Magnetic Arrangement Research Articles

Role of f-electrons in determining insulator to metal phase transitions of Ca(La1−xCex)2S4 (0 ≤ x ≤ 1) solid solution: A DFT + U study

For efficient usage of the rare earth-based materials in electronic or optoelectronic applications, their 4f electrons' behaviors must be understood properly. We have presented Hubbard U corrected density functional theory (DFT+U) study of structural, magnetic, electronic, and optical properties of a rare-earth chalcogenide system, Ca(La1−xCex)2S4 (0 ≤ x ≤ 1). A unique site selection technique based on local magnetic moment arrangements was applied to build the atomic arrangements for a Ce doped Ca(La1−xCex)2S4 solid solution. The incorporation of f-electrons by Ce doping modifies the properties of the parent compound, CaLa2S4. In conjunction with the DFT + U method, we applied spin–orbit coupling to determine the magnetic ground state. The inclusion of 25% Ce transforms the non-magnetic parent compound to an antiferromagnetic (AFM) compound, and AFM magnetic ordering remains unaltered throughout the whole solid solution series. In addition, these compounds also undergo insulator to semiconducting to metallic phase transitions as Ce concentration increases. While CaLa2S4 is an insulator, Ca(La1−xCex)2S4 with x = 0.25 and 0.50 are n-type semiconductors, and on the other hand, compounds with x = 0.75 and 1.0 are found to have metallic band structures. The Ce atoms in these materials were found to be in a mixed valence state, Ce3+/4+. We explained these phase transitions from the calculated electronic structures. In addition, we have presented an explanation for the experimentally observed red-orange colors of Ca(La0.25 Ce0.75)2S4 and CaCe2S4 compounds.

Comparative Analysis of Parallel Hybrid Magnet Memory Machines with Different PM Arrangements

This paper presents a comparative analysis of two parallel hybrid magnet memory machines (PHMMMs) with different permanent magnet (PM) arrangements. The proposed machines are both geometrically characterized by a parallel U-shaped hybrid PM configuration and several q-axis magnetic barriers. The configurations and operating principles of the investigated machines are introduced firstly. The effect of magnet arrangements on the performance of the proposed machines is then evaluated with a simplified magnetic circuit model. Furthermore, the electromagnetic characteristics of the proposed machines are investigated and compared by the finite-element method (FEM). The experiments on one prototype are carried out to validate the FEM results.

Influence of dental magnets on human brain activity: A quantitative EEG analysis.

The magnetic field is known to attenuate mental depression, but it is not clear on the effect of dental magnets on human brain activity. Therefore, this study was to determine the influence of magnetic field from intraoral magnets on the human brain activity by analyzing the changes in alpha waves. Twenty complete denture male patients aged between 50 and 60 years were included after their consent. The neodymium-iron-boron sintered magnet was incorporated into the existing mandibular denture bilaterally in canine region. The participants were subjected to electroencephalogram (EEG) and the output measured alpha waves at three phases: (i) without placement of magnets (WM0), (ii) 30 days post-magnet placement in the mandibular denture (WM), and (iii) after 6 months post-removal of magnets (WM6). The data obtained was skewed (non-parametric), and hence multivariate analysis using Friedman test, and bivariate analysis using Wilcoxon signed rank test and Mann-Whitney test were done to assess the significant difference among the groups. The comparison of alpha waves between different phases showed a significant difference in all the pairs (p<.05) except WM-WM6. Comparison of alpha waves between right and left hemisphere showed no statistically significant difference (p>.05). We concluded that dental magnets had an influential effect on the alpha waves in the brain on both the left and right hemispheres. The removal of dental magnets retained the changes in brain activity even after 6 months of removal, denoting the alternative therapy to management of mental depression.

Recovery of Magnetic Catalysts: Advanced Design for Process Intensification.

