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In this paper, an 18-slot/26-pole vernier permanent magnet synchronous machine (VPMSM) with coil pitch of two slot pitches is proposed based on a nine-slot/18-flux-modulation-pole/26-pole VPMSM with concentrated tooth-coil windings. Compared with the original VPMSM, the number of slots is doubled and the phase winding connection is adjusted to reduce the space harmonic content, the phase inductance, and hence, improve the power factor. This paper shows that the proposed VPMSM increases power factor from 0.73 to 0.95 with better torque and flux-weakening capability. Moreover, a series of VPMSMs with high-power factor is proposed from the same design principle and given design guidelines. [ABSTRACT FROM AUTHOR]

Nd–Fe–B magnets for electric vehicles are required to have high coercivity, and heavy rare earth elements are added. However, it is necessary to reduce the heavy rare earth element that is a scarce resource. Decreasing the grain size is an effective method of increasing $H_{\mathrm {cj}}$ , and hot-deformed magnets which are consisted of rapidly quenched powders are known to have fine grains. This paper focused on coarse grains observed in the microstructure of hot-deformed magnets. Measuring the local magnetic properties by XMCD, it was shown that the coarse grain areas had lower magnetic properties than those of the fine grain areas. The coarsening was located at the powder interface. Therefore, the crystal growth behavior in the powder was investigated in detail. Due to the Fe concentrated in the powder along the wheel side of the melt-spun, Nd2O3 and $\alpha $ -Fe were grown as the primary crystals. It is considered that the coarsening of hot-deformed magnets originates in those heterogeneous crystallizations. In order to prevent the coarsening, this paper focused on the heating rate of heat treatment of powders. The coarsening was prevented under the conditions, over 400 °C/min of heating rate and over 600 °C of heating temperature. The rapid heating of powders using the free-fall-type furnace prevented the coarsening in hot-deformed magnets. As a result of decreasing the coarse grains, $H_{\mathrm {cj}}$ was increased from 1584 to 1614 kA/m and $M_{r}$ was increased from 1.33 to 1.40 T. [ABSTRACT FROM AUTHOR]

The development of a thin and broadband microwave absorber using the microwave absorbing material (MAM) alone is a very challenging task for the researchers and industries. Therefore, a technique for developing a novel hybrid microwave absorbing coating (MAC) using particle-size-controlled hard–soft ferrites with optimized compositions is described and experimentally validated. The novelty of this paper is the possibility of enhancing and tuning the reflection loss (RL) properties of traditional MAMs by simply adjusting their particle size. The main target of this paper is to obtain wideband absorption corresponding to RL ≤ −10 dB and a lower coating thickness (≤ 2 mm). First, ferrite nanoparticles are synthesized and subsequently grown into distinct shapes and sizes by giving judicious heat treatment using a “bottom up” nanofabrication approach. Furthermore, these distinctly shaped and sized particles, i.e., spherical and flaky (20–30 nm), hexagonal (80–100 nm), and pyramidal (200–250 nm), are blended with one another in different proportions (1:1:1, 2:1:1, 1:2:1, and 1:1:2). An extensive morphological and electromagnetic (EM) characterization is carried out. An efficient theoretical and empirical model is used to investigate the EM properties of the heterogeneous MAC with respect to frequency and particle size. A fabricated MAC possesses an RL of −33.5 dB at 10.8 GHz with −10 dB absorption bandwidth of 4.2 GHz (covering the entire X-band region). Moreover, the ferrite layer coating thickness is only 2 mm. A good correlation between theoretical and measured results demonstrates the potential of the adopted approach for various practical EM applications. [ABSTRACT FROM AUTHOR]

Leakage inductance and frequency-dependent resistance of windings are the key parameters for the design of magnetic devices. This paper focuses on analytical or semi-analytical calculation techniques to be integrated into a medium frequency transformer optimization process. To this extend, a review of the currently most used method to calculate the inductance and resistance of windings transformer is established. Based on this review, new calculation methods are developed. Magnetic field cartography is evaluated on the basis of 2-D structures thanks to a combination of Ampère’s law and the image method. From this magnetic field map, leakage inductance can be calculated. The obtained accuracy with this method is equivalent to 3-D finite-element modeling (FEM). For frequency-dependent resistance evaluation, new methods based on 2-D or 1-D approach are compared to FEM and reviewed models. An analysis of the behavior of each model is done, showing that newly developed models are more suitable in the case of a medium frequency transformer design in terms of accuracy, robustness, and calculation time. This paper could be useful to the designers of magnetic devices because newly developed models could easily be adapted to various geometries, such as toroidal structures or even inductors. [ABSTRACT FROM AUTHOR]

Magnetic flux leakage (MFL) response predicting is important for defect estimation. This paper first proposes a concept of basic signal by discovering the combination property of the MFL response. The basic signal can be used to predict the MFL response conveniently by a basic signal combination method (BSCM), which is also innovatively put forward in this paper. In this method, the basic signal is calculated in advance, and the MFL response can be calculated by several transformation and combination operations. Both the simulation and experimental results demonstrate the feasibility of BSCM. Compared with other traditional methods (magnetic dipole method and finite-element method), BSCM shows a good performance on both the computational speed and accuracy. [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]

The non-destructive testing technique known as magnetic flux leakage (MFL) is used for the inspection of storage tank floors (mild steel plate). This paper focuses on the finite-element analysis of the velocity effects on the induced flux and its distribution in the plate thicknesses of 6 through to 20 mm thick 1020 grade steel. When there is a velocity difference between the plate and the excitation system, eddy currents are induced opposing the applied magnetic field distorting its profile. This has an adverse effect on MFL inspection by altering signal responses thus limiting achievable inspection velocities. An investigation of velocities ranging from 0.5 to 3 m/s is undertaken on both defect-free plates and plates containing spherical 40% through wall thickness defects simulated for both near/top and far/bottom surfaces. From the results, it is indicated that the flux density distribution through the plate decreases as a function of depth. Once a plate depth of 16 mm is reached, it is shown that the flux density is significantly reduced toward the underside of the plate. These combined effects influence defect detectability on larger plate thicknesses for the specific yoke design used in this paper. [ABSTRACT FROM AUTHOR]

