Papers by Laurent Krähenbühl
The notion of essential orders was first introduced for the handling of decoupling problems. This... more The notion of essential orders was first introduced for the handling of decoupling problems. This paper focuses more on their interpretation, namely on the fact that each essential order corresponds to the highest time-differentiation order of a specific output appearing in the inverse model. During inverse modeling, this can in particular be useful for checking whether the specifications are appropriate to the structure of the given model. The aim of this paper is to define two procedures to graphically determine the essential orders directly from a bond graph (BG) model of a linear time-invariant system. Their usefulness is then justified in the context of a bond-graph based methodology for design problem analysis.
2013 IEEE International Conference on Mechatronics (ICM), 2013
In the context of mechatronic systems design, this paper addresses a parameter tolerance synthesi... more In the context of mechatronic systems design, this paper addresses a parameter tolerance synthesis with respect to specifications including output epistemic uncertainties. The methodology proposed here concerns uncertainties modelled with fuzzy logic. The procedure relies on output uncertainties propagation through an inverse model. Design parameter tolerance is then synthesized. The results are validated injecting designed parameters in the direct model. The methodology is illustrated on a linear model with specifications including combined uncertainties.
2019 22nd International Conference on the Computation of Electromagnetic Fields (COMPUMAG), 2019
A test-case for examining the energy-based hysteresis model is presented. An experimental setup c... more A test-case for examining the energy-based hysteresis model is presented. An experimental setup constituted of a E-E core transformer is built in order to study the vector hysteresis modeling and multiple harmonic signals in different configurations. Simulation results are compared to measurements made on a soft ferrite Mn-Zn and discussed.
⎯ A finite element subproblem method is developed to correct the inaccuracies proper to perfect ... more ⎯ A finite element subproblem method is developed to correct the inaccuracies proper to perfect conductor and impedance boundary condition models, in particular near edges and corners of conductors, for a large range of conductivities and frequencies. Local corrections, supported by fine local meshes, can be obtained from each model to a more accurate one, allowing efficient extensions of their domains of validity.
Wide range progressive refinements of the inductors in magnetic vector potential finite element f... more Wide range progressive refinements of the inductors in magnetic vector potential finite element formulations are done with a subproblem method. Their current sources are first considered via magnetomotive force or Biot-Savart models up to their volume finite element models, from statics to dynamics. A novel way to define the associated source fields is proposed to lighten the computational efforts, via the conversion of the common volume sources to surface sources, with no need of any pre-resolution. Accuracy improvements are then efficiently obtained for local currents and fields, and global quantities, i.e. inductances, resistances, Joule losses and forces.
The importance of the radiated equivalent sources characterization andElectromagnetic Compatibili... more The importance of the radiated equivalent sources characterization andElectromagnetic Compatibility studies has been emphasized in the presentliterature. It mentions the methodology based on the multipolar expansion inspherical harmonics of the near-field sources. Details of this methodology andof the prototypes suitable for determining components of the multipolarexpansion are shown, for instance, in (Vincent, Benjamin, et al. "Loopantennas for near-field multipolar-expansion identification: first experimentalvalidations." Instrumentation and Measurement, IEEE Transactions on 59.12(2010): 3086-3092.), and T. Q. V. Hoang, A. Breard, and C. Vollaire, “NearMagnetic Field Coupling Prediction Using Equivalent Spherical HarmonicSources,” IEEE Trans. on EMC, Vol. 56, n°6, pp. 1457-1465, 2014.).Nevertheless, these prototypes requires that either the device under test or theloop sensors be constantly positioned between all the measurements, to get theproper components necessary to...
RESUME-Les modeles d'hysteresis sont necessaires en genie electrique pour pouvoir prevoir cer... more RESUME-Les modeles d'hysteresis sont necessaires en genie electrique pour pouvoir prevoir certaines formes d'ondes ou les pertes correspondantes. Parmi tous les modeles d'hysteresis statique, le "Vector-Play Model" possede certaines proprietes interessantes (intrinsequement vectoriel, aspect thermodyna-mique, precision « ajustable »). Cependant l'identification de ses nombreux parametres restait une des difficultes majeures pour son utilisation. Ce probleme semble avoir ete resolu grâce a une nou-velle methode d'identification parue dans la litterature. De plus, elle semble etre en mesure de pouvoir donner des informations sur l'anisotropie et sur la micro-structure de materiaux F eSi. Nous proposons ici de tester cette nouvelle methode sur des materiaux de nature tres differente pour voir si les resultats precedents sont generalisables.
