Jean-Luc Mattei - Academia.edu (original) (raw)

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Papers by Jean-Luc Mattei

En raison de la tendance toujours croissante de miniaturisation de dispositifs micro-ondes, la mi... more En raison de la tendance toujours croissante de miniaturisation de dispositifs micro-ondes, la miniaturisation d’antennes se presente comme l’un des defis auxquels font face les concepteurs d’antennes. Dans cet objectif, des substrats a haute permittivite sont employes pour diminuer les dimensions physiques de l’antenne. Toutefois on observe alors une degradation de l’efficacite de l’antenne, et une diminution de sa bande passante [1,2]. Pour une application aux frequences inferieures a 1GHz environ, l’emploi de substrats magneto-dielectriques peut permettre de surmonter ces limitations. En effet il a ete montre assez recemment [3] que la contribution de la permeabilite µ’ du substrat magneto-dielectrique conduit a une diminution des pertes totales, contrairement a la permittivite e’, dont l’effet mene a un accroissement des pertes. L’influence defavorable de e’ sur l’efficacite de rayonnement (η) et sur la largeur de bande (BW) est donc contrebalancee par l’impact de µ’.

ChemCatChem, 2013

ABSTRACT A TiO2-supported AuPd bimetallic catalyst with an Au/Pd atomic ratio of 8 was prepared b... more ABSTRACT A TiO2-supported AuPd bimetallic catalyst with an Au/Pd atomic ratio of 8 was prepared by deposition-precipitation with urea, and its activity in CO oxidation at room temperature was compared to the one of a monometallic Au/TiO2 catalyst. X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analyses suggest that Au-Pd/TiO2 contains bimetallic nanoparticles after reduction under H2 at 500 °C although the presence of monometallic Au particles cannot be totally excluded. The evolution of the AuPd nanoparticles surface composition during exposure to O2 and CO/O2 was studied in situ by environmental high resolution electron microscopy (ETEM) and DRIFTS. Pd segregation at the surface of the bimetallic nanoparticles was evidenced by DRIFTS and directly observed by ETEM under O2 and CO/O2 with the formation of Aucore-Pdshell structure. The changes in the surface composition of the Au-Pd nanoparticles under CO/O2 was paralleled with the higher rate of deactivation in the first reaction stages observed for Au-Pd/TiO2 compared to Au/TiO2, which could be related to the possible replacement of Au in low coordination sites, at the origin of the high activity in CO oxidation, by Pd atoms. These results noticeably underline the modifications induced by the reactant that can undergo a bimetallic AuPd catalyst.

Journal of Applied Physics, 2006

The theoretical approach proposed here was aimed at accurately describing the electromagnetic res... more The theoretical approach proposed here was aimed at accurately describing the electromagnetic response of self-biased Y-junction circulators made of polycrystalline hexaferrites. The accuracy of circulator response was enhanced by considering the real magnetization state of the material through a calculation of the permeability tensor; this tensor remains valid whatever the strength of the local effective dc field in the ferrite is. Moreover, the hysteresis phenomenon was introduced in the calculation of tensor through the use of the Stoner and Wolhfart ͓IEEE Trans. Magn. 27, 3475 ͑1948͔͒ law; as a consequence, the tensor took into account the privileged direction of easy-axis distribution due to the manufacturing process, which allowed us to treat the polycrystalline hexaferrites as being magnetically self-biased. However, the results issued from our approach indicate that this higher accuracy is at the expense of Y-junction circulator performances, which are far from those reported in the literature or obtained with electromagnetic commercial simulators and based on the frequent assumption of saturated hexaferrite, even at the remanent state.

IEEE Transactions on Magnetics, 2000

The electromagnetic analysis of a Y-junction circulator proposed here is more realistic than the ... more The electromagnetic analysis of a Y-junction circulator proposed here is more realistic than the conventional one, as it accounts for two aspects that are usually neglected despite their frequent occurrence in practice: 1) the nonuniformity of the dc-bias field met in planar technology and 2) the introduction of a tensor to take into account all the magnetization states of the ferrite material. Slicing the ferrite sample into concentric zones allows us to consider the radial variation of the bias field in the electromagnetic calculation. A magnetostatic calculation of the internal field provides the true internal field within each region of the ferrite disk. We replace the Polder tensor, which describes only one specific magnetization state of the material, with another tensor that allows the true magnetization of the ferrite rings to be taken into account.

Ceramics International, 2016

Materials Research Bulletin, 2016

Journal of Magnetism and Magnetic Materials, 2016

2015 European Microwave Conference (EuMC), 2015

Etudes Et Recherches Des Laboratoires Des Ponts Et Chaussees Serie Sciences De L Ingenieur, 2006

In this paper, the main microwave applications of magnetized materials are briefly recalled. The ... more In this paper, the main microwave applications of magnetized materials are briefly recalled. The theories developed to predict their dynamic behavior are presented. Then the measurement methods that enable us to compare the theoretical results with experimental data are described. Propects about the needs in new microwave magnetic structures for future applications are finally discussed. We focus these prospects on millimeter self-biased circulators using hexaferrites set in a remanent state. These considerations highlight the need for thorough investigations targeted to the design of magnetized material-based microwave devices to take into account, at the same time, the dc field non-uniformity, the unsaturated state of certain regions of the magnetized substrate and realistic values for the permeability tensor components.

This paper presents two novel designs based on the design of a 3D compact inverted F antenna whic... more This paper presents two novel designs based on the design of a 3D compact inverted F antenna which is dedicated to low frequencies handheld applications. Good performances, compactness and low frequencies are obtained thanks to a magneto-dielectric material. Indeed, using a magneto-dielectric material in comparison to use a pure dielectric material allows obtaining a wideband compact antenna. A complete study will show the advantage of using a magneto-dielectric material. Since reconfigurable radiation patterns allow improving the quality and reliability of wireless links, for both designs, two antennas are used to release this feature over its matched band.

Journal of Magnetism and Magnetic Materials, 2000

Experimental variations of the ferromagnetic resonance (FMR) recorded on soft composite bodies ar... more Experimental variations of the ferromagnetic resonance (FMR) recorded on soft composite bodies are presented and their interpretation is undertaken. A successful application is performed for the Kittel expression of the FMR, initially written for an ellipsoid placed in vacuum, to a magnetic inclusion of the composite. This model includes the demagnetizing e!ects due to the magnetic inclusions.

2010 14th International Symposium on Antenna Technology and Applied Electromagnetics & the American Electromagnetics Conference, 2010

New magneto-dielectric material with improved electromagnetic properties in UHF band is manufactu... more New magneto-dielectric material with improved electromagnetic properties in UHF band is manufactured. These electromagnetic properties, in particular the low levels of losses, show that this material could be useful to the design of miniaturized antennas in the VHF-UHF (300MHz-700MHz) range of frequency. This new material has been used to load a small coplanar slot antenna. Performances of the antenna as well as the new material is presented and compared with commercial magnetodielectric materials.

In this article, we present a frequency reconfigurable antenna for digital video broadcasting on ... more In this article, we present a frequency reconfigurable antenna for digital video broadcasting on handheld devices standard. By loading a printed inverted F antennas with a varactor diode, the resonance frequency can be tuned from 470 to 862 MHz. Furthermore, a magneto dielectric superstrate is used to reduce the dimension of the antenna while keeping a large bandwidth. To study the performance improvement due to the magneto-dielectric resonator,a comparison is performed with a reference antenna without magneto-dielectric superstrate.