Search Results (94)

This study investigates the influence of chirality on the dynamic susceptibility of concentric nanotori via micromagnetic simulations. The aim is to analyze the ferromagnetic resonance characteristics of coupled nanotori structures and compare them across various ring separation distances, thus providing an insight into how vortex configurations with identical or differing chiralities affect their dynamic properties. We analyze the energetic differences between the two vortex configurations and find them to be negligible; however, these minor differences suffice to explain the significant discrepancies in the demagnetization field observed between the nanotori. We examine the dynamic susceptibility spectrum and the spatial localization of the ferromagnetic resonance modes for different nanotori separations. Our findings demonstrate that the resonant oscillation frequencies are significantly influenced by the magnetostatic interactions between the nanotori, which can be effectively modulated by varying the distance between them. Furthermore, for smaller separations, the frequency peaks in the dynamic susceptibility markedly diverge between the two vortex configurations, demonstrating that the observed differences in the demagnetization field between the rings strongly influence the frequency response. In summary, our results indicate that both the inter-ring distance and the vortex configuration play a crucial role in determining the frequency response of the system. Full article

The residual magnetism of the iron core of power transformers can cause an excitation inrush current, posing a threat to the safe and stable operation of the power grid. This paper proposes a transformer remanence measurement method based on a demagnetization hysteresis loop to address the problems of large errors, complex operation, and poor universality in existing remanence measurement methods. This method is designed for off-grid transformers to avoid potential interference to the power grid caused by current pulses during the measurement process. This method constructs an RLC oscillation circuit that utilizes capacitor energy storage and iron core magnetic field energy conversion, combined with the dynamic characteristics of hysteresis loops, to achieve accurate measurement of residual magnetism and synchronous demagnetization. The effectiveness of this method has been verified through residual magnetism measurement experiments on ring transformers and large converter transformers, and it can be applied in specific engineering practice operations. Theoretical analysis shows that the charging range of energy storage capacitors is affected by the hysteresis characteristics of the iron core and the saturation magnetic flux, and the residual magnetization value can be directly calculated based on the difference in the intersection point of the longitudinal axis of the demagnetization hysteresis loop. Simulation and experimental results show that the measurement error of the proposed method is less than 5%—significantly better than traditional methods. This method does not require complex control strategies, has high precision and efficiency, and can provide reliable technical support for residual magnetism detection and suppression of off-grid power transformers. Full article

The instability in rare-earth material supply and rising costs have driven research into rare-earth-free electric motors. Among various alternatives, wound rotor synchronous motors (WRSMs) stand out due to their adjustable excitation, enabling high torque at low speeds, and efficient field weakening at high speeds. Unlike permanent magnet synchronous motors (PMSMs), WRSMs offer greater operational flexibility and eliminate the risk of demagnetization. However, accurately modeling WRSMs remains challenging, especially when considering axial fringing flux and leakage components, which significantly affect motor performance. To address this challenge, this paper proposes a 3D nonlinear magnetic equivalent circuit (MEC) model that explicitly incorporates axial flux components and leakage paths in WRSMs with overhang rotor structures. Unlike conventional 2D MEC models, which fail to capture axial flux interactions, the proposed approach improves prediction accuracy while significantly reducing computational costs compared to full 3D finite element analysis (FEA). The model was validated through comparisons with 3D FEA simulations and experimental back-EMF measurements, demonstrating its accuracy and computational efficiency. The results confirm that the 3D nonlinear MEC model effectively captures axial flux paths and leakage components, making it a valuable tool for WRSM design and analysis. Future research will focus on further refining the model, incorporating hysteresis loss modeling, and developing hybrid MEC–FEA simulation techniques to enhance its applicability. Full article

