N. Burais

Electromagnetic fields and human body: a new challenge for the electromagnetic field computation

The electromagnetic fields have a great influence on the behaviour of all the living systems. The as low as reasonably achievable (ALARA) principle imposes, in case of long exposures to low (i.e. power systems) or high frequency (i.e. microwave systems or cell phones) fields, some limitations to the radiated fields by the industrial equipment. On the other hand, some benefits can be taken from the effects of the electromagnetic fields on the living being: the hyperthermal technique is well known for the treatment of the cancer. Either we want to be protected from the fields, or we want to take benefit of the positive effects of these fields, all the effects thermal as well as genetic have to be well known. Like in any industrial application, the electromagnetic field computation allows a better knowledge of the phenomena, and an optimised design. Hence, there is a very important challenge for the techniques of computation of electromagnetic fields. The major difficulties that appear are: (1) related to th...

Numerical solution of eddy currents problems including moving conducting parts

In the study of transient or steady-state eddy current effects, a general diffusion equation derived from Maxwells equations is solved by a classical finite element method for the spatial problem with time discretization. The moving part of the system is taken into account by a mesh distortion where the mesh points associated with this part have to follow the displacement. This technique can be used when the movement is time harmonic and displacement limited in order to obtain a few distorted mesh. It is applied to an axisymmetric apparatus and eddy current losses calculations are compared with experimental results.

Electromagnetic field formulation for eddy current calculations in nondestructive testing systems

The authors present the most practical configuration for detecting cracks in material, by applying an electromagnetic field along the largest dimension of the crack. An electromagnetic field formulation of the system equation is proposed using Maxwells relations and separating the magnetic field into externally applied field and reaction field. The system equation is solved by using two classical methods : finite element technic for spatial problem and finite difference for time discretisation. So two dimensional eddy currents can be calculated immediately and related to the excitation characteristics for impedance calculation. Eddy currents lines in material for different cracks and sensor positions are presented. Theoretical results show important impedance changes.

Numerical modelling of iron losses in ferromagnetic steel plate

This paper describes a method of calculating the iron losses from a few macroscopic experiments for non-oriented steel plate with sinusoidal and non-sinusoidal excitations, taking into account saturation and hysteresis. With macroscopic considerations, iron losses are calculated using the Poynting vector and Maxwells relations, and can be separated into two components : hysteresis and eddy current losses. These losses are studied by means of a method combining the finite element technique for spatial problem and the finite difference technique for time discretisation, associated to the Preisach model for simulation of hysteresis. Computed and experimental results are presented for sinusoidal and non-sinusoidal flux.

Modeling of induced current into the human body by low-frequency magnetic field from experimental data

The induced currents into the human body by a low-frequency magnetic field are computed using three-dimensional finite elements and a special /spl phi/-A formulation. This magnetic field is generated by a real (possibly unknown) power system. The stray field is characterized by an equivalent multipole, fitted from some local measurements of the field, which is a good compromise between accuracy and number of degrees of freedom. The methodology is validated on a test-device using the software FLUX3D.

Study of eddy currents non destructive testing system in riveted assemblies

In order to optimize eddy current sensors, we have to simulate electromagnetic phenomena to predict sensors response. 2D and 3D codes can be used but what kind of result can be expected from each of these codes? In this paper, performances of 3D formulations are tested using the FEM package Flux3d. Adapted coupled formulations and boundary conditions are used to study eddy currents perturbation by flaws in aircraft riveted assemblies. Physical information about the influence of flaw depth is obtained. The 3D calculations allow us to choose the most adapted measurement quantity and to define the position of the measurement sensors. Then, for optimizing the sensor, the 2D FEM package Fissure is used taking into account the 3D results.

Electromagnetic field analysis in remote field eddy current testing systems

A model and a general nondestructive testing (NDT) and nondestructive evaluation (NDE) package are presented for developing and optimizing electromagnetic sensors. The package has been applied to sensors for remote field control and provides much information for optimizing, for example, the distance between excitation and measurement coils. Some precautions must be taken to obtain high-quality results. The mesh must be the same in order to compare materials with and without a crack. Also, in the NDT technique the measurement coil is far from the excitation coil, so that the study domain, including air, is very large. The quality of the results can be increased by coupling the finite-element method on this domain to the boundary integral equation for the exterior domain. >

Computation of the induced current density into the human body due to relative LF magnetic field generated by realistic devices

A three-dimensional finite-element formulation to compute induced currents into the human body due to relative low-frequency magnetic field is described. Magnetic source field and induced currents are computed separately, allowing to handle sources due to realistic devices. This method is validated using analytical solutions over a sphere. The limit of validity of the formulation is established. Computations using an accurate model of the human body are presented.

Generalization of the ideal crack model in eddy-current testing

In the ideal crack model in eddy-current testing frame, the field-flaw is equivalent to a current dipole layer on its surface. This model has shown its efficiency, as well for the computing accuracy, as for the CPU time. The goal of this paper is to improve this model taking into account the inclination, the conductance, and the low thickness of the crack.

Optimal characterization of LF magnetic field using multipoles

The LF magnetic field (50u2009Hz‐100u2009kHz) generated in the air by electrical appliances is characterised using multipoles. The maximum likelihood estimation of an equivalent multipolar source is computed using a genetic algorithm. The choice of the position and the number of measurement points are discussed.