Search Results (11)

This report is on Co and Ti substituted M-type barium and strontium hexagonal ferrites that are reported to be single phase multiferroics due to a transition from Neel type ferrimagnetic order to a spiral spin structure that is accompanied by a ferroelectric polarization in an applied magnetic field. The focus here is the nature of magnetoelectric (ME) interactions in the bilayers of ferroelectric PZT and Co and Ti substituted BaM and SrM. The ME coupling in the ferrite-PZT bilayers arise due to the transfer of magnetostriction-induced mechanical deformation in a magnetic field in the ferrite resulting in an induced electric field in PZT. Polycrystalline Co and Ti doped ferrites, Ba (CoTi)_x Fe_12−2xO_19, (BCTx), and Sr (CoTi)_x Fe_12−2xO₁₉ (SCTx) (x = 0–4) were found to be free of impurity phases for all x-values except for SCTx, which had a small amount of α-Fe₂O₃ in the X-ray diffraction patterns for x ≤ 2.0. The magnetostriction for the ferrites increased with applied filed H to a maximum value of around 2 to 6 ppm for H~5 kOe. BCTx/SCTx samples showed ferromagnetic resonance (FMR) for x = 1.5–2.0, and the estimated anisotropy field was on the order of 5 kOe. The magnetization increased with the amount of Co and Ti doping, and it decreased rapidly with x for x > 1.0. Measurements of ME coupling strengths were conducted on the bilayers of BCTx/SCTx platelets bonded to PZT. The bilayer was subjected to an AC and DC magnetic field H, and the magnetoelectric voltage coefficient (MEVC) was measured as a function of H and frequency of the AC field. For BCTx-PZT, the maximum value of MEVC at low frequency was ~5 mV/cm Oe, and a 40-fold increase at electromechanical resonance (EMR). SCTx–PZT composites also showed a similar behavior with the highest MEVC value of ~14 mV/cm Oe at low frequencies and ~200 mV/cm Oe at EMR. All the bilayers showed ME coupling for zero magnetic bias due to the magnetocrystalline anisotropy field in the ferrite that provided a built-in bias field. Full article

This paper introduces an effective method to improve the performance of a proton exchange membrane fuel cell (PEMFC) system powering a switched reluctance motor (SRM). Problems arise in this system due to the inherent torque and current ripples of the SRM, which result from its saliency and nonlinear magnetic characteristics. Another cause for these ripples is the unsmoothed DC voltage applied to the SRM caused by the switching operations of the DC-DC converter. These ripples are reflected in the PEMFC, leading to more losses and a reduced lifespan. Key parameters that can help mitigate torque and current ripples include the appropriate turn-on and turn-off angles of the SRM phases, as well as the DC-link voltage controller gains. This paper investigates three objectives to compare their effects on the PEMFC system: the SRM torque ripple factor, the DC-link voltage ripple factor, and the PEMFC current ripple factor. These objectives are optimized individually using the single-objective particle swarm and stochastic fractal search algorithms. Additionally, the multi-objective Lichtenberg and multi-objective Dragonfly algorithms are applied to optimize the three objectives concurrently. The optimal decision parameters are obtained from the Pareto front solution using the technique of the order of preference by similarity to the ideal solution method. The final results demonstrate that significant enhancement in the PEMFC current ripples and DC-link voltage ripples can be achieved by appropriately selecting the decision parameters using any proposed objective. Full article

We carefully investigated the effects of La-Co co-substitution and magnetic field pressing (MFP) on the structural and magnetic properties of SrM hexaferrites. Samples composed of Sr_1−xLa_xFe_12−xCo_xO₁₉ were sintered at 1230 °C for 2 h in air with sintering additives composed of 0.7 wt% CaCO₃ and 0.7 wt% SiO₂. A single M-type phase was confirmed to exist up to x = 0.3. Rietveld refinement revealed a slight decrease in lattice parameter a and the unit cell volume (V_cell) with an increasing x, while parameter c showed a significant decrease. The saturation magnetization (M_s) values increased from 70.90 to 72.40 emu/g with an increasing x from 0.0 to 0.15 and then decreased to 71.38 emu/g with further increasing of x to 0.3, while the anisotropy field (H_a) increased from 17.7 to 25.9 kOe, leading to a continuous increase in the intrinsic coercivity (H_ci), from 3.52 to 5.00 kOe, respectively. Using the MFP process, the c-axis of M-type hexaferrite grains could be effectively aligned to the applied field direction, which significantly affected the microstructures and, thus, magnetic properties of samples. Unlike non-MFP samples, exhibiting a significant increase in the average grain size (d_avg) but almost unaltered average thickness (t_avg) with an increasing x from 0.0 to 0.3, MFP-processed samples exhibited almost unaltered d_avg values but a continuous decrease in t_avg. Consequently, the variation in remanent flux density (B_r) versus x followed that of M_s versus x and thus exhibited the highest B_r of 4.05 kG for x = 0.15, leading to the highest maximum energy product {(BH)_max} of 3.62 MGOe. With an increasing x from 0.0 to 0.3, the H_ci values continuously increased from 3.14 to 3.84 kOe mainly due to a continuous increase in H_a, although they were significantly lowered in comparison with those of non-MFP samples because of a large increase in B_r for a given composition x. A higher M_r/M_s ratio always resulted in a larger (BH)_max in our samples regardless of x. A careful comparison of the microstructures and magnetic properties between MFP and non-MFP samples provided valuable insights into a broad area of permanent magnet optimization. Full article

