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This paper focuses on the light interference in biogenic guanine crystals that have interesting optical properties such as high reflectivity and optical biaxiality. In this paper, we find that a Moiré effect pattern is generated on a single guanine crystal of goldfish combining with the mirror surface substrate. An observation system, in this paper, is consisted with telecentric lens and coaxial vertical illumination using blue LED light source. It is clearly seen that homogeneous light and shade stripe patterns are observed on the broadest surface of the single guanine crystal plate floating in water. By contrast, when the guanine crystals are set on the substrates having the diffused reflection surface, this light and shade stripe pattern is not observed on the single guanine crystal but observed on two cross-stacked crystals as reported before. These results show that the light and shade stripe pattern on the single guanine crystal is produced by the optical interference, so-called Moiré effect, between guanine crystal and the mirror substrate surface. The angle dependence of reflection brightness and the magnetic orientation of guanine crystal are investigated by using Moiré patterns. Furthermore, we demonstrate that small curvatures and steps can be optically detected and estimated by the pattern change of Moiré stripes. It is confirmed that the direction of curvature is detected by controlling the guanine crystal orientation with magnetic fields and the curvature shape is reproduced from the Moiré pattern. [ABSTRACT FROM AUTHOR]

This paper introduces a possible mechanism to explain the changes in neurons following extremely low frequency magnetic fields (ELF-MFs). The model in this paper contains two parts: the physical part and the bio-trigger part. The first part is an electric current equation, which is a generalization of the Nernst–Plank equation with the exposure of ELF-MF, and the second bio-part is a phenomenological model, which is a simple two-state channel with two steady state open (O) state and closed state (C). The two parts are complementary. The first part is utilized to explain changes about synaptic plasticity following ELF-MF exposure at embryonic and postnatal age. The second part is used to simulate the process of three different types of neurons reported by previous papers. According to the results, the present model is feasible for the simulation process. The concept of ion mobility or permeability is emphasized in this paper in part I, and channel state transition probabilities are paid much attention to in part II. In this paper, the ion mobility or permeability is supposed to have close relationships with ion channel transition probabilities, which connects the two parts of the model together. [ABSTRACT FROM PUBLISHER]

This paper describes an investigation into the combined effects of magnetoconvection and an externally applied magnetic field on the thermal performance of vegetable oil-based magnetic nanofluids with different volume fractions of magnetic nanoparticles. The mineral-based oil has conventionally been used in power transformers because it has high dielectric strength and good cooling performance under normal operating conditions. Because of the environmental impact, eco-friendly vegetable-based transformer oils have been substituted for mineral-based insulating oils. To date, related studies have only reported on the characteristics of dielectric breakdown in vegetable oil-based magnetic nanofluids without any real electromagnetic systems. Furthermore, the thermal characteristics of vegetable oil-based magnetic nanofluids have not yet been fully investigated. Thus, the aim of this paper was to examine the cooling performance by adding magnetic nanoparticles to the vegetable-based transformer oil. To quantitatively analyze this effect, a multi-physics technique that incorporates magnetic-thermal-fluidic fields was developed as based on quasi-static magnetic field approximation and conjugate heat transfer. To validate the numerical results, corresponding experiments were successfully carried out via application in a simple electromagnetic system with varying insulating liquids. [ABSTRACT FROM AUTHOR]

This paper investigates the feasibility of novel data-driven deep learning (DL) models to predict the solution of Maxwell’s equations for low-frequency electromagnetic (EM) devices. With ground truth (empirical evidence) data being generated from a finite-element analysis solver, a deep convolutional neural network is trained in a supervised manner to learn a mapping for magnetic field distribution for topologies of different complexities of geometry, material, and excitation, including a simple coil, a transformer, and a permanent magnet motor. Preliminary experiments show DL model predictions in close agreement with the ground truth. A probabilistic model is introduced to improve the accuracy and to quantify the uncertainty in the prediction, based on Monte Carlo dropout. This paper establishes a basis for a fast and generalizable data-driven model used in the analysis, design, and optimization of EM devices. [ABSTRACT FROM AUTHOR]

Use of low static magnetic fields for nuclear magnetic resonance (NMR) signal detection remains a challenge due to low signal-to-noise ratio, low energy difference between energy levels, and less spin transitions due to limited availability of spins. Despite these challenges, different measurement techniques based on low static magnetic fields, stray magnetic fields, and non-uniform fields have been implemented. In this paper, an approach toward using low static fields generated by permanent magnets for portable magnetic resonance applications is described. Finite element simulation models of different magnet geometries are used to develop an estimate of the magnetic field distribution exterior to the magnet. A concentric ring magnet geometry is selected to obtain flexible control of localized regions of uniform magnetic field. An estimate of the NMR voltage for different magnet sizes and orientations is presented. It is expected that the findings of this paper would be valuable for design of future portable magnetic resonance systems. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of the direct- and quadrature-axis inductances for linear tubular actuators with permanent magnet arrays, highlighting and featuring how they are affected by the end effects. A semi-analytical and an experimental analysis are performed to prove the influence of end effects on self- and mutual inductances. The synchronous parameters, i.e., d - and q -axis inductances of the actuator, are determined using a semi-analytical method and an experimental method. Once the synchronous parameters are all identified, high performance control methods (such as direct force control and vector control) may be implemented. [ABSTRACT FROM AUTHOR]

