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Magnetostatic edge-element formulation leads to a singular linear system of equations. Although a reduced system of equations can be derived by imposing the zero-tree gauge condition, the gauging causes undesirable deterioration in the convergence property of conventional iterative solvers. In this paper, we develop a new preconditioning technique that overcomes the slow convergence caused by zero-tree gauging, by utilizing the folded preconditioning proposed in our previous paper. Moreover, we present a novel theorem that clarifies the coincidence of the spectra of the preconditioned matrices when folded preconditioning is used.

This paper proposes an implicit error correction method that corresponds to the explicit error correction methods, such as Hiptmair's hybrid smoother and the conventional multigrid method. The A-phi method can be seen as the implicit error correction method corresponding to the hybrid smoother. Numerical tests confirm that the A-phi method produces a similar correction effect on the error belonging to the kernel of the discrete curl operator as that of the hybrid smoother. Furthermore, this paper introduces an implicit correction multigrid method, which is the implicit error correction version of the conventional multigrid method. In this method, linear systems on all levels in a multigrid method are combined into a large linear system. This linear system is solved by an iterative solver, and any preconditioning techniques can be used. Numerical tests show that the proposed method involves coarse grid correction effects and achieves a convergence rate independent of the grid-size, thus confirming the effectiveness of the implicit error correction method.

The objective of this paper is to provide suitable approximations of effective permeability for magnetic concentration cores. This core has a dumbbell shape so that the magnetic flux is concentrated to the coil winding part of the core. It is well known that the demagnetizing factor strongly depends on the core shape, which defines the effective permeability. Although several researchers have already proposed an approximation for a dumbbell-shaped core, they did not take into account the flange part length. In this paper, a novel approximation for a dumbbell-shaped core is proposed. It is based on the demagnetizing factor and correction terms related to the aspect ratio of both the flange and coil winding part. From experimental results, the validity of the approximation is confirmed., Article, IEEE TRANSACTIONS ON MAGNETICS. 51(1):4000304 (2015)

This paper presents the optimization of a meander line antenna finite-element model by means of an adaptive genetic algorithm (GA). To search for optimal antenna configurations, the present method employs a GA with an adaptive method that adjusts the characteristics of its selection, crossover, and mutation operators in order to maintain a diverse set of high-quality candidate solutions during its execution. It is shown that the present method can find an optimal solution faster than the conventional GA. Moreover, the fitness values of the optimal solutions obtained by the present method are better than those obtained by conventional GA.

Eddy-current (EC) displacement sensors are used in a device for measuring the shaft vibration of turbines. An EC displacement sensor is composed of a sensor probe and an impedance/output voltage (Z/V) converter. In a power plant in the U. S., the type of the sensor probe and the displacement from the turbine shaft to the tip of the sensor probe (displacement x) are not controlled. For this reason, when only the Z/V converter breaks down, the plant is stopped and dismantled, and both the Z/V converter and the sensor probe are replaced. This results in two problems, i.e., the unstable supply of electric power when the power plant is stopped and the high cost of dismantling the plant. If both the type of the sensor probe and x are identified during turbine operation, the aforementioned problems could be solved. In this paper, we describe that the three types of the sensor probe and x can be identified by comparing the measured the maximum quality factor Q(EC) (max) and frequency f(o) at Q(EC) (max) with the Q(EC) (max) versus f(o) characteristics of sensor probes., Article, IEEE TRANSACTIONS ON MAGNETICS. 47(10):3554-3557 (2011)

The purpose of this study is to demonstrate the energy harvesting of power-line magnetic noise. To the best of the authors' knowledge, no research has yet been carried out to confirm this possibility. In this paper, we present a simple circuit design model, and confirm its validity by experimental results. For small self-sufficient devices in a wireless sensor network, the target energy level is 1 mW. We prepare an energy harvesting module with an air-core coil and resonant capacitor. From experimental and simulated results, we investigate the desired conditions for harvesting 1 mW from a uniform magnetic field of 60 Hz. Through experimental results with iron cores, the benefits and drawbacks of the use of a magnetic core are also discussed. With our best harvested module, we successfully demonstrated the energy harvesting of 6.32 mW from a magnetic field of 21.2 μT at 60 Hz. If the usable magnetic flux density increases tenfold, the harvesting energy increased 100-fold. If the magnetic flux density is at an acceptable level in a public space of 200 μT at 60 Hz, the harvesting power density becomes 130 μW/cm3. This value is comparable to the value of an energy harvesting module of a light source during a cloudy day., Article, IEEE TRANSACTIONS ON MAGNETICS. 47(10):4441-4444 (2011)

The A-phi formulation, which is widely used in electromagnetic analysis, leads to a redundant linear system of equations that includes a substantial number of redundant degrees of freedom (DOF). We can derive a redundancy-reduced linear system of equations by eliminating the redundant DOF, thereby decreasing the computation costs per iteration for iterative solvers, such as the incomplete Cholesky conjugate gradient (ICCG) solver. This does not, however, result in a reduction in total computation time, due to significant convergence deterioration. In this paper, we present a solution to this problem in the form of folded preconditioners. First, the theorem presented reveals that, for any preconditioned Krylov subspace method for the original redundant linear systems, we can derive the equivalent Krylov subspace method for the redundancy-reduced linear systems by using the corresponding folded preconditioner. As an uncomplicated example, the standard ICCG solver for the original redundant systems has exactly the same convergence property as the CG solver for the redundancy-reduced systems using the folded variant of the IC preconditioner (the folded IC preconditioner). Furthermore, we discuss efficient computational procedures for the folded preconditioners and the design of Krylov subspace algorithms using the preconditioners. A sample full-wave analysis demonstrates the good performance of a newly developed solver, the conjugate orthogonal conjugate gradient (COCG) method with the folded IC preconditioner. The new solver not only lowers the computation costs per iteration by reducing the number of DOF, but also completely avoids the convergence deterioration.

