The 50 most-cited articles in IEEE Transactions on Magnetics, 2016

Wireless charging electric vehicles (EV) is the development trend of EV. However, the battery taken by EVs has the disadvantages of big volume, long time to recharge, and limited driving distance. In this paper, an innovative dynamic wireless charging system based on magnetic coupled resonant power transmission is presented. The transmitting coil of this charging system can selectively turn ON/OFF for charging vehicles while driving. The structures of the transmitting coil and receiving coil are researched and improved. In addition, the dispersed coupling structure named grouped periodic series spiral coupler is proposed, and its characteristics are described. A simulation of coupling coefficients at different D values is carried out. A prototype is built to experiment on the dynamic wireless charging process of EV. Meanwhile, the coil coupling and variation of transmission efficiency are analyzed. The comparison of the experiment indicated that the EV can obtain a stable charging process under 25 mm transmission distance using the improved receiving coil with R:H:D = 4:5:13.…

Although three-phase permanent magnet (PM) motors are dominant in industry, multi-phase PM synchronous motors present higher torque-to-weight ratios, better efficiency, and low torque ripple compared with three-phase conventional PM motors. These features make fault-tolerant multi-phase PM motors become attractive for safety-critical applications. In this paper, a novel PM multi-phase motor design with a dual three-phase asymmetric stator winding is proposed. The winding structure of the proposed motor is unconventional due to selected slot-pole combinations. Therefore, an asymmetric winding is needed. The detailed finite-element analysis of the proposed motor and a performance comparison between the conventional integer-slot (72-slot/12-pole motor) with symmetric winding and the unconventional fractional-slot (78-slot/12-pole motor) PM motors with asymmetric windings is performed to see the benefits of the proposed motor. It was shown that the novel unconventional multi-phase PM motor has excellent torque quality and slightly higher torque density levels.

This paper presents a detailed magnet defect fault detection analysis through fluxgate sensors by monitoring the leakage flux around permanent magnet synchronous motors. The flux spectra of electric machines contain direct and most critical information to monitor and characterize magnet defect faults and their progressions. In the mainstream diagnosis techniques based on phase current and back-EMF analysis, the fault corresponding signature characteristics may vary and cause misleading results depending on motor topology, winding configuration, number and location of defective magnets, and controller parameters. In this paper, it is shown that leakage flux analysis provides some superior results for magnet defect diagnosis. For this purpose, the fault patterns in the leakage flux spectrum are exhaustively analyzed at different torque/speed profiles. Simulation and experimental results show that the deployment of a direction sensitive fluxgate sensor in magnet defect fault detection yields very promising results both in time and frequency domain analyses.

Native application of finite-element method (FEM) to the analysis of skin and proximity effects in multi-turn coils results in large equation systems, whose solution needs long computational time. This paper proposes a semi-analytical approach to overcome this problem. For the analysis of the proximity effect, the complex permeability of a round conducting wire immersed in uniform time-harmonic magnetic fields is represented in a closed form. Then, the homogenized complex permeability over the cross section of the multi-turn coil is analytically evaluated using the Ollendorff formula. The magnetoquasistatic problem is thus replaced by the magnetostatic one, in which the multi-turn coil is treated as a uniform material with the homogenized complex permeability. The skin effect is taken into consideration by introducing the corresponding impedance in the circuit equation. The proposed method is shown to give the impedance of multi-turn coils, which is in good agreement with that obtained by the conventional FEM as well as experiments.

This paper introduces a novel topology for generating a spatial third-harmonic current component to excite the rotor field winding of a wound rotor synchronous machine to achieve brushless operation. In this topology, each of the three-phase windings on the stator is connected with a switch in parallel. In particular, two antiparallel thyristors are used to switch during positive and negative half cycles. Two windings are mounted on the rotor of the machine: 1) the harmonic winding and 2) the field winding. Zero-sequence currents are generated, when the switches are closed near zero crossing for a short time interval. Consecutive operation of the switches creates an additional spatial third-harmonic current pulsating in the stator winding. The number of poles of the stator winding and the field winding is the same (four-poles in this case) to intercept the torque generation component of the air-gap flux, whereas, the number of poles of the harmonic windings is adjusted (12-poles in this case) to intercept the harmonic component of the air-gap flux and develop voltage across the…

Axial flux permanent magnet (AFPM) motors are frequently used in many applications. Axial gap coreless motors with surface-mounted magnets are the most noteworthy ones due to their potentially higher efficiency and smaller axial length. In this paper, a new spoke-type AFPM coreless disk motor with dual rotor and single stator is proposed with sinusoidal rotor segments. This new disk-type motor is an interior PM (IPM) motor with spoke-type rotor and variable air gap to obtain sinusoidal back Electro-Motive Force waveform. It is shown that it is possible to increase the air-gap flux density in the proposed new coreless AF-IPM motor and increase the torque output compared with the conventional surface-mounted AFPM motors.

