Search Results (12,951)

To address the issue of insufficient output voltage of the self-powered unit of intelligent bearings under low-amplitude working conditions, a piezoelectric–friction composite energy harvester driven by rotating magnetic force is proposed based on the multi-physical field coupling and synergy of magnetoelectric, piezoelectric and triboelectric effects, which effectively enhances the voltage output in low-amplitude vibration environments. The intelligent bearing adopts an extended structure, consisting of an outer ring sleeve, an inner ring extension ring, magnetic poles and a composite energy harvester. The outer ring sleeve is nested on the outer ring of the bearing and fixes the composite energy harvester, while the inner ring extension ring is fixed on the inner ring of the bearing and installs the magnetic poles. The composite energy harvester adopts a magnetic double-mass block single-crystal piezoelectric simply supported beam structure and integrates a contact-separation type triboelectric nanogenerator in the vibration direction, achieving the collaborative power supply of the piezoelectric and triboelectric units. A mechanical-electrical coupling dynamic model of the composite energy harvester is developed. Using COMSOL software, the effects of various structural dimensions and magnetic pole configurations on the output voltage are analyzed. Experimental validation confirms the model’s effectiveness. The results demonstrate that the energy harvester operates effectively under varying bearing rotational speeds. The rotational speed of the magnetic poles has little influence on the output voltage amplitude but primarily affects its frequency. Under the condition that the rotational speed is within 600 r/min, the piezoelectric module stably outputs a peak voltage of approximately 16.6 V, and the triboelectric unit stably outputs a peak voltage of approximately 4.4 V, which can effectively meet the self-driving requirements of intelligent bearings. Full article

This study investigates the effect of complex nanomodification combined with the simultaneous application of magnetic fields and mechanical vibration on the structure formation and performance properties of medium-alloy steel 40CrNi3MoV. Improving the structural homogeneity and operational characteristics of such steels remains an important task due to their widespread use in components operating under severe loading and wear conditions. The introduction of the nanostructured modifier InSteel-7 at a concentration of 0.03%, together with simultaneous magnetic and vibrational treatment of the melt, resulted in pronounced structural homogenization and grain refinement. Quantitative metallographic analysis using Thixomet Pro image analyzer revealed a significant refinement of the dendritic structure, with the secondary dendrite arm spacing decreasing from 73.9 μm to 27.9 μm. X-ray phase analysis confirmed the preservation of phase composition while indicating increased structural uniformity of the BCC matrix. Energy-dispersive spectroscopy and elemental micro-mapping demonstrated high chemical purity of the alloy and a uniform distribution of the modifier components. The combined treatment significantly improved the mechanical and tribological characteristics of the material. The average hardness increased from 390 HV to 510 HV, while tribological tests showed a reduction in wear track depth from 5.16 μm to 0.87 μm and a decrease in surface roughness from Ra 2.13 μm to 0.20 μm, indicating enhanced wear resistance. Full article

We suggest Josephson interferometry as a quantitative probe of spin–orbit-driven phenomena in superconducting heterostructures. Two distinct mechanisms are analyzed: (i) intrinsic helical superconductivity, producing asymmetric Fraunhofer patterns with lobe deformations and field-reversal asymmetry, and (ii) emergent interfacial magnetism in ferromagnet–superconductor hybrids, where Rashba spin–orbit coupling generates spontaneous fields that rigidly shift the interference fringes. The predicted signatures—flux-shifted interference minima, anisotropic critical current suppression, and angle-dependent pattern distortions—provide direct experimental access to finite-momentum pairing and interface-localized fields via standard Josephson current measurements. Full article