This paper presents a comparison of two types of isotropic vector play models and their generalized models. The first vector model is represented by a superposition of scalar play models. The other type is given by a geometrical vectorization of play hysteron. The rotational hysteresis losses of both models are discussed. A method is proposed to adjust the simulated rotational hysteresis loss to a measured loss.

This paper introduces a simple way to evaluate the preconditioning effect in the shifted ICCG method. The proposed evaluation index is easily calculated with little additional memory in an incomplete factorization process; thus, it can be used for setting appropriate parameters for the solver, such as an acceleration factor and the ordering of unknowns, prior to the time-consuming iteration process. Numerical results show that the evaluation index gives the good estimate of the number of iterations necessary for convergence

This paper presents a parallel algebraic multigrid (AMG) solver for linear systems of equations arising in magnetic finite edge-element analyses. To parallelize the smoothing process, which consumes most of the computational costs of the AMG algorithm, we apply multicolor (MC) ordering to the symmetric Gauss-Seidel (SGS) method. Advantages of MC ordering are: 1) that the number of processors employed does not affect the convergence of the approximate solution and 2) that only the information of the coefficient matrix is utilized to parallelize the smoother. The numerical results show that the developed solver achieves sufficient scalability in magnetic finite edge-element analyses.

The algebraic multigrid (AMG) method is an algebraic multilevel solver for linear systems of equations, which stem from the discretization of partial differential equations. This paper develops an efficient AMG solver for singular linear systems of equations arising from electromagnetic finite element (FE) analyses using edge elements. The presented solver can solve singular equations using a technique similar to the shifted incomplete Cholesky conjugate gradient method. Shifted global coefficient matrices are utilized to construct the AMG preconditioner. The numerical results show that the proposed AMG conjugate gradient (AMGCG) solver can converge with a wide range of "shift".

The algebraic multigrid (AMG) method is an efficient solver for linear systems arising in finite element analyses. The AMG method is applicable at a matrix level, different from the geometric multigrid solvers. This paper proposes a combination of the parallel processing technique and the AMG method as a fast solver for electromagnetic field analyses. While the AMG method consists of a setup phase and a solution phase, parallel processing of the former phase is difficult. We present the use of long-range interpolation instead of the conventional direct interpolation for improvement of the parallel efficiency of the AMG setup phase. A magnetostatic analysis and an eddy-current analysis show the solver performance. The numerical results show that parallelized AMG is a fast solver and has sufficient scalability, as compared with the conventional solver.

The present paper proposes a new method for the construction and ordering of edge elements for parallel computation. The use of virtual nodes generated in each volume element is presented as a means of introducing parallel ordering theory developed in finite difference analyses to finite edge element analyses. Eight-corner ordering and multi-color ordering are examined in the context of 3-D eddy-current analysis. The proposed method using 8-corner ordering can parallelize the ICCG solver in a finite edge element analysis without decreasing the convergence rate. A good balance between convergence and parallelism in the ICCG solver is obtained in the case of multi-color ordering.

This paper presents identification methods for 3-D isotropic vector hysteresis models represented by the superposition of stop and play models. Their properties of rotational hysteresis losses are discussed. The vector models are generalized to control their rotational hysteresis losses

In this paper, we proposed and verified the feasibility of a unique wireless power transfer structure called a rail transformer to drive multiple low-power devices such as electronic shelf label (ESL) devices. The rail transformer is composed of a rectangular, circular-shaped transmitting yoke and two transmitting coils to provide wireless power. Multiple receiving yokes coupled with receiving coils are installed across the elongated edge of the transmitting yoke. It can be driven by low-frequency ac power at 50/60 Hz. In our prototype, the transmitting yoke is 900 mm long and 15 mm wide. We obtained the minimal induced wireless power, and the voltage was similar to 61 mW and 3.5 V, which is sufficient to drive a typical ESL device. By designing a nonuniform gap thickness between the transmitting and the receiving yokes at the specific locations, we improved the uniformity of the induced power for multiple ESL devices., Article, IEEE TRANSACTIONS ON MAGNETICS. 51(11):8402904 (2015)

This paper reports on the growth and properties of bilayer structures consisting of insulating epitaxial Cu/sub 3/N films grown on epitaxial ferromagnetic /spl gamma/''-Fe/sub 4/N films. The interface between the layers is successfully probed with Mossbauer spectroscopy. In our fully epitaxial system, no intermixing occurs at the interface. Depending on the growth parameters (gas mixture, deposition temperature), the interface is also free of undesired nitride phases.