The effects of La-Co co-substitution on the structural and magnetic properties of strontium M-type hexaferrites (SrM) were carefully investigated for the Sr_1−xLa_xFe_12−xCo_xO₁₉ (0.0 ≤ x ≤ 0.3) polycrystalline samples prepared by solid-state reaction in air. Without the use of sintering additives, La-Co co-substituted SrM single phases could be obtained from polycrystalline bulk samples by employing proper processing conditions. The lattice parameter a initially increases with increasing x from 0.0 to 0.1 but gradually decreases with increasing x to 0.20, and then remains almost unaltered up to x = 0.3; the lattice parameter c monotonously decreases with increasing x from 0.0 to 0.25, but it turns to an increase when x = 0.3. The reduction in c/a ratios and V_cell values with increasing x up to x = 0.25 are obviously attributable to the decreasing size effect resulting from La³⁺ substitution at the Sr²⁺ site, which surpasses the increasing size effect due to Co²⁺ and Fe²⁺ occupancy at the Fe³⁺ site. Meanwhile, with increasing x from 0.0 to 0.3, while the saturation magnetization (M_S) continuously decreases from 75.90 to 72.07 emu/g, the magnetic anisotropy field (H_a) increases from 20.1 to 24.7 kOe, leading to an increase in the intrinsic coercivity (H_ci) from 2.68 to 3.99 kOe. The gradual increase in H_a with x, probably caused by a gradual decrease in the crystallographic symmetry, is inversely proportional to the variation in the c/a ratios up to x = 0.25 as usual except when x = 0.3, of which deviation needs further study. Full article

The torque ripple of a switched reluctance motor (SRM) limits its application in electric vehicles. This paper proposes a DITC system for SRMs based on a novel multilevel converter (MLC), which aims at the problem that the torque ripple cannot be effectively suppressed for the conventional direct instantaneous torque control (DITC) of an SRM due to the limitation of the DC bus voltage in the asymmetric half-bridge converter (AHBC) and the single control strategy formulated in the commutation region. Based on the advantages of fast excitation and fast demagnetization for the proposed MLC and the torque distribution characteristics for each phase winding in the commutation region, a novel torque hysteresis control strategy is developed to improve the torque-following ability of the DITC and achieve the purpose of minimizing the torque ripple in the commutation region. In addition, multiobjective optimization control of the motor is carried out to improve the efficiency of the DITC system while suppressing the torque ripple. The effectiveness of the proposed SRM drive scheme is verified by experiment, which is of great significance for the application of SRMs in electric vehicles. Full article

A series of charge-balanced Si⁴⁺-M^1+,2+ (M = Mg²⁺, K⁺, Li⁺) substitution compositions with the chemical formulae of SrFe_12−2xSi_xMg_xO₁₉ (x = 0, 0.05, 0.1, 0.2), Sr_1−yFe_12−ySi_yK_yO₁₉ (y = 0.05, 0.1, 0.2), and SrFe_12−z(Si_0.6Li_0.6)_zO₁₉ (z = 0.05, 0.1, 0.2, 0.4, 0.6) were prepared using conventional ceramic processes. While the sole doping of Si with x = 0.1 (SrFe_12−xSi_xO₁₉ (x = 0.1)) causes a noticeable Fe₂O₃ phase formation, the co-doping of Si-Mg and Si-Li allow a single M-type phase formation with x up to x = 0.1 and z = 0.4, respectively. Notably, a 2.6% increase in the saturation magnetization was obtained for Si-Li-substituted SrM with z = 0.05—that is, SrFe_11.95Si_0.03Li_0.03O₁₉. Enhancement of the magnet performance can also be achieved when anisotropic permanent magnets are fabricated based on the substitution composition SrFe_11.95Si_0.03Li_0.03O₁₉. The remnant magnetic flux density was improved by 2.5% compared to that of the unsubstituted SrM (from 4207 to 4314 G). The maximum energy product (BH_max) value also increased from 4.24 to 4.46 M·G·Oe. The enhancement in permanent magnet performance is attributed to the increase in the M_S of SrM by the optimal Si-Li substitution. This is a promising result because enhanced permanent magnet performance is achieved with intrinsic magnetic property improvement. Full article