This paper presents the results of numerical calculation of steady-state magnetorheological fluid flow in the gap of an eccentric seal subjected to an external radial magnetic field. A coupled problem combining magnetic field analysis and laminar viscoplastic flow with Bingham rheology is solved to obtain pressure and velocity distributions within the seal gap, from which the hydrodynamic reaction forces of the fluid film and the rotor friction torque are determined. A parametric study was conducted in the ranges of rotor angular velocity ω = 100–400 rad/s, relative eccentricity ε = 0–0.9, and magnetic flux density B₀ = 0–0.5 T at the pressure differential Δp = 2 atm. Analysis of the results shows that increasing the magnetic flux density from 0 to 0.5 T leads to an increase in the seal reaction force from 12 N to 642 N and the friction torque from 0.35 N·m to 11.23 N·m. The most intensive growth of both characteristics is observed in the range B₀ = 0–0.3 T, beyond which saturation occurs as the MRF yield stress reaches its plateau value. An optimal control range of B₀ = 0.1–0.2 T was determined, ensuring maximum seal energetic efficiency as quantified by the load capacity-to-friction torque ratio, which is maximized at 70 N/(N·m). Based on the obtained results, the consequences of using magnetorheological seals on the performance of the rotor system are discussed, including the analysis of the sealing effect on rotor-dynamic stability. Within the proposed optimal range, it is shown that an increase in magnetic flux density leads to a sign reversal of the horizontal reaction F₂, while the monotonic growth of the ratio |F₂|/F₁ indicates an intensification of cross-coupling and a corresponding reduction in the rotordynamic stability margin at higher values of B₀. Full article

Superhydrophobic fiber films, as a typical superhydrophobic material, have advantages such as self-cleaning, non-wettability, and pollution resistance. They can be widely used in oil-water separation, antibacterial, anti-pollution, anti-icing, and self-cleaning fields. Traditional electrospun superhydrophobic fiber films face difficulties in fabricating fibers with large contact angles due to the non-Newtonian fluid flow and Taylor cone jet trajectory limitations. To address this challenge, this study develops a novel ultrasonic-magnetic field coupling electrospinning strategy for fabricating poly(methyl methacrylate)-polystyrene (PMMA-PS) fibrous films with enhanced superhydrophobicity. Physical, chemical, and contact angle measurements were used to analyze the morphology, composition, and hydrophobic properties of the fabricated films. The results showed that by controlling the blend ratio of PMMA and PS and optimizing the electrospinning process with ultrasonic vibration and magnetic field coupling, PMMA-PS fibers with better fiber refinement, closer spindle-shaped arrangements, and significantly increased roughness were successfully fabricated. When using 15% PMMA and 15% PS solutions, the static contact angle of the resulting fiber films reached 173.1°, demonstrating the best superhydrophobicity. The study suggests that optimizing the surface morphology of the nanofibers is an effective method to improve hydrophobicity and provides a new approach for fabricating superhydrophobic fiber films. Full article

Background/Objectives: Most brain magnetic resonance imaging (MRI) is performed in supine position, although posture may influence cerebrovascular signal characteristics through gravity-related physiological changes. However, posture-dependent vascular signal alterations on low-field MRI have not been sufficiently quantified. This study aimed to quantify posture-related internal carotid artery (ICA) signal alterations using low-field MRI by comparing seated and supine images with intensity-, noise-, and texture-based metrics. Methods: Nine healthy adults (20–69 years old; one female) underwent 0.25 T tilting MRI in supine and seated postures. 3D gradient echo T1-weighted images were obtained. The bilateral ICA regions of interest (ROI) and adjacent reference ROI were manually delineated. The signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), signal intensity ratio (SIR), gray-level co-occurrence matrix (GLCM) texture features (contrast, correlation, energy, and homogeneity) were extracted and compared between postures using Wilcoxon signed-rank tests. Results: Seated posture produced significantly higher ICA signal intensity metrics than the supine posture, with increased SNR (median 17.11 vs. 13.48), CNR (median 21.94 vs. 18.36), and SIR (median 10.84 vs. 9.54) (p = 0.004). GLCM texture analysis demonstrated a significant decrease in contrast in the seated position (median 62.01 vs. 145.92; p = 0.004), whereas correlation, energy, and homogeneity showed no significant between-posture differences. Conclusions: Low-field MRI was sensitive to posture-dependent ICA signal alterations. ICA-based metrics may provide quantitative markers of gravity-related cerebrovascular adaptation. Full article