In this paper, rotor inter-turn faults in salient-pole synchronous machines are investigated using finite-element analysis. The machine under study is a 22 MVA eight-pole hydropower generator with fractional-slot windings. Simulated faulty cases include 1, 2, 5, 10, and 20 short-circuited turns (out of 58 turns) in one rotor pole. In the electromagnetic analysis, the effect of faults on airgap flux density and radial forces is studied. Furthermore, this paper investigates online detection of inter-turn faults using spectral analysis of stator voltage or current is studied. The amplitude of fault-related harmonics is investigated at various fault severities, as well as at no-load and full-load operations. This paper also discusses the effects of damper bars, an influence of parallel circuits in the stator windings, and influence of the pole pair number. In addition, a comparison between fault-related harmonics in the case of dynamic eccentricity and rotor inter-turn faults is presented. [ABSTRACT FROM AUTHOR]

Cogging torque is due to the interaction between a magnet’s magnetomotive force and a slotted stator or rotor structure. In this paper, a compact equation for cogging torque is presented for surface-mounted permanent magnet motors. This equation has four terms of field interactions involving tangential and radial components of airgap flux density. These four terms are considered as sources of cogging. Variations of these sources with pole embrace are examined. In earlier publications, closed-form expressions for pole embrace corresponding to the minimum cogging were presented considering only radial fields. In this paper, an attempt is made to recognize the influence of tangential fields in cogging. The compact form given here distinctly reflects the significance of both radial and tangential field components. Furthermore, to study the trends of cogging sources with pole number and airgap radius, simplified expressions for harmonic content of field components are derived using the first-order binomial approximation. The analysis on cogging presented in this paper helps in determining search domains in which optimum embrace for minimum cogging can be found when both the radial and tangential field components are considered. [ABSTRACT FROM AUTHOR]

A computational technique is presented in this paper which improves finite element method (FEM) in solving inverse problems. Subregion method is used to select and isolate the area of interest where design parameters for defect shape are updated. An elastic mesh generator is developed in this paper to generate optimal meshes in the selected area to save connectivity matrix until having the most accurate design parameters. Using subregion FEM in solving inverse problems will help in minimizing processing time and memory usage in addition of reducing solution complexity. A 2-D eddy current testing (ECT) problem of detecting and characterizing the location and shape of a defect by separating the defect from entire domain is used to validate the presented subregion FEM algorithm. The elastic mesh generator is investigated to update the preselected design parameters of the defect in each iteration. This meshing technique adds the specialty of using subregion method in inverse problems where elements and nodes numberings are saved inside and outside the defect region. Both the genetic algorithm and simulated annealing optimization techniques are developed to get the accurate defect parameters. The presented subregion FEM results have been verified computationally using conventional FEM. Excellent results of signals agreement and processing time minimization with a factor of 90% with an accuracy of 98% have been achieved. In addition, the presented subregion FEM algorithm has been verified experimentally using aluminum (T6061-T6) and mild steel plate (0.15%–0.30% carbon and Fe) samples. This experiment is carried using an elongated excitation coil in a fixed position mounted on the top of the sample and tunneling magnetoresistive sensor to measure magnetic field. The measured magnetic fields were used as input to the inverse subregion FEM solver and the machined artificial defects were characterized with excellent accuracy. [ABSTRACT FROM AUTHOR]

As an efficient non-destructive testing method, magnetic flux leakage (MFL) has been widely used for damage detection in ferromagnetic materials. The magnetic dipole theory is a traditional method to calculate the magnetic leakage field. In this paper, the magnetic leakage field functions of a slot in a 2-D infinity plate are obtained using the magnetic dipole theory. Equations of the magnetic leakage field are converted into the convolution of two other functions. Spatial spectral equations of the MFL are developed according to the convolution theorem using the Fourier transform (FT) method. The results are analytical functions different from other numerical methods, such as the discrete FT and fast FT methods, and the calculation speed is fast. The results show that the $y$ -component of the magnetic leakage field has 90° phase shift with the $x$ -component. This result has clear physical significance compared with the traditional MFL equations using the magnetic dipole theory. Different spatial spectral curves for different defects are presented in this paper. Since there is a sinc function for the width value in the equation, the width value can be deduced from the first zero-crossing point in the spatial spectrum curves. A new method is proposed to determine the width value using the relationship $w =1/f_{s}$ , where $f_{s}$ is the first zero cross point. Two specimens with different cracks are investigated, and the experimental results show this method can be used as an inverse MFL data interpretation technique. [ABSTRACT FROM AUTHOR]

A large circular transmitter (power pad) is often utilized for inductively wireless charging so that the power receiver can position itself freely within the power pad. However, the uneven magnetic field distribution leads to the impedance mismatch and the variable transferred power due to the misalignment between a receiving coil and a relatively large transmitter coil. In this paper, the effects of the turn numbers, trace spacing, and coil size on the uniformity of magnetic field distribution over a planar spiral coil (PSC) are investigated based on an analytical model. Then, the genetic algorithm is used to optimize the trace width and spacing of a ten-turn PSC with the fixed outer and inner diameters, whereas the magnetic field is numerically calculated by HFSS software. The geometrically optimal PSC is obtained with the trace width approximately equal to trace spacing for each turn by minimizing the coefficient of variation (COV) of magnetic field within an effective charging area over the coil. The results showed that the simulated and measured COVs of magnetic field were 0.130 and 0.121, respectively, which are obviously less than that of the uniformly spaced regular coil and show a little less than that of the optimally spaced coil with fixed trace width. Therefore, the trace spacing is a major consideration to achieve the uniform magnetic field, whereas the trace width variation is applied to refine the evenness of field. It is also expected that the proposed GA-based optimization is well applied to design other Txs with conformable shape in inductively WPT systems for stable power delivery regardless of the receiver positions. [ABSTRACT FROM AUTHOR]

