János Füzi

Isotropic vector Preisach particle

Abstract A Preisach-type pseudoparticle is proposed, to describe macroscopic vector magnetic behaviour of isotropic materials. The magnitude of magnetization is computed by means of the classical Preisach model with the projection of field strength on its direction as input. The orientation of the magnetization vector is governed by the equilibrium between its vector product with the field strength and a friction-like opposing torque proportional to the square of its magnitude. The behaviour of the model is studied in various conditions and the results compared to experiments reported in literature.

Anisotropic vector Preisach particle

The static 2D vector magnetic behaviour of an anisotropic silicon iron sheet is modelled by a particle which depicts its space-averaged behaviour. The magnitude of magnetization is governed by a classical Preisach operator with the projection of field strength on the magnetization direction as input. Its orientation is determined by the equilibrium between the field strength orientation and the anisotropy of the sheet.

Features of two rate-dependent hysteresis models

Abstract Two rate-dependent models of ferromagnetic hysteresis are compared and their features illustrated by examples. An internal dynamic generalization of the classical Preisach model (CPM) replaces the ideal hysteresis switches of the CPM by operators with outputs that change at a finite rate. The external dynamic model uses the CPM as it is, but delays its input with respect to the actual field strength variation. The behavior of the two models in identical conditions are compared and their performance evaluated in terms of complexity of numerical implementation, possibility of parameter identification, ability to reproduce—and, of course, predict—experimental results, computational speed and memory requirement.

Equivalence of Magnetic Metamaterials and Composites in the View of Effective Medium Theories

The electromagnetic response of metamaterials is governed by the collective behavior of engineered electric and magnetic dipoles. Therefore metamaterials may be replaced by hypothetical composites of spherical particles embedded in a host material. The effective electric permittivity and magnetic permeability of such systems can be computed with high-frequency extension of the Maxwell-Garnett mixing rule. The validity of this assumption is discussed and the features of the model are presented by calculating the effective electromagnetic material parameters of a deep subwavelength spherical composite in three different ways: with the Maxwell-Garnett mixing rule, high-frequency mixing rule and directly extracted from transmission reflection data. Afterwards the developed theory is applied to find the parameters of a composite with similar magnetic response as a metamaterial built of split ring resonators or fishnet structures.

Neutron beam conditioning for focusing SANS spectrometers

Multibeam focusing offers an appealing compromise between high resolution and high incident flux configurations for SANS spectrometers. In fact so many spectrometers operate in parallel as the number of channels in the collimator. Each channel provides high resolution by small spot size on the detector and long sample-to-detector distance, involving significant limitation of the transmitted beam phase space volume, thus reducing the flux. The flux on the sample is increased by the large number of channels. In view of the multibeam collimation it is beneficial to increase the beam cross section and decrease the divergence at the same time. Two aspects related to the use of rotational velocity selectors are investigated. First the transmitted phase space is determined from the selector parameters. It is found that the beam azimuthal divergence with respect to the rotor axis has a significant effect on the selectivity. Neutrons flying along different paths are treated differently, leading eventually to energetic non-uniformity of the illumination of various collimator channels. Then the effect of the gap in the neutron guide at the selector location on the phase space uniformity at the collimator entrance is investigated and optimal selector location along the beam is proposed together with optimal neutron guide shape in the vicinity of the gap, which accommodates the selector.

Neutron Beam Phase Space Mapping

The phase space of neutron beams is mapped by means of energy-resolved neutron imaging using a 2D position-sensitive detector in time-of-flight regime. The beam is viewed through a pinhole with adjustable position with respect to the beam axis, mapping the beam cross-section. The neutron beam flux and divergence are measured with respect to position and wavelength. The results can be used in subsequent downstream instrument design and optimization, as input and/or test data for simulation codes as well as for characterization of upstream elements (neutron sources, monochromators, guides etc). Results of measurements performed at the exit of a tapered supermirror guide on a beam at the Budapest Neutron Centre are presented.

Strong coupling in electromechanical computation

Abstract A method is presented to carry out simultaneously electromagnetic field and force computation, electrical circuit analysis and mechanical computation to simulate the dynamic operation of electromagnetic actuators. The equation system is solved by a predictor–corrector scheme containing a Powell error minimization algorithm which ensures that every differential equation (coil current, field strength rate, flux rate, speed of the keeper) is fulfilled within the same time step.

Two-dimensional field model for single-sheet tester

Abstract The investigation of the magnetic field in a circular-shaped single-sheet tester is developed under circular polarised field intensity as well as flux density. The non-linear anisotropy of the material is represented by a vector realisation of the Jiles−Atherton hysteresis operator. The monitored data of the components in the field vectors are simulated with the averaged values of the field resulted by the numerical analysis of the non-linear eddy current problem.

Magnetic material and motion

A numerical analysis based on global variational method is developed for simulation of on-line testing of magnetic sheet moving in a cross-directed field of magnetic poles. Considering the eddy currents and the hysteresis of the material, the modification effect resulting from the motion of the sheet is studied.