Academic literature on the topic 'Running magnetization'

Multiple field-induced plateaus in αCoV2O6 at low temperatures were revealed earlier by M. Lenertz et al. [J. Phys. Chem. C 115, 17190 (2011)] and carefully investigated recently by M. Nandi and P. Mandal [J. Appl. Phys. 119, 133904 (2016)]. Four equidistant steps were observed in the magnetization curve. We present a model to describe this phenomenon. A magnetic structure of this substance is formed by highly anisotropic triangular lattice of Ising chains running along the b axis. Due to a three-fold degeneracy of three-sublattice magnetic ordering, domain boundaries appear. Their transformation under magnetic field variation leads to two additional steps in the 1/3 magnetization plateau and gives rise to complex magnetic behavior observed experimentally. The domain structure in αCoV2O6 occurs to be strongly anisotropic because a lifetime of the metastable states depends greatly on the configuration orientation. A strong dependence of the magnetization curve on magnetic field sweep time is predicted.

Background: The effect of residual stress resulted from the manufacturing process on the performance of bogie frame has been attracting more and more attention with the increasing of running speed of maglev vehicle, which could develop cracks on the frame and compromise the operational safety. Aim: It is necessary to determine and understand the distribution rules of residual stress on the bogie frames. Methods: Barkhausen effect is one of the effective methods used to measure residual stress. Results: This paper presents a experiment system designed for residual stress detection and the principle of electromagnetic stress detection is expounded, finite element simulation analysis on magnetization device is carried out, and the effect of magnetization under different excitation conditions is analyzed. Conclusion: The feasibility of the online magnetic detection method of internal stresses in bogie frame is verified through the simulation, which would provided the basis for bogie frames internal stresses detection.

Abstract Objectives We investigate the possibility to exploit high-field MRI to acquire 3D images of Purkinje network which plays a crucial role in cardiac function. Since Purkinje fibers (PF) have a distinct cellular structure and are surrounded by connective tissue, we investigated conventional contrast mechanisms along with the magnetization transfer (MT) imaging technique to improve image contrast between ventricular structures of differing macromolecular content. Methods Three fixed porcine ventricular samples were used with free-running PFs on the endocardium. T1, T2*, T2, and M0 were evaluated on 2D slices for each sample at 9.4 T. MT parameters were optimized using hard pulses with different amplitudes, offset frequencies and durations. The cardiac structure was assessed through 2D and 3D T1w images with isotropic resolutions of 150 µm. Histology, immunofluorescence, and qPCR were performed to analyze collagen contents of cardiac tissue and PF. Results An MT preparation module of 350 ms duration inserted into the sequence with a B1 = 10 µT and frequency offset = 3000 Hz showed the best contrast, approximately 0.4 between PFs and myocardium. Magnetization transfer ratio (MTR) appeared higher in the cardiac tissue (MTR = 44.7 ± 3.5%) than in the PFs (MTR = 25.2 ± 6.3%). Discussion MT significantly improves contrast between PFs and ventricular myocardium and appears promising for imaging the 3D architecture of the Purkinje network.

We present the magnetic properties of the metal-organic framework {[CoCxAPy]·2.15 H2O}n (Cx = bis(carboxypropyl)tetramethyldisiloxane; APy = 4,4`-azopyridine) (1) that builds up from the stacking of 2D coordination polymers. The 2D-coordination polymer in the bc plane is formed by the adjacent bonding of [CoCxAPy] 1D two-leg ladders with Co dimer rungs, running parallel to the c-axis. The crystal packing of 2D layers shows the presence of infinite channels running along the c crystallographic axis, which accommodate the disordered solvate molecules. The Co(II) is six-coordinated in a distorted octahedral geometry, where the equatorial plane is occupied by four carboxylate oxygen atoms. Two nitrogen atoms from APy ligands are coordinated in apical positions. The single-ion magnetic anisotropy has been determined by low temperature EPR and magnetization measurements on an isostructural compound {[Zn0.8Co0.2CxAPy]·1.5 CH3OH}n (2). The results show that the Co(II) ion has orthorhombic anisotropy with the hard-axis direction in the C2V main axis, lying the easy axis in the distorted octahedron equatorial plane, as predicted by the ab initio calculations of the g-tensor. Magnetic and heat capacity properties at very low temperatures are rationalized within a S* = 1/2 magnetic dimer model with anisotropic antiferromagnetic interaction. The magnetic dimer exhibits slow relaxation of the magnetization (SMM) below 6 K in applied field, with a tlf ≈ 2 s direct process at low frequencies, and an Orbach process at higher frequencies with U/kB = 6.7 ± 0.5 K. This compound represents a singular SMM MOF built-up of Co-dimers with an anisotropic exchange interaction.