This paper deals with equivalent 2-D finite-element (FE) models of permanent magnet lead screw (PMLS), to accurately predict the thrust force. Due to the helical-shape permanent magnets (PMs), the magnetic fields of PMLS are typically 3-D and non-symmetric. However, the PMLS is approximately symmetric in some cases and an equivalent 2-D axis-symmetric FE model is developed instead of 3-D models. The problem lies in that no evaluation about the accuracy and applicability of the 2-D axis-symmetric FE model was offered in previous literature. In this paper, the 2-D axis-symmetric FE model is derived based on the concept of equivalent current sheets of PMs. The limitations of the existing 2-D axis-symmetric FE model are clarified, and a novel equivalent 2-D torque FE model is then proposed to predict thrust force with the gear ratio when the 2-D axis-symmetric FE model is not appropriate. It is shown that the choice of equivalent 2-D FE model depends on the lead angle of PMLS, 2-D axis-symmetric FE model is applicable in the range of (0°, 15°), and 2-D torque FE model is preferred in the range of (65°, 90°). [ABSTRACT FROM AUTHOR]

This paper presents an engineering modeling methodology for magnetostrictive materials based on a simplified piezo-electric governing equation. For verifying the modeling performance, a proof-of-concept non-contact strain sensor utilizing a prototype magnetostrictive (Fe–Ga alloy, Galfenol) strip on a steel plate is used to evaluate sensor performance prediction. Typically, the performance of Galfenol is measured in a compressional load region because it has a higher response. However, in this paper, we are aiming to develop a sensor for tensile stress measurement. To achieve a compression effect from a tension load in the sensing element, a Galfenol strip is aligned perpendicular to a tension bar so that tension in the bar creates compression in the strip via the Poisson effect. The experimental setup in this paper consists of a polycrystalline Galfenol strip bonded in the horizontal direction of a steel dog-bone shaped tension specimen. Permanent magnets are attached at each end of the Galfenol strip to provide an even magnetic bias field through the strip. The magnetic flux through the Galfenol strip is measured with non-contact Hall sensors during the tensile load test. The simulation results agree well with the experiments for the value of $H$ studied. [ABSTRACT FROM AUTHOR]

This paper focuses on the design, performance modeling, and evaluation of probabilistic logic using superparamagnetic nanomagnets for which there exists a strong interplay between deterministic dynamics and intrinsic thermal noise. The switching element in the spin domain is chosen as the giant spin-Hall effect (GSHE) device that operates based on the dipolar coupling phenomenon in a two-magnet system to achieve low-energy ( $\approx ~1.3$ fJ/b) and low-power ( $\approx ~0.5~\mu $ W) switching characteristics. The use of spin currents on the order of a few tens of mA/ $\mu $ m2 in the subcritical regime to operate the GSHE device yields nondeterministic switching behavior with probability of correctness less than 100%. Therefore, the proposed technique allows us to trade off circuit accuracy for tremendous reduction in energy and power dissipation. In this paper, we identify the required dimensions and material parameters of the read–write units to ensure robust magnetic dipolar coupling for reliable operation of the GSHE switch. Then, through Monte Carlo simulations, we evaluate the probabilistic switching behavior of the GSHE switch as a function of the input spin current amplitude and pulsewidth for various orientations of the magnetization vectors. The delay of the GSHE switch is quantified using a probability distribution function owing to the randomness imparted to the dynamics by intrinsic thermal noise of the nanomagnets. The relationship between the probability of correctness and the energy dissipation of the GSHE switch is quantified. The results are extended to evaluate the performance and circuit error rate of complex logic gates, such as NAND and NOR, constructed using the GSHE switch. It is shown that unlike the probabilistic CMOS (PCMOS) logic, the circuit error rate in the GSHE logic becomes a function of the input vector combination and the prior state of the switch. These nuances are captured in the compact model of the circuit error rate of multiple-input GSHE logic developed in this paper. The performance of the probabilistic GSHE logic is compared with that of PCMOS logic at the 14 nm technology node. Since the noise generation process in PCMOS logic has a limited bandwidth of tens of megahertz and consumes tens of microwatt power, the peripheral circuitry becomes prohibitive. By utilizing the inherent thermal stochasticity, nanomagnets provide a clear advantage to implement probabilistic computing platform targeted toward error-tolerant applications such as those from the image processing and machine learning domains. [ABSTRACT FROM AUTHOR]

The current models of the resonant magnetoelectric (ME) effect are based on Newton’s equation of motion and some given conditions which are various in published papers. Even some results are in conflict with Gauss’s law in magnetics. This paper provides the energy method to model ME effects. The energy method is based on linear constitutive equations and the principle of minimum energy. By constructing and solving the constraint problem of the variational principle, more reasonable conditions are deduced for simplifying Newton’s motion equation. The induced additional fields of externally applied fields are considered during the process of deducing by Gauss’s law for electricity or magnetism. The coefficients of direct/converse ME effects are obtained and compared with the models in the previous papers. The proposed model avoids conflict with Gauss’s law and provides another insight into understanding the resonant and static ME effects. [ABSTRACT FROM PUBLISHER]

Typical vibrational harvesters using a high-permeability beam in a cantilever configuration exploit the field generated by a couple of counter-polarized permanent magnets facing the vibrating strip at the free end. Such a canonical position of the magnets does not permit one, however, to highlight the importance of the bias field pattern. A proof of concept archetype is realized in this paper, by which the influence of the magnetization profile along the length of the vibrating ferromagnetic beam is put in evidence. It demonstrates, in particular, that significant variations, even by a factor of three, of the output power can be obtained by a modification of the magnets arrangement. We discussed in this paper the behavior of a cantilever-based generator, where an Fe–Co high-permeability beam is made to vibrate inside an inhomogeneous magnetic field generated by permanent magnets, whose arrangement can modified in order to vary the magnetization profile along the vibrating laminae. The effects of such a profile are measured and analyzed by means of a simple 2-D numerical model, showing that the generated power can be enhanced by conveniently acting on the magnets configuration. The measurements show that, with a host acceleration of $5g$ rms ( g = 9.81$ m/ \text{s}^{2} ), a 6.72 mW time average output power is obtained for operating frequencies around 60 Hz. [ABSTRACT FROM AUTHOR]

