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Purpose: To investigate whether the risk of peripheral nerve stimulation increases in the presence of bulky metallic prostheses implanted in a patient's body. Methods: A computational tool was used to calculate the electric field (E‐field) induced in a realistic human model due to the action of gradient fields. The calculations were performed both on the original version of the anatomical model and on a version modified through "virtual surgery" to incorporate knee, hip, and shoulder prostheses. Five exam positions within a body gradient coil and one position using a head gradient coil were simulated, subjecting the human model to the readout gradient from an EPI sequence. The induced E‐field in models with and without prostheses was compared, focusing on the nerves and all other tissues (both including and excluding the bones from the analysis). Results: In the nerves, the most pronounced increase in the E‐field (+24%) was observed around the knee implant during an abdominal MRI (Y axis readout). When extending the analysis to encompass all tissues (excluding bones), the greatest amplification (+360%) occurred around the knee implant during pelvic MRI (Z axis readout). Notable increases in E‐field peaks were also identified around the shoulder and hip implants in multiple scenarios. Conclusion: Based on the presented results, further investigations aimed at quantifying the threshold of nerve stimulation in the presence of bulky implants are desirable. [ABSTRACT FROM AUTHOR]

Boundary Element approaches are developed to evaluate the human exposure to low-frequency electromagnetic fields, estimating the current density distribution inside the body. The reference man proposed in the IEC Standards is adopted to model the human body. The validation is performed by comparison with analytical and finite-element solutions. Various exposure conditions, typical in electric substations and industrial environment, are finally investigated through the proposed approaches. Index Terms--Boundary Element methods (BEMs), human exposure to electromagnetic fields, standards.

This paper compares two numerical schemes for the simulation of magnetization dynamics in 3-D particles. The first one is based on the finite-difference computation of the Landau-Lifshitz equation and on the magnetostatic field evaluation by fast Fourier transforms. The second one handles the spatial discretization of the effective field expression by a nodal finite-element method and solves the Poisson equation with a finite-element/boundary-element technique. The convergence of the methods is studied by varying the time and space discretization. Index Terms--Finite-difference (FD) methods, finite-element methods (FEMs), magnetization reversal, micromagnetics.

This paper presents a 3-D dynamic micromagnetic numerical scheme, based on the decoupling of the effective field evaluation from the treatment of the Landau--Lifshitz equation. The weak formulation of the effective field expression is spatially discretized through a nodal finite element approach. The micromagnetic equation is locally computed, performing the time integration with a finite difference scheme, based on midpoint rule and able to preserve the magnetization nonconvex constraint. Different techniques are compared for the evaluation of the magnetostatic field, such as finite element/boundary element method, standard finite element approach with first-order asymptotic boundary conditions, and Green integral formulation. Index Terms--Finite element methods, magnetization processes, micromagnetics, numerical analysis.

This paper presents the comparison between two different numerical schemes for the analysis of switching phenomena in magnetic thin films. The first one is based on the finite-difference computation of the Landau--Lifshitz equation and on the magnetostatic field evaluation by fast Fourier transforms. The second one handles the spatial discretization of the Landau--Lifshitz equation by the edge finite-element method and solves the Poisson equation for the magnetostatic field with a hybrid finite element/boundary element technique. Index Terms--Finite-difference methods, finite-element methods, Landau--Lifshitz equation, magnetization reversal, thin films.

This paper presents a mathematical homogenization technique able to handle fine periodic structures in presence of magnetic saturable/hysteretic media. The modeling approach, based on the multiple scale expansion theory, enables the evaluation both of equivalent electric parameters and effective magnetization curves (or hysteresis loops). The results of the homogenization technique are validated by comparison with those provided by a standard finite element solution of a two-dimensional current driven problem defined on the heterogeneous domain. Index Terms--Homogenization techniques, nonhomogeneous media, nonlinear differential equations, soft magnetic materials.

This paper deals with the evaluation of higher order spatial derivatives in electromagnetic-field problems with heterogeneous media handled through a multiscale expansion technique. A comparison is performed on the higher derivative computation, considering an element-free Galerkin approach, and bicubic spline interpolations as well as least-square approximations of piecewise finite-element solutions. Index Terms--Element-free Galerkin (EFG) method, higher order derivatives, multiscale expansion theory, nonhomogeneous media.