The quantification of steroid hormones of individual zebrafish (Danio rerio) provides perspective to understand endogenous hormone function. A UPLC–TOF–MS method was developed to provide a reproducible, sensitive, and efficient assay to determine the concentration of steroid hormones, including cortisol, testosterone, androstenedione, 11-deoxycortisol, 11-deoxycorticosterone, and 17-hydroxyprogesterone in whole-body homogenates of each zebrafish. Solid-phase extraction was used to sample matrix clean-up and acquired a recovery from 89.7% to 107.9%. The analytes were separated on an Aquity BEH C18 column using gradient elution. Mass spectrometric analysis was performed by single reaction monitoring (SRM) using positive electrospray ionization mode. The total running time was 6 min, which was greatly shortened compared with a previously reported method. The developed method exhibited excellent linearity for all the analytes, with regression coefficients higher than 0.99. The limit of detection varied between 0.1 and 0.5 ng/L and the limit of quantification was 0.5–1.7 ng/L for all analytes. The precision of the method was assessed on replicate measurements and was found to be in the ranges of 1.9 % to 6.6% and 4.3% to 8.6%, for intra- and inter-day analysis, respectively. This method was validated according to FDA guidance and applied to determine steroid hormone levels in the tissue homogenate of zebrafish acutely treated with caffeine and ethanol. Full article

To investigate the influence of control and structure parameters on the starting performance of a switched reluctance motor, a 12/8 pole switched reluctance motor is analyzed in this paper. The novel field-circuit coupled finite element method of switched reluctance motor is proposed in the paper. The influence of the controller on the switched reluctance motor is considered. The influence of rotor initial position angle, starting mode, starting current, and structure parameters on the starting performance of the switched reluctance motor is studied using the field-circuit coupled finite element method. The starting performance of the switched reluctance motor is obtained under the different control and structure parameters. The alternating starting mode of single- and two-phase winding can improve the starting torque of switched reluctance motor (SRM). As the stator pole arc coefficient increases, the starting torque of SRM increases. The appropriate reduction of the air gap length can improve the starting torque of SRM. Experimental results of the prototype are compared with the calculation results, which verifies the reliability of the calculation method and accuracy of the calculation results. Full article

This paper presents a characteristics analysis and performance comparison of high-speed two-phase 4/2 and hybrid single-phase 4/4 switched reluctance motors (SRMs). Although the motors are advantageous as high-speed drives, both conventional structures have high torque ripple as a result of the presence of the torque dead zone. In this paper, solutions to the torque dead zone problem for each motor are discussed. For the 4/2 SRM, a wide-rotor stepper-type is adopted, while for the 4/4 SRM, the structure is changed to a hybrid by adding permanent magnets (PMs). Both motors have a non-uniform air gap to modify their inductance profile, which leads to the elimination of the torque dead zone. A finite-element method was used to analyze the characteristics of each motor. Then, the manufactured motors were tested through experiments, and lastly, their performance was compared. Full article

Switch reluctance (SR) motors attract attention as a motor that does not use permanent magnet material. So it is a strong candidate for electrical vehicle (EV) application. In EV application axial flux machines are preferred over radial flux machines due to high power density. In this Article novel axial field switched reluctance motor (AFSRM) design is presented which intend to improve the output torque by single flux path distribution in C- core stator. Unlike conventional radial field SRMs, the windings of the C-core stator can be individually wound without complex winding equipment. This topology has an 8/6 pole dual air gap single rotor and single C-core stator configuration without overlapping winding arrangement. Computer Aided Design (CAD) is used to calculate the phase inductance and average torque for a novel AFSRM topology. The two and three-dimensional Finite element (FE) analyses is carried out to validate obtained CAD results. Full article

This paper analyzes how distributed inverters can further increase the fault tolerance of switched reluctance traction drives. The drive under investigation is an outer-rotor direct-drive switched reluctance machines (SRM) for railway traction. The phases of SRMs are magnetically and to a certain extend electrically decoupled. Hence, in case of a fault inside a phase, the remaining phases can continue operation with reduced power. With the distributed inverter concept at hand, each coil of a phase is excited by its own modular inverter. This increases the redundancy, simplifies integration of machine and inverter, and enables a new degree of freedom regarding the control of the machine. Especially for electric drives used in railway traction or electric vehicles, redundancy avoids all the inconveniences of a standstill in case of a fault, enabling a so-called limp home capability. This paper shows, how open- and short-circuit faults of single coils or modules of the proposed drive influence average torque, torque ripple, and noise and vibration. Therewith, it will be shown that with the SRM and the distributed inverter it is possible to continue operation in case of the analyzed faults. Full article