Electromagnetic tracking systems are used extensively in biomedical devices, gaming consoles, and animation because they are inexpensive and do not require line of sight. However, the measurement range is limited by the amplitude of the induced voltage in the sensing coil. The induced voltage is a function of the transmitter parameters such as the coil dimensions, signal power, and frequency. The transmitted power is typically restricted by the physical constraints in the application. This paper develops an algorithm to optimize the dimensions of the transmitting coil for maximum induced voltage. The proposed method is suitable for a transmitter consisting of three concentric orthogonal transmitting coils of the type commonly used in six-degree-of-freedom localization. The simulation and experimental results are presented, which demonstrate the efficacy of the proposed method. [ABSTRACT FROM PUBLISHER]

Recently, dual-rotor motor (DRM) has emerged as an alternative for an induction motor (IM) or a permanent-magnet (PM) motor for electric vehicle application, due to its better drive performance and better torque density. This paper presents an analytical model for the hybrid IM-PM configuration of DRM. The analytical model can be used to predict induced bar currents, electromagnetic torque generated, and magnetic fields in various regions of the motor. The mentioned calculations are performed under steady-state conditions. The analytical method is developed using the subdomain model approach in 2-D polar coordinates. Appropriate governing equations along with boundary conditions across all the sub-domain regions of the DRM are employed to calculate the magnetic vector potential in all the regions. The developed analytical model has been validated with finite-element analysis for various operating conditions, and high accuracy has been achieved for all the results. [ABSTRACT FROM AUTHOR]

This paper introduces an analytical approach for an effective evaluation of the variation of the magnetic field generated by complex coils due to deformations with respect to the nominal configuration. The coils are described with a set of synthetic design parameters, and the deformations can be described as variations of such parameters. This paper proposes a method to evaluate the derivatives of the magnetic field with respect to the design parameters by splitting them into a magnetic factor and a geometrical factor. A comparison with the classical finite-differences approach is carried out. This paper focuses on the context of sensitivity analysis, but the methodology is quite general and can easily be extended in other fields. [ABSTRACT FROM AUTHOR]

This paper presents an analytical model of magnetic field of a permanent magnet synchronous motor (PMSM) with a trapezoidal Halbach permanent magnet array (THPMA). Compared with conventional Halbach array, the shape of each magnet in THPMA is transformed from rectangle to trapezium in polar coordinates. The THPMA is delaminated indefinitely radially and each layer is approximately considered to be a conventional Halbach array. The air-gap magnetic field of each layer is analyzed with the scalar magnetic potential. Then, the air-gap magnetic field of the THPMA is obtained by superposing magnetic fields of all layers. The validity of the analytical model is verified by a finite-element model (FEM). The air-gap flux density is optimized by adjusting the center angle coefficients of the THPMA, and a no-load phase back electromotive force (EMF) with the harmonic distortion rate (THD) of 0.75% is obtained by FEM. The back EMF is basically consistent with the measured result of a prototype motor. [ABSTRACT FROM AUTHOR]

The utilization of a bismuth-substituted iron garnet as a magnetooptic Faraday rotator (MOFR) has been reported for all-optical networking purposes as well as for other applications. Our measurements and observations demonstrate that the MOFR saturates once a significantly large magnetic field (>225 G) is applied. After the applied magnetic field enters the saturation region, the material’s magnetic domains can become pinned at intermediate levels of magnetization. Pinning in this form has not been reported nor well studied for this application. In this paper, a method to detect and describe anomalous pinning in terms of Faraday rotation is presented. Measurements on the changes in the state of polarization that a pinned material produces are examined. This paper will also present practical methods for unpinning the MOFR material, which are traditionally considered to be challenging. [ABSTRACT FROM AUTHOR]

In this paper, we propose a loss calculation method considering minor hysteresis loops for permanent magnet (PM) motors driven by pulsewidth modulated (PWM) inverters. In the governing equation of the proposed method, both the effects of the major and minor hysteresis phenomena are expressed by a reaction magnetic field. This field is determined by iterative calculations of finite-element analysis (FEA) with a simple hysteresis modeling that considers the minor loops. The proposed method is applied to a PM motor, and the experimental verification is carried out. It is clarified that the minor hysteresis loops affect not only the hysteresis loss but also the eddy current loss because the skin depth varies with the differential permeability of the minor loops. [ABSTRACT FROM AUTHOR]

In this paper, two novel double-sided hybrid-excitation flux-reversal linear motors (DSHEFRLM) with the surface (S-) and interior (I-) permanent-magnet(PM) arrangements are proposed and comparatively investigated. The proposed motors feature an asymmetrical double-sided primary configuration which enables the armature and field excitations to be placed separately. Through 2-D finite-element method (FEM), two motor structures with different slot/pole combinations are optimized, and then, the magnetic fields and electromagnetic performances are calculated, including inductances, no-load flux linkage, thrust characteristics, and PM demagnetization capability. By comparison, it is found that S-DSHEFRLMs show larger thrust density while I-DSHEFRLMs exhibit superior flux-adjusting capability. Finally, these predicted results are validated by 3-D FEM. [ABSTRACT FROM AUTHOR]

This paper presents an identification algorithm of the scalar Preisach model by using a set of symmetric minor hysteresis loops and suggests an improved vector Preisach model to describe the vector and anisotropic hysteresis behavior of a non-oriented (NO) electrical steel sheet (ESS) under rotating magnetic fields. Symmetric minor hysteresis loop is quite easy measured, so an identification algorithm based on symmetric minor hysteresis loop instead of first-order reverse curve is presented in this paper. The vector Preisach model employs a nonlinear coefficient, which is a function of magnitude and a direction of magnetic flux density, to describe the anisotropic property of the NO ESS and increases the numerical accuracy. The validity of the suggested vector Preisach model is investigated through comparisons with the experimental results under various magnetic field conditions. [ABSTRACT FROM AUTHOR]