As CMOS technology scales down to the nanoscale, high leakage power consumption becomes one of the major concerns in the design of electronic circuits. To overcome this challenge, nano-emerging technologies and logic-in-memory (LIM) structures are being studied. Magnetic tunnel junction (MTJ) is an emerging spin-based device, which consumes very minimal leakage power in conjunction with CMOS transistors. In this paper, we propose a novel MTJ/CMOS design, which consumes low power and has lower delay than the existing LIM-based MTJ/CMOS designs. The proposed MTJ/CMOS designs have lower power and lower delay by charge sharing the output nodes during the pre-charge phase. The designs are simulated using 45 nm CMOS technology with perpendicular anistropy CoFeB/MgO MTJ model using a Cadence Spectre simulator. From the simulation results, we can see that the proposed MTJ/CMOS OR, AND, XOR, MUX, and full adder designs have 31.35%, 40.15%, 49.17%, 35.86%, and 42.62% lower power-delay-product, respectively, compared with the existing MTJ/CMOS designs. Furthermore, in this paper, we have also studied the usage of integrating nano-electronic devices, such as a carbon nanotube field-effect transistor and a Fin field-effect transistor, in the proposed circuits along with the MTJ devices. [ABSTRACT FROM AUTHOR]

This paper is focused on the on-load back-electromotive force (EMF) assessment in a permanent magnet synchronous machine (PMSM) using Maxwell stress tensor along with the frozen permeability method (FPM). Although the back EMF is only measured at open-circuit condition, it is known that the on-load back EMF is heavily affected by electric loading and magnetic saturation. Since the main torque component of the PMSM is the mutual torque and it is based on the interaction between the back EMF and stator current, any distortion in the on-load back EMF will affect the electromagnetic torque and increase the torque ripple. A misleading on-load back-EMF waveform with some spikes around the commutation points is found if the on-load back EMF is assessed by means of differentiating the on-load PM flux linkage. This way, this paper proposes a new numerical method to assess the on-load back EMF in order to avoid all the shortcomings of the existing method. First of all, a quick review on the results achieved by other researchers is shown. Next, a review on the FPM is done in order to clarify the points where this method will be changed to overcome the drawbacks highlighted previously. Furthermore, a new method is introduced and explained in small details. Finally, the results for different rotor configurations and different electrical loads are presented in order to validate the proposed method’s accuracy against experiments and other numerical techniques. [ABSTRACT FROM AUTHOR]

This paper proposes the multi-material topology optimization for the simultaneous design of segmented permanent magnet (PM) arrays, coil, and iron materials in magnetic actuators. Specifically, the proposed approach can find the optimal layout and shape of PM, coil, and iron materials, as well as the optimal border and magnetization direction of segmented PM arrays. For designing the layout and shape of actuator components, the discrete material optimization-type material interpolation scheme is employed in this paper. To attain the design of segmented PM arrays, an orientation design variable in Cartesian coordinate is utilized with the penalization scheme for the discrete PM magnetization directions. To validate the effectiveness of the proposed actuator design approach, two numerical examples are presented. In the examples, the actuator components (i.e., segmented PM arrays, coil winding, and back iron) are designed aiming for maximizing the magnetic force magnitude acting on the actuator plunger. [ABSTRACT FROM AUTHOR]

One of the main engineering applications of ferrofluids is in magnetic fluid seals, working in rotary motion. An area, which has so far been insufficiently examined, is the mechanism of leaks between seal stages in this type of seal. This is an important issue in order to understand the principle of the seal operation and to properly design this type of seal. This paper presents the results of research into the mechanism of leaks between stages in multi-stage magnetic fluid seals. The tests were conducted when the pressure of the sealing air increased and reached its maximum value. The influence of the magnetic fluid properties, such as saturation magnetization or dynamic viscosity, was taken into account. Studies were performed for different seal temperatures. Experiments allowed models for determining the maximum pressure of the multi-stage seal to be proposed, based on the information about this pressure for a one-stage seal. This paper presents the comparative results of the critical pressure value obtained from experimental studies and calculations based on numerical simulations. [ABSTRACT FROM PUBLISHER]

In motor manufacturing, blanking process of non-oriented electrical steel inevitably induces plastic deformation and residual stress near the blanked edge and thus leads to the deterioration of magnetic properties. However, as for the newly developed non-oriented electrical steel, the scale of grain size is close to both blanking clearance and thickness. Grain size integrated with blanking clearance thus significantly affects the blanked edge quality. In order to reveal the effects of grain size and blanking clearance on magnetic properties deterioration, systematic blanking tests have been conducted using various non-oriented electrical steel sheets (same chemical composition, three thicknesses, and three grain sizes) in a considered clearance range. The blanked edges are characterized by means of optical microscopy, scanning electron microscopy, and micro-hardness tests. Magnetic domain structures are also observed by magnetic force microscopy. The iron losses are measured by single sheet tester method. The burnished ratio decided by clearance and grain size can be taken as the indicator to assess the deterioration of magnetic properties. The blanked edge with larger burnished ratio leads to lower increase of micro-hardness, less degradation of domain structure, and less deterioration of iron loss. In this paper, about 5.8% iron loss can be reduced by optimization of blanking clearance, which is quite pronounced for energy saving. In further study, an approximate linear function of the ratio of optimum clearance to gain size with D^-1/2 is empirically proposed to demonstrate the grain size dependence on optimum clearance determination. This paper thus provides an in-depth understanding and guidance for reducing the deterioration of magnetic properties caused by the blanking process. [ABSTRACT FROM PUBLISHER]