High cogging torque is a common drawback of the interior permanent magnet machine. In this paper, a novel technique is adopted to reduce cogging torque and torque ripple by using an asymmetrical V-type rotor configuration. First, the analysis modes are presented, and the proposed rotor is optimized by the hybrid design of experiment. A satisfactory set of parameters is determined. Next, the cogging torque and the torque ripple of the proposed model are compared with those of the basic model. The results demonstrate that the cogging torque and the torque ripple are reduced significantly by the adoption of the proposed rotor. Then, the performance of the proposed model rotating clockwise is compared that of the proposed model rotating counterclockwise to evaluate the effectiveness of the proposed rotor. Finally, the validity of the proposed method is confirmed by experiment.

This paper studies the online parameter estimation of permanent magnet synchronous motor (PMSM) with the consideration of magnetic saturation and proposes a novel current injection method to estimate parameters, including winding resistances, dq-axis inductances, and rotor flux. During the current injection, the inductances will vary due to magnetic saturation, neglecting which will cause great estimation error especially in the inductance estimation. This paper proposes to use simplified equations to model the self- and cross-saturation effects during the current injection. By incorporating this saturation model into the PMSM steady-state equations, the varying dq-axis inductances due to magnetic saturation as well as the rotor flux can be accurately estimated. In addition, the estimation of winding resistance is independent of other parameters and does not get affected by the magnetic saturation. The proposed approach is validated through both the numerical and experimental studies on a laboratory interior PMSM.

This paper proposes an outer-rotor V-shaped permanent magnet flux switching (V-PMFS) motor for potential applications in in-wheel direct drive system. However, the cogging torque and torque ripple of the outer-rotor V-PMFS motor are relatively high, which may lead to mechanical vibration and acoustic noise, especially in low speed operation. To improve the overall performances of the outer-rotor V-PMFS motor, a multi-objective optimization method based on multi-level design method is proposed. According to the effect of the design variables on the optimization objectives, sensitivity analysis method is used to divide the design variables into two levels. Then, the two levels of design variables are optimized with two different optimization methods. After optimization, electromagnetic performances between initial and optimal motors are compared. Finally, a prototype motor is manufactured and tested. Both electromagnetic performance analyses and experimental results verify the validity of the proposed optimization method.

Transcranial magnetic stimulation (TMS) is a tool for neuromodulation that uses a time-varying magnetic field to stimulate the brain via an induced electric field (E-Field). Clinical data from Premier Psychiatric Research Institute on repetitive TMS (rTMS) for the treatment of depression shows that patients older than 55 years respond to deep rTMS with better efficacy than younger patients. Brain volume shrinks with age in adults older than 40 years, increasing the distance between their brain and scalp. In this paper, we have investigated how the induced E-Field from TMS is affected by brain-scalp distance (BSD). We have developed heterogeneous head models from MRI data of 50 subjects and created simplified head models using concentric spheres. Using finite-element analysis, we simulated TMS on these models to test the role of BSD in determining the strength and distribution of the E-Field.

This paper presents the results of an investigation focused on the rotor eddy-current losses of a permanent magnet (PM) synchronous machine that is equipped with fractional-slot concentrated windings (FSCWs). Major spatial harmonics that induce the most significant rotor eddy-current losses are identified and evaluated. Time-stepped finite-element analysis results are presented to compare the predicted losses in the proposed FSCW-PM machine designs. It is shown that the lowest total eddy-current losses in the rotor core and magnets are achieved by introducing flux barriers into the rotor back iron along the d -axis.

Vernier permanent-magnet (VPM) machines attract more and more attention recently because of the high-torque density and low-speed operation features. Due to the vernier structure for field modulation, its power factor (PF) usually is lower than that of the conventional PM machines. In this paper, a new linear VPM machine for improving the PF is proposed. By using an auxiliary dc field winding to provide an additional excitation, the air-gap flux excited by PMs is compensated. The proposed machine has a similar structure to the split-pole VPM machines with surface-mounted PMs. For implementing the auxiliary dc field winding, a parallel-hybrid excitation topology and consequent-pole PM machine structure are adopted. The machine topology, modeling, and operating principle are discussed. Both simulation and experimentation show that the PF of the machine can be improved by the auxiliary dc field excitation.

Permanent magnet-based localization is a very promising method for the tracking of minimally invasive medical devices inside the human body, such as a wireless capsule endoscope. Current research mainly focuses on single-object tracking or multi-object tracking using the same magnets, which make it difficult to identify each target based on only the position information. In this paper, we proposed a multiple objects positioning and identification method based on the magnetic tracking system. The tracking system is built based on a magnetic sensor array. The multi-magnet tracking method has been applied to estimate the position and orientation information of each magnet by using the Levenberg-Marquardt algorithm. In this method, each magnetic target has a different magnitude of the magnetic moment. During the tracking, each magnet can be identified with its magnetic moment value. The feasibility of the proposed method is verified by simulation and experimental results.