Objective: To report on a series of three cases in which problems with rotating magnets (blocked rotation, demagnetization) occurred in cochlear implants and to resolve these problems without surgical intervention. Methods: Of the 3635 devices with rotating magnets implanted at this tertiary referral hospital, 2 exhibited rotation blockage (associated with misalignment of the coil or audio processor), and 1 was partially demagnetized in a 1.5 T MRI scanner. Results: One blockage resolved spontaneously without intervention. The second blockage was resolved in the static field of a 3T MRI scanner, where the demagnetized magnet was also re-magnetized to its original strength. Surgical intervention or re-implantation was not necessary in either case. Conclusions: Surgical intervention or re-implantation is not primarily required in the event of problems with the rotating implant magnet. Prior to surgery, technical analysis can lead to a conservative solution. Full article

Magnetoplasmadynamic thrusters represent a promising Electric Propulsion technology for future space missions; however, their optimization is hampered by the lack of accurate performance models in the emerging regime of low power (<12 kW) and high magnetic fields (>0.1 T), where traditional formulations prove inadequate. In this work, a new semi-empirical model for predicting the thrust and discharge voltage of argon-fed MPD thrusters was developed and validated. Starting from state-of-the-art physical models, multi-factorial correction factors were introduced to account for the coupled effects of discharge current (8–180 A), mass flow rate (3–21 mg/s), and applied magnetic field (up to 0.6 T). The model was calibrated and validated using a comprehensive and homogeneous collection of experimental data from the literature. A comparative analysis demonstrates that the corrected model significantly reduces prediction errors (0–9%) compared to reference models available in the literature (8–50%). In particular, the model exhibits remarkably superior accuracy in both the Self-Field and Applied-Field regimes, overcoming the main limitations of previous formulations and providing more robust estimates across a wide operational envelope. The developed model constitutes a reliable and physically consistent tool for the analysis and preliminary design of low-power, argon-fed magnetoplasmadynamic thrusters, enabling more effective optimization for this class of propulsion systems. Full article

The eddy current braking system (ECBS) is a crucial non-contact technology for high-speed railway. Conventional DC-excited systems face significant challenges such as excessive rail heating and high-capacity power supply requirements. This paper proposes a novel ECBS with AC excitation and auxiliary capacitor to achieve integrated energy recovery and power supply optimization. To evaluate its performance, a rigorous analytical framework is developed. First, a 2D subdomain model is established by incorporating the longitudinal end effect to solve the magnetic field distribution. Subsequently, an equivalent circuit is derived from the subdomain results to investigate steady-state braking characteristics and power flow. Analysis results demonstrate that the proposed system not only generates controllable braking force but also converts a portion of kinetic energy into storable electrical energy, effectively mitigating secondary rail heating. Most significantly, the implementation of an optimal auxiliary capacitor (134 μF) is found to reduce the required inverter capacity compared to inverter-only conditions. These findings provide a theoretical foundation and a practical design tool for developing high-performance, energy-efficient braking systems in high-speed transportation. Full article

Surface Acoustic Wave (SAW) magnetic sensors are traditionally fabricated on rigid substrates, which severely limits their application on curved or irregular surfaces. To address this critical limitation, this paper presents a novel flexible SAW magnetic sensor based on a grating-arrayed Terfenol-D thin film deposited on a 50 µm thick flexible lithium niobate (LiNbO₃) substrate. Unlike conventional designs using a continuous magnetostrictive layer, the proposed grating-arrayed structure is designed to aid in hysteresis compensation and minimize measurement errors associated with residual magnetization. As demonstrated experimentally, the sensors achieve a high sensitivity of 85.8 kHz/mT for devices with λ-wide gratings and a maximum frequency shift of 377 kHz at 5 mT. A systematic investigation reveals that sensitivity is critically dependent on the grating width and film thickness, with 500 nm thick gratings yielding optimal performance. Crucially, the sensor’s functionality under mechanical deformation is validated, and a differential measurement method is introduced to effectively compensate for stress-induced frequency shifts, ensuring reliable operation in practical, non-ideal conditions. The results confirm the sensor’s robust performance under the tested stress conditions, positioning this flexible SAW magnetic sensor as a promising solution for advanced, conformable sensing applications. Full article