This paper presents a method for the treatment of multiply connected regions within the semi-explicit time-domain discontinuous Galerkin (DG) eddy current solver based on the ${H}$ – $\Phi $ field formulation. The suggested method utilizes a multivalued magnetic scalar potential over a cutting surface that divides a multiply connected domain into two simply connected regions. The multivalued magnetic scalar potential in the nonconductive domain ($\Phi $ -domain) is regularly updated after a sequence of time steps of the explicit vector DG-finite element method solver in the electrically conductive domain (${H}$ -domain) yielding an accurate time-domain solution of the magnetic field in the multiply connected space surrounding the eddy current region. The efficiency and accuracy of the method are demonstrated by a 3-D example and the obtained results are verified by comparison against the corresponding frequency-domain solution. [ABSTRACT FROM AUTHOR]

This paper introduces a localization protocol that fills a gap among already existing methods, such as ground penetrating radar or methods based on inductive prospecting. The principle is to attach a radio frequency identification (RFID) tag to a non-metallic object of interest buried in a non-magnetic soil and deduce its depth from the magnetic induction in the near field regime between the buried tag and an RFID antenna. Electromagnetic propagation in soils has been extensively studied in geophysics. The higher the frequency, the lower the penetration depth. The standard frequency range in geophysics is lower than 100 kHz to reach penetration depth as high as several tens of meters and the soil conductance is the main influencing factor. When working with passive RFID tags, their received power and, consequently, the detection range in air grows with the frequency. A frequency tradeoff for the detection in media lies in the range of 10–50 MHz, where the authorized RFID frequency is 13.56 MHZ. In this range, the wavenumber in weakly saline soils depends essentially on the medium dielectric permittivity (see). In this paper, we calculate the precision of the estimation of the burying depth of the tag in terms of the standard deviation and the corresponding bias up to two uncertain parameters—the penetration depth and the activation field. The laboratory experiments provide results supporting the chosen model. [ABSTRACT FROM AUTHOR]

This paper presents a magnetic safety evaluation of the static magnetic field produced by magnetic floors with permanent magnet properties utilized in the construction industry. The magnetic floors analyzed in this paper are composed by a concentration of 85% of isotropic strontium (Sr) ferrite powder mixed with chlorinated polyethylene. The magnetic floors are magnetized and tested in the laboratory to measure the magnetic field levels in different regions of the magnetic floors and magnetic subfloors. Finite-element (FE) simulations are carried out to compute the magnetic field produced by magnetic floors. The numerical results and laboratory tests are compared and analyzed. Values of the magnetic field between 2 and 50 mT are computed and measured in different regions of magnetic floors. Finally, the static magnetic field levels obtained in the magnetic floors are compared with the permitted magnetic field values for different electronic devices, pacemakers, and other common objects utilized by persons in buildings. The results obtained in this paper show that magnetic floors are safe, and they can be employed in buildings without putting in risk electronic devices or persons with pacemakers. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the effect of temperature variations on the off-diagonal giant magneto-impedance (GMI) response. This paper is based on a theoretical model describing the GMI-based sensor response. The modeling has been extended to include the resistivity dependence versus the temperature. It allows to calculate both temperature sensitivity and intrinsic magnetic field sensitivity, whose ratio leads to the determination of the magnetic field offset drift versus the temperature. Thanks to an original conditioning circuitry based on a double ac current excitation instead of the classical one, we achieved an improvement of the long-term stability and minimized the sensor temperature dependence. Experimentally obtained results have been compared with the expected offset drift for the classical GMI, and with the expected fluctuation reduction while adopting this technique, showing a relatively good agreement with the proposed modeling. [ABSTRACT FROM AUTHOR]

For testing a conductive pipeline, remote field eddy current testing (RFECT) is used, which is composed of solenoidal exciter coil and receiving sensor coils. In RFECT, there is remote field zone where the eddy current distributions are concentrated on the external surface of the pipe wall. Therefore, it is possible to detect a defect that occurs on the external surface of the pipe wall even if the receiving coils are located inside the pipe. From the measured coil signals, it is necessary to decompose background offset and predict the pattern of defect signal in order to estimate the defect size for the maintenance of underground pipelines eventually. In the process, the amplitude variations of the induced magnetic field at sensor coils are closely related to defect depth. Therefore, it is important to analyze and eliminate distortions of measured RFECT signals. This paper analyzes the effects of the induced magnetic field on the sensing signals with respect to different depth sizes in the RFECT system. The amplitude and the distribution pattern of defect signals are computed by a 3-D finite-element method and the method to eliminate the signal distortions caused by induced magnetic fields are presented. Simulated results in this paper agreed well with measuring ones. [ABSTRACT FROM AUTHOR]

Current density distribution in electric arcs inside low-voltage circuit breakers (LVCBs) is a crucial parameter for us to understand the complex physical behavior during the arcing process. In this paper, we investigate the inverse problem of reconstructing the current density distribution in arcs by inverting the magnetic field. This paper is focused on the modeling and computational phase for the magnetic inverse problem when linear ferromagnetic regions are considered in the model. To address the ill-posedness of the inverse problem, the standard method of least-squares approximation by Tikhonov regularization is studied, complemented with the generalized cross-validation criterion for regularization parameter selection. Considering the inclusion of a ferromagnetic region, two regularization approaches have been analyzed for the formulation of the currents in splitters and their corresponding magnetic field contribution. Effects of several features on the performance of the regularized solution have been investigated, including the signal-to-noise ratio, the value of permeability of the splitters, and the measurement distance. The numerical tests show the direct accessibility for the 3-D current density distribution with the proposed scheme, providing the accuracy and robustness for the applicability to study the arc behavior in LVCBs. [ABSTRACT FROM AUTHOR]