The design of microdevices in which components with magnetic character must be separated and recovered from reactive media benefits from the advantages of microfluidics and meets the criteria for process intensification; however, there are open questions, such as the design of the most appropriate magnet arrangement, that need further research in order to increase the magnetic gradient exerted on the particles. Herein, we focus on the continuous recovery of magnetic microparticles, that can be used as support to facilitate the recovery of biocatalysts (magnetic microcatalysts, MMCs) from biological fluids. We analyze and compare the performance of two typical magnetophoretic microdevices for addressing bead recovery: (i) annular channels with a quadrupole orientation of the permanent magnets (quadrupole magnetic sorter, QMS) and (ii) the standard design, which consists of rectangular channels with a single permanent magnet to generate the magnetic field. To this end, an experimentally validated computational fluid dynamics (CFD) numerical model has been employed. Our results reveal that for devices with the same width and length, the micro-QMS, in comparison to a rectangular channel, could accomplish the complete particle retrieval while (i) processing more than 4 times higher fluid velocities, treating more than 360 times higher flow rates or (ii) working with smaller particles, thus reducing by 55% the particle mass. Additionally, the parallel performance of ≈300 micro-QMSs fulfills the processing of flow rates as high as 200 L·h–1 while entirely capturing the magnetic beads. Thereby, this work shows the potential of the QMS advanced design in the intensification of the recovery of catalysts supports of magnetic character.

Contactless Mechanical Power Transmission Through the High-T c Superconducting Pinning Effect.

Mechanical power transmission (MPT) components are almost indispensable for every engineering equipment with motions. In order to satisfy some rigorous requirements, such as contamination free and zero leakage in the mixing process of biomedical solutions, a contactless MPT mode was proposed in this study based on the high-Tc superconducting flux pinning mechanism. It makes the stirring container with the driven part inside that can be totally isolated from the external environment. The physical principle of superconducting flux pinning effect was discussed firstly to explore a feasible structural scheme, which can completely restrain all the six degrees of freedom (DOFs) by the linkage of magnetic flux lines. Then, a measurement device was established to verify and investigate the proposed contactless MPT mode. The motion can be transferred synchronously from the superconducting driving part to the permanent magnet driven part since they are unified as an integrity through the pinned flux lines. The influence of driving speed, cooling clearance, and magnet arrangement on the transmitted torque was analyzed. The verified contactless MPT mode also has the advantages of self-stability and overload protection, which can avoid the drawbacks of traditional permanent magnetic transmission mode.

Catalytic Activity Enhancement of Cu-Zn-Based Catalyst for Methanol Steam Reforming with Magnetic Inducement

Magnetic inducement was applied during metal loading to enhance Cu-Zn catalysts for methanol steam reforming in the temperature range of 200–300 °C. The supports used in this study were the γ-Al2O3 support and CeO2-Al2O3 supports prepared under different magnetic environments. Cu-Zn loading between the north and south poles (N-S) on the CeO2-Al2O3 support, prepared between two north poles (N-N), led to the highest H2 production at 300 °C (2796 ± 76 µmol/min), which is triple that of Cu-Zn/CeO2-Al2O3 prepared without magnetic inducement and ~11-fold the activity of the Cu-Zn/Al2O3 reference catalyst. The N-S magnetic environment during metal loading leads to lower reduction temperatures and larger Cu(1+):Cu(2+) ratio. These results showed that the pole arrangement of magnets during metal loading could affect the catalytic activity of the Cu-Zn catalyst owing to its influence on the reducibility and the oxidation state of Cu active metal.

Large magnetocaloric effect in EuGd2O4 and EuDy2O4

Magnetization, heat capacity and direct measurements of the magnetocaloric effect show that EuGd2O4 and EuDy2O4 have a remarkably large magnetocaloric effect at cryogenic temperatures, owing to their high magnetic density and low ordering temperatures. The Gd derivative orders antiferromagnetically at TN = 4.6 K, while its magnetocaloric effect largely exceeds that of the reference refrigerant Gadolinium Gallium Garnet (GGG) above 5 K. The Dy derivative undergoes two phase transitions at TC1 = 3.65 K and TC2 = 4.7 K, respectively, which are the result of a peculiar magnetic arrangement: the first Dy sublattice is parallel to the crystallographic c-axis, while the Eu sublattice makes a variable angle from 0o to 45o with the direction of the second Dy sublattice that lies in the ab-plane. EuDy2O4 has a lower magnetocaloric effect than EuGd2O4, yet larger than GGG. Both ordering mechanisms are semi-quantitatively explained within the frame of a mean-field simulation, which takes into account the magnetic anisotropy strength of the participating magnetic ions.