Previous works investigated particle trajectories in hard disk drives (HDDs) with the actuator arm and the head gimbals assembly at a fixed position. Actually, internal fluid field characteristics of HDDs can be greatly changed by the arm swing during track-seeking operations, which can affect particle trajectories and trapping status. In this paper, using the dynamic mesh method in a 2.5 in HDD for the first time considers the arm swing in the computational fluid dynamics (CFD) simulation. Al2O3particle trajectories in this HDD are studied by the CFD solver FLUENT with user-defined functions. The trapping criterion for Al2O3particles is used as a boundary condition for colliding surfaces. Simulation results reveal that the particle undergoes a larger number of collisions with the disk surface for the average seek time of 12 ms than for the average seek time of 6 ms. In addition, the faster the arm swings, the larger the number of particles that gather near the arm, and the shorter time it will take for particles to be trapped. Moreover, particle-surface collisions can successively…

Demagnetization fault detection of in-service permanent magnet synchronous machines (PMSMs) is a challenging task, because most PMSMs operate under nonstationary circumstances in industrial applications. A novel approach based on tracking characteristic orders of stator current using Vold–Kalman filter is proposed to detect the partial demagnetization fault in PMSMs running at nonstationary conditions. The amplitude of envelope of the fault characteristic orders is used as fault indictor. Experimental results verify the superiority of the proposed method on the partial demagnetization online fault detection of PMSMs under various speed and load conditions.

The high-frequency transformer is an important device in the modern electrical system, and the performance requirement for this device has recently become more and more important. Thus, it is necessary to model high-frequency transformer accurately and the key is to calculate the capacitance. In this paper, the capacitance of the foil winding in the high-frequency transformer is calculated by using the static capacitance model and the finite-element method (FEM), respectively. The relative error is about 0.4% by comparing the FEM. To calculate the capacitance of solid wire accurately, a new static capacitance model is proposed considering that the actual electric field lines gradually changed in the windings. Compared with the finite-element model, the proposed model is more accurate than the traditional models. The capacitances of two wires calculated by the proposed model and the finite-element model are 115.56 and 114.76 pF, respectively. The dynamic capacitance of transformer windings is analyzed by considering the uneven charge distribution. A dynamic capacitance analytical…

In this paper, an improved design of an ironless axial flux permanent magnet synchronous generator (AFPMSG) is presented for direct-coupled wind turbine application considering wind speed characteristics. The partial swarm optimization method is used to perform a multi-objective design optimization of the ironless AFPMSG in order to decrease the active material cost and increase the annual energy yield of the generator over the entire range of operating wind speed. General practical and mechanical limitations in the design of the generator are considered as optimization constraints. For accurate analytical design of the generator, distribution of the flux in all parts of the machine is obtained through a modified magnetic equivalent circuit model of AFPMSG. In this model, the magnetic saturation of the rotor back iron cores is considered using a nonlinear iterative algorithm. Various combinations of pole and coil numbers are studied in the design of a 30 kW AFPMSG via the optimization procedure. Finally, 3-D finite-element model of the generator was prepared to confirm the validity…

This paper proposes a six-phase surface-mounted permanent-magnet machine with a 24-slot/10-pole fractional slot winding, which not only eliminates the air-gap flux subharmonics, but also minimizes the effect of slot harmonics, which highly affect both the core and magnet losses. The six-phase winding design also offers an improved drive train availability for electric vehicle applications due to its inherent high fault-tolerant capability. When compared with a three-phase design, the proposed winding offers approximately 3.5% improvement in torque density, a significant reduction in both the core and magnet losses, and an improved overall efficiency. The proposed winding is deduced based on the stator shifting concept of two 12-slot/10-pole stators with single tooth windings. The coil span of the resulting machine will be two slots, which stands as a compromise between single tooth and distributed windings. The concept of stator shifting is first presented, and then, a prototype machine is designed and simulated using the 2-D finite-element analysis to validate the proposed concept.…

Consequent-pole permanent magnet (PM) synchronous machines (PMSMs) provide especial features by the use of alternate PM and ferromagnetic poles. The design of these types of electric machines requires an accurate model due to the asymmetrical flux distribution in the air gap under adjacent poles. The equivalent magnetic circuit technique can hardly offer an accurate model for consequent-pole PMSMs. To this end, a 2-D analytical model is presented for consequent-pole slotted stator PMSMs to accurately compute the magnetic field distribution due to PMs and armature reaction. The slotting effects and the tooth-tip effects are taken into consideration by using the subdomain technique. The proposed model is used to calculate the magnetic flux density distributions of three consequent-pole PMSMs: an 8-pole, 9-slot machine with a non-overlapping winding; a 4-pole, 15-slot machine with an overlapping winding; and a 10-pole, 12-slot machine with a non-overlapping winding, each with three different magnetization patterns, i.e., radial, parallel, and Halbach. Based on the magnetic flux…