Wire rope breakage, as damage easily produced during the service period of wire rope, is an important factor affecting the safe operation of elevators. Especially in the high-speed elevator operation process, the problem of magnetization unsaturation caused by speed effects can easily lead to deformation of the magnetic flux leakage detection signal, thereby affecting the accuracy and reliability of wire breakage quantitative detection. Therefore, this article focuses on the problem that existing wire rope detection methods cannot perform non-destructive testing on high-speed elevator wire ropes and conducts design and experimental research on a high-speed running wire rope breakage detection device based on the principle of multi-stage excitation. The main research content includes simulation research on the multistage excitation, structural design, and simulation optimization of open–close copper sheet magnetizers and the building of a detection device for wire rope breakage detection experimental research. The simulation and experimental results show that the multistage magnetization method can effectively solve the problem of magnetization unsaturation caused by the velocity effect. The multistage excitation device has a good wire breakage recognition effect for speeds less than or equal to 3 m/s. It can detect magnetic leakage signals with a minimum of four broken wires and has good detection accuracy. It is a new and effective wire breakage detection device for high-speed elevator wire rope, providing important technical support for the safe and reliable operation of high-speed elevators.

A theoretical analysis enables effects generated by the magnetic core anisotropy of an induction motor to be determined qualitatively. Relationships formulated between currents and magnetic flux linkages that are associated with three-phase stator windings enable the qualitative determination of spectra of currents or voltages of a typical induction motor. These relationships account for nonlinear and anisotropic magnetization characteristics of the motor core, both during idle running and motor starting. Based on these relationships, components of the amplitude Fourier spectra of symmetrical components of currents or voltages, which are useful in the diagnostics of stator or rotor core anisotropy, were selected. Field calculations were performed for the core of a two-pole 5.5 kW motor supplied by three-phase sinusoidal currents. The components of the induced voltage Fourier spectra in both the idle running and short-circuit state were similar to analogous components predicted based on theoretical studies. The components occurring in the spectra, which were obtained based on field calculations, were distinguished in the measured spectra of the symmetrical components of the phase currents. These components were applied to estimate representative current signal levels in the diagnostics of motor core anisotropy. Relative values of these signals did not exceed 60 dB; however, they were significant for assessing the internal asymmetry level of the motor stator or rotor core. The results of laboratory measurements confirmed the results of the theoretical analysis.

Hard disk drives (HDDs) employ the magneto-resistive (MR) head to sense the change in magnetic flux via the transitions of magnetization pattern, resulting in a readback signal. Thus, head instability plays an important role on the reliability of HDDs because it can deteriorate the system performance considerably. Baseline popping (BLP) is one of the crucial problems caused by the head instability, whose effect can distort the readback signal to the extent of causing a sector read failure. This paper proposes three BLP detection and correction algorithms for a perpendicular magnetic recording (PMR) system. Specifically, to suppress the BLP effect experienced in the readback signal, the first algorithm is based on an averaging filter and a threshold detector; the second one relies on the estimated BLP signal obtained from a linear curve fitting technique; and finally the third one uses two sequence detectors running in parallel. Experimental results indicate that the third algorithm performs better than the other schemes because it can detect and correct the BLP better than the others, especially when the peak BLP amplitude is large.

Purpose This paper aims to investigate the performance of a ferrofluid-based hydrodynamic journal bearing system. Design/methodology/approach This paper presents a new design of ferrofluid-based hydrodynamic journal bearing. An experimental set-up consisting of a magnetic shaft along with a brass bearing was modified and developed. A permanent magnet was used to make the selected shaft material magnetic. The load and speed were varied to conduct the analyses for different test conditions. Findings The paper provides information about a design of ferrofluid-based journal bearing and its improved performances. For moderate to higher loads at different shaft speeds, it was found that because of the magnetization effect, the maximum film pressure in case of a ferrofluid lubricant increased up to approximately 60 per cent, compared with that of the conventional lubricant-based journal bearing system. Besides, the temperature rise was found smaller for ferrofluid lubricants, thus making the system cooler while running. Originality/value This paper offers a new design of magnetic bearing system for the experimental analysis by utilizing a magnetic shaft with a non-magnetic bearing. The present ferrofluid-based bearing design is less complicated from manufacturing point of view.