Toward Less Rare-Earth Permanent Magnet in Electric Machines: A Review

Many electric traction drive systems (ETDSs) are driven by electric motors primarily composed of high-energy rare-earth (RE) permanent magnets (PMs), such as neodymium-iron-boron (NdFeB) and samarium-cobalt (SmCo). Given the high cost of RE materials, there is a great interest among various industry sectors in searching for breakthrough technologies that reduce the consumption of high-energy RE magnets in their electromechanical energy conversion systems. The reduction of the magnetic volume is typically realized either by replacing a portion of the high-energy RE magnet with the low-energy ferrite magnet (knows as hybrid structure) or by modifying the magnetic arrangement of the machine itself, where a portion of the physical RE magnets is removed and replaced by induced magnets (known as consequent-magnetic pole structure). For this purpose, this article presents a review of the current state-of-the-art motor typologies with less-RE PMs and their key design challenges, followed up by a series of recommended guidelines to overcome related design challenges.

Lattice symmetry breaking transition and critical size limit for ferroic orders in nanophase BiFeO3

Finite size effects on the ferroic orders in $\mathrm{BiFe}{\mathrm{O}}_{3}$ are studied by atomic pair distribution function analysis and magnetic measurements. While bulk rhombohedral $\mathrm{BiFe}{\mathrm{O}}_{3}$ exhibits ferroelectricity and antiferromagnetism with a cycloidal magnetic moment arrangement leading to zero magnetization and weak magnetoelectric coupling, $\mathrm{BiFe}{\mathrm{O}}_{3}$ nanoparticles with a size smaller than the spin cycloid period of 62 nm preserve their polar rhombohedral structure and develop ferromagnetism, thus exhibiting coexisting polarization and nonzero magnetization that enhances the magnetoelectric coupling. When the nanoparticles become smaller than 17 nm, however, their crystal lattice expands and becomes nonpolar cubic. They also become superparamagnetic and thus simultaneously cease exhibiting both ferroelectricity and ferromagnetism. Our findings shed light on the interaction between the lattice structure and ferroic orders in nanophase perovskites and also provide a rare example of a lattice symmetry breaking phase transition that determines their critical size.

Towards self-powered technique in underwater robots via a high-efficiency electromagnetic transducer with circularly abrupt magnetic flux density change

In this article, we present a high-efficiency electromagnetic transducer harvesting kinetic energy from the ocean current for self-powered technique in underwater robots to tackle the electric energy replenishment problem. A circular magnet array with alternating magnet arrangement was employed for providing a sudden change in magnetic flux density. A gear train was introduced into the compact design to greatly increase the rotation speed of the rotor. The finite element method is used to simulate and compare the magnetic flux density distributions and the induced voltages in the coil under different magnet arrays (conventional Halbach magnet array and proposed alternating one) with different magnet dimensions and numbers. The finite element method analysis shows that the alternating array displays a much larger changing magnetic flux density rate resulting in high induced electromotive forces. The experimental results based on a fabricated prototype indicate that the transducer yields maximum average output power of about 0.51 W with an energy conversion efficiency of 30.91% under the water flow speed of 0.64 m/s with a load resistance of 1 kΩ. We also investigated the capability of the transducer for self-powered applications in underwater robots. The transducer charged a 20 mF capacitor from 0 V to 29 V in 50 s. Also, the prototype charged a lithium battery embedded inside an underwater robot by 75% within 400 s. This study, with a broad application prospect, can advance the future development of self-powered underwater robotic systems.

New coil configurations with 2G-HTS and benefits for applications

A scalable concept to prepare high current density windings with high-temperature superconducting material is introduced. The concept covers miniaturized high-current windings and large coils for applications in energy technology as well. The principle is based on a circular disk-up-down-assembly (‘DUDA’) and extended to rectangular coils. First measurements on the assemblies (≈40 turns) in liquid nitrogen are presented as a proof-of-concept. Centre fields of ≈40 mT and ≈340 mT are measured during steady operation and pulsed operation respectively. Operating the assemblies at lower temperatures will strongly increase the current and field performance. Lowering the contact resistance might lead to further improvements. Due to the homogenous structure in the radial direction, shear stresses are minimized and large winding heights can be realized in principle. The DUDA concept of coil windings can be used to build even more sophisticated magnetic arrangements, e.g. Halbach-arrays, or complex windings for new stator configurations of rotating machines. The optional miniaturization offers compact and powerful magnets, e.g. for accelerators too.