Skin depth is an important parameter that quantifies depth of inspection of eddy current (EC) nondestructive testing. The formula which states that the skin depth is inversely proportional to the square root of the product of frequency, permeability, and conductivity has been widely used for calculating skin depth for many decades. It has been noticed that the true skin depth is less than that obtained by the formula when the EC is excited by the ac current in a pancake coil. In-depth and convincible explanation of this discrepancy has not been published. This paper studies this problem by finite-element analysis and concludes that the difference is due to two reasons. One is that the EC associated with pancake coil diffuses with increasing depth, whereas there is no diffusion effect of EC associated with uniform plane field which is the assumption of the conventional formula. The other reason is that the ECs induced by wire segments symmetric about the coil axis cancel each other and the cancellation becomes more severe with increasing depth due to the diffusion of EC. This paper also investigates the influence of each of coil parameters on skin depth. Then, a new formula for estimating skin depth is proposed. [ABSTRACT FROM AUTHOR]

Magnetic nanostructures have potential applications in ultrahigh-density magnetic storage. In this paper, the dynamics of the dual magnetic vortices in elliptical Permalloy nanodisk are investigated using micromagnetic modeling. Under the stimulation of the short-axis ( $y$ -axis) Gaussian field pulse and long-axis ( $x$ -axis) constant field, the equilibrium positions of dual-vortex cores can be driven away from the initial positions. The displacement in the $y$ -direction is proportional to the magnitude of the $x$ -axis constant field. The displacement in the $x$ -direction exhibit periodic reliance on the pulsewidth of the $y$ -axis Gaussian field pulse. The threshold value of pulse strength for dual-vortex motion increases with the magnitude of the $x$ -axis constant field. The mechanism of polarity and chirality switching in dual-vortex cores are studied through analyzing the trajectories of vortex cores in the annihilation and nucleation processes. The switching of polarity exhibits an oscillatory dependence on the pulsewidth and strength. The minimum pulse strength required for chirality switching is 120 mT, while the corresponding pulsewidth is influenced by the $x$ -axis constant field. This paper provides insights on the magnetization dynamics of nanostructures containing dual vortices subject to external excitations. [ABSTRACT FROM AUTHOR]

Arrays of nanosized hollow spheres of Ni were studied using micromagnetic simulation by the Object Oriented Micromagnetic Framework. Before all the results, we will present an analysis of the properties for an individual hollow sphere in order to separate the real effects due to the array. The results in this paper are divided into three parts in order to analyze the magnetic behaviors in the static and dynamic regimes. The first part presents calculations for the magnetic field applied parallel to the plane of the array; specifically, we present the magnetization for equilibrium configurations. The obtained magnetization curves show that decreasing the thickness of the shell decreases the coercive field and it is difficult to obtain magnetic saturation. The values of the coercive field obtained in our work are of the same order as reported in experimental studies in the literature. The magnetic response in our study is dominated by the shape effects and we obtained high values for the reduced remanence, Mr/MS = 0.8 . In the second part of this paper, we have changed the orientation of the magnetic field and calculated hysteresis curves to study the angular dependence of the coercive field and remanence. In thin shells, we have observed how the moments are oriented tangentially to the spherical surface. For the inversion of the magnetic moments we have observed the formation of vortex and onion modes. In the third part of this paper, we present an analysis for the process of magnetization reversal in the dynamic regime. The analysis showed that inversion occurs in the nonhomogeneous configuration. We could see that self-demagnetizing effects are predominant in the magnetic properties of the array. We could also observe that there are two contributions: one due to the shell as an independent object and the other due to the effects of the array. [ABSTRACT FROM PUBLISHER]

This paper describes the numerical and experimental validation of a novel non-contact dc electromagnetic propulsion concept. In the proposed approach, a propulsion coil carrying a dc current is surrounded by a dc transversal multipole field created inside of a launch tube. The interaction between the transversal dc magnetic field and a dc propulsion coil results in the generation of axial (thrust) force with no need of sliding contacts. This paper describes a numerical assessment of the field-current-force interactions based on both analytical calculations and finite elements, and the corresponding validation experiments. The experiments demonstrate the generation of contactless axial (thrust) force in a dc launch coil using a dc transversal multipole field, and provide a benchmark for the model-based prediction of the field-current-force interactions. Partial magnetic shielding of the propulsion coil is used to selectively attenuate the magnetic field experienced by the thrust coil in a way that a net thrust force is achieved. Experimental measurements confirmed that it is indeed possible to generate contact-free thrust force on a dc propulsion coil using a dc multipole magnetic field, and the measured values of thrust force are in good agreement with the corresponding predictions. [ABSTRACT FROM PUBLISHER]

Computer simulations of the magnetizing process have been carried out by applying a numerical model to the theory of magnetization and demagnetization for magnetic materials. The numerical model (written using the Python programming language) is able to calculate the magnetization/demagnetization of the permanent magnet material according to its $B$ – H$ curves. This numerical model is combined with an existing finite-element method (FEM) model in which the result of computations is the approximated potential value in the FEM mesh. The aim of this paper was to develop a tool able to simulate the behavior of an anisotropic sintered permanent magnet during the demagnetization process. The permanent magnet material that has been studied in this paper is sintered Nd–Fe–B and it was modeled taking into account an average misalignment angle related to the magnet easy axis. This model also takes into account different demagnetizing field directions, such as a demagnetizing field perpendicular to the orientation direction, which is often ignored. It is shown that even a demagnetizing field perpendicular to the magnetization direction can produce visible demagnetization effects. A Gaussian distribution of the average misalignment angle in the permanent magnet material is also taken into account as well as its variation. Demag curves have been calculated varying the misalignment angle and the intensity and direction of the external magnetic field. The simulation results are in perfect agreement with the {1}/{\cos \theta} law. The model can be applied in many magnetization and magnetic tuning applications. [ABSTRACT FROM PUBLISHER]