The Yucatán Peninsula, a key region of the ancient Maya civilization, has long presented challenges in establishing absolute chronological frameworks for its cultural practices. While the central regions of Mesoamerica have been extensively studied, the southern areas, including the Yucatán, remain underexplored. Limekilns, integral to lime production in pre-Hispanic Maya society, are well suited for archaeomagnetic studies due to the high temperatures (>700 °C) required for their operation. This study analyzed 108 specimens from 12 limekilns near Mérida, Yucatán, using rock-magnetic experiments and progressive alternating field demagnetization to refine the absolute chronology and determine the continuity of the lime production technology. Thermoremanent magnetization was predominantly carried by magnetite-like phases. Archaeomagnetic directions were successfully obtained for ten kilns with robust precision parameters. Age intervals were calculated using global geomagnetic models (SHA.DIF.14K, SHAWQ.2K), local paleosecular variation curves, and a Bootstrap resampling method. The analysis identified apparently two distinct chronological clusters: one between 900 and 1000 AD, associated with the Late–Terminal Classic period, and another near 1500 AD, just prior to the Spanish conquest. These findings reveal an apparent 500-year hiatus in lime production, followed by the potential reuse of kilns. Our study refines the chronological framework for Mayan lime production and its cultural and technological evolution. The integration of archaeomagnetic methods demonstrates their far-reaching applicability in addressing questions of continuity, reuse, and technological adaptation, contributing to broader debates on ancient pyrotechnological practices and their socioeconomic implications. Full article

With their cost-effective manufacturing process, hybrid stepper motors (HSMs) are a popular choice for position control in low-power industrial applications. These versatile motors offer a compelling solution for reducing system costs and size since at standstill/low speeds, HSMs typically have higher torque density with respect to low-power permanent magnet (PM) motors. This higher torque density determines a reduced use of rare-earth PMs and, therefore, a lower environmental footprint. In practical applications, the commonly used microstepping control faces low efficiency, low dynamic performance, vibrations, and a variable maximum continuous torque depending on the working point. In this paper, the operating region of an HSM is extended in the field-weakening (FW) region, showing how field-oriented control (FOC) with FW allows one to strongly increase the drive performance with a slight cost increase thanks to the availability of low-cost magnetic encoders. Due to the fact that FOC provides only the requested current, the HSM faces lower temperatures, lower insulation degradation, and lower permanent magnet demagnetization issues. An experimental evaluation comparing the commonly used microstepping and the proposed FOC with FW is performed on four commercial HSMs with different DC voltage power supplies using an industrial test bench. In particular, the experimental campaign has a focus on steady-state conditions in the case of the maximum continuous torque, showing the advantages of FOC with FW because the advantages in transient conditions are well known. Full article

This review explores a method of visualizing a demagnetization field (H_d) within a thin-foiled Nd₂Fe₁₄B specimen using electron holography observation. Mapping the H_d is critical in electron holography as it provides the only information on magnetic flux density. The H_d map within a Nd₂Fe₁₄B thin foil, derived from this method, showed good agreement with the micromagnetic simulation result, providing valuable insights related to coercivity. Furthermore, this review examines the application of the wavelet hidden Markov model (WHMM) for noise suppression in thin-foiled Nd₂Fe₁₄B crystals. The results show significant suppression of artificial phase jumps in the reconstructed phase images due to the poor visibility of electron holograms under the narrowest fringe spacing required for spatial resolution in electron holography. These techniques substantially enhance the precision of phase analysis and are applicable to a wide range of magnetic materials, enabling more accurate magnetic characterization. Full article

Permanent magnet synchronous motors (PMSMs) play a crucial role in industrial production, and in response to the problem of PMSM turn-to-turn short-circuit and demagnetization faults affecting production safety, this paper proposes a PMSM turn-to-turn short-circuit and demagnetization fault diagnostic method based on a convolutional neural network and bidirectional long and short-term memory neural network (CNN-BiLSTM). Firstly, analyzing the PMSM turn-to-turn short-circuit and demagnetization faults, one takes the PMSM stator current as the fault signal and optimizes the variational modal decomposition (VMD) by using the Gray Wolf Optimization (GWO) algorithm in order to achieve efficient noise reduction processing of the stator current signal and improve the fault feature content in the stator current signal. Finally, the fault diagnostics are classified by using the CNN-BiLSTM, which collects advanced optimization algorithms and deep learning networks. The effectiveness of the method is verified by simulation experiment results. This scheme has high practical value and broad application prospects in the field of PMSM turn-to-turn short circuit and demagnetization fault diagnosis. Full article