전기자동차 매립형 영구자석 동기 전동기의 토크 리플 및 토크를 고려한 로터 및 영구자석 설계

The aim of this research was to investigate the torque performance of the motor in an electric vehicle depending on the rotor shape and air gap. The research focused on numerical comparison of torque performance of new rotors based on the average torque and torque ripple rate, which appeared according to the number and placement of permanent magnets. This research was numerically analyzed by MAXWELL V21.1. Average torque values in cases 1, 2, and 3 were increased, but vibration and noise in cases 1 and 3 were increased as the torque ripple rate increased. Considering the average torque and torque ripple rate, the torque performance of case 2 was the most optimal. Compared with Model N, the average torque of case 2 was increased by 9.1% and the torque ripple rate was reduced by 1.5%. The torque performance according to the size of air gap was compared with the basic model of case 2, which showed the best performance. An air gap of 0.7 mm applied to Model N showed the best torque performance. An additional magnet on case 2 and air gap of 0.7 mm provided the best torque performance and improved the driving motor performance for motor durability.

A new hybrid method for reducing cogging torque in the AFPM wind generator

ABSTRACT Reducing the cogging torque in the axial flux permanent magnet (AFPM) generators is an important study area. Especially, AFPM generators with open slotted and rectangular-shaped poles have high cogging torque and high total harmonic distortion (THD). Generators used in wind turbines require minimal mechanical vibration and a smooth sinusoidal wave. In this study, a new hybrid method is proposed to reduce the cogging torque and increase electrical performance. The proposed method involves combining two techniques to reduce cogging torque, including magnet placement angle and magnet grouping technique. In the proposed hybrid method, the electrical performance of the AFPM generator has improved for the minimum cogging torque. This proposed new method is cost-effective and easy to apply. 3D finite element method (FEM) and experimental verifications were performed for the accuracy of the proposed method. When the results are examined, cogging torque was improved by at least 80% with the new hybrid method. However, the electrical performance has been improved for 10% power loss, and the total harmonic distortion (THD) has been reduced to less than 3%.

Investigation on a broadband magnetic levitation energy harvester for railway scenarios

In this study, a Magnetic Levitation Energy Harvester (MLEH) was designed and fabricated. The magnetic field distribution and power generation performance of multiple cylindrical magnets were studied. The full factorial design (FFD) of L20 (22 × 5) test was carried out with the sliding magnet arrangement, coil arrangement and wiring method as the control factors, and the output power as target factor. Sweeping-frequency vibration tests and railroad spectrum random vibration tests were conducted to verify the power generation capacity of the prototype. Experimental results show that the device has a broadband response and the railroad vibration test proves the effectiveness of harvester in the application scenario for powering the rail-side sensors. The range of maximum output voltage, power and corresponding frequency in sweeping-frequency vibration tests with the amplitude of 1 to 10 mm and frequency of 5 to 50 Hz are 1.5 to 4.5 V; 1.80 to 17.0 mW and 9.7 to 30.8 Hz. The maximum output voltage and power are 1.33 V and 1.47 mW based on the measured railroad spectrum. Finally, a retrospective review in the efficiency, effectiveness and volume figure of merit is conducted to evaluate the performance of MLEH, indicating a high power density of the proposed harvester.

Design and Analysis of a New Dual-Stator Consequent-Pole Flux Reversal Machine With Triple-PM Excitation

This article proposes a new dual-stator consequent-pole (CP) flux reversal machine with triple-PM excitation (T-DSCPFRPMM), in which the two stators and rotor are all incorporated with CP permanent magnet (PM) arrangement. The employment of triple-PM excitation is beneficial to enhance the flux densities in the inner and outer air gaps. In addition, the ferromagnetic poles of rotor and stators are, respectively, used to modulate the magnetic field excited by stator-PM and rotor-PM, which introduces the bidirectional flux modulation effect into the proposed machine to enhance the torque production. The topology, operation principle, and design consideration of the proposed T-DSCPFRPMM are analyzed, respectively. The electromagnetic performances of the proposed machine under stator-PM excitation only, rotor-PM excitation only, and triple-PM excitation are evaluated and compared by finite-element analysis. The predicted results show that by using triple-PM excitation, the proposed machine can offer the superior torque production with low torque ripple, excellent overload torque capability, high efficiency and high-power factor, which are desirable for direct-drive applications.

