Search

This article proposes a numerical formulation for handling mixed-dimensional elements embedded in a standard three-dimensional (3d) mesh, avoiding thus the volume meshing of filaments and strips. The method is then applied to predict the temperature heating and cooling profile of gradient coils in magnetic resonance imaging. These coils are typically constructed from copper wires or tracks and embedded in an epoxy layer. It was found that the new method significantly reduces the computational time of steady-state and transient simulations, with speedups in the range of 3.5-5. The method proved to be accurate, with relative errors below 0.5% for steady-state simulations and 1.5% with respect to a complete 3d simulation. [ABSTRACT FROM AUTHOR]

Purpose This article aims to present a fast, efficient and accurate multi-layer integral method (MIM) for the evaluation of complex spatiotemporal eddy currents in nonmagnetic and thin volumes of irregular geometries induced by arbitrary arrangements of gradient coils. Methods The volume of interest is divided into a number of layers, wherein the thickness of each layer is assumed to be smaller than the skin depth and where one of the linear dimensions is much smaller than the remaining two dimensions. The diffusion equation of the current density is solved both in time-harmonic and transient domain. Results The experimentally measured magnetic fields produced by the coil and the induced eddy currents as well as the corresponding time-decay constants were in close agreement with the results produced by the MIM. Relevant parameters such as power loss and force induced by the eddy currents in a split cryostat were simulated using the MIM. Conclusion The proposed method is capable of accurately simulating the current diffusion process inside thin volumes, such as the magnet cryostat. The method permits the priori-calculation of optimal pre-emphasis parameters. The MIM enables unified designs of gradient coil-magnet structures for an optimal mitigation of deleterious eddy current effects. Magn Reson Med 71:1912-1922, 2014. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The aim of this paper is to propose an approximate technique for the reconstruction of magnetic-field distribution in the proximity of unknown sources. The method is based on two nested optimization algorithms-the external one is responsible for the definition of the geometry of the equivalent-source system, while an internal procedure based on least-square minimization is used to identify the currents of the sources. The goal is to minimize the deviation between the reconstructed and actual field. It is shown that under magnetic quasi stationary conditions, the proposed approach is able to reconstruct the field distribution of a complex 3-D environment as medium-voltage/low-voltage substations. The main limitation is the availability of magnitude and phase of the measured magnetic field. This information is not usually provided by standard probes but can be obtained by a proper measurement setup. The proposed technique allows accurate reconstruction of the magnetic field even in the case of many sources without requiring their accurate geometrical description and is suitable for the evaluation of stray fields and the design of magnetic shielding. [ABSTRACT FROM AUTHOR]

The paper presents a two-stage approach to solve a class of nonlinear 3-D eddy current problems with high saturation, typical of induction heating processes. The proposed method separates the problem of heavy nonlinearity from the complexity of the geometry, by resorting to a 1-D fast nonlinear solver which is coupled with a linear 3-D solver. Under certain hypotheses on the geometry, the approach is shown to be effective and accurate. Comparison with a commercial 3-D nonlinear code are provided. [ABSTRACT FROM AUTHOR]

This paper presents a methodology to study nonlinear electromagnetic phenomena inside ferromagnetic pieces where eddy currents are driven by an external supply source in the medium frequency range. The proposed methodology takes, as reference, a nonlinear time-harmonic solution of the iron part and then identifies, by means of an optimization procedure, the magnetic permeability values of an equivalent layered linear material which would give the same value of Joule losses of the nonlinear case. This approach has been applied to a test configuration obtaining good results. [ABSTRACT FROM AUTHOR]

In this study, the human exposure to the magnetic field emitted by a wireless power transfer (WPT) system during the static recharging operations of a compact electric vehicle (EV) is evaluated. Specifically, the influence of the posture of realistic anatomical models, both in standing and lying positions, either inside or outside the EV, is considered. Aligned and misaligned coil configurations of the WPT system placed both in the rear and front position of the car floor are considered as well. Compliance with safety standards and guidelines has proven that reference levels are exceeded in the extreme case of a person lying on the floor with a hand close to the WPT coils, whereas the system is always compliant with the basic restrictions, at least for the considered scenarios. [ABSTRACT FROM AUTHOR]