Element-free galerkin method in eddy-current problems with ferromagnetic media

This paper focuses on the application of the element-free Galerkin method to the solution of eddy-current problems in ferromagnetic media. The method is first validated by comparison with an analytical linear solution, discussing the role of the numerical parameters that affect the solution accuracy. Then, the application is extended to nonlinear and hysteretic media, adopting the fixed point iterative scheme and the classical Preisach model. The proposed method is also tailored for nonhomogenous structures. The merits and drawbacks with respect to a finite-element approach are discussed for all the considered problems.     

Influence of probe size on the measurement accuracy of non-uniform ELF magnetic fields

The accuracy of extremely low frequency (ELF) magnetic field measurements can be sensitively varied by the meter probe size when the spatial distribution of the magnetic flux density is highly non-uniform, e.g. if the measurement point is close to the field source. The deviation between measured and actual field varies from point to point depending on the probe dimension and on the source configuration, once the other measurement conditions are fixed. The analysis of this effect is developed through a two-dimensional numerical model that enables the evaluation of the actual field value and of the corresponding probe indication. The error distribution, i.e. the deviation between actual and measured value, is computed for magnetic fields generated by industrial three-phase systems under both balanced and unbalanced supply conditions. The analysis shows how, for a given source, the error depends not simply on the distance from the source in relation to the probe size, but on its spatial distribution, which is complex and cannot be a priori predicted without using a computational tool such as the one proposed.     

Advanced model of laminated magnetic cores for two-dimensionalfield analysis

A numerical model for the analysis of laminated ferromagnetic cores of electromechanical devices is presented. The model is based on the finite-element solution of the two-dimensional (2-D) electromagnetic field problem in the lamination plane; a dynamical relation between local magnetic flux density and magnetic field strength is obtained by solving for the one-dimensional (1-D) eddy-current field developed in the lamination depth. The hysteresis of the magnetic material is accounted for by the Preisach approach. The model is first validated by comparison with an alternative held formulation available for axis-symmetric structures; finally, an application to a more complex 2-D laminated core is presented and the numerical results are confirmed by comparison with measured waveforms of electrical and magnetic quantities     

On the use of TEM cells for the calibration of power frequency electric field meters

This paper focuses on the performances of TEM cells when used in the calibration of power frequency environmental electric field meters. The spatial non-uniformity of the electric field inside a TEM cell is analyzed through experimental investigations and three-dimensional Boundary Element modeling to evaluate the field experienced by the sensing elements of actual 3D meter probes. The perturbation caused by the probe support is also taken into account. The uncertainty component associated with the spatial non-uniformity in the volume taken up by typical power and low frequency field probes is estimated. The field non-uniformity is also evaluated in relation to the use of TEM cells of reduced size. Finally, the field non-uniformity is exploited to predict the performance of an actual field meter operating in significant field gradients.     

Measuring the Hysteresis Loop of Permanent Magnets With the Pulsed Field Magnetometer

We discuss a comprehensive approach to the characterization of permanent magnets with the pulsed field magnetometer. The approach is based on a systematic comparison of the results obtained by this method with those from the conventional closed-circuit and open-sample methods and on the assessment of the dynamic phenomena engendered by the application of the fast exciting field pulse. Such phenomena derive from the thermal fluctuation after effect and the eddy currents, whose contributions to hysteresis loop swelling are brought to light and separately evaluated. We show that the quasi-static hysteresis loop can be retrieved from the dynamically obtained one by compensating for the magnetic viscosity field, found to be proportional to the coercive field, and the eddy-current counterfield. A simple analytical formulation accounts for and predicts the effect of the counterfield.     

Analysis of Losses in a Magnetostrictive Device Under Dynamic Supply Conditions

This paper, starting from previous experiences in modeling the magneto-mechanical behavior of magnetoelastic materials, faces the problem of loss evaluation of a magnetostrictive device. Measurements and simulations in a prototype actuator are here presented and compared, showing a general good agreement. The model is consequently used for a reliable loss separation. The effects of magnetization bias, preload and supply frequency on electric and magnetic losses are deepened and discussed.      

Additional losses in induction machines under synchronous no-load conditions

The paper examines factors and parameters that affect the additional losses produced in the rotor cage of an induction motor during a no-load test at synchronous speed. The analysis uses a numerical approach based on a finite-element step-by-step procedure, taking into account the rotor movement. Iron losses are evaluated according to the loss separation theory. Additional losses are computed on the basis of predictions of high-frequency phenomena induced in the rotor cage. The model has been validated by comparison with experiments performed on a specific laboratory setup, consisting of a stator that can be equipped with two different rotors. The numerical approach was used to investigate the role of different parameters (supply conditions, geometrical dimensions, material properties) affecting the additional losses.     

Numerical Analysis of the Influence of Geometry and Temperature on Switching Processes in Magnetic Nanostrips

The present paper numerically investigates the micromagnetic behavior of permalloy nanostrips, starting from the space-time integration of the Landau-Lifshitz-Gilbert equation. The analysis is performed on objects with variable longitudinal size of the order of some hundreds of nanometers. The attention is focused on the role of geometrical properties (e.g., scaling factor and end shape) and of thermal agitation on magnetization reversal processes. The thermal effects are included in the model following the Langevin approach.