Three caesium-bearing borophosphates, Cs[BP2O6(OH)2] (I), Cs0.51Mn1.17(H2O)2[BP2O8]·0.45H2O (II) and CsMn[BP2O8(OH)] (III), were synthesized by a hydrothermal method at 473–523 K. Their crystal structures have been studied by means of single-crystal X-ray diffraction; all three structures comprise borophosphate chain anions with a B:P ratio of 1:2. The unique construction of (I) is based on four-membered-ring chains running parallel to the [010] direction. These protonated borophosphate chains are linked via hydrogen-bond interactions to form a 3D framework with caesium cations incorporated. (II) is the first Cs and Mn2+,Mn3+ member of a known family characterized by [BP2O8]∞ helical chains running along [001]. These chains are connected through MnO4(H2O)2 octahedra to form a 3D framework. The caesium cations are disordered over two independent positions in the channels, which they occupy together with water molecules. An additional MnO2(H2O)3 bipyramid statistically shares a common edge and two corners with three main Mn octahedra to form tetrameric clusters. The topological relation between the chain anionic fragments of (I) and (II) as well as the structural relation between (I) and previously studied boro- and berillophosphates are discussed. Compound (III) presents the first Mn member of the A I M III[BP2O8(OH)] family and is characterized by a 3D framework built by open-branched borophosphate chains and MnO5 semi-octahedra sharing vertices. The measurements of thermodynamic properties, i.e. magnetization M and specific heat C p, to 2 K and 30 T, provide evidence that (II) orders antiferromagnetically at the Néel temperature T N = 4.6 K and exhibits a plateau-like feature under the action of an external magnetic field accompanied by a pronounced magnetocaloric effect.

There is a compelling desire by power generating plants to continue running existing stations and components for several more years, despite many of them have surpassed their design service life. The idea is to avoid premature retirement, on the basis of the so-called design life, because actual useful life could often be well in excess of the design life. This can most readily be achieved by utilizing nondestructive monitoring methods to monitor the degradation of the microstructure, either when a station is down for maintenance or preferably when it is under operation. This study evaluates the use of quasi static hysteresis measurements as a possible procedure to evaluate creep in a 410 martensitic stainless steel, a material utilized in power plant components. The creep rupture tests were conducted at stresses of 100 and 200 MPa, temperatures of 500°C and 620°C, and the times varied between 48 and 120 hours. Following the creep tests all specimens were evaluated magnetically and then metallurgically by optical and scanning electron microscopy, x-ray diffraction (XRD) and by energy dispersive spectroscopy (EDS). The microstructural changes were compared with the magnetization changes. It was determined that the changes in the hysteresis curves were clearly detectable and correlated with the creep-induced damage.

