics, 2000

An overview of the polarization method is presented. The method can by applied for different regi... more An overview of the polarization method is presented. The method can by applied for different regimes of the electromagnetic field as well as for electric circuits. Criteria for the choice of the permeability are proposed, so that the iterative scheme leads to a Picard-Banach fixed point procedure. The errors are evaluated. An efficient overelaxation method is presented. The modality of using FEM numerical method is analyzed in order to ensure the convergence of the method.

The aim is to introduce shielding of nonsinusoidal waveforms through a basic shielding structure ... more The aim is to introduce shielding of nonsinusoidal waveforms through a basic shielding structure allowing a one-dimensional field model. By providing analytical solutions, it is hoped that this novel approach will contribute to a better understanding of shielding problem~ raised by power electronics circuitry where discontinuous waveforms are typical. The approach is based on the eigenfunction expansion of the field. This approach represents an alternative to the classical harmonic analysis of time periodic waveforms. Quasi-stationary magnetic fields are assumed.

The aim is to report experimental results on low energy medium current electron beams in a better... more The aim is to report experimental results on low energy medium current electron beams in a better agreement with space charge model. The experiments were performed using a laboratory installation specially designed for electron beam (EB) diagnosis and dynamics referred to as DIADYN. It includes a vacuum electron source, a beam channel consisting of two axially symmetric magnetic lenses, as well as two beams profile monitors. Our previously reported investigations were focused on the nondestructive beam diagnosis at the source exit and on the beam dynamics in the transport channel. In the present work we report on hardware adjustments of the EB channel that led to a better agreement between calculated and experimental data. DIADYN proved to be a suitable educational tool for an in depth understanding of EB physical and engineering aspects.

An efficient procedure for the analysis of shielding effectiveness can be performed by the curren... more An efficient procedure for the analysis of shielding effectiveness can be performed by the current sheet integral equation in thin shields (CSIE). In the presence of ferromagnetic bodies and, moreover, in the periodic regime, where higher harmonics appears due to the nonlinearity of B-H characteristic, this equation can not be obtained directly. In this paper a method based on CSIE is proposed, where the nonlinear media are treated using the polarization fixed point method (PFPM). At each iteration, a Fourier analysis is performed, and CSIE is solved for each harmonic having imposed currents and the polarization harmonics as electromagnetic field sources. To speed up the iterative process the harmonic selection is progressive. The convergence of the proposed procedure is always insured.

International Journal of Applied Electromagnetics and Mechanics

ABSTRACT The paper presents a very useful method for computation of the sensitivities of electric... more ABSTRACT The paper presents a very useful method for computation of the sensitivities of electrical machines, taking into account the non-linearity of the ferromagnetic bodies. In the first step, the magnetic field in non-linear media and the performances of the given machine are calculated. The non-linear medium is replaced with a linear medium having a magnetic polarization that is iteratively corrected by the flux density. Each linear field problem is solved using the periodic Green function. In the second step, the difference of the magnetic field due to the small modification is computed directly. The polarization of the eliminated ferromagnetic domain is the field source. The B-I relation is given by Frechet first derivative.

Nowadays, the medical practice is limited to exploring the thermal field on the breast surface, t... more Nowadays, the medical practice is limited to exploring the thermal field on the breast surface, the infrared images being interpreted by specialist doctors with experience in this domain. The specialists succeed in the early detection of some abnormalities in the cell activity, that could represent the beginning of a malignant tumor development. Unfortunately, a procedure to determine the position and the dimensions of the tumor (a thermographical "radiography") has not been found yet.

7th Joint MMM-Intermag Conference. Abstracts (Cat. No.98CH36275), 1998

Journal of Materials Processing Technology, 2005

Two procedures in the boundary element method (BEM) for multiply connected domains are reported. ... more Two procedures in the boundary element method (BEM) for multiply connected domains are reported. The first procedure introduces cuts such that the multiply connected domain is transformed into a simply connected one, so that it allows the use of the scalar potential. Each cut introduces an additional term containing the "hall" current multiplied by the solid angle under which the cut is seen. The second procedure is based on a novel magnetic vector potential formulation. It uses edge elements and tree-cotree spanning. A zero normal component of this vector potential A and the condition for its line integral along any closed path on the boundary are imposed, such that the continuity of the normal component of the magnetic flux density be rigorously satisfied. The unknowns are the tangential components of × A and the tree edge element values.