This paper investigates the influence of supply, circuit and magnetic material parameters on the occurring of fundamental-mode ferroresonance in a series inductance--capacitance--resistance (LCR) circuit with a nonlinear inductor. The analysis is developed using a modeling approach, validated by experiments, which accurately describes the magnetic behavior (dynamic hysteresis and eddy currents) of the saturable inductance. The conditions leading to subharmonic ferroresonance are also investigated. Index Terms--Ferroresonance, finite-element method, hysteresis, skin effect.

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. Index Terms--Eddy currents, element-free Galerkin method, hysteresis, meshless method.

The paper focuses on the numerical computation of the stray parameters of coils for reference magnetic field generation. The coils are modeled by the multiconductor transmission line approach, where the inter-turn capacitances are evaluated through a hybrid finite element/boundary element method. The influence of the turn arrangement and the support dielectric characteristics is investigated with the aim of evaluating the system performance with the increase of frequency. Index Terms--Calibration systems, hybrid methods, stray capacitance.

The thin layer technique is extended to the analysis of passive shields for the mitigation of pulsed magnetic fields. The interface conditions between the two sides of the shell are determined by discretizing the diffusion equation along the shell thickness. The proposed formulation is validated by comparison with a standard hybrid finite element--boundary element method solution. Finally, some applications on problems related to industrial and laboratory environments are presented. Index Terms--Electromagnetic shielding, electromagnetic transient analysis, modeling.

This paper presents an advanced finite-element model for analyzing the dynamic behavior of electromechanical devices. The numerical approach includes nonlinear supply circuits, eddy-current and hysteresis effects, and mechanical quantities. The motion of the armature can be handled by means of two alternative approaches, based on the overlapping mesh or on the coupling of finite-element and boundary-element methods. The paper validates the model by comparing it to experimental results on an ac electromagnet with shading rings and then applies it to the analysis of fast actuators. Index Terms--Dynamic analysis, eddy currents, electromechanic devices, FEM, hybrid FEM-BEM, hysteresis.

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. Index Terms--Finite-element analysis, induction motors, losses.

This paper presents two approaches for nonlinear dynamic modeling of voltage-driven magnetic circuits. The field approach is based on a finite-element method; in two-dimensional laminated cores, an in-plane magnetic analysis is coupled with a one-dimensional eddy current solution across lamination thickness. The lumped parameter approach subdivides the magnetic core in flux tubes according to geometrical symmetries and solves the coupled electric and magnetic circuits. The two methods are applied to the analysis of magnetic cores and comparisons between them, and experimental data are performed and discussed. Index Terms--Eddy currents, finite-element method (FEM) analysis, magnetic circuits.

An extension of the thin shell formulation for the analysis of the shielding efficiency of muitilayered passive shield is presented in the paper. After a validation of the propose approach by comparison with analytical results in the case of cylindrical shield placed in a uniform field, the model is applied t the analysis of shielding configurations of practical interest. Index Terms--Hybrid FEM-BEM model, magnetic shielding.

Two two-dimensional (2-D) finite-element techniques for the analysis of the electromechanical dynamics in electrical devices are presented and compared. The techniques are based on a hybrid finite-element method/boundary-element method (FEM/BEM) formulation and on an FEM approach with overlapping meshes, respectively. The merits and drawbacks of the two approaches are discussed when applied to the analysis of electromechanical devices under different operating conditions. Index Terms--Boundary-element method, electromechanical dynamics, finite-element method.

We have investigated the influence of eddy currents and hysteresis on the behavior of electromagnetic devices with cylindrical geometry. We used a finite-element procedure to analyze voltage-driven electromagnetic problems (i.e., interaction with supply circuits) under periodic and transient supply conditions. We represented the magnetic hysteresis of the core by a stop hysteron model, and developed the investigation on different kinds of cylindrical electromagnets, having previously validated the numerical model by comparison with experimental data. The effects of diffusion and hysteresis phenomena are put in evidence and discussed here. Index Terms--Diffusion, eddy currents, electromagnets, hysteresis.

The paper presents a comparative analysis of different theoretical iron losses evaluation techniques, coupling finite-element calculations and material modeling. This coupling can be performed at different levels: as a postprocessing step or inside the nonlinear solution loop. Comparisons on an induction machine structure are performed and results are compared and discussed. Index Terms--Electrical machines, finite element, hysteresis, iron losses.