Les Machines Synchrones à Aimants Permanents (MSAPs) sont largement utilisées pour les applications d'électrification des transports. En produisant son flux magnétique à partir des aimants à base des terres rares (par exemple, Nd-Fe-B), ces machines ont été remise en question ces dernières années en raison des risques d'approvisionnement, de la variabilité des prix et des défis environnementaux liés à ces matériaux magnétiques mentionnés. À ce scénario, s'ajoutent également les limitations d'usage des MSAPs dans de grandes plages de couple-vitesse, nécessitant généralement des stratégies de défluxage, mises en œuvre en imposant une valeur de plus en plus négative à la composant direct du courant statorique à mesure que la machine accélère. Dans le cas de machines à pôles lises, en conséquence du défluxage, les pertes par effet Joule augmentent et le rendement réduit. Capables de fonctionner dans une large plage couple-vitesse, les Machines à Mémoire de Flux Variable (MMFVs) ont émergé comme une option caractérisée par une densité de flux magnétique réglable à partir des impulsions de courant de courte durée alimentant les enroulements de l'armature. Tout cela grâce à la boucle d'hystérésis fortement non linéaire qui caractérise les aimants à faible force coercitive utilisés comme source de flux. Les alliages Al-Ni-Co sont le choix de nombreuses recherches pour ces applications. Des matériaux magnétiques similaires comme le Fe-Cr-Co sont encore peu explorés, malgré leurs avantages comme sa faible teneur en Cobalt et ses propriétés mécaniques. Dans ce cadre, cette thèse propose l'étude d'une MMFV du type simple, avec une paire de pôles et sans enroulement dédié à la magnétisation. La géométrie de la machine est conçue à partir d'une MSAP, pour laquelle un rotor à base des aimants Nd-Fe-B est remplacé par un cylindre massif à base de FeCrCo36/5. Tout d'abord, nous nous concentrons sur l'étude du comportement magnétique de l'aimant lorsqu'il est inséré dans l'environnement de la machine. En raison de l'anisotropie différenciant la boucle d'hystérésis du Fe-Cr-Co dans les directions facile ou difficile d'aimantation, deux méthodologies sont proposées pour décrire le profil d'aimantation partielle via des tests expérimentaux à l'arrêt et des simulations par éléments finis. Les résultats obtenus sont comparés à la référence définie par des mesures à partir d'un équipement idéal (HysteresisGraph). Les effets dû à la géométrie et saturation du stator, et encore, à l'anisotropie de forme, justifient les différences observées. Les études qui suivent sont focalisés sur la magnétisation et le contrôle du couple en dynamique à partir de l'utilisation d'un algorithme de commande sans capteur de position au rotor. Dans ce contexte, cette recherche propose l'implémentation d'une Boucle à Verrouillage de phase du type Proportionnel Intégral pour estimer la position et la vitesse du rotor à partir de la mesure des tensions statoriques. Une attention est portée sur la compensation de l'angle de décalage nécessaire pour ajuster la position mentionnée en fonction du système d'acquisition (filtres actifs) et des caractéristiques de la méthode d'estimation utilisée. Une étude de sensibilité paramétrique identifie les inductances d'axes d et q comme des paramètres critiques pour l'estimation de l'angle de correction. Ainsi, cette thèse s'intéresse également à proposer une méthodologie pour décrire ces inductances à partir simulations par éléments finis. Les effets d'anisotropie de l'aimant et aussi la saturation statorique sont prises en compte. Une réluctance variable est identifiée dans la machine et son impact sur l'angle de correction étudié
Permanent Magnet Synchronous Machines (PMSMs) have been widely used for electrification transportation applications. Producing their magnet flux from rare-earth magnets (e.g. Nd-Fe-B magnets), these machines have had their long-term use increasingly questioned due to the risks of supply, price variability and the environmental challenges related to the extraction and recycling of these mentioned materials. To this scenario, can be also added the limitations of PMSMs for being used in large torque-speed ranges, requiring usually the implementation of flux-weakening strategies, based on supplying the machine with an increasingly negative direct stator current component as the rotor speed also increases. In case of non-salient pole machines the Joule losses can be enhanced and the efficiency consequently reduced. Capable of operating in a wide torque-speed range, the Variable Flux Memory Machines (VFMMs) have emerged as an option characterized by controllable magnetic flux density from short-time currents pulses supplying the armature windings. All this thanks to the highly non-linear hysteresis loop characterizing the low coercive force magnets used as source of flux. Al-Ni-Co alloys has been the choice of many researches for these applications. However, similar magnetic materials as Fe-Cr-Co are still little explored, besides advantageous characteristics as their lower content of Cobalt and mechanical proprieties. Within this framework, this thesis proposes the study of single-type AC-magnetized single pole pair VFMM, composed of a Fe-Cr-Co-based rotor. The machine geometry is designed from a PMSM, in which the rotor pf Nd-Fe-B is directly replaced by a solid cylinder of FeCrCo36/5. First, a focus on the study of the magnetic behavior of the magnet when inserted in the machine environment. Because of the anisotropy differentiating the hysteresis loop of the FeCrCo36/5 in the a easy or hard magnetization directions, two different methodologies are proposed for describing the partial magnetization profile via experimental tests at standstill and Finite Element Analysis simulations. The achieved results are compared with the reference obtained from an ideal measuring equipment (HysteresisGraph). The effects of a stator saturation and geometry as also the anisotropy shape are explored for justifying the differences observed. A following study focused on the magnetization under operation and the torque control is developed considering the an adapted sensorless algorithm. In this context, the present research proposes the use of a Proportional Integral Phase Locked-Loop for estimating the rotor position and speed. An attention is given to the offset angle compensation required for adjusting the mentioned position according to the acquisition system (active filters) and the characteristics of the estimation method used. A parametric sensitivity study allows the identification of the dq-axis inductances as the most critical parameters to an accurate correction angle estimation. For this reason, this research thesis is also interested in proposing a methodology to describe the d- and q-axis inductances from FEA simulations performed by considering the anisotropy effects of the magnet and also the saturation of the stator material. A variable reluctance is identified in the machine and its effect on the correction angle is studied