Permanent magnet-assisted synchronous reluctance motors (PMA-SynRMs) are widely used in various fields due to their significant advantages, including strong torque output, high efficiency, excellent speed regulation, and low cost. The PMA-SynRM with asymmetric-rotor structure has a weaker anti-demagnetization performance than the conventional PMA-SynRM due to its multi-layer and thin permanent magnets construction. According to the finite element (FEM) simulation analysis, the anti-demagnetization performance of the asymmetric-rotor PMA-SynRM can be improved by adding bypass magnetic bridges on the ribs of the flux barriers and by changing the positions of the permanent magnets. The rotor structure of the proposed model is globally optimized by combining the two methods. Anti-demagnetization performance is improved as much as possible under the premise of ensuring the torque performance of the basic model. After multi-objective optimization, there is almost no difference between the optimized model and the basic model in terms of no-load air-gap flux density, no-load Back-electromotive force (EMF), and average torque. The maximum demagnetization rate of the optimized model is reduced by 81.44% compared with the basic model, and the anti-demagnetization performance is significantly improved. At the same time, the torque ripple is also reduced by 44.14%, which is obviously reduced. Compared with the basic model, the optimized model has better stability and reliability. Full article

A demagnetization study was conducted on a magnetically shielded room (MSR) at Fraunhofer IPM, designed for applications such as magnetoencephalography (MEG) and material testing. With a composite of two layers of mu-metal and an intermediate aluminum layer, the MSR must provide a residual field under 5 nT for the successful operation of optically pumped magnetometers (OPMs). The degaussing process, employing six individual coils, reached the necessary residual magnetic field within the central 1 m³ volume in under four minutes. Due to the low-frequency shielding factor of 100, the obtained average residual field is shown to be limited by environmental residual field changes after degaussing and not by the degaussing procedure. Full article

We report the Magnetospheric Multiscale (MMS) observation of a bifurcated reconnecting current sheet in Earth’s dayside magnetosheath. Typical signatures of the ion diffusion region, including sub-Alfvénic demagnetized ion outflow, super-Alfvénic electron flows, Hall magnetic fields, electron heating, and energy dissipation, were found when MMS traversed the current sheet. The weak ion exhaust at the current sheet center was bounded by two current peaks in which super-Alfvénic electron flow directed toward and away from the X line were observed, respectively. Both off-center current peaks were primarily carried by electrons, one of which was supported by field-aligned current, while the other was mainly supported by current driven by electric field drift. The two current peaks also exhibit other differences, including electron heating, electron pitch angle distributions, electron nongyrotropy, energy dissipation, and magnetic field curvature. An ion-scale magnetic flux rope was detected between the two current peaks where electrons showed field-aligned bidirectional distribution, in contrast to field-aligned distribution parallel to the magnetic field in two current peaks. The observed current sheet was embedded in a background shear flow. This shear flow worked together with the guide field and asymmetric field and density to affect the electron dynamics. Our results reveal the reconnection properties in this special plasma and field regime which may be common in turbulent environments. Full article

Oil and gas pipelines are subject to soil corrosion and medium pressure factors, resulting in stress concentration and pipe rupture and explosion. Non-destructive testing technology can identify the stress concentration and defect corrosion area of the pipeline to ensure the safety of pipeline transportation. In view of the problem that the traditional pipeline inspection cannot identify the stress signal at the defect, this paper proposes a detection method using strong and weak magnetic coupling technology. Based on the traditional J-A (Jiles–Atherton) model, the pinning coefficient is optimized and the stress demagnetization factor is added to establish the defect of the ferromagnetic material. The force-magnetic relationship optimization model is used to calculate the best detection magnetic field strength. The force-magnetic coupling simulation of Q235 steel material is carried out by ANSYS 2019 R1 software based on the improved J-A force-magnetic model. The results show that the effect of the stress on the pipe on the magnetic induction increases first and then decreases with the increase in the excitation magnetic field strength, and the magnetic signal has the maximum proportion of the stress signal during the excitation process; the magnetic induction at the pipe defect increases linearly with the increase in the stress trend. Through the strong and weak magnetic scanning detection of cracked pipeline materials, the correctness of the theoretical analysis and the validity of the engineering application of the strong and weak magnetic detection method are verified. Full article