Although cogging torque in magnetic gears (MGs) has been studied, the additional degree of freedom inherent to MGs makes it unclear exactly what is defined as the cogging torque of a MG. Although MGs generally have relatively smooth torque transfer characteristics, this paper reveals that when the gear is used in an up-speed configuration, cogging effects may be amplified under startup conditions. This paper distinguishes between two kinds of cogging torque in MGs, termed the synchronous cogging torque and the true cogging torque. Calculation of the true cogging torque is more difficult than the synchronous cogging torque, but an approximation to the true cogging torque can be obtained using the synchronous cogging torque. The theory is verified experimentally and supported further by results from dynamic simulations. The impact on magnetically geared machines is also considered. [ABSTRACT FROM AUTHOR]

An analytical method for calculating the no-load magnetic field of external rotor permanent magnet brushless direct current motor (PMBLDCM) used as in-wheel motor of electric vehicle in the stator static coordinate and the rotor motion coordinate is presented in this paper. First, the analytic formulas of slotless permanent magnetic field in both coordinate systems are derived, respectively. Then, the complex relative permeance of external rotor PMBLDCM in both coordinate systems is calculated. Finally, the analytical solution of the no-load magnetic field in both coordinate systems is derived by applying the magnetic potential multiplied by the complex relative permeance. In this paper, a 46-pole-51-slot external rotor PMBLDCM is taken as an example, and the accuracy of the proposed analytical model is verified by the finite-element results. Based on the analytical model, the influences of the stator slotting effect on the no-load magnetic field of the external rotor and the inner stator are analyzed. The spatial order characteristics and frequency characteristics of the no-load magnetic field of the external rotor PMBLDCM in both coordinate systems are revealed, respectively. [ABSTRACT FROM AUTHOR]

This paper presents an approach to obtain high torque density in induction motor (IM) design by optimizing the search algorithms and processes. Optimal design of electrical machines has many sub-optimal peaks and requires significant computation time. To solve this problem, this paper proposes a new cost pattern value method (CPVM) for local search algorithms employed in optimal design. The CPVM concept is an intelligent strategy that digitizes the gradient over the searching region by sharing information between neighboring points. When the algorithm converges quickly to local optimum by a normalized weight method, it provides a mechanism to escape from that region. The validity of the proposed approach was evaluated using a benchmark function, and it was applied to optimal design of a 260 kW IM to maximize torque production based on a finite-element analysis. For better accuracy, we employ slip-frequency analysis compatible with vector control for an IM numerical analysis. [ABSTRACT FROM AUTHOR]

The aim of this paper is to introduce and to study the performance of some multiscale finite-element formulations for the eddy current problem in laminated iron in two dimensions. The case of the main magnetic flux that is parallel to the laminates and assumed to be perpendicular to the plane of projection is considered. Exact solutions of relevant boundary value problems for eddy currents are presented. Multiscale formulations based on the magnetic vector potential (MVP) and the single component current vector potential and on a mixed formulation of the MVP and the current density are discussed. An approach for a multiscale formulation with the MVP is constructed at the best based on an exact solution. The associated weak form of the multiscale finite-element method (MSFEM) is presented. Similar to the MVP, multiscale formulations for the single component current vector potential and for a mixed formulation with the MVP and the current density are studied. This paper does not present a mathematical analysis of the MSFEM for eddy currents in laminates. The performance of the MSFEM is studied by numerous numerical experiments of different examples. This paper covers the topics exact integration versus averaging of coefficients, stability of the MSFEM in a particular case, p-refinement of micro-shape functions and standard finite-element polynomials and edge effect. Simulations show the capability of MSFEM to approximate eddy currents in iron laminates efficiently and accurately. The simulations shall also provide a collection of numerical examples to evaluate other multiscale or homogenization methods. [ABSTRACT FROM AUTHOR]

The topology and breakpoints of the grounding grid will directly affect its working performance. This paper proposed a resistivity reconstruction method based on magnetic detection electrical impedance tomography (MDEIT) to measure the topology and breakpoints of the grounding grid. First, this paper describes the forward problem of grounding grid detection in MDEIT, and calculates the magnetic-field distribution above the grounding grid. Then, the resistivity reconstruction method based on the least squares method is proposed. Finally, this paper verifies the feasibility of the proposed method by a numerical example, which shows that the proposed method can be applied to measure the topology and breakpoints of the grounding grid. [ABSTRACT FROM AUTHOR]

In the estimation of moisture content of the inverted-type oil-immersed current transformer (IOCT) insulation system, the interfacial polarization between oil-immersed insulation paper and semi-conductive paper should be considered. The classical model functions of frequency-domain dielectric spectroscopy (FDS) are no longer applicable. Therefore, the planar layered two-phase system model is applied in this paper. First, the FDS of oil-immersed paper and semi-conductive paper with certain moisture content is measured using Alpha-A broadband dielectric spectrometer. Then, the FDS of oil-immersed insulation paper is explained using the Havriliak–Negami (H–N) model function and the amendatory H–N model function considering that the dc conductance is used to explain the FDS of semi-conductive paper. The two functions are substituted into the planar layered two-phase system model. The model parameters are fit by means of least-squares technique. Finally, the numerical relationship between the chosen characteristic parameter and the moisture content of the IOCT insulation system is obtained by least-squares technique. In engineering, one can use the results considering the influence of interfacial polarization to estimate the moisture content of the IOCT insulation system. [ABSTRACT FROM AUTHOR]

Space charge distribution is a valuable indicator of ion flow field and is widely utilized to assess electromagnetic environment for transmission line. The finite-element method (FEM) is widely used to solve this problem. However, Kaptzov assumption in FEM assumes that onset voltage is unchangeable after corona occurs, which does not tally with the actual situation. This paper adopted the finite-element iteration method (FEIM), which uses empirical formula instead of assumptions to calculate the charge density. The surface field intensity is not constant in the empirical formula because the empirical formula takes the effects of space charge on surface field into consideration. So this is more consistent with actual situation. In order to verify the accuracy of the algorithm, sound pulse method is applied to measure the charge density around the conductor in the laboratory. Simulation results show that the charge density obtained in this paper agrees with the data in the experiment, which verifies the validity of the empirical formula for calculation of space charge density. Compared with a method considering Kaptzov assumption, FEIM is closer to the experiment in area around conductor line and near the ground. This indicates that empirical formula in FEIM is more effective than Kaptzov assumption in these two domains. [ABSTRACT FROM AUTHOR]