We investigate the impact of ultrastrong magnetic fields on the structure of neutron stars within a density-dependent relativistic mean-field framework (DDME2). In the first case, we incorporate a magnetic field framework through Landau quantization of charged particles, yielding anisotropic pressure contributions and showing that field-induced stiffening increases stellar radii, maximum masses, and tidal deformabilities. To capture anisotropic stresses and geometric distortions, we employ axisymmetric equilibrium configurations computed with the XNS 4.0 code under the extended conformally flat condition. For magnetic field strengths up to $4.5\times {10}^{17}$ G, we analyze purely poloidal and toroidal geometries across a representative mass range (1.2–2.0 $M_{\odot }$). Axisymmetric models reveal that purely toroidal fields induce prolate deformations reaching $|\overline{e}| \approx 0.67$ for a 1.2 $M_{\odot }$ star, while purely poloidal fields drive oblate deformations with $\overline{e}\approx 0.24$, both diminishing with increasing stellar mass as greater gravitational binding resists magnetic reshaping. These macroscopic effects, combined with microphysical stiffening, have direct implications for gravitational-wave emission and systematic biases in radius measurements. Our study provides a systematic mapping between magnetic field strength, topology, and dense-matter stiffness, offering constraints relevant to multimessenger observations of magnetized neutron stars. Full article

The visualization of embryonic and fetal brain development at mesoscopic resolution represents a critical frontier in developmental neuroscience. This review presents advances in high-field magnetic resonance imaging (HF-MRI) that achieve unprecedented spatial resolution in ex vivo human embryonic and fetal brain specimens. This mesoscopic imaging capability bridges the gap between conventional clinical MRI and histological microscopy, enabling three-dimensional visualization of transient developmental structures including cortical lamination, ganglionic eminences, and emerging white matter pathways. We review the technical foundations of HF-MRI, present methodological advances that enable mesoscopic resolution, demonstrate applications across gestation, and discuss validation through histological correlation. The integration of multimodal imaging approaches—including T1-weighted, T2-weighted, T2*-weighted, diffusion tensor imaging, and quantitative relaxometry—provides comprehensive characterization of tissue microstructure and connectivity during critical periods of neurodevelopment. These advances offer transformative potential for understanding normal brain development, identifying early markers of neurodevelopmental disorders, and establishing high-resolution atlases of human prenatal neuroanatomy. Full article

Magnetic sensors based on the colossal magnetoresistance (CMR) effect in manganite thin films are promising for high-field measurements due to their wide operating range, low magnetoresistance anisotropy, and ability to function without full saturation at extremely high magnetic fields. However, the long-term stability of their transport properties remains a key challenge for practical sensor applications. In this work, accelerated aging of nanostructured La_1−xSr_xMn_yO₃ thin films was investigated for two manganese compositions: nominally stoichiometric (y = 1.05) and Mn-excess (y = 1.15). The electrical resistivity and magnetoresistive properties strongly depended on the manganese content and substrate type. Accelerated aging was induced by annealing at 100 °C in an argon atmosphere, and the evolution of the transport properties was analyzed using a stretched-exponential relaxation model. The analysis of the extracted parameters indicated defect-related mechanisms governing transport stability. It was found that despite the increase in resistivity during thermal treatment, the magnetoresistance changes were insignificant. The results provide insights into the aging behavior of nonstoichiometric manganite films and offer guidance for optimizing stabilization procedures in CMR-based magnetic field sensors. Full article

As critical equipment in the petroleum industry, coiled tubing is prone to safety hazards, including stress concentrations and fatigue failure, under complex operating conditions. An online enhanced metal magnetic memory detection method was employed to reduce noise in surface magnetic field signals from tubing subjected to 35 MPa of internal pressure across different fatigue cycles. Conventional signal processing methods have difficulty effectively extracting characteristic magnetