Muriel Darces

Design of a spiral antenna with coplanar feeding solution

A new design of spiral antenna is presented in this paper. The shape of the antenna is similar to that of the traditional Archimedean spiral antenna. However, this design allows to feed the antenna on the same plane, which is useful to conform the antenna on various surfaces. Two sources feed the structure. Loads placed along the arms and in the center of the antenna are used to decrease reflections at the end of the arms. Antenna behavior is studied using the software FEKO which is based on method of moments (MoM). This antenna shows the same characteristics as a traditional spiral antenna while being fed outside with coplanar feeding solution. The antenna is studied without a ground plane.

Efficient computation of macro-domain basis functions when applying the characteristic basis function method to the modeling of forest scattering

In this work, we discuss the use of diagonal representation (DR) of the macro-domain basis functions, in the context of the characteristic basis function method (CBFM) applied to forest scattering problem. We examine the suitability of this enhancement technique for heterogeneous natural forests. Results show that the use of the DR for the MBFs, according to certain criteria, enables us to significantly reduce the CPU time needed to generate the CBFs with little loss of accuracy, and without increasing memory costs. Consequently, the strategy of using the DR for the computing of the CBFs enables us to simulate larger forest scenes and to do so at higher frequencies.

Prediction of Sky and Surface Wave Radiation of a Wideband HF Antenna

In this letter, the prediction of the radiation of wideband HF antennas is investigated. The ground upon which they are placed mainly influences the sky wave and the surface wave mode radiated by these antennas. Classical methods of simulation or measurement applied to microwave radiating structures are not suitable for this kind of antenna. Thus, this letter proposes a method to perform a near field to far field transformation, adapted to the problem of interest, and based on a power criterion. This criterion requires both the electric and magnetic near fields, but by using an appropriate approximation, it is possible to assert that only the measurement of the electric near field is required. Far field radiation has been computed at two different frequencies within a bandwidth of 1.3:1 (28.5%).

Kriging method to perform scintillation maps based on measurement and GISM model

This paper presents an ionosphere scintillation mapping algorithm. The technique used is a Kriging technique, well known in geostatistics. It is an interpolation method applied to a set of random data, namely, in this application, to the intensity scintillation (S4) index. The paper focuses on the importance of the regression model used in the algorithm. The one-dimensional and then the two-dimensional problems have been investigated. One example of results combining measurement data recorded by two different networks in Peru is presented. The accuracy of the results has been verified using a cross-validation technique, which consists in removing part of the known data set and comparing the interpolated results to it.

Simulation of indirect effects of lightning on an aircraft engine

This paper presents a new approach for simulating the indirect effects of a lightning impact on an aircraft engine. Based on macro modeling, it performs a model reduction of the lightning current on a geometric support called a “patch”. The associated macro finite element space allows for reliable and sufficiently fast resolution so that parameter analysis can be carried out.

Fast computation of macro-basis functions in the context of modeling the problem of scattering from forests

The aim of this research work is to discuss the use of the diagonal representation (DR) for the construction of the macro-basis functions (MBFs) when applying the Characteristic Basis Function Method (CBFM) to the problem of modeling of scattering from forests. We have applied the CBFM to improve the performances of a previously studied 3D full-wave model in order to solve electrically large forest simulation scenes. This efficient domain decomposition method has shown good performance both in terms of CPU time and memory while achieving a satisfactory level of accuracy compared to that of a conventional Method of Moments (MoM). Therefore, it enables us to solve forest EM problems of upward of 2 million unknowns by consuming only a reasonable amount of CPU time and using just 48 GB of shared memory (Fenni I.; Roussel H.; Darces M.; Mittra R., AP IEEE Trans., 62–8, 4282–4291, 2014).

A precise technique for ground wave radiation and propagation over an irregular surface

This paper deals with the problem of HF surface wave radar. The goal is to integrate in a unique tool the antenna radiation and the propagation calculations in order to make the analysis consistent.

Prediction of HF wave propagation for “over the horizon” radar application

This paper deals with the problem of HF surface wave radar. The goal is to integrate in a unique tool the antenna radiation and the propagation calculations in order to make the analysis consistent. Only the antenna problem is presented here. However the way the propagation problem will be further considered is presented. Cross check of the tool validity and robustness were insured by developing concurrently several techniques, mixing measurements and theoretical techniques.

Fast computing of large 3D dielectric forest scattering problems using the Characteristic Basis Function Method with the Adaptative Cross Approximation algorithm

This paper presents the hybridation of the Characteristic Basis Function Method with the Adaptative Cross Approximation algorithm while generating the reduced linear equation system. The proposed method is applied to 3D scattering model in the context of forest remote sensing. It enables us to realize a significant improvement of the performances of the CBFM both in terms of memory use and CPU time while maintaining a good level of accuracy compared to the CBFM solution.

Statistics as a toolbox for electromagnetic interferences modeling

Summary form only given. Safety and security of critical infrastructures rely on the robustness of the involved systems to electromagnetic interferences from the electromagnetic compatibility point of view. In recent years, documented electromagnetic interferences attacks have demonstrated the susceptibility of devices (F. Sabath, European Electromagnetics EUROEM 2012, pp.65, 2-6 July 2012) as well as the potential unintentional electromagnetic compromising emanations radiated by the concerned information systems (Vuagnoux, M.; Pasini, S.; 2010 IEEE International Symposium on EMC, pp.121-126, 25-30 July 2010) that may result in the leakage of sensitive information. The damaging effects of EMI pose unacceptable risks in critical applications. It is therefore necessary to manage such interferences in order to reduce the risks to tolerable levels. Most studies and their inherited standards mainly focus on the general trends and central tendencies. Nevertheless it has been demonstrated in many domains (e.g. storms prediction or trading) that extreme events should be part of the analysis, especially when security and safety are under concern. The power-grid acts as a guiding structure for electromagnetic interferences; it is hence a good context to derive statistical formalisms. Based on the electromagnetic topology (JP. Parmantier and S. Bertuol, CRIPTE Training and Electromagnetic coupling on cable networks, 2011, ONERA, France), the modeling of Low Voltage distribution network has been achieved. It has been observed that the variability of the input modeling parameters may impact the accuracy of results. Those parameters were classified depending on their effects on the propagation of electromagnetic interferences in the power grid thanks to the Generalized Experimental Design (D. C. Montgomery, Design and Analysis of Experiments, Wiley, 2012). This method has also been applied to compute the interactions between parameters. We consider a spurious current induced by an external excitation signal as a physical quantity. Its distribution can be described using the statistical moments. The analysis of the higher-order statistical moments of both central tendencies and extreme values (H. Taleb, The Black Swan: the impact of the highly improbable, Random House, New York, N.N. 2010) and the exhibition of their differences raised the need for a well-defined theory in order to precisely describe the extreme events. This has been achieved thanks to the Extremal Types Theorem (N. Tajvidi, PhD thesis, Department of Mathematics, Chalmers, Göteborg, 1996) and, more precisely, by following the Peaks-Over-Thresholds approach. This methodology consists in approximating the distribution of excesses over some thresholds by a Generalized Pareto Distribution. The distribution of the related quantities can be described using the so-called Hybrid Pareto Distribution, which is related to the combination of the adjusted central tendencies distribution with the adjusted extreme values distribution. The Value-At-Risk analysis can be applied to manage risks induced by electromagnetic interferences.