In this paper, open boundary techniques are employed to represent the Cauer ladder network (CLN) for unbounded eddy-current problems. Recently, a novel and effective model order reduction method, called the CLN method, has been proposed in which linear eddy-current fields are represented by a CLN. The CLN method was initially formulated for closed domain eddy-current problems. This paper demonstrates that the CLN method can be extended to unbounded-domain problems when combined with conventional open boundary techniques. The CLN network parameter extractions of two parallel busbars are demonstrated as a numerical example. [ABSTRACT FROM AUTHOR]

Magnetically mediated thermoacoustic imaging (MM-TAI) is an emerging medical electrical parameter imaging technology; it has the advantages of high contrast of electrical impedance imaging and high resolution of ultrasound imaging; it can realize the early diagnosis of disease in the tissues comparing with structure imaging technology. The magnetically mediated thermoacoustic (TA) effect is analyzed in this paper through the theoretical inference, numerical calculation, and experiment. Pulsed excitation is considered in the analysis, which is different from previously reported research. The pulsed magnetic field is applied to the low conductivity sample such as gel phantoms (0.2, 4, and 2.5 S/m); then the Joule heat is generated inside the objects and an acoustic signal is excited due to heat expansion. The acoustic signal is detected and the image is reconstructed from TA source to conductivity. This paper has laid the foundation for the MM-TAI in biological tissues. [ABSTRACT FROM AUTHOR]

This paper presents new results on a novel coupled-physics modality called magneto-acousto-electrical tomography (MAET). With static magnetic field, a beam of ultrasound is applied to the sample to be imaged; the ultrasonic vibration can lead to the separation of the charges due to the Lorentz force and produces the current distributed in the object. In this paper, simulations were conducted on biological tissue model, and the electrical properties were reconstructed, which could reflect the state of physiological or pathological. We also conducted experiments to detect the voltage signal of microvolt level by the electrodes placed around the sample. The series of experiments were conducted on low-conductivity (0.2 S/m) animal gelatin phantom and real biological tissue, successively placed in a 260 mT magnetic field and sonicated with a plane ultrasonic transducer of central frequency 2.25 MHz. In this paper, we obtained axis resolution of 1 mm, much more significant improvement than the previous reports. More importantly, the experimental result does also demonstrate the feasibility of MAET to image the electrical properties of biological tissue. [ABSTRACT FROM AUTHOR]

The near-field communication (NFC) technique finds wide applications in many aspects of modern life, e.g., contactless payment systems or authentication. Regardless of the application, typically, the requirements on the antenna structure are manifold. Frequently, limitations in the available space make the antenna design quite challenging. Beside geometrical limitations, also the matching of the antenna structure to the analog front end of the NFC transponder IC has to be taken into account. Furthermore, the NFC antenna together with the connected IC has to fulfill specific standardized values. In this paper, the optimization of an NFC antenna structure including the needed matching circuit in the multi-objective sense is proposed. Due to its simplicity and the consequently reduced computational effort, the partial-element electric circuit (PEEC) method is applied to carry out the needed field computation in the so-called NFC operating volume. Furthermore, the PEEC method offers the possibility of simply connecting lumped components to the antenna structure within the numerical analyses, which enables the optimization of the matching circuit parallel to the optimization of the antenna structure. The optimization relies on a stochastic optimization strategy, namely, the firefly algorithm (FFA). In this paper, an extended version of the general FFA is applied. [ABSTRACT FROM AUTHOR]

In this paper, we propose a design process for a plasmonic grating structure to induce the resonance at a target wavelength. In a specific condition, surface gratings may induce the surface plasmon propagation due to the diffraction and the resonance wavelength of the surface plasmon propagation is dependent on the grating shape. The grating configuration was designed by the topology optimization scheme based on the reaction-diffusion equation. To shift the resonance wavelength to the target wavelength, this paper maps the frequency response function to a probability distribution function (PDF). The mean value from the PDF becomes a part of the objective function and the design objective is set to minimize the distance between the present resonance wavelength and the target wavelength while keeping the energy intensity. The process of simulation and optimization was performed using the commercial package COMSOL combined with MATLAB programming. [ABSTRACT FROM AUTHOR]

Electromagnetic devices containing permanent magnet (PM) are common and typical electromagnetic devices that have advantages of low-power consumption, small size, high sensitivity, and its optimization problem has aroused widespread concern. Calculation accuracy of electromagnetic properties and efficiency of optimization processes are two important factors that affect the optimization effect of electromagnetic devices. A fast calculation method was proposed in this paper that aimed at electromagnetic devices with PM characteristics of strong non-linearity and low solving precision. The response surface method was used to derive the basis function, and the error between actual measured values and calculated values was modified by the Kriging method. On the basis of the calculation model, the distributed collaborative strategy was adopted to fulfill the parallel execution of the fast computation. Simultaneously, the updating strategy of particles was improved, and the robustness of the multi-objective particle swarm optimization algorithm in solving the optimization problem of electromagnetic devices with PM was enhanced. Effectiveness of the method proposed in this paper was verified by the case study of a specific type of electromagnetic relay with PM. [ABSTRACT FROM AUTHOR]