In recent studies, we introduced the concept of functionalized magnetic force as a method to prevent nanoparticles from sticking to vessel walls caused by extensive simulation and in vitro experiments involving a Y-shaped channel. In this paper, we further investigated the effectiveness of the functionalized magnetic force with a realistic 3-D vessel through simulations. For the simulations, we considered a more realistic continuous injection of particles with different magnetic forces and frequencies. Based on the results from our simulation studies, we performed in vivo mice experiments to evaluate the effectiveness of using a functionalized magnetic force to aid magnetic nanoparticles (MNPs) in crossing the blood–brain barrier (BBB). To implement the functionalized magnetic force, we developed an electromagnetic actuator regulated by a programmable direct current power supply. Our results indicate that a functionalized magnetic field (FMF) can effectively prevent MNPs from sticking, and also guide them across the BBB. We used 770 nm fluorescent carboxyl MNPs in this paper. Following intravenous administration of MNPs into mice, we applied an external magnetic field to mediate transport of the MNPs across the BBB and into the brain. Furthermore, we evaluated the differential effects of FMFs (0.25, 0.5, and 1 Hz) and constant magnetic fields (CMFs) on the transport of MNPs across the BBB. Our results showed that an FMF is more effective than a CMF in the transport and uptake of MNPs across the BBB in mice. In particular, applying an FMF with a 3 A current and 0.5 Hz frequency mediated the greatest transport and uptake of MNPs across the BBB in mice. [ABSTRACT FROM PUBLISHER]

In previous studies on precise computation methods of iron loss, it has been shown that the 1-D dynamic magnetic field analysis with hysteresis in post-processing is effective. However, there is a problem in that the hysteresis makes the convergence of nonlinear iterations unstable. This paper proposes a stabilization method for the 1-D dynamic magnetic field analysis with hysteresis. The proposed method is characterized as an approach for improving the initial value and the step size in the Newton–Raphson method. The results of this paper showed that the convergence characteristic of the nonlinear 1-D magnetic field analysis for variety flux density waveforms of each part in an electric motor is improved using the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents an analytical calculation method for the computation of the magnetic vector potential of an axisymmetric solenoid in the presence of an iron shield and a ferromagnetic core. The proposed method can be used as a fast analytical computation technique for accelerating the design optimization process of the solenoid systems. In this paper, the analysis of the current carrying coil in the presence of the ferromagnetic materials is treated as a boundary value problem. The solution approach is based on partitioning the solution domain into distinct regions. The general form of the solution to Maxwell’s equation in each region along with the corresponding boundary conditions is obtained using the Fourier analysis and the separation of variables. The final solution to the boundary value problem is constituted by considering the continuity of the magnetic vector potential, as well as the magnetic field, on the interfaces between the regions. Finally, the proposed analytical computation method is applied on an electromagnetic actuator. The magnetic vector potential is computed over the entire solution domain, and the result is compared with that of the finite-element method. [ABSTRACT FROM AUTHOR]

In this paper, a 3-D multiphysics finite-element study of microelectromechanical systems (MEMS) reed magnetic sensors is presented. This paper employs several governing equations to simulate the MEMS reed sensors, calculate their magnetostatic body force, and track the resultant mechanical displacements. The MEMS beams used are trilayer gold/Ni/gold, and the sensing ranges of the sensors are in milli-Tesla. The results in this paper point to an optimal sensor design, which is then fabricated and verified by the experimental tests. This paper presents a general performance map of the MEMS reed sensors, illustrating their performance under various field conditions. Several sensor devices are fabricated and tested, with the measured data showing good agreement with the simulation results. [ABSTRACT FROM AUTHOR]

Gyrotrons are high-frequency, high-power microwave sources with potential applications in plasma generation, energy generation, spectroscopy, and security. The Department of Science and Technology initiated the development of a 42 GHz, 200 kW, continuous wave (CW) gyrotron for the Indian Tokamak system through a multi-institutional project. The activity is targeted toward indigenous development of India’s first high-power gyrotron. In gyro-devices, frequency of operation is determined by the cyclotron frequency, and thereby the magnetic field. The development of a high-field intensity normal conducting cavity magnet was an imperative step during the testing and integration of the gyrotron tube assembly to achieve the desired beam transmission with a moderate operating cost. A high and spatially homogeneous magnetic field (1.61 T) is required to be established in the beam–wave interaction region by the cavity magnet. The desired magnetic field, as a function of axial distance from the gun to the collector, is governed by the requirements of gun optics, focusing field in the interaction region, and the adiabatic expansion of the beam into the collector. A water cooled electromagnet has been designed to produce the requisite magnetic field in the cavity region over an axial length of 40 mm with field homogeneity better than ±0.35%. Magnet design was optimized to meet the field requirements in the cavity and cathode gun. Magnetic field simulations were carried out in conjunction with the electrostatic field and space charge analysis. This paper presents finite element computations, design optimization, development and testing of a continuous duty iron core electromagnet for a first harmonic interaction mode (TE03) gyrotron cavity. Magnetic, electrical, thermal, and hydraulic design of the electromagnet is discussed in this paper. [ABSTRACT FROM AUTHOR]