As an important driving device, the permanent magnet synchronous motor (PMSM) plays a critical role in modern industrial fields. Given the harsh working environment, research into accurate PMSM fault diagnosis methods is of practical significance. Time–frequency analysis captures the rich features of PMSM operating conditions, and convolutional neural networks (CNNs) offer excellent feature extraction capabilities. This study proposes an intelligent fault diagnosis method based on continuous wavelet transform (CWT) and CNNs. Initially, a mechanism analysis is conducted on the inter-turn short-circuit and demagnetization faults of PMSMs, identifying and displaying the key feature frequency range in a time–frequency format. Subsequently, a CNN model is developed to extract and classify these time–frequency images. The feature extraction and diagnosis results are visualized with t-distributed stochastic neighbor embedding (t-SNE). The results demonstrate that our method achieves an accuracy rate of over 98.6% for inter-turn short-circuit and demagnetization faults in PMSMs of various severities. Full article

Irreversible demagnetization processes in high-performance Fe-Nd-B magnets were investigated using a novel test rig. Designed to capture local magnetic field distributions and integral average magnetization in situ, the rig operates under field and temperature conditions similar to those found in electric motors. Validation against established techniques such as the hysteresisgraph and Hall mapper confirmed its accuracy. Furthermore, we observed the ability to detect even small variations of less than 2.5% in coercive field strength across the sample volume using field scans. The system significantly reduces measurement times from days to hours, enabling efficient in situ detection of magnetic field distributions during the whole demagnetization process. Full article

Temperature rise of the tubular permanent magnet linear generator (TPMLG) might lead to insulation failure and demagnetization of permanent magnets, affecting the safe and stable operation of other equipment and the entire system. Herein, a bidirectional electromagnetic–thermal coupling method for analyzing the electromagnetic loss and thermal characteristics of a TPMLG considering the effect of increased temperature on the permanent magnet was proposed. To study the electromagnetic–thermal characteristics of the TPMLG under stable power generation, a two-dimensional electromagnetic field model and a three-dimensional temperature field model were established and coupled. The temperature field of the TPMLG was numerically calculated using computational fluid dynamics over finite volume method under natural air cooling and forced air cooling conditions. Effects of loss and air flow velocity on the steady temperature field were investigated. Results indicated that copper loss increased by 24.5% considering the influence of temperature rise. The windings’ top central position in the TPMLG was the spot with the highest temperature of 127.8 °C and there was a potential demagnetization risk for the permanent magnets. Some reference for future research of clarifying thermal characteristics and cooling design was provided. Full article

This study deals with two different aspects of the high-strength low-alloyed 1100 MC steel. The first is associated with the remarkable heterogeneity (linked with surface decarburization) in the surface state produced during sheet rolling with respect to the sheet width. The variable thickness surface layer exhibits a microstructure different from that of the deeper bulk. Variation in the thickness of the thermally softened near-surface region strongly affects Barkhausen noise as well. This technique can be considered a reliable tool for monitoring the aforementioned heterogeneity. It can also be reported that the opposite sides of the sheet are different with respect to the surface state, the heterogeneity distribution, and the corresponding Barkhausen noise. These aspects indicate different conditions during hot rolling followed by rapid quenching on the upper and lower rollers. Furthermore, it was found that the degree of decarburizing and the corresponding surface heterogeneity is also a function of C content, and steels with lower C content exhibit less pronounced surface heterogeneity. The second aspect is related to the remarkable asymmetry in Barkhausen noise emission with respect to two consecutive bursts. This asymmetry is due to the presence of remnant magnetization in the sheet produced during manufacturing. The remnant magnetization is coupled to the magnetic field produced by the excitation coil of the Barkhausen noise sensor and strongly contributes to the aforementioned asymmetry. The remnant magnetization attenuates the domain wall mobility, which results in weaker Barkhausen noise. Moreover, the Barkhausen noise envelopes and the extracted features such as the position of the envelope maximum and its width are strongly affected by the remnant magnetization. Insufficient demagnetization makes the body magnetically softer and makes a wider range of magnetic fields in which Barkhausen noise emission can be detected. As soon as sufficient removal of this remnant magnetization is carried out in the vanishing magnetic field (demagnetization), the aforementioned remarkable asymmetry is fully lost. Full article