The present study aims to examine the influence of a static magnetic field (SMF) on Human Embryon... more The present study aims to examine the influence of a static magnetic field (SMF) on Human Embryonic Kidney (HEK) 293 cell physiology. HEK cells have been exposed for 72 h to a 0.5 T uniform SMF. The potential effects were investigated by comparing the electrorotation spectrum and the electrical characteristics of exposed and unexposed cells. The results show no significant differences between control and exposed HEK cells.
A predictive EMC method for inductive coupling, using measurements carried out on a sphere encomp... more A predictive EMC method for inductive coupling, using measurements carried out on a sphere encompassing a tested device, is at the moment under development in our laboratory. This method makes it possible to construct an equivalent source in the form of a sum of multipole terms. Once the equivalent sources of two devices have been designed, their inductive coupling can be calculated to prevent future EMC problems. Therefore, we have developed a measurement bench which allows the sensor to describe a spherical surface around the device we want to characterize. In this article, we present two methods for choosing the position of the measurement points (depending on the number of measurements and the chosen sensor) by minimizing the reconstruction error. The first one determines the position of the measurement points in order for them to be equidistant. In the second one, the source is considered to be random, and we maximize the determinant of the covariance matrix as a function of th...
Les methodes d'impedance de surface sont parmi les plus efficaces pour resoudre les problemes... more Les methodes d'impedance de surface sont parmi les plus efficaces pour resoudre les problemes de courants de Foucault a faible profondeur de penetration (δ) en regime harmonique lineaire. Cependant l'effort de calcul devient considerable lorsqu'on s'interesse a une large gamme de frequences (ou de conductivites), car chacun des resultats correspond a la resolution d'un probleme d'elements finis en valeurs complexes ; de plus, l'erreur est en δ^2 et augmente donc tres vite avec δ. Nous avions precedemment montre qu'un developpement limite permet des parametrisations en δ des solutions, tres precises pour toutes les valeurs de δ comprises entre la limite conducteur parfait (δ→0) et les premiers resultats accessibles par maillage de l'effet de peau, avec un cout numerique equivalent a celui de 2 resolutions. Nous comparons ici la precision de deux des methodes possibles pour construire un tel developpement limite.
Nous presentons une nouvelle approche pour la modelisation efficace d'un empilement de toles,... more Nous presentons une nouvelle approche pour la modelisation efficace d'un empilement de toles, dans le cas harmonique lineaire : dans la situation 1D ou la forme de la solution est connue analytiquement suivant l'epaisseur de chaque tole, la solution exacte en formulation (A, gradV) peut etre representee avec seulement un degre de liberte par inter-tole (plus une inconnue gradV par tole). En utilisant un element d'ordre un par tole, et en modifiant la permeabilite complexe utilisee, nous construisons une matrice d'elements finis representant exactement la solution 1D pour la direction normale aux toles. Nous montrons qu'il est possible, sans reelle perte de precision, de mailler moins fin le cœur du paquet de toles, via un couplage avec l'homogeneisation classique. De premiers resultats pour une extension 2D sont egalement presentes. Cette technique pourrait aussi s'appliquer aux milieux conducteurs massifs, rendant possible la resolution sur un meme maill...
The computation for the distribution of the electric field ∇ϕ within biological tissues is crucia... more The computation for the distribution of the electric field ∇ϕ within biological tissues is crucial in the medical treatment based on electroporation in order to make the appropriate choice for both the electrodes and the parameters of the voltage pulses. To perform this kind of simulations, a constitutive law has to be built to establish the relation between the electric field and the total current density induced inside the tissue: it must include, in one hand, the current that flows through the extra cellular medium and, in the other hand, the current that flows through the cells when the membrane is firstly charging during the rise time of the pulse and then electroporated (L. M. Mir et al. "Dynamic modeling of electroporation for the computation of the electric field distribution inside biological tissues during the application of the pulse voltage", 1st Word Congress on Electroporation, Slovenie, 2015).
IEEE Transactions on Magnetics, 2020
We study the harmonic magnetodynamic behavior (without wave propagation) of a resonant surface me... more We study the harmonic magnetodynamic behavior (without wave propagation) of a resonant surface metamaterial, made up of many identical and regularly arranged LC cells. The circuit model gives the exact solution, but is not numerically efficient for the simulation of very large structures (e.g. 1000×1000 cells). For the first time, we highlight the modal character of the solutions, which makes it possible to explain their frequency and spatial related properties. From these results, we show under what assumptions it is possible to homogenize the metamaterial, which opens the way for using this approach together with efficient numerical methods.