This paper concerns a coupled analysis of the stray magnetic field and the external housing vibration of a synchronous machine to detect rotor short-circuit faults. Indeed, in addition to the possibility to measure these parameters with non-invasive equipment, these two measures depend on the air-gap flux density that is directly impacted by the short circuits of any nature. Hence, correlating these two quantities, it is achievable to confirm or discard an eventual motor fault. This method allows both to develop an analysis of non-invasive manner and to establish the magnetic state of a synchronous generator in normal operation. The experimental survey of stray magnetic field and housing vibration spectrum is shown as a promising alternative at low cost and easy to implement and to determine, for instance, rotor turn-to-turn winding faults. Faulty and healthy signatures are drawn from the measured spectra to determine a degree of healthy state of the synchronous machine.

Soft magnetic properties of magnetic cores assembled with Fe81.8Cu1.0Mo0.2Si4B14nanocrystalline alloy ribbon are discussed. The nanocrystalline alloy ribbon was cast in an amorphous phase by a melt quenching method, and a nanocrystalline phase was obtained by high-heating rate annealing. A medium-size toroidal core assembled with this nanocrystalline alloy ribbon exhibits magnetic flux density B800at 800 A/m of 1.74 T, core loss P16/50at 50 Hz, and at 1.5 T of 0.29 W/kg. A racetrack-shaped core, which includes curved and straight sections in the same core, exhibits core losses at 1.0 T and at 400 Hz and 1 kHz of 1.5 and 5 W/kg, respectively. These core losses are as low as those of Fe-based amorphous alloys. A medium-size toroidal core assembled with this nanocrystalline alloy ribbon, secondarily annealed under a perpendicular magnetic field, exhibits core loss P2/10kat 0.2 T and at 10 kHz of 2 W/kg. This value of core loss is one of the lowest values for the metallic magnetic cores, which have a saturation induction Bshigher than 1.5 T. A core assembled with this material can be…

Field-programmable gate arrays (FPGAs) based on static random access memory (SRAM) are more common than other types, including flash and anti-fuse, because of their infinite configurability and high performance. However, following the scaling down of CMOS technology, standby power of the CMOS circuits are becoming crucial. Logic circuits based on magnetic RAM (MRAM) can be an attractive replacement for SRAM-based logics thanks to their zero leakage and CMOS compatibilities. Furthermore, in FPGA design, using MRAM logics instead of SRAM logics results in some more advantages including non-volatility and high radiation reliability. In this paper, effects of radiation-induced soft errors on MRAM-based FPGAs (MFPGAs) are taken into account. Soft error tolerance of the previous MFPGAs are discussed and a new MFPGA structure is proposed. It is shown that the proposed non-volatile, low-power, and high-speed MFPGA is highly robust against radiation-induced soft errors. It is also shown that the proposed MFPGA offering a high radiation robustness does not incur a considerable design overhead…

Magnetic flux leakage (MFL) method is the most widely used non-destructive testing techniques for detection and characterization of defects in product transmission pipelines. The maximum safe operating pressure is a crucial parameter in practice, which is predicted with respect to the length, width, and depth of defects. In a previous work, an algorithm is devised to detect and estimate the width of the defect based on MFL signals. In this paper, an efficient method based on axial MFL level contours is devised to estimate the length of the defect. This method uses the patterns of signal level contours in the region corresponding to the defect's area. In addition, a Gaussian radial basis function neural network (NN) is trained to approximate the depth of the defect. The NN is fed with the estimated length, width, and signal peak-to-peak values, and the output of the network is the estimated depth. The proposed detection and estimation method is applied to MFL measurements to detect and determine the sizing of metal loss defects. The efficacy and accuracy of the proposed methods are…

Spin-transfer-torque magnetic random access memory (STT-MRAM) is a promising emerging memory technology because of its various advantageous features such as scalability, non-volatility, density, endurance, and soft-error immunity. However, high write energy and long write latency are the major obstacles for this technology. The long write latency of the STT-MRAM is primarily due to two reasons. First, the bit-cell switching is asymmetric, which means that one write direction is significantly slower than the other. Second, the stochastic switching behavior of the bit-cell mandates a significant margin for a target write error rate (WER). In this paper, we propose static and dynamic circuit-level techniques to reduce the overall write latency. The static technique reduces the impact of write asymmetry by increasing the write current only for the slow writes. The dynamic technique additionally targets the write margin by dynamically increasing the write current in a stepwise manner to mitigate the negative impact of the stochastic switching behavior. Experimental results show that our…

This paper investigates the contribution of current harmonics to average torque and torque ripple in switched reluctance machines. In order to account for the magnetic saturation under different current amplitudes and waveforms, the self-inductances are obtained by finite element calculation using frozen permeability method and subsequently used in the analytical derivation of an instantaneous torque equation based on the Fourier series analyses. Five different current waveforms are also considered in order to identify the contribution of current harmonics. It is found that the average torque is mainly contributed by the dc, first, and second current harmonics. Meanwhile, the fourth and fifth current harmonics have high influence on the torque ripple but much lower contribution to the average torque. In addition, the optimization of current waveforms in terms of the maximum average torque under a given RMS current is also discussed. All analytical analyses are validated by direct nonlinear finite element and experimental results.