ABSTRACT An efficient procedure for the analysis of shielding effectiveness can be performed by t... more ABSTRACT An efficient procedure for the analysis of shielding effectiveness can be performed by the current sheet integral equation in thin shields (CSIE). In the presence of ferromagnetic bodies and, moreover, in the periodic regime, where higher harmonics appears due to the nonlinearity of B-H characteristic, this equation can not be obtained directly. In this paper a method based on CSIE is proposed, where the nonlinear media are treated using the polarization fixed point method (PFPM). At each iteration, a Fourier analysis is performed, and CSIE is solved for each harmonic having imposed currents and the polarization harmonics as electromagnetic field sources. To speed up the iterative process the harmonic selection is progressive. The convergence of the proposed procedure is always insured.

The ferromagnetic shields represent an effective solution for the time constant and low frequency... more The ferromagnetic shields represent an effective solution for the time constant and low frequency magnetic fields attenuation. This paper presents an efficient method for evaluation the ferromagnetic shielding. It needs the computing of the time-periodic eddy currents in nonlinear media. Using the Polarization Fixed Point Method and the Fourier decomposition of the time-periodic magnetization, the electromagnetic field is obtained by solving the eddy-current integral equation for each harmonic. The magnetic field in shielded zone is produced by the imposed current distribution, the induced currents and the magnetization of ferromagnetic bodies, the integral equation is applied only on the shield domain which occupies a very reduced space or, if other conducting bodies are in the vicinity of the shield, the integral equation is extended only for them. The system matrix is inverted only once, before the iterations and remains unchanged.

An overview of the polarization method is presented. The method can by applied for different regi... more An overview of the polarization method is presented. The method can by applied for different regimes of the electromagnetic field as well as for electric circuits. Criteria for the choice of the permeability are proposed, so that the iterative scheme leads to a Picard-Banach fixed point procedure. The errors are evaluated. An efficient overrelaxation method is presented. The modality of using FEM numerical method is analyzed in order to ensure the convergence of the method

2008 4th European Conference on Circuits and Systems for Communications, 2008

IEEE Transactions on Magnetics, 2000

An overview of the polarization method is presented. The method can by applied for different regi... more An overview of the polarization method is presented. The method can by applied for different regimes of the electromagnetic field as well as for electric circuits. Criteria for the choice of the permeability are proposed, so that the iterative scheme leads to a Picard-Banach fixed point procedure. The errors are evaluated. An efficient overelaxation method is presented. The modality of using FEM numerical method is analyzed in order to ensure the convergence of the method.

The aim is to introduce shielding of nonsinusoidal waveforms through a basic shielding structure ... more The aim is to introduce shielding of nonsinusoidal waveforms through a basic shielding structure allowing a one-dimensional field model. By providing analytical solutions, it is hoped that this novel approach will contribute to a better understanding of shielding problem~ raised by power electronics circuitry where discontinuous waveforms are typical. The approach is based on the eigenfunction expansion of the field. This approach represents an alternative to the classical harmonic analysis of time periodic waveforms. Quasi-stationary magnetic fields are assumed.

The aim is to report experimental results on low energy medium current electron beams in a better... more The aim is to report experimental results on low energy medium current electron beams in a better agreement with space charge model. The experiments were performed using a laboratory installation specially designed for electron beam (EB) diagnosis and dynamics referred to as DIADYN. It includes a vacuum electron source, a beam channel consisting of two axially symmetric magnetic lenses, as well as two beams profile monitors. Our previously reported investigations were focused on the nondestructive beam diagnosis at the source exit and on the beam dynamics in the transport channel. In the present work we report on hardware adjustments of the EB channel that led to a better agreement between calculated and experimental data. DIADYN proved to be a suitable educational tool for an in depth understanding of EB physical and engineering aspects.

An efficient procedure for the analysis of shielding effectiveness can be performed by the curren... more An efficient procedure for the analysis of shielding effectiveness can be performed by the current sheet integral equation in thin shields (CSIE). In the presence of ferromagnetic bodies and, moreover, in the periodic regime, where higher harmonics appears due to the nonlinearity of B-H characteristic, this equation can not be obtained directly. In this paper a method based on CSIE is proposed, where the nonlinear media are treated using the polarization fixed point method (PFPM). At each iteration, a Fourier analysis is performed, and CSIE is solved for each harmonic having imposed currents and the polarization harmonics as electromagnetic field sources. To speed up the iterative process the harmonic selection is progressive. The convergence of the proposed procedure is always insured.

