Christophe Guérin

Influence of skull anisotropy for the forward and inverse problem in EEG : Simulation studies using FEM on realistic head models

For the sake of realism in the description of conduction from primary neural currents to scalp potentials, we investigated the influence of skull anisotropy on the forward and inverse problems in brain functional imaging with EEG. At present, all methods available for cortical imaging assume a spherical geometry, or when using realistic head shapes do not consider the anisotropy of head tissues. However, to our knowledge, no study relates the implication of this simplifying hypothesis on the spatial resolution of EEG for source imaging.

A nonlinear circuit coupled t-t/sub 0/-/spl phi/ formulation for solid conductors

A new three-dimensional (3-D) finite element formulation based on the use of the magnetic scalar potential is proposed. It allows the description of multiply connected solid conductors coupled to electric circuits and to take into account the nonlinearities. Like the solutions using the magnetic vector potential, it is a general formulation and offers powerful solutions but at a lower cost.

Coupled problem computation of 3-D multiply connected magnetic circuits and electrical circuits

This paper presents the theory and the validation of a new finite-element formulation to realize the coupling between electrical circuits and multiply connected magnetic circuits, using a magnetic scalar potential as state variable. For this purpose, we used formulations in reduced magnetic scalar potential versus T/sub 0/ taking into account electrical circuits and a total magnetic scalar potential taking into account cuts.

Three dimensional magnetostatic finite elements for gaps and iron shells using magnetic scalar potentials

This paper deals with magnetostatic element formulations for modelling narrow gaps in an iron core, as well as thin iron shells. These special elements have been developed for gaps in transformers or motors. Nodal elements are used with magnetic scalar potentials as state variable. The principle and the formulations of the new finite elements are described. Three numerical examples are then presented so as to validate and verify the usefulness of the special elements in terms of reduction of number of unknowns and CPU time. >

3D eddy current losses calculation in transformer tanks using the finite element method

The authors discuss the 3-D electromagnetic modeling of a transformer to evaluate eddy current losses in the tank. To achieve this, several numerical methods are used with two 3-D field computation packages. Conventional volume elements and shell elements are used for the modeling of thin conducting regions. Surface elements are used for the modeling of conducting regions with a reduced skin depth. The results, along with several characteristics of the tank and magnetic core, are compared. The influence of the characteristics of these two components is investigated. >

Homogenization for Periodical Electromagnetic Structure: Which Formulation?

This paper proposes a general finite element approach for the frequency-domain homogenization of electromagnetic periodical structures. Based on local finite element resolutions on a cell, the method allows taking into account the local effects at the macroscopic level through the determination of equivalent macroscopic permeability and conductivity laws. Examples of the modeling of eddy current losses in windings are presented.

3-D modeling of thin wire and thin plate using finite element method and electrical circuit equation

This paper presents a method of modeling an electric circuit of thin wire and thin plate submitted to an electromagnetic field. The proposed method requires a preliminary electrokinetic computation to find the current distribution on the plate due to a unit current and the magnetic field distribution. To compute the final current in the system, we model the thin plate as an electrical circuit component.

A current transformer modeling

This paper presents the modeling of a current transformer by various methods with the FLUX3D software. The technique used is based on the finite element method coupled with electric circuits. A magnetic scalar potential reduced versus T0 formulation (T0ϕ−ϕ) taking into account the electric circuits with an air‐gap is used for this purpose. The air‐gap is described either by a thin volume region or by a surface region.

Circuit-Coupled

A finite-element formulation based on the use of magnetic scalar potential is proposed. It allows to describe circuit-coupled electromagnetic formulation using magnetic scalar potential in presence of multiply connected solid conductors (with holes), treated by surface impedance condition. This formulation offers powerful solutions at a low cost. An example of application is given.

{\bf t}_{0}\hbox {-}\phi

In this paper, different ways to compute electromagnetic source fields for non-meshed coils will be described for magnetic vector potential A and electric scalar potential V formulation (A - V formulation). The originality of this paper is demonstrated by the source computations for A- V formulation with non-meshed coils. Usually, coils for A- V formulation are meshed, and non-meshed coils are studied with reduced magnetic vector potential Ar and electric scalar potential V formulation (Ar - V formulation). Different source computations for A - V formulation will be applied on an induction machine with non-meshed coils.