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We describe a theoretical approach for determining the permeability tensor of polycrystalline ferrites regardless of their magnetization state. To take into account both the demagnetizing dynamic fields related to the magnetic domain and grain shapes and the magnetic interactions between adjoining domains and between adjoining grains, we transform the classical Landau-Lifschitz-Gilbert equation into a coupled two-equation system. We introduce statistical distribution laws for both the domain and grain demagnetizing coefficients into the calculation to take the domain and grain shape diversity into account and derive static vectorial quantities such as the internal magnetic dc field and magnetization in each domain that depends on the applied de magnetic field from the Stoner-Wohlfarth hysteresis model. We compare results with those for existing models for various magnetized states. Then we apply the model to predict the permeability tensor behavior of barium hexaferrite thin film, especially in the remanent state, which is of great interest for the design of self-biased Y-junction circulators in the millimeter-wave range. Index Terms--Anisotropic media, ferrites.

A theoretical approach to calculate the permeability tensor of polycrystalline ferrites in various magnetization states, from the completely demagnetized state to saturation is described. Demagnetizing dynamic fields related to the magnetic domain and grain shapes are introduced in the initial equations to describe the interactions between domains in a grain and between grains.

This paper describes a mathematical model enabling the calculation of the effective permeability tensor of heterogeneous magnetic materials set in various magnetization states. The theoretical approach we propose permits to predict the microwave behavior of unsaturated magnetic loaded composites as well as those of unsaturated polycrystalline ferrites. The model gives all the complex components of the permeability tensor in a single calculation phase whatever the magnetization state of the material is. This is useful for the computer-aided design of microwave magnetic devices. The calculation of the effective permeability tensor is carried out from a limited number of parameters: saturation magnetization, anisotropy field, damping factor, external dc field strength, concentration, and shape of the magnetic particles or domains. The model is predictive in the way that the magnetization state of the material is determined from the strength of the external dc magnetic field applied on the material. Index Terms--Magnetic anisotropy, magnetic hysteresis, nonhomogeneous media, permeability.

We compare the diagonal [micro] and off-diagonal [kappa] permeability tensor components of magnetized polycrystalline ferrites given by the theoretical model of Gelin and Berthou with experimental ones at microwave frequencies. We used a broad-band and noniterative measurement technique recently developed within our research group. Whatever the ferrite magnetization state is, simulated and measured [micro] and [kappa] points agree well. This study provides an experimental validation of the Gelin--Berthou model. Moreover, by using this characterization method, we show how the measurement of the magnetic properties can be affected by the size of the ferrite sample under test. Index Terms--Anisotropic media, demagnetizing fields, ferrites, permeability, scattering parameters.

A theoretical approach for accurately describing the electromagnetic response of a self-biased Y-junction circulator composed of a polycrystalline hexaferrite operating at millimeter wavelengths is presented. The results obtained from the proposed approach are compared in the case of polycrystalline hexaferrite-made circulator operating at remanence.

The validation of powders technology for microwave applications, was proved by ferrimagnetic powder loaded composites, which exhibit a nonreciprocal effect. To prove the same, the demonstration in the case of thick ferromagnetic powder loaded layers deposited by silkscreen printing was reproduced.

Communities of Practice are frequently seen as key enablers of efficient corporate operations in knowledge-intensive industries. They can improve internal communications and knowledge sharing both within an organization and between the organization and its external partners. Despite the positive effects a Community of Practice may have at any one point in time, however, its successful management over the long term requires adaptations to take into account the different stages in the life cycle of the Community. The objective of this article is to reveal the secrets of successful long-term management of Communities of Practice; we do this using a case study of Schneider Electric, a global leader in energy-efficiency management. The article will examine the Human Machine Interface Community, which has 400 active members in more than 60 countries. © 2011 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The topic of this paper is the study of electrically tunable phase-shifters based on the use of liquid crystals. The dielectric characterization of the commercial liquid crystal involved in this study allows us to determine its dielectric permittivities (with and without DC voltage applied) and then its dielectric anisotropy. In this way, two phase-shifter configurations were studied. Every devices propose inverted microstrip line. The two circuits have been realized with coplanar accesses to be use in the millimeter-frequency range. With the aim to improve the phase shift parameter (in °/GHz/cm), our work aims to reduce the transmission line. Instead of a rectilinear transmission line, this one is based on a symmetric stub line. The phase shift obtained is enhanced from 0.87°/GHz/cm to 2.77°/GHz/cm. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 338–341, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20463 [ABSTRACT FROM AUTHOR]

Presents a physical model of the properties of polycrystalline ferrites below magnetic saturation. Characterization of properties through permeability tensor as functions of magnetization states, anisotropy field and frequency; Homogeneity of medium through medium approximation; Comparison of results for different states with empirical formulations of permeability tensor components.

Proposes a model which provides integral expressions for all magnetic permeability tensor components, that can be treated numerically without difficulties, in microwave devices. How the causal aspect that is required when numerical time-domain methods are used is provided by the model; Demonstration of the validity of the model.

In order to develop a new kind of filter that makes a compromise between quasi-optical and more traditional bandpass filtering techniques at millimetre wavelengths, a theoretical modelling of grids in oversize and monomodal waveguides is performed using a variational method. [ABSTRACT FROM AUTHOR]

Presents a study which outlines the finite-difference time-domain (FDTD) treatment of partially magnetized ferrites which are characterised by a permeability tensor model. Comparison of numerical and analytical results of study; Information on a classical FDTD model; Description of an FDTD algorithm for an unsaturated ferrite.

Presents a study which proposed a measurement method that permits the determination of the complex permeability and permittivity of rectangular samples of various thickness. Electromagnetic analysis of the cell; Experimental results; Conclusion.