International Journal of Applied Electromagnetics and Mechanics

ABSTRACT The paper presents a very useful method for computation of the sensitivities of electric... more ABSTRACT The paper presents a very useful method for computation of the sensitivities of electrical machines, taking into account the non-linearity of the ferromagnetic bodies. In the first step, the magnetic field in non-linear media and the performances of the given machine are calculated. The non-linear medium is replaced with a linear medium having a magnetic polarization that is iteratively corrected by the flux density. Each linear field problem is solved using the periodic Green function. In the second step, the difference of the magnetic field due to the small modification is computed directly. The polarization of the eliminated ferromagnetic domain is the field source. The B-I relation is given by Frechet first derivative.

Nowadays, the medical practice is limited to exploring the thermal field on the breast surface, t... more Nowadays, the medical practice is limited to exploring the thermal field on the breast surface, the infrared images being interpreted by specialist doctors with experience in this domain. The specialists succeed in the early detection of some abnormalities in the cell activity, that could represent the beginning of a malignant tumor development. Unfortunately, a procedure to determine the position and the dimensions of the tumor (a thermographical "radiography") has not been found yet.

7th Joint MMM-Intermag Conference. Abstracts (Cat. No.98CH36275), 1998

Journal of Materials Processing Technology, 2005

Two procedures in the boundary element method (BEM) for multiply connected domains are reported. ... more Two procedures in the boundary element method (BEM) for multiply connected domains are reported. The first procedure introduces cuts such that the multiply connected domain is transformed into a simply connected one, so that it allows the use of the scalar potential. Each cut introduces an additional term containing the "hall" current multiplied by the solid angle under which the cut is seen. The second procedure is based on a novel magnetic vector potential formulation. It uses edge elements and tree-cotree spanning. A zero normal component of this vector potential A and the condition for its line integral along any closed path on the boundary are imposed, such that the continuity of the normal component of the magnetic flux density be rigorously satisfied. The unknowns are the tangential components of × A and the tree edge element values.

ABSTRACT An efficient procedure for the analysis of shielding effectiveness can be performed by t... more ABSTRACT An efficient procedure for the analysis of shielding effectiveness can be performed by the current sheet integral equation in thin shields (CSIE). In the presence of ferromagnetic bodies and, moreover, in the periodic regime, where higher harmonics appears due to the nonlinearity of B-H characteristic, this equation can not be obtained directly. In this paper a method based on CSIE is proposed, where the nonlinear media are treated using the polarization fixed point method (PFPM). At each iteration, a Fourier analysis is performed, and CSIE is solved for each harmonic having imposed currents and the polarization harmonics as electromagnetic field sources. To speed up the iterative process the harmonic selection is progressive. The convergence of the proposed procedure is always insured.

The ferromagnetic shields represent an effective solution for the time constant and low frequency... more The ferromagnetic shields represent an effective solution for the time constant and low frequency magnetic fields attenuation. This paper presents an efficient method for evaluation the ferromagnetic shielding. It needs the computing of the time-periodic eddy currents in nonlinear media. Using the Polarization Fixed Point Method and the Fourier decomposition of the time-periodic magnetization, the electromagnetic field is obtained by solving the eddy-current integral equation for each harmonic. The magnetic field in shielded zone is produced by the imposed current distribution, the induced currents and the magnetization of ferromagnetic bodies, the integral equation is applied only on the shield domain which occupies a very reduced space or, if other conducting bodies are in the vicinity of the shield, the integral equation is extended only for them. The system matrix is inverted only once, before the iterations and remains unchanged.

An overview of the polarization method is presented. The method can by applied for different regi... more An overview of the polarization method is presented. The method can by applied for different regimes of the electromagnetic field as well as for electric circuits. Criteria for the choice of the permeability are proposed, so that the iterative scheme leads to a Picard-Banach fixed point procedure. The errors are evaluated. An efficient overrelaxation method is presented. The modality of using FEM numerical method is analyzed in order to ensure the convergence of the method

2008 4th European Conference on Circuits and Systems for Communications, 2008