This paper proposes a method of reducing total torque ripple by magnets shifting. The key of this method is to consider the reluctance torque ripple, because the reluctance torque ripple is the main source of torque ripple in inset permanent magnet synchronous motor. This method is realized by appropriately choosing Repeating Unit, which indicates a group of poles producing torques with consistency in waveforms and phases. Meanwhile, the uniform analytical expressions of torques with magnets shifting are established, including cogging torque, reluctance torque, and total torque. Moreover, the total torque ripple can be reduced greatly, and the average total torque loss is acceptable when one pole-pair is chosen as one Repeating Unit and the shifting angles of Repeating Unit are 3.75 and 1.875 mechanical degrees. These theoretical analyses are verified by the finite-element method.

This paper presents a dual-stator brushless doubly fed induction generator-based stand-alone wind energy conversion system (DSBDFIG-SA-WECS). With the advantages of compact structure, high reliability, and low cost, the DSBDFIG-SA-WECS shows great potential in wind energy applications. Based on the traditional stator-flux-oriented control (SFOC), an improved direct voltage control (DVC) is proposed for stand-alone operation. Performance analysis is carried out to evaluate SFOC and DVC in the aspects of control objects, orientation, feedback, and parameters involved. The DVC method is simple, robust, and cost-effective with the outer stator current sensors eliminated, and there are no extra parameters involved that the control performance can be enhanced. Fair comparisons are made in simulation to demonstrate better performance of the proposed DVC, and the effectiveness of DVC is further validated by experiment under variable speed condition.

In this paper, the end effects of a partitioned stator flux reversal permanent magnet (PM) machine with a surface-mounted PM (SPM) inner stator and a consequent pole PM (CPM) inner stator are comparatively analyzed. It is found that due to higher saturated inner stator steel in a CPM machine, it suffers from larger end effect than the SPM machine. Influence of armature reaction on end effect is investigated by a finite-element (FE) analysis, together with that of aspect ratio, i.e., axial stack length to stator outer diameter. Furthermore, it is found that in the CPM machine, the optimal PM arcs for the highest average electromagnetic torque predicted by 2-D and 3-D FE are different due to the variation of end effect with PM arc. Prototypes with both SPM and CPM inner stators are built and tested to verify the FE analysis.

The use of a horizontal arrangement of wall shunts is proposed in this paper as a cost-effective way to reduce the stray losses in power transformers. This paper compares the performance of horizontal wall shunts with the available alternative (vertical shunts). A 3-D finite-element analysis (FEA) is used for the calculation of stray losses in tank walls, and other structural parts. A novel hybrid numerical/analytical method is proposed for the calculation of stray losses inside the magnetic shunts. The proposed method is based on the double Fourier series expansions of the magnetic field distribution at the surface of the shunts, which is determined using 3-D FEA. A 200 MVA power transformer is investigated as a case study where the stray losses are calculated with and without the vertical and horizontal shunts. A parametric FEA is carried out to find the optimal placement of the horizontal shunts on the tank walls. Results show that the proposed horizontal magnetic shunts arrangement are as effective as the conventional vertical shunts in reducing the stray losses while reducing…

This paper presents the analysis of a brushless doubly fed reluctance machine (BDFRM) for renewable energy applications with an emphasis on the rotor design. The BDFRM stator includes two sets of windings, i.e., the control winding (CW) and power winding (PW). The PW is connected to the grid, while the CW links the grid by a power converter of fractional rating to regulate the operating speed. This reduces the converter cost, and the brushless configuration enhances the reliability. In this paper, the reluctance rotor of the BDFRM, which is similar to that of a synchronous reluctance machine, is designed and analyzed in order to improve the performance. The influence of the total MMF and its allocation to the two stator windings are also discussed in relation to the machine performance. Finite-element analysis is used for performance simulation. The experimental study validates the proposed design for a small BDFRM.

Surface-mounted permanent-magnet (PM) synchronous motors are widely applied to electric vehicles, where iron losses reduction is a crucial target. This paper proposes a new method of PM shape optimization to reduce the harmonics of magnetic field and, hence, iron losses. The proposed method is based on the analytical calculation of magnetic field distribution with a non-uniform PM shape, which can save much computation time compared with the parameter sweep method. The validity of the method is verified by 2-D finite-element analysis.