An experimental platform for studying the radiation effects of laser accelerated protons on mammalian cells

An experimental platform was designed to study the effects of laser accelerated protons (LAPs) on mammalian cells. The protons, in the MeV energy range, originate from the rear side of a thin 5 µm Ti foil target following the interaction with a high power laser pulse and are accelerated by the target normal sheath mechanism. A tape Ti foil target was developed, allowing a shot repetition rate of up to 5 Hz, which corresponds to the rate of the laser system. A dipole magnet arrangement was used for energy dispersion and to separate the proton burst from electrons and x rays. The absorbed radiation dose at the cell port was measured with CR39 plastic detectors and calibrated imaging plates. An epifluorescence microscope with compact open-beam optics was developed to image live cells and their spatiotemporal properties during and after irradiation. To demonstrate the functionality of all components of the platform, biological proof of concept experiments were carried out using two suspension (Jurkat and Ramos) and two adherent (HeLa and A-549) cell lines. A multitude of biological procedures and analytical techniques were established on-site or in laboratories nearby. For example, we analyzed DNA double-strand break (DSB) induction and repair by detecting the γH2A.X signal by fluorescence microscopy and flow cytometry. The observed dose-dependent increase in DSB induction confirms that DNA damage is induced in cells after exposure to LAPs.

Diamagnetically levitating resonant weighing scale

Diamagnetic levitation offers stable confinement of an object from its environment at zero power, and thus is a promising technique for developing next generation unclamped resonant sensors. In this work, we realize a resonant weighing scale using a graphite plate that is diamagnetically levitating over a checkerboard arrangement of permanent magnets. We characterize the bending vibrations of the levitating object using laser Doppler vibrometry and use microgram glass beads to calibrate the responsivity of the sensor's resonance frequency to mass changes. The sensor is used for real-time measurement of the evaporation rate of nano-litre droplets with high-accuracy. By analyzing the resonator's frequency stability, we show that the millimeter graphite sensor can reach mass resolutions down to 4.0 ng, relevant to biological and chemical sensing concepts.

Appropriate Delivery of Antitachyarrhythmia Therapy Despite Magnet Placement Over Implanted Cardioverter-Defibrillator: A Case Report

The fundamental perioperative concern for patients with implantable cardioverter-defibrillators (ICDs) is the potential for electromagnetic interference (EMI) from monopolar electrosurgery. The ICD may interpret electromagnetic signals as a tachyarrhythmia and deliver an inappropriate shock to the patient. Magnet placement is often used to avoid this problem since a magnet will often deactivate an ICD’s tachyarrhythmia therapy. We report a case in which magnet placement over an ICD failed to suspend tachyarrhythmia therapy because of imprecise magnet positioning. This case demonstrates the possibility for error when relying on a magnet to suspend tachyarrhythmia therapies.

Cover Picture: Electro‐Conductive Single‐Molecule Magnet Composed of a Dysprosium(III)‐Phthalocyaninato Double‐Decker Complex with Magnetoresistance (Angew. Chem. Int. Ed. 39/2021)

A one-dimensional arrangement of single-molecule magnets (SMMs), namely partially oxidized dysprosium(III) phthalocyaninato double-decker complexes, [DyPc2]Ix, was synthesized in the Communication by Keiichi Katoh, Masahiro Yamashita et al. on page 21179 by using electro-oxidation and chemical oxidation. The results of spectrophotometric analysis on [DyPc2]Ix are consistent with the Drude model, which theoretically explains the optical response of the metal. Since conductivity was observed at temperatures lower than the spin blocking temperature (TB), magnetoresistance (MR) effects observed as magnetic hysteresis were observed for the SMM. This strategy may pave the way for the construction of electro-conductive SMMs as spin valves.

Self-powered 5G NB-IoT system for remote monitoring applications

In the new era of 5G and artificial intelligence of things (AIoT), remote monitoring and early warning based on widely distributed self-powered wireless sensing system are particularly important. However, the high power consumption, limited communication range and operation lifespan of this system are serious obstacles in practical applications. Here, we report a self-powered 5G narrowband IoT (NB-IoT) system for remote fire monitoring, driven by a magnetic-assisted noncontact energy harvester (MN-EH) which hybridizes piezoelectric and electromagnetic generator. The rotational MN-EH device can efficiently convert wind energy into electrical power while NB-IoT makes it possible to trade off the low-power and long-range transmission. With the magnetic coupling mechanism, the device can avoid degradation and abrasion to improve the reliability. Through optimizing a magnetic arrangement, the rotating peak torque can be reduced more than 93%. The MN-EH is further developed to power the NB-IoT system which can acquire temperature and CO concentration and transmit them to the cloud server every ~13 min. This work provides an effective strategy and paves the way for practical applications of self-powered remote monitoring system.