Effect of transition layers on the electromagnetic properties of composites containing conducting fibres

The approach to calculating the effective dielectric and magnetic response in bounded composite materials is developed. The method is essentially based on the renormalisation of the dielectric matrix parameters to account for the surface polarisation and the displacement currents at the interfaces. This makes it possible the use of the effective medium theory developed for unbounded materials, where the spatially-dependent local dielectric constant and magnetic permeability are introduced. A detailed mathematical analysis is given for a dielectric layer having conducting fibres with in-plane positions. The surface effects are most essential at microwave frequencies in correspondence to the resonance excitation of fibres. In thin layers (having a thickness of the transition layer), the effective dielectric constant has a dispersion region at much higher frequencies compared to those for unbounded materials, exhibiting a strong dependence on the layer thickness. For the geometry considered, the effective magnetic permeability differs slightly from unity and corresponds to the renormalised matrix parameter. The magnetic effect is due entirely to the existence of the surface displacement currents.Comment: PDF, 33 pages, 10 figure

THE EFFECT OF APPLIED STRESS ON THE POWER LOSS, DYNAMIC MAGNETOSTRICTION AND DOMAIN BEHAVIOUR OF INDIVIDUAL GRAINS OF SILICON-IRON IN A POLYCRYSTALLINE MATRIX

On a mesuré par une méthode thermique la perte de puissance des grains individuels de Fe-Si dans un échantillon polycristallin ainsi que le mouvement des parois par effet Kerr. On a étudié l'effet d'une tension (0 ± 7 x 106 N.m-2) sur la perte de puissance et le mouvement des parois. On a déterminé l'effet d'une tension et d'une compression appliquées perpendiculairement au plan de l'échantillon sur la magnétostriction dynamique. On a développé un modèle basé sur la structure des domaines observée, qu'on a vérifié par des mesures supplémentaires.The power loss of individual grains of silicon-iron in a polycrystalline sample has been measured using a thermal method, and the domain wall motion studied by the Kerr magneto-optic technique. The effect of applied stresses (0 ± 7 x 106 N. m-2) on both the power loss and domain motion has been investigated. The effect of both compressive and tensile stresses applied in two perpendicular directions in the plane of the sheet on the dynamic magneto-striction has been determined. A theoretical model based on the observed domain structure has been developped to explain the experimental results ; and a verification of the proposed model has been attempted by making additional measurements

Micro wires and process for their preparation

Filing Date: 2002-04-03.-- Priority Data: GB 0108373.2 (2001-04-03)A Co-Fe-Mn-B-Si alloy suitable for use in the manufacture of micro wires which exhibit bistable magnetic behaviour, the alloy comprising: Iron from 2 to 15 at . % Manganese from 3 to 7.5 at . % Boron from 12 to 16 at. % Silicon From 8 to 14 at . % Cobalt - balance Wherein the alloy exhibits an essentially rectangul ar magnetisation loop