Sébastien Lalléchère

Modeling complex systems for EMC applications by considering uncertainties

The objective of this work is to present a new approach to the random modeling of complex systems in ElectoMagnetic Compatibility (EMC). This contribution aims to compute high orders statistics and study the impact of parameter uncertainties on various EMC topics including transmission lines, radiation and immunity problems. The agreement between results from the Stochastic Collocation (SC) method and Monte-Carlo (MC) simulations guarantee the SC accuracy and robustness. The combination of SC with computations from analytical and tridimensional numerical models (Finite Difference in Time Domain) underlines its advantages (efficiency, non-intrusive integration).

Mode Stirred Reverberation Chamber (MSRC): a large and efficient tool to lead high frequency bioelectromagnetic in vitro experimentation

An important aspect of the studies undertaken in bioelectromagnetism relates to the choice of exposure facility. The characteristics of a real electromagnetic environment are far more complex compared to the one plane wave irradiation set-up used in the majority of bioelectromagnetic studies. Moreover, biological requirements should represent the starting point in the design of an in vitro exposure system. Indeed it is important to avoid altering the electromagnetic properties of the exposure system in the presence of biological equipments. Related to these two essential points, this article contributes to show the advantages of a Mode Stirred Reverberation Chamber (MSRC) to guarantee a controlled electromagnetic environment around biological materials for in vitro experimentation. An example of irradiation of in vitro human skin cells cultures is considered to illustrate this paper. In order to show that the biological conditions and the physical requirements for in vitro experiments are checked, two aspects are described. Firstly we achieved the characterization of the electromagnetic fleld generated around the biological system (both equipments and cultures). Secondly the analysis of the Speciflc Absorption Rate (SAR) inside the biological medium was evaluated both numerically and experimentally. Initially,

Reliability and Sensitivity Analysis of Transmission Lines in a Probabilistic EMC Context

Uncertainty propagation plays an important role in electromagnetic compatibility when high safety standards are imposed. This paper addresses the safety assessment of transmission lines under uncertain radiated electromagnetic constraints. The purpose is to estimate the probability that the current at a terminal load exceeds a prescribed threshold. This paper details the basics of the most efficient methods specifically tailored to assess small failure probabilities. A focus is put on global and local sensitivity analyses that provide the analyst with important results regarding the design of transmission lines. This paper is illustrated with two application examples that highlight the strengths and limits of reliability assessment methods in light of physical interpretations of the obtained results.

Stochastic EMC/EMI Experiments Optimization Using Resampling Techniques

Recent studies have shown high interest in statistical methods dedicated to the prediction of the maximum confidence levels in simulations and measurements for risk assessment in electromagnetic compatibility. In particular, it has been shown that one of the main issues remains the access to a number of samples allowing the assessment of the risks in regards to test setup random variables. In this paper, it is argued that a real-time bootstrapping module enables to optimize the number of experiments while estimating the maximum confidence levels of the accessible samples. An efficient technique is presented to substitute the full experimental requirements to a simple and low time-consuming mathematical algorithm. The benefits expected of this method are illustrated throughout experimental shielding effectiveness power measurements. Based upon an optimized statistical approach, the first statistical moments (e.g., mean and standard deviation) of power received inside a cabinet are provided jointly with an accurate assessment of powers quantiles, leading to a better evaluation of extreme values.

Reliability-Aware Optimization of a Wideband Antenna

A framework for optimization of wideband antennas including statistical reliability considerations is proposed. Using predetermined tolerances of the manufacturing process, the reliability analysis provides a failure probability of the considered antenna according to imposed specifications. In addition, a sensitivity analysis is conducted in order to quantify the relative weight of the antennas parameters on the variability of |S11|. On this basis, a reliability-aware definition of optimization parameters can be derived to minimize failure probability during fabrication. For demonstration, a particular type of antenna, namely the tapered half-mode substrate-integrated waveguide (HMSIW) leaky-wave antenna, is chosen for the reliability analysis and optimization. This antenna is optimized for operation in the band from 7 to 14 GHz (with specification |S11| <; -10)with a calculated failure probability of less than 1%. A fabrication of the designed prototype yields measurements showing a strict adherence to specifications, which exemplifies the relevance of the statistical analysis. The study can be generalized to any wideband antenna provided that a fast computation of cost function can be obtained.

Unscented transform and stochastic collocation methods for stochastic electromagnetic compatibility

This paper deals with the current growing interest concerning the use of stochastic techniques for electromagnetic compatability (EMC) issues. Various methods allow to face this problem: obviously, we may focus on the Monte Carlo (MC) formalism but other techniques have been implemented more recently (the unscented transform, UT, or stochastic collocation, SC, for instance). The aim of this work is to solve a stochastic electromagnetic compatibility problem (transmission line) with the UT and SC techniques and to face them with the reference MC results.

Safety assessment of a transmission line with EMC requirements

This paper addresses the safety assessment of an ElectroMagnetic Compatibility (EMC) device, namely a transmission line. We assume that both the physical parameters of this transmission line and those of the illumination wave are uncertain. The objective is to assess the probability of occurrence of an extreme event defined in terms of requirements imposed on the current circulating in the line. The work is based on methods of the structural reliability research community. The efficiency and accuracy of the applied methods are compared with reference results obtained by simulations.

Stochastic approaches for ElectroMagnetic Compatibility: A paradigm from complex reverberating enclosures

The aim of this paper is to enforce stochastic techniques in a classical ElectroMagnetic Compatibility (EMC) issue. An experimental setup has been developed ex nihilo to model it. First, a quick glance over the physical context will give precisions about the objectives of this work. Then, the statistical developments are derived both from classical (but costly) Monte Carlo (MC) technique and other advanced stochastic methods. Finally, the presented results will lay emphasis on part of the accuracy, limits and abilities of the developed formalisms to improve the physical understanding of applied EMC issues.

Numerical Total Scattering Cross Section from Reverberating Electromagnetic Experiments

The total scattering cross section (TSCS) of various targets is computed in this letter from a numerical method in a reverberation chamber (RC). Theoretically TSCS measurements need both a free-space environment (for instance anechoic chamber modeled numerically by absorbing boundary conditions) and various plane waves’ stimulations. The method developed allows predicting the TSCS from few simulations in a RC. The foundations and numerical results presented demonstrate the ability of the technique to straightforward compute the TSCS with the finite difference in time domain (FDTD) method. The agreement from these TSCS treatments in RC is finally obtained considering the expected results in free-space.

A Stochastic Analysis of the Transient Current Induced along the Thin Wire Scatterer Buried in a Lossy Medium

The paper deals with the stochastic collocation analysis of a time domain response of a straight thin wire scatterer buried in a lossy half-space. The wire is excited either by a plane wave transmitted through the air-ground interface or by an equivalent current source representing direct lightning strike pulse. Transient current induced at the center of the wire, governed by corresponding Pocklington integrodifferential equation, is determined analytically. This antenna configuration suffers from uncertainties in various parameters, such as ground properties, wire dimensions, and position. The statistical processing of the results yields additional information, thus enabling more accurate and efficient analysis of buried wire configurations.