The high stability of the dual-excited synchronous generator (DESG) can enhance the reliability of power supply for critical users. Based on the traditional synchronous generator (TSG), a DESG with two sets of symmetrical field windings on the rotor is presented in this paper. The rotor slots are spaced equally over the whole rotor surface of DESG, which is different from the structure of TSG. Such structures of DESG are expected to enhance the reliability and give the electromagnetic performances, such as air-gap flux density and electromotive force (emf) that are close to those of TSG. For this purpose the relationship between the excitation magnetomotive forces (mmf) of the single- and dual-axis excited DESG is investigated. The mmf with a different rotor pitch is calculated by the finite-element simulation, and the simulation results agree with those by the theoretical derivation. The excitation air-gap flux density, emf, and the magnetic saturation in stator and rotor cores are calculated under different excitation modes, and the results are compared with those of TSG. In order to validate the simulation results, the emf of 10 kW DESG model machine is measured under different excitation modes. This paper provides the theoretical basis for the design and manufacture of large DESGs. [ABSTRACT FROM AUTHOR]

In this paper, the usage of the Parareal method is proposed for the time-parallel solution of the eddy current problem. The method is adapted to the particular challenges of the problem that are related to the differential algebraic character due to non-conducting regions. It is shown how the necessary modification can be automatically incorporated by using a suitable time-stepping method. This paper closes with the first demonstration of a simulation of a realistic four-pole induction machine model using Parareal. [ABSTRACT FROM AUTHOR]

This paper aims at describing the influence of shielding on the magnetizing magnetic field measured with an H-coil system, used in a double-yoked single-sheet tester. By the mean of a positioning system especially conceived for the purpose of this paper, the magnetic field is measured at different distances from the laminated sheet. The evolution of this field along the perpendicular line thus defined shows a distinctive behavior, whether the measure is realized in the presence of a magnetic shield or not. A description of the obtained experimental results is made, and a comparison with numerical models is realized. Finally, an explanation over the observed phenomena based on physical principles of electromagnetism is proposed. [ABSTRACT FROM AUTHOR]

Accurate and simple magnetic material behavior law is necessary to correctly model complete electromagnetic systems. In this paper, a new formulation based on the scalar quasi-static hysteresis Preisach model extended to dynamic behavior using fractional derivation dynamic contribution is proposed. The fractional contribution is solved using convolution which highly reduces the numerical issues. The order of the fractional derivation provides a new degree of freedom and allows to correctly obtain simulation results on a very large frequency bandwidth. By using such formulation, space discretization techniques (finite differences, finite elements) are avoided which are highly space and time consuming while keeping the global simulation results precise. The numerical implementation of the problem and some experimental validations are shown in this paper. [ABSTRACT FROM AUTHOR]

This paper presents the design of cryogenic induction motor submerged in liquefied natural gas (LNG) for operating LNG spray pump. In cryogenic environment of −163 °C, the torque characteristics of induction motor differ greatly from the operating conditions at room temperature. So, in order to obtain the operating characteristics corresponded with design specifications of the induction motor in cryogenic environment, it is necessary to redesign motor dimensions from the result of conventional design by reflecting the changes of material properties under the very low temperature (VLT). This paper focused on the design of cryogenic induction motor considering the variation of resistivity for the stator windings and rotor bars. Also, the distribution of magnetic flux density and magnetic saturation effect on the steel core are analyzed by using 2-D finite-element method for ac sinusoidal time varying excitations under the VLT. The result of proposed method considered the magnetic and electric characteristics of matters in VLT successfully, so that the motor performances at the cryogenic temperature fit well with expected. The designed motor was fabricated and torque performance measured in VLT agreed well with design goals. [ABSTRACT FROM AUTHOR]

This paper presents a research work on the electromagnetic loss modeling and demagnetization analysis for a high-speed permanent magnet machine (HSPMM). The iron loss is estimated by improved modeling considering harmonics and rotational magnetic field effects to achieve high precision; rotor eddy current loss is researched and comprehensively investigated using finite-element method (FEM). The auxiliary slot and PM beveling are also proposed to reduce the rotor eddy current loss for machine at high-speed operation. Temperature-dependent PM demagnetization modeling is utilized in HSPMM FEM analysis to investigate machine performance due to temperature variation, while optimized rotor structures are proposed and comparatively researched by FEM to improve the machine anti-demagnetization capability in harsh conditions. The HSPMM temperature is estimated based on the calculated loss results and machine computational fluid dynamic modeling. Experimental measurements on the prototype machine verify the effectiveness of the machine electromagnetic and thermal modeling in the paper. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of the core loss observed in the stator of a permanent magnet linear synchronous generator. Core loss is usually calculated using the classical Steinmetz equation, but it leads to erroneous results. Consequently, several researchers have proposed modified versions of this equation, taking into account the hysteresis loss, eddy current loss, and excess loss. In this paper, we calculated all loss coefficients from the Epstein test data using a curve fitting method. Moreover, we separated the rotating and alternating fields based on the time harmonics observed with changes in the magnetic flux density. In addition, we considered the 2-D and 3-D plane flux paths that cause magnetic flux leakage. Finally, the core loss of the linear machine was calculated using a modified Steinmetz equation that considers the flux path. [ABSTRACT FROM AUTHOR]

Recently, electric power consumption has increased rapidly owing to the development of electric devices, and thus environmental problems such as global warming have come to the fore. Therefore, developed and developing countries are preparing various measures to prevent global warming. Minimum energy performance standards (MEPS) are one of the representative measures. MEPS is an efficiency regulation for induction motors that limits the minimum efficiency with regard to the power of the induction motors, in order to save energy. Studies have been conducted on induction motors to improve the efficiency and to satisfy MEPS. However, It is very difficult to satisfy the efficiency of induction motor for MEPS. Therefore, synchronous reluctance motors (SynRMs) are actively being studied to replace induction motors. In this paper, a SynRM is designed using a Kw-map. Moreover, to improve the output characteristics, the rib thickness of the SynRM is optimized using the response surface method. Finally, the validity of the design method, proposed in this paper is verified with a real test using the prototype. [ABSTRACT FROM AUTHOR]