Recently, the demagnetization has been actively researched to reduce the magnetic field of a warship according to the development of the magnetic detection technology of the magnetic mines. In these studies, it was assumed that the warship was composed of one magnetic material in order to establish an effective deperming protocol. However, since the actual warship was composed of various materials, the magnetic interaction between the materials inevitably occurs during the demagnetization process. Due to the interaction, demagnetization may not be performed well. Therefore, in this paper, the effects of interactions in demagnetization of multiple materials were studied by using the Preisach model, and the optimal protocol was proposed. [ABSTRACT FROM AUTHOR]

This paper presents the magnetic field analysis for the double layer Halbach array voice coil actuator (VCA). This VCA is composed of a stator and a mover supported by the flexure-based bearings. The mover gets three coils winded on the skeleton. The stator comprises the closed yoke and the double layer Halbach array permanent magnets (PMs). The boundary condition of the quadrangularly surrounded yoke and the aperiodic distribution of the Halbach array PMs complicate the magnetic analysis process. An equivalent VCA structure that has almost identical air-gap flux distribution to the original one is, therefore, proposed. For the equivalent structure, the boundary condition is simple and the Halbach array PMs is periodically distributed, thus the analysis process of air-gap flux density distribution via Fourier analysis is simplified. The equivalence between these two structures is validated by finite-element analysis (FEA). The analytical model is built by adopting Fourier analysis. The results of the FEA and experiments confirm the correctness of the developed model and prove the feasibility of the analytic method with the equivalent structure. [ABSTRACT FROM AUTHOR]

In this paper, the magnetorheological (MR) absorber with multi-stage parallel coil structure is designed, which can realize various magnetic field variations through the working coil combination to meet different impact applications. To analyze the influence of different magnetic field distributions on the mechanical characteristics of the MR absorber and provide a theoretical basis for the subsequent open-loop control strategy, the coupling simulation analysis and impact test are carried out in this paper. Based on the COMSOL Multiphysics software, the conjugate heat transfer model and magneto-flow coupling simulation model are established. Considering the shear thinning effect of the MR fluid in the impact process, the modified Herschel–Bulkley constitutive model of MR fluid is embedded into the coupling model. The influence of four parameters on the mechanical performance of the MR absorber is considered, which includes the piston movement speed, the current amplitude, the number of working coils, and the distribution state of the magnetic field. In addition, the orthogonal evaluation method is used to quantitatively investigate the influence degree of these factors. Finally, the impact tests are conducted and verified the simulation results, that is, the magnetic field distribution near the fluid channel inlet has a more pronounced throttling effect and can get a greater output force under the symmetrical distribution of magnetic field. [ABSTRACT FROM AUTHOR]

Among various types of motors, permanent magnet (PM) motors, due to their high energy density, are mainly used for electric-based propulsion systems. In this paper, an improved analytical model for PM motor has been presented. The model considers important factors, such as armature reaction, slotting effect, and influence of non-linear material property on motor’s behavior. Moreover, the main contributions of this paper are the representation of stator windings with exact winding width using Fourier series and the consideration of effects of non-linear ferromagnetic material property. Using this model, it is possible to determine air-gap magnetic field, flux linkage, back electromotive force, cogging torque, and electromagnetic torque with high accuracy. Results from the proposed model are compared with other analytical model and also with those from a finite-element analysis (FEA). The results obtained from the proposed method match closely with the FEA. [ABSTRACT FROM PUBLISHER]

Advanced sensing techniques are key technologies required for the smart grid. Magnetic tunnel junction (MTJ) sensors hold great promises in the distributed linear current sensing, with small size, low price, and excellent performances. In this paper, MTJ Wheatstone bridge sensors were fabricated, attaining a typical sensitivity of 4.94 mV/V/Oe with an offset of −2.84 mV/V. A contactless current sensor based on the MTJ sensor was designed and realized, achieving a sensitivity of 7.75 mV/A and an offset of −8.68 mV. We can adjust the sensitivity and the linear range of the sensor by changing the gap of the magnetic core, and make the sensor much less susceptible to electrical wire’s location and orientation. This paper provides a practical current sensing technique for smart grid applications. [ABSTRACT FROM AUTHOR]

In this paper, the design and development of a double-sided air-cored tubular generator (DSTG) is presented. The characteristics of air-cored slot-less structures are investigated in terms of power density and efficiency. This is highly desirable for small- and medium-sized renewable energy conversion systems. In this paper, an analytical tool based on the magnetic vector potential method is built in order to achieve a fast but accurate method by which the machine is analyzed. The analytical model is validated by finite-element (FE) analysis. Further design improvements based on the analytical and FE models are then suggested in order to enhance the performance of the DSTG. The final design of the DSTG is validated by the test results from a developed prototype of the DSTG. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach for incorporating noncuboidal and rotated cuboidal sources of magnetic field in 3-D Fourier modeling. Based on the periodicity present in the geometry, a Fourier integral is applied in two directions. By changing the integration boundaries in the $y$ -direction to a linear function of the $x$ -direction, nonideally shaped magnetic field sources (i.e., coils and permanent magnets) are incorporated. From the electromagnetic example geometries analyzed in this paper, the magnetic field as derived with 3-D Fourier is over 99% accurate compared to 3-D finite-element models. [ABSTRACT FROM AUTHOR]

In the fabrication of linear magnetic tunnel junction (MTJ) sensors, the utilization of magnetic bias field along the easy-axis direction makes the response of MTJ nonlinear, and the Néel and magnetostatic coupling usually induces a strong interlayer coupling field along the hard-axis direction. In this paper, we investigated the influence of hard-axis and easy-axis bias fields on the linearity of MTJ magnetic sensor. The prediction and optimization of linearity were done by applying an appropriate hard-axis bias field in the specific easy-axis bias field and the practical tunnel magneto-resistance (TMR) ratio, and the model was verified by experiments. This paper can give guidance to improve the linearity and to maximize the practical TMR ratio of the MTJ sensors under a given linearity requirement. [ABSTRACT FROM AUTHOR]