International Journal of Applied Electromagnetics and Mechanics, 2014
ABSTRACT The modeling of eddy currents in conductors is split into a sequence of progressive fini... more ABSTRACT The modeling of eddy currents in conductors is split into a sequence of progressive finite element subproblems. The source fields generated by the inductors alone are calculated at first via either the Biot-Savart law or finite elements. The associated reaction fields for each added conductive region, and in return for the source regions themselves when massive, are then calculated with finite element models, possibly with initial perfect conductor and/or impedance boundary conditions to be further corrected. The resulting subproblem method allows efficient solving of parameterized analyses thanks to a proper mesh for each subproblem and the reuse of previous solutions to be locally corrected.
IEEE Transactions on Magnetics, 2020
An unstructured-PEEC method for modelling electromagnetic thin regions is proposed. Two coupled c... more An unstructured-PEEC method for modelling electromagnetic thin regions is proposed. Two coupled circuits representations are used for solving both electric and/or magnetic effects in thin regions discretized by a finite element surface mesh. Dynamic effects across the the thickness of the sheet are modeled by equivalent complex conductivity and reluctivity. Non simply connected regions are treated with fundamental branch independent loop matrices coming from the circuit representation. The formulation enables the computation of eddy current losses and can be coupled with external circuits, PEEC cables or coil thanks to the circuit representation.
Journal of Microwaves, Optoelectronics and Electromagnetic Applications, 2011
This paper presents an evaluation of the phase shifting excitation and load effects in a Transmis... more This paper presents an evaluation of the phase shifting excitation and load effects in a Transmission Line Exciting Chamber. This chamber is suggested as an alternative for immunity tests because of the restrictions related to canonical chambers. Here, two methods are used to calculate the E-field: a semi-analytic approach and a numerical one. The semi-analytic method is based on the modal expansion while a software is used for numerical simulations. The results regarding the E-field profile and the related statistical indexes of merit are presented and used to evaluate the chamber performances. Experiments were also conducted in order to evaluate the chamber. Index Terms-Reverberation chamber, random excitations and loads, transmission lines. I. INTRODUCTION Canonical chambers-like Reverberation Chambers (RC) and TEM chambers-are generally used for electromagnetic immunity testing despite their particular operational restrictions. RCs using mechanical paddles or frequency stirring provide a statistical E-field uniformity in all the directions inside the working volume [1], [2]. Nevertheless, the operation frequency of RCs is inversely proportional to the chamber dimensions and it is a constraint for low frequency tests. The international standards recommend the RC configuration for immunity tests over 80 MHz frequencies [2], [3]. Among the first published works concerning RCs we can mention [4],[5], [6], and [7]. These authors have proposed two different approaches in order to change the boundary conditions inside the chamber: constant rotating paddles and step-by-step paddles. On the contrary, TEM chambers operate in the low frequency range. Introducing a stripline inside the chamber, a deterministic E-field uniformity is reached over a working area parallel to the plate, but not for all the polarizations in the chamber volume. Some early works with TEM cells were proposed by [8]. The performances of the TEM cells were extended in all polarizations using three orthogonal striplines [9]. An overview on the usual electromagnetic compatibility test methods is presented in [10], and herein a comprehensive list of references on these methods can be founded. Recently, an alternative concept called Transmission Line Exciting Chamber (TLEC) has been
COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, 2017
Purpose This paper aims to develop a methodology for progressive finite element (FE) modeling of ... more Purpose This paper aims to develop a methodology for progressive finite element (FE) modeling of transformers, from simple to complex models of both magnetic cores and windings. Design/methodology/approach The progressive modeling of transformers is performed via a subproblem (SP) FE method. A complete problem is split into SPs with different adapted overlapping meshes. Model refinements are performed from ideal to real flux tubes, one-dimensional to two-dimensional to three-dimensional models, linear to nonlinear materials, perfect to real materials, single wire to volume conductor windings and homogenized to fine models of cores and coils, with any coupling of these changes. Findings The proposed unified procedure efficiently feeds each SP via interface conditions (ICs), which lightens mesh-to-mesh sources transfers and quantifies the gain given by each refinement on both local fields and global quantities, with a clear view on its significance to justify its usefulness, if any. I...
2016 Asia-Pacific International Symposium on Electromagnetic Compatibility (APEMC), 2016
Using the method of multipolar expansion in spherical harmonics, the electromagnetic interference... more Using the method of multipolar expansion in spherical harmonics, the electromagnetic interference between two systems can be determined from their equivalent models. However, a multipolar expansion depends on the position of the origin: a bad choice can yield a complicated equivalent model, even for a simple source. As a consequence, the calculation of the coupling between two sources can also become more complex and require a high degree of the multipolar expansion to reach the convergence. In this paper, we propose a method to find the optimal origin for the spherical harmonics expansion. The approach can also be exploited for the localization of the electronic components in a black box.
IEEE Transactions on Magnetics, 2016
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Papers by Laurent Krähenbühl