As a reliable and non-destructive technique, frequency response analysis (FRA) has been widely recognized for transformer winding deformation detection and assessment. In this paper, frequency response functions (FRFs) are obtained by two different FRA measurement connection ways, namely, end-to-end voltage ratio (EE) and transfer voltage (TF) ratio measurements. At the same time, according to the two ways, sensitivities of the FRFs to electrical parameters of the equivalent circuit model of the transformer winding are investigated. Based on Tellegen theorem, adjoint network method is derived to calculate the values of the sensitivities of FRFs to electrical parameters. Meanwhile, the sensitivity characteristics of circuit parameters are studied. In addition, by comparing the sensitivity results of the two ways, the variation laws of the sensitivities under the two different connection approaches are determined. Besides, this paper can provide a new and objective method to interpret the FRA results and give us a better understanding how much the parameter variations can influence the FRA measurement results. [ABSTRACT FROM AUTHOR]

In this paper, the eigenmodes and quality factors of cavity resonators are computed by a non-linear finite element eigenvalue solver, exploiting surface impedance boundary conditions (SIBCs). In the last few years, the accurate calculation of losses and resonance frequencies of (super)conducting cavities has become a central part in the design of high-performance particle accelerators. However, solving the governing equations in the material is computationally unfeasible, since its penetration depth is many orders of magnitude smaller than the cavity dimensions. Therefore, the material behavior is modeled by an SIBC. However, the SIBC introduces a square-root operator in the corresponding eigenvalue formulation. This necessitates the use of a non-linear eigenvalue solver, for which a contour integral approach is proposed. This paper recommends a generic approach for coupling an SIBC formulation with a non-linear eigenvalue solver. [ABSTRACT FROM AUTHOR]

The magnetic recording industry is perennially trying to grow the areal density by optimizing the head/media, the coding/signal processing, and the bit length (BL) and track pitch (TP) of the data written on the medium. Writing data at smaller BL or TP on the medium lead to loss of SNR during readback, which can be corrected by the coding and signal processing subsystem at the cost of the code rate $R$ . The optimization of the BL, TP, and code rate for a given head and media is the task of the system integrator. In this paper, we make use of an advanced channel model: the grain-flipping probability model, to perform an equivalent optimization together with a software recording channel that is able to include the impact of the generalized partial response equalizer, soft-output Viterbi algorithm detector, and low density parity check decoder on the final performance. In this paper, we vary the BL, TP, and code rate $R$ in the simulations to search for the highest user areal density achievable for a given head/medium setup. We investigate the effect of having a constant reader width (RW) as well as with RW proportionate to TP in our channel model. We also investigate the effect of more advanced 2-D coding and detection schemes on the final system performance. [ABSTRACT FROM PUBLISHER]

Two-dimensional magnetic recording (TDMR) is a promising technology for boosting areal densities (ADs) using sophisticated signal processing algorithms within a systems framework. The read/write channel architectures have to effectively tackle 2-D inter-symbol interference (ISI), 2-D synchronization errors, media and electronic noise sources, as well as thermal asperities resulting in burst erasures. The 1-D low-density parity check (LDPC) codes are well studied to correct large 1-D burst errors/erasures. However, such 1-D LDPC codes are not suitable for correcting 2-D burst errors/erasures due to the 2-D span of errors. In this paper, we propose construction of a native 2-D LDPC code to effectively correct 2-D burst erasures. We also propose a joint detection and decoding engine based on the generalized belief propagation algorithm to simultaneously handle 2-D ISI, as well as correct bit/burst errors for TDMR channels. This paper is novel in two aspects: 1) we propose the construction of native 2-D LDPC codes to correct large 2-D burst erasures and 2) we develop a 2-D joint signal detection-decoder engine that incorporates 2-D ISI constraints, and modulation code constrains along with LDPC decoding. The native 2-D LDPC code can correct >20% more burst erasures compared with the 1-D LDPC code over a 128 $\times $ 256 2-D page of detected bits. Also, the proposed algorithm is observed to achieve a signal-to-noise ratio gain of >0.5 dB in bit error rate performance (translating to 10% increase in ADs around the 1.8 Tb/in2 regime with grain sizes of 9 nm) as compared with a decoupled detector-decoder system configuration over a small 2-D LDPC code of size 16 $\times $ 16. The efficacy of our proposed algorithm and system architecture is evaluated by assessing AD gains via simulations for a TDMR configuration comprising of a 2-D generalized partial response over the Voronoi media model assuming perfect 2-D synchronization. [ABSTRACT FROM PUBLISHER]

This paper presents a new axial flux permanent magnet machine, named ring winding axial flux machine (AFM). The ring winding AFM (RWAFM) takes the advantage of segmented stator of yokeless and segmented armature topology with those of decoupled phases and ring winding of transverse flux topology. In this paper, the geometry of the RWAFM is introduced in detail. Furthermore, the working principle and torque production theory are discussed. To validate the concept and confirm manufacturability of the proposed topology, a prototype is fabricated. The performance of the RWAFM is studied through experimental tests, 3-D finite-element simulations, and analytical discussions. [ABSTRACT FROM PUBLISHER]

In this paper, the air-gap flux density components in the eccentric surface-mounted phase modulation (SPM) machines are predicted analytically. In the provided model, the slotting effects of the armature are taken into account. In the modeling process, conformal transformations (CTs) are employed to obtain an equivalent concentric slotless machine for the eccentric slotted PM machine. To satisfy the condition of using CTs, i.e., having a Laplace equation, the PMs are replaced with an equivalent current sheet at the surface of the rotor. The approach of finding this current sheet is approved by the basis of the electromagnetic theory. One of the contributions of this paper is that the provided model is capable of modeling the eccentric SPM machines with any PM magnetization pattern by means of CTs. Substituting the predicted air-gap flux density components in the Maxwell stress tensor, the machine unbalanced magnetic force and its cogging torque are computed. Finally, the accuracy of the obtained results is evaluated by means of finite-element analysis. [ABSTRACT FROM PUBLISHER]