The application of magnetic nanoparticles (MNPs) in a biomedical context is a rapidly developing field. The MNP suspended in aqueous liquids can be introduced into the blood stream or the tissue of a patient, allowing for the utilization of magnetic effects, such as magnetic losses, magnetic forces, and localized sources of magnetic fields.

The knee point in the B-H curve of a permanent magnet (PM) is considered crucial in electric motor applications. In the case of severe fault conditions, such as overheating or a short circuit in electric motors, the working point might fall below the knee point causing irreversible demagnetization of the PM. Hence, the remanence flux decreases and the motor operation would be reduced or stalled. In this paper, two demagnetization models of PMs are investigated, i.e., a linear model and an exponential model. Demagnetization curves for NdFeB were measured at temperatures varying from room temperature to 180°C. It was found that all the parameters in the exponential model, including Br, Hjc, μr, and the fitting parameter K1, are temperature dependent. Therefore, an exponential model can be developed as a function of temperature which allows a more efficient implementation within electric motor applications using PMs. However, comparison of the exponential and linear models indicates that the latter has a better accuracy near the knee point for the demagnetization curves of NdFeB…

Magnetostriction of grain-oriented 3% SiFe sheets was measured prior to assembly into model transformer cores. Core vibration was measured using a laser scanning vibrometer and harmonic spectra of acoustic noise were evaluated from the microphone outputs. Explanations show why no correlation exists between vibration harmonics profiles and A-weighted acoustic noise spectra. High localized vibration did not cause high noise due to phase differences in surface vibrations, and it is shown that this is the main reason why the A-weighted noise of a three-phase core can be less than that of an equivalent single-phase core. Noise from cores assembled from low magnetostriction materials was not always lowest because of the variable effect of electromagnetic forces.

The detection of the inner corrosion of steel construction, specifically backside corrosion of a steel plate, is highly demanded to maintain safety. Eddy-current testing (ECT) is widely used as a nondestructive testing and an evaluation method for detecting surface and subsurface flaws. However, the ECT is usually applied to non-ferromagnetic materials, but has difficulties when applied to ferromagnetic materials with high permeability, since the skin depth is smaller, and the signal-to-noise ratio (SNR) decreases due to magnetic flux fluctuation. In this paper, we developed a magnetic probe using an anisotropic magnetic resistance (AMR) sensor with the sensitivity of 1 nT/√Hz that can detect inner corrosion at extremely low frequency. We also developed an analysis method using magnetic spectroscopy to delete the magnetic flux fluctuation. To improve the SNR of the detected signal, a small cancellation coil around the AMR sensor canceled the applied magnetic field directly coupled to the sensor. The frequency of the applied magnetic field ranged from 1 Hz to 1 kHz. The sensor output…

This paper proposes new fault-tolerant permanent magnet vernier (FTPMV) machines with Halbach array. By utilizing a flux concentration of Halbach array, the performances of the proposed machines are significantly enhanced. In addition, influences of rotor yoke materials on performances of the proposed machines are investigated, revealing that both ferromagnetic and nonmagnetic rotor yokes can be applicable to the FTPMV machines. Significant torque and power factor enhancements can be achieved in the proposed FTPMV machines with a ferromagnetic rotor yoke and a nonmagnetic rotor yoke, respectively. In addition, the reduced magnetic gearing effect in the proposed nonmagnetic rotor yoke machine can be compensated by the flux concentration of Halbach array, thus enabling the machine to obtain comparable torque capability with the existing one. The electromagnetic performances of the existing and proposed machines are analyzed and compared by using the time-stepping finite-element method, verifying the effectiveness of the theoretical analysis.

Owning to its extremely long endurance, small size, cost-effective employment, easy, and fast transported properties, the merits of autonomous underwater vehicles (AUVs) exceed those of manned underwater vehicles. Therefore, it has become an indispensable member in navies throughout the world, as well as with oceanographic research, commercial resource explorations, and especially the underwater search and rescue (SAR) sectors. Up to date, the tragic MH370 and QZ8501 flight incidents have dramatically increasing the awareness of high-performance SAR equipment, which in turn will stimulate the states party to the incident to urgently upgrade their shallow- and deep-sea SAR equipment. To extend the range (endurance) and shorter the searching period for the next generation SAR AUV, a sea water cooled high-power density magnetically slotless permanent magnet brushless motor is proposed and integrated with pump-jet's impeller to achieve designated shaftless pump-jet propulsor. In this paper, the developed shaftless pump-jet propulsion system is applied in Naval University of Engineering…

Zeroth mode of vibration is investigated in low-speed high-torque surface-mounted permanent magnet (PM) machines with non-overlapping concentrated windings. Magnetic field distribution in the air gap is computed using time-stepping finite-element analysis, and Maxwell stress tensor is then employed to calculate the radial force density. Based on the time variation of the mean value of the radial force density spatial distribution, the zeroth-order radial forces are studied. Simple structural equations are used to compare the stator deformations for the machines under investigation. Contribution of the zeroth mode to produce vibration is analyzed and compared with the lowest non-zero mode. The influence of pole and slot combinations and the effect of rectifier load are discussed. This paper is carried out to investigate whether or not the zeroth-order radial forces can be of importance in the presented surface-mounted PM machines that are not connected to pulsewidth modulation (PWM) converters.

