Microwave properties of diluted composites made of magnetic wires with giant magneto impedance effect

International audienceIn this paper, the theoretical description of wire media made of magnetic wires. We show that there is a close link between the Giant Magneto Impedence effect (GMI) in individual wires, and free-space microwave properties of the composite wire media. The demonstration with tunable dielectric constant under a static magnetic field

Effect of the magnetic properties of the inclusions on the high-frequency dielectric response of diluted composites

International audienceThe high-frequency permittivity of composites consisting of a lattice of ferromagnetic wires is investigated. Experimental results using free space or coaxial line microwave measurements are reported. It is shown that the dielectric response is strongly dependent on the magnetic properties of the wires. Negative real permittivity is observed over a wide frequency range for wires with circumferential magnetization, while a resonant behavior is observed on wires with an axially magnetized core. In addition, it is shown that a moderate external field can induce large changes in the dielectric response. We prove that the underlying physics of these composites made of oriented magnetic wires is basically the same as the giant magnetoimpedance (GMI) effect. A model based on GMI equations is proposed which predicts this unusual dielectric phenomenon

Effect of the magnetic properties of the inclusions on the high-frequency dielectric response of diluted composites

International audienceThe high-frequency permittivity of composites consisting of a lattice of ferromagnetic wires is investigated. Experimental results using free space or coaxial line microwave measurements are reported. It is shown that the dielectric response is strongly dependent on the magnetic properties of the wires. Negative real permittivity is observed over a wide frequency range for wires with circumferential magnetization, while a resonant behavior is observed on wires with an axially magnetized core. In addition, it is shown that a moderate external field can induce large changes in the dielectric response. We prove that the underlying physics of these composites made of oriented magnetic wires is basically the same as the giant magnetoimpedance (GMI) effect. A model based on GMI equations is proposed which predicts this unusual dielectric phenomenon

Evidence of the Superparamagnetic State in the Zero-Field Microwave Susceptibility Spectra of Ferrimagnetic Nanoparticles

International audienceStatic and dynamic magnetic properties of Zn0.4Fe2.6O4 nanoparticles synthesized by thermal decomposition have been investigated. Two ranges of diameter have been used: small particles (diameter about 6.2 nm) and larger ones (diameter about 22.4 nm). The nanoparticle microstructure has been characterized by transmission electron microscopy. The temperature dependence of the zero-field dynamic permeability for both nanoparticle sizes has been studied, revealing a superparamagnetic state for the small ones. Effects of the nanoparticle size on the dynamic permeability have been studied, and linked to the superparamagnetic state. A dynamic susceptibility model has been found to reproduce the experimental behavior as well as its temperature dependence

Compressed perovskite aqueous mixtures near their phase transitions show very high permittivities: New prospects for high-field MRI dielectric shimming

International audiencePurpose: Perovskites are greatly used nowadays in many technological applications because of their high permittivity, more specifically in the form of aqueous solutions, for MRI dielectric shimming. In this study, full dielectric characterizations of highly concentrated CaTiO 3 /BaTiO 3 water mixtures were carried out and new permittivity maxima was reached. Methods: Permittivity measurements were done on aqueous solutions from 0%v/v to dry powder. The permittivity dependence with pressure was investigated. Scanning electron micros-copy images were performed on a few representative solutions. BaTiO 3 pressed pads of different thicknesses, permittivities, and distances to the head were compared in a 7T MRI scanner. Results: Perovskite aqueous mixtures undergo a pressure-dependent phase transition in terms of permittivity, with increasing water content. A new relative permittivity maximum of 475 was achieved. Microscopic images revealed structural differences between phases. A B þ 1 improvement in the temporal lobe was obtained with thin, high permittivity BaTiO 3 head. Conclusions: This new preparation method allows improved pad geometry and placement, as a result of the high relative permittivity values achieved. This method has great significance for medical applications of MRI dielectric shimming, being easy to replicate and implement on a large scale

Evaluation of new MR invisible silicon carbide based dielectric pads for 7 T MRI

International audiencePurposeThe use of dielectric pads to redistribute the radiofrequency fields is currently a popular solution for 7 T MRI practical applications, especially in brain imaging. In this work, we tackle several downsides of the previous generation of dielectric pads. This new silicon carbide recipe makes them MR invisible and greatly extends the performance lifespan.MethodWe produce a set of two 10x10x1cm3 dielectric pads based on silicon carbide (SiC) powder dispersed in 4-Fluoro 1, 3-dioxalan-2-one (FEC) and polyethylene Glycol (PEG). The stability of the complex permittivity and the invisibility of the pads are characterized experimentally. Numerical simulations are done to evaluate global and local SAR over the head in presence of the pads. B0, B1+ and standard imaging sequences are performed on healthy volunteers.ResultsSiC pads are compared to state-of-the-art perovskite based dielectric pads with similar dielectric properties (barium titanate). Numerical simulations confirm that head and local SAR are similar. MRI measurements confirm that the pads do not induce susceptibility artefacts and improve B1+ amplitude in the temporal lobe regions by 25% on average.ConclusionWe demonstrate the long-term performance and invisibility of these new pads in order to increase the contrast in the brain temporal lobes in a commercial 7 T MRI head coil

PCSC - Portail Calcul Stockage Cloud

Le Portail Calcul Stockage Cloud (PCSC) est un projet d'annuaire collaboratif des solutions de calcul, de stockage et de cloud.Le projet est ouvert, construit collectivement et facilement accessible.Objectifs :• inventorier les infrastructures existantes (outil d'aide à la saisie en ligne, description au format JSON, compatibilité avec le portail européen EOSC),• accompagner les utilisateurs dans le choix d’une infrastructure (sélection, condition d'accès, etc.),• documenter l'usage des solutions de calcul, de stockage ou de cloud (explication et description des solutions, comment les utiliser, cas d'usages, glossaire,trucs et astuces).Portail Calcul Stockage Cloud (PCSC) is a project to build a collaborative directory for computing infrastructures (computing, data storage and cloud usages).The project is opened, jointly built and easily accessible.The main targets are:• to map out existing infrastructures (in JSON format and EOSC portal compliant)• to help users to choose the right infrastructure• to provide documentation on the use of infrastructures including a glossary, tips and tricks and usage docs

PCSC - Portail Calcul Stockage Cloud

Le Portail Calcul Stockage Cloud (PCSC) est un projet d'annuaire collaboratif des solutions de calcul, de stockage et de cloud.Le projet est ouvert, construit collectivement et facilement accessible.Objectifs :• inventorier les infrastructures existantes (outil d'aide à la saisie en ligne, description au format JSON, compatibilité avec le portail européen EOSC),• accompagner les utilisateurs dans le choix d’une infrastructure (sélection, condition d'accès, etc.),• documenter l'usage des solutions de calcul, de stockage ou de cloud (explication et description des solutions, comment les utiliser, cas d'usages, glossaire,trucs et astuces).Portail Calcul Stockage Cloud (PCSC) is a project to build a collaborative directory for computing infrastructures (computing, data storage and cloud usages).The project is opened, jointly built and easily accessible.The main targets are:• to map out existing infrastructures (in JSON format and EOSC portal compliant)• to help users to choose the right infrastructure• to provide documentation on the use of infrastructures including a glossary, tips and tricks and usage docs

PCSC - Portail Calcul Stockage Cloud

Le Portail Calcul Stockage Cloud (PCSC) est un projet d'annuaire collaboratif des solutions de calcul, de stockage et de cloud.Le projet est ouvert, construit collectivement et facilement accessible.Objectifs :• inventorier les infrastructures existantes (outil d'aide à la saisie en ligne, description au format JSON, compatibilité avec le portail européen EOSC),• accompagner les utilisateurs dans le choix d’une infrastructure (sélection, condition d'accès, etc.),• documenter l'usage des solutions de calcul, de stockage ou de cloud (explication et description des solutions, comment les utiliser, cas d'usages, glossaire,trucs et astuces).Portail Calcul Stockage Cloud (PCSC) is a project to build a collaborative directory for computing infrastructures (computing, data storage and cloud usages).The project is opened, jointly built and easily accessible.The main targets are:• to map out existing infrastructures (in JSON format and EOSC portal compliant)• to help users to choose the right infrastructure• to provide documentation on the use of infrastructures including a glossary, tips and tricks and usage docs

PCSC - Portail Calcul Stockage Cloud

International audiencePortail Calcul Stockage Cloud (PCSC) is a project to build a collaborative directory for computing infrastructures (computing, data storage and cloud usages).The project is opened, jointly built and easily accessible.The main targets are:• to map out existing infrastructures (in JSON format and EOSC portal compliant)• to help users to choose the right infrastructure• to provide documentation on the use of infrastructures including a glossary, tips and tricks and usage docs.Le Portail Calcul Stockage Cloud (PCSC) est un projet d'annuaire collaboratif des solutions de calcul, de stockage et de cloud.Le projet est ouvert, construit collectivement et facilement accessible.Objectifs :• inventorier les infrastructures existantes (outil d'aide à la saisie en ligne, description au format JSON, compatibilité avec le portail européen EOSC),• accompagner les utilisateurs dans le choix d’une infrastructure (sélection, condition d'accès, etc.),• documenter l'usage des solutions de calcul, de stockage ou de cloud (explication et description des solutions, comment les utiliser, cas d'usages, glossaire,trucs et astuces)