This paper presents a comparative study on different microfabricated inductors (microtransformers), which are suitable for high-frequency power application. The main topic of this study is comparing and analyzing the effect of some factors such as material type, number of turns, and coil form on microinductor performance considering a fixed chip size, fixed magnetic core size, and core form. Two different microtransformer designs with different magnetic core materials are considered in this work. The core materials used in this work are NiFe45/55 and CoFe45/55. Also, two types of device packages are developed, namely, Quad Flat No-Lead and FR4 embedded packages. For device testing, different high-frequency switching regulators available on the market are used. This study shows the influence of different parameters on the performance of a certain high-frequency application. In this paper, we discuss the influence of the design, magnetic material, and package type on thermal performance and the efficiency of the power application. [ABSTRACT FROM AUTHOR]

This paper introduces an alternative pathway to designing an efficient interior permanent magnet machine (IPMM) for direct–drive (D-D) wind energy applications. It analyzes the design optimization methodology in great detail, employing multiple experimental verifications to acutely pinpoint the most desirable and feasible format. The focal objectives of minimizing cogging torque, torque ripple, and maximizing efficiency were among the priority design goals and obtained through design optimization. It is demonstrated in the process that both the torque ripple and the cogging torque can be reduced to less than 5% by adjusting the slot and pole dimensions, without any other alterations in rotor pole shaping or skewing. This paper leads the way, pioneering experimental substantiation of theory, by varying existing geometrical parameters, winding, and pole design of a basic IPMM to come up with a highly efficient wind turbine generator with negligible cogging torque and torque ripple. The electromagnetic is at the heart of this paper’s design goals, as parameter optimization is essential for a wind turbine application. The winding layout is brought under scrutiny and both the distributed and concentrated wound IPMMs are compared to further adopt the design optimization. The superiority of the concentrated-wound design is demonstrated, and consequently a prototype machine is constructed based on the proposed design for experimental verification. The results from the experiment verify the feasibility of the proposed design for D-D wind turbine applications. [ABSTRACT FROM AUTHOR]

This paper focuses on analytical methods of a finite-element method (FEM)-based edge heating system. The edge heating system plays a role in maintaining the temperature in the hot rolling process of carbon steel. Carbon steel moves along the production line and maintains the temperature by the edge heating system in the process. Power-of-the-edge heating system is transmitted to carbon steel during the process. Eddy currents are generated in carbon steel by Faraday’s law of electromagnetic induction, and eddy current loss serves as a heat source to increase the temperature. Thus, there is a need for accurate electromagnetic-field analysis and thermal analysis because the eddy current path generated in carbon steel greatly affects the heat distribution in carbon steel. This multiphysics analysis requires high reliability. Accordingly, this paper presents a coupling analysis method using an FEM-based coordinate mapping method as a more accurate analytical method. This paper also established an analytical approach to the edge heating system using the ductility analytical method of this coordinate mapping method. [ABSTRACT FROM AUTHOR]

In this paper, a new shaded-pole main exciter (ME) with additional short-circuited coils for aircraft three-stage starter–generator (SG) is proposed and investigated. The basic structure, winding configurations, operating principle, and start system structure of the presented shaded-pole ME are illustrated in detail. The comparative study between the original ME and the shaded-pole ME with respect to the starting mode performances is conducted by 2-D finite-element method (FEM). A prototype SG with original ME has been developed, and the experimental results are essentially consistent with the simulation results by the FEM utilized in the predictions in this paper. Simulation data and waveforms verify that the proposed shaded-pole ME is a good candidate for aircraft machines to satisfy the dual function of starter and generator. [ABSTRACT FROM AUTHOR]

To realize a compact, lightweight and high-efficiency megahertz (MHz) switching DC–DC converter using SiC/GaN power device, inductor/transformer core must have small core loss at such high frequency to maintain high efficiency of the converter. This paper focuses on Fe-based amorphous (Fe-AMO) alloy powder used in metal composite bulk magnetic core for MHz switching DC–DC converter, where fine Fe-AMO powder with a mean diameter of 2.56~ \mu \textm was used to suppress MHz band eddy current inside the Fe-AMO powder body. When applying Fe-AMO powder to the closely packed composite core together with epoxy resin, high electrical-resistivity layer must be formed on the Fe-AMO powder surface in order to suppress the overlapped eddy current between adjacent Fe-AMO powders. In this paper, about 10 nm-thick oxidized layer of the Fe-AMO powder surface was successfully formed by using annealing in dry air. This paper describes on the surface-oxidized Fe-AMO powder/epoxy-resin composite bulk core transformer and its application to GaN power device MHz switching LLC resonant DC–DC converter. By using the Fe-AMO composite core transformer, the fabricated 48 V-input/24 V-output LLC resonant converter exhibited 90% over efficiency in the output power range of 24 to 120 W, which was higher efficiency when using the Ni–Zn ferrite core transformer. [ABSTRACT FROM AUTHOR]

A variable inductor consists of a magnetic core, primary dc windings, and secondary ac windings. The effective inductance of the secondary ac winding can be controlled by the primary dc current because of its nonlinear magnetic characteristic. Hence, variable inductors can be applied as a reactive power compensator for voltage stabilization in electric power systems, and have desirable features such as a simple and robust structure, low cost, and high reliability. In a previous paper, a concentric-winding-type three-phase variable inductor with a 2-D structure has been proposed. It was demonstrated that the 2-D variable inductor has good controllability and a low distortion current. To further increase productivity and reduce costs, this paper presents a novel concentric-winding-type three-phase variable inductor with a 3-D structure. It is demonstrated that the leakage flux of the proposed 3-D variable inductor is reduced by more than 30%. Furthermore, a 6.6 kV–100 kVA 3-D variable inductor is designed and compared to its 2-D counterpart. It is proved that eddy current loss, which is induced within an oil-immersed self-cooled tank because of leakage flux from the variable inductor, can be reduced to one-third of that of the 2-D variable inductor. [ABSTRACT FROM AUTHOR]