Ni0.2Mg0.8-xZnxFe2O4(x = 0.2, 0.4, 0.6, and 0.8) ferrites are synthesized via microwave solid-state reaction method. The diffraction study confirms the cubic spinel structure of samples. The fracture surface is analyzed by scanning electron microscope. In addition, the X-band (8.4-12 GHz) electromagnetic interference (EMI) properties are investigated. The NiMgZn ferrite system attributes the total EMI shielding effectiveness (SET) altering between 9 and 12 dB, which provides the electromagnetic shielding applications. The variation of electromagnetic parameters such as dielectric constant (ε'), loss (ε"), magnetic permeability (μ'), and magnetic loss (μ") as a function of X-band frequency is elucidated.

A hybrid method combining 2-D finite-element (FE) method and analytical model is proposed for permanent magnet (PM) eddy current loss calculation in interior PM machines under pulsewidth modulation (PWM) voltage source inverter (VSI) supply, in which the PM eddy current reaction effect and PM axial segmentation are taken into consideration. First, the 2-D time-stepping (TS) FE analysis results considering and neglecting PM eddy current under PWM VSI supply are compared so that the cause of PM eddy current loss, the increase of high-order armature current components due to PM eddy current effect, and the decrease of the high-order components in average flux density due to leakage flux are revealed. Second, an analytical model for PM eddy current loss calculation using voltage input is deduced with the average flux density as input and a leakage flux factor is introduced in the model to meet the real case in PM machine. Moreover, the 3-D frequency FE analysis is used to verify the derived model. Third, the ratio between the average flux density and the imposed flux density is defined…

This paper proposes an analytical method that combines the superposition concept and the subdomain method to predict the cogging torque of permanent magnet (PM) machines with a rotor eccentricity. The original eccentric machine is first divided into several sections along the air-gap circumferential direction. Then, the equivalent air-gap lengths of all sections will be determined and individually used to build up a series of concentric models representing each section. By the superposition method, the air-gap flux density of the original eccentric machine can be synthesized from that of every concentric model predicted through the subdomain method. Consequently, the cogging torque can be predicted by the integral of Maxwell stress tensor based on the synthesized air-gap flux density. To prove the efficacy of the proposed method, two fractional-slot PM machines with different slot/pole number combinations are taken as examples, together with the validation of a finite-element analysis.

A double-stator flux-switching permanent magnet (DS-FSPM) machine using ferrite is proposed to replace an interior permanent magnet synchronous motor (IPMSM) on hybrid electric vehicles. A conventional FSPM machine is designed, and its torque characteristic is analyzed by a frozen permeability method. It is verified that magnetic saturation causes the reduction of flux linkage generated by PM and leads to the deterioration of electromagnetic torque. A DS-FSPM machine is effective for magnetic saturation because of its unique structure and makes the improvement of efficiency and power density. The proposed DS-FSPM machine achieves distinct performance enhancement compared with an IPMSM, even by utilizing ferrite PM.

Permanent magnet brushless (PMBL) motors have been widely applied in electric vehicles, since they inherently offer high efficiency, high power density, and free maintenance. However, because of the existing problem of uncontrollable flux, their constant-power speed range is relatively narrow. In order to gain a wide speed range, by employing the new concept of the flux-intensifying effect, a new flux-intensifying PMBL (FI-PMBL) motor is proposed in this paper. The proposed motor is innovatively designed, where the topology of two-layer segmented PMs and non-uniform air gap are adopted to make the corresponding d -axis inductance Lq, which is far different from the conventional interior PM motor. By using the finite-element methods, the electromagnetic performances of the proposed motor are evaluated in detail. Simulation results show that the proposed motor possesses preferable flux-weakening capability and wide speed range. In addition, the experimental results of the FI-PMBL prototype are given to verify the performances of the motor.