This paper presents a method that has been developed to determine the quantity of accumulated magnetic particles in mice tissues using magnetization measurements. Dispersions of platelet Fe3O4 particles with the size of 30–50 nm and a saturation magnetization of $\sim 80$ Am2/kg were intravenously administered to mice. Primary tissues were dried to measure the magnetization. The amounts of Fe3O4 particles accumulated in the tissues were obtained by dividing the magnetization of tissues by the magnetization of Fe3O4 particles under a magnetic field of 39.8 kA/m. A remarkable accumulation of particles was observed in the liver and the spleen, being supported by the observation of tissues using Prussian blue staining. Total Fe3O4 particles accumulated in primary tissues were $\sim 38$ –40 and 40–44 wt% against the particles in administered dispersions with 3 and 0.4 wt% contents, respectively. The method developed in this paper is considered to be effective for verifying magnetic hyperthermia and thermoablation therapies, in which the quantity of accumulated particles directly reflects the heating power required for those therapies. [ABSTRACT FROM AUTHOR]

This paper deals with the optimal design of a new synchronous motor particularly suitable for electric vehicles. The unique advantage of this motor is its possibility to realize field weakening at high speeds, which is the most important demand for such drives. The main design goal is to identify the dimensions of certain crucial regions of the machine in order to avoid saturation of the iron and to minimize the mass to volume ratio, while simultaneously maximizing the torque. The originality of the contribution is manifold: formulating the design problem in multiobjective terms, solving it by means of evolutionary computing, solving the associated direct problem based on a three-dimensional finite element analysis (3-D-FEA) field model, considering a reduced set of design variables by means of response surface method, referring to a real-life problem. [ABSTRACT FROM AUTHOR]

We have previously been proposed a novel adaptive finite-element method (FEM) based on a magnetic field conservation indicator and a non-conforming mesh-refinement technique. However, we have applied to a very simple model consisting of a single permanent magnet for basic verification of the proposed method. In this paper, we have improved an error indicator, and tried to apply a newly proposed adaptive FEM to more complicated models, where ferromagnetic material is included. The newly proposed method is superior in torque error estimation to the Zienkiewicz-Zhu error estimation method in a 3-D permanent magnet motor model. [ABSTRACT FROM AUTHOR]

We propose a new method of estimating magnetocardiography (MCG) current sources using reconstructed magnetic field data. Because, our MCG sensors were arranged in a 2-D plane, they could only detect the magnetic field data generated in front of the torso, which leads to estimation of blurred source imaging from deep sources. In this paper, we reconstructed the magnetic field data that cannot be detected by the MCG sensors. The locations of the reconstructed magnetic field data were also in a 2-D plane and parallel to the sensor array. The proposed method shows that it reduced the current-source extension and enhanced the spatial resolution for deep sources. We evaluated the current-source extension and spatial resolution at R peak. The active regions of the ventricular depolarization and repolarization were obtained using time integration with the current sources estimated at QRS complex and T wave, respectively. The proposed method can estimate high spatial resolution source imaging, especially for current sources that are far from the MCG sensors. [ABSTRACT FROM AUTHOR]

In this paper, an analysis method and a measurement method for anisotropic magnetic shielding effectiveness (MSE) are discussed. Some magnetic sensors and memories require small magnetic shielded packages to decrease the influence of external magnetic noise. Whereas, the packages are applied for the external noise from various directions, sensitivity of the magnetic device in the package is affected by the direction and intensity of applied field noise. Influenced by the directions of external and internal magnetic fields, MSE of the shielded package varies several dozen decibels. Therefore, understanding the anisotropic MSE of the shielded package is indispensable for designing a shielded package that prevents malfunctions attributable to external magnetic noise. The $3 \times 3$ MSE matrix and the directivity of MSE are introduced as evaluation indicators of the anisotropic MSE. The MSE matrix and the directivity of MSE revealed that the MSE of the fabricated package varied significantly, from 24 dB to more than 60 dB, according to the direction of external field and internal field. [ABSTRACT FROM AUTHOR]

This paper introduces a comparative study of two different hysteresis models, limiting loop model and elemental operator model. The former is regarded as a mathematical approach based on the traditional Preisach model. To circumvent the difficulty of determining the distribution function in the Preisach model, the data of the limiting hysteresis loop and a function transform on the Preisach diagram are employed. The latter is a physical method which adopts a vectorial elemental operator with biaxial anisotropy based on the magnetization mechanisms of the ferromagnetic material. These two models are analyzed and compared in terms of the underlying principle, numerical implementation, and calculation accuracy in this paper. To verify the introduced models, the magnetic properties of non-oriented silicon steel Lycore-140 and soft magnetic composite material Somaloy 500 under alternating excitations are measured and compared with simulated results, which show the validity and practicability of the models but with different calculation accuracy and speed. [ABSTRACT FROM AUTHOR]

Applications of magnetic memory devices greatly benefit from ultra-fast, low-power switching. In this paper, we propose a method for how this can be achieved efficiently in a nano-sized synthetic antiferromagnet by using perpendicular-to-the-plane picosecond-range magnetic-field pulses. Our detailed micromagnetic simulations, supported by analytical results, yield the parameter space where inertial switching and relaxation-free switching can be achieved in the system. We furthermore discuss the advantages of dynamic switching in synthetic antiferromagnets and, specifically, their relatively low-power switching as compared with that in single ferromagnetic particles. Finally, we show how the excitation of spin waves in the system can be used to significantly reduce the post-switching spin oscillations for practical device geometries. [ABSTRACT FROM AUTHOR]