Despite decades of research and development of Alnico alloys, significant uncertainties in the underlying structure-property relationships remain. Here, we report on the effects of Ti on the Alnico microstructure and nanostructure, and the corresponding influence on magnetic properties. We show that Ti fosters the conditions resulting in the formation of Cu-Ni-rich bridges in the α1phases between the α2phases. For Alnico containing Ti, a typical chessboardlike morphology with Cu-Ni-rich bridges is observed, whereas in the absence of Ti, the α1phases connect to each other readily, especially with a high Co concentration, and a mazelike morphology with Cu-rich white-plate precipitates rather than Cu-rich bridges is observed. Furthermore, in Alnico containing Ti, an inhomogeneous distribution of Ni is found in the α2phases, including loops with high Ni concentration surrounding the α1phase and high concentrations in the bridges as well. An increase in the Cu concentration is also observed in the loops around the α1phases (Ni-Cu loops), and direct contact between the Cu-Ni-rich bridges…

This paper proposes the optimal design of a new interior permanent magnet (IPM)-type brushless dc (BLdc) motor using low-price ferrite magnets. The new IPM motor has the structure of C-type ferrite magnets featuring a flared shape to obtain high motor performance. To maximize the flux density and minimize the torque ripple, the flared-shape rotor structure is optimized by algorithms, such as the Kriging method based on Latin hypercube sampling and a genetic algorithm. The analyses of basic and optimal designs utilize a 3-D finite-element method, and then, the validity of the optimal design is verified through fabrication of actual prototypes.

Inductively coupled power transfer (ICPT) technology realizes energy transfer across relatively large air gap with magnetic coupling. However, the flexibility of traditional ICPT system is limited because only one-degree freedom is allowed. This paper proposes the design, simulation, and implementation of a novel multi-degree of freedom power pickup mechanism for ICPT system, which can receive power at arbitrary angle in space. The pickup mechanism is designed of regular tetrahedron structure, and the pickup coils are fixed on its six edges. An optimal winding strategy of the six coils is proposed to increase the output power capacity through theoretical analysis and Maxwell simulation. The experimental results show that the pickup mechanism has a good power pickup capacity, and system efficiency is relatively high at any angle of the pickup mechanism.

In magnetic flux leakage type nondestructive testing (NDT), there exists velocity effect, which may cause the distortion of the defect signals and reduce the estimated accuracy of defect profile. In this paper, the distortions are analyzed by using finite-element method (FEM), and the influence of velocity effect on reconstruction of defect profiles is discussed under the condition of the simulation and experiment. This paper proposes an effective method for reconstructing arbitrary defect profiles in different velocity conditions. In the proposed method, the FEM considering velocity effect is employed as the forward model. A weighting conjugate gradient algorithm is applied to update the defect profile iteratively in two gradient directions. The algorithms effectiveness is tested on a series of artificial defects under various velocity conditions. The results demonstrate that the proposed model can achieve the better reconstruction accuracy than the ignoring velocity effect models. The properties of the presented method are so stable and robust that they make our approach a…

Domain wall nanomagnet (DWNM)-based devices have been extensively studied as a promising alternative to the conventional CMOS technology in both the memory and logic implementations due to their non-volatility, near-zero standby power, and high integration density characteristics. In this paper, we leverage a physics-based model of a DWNM device to design a highly scalable current-mode majority gate to achieve a novel one bit full-adder (FA) circuit. The modeled DWNM specifications are calibrated with the experimentally measured data. The functionality of the proposed DWNM-based FA (DWNM-FA) is verified using a SPICE circuit simulator. The detailed analysis and the calculations have been performed to realize the proposed DWNM-FA delay and power consumption corresponding to the various induced input currents at different operating temperatures. The power-delay product of DWNM-FA is examined to tune the operation within the optimum induced input current region to obtain desired power-delay requirements over a range of 200 μA to 1 mA at temperatures from 298 to 378 K. Finally, the…

Linear induction motors (LIMs) are being gradually applied in the urban rail transit due to their simplified mechanical structure and feasibility for both low-speed and high-speed operations. Direct-torque control (DTC) is a classical control scheme that can be readily extended to LIMs. However, due to the high thrust ripple and poor dynamic performance for the low-speed operation, control performance of DTC is not satisfactory. This paper is to propose an explicit model predictive control to be combined with the DTC scheme. First, the LIM model is presented and discretized. Then, the LIM drive and its operating principle are discussed. Thirdly, the controller design, including control variables, and the objective function are depicted. Finally, both the simulation and the experiment are engaged for verifying the proposed control algorithm.

One detrimental by-product of heat-assisted magnetic recording writing is the creation of head contamination. Here, we present the current understanding of the driving forces, growth mechanisms, and growth rates of write-induced head contamination. The combination of an evaporation and condensation model with shear forces suggests a flow of lubricant on the head may precipitate contamination. The contamination is observed to grow in the head-media gap until it contacts the media surface, at which point an additional material pickup mechanism can be activated. Evidence of contact-induced transfer and a chemical reaction of the contamination is presented, and the impacts of contamination on head temperatures and thermal gradient is presented. Depending on the contamination properties, head temperatures may be increased substantially, leading to increased reliability risk. Consistent with previous analyses, we find that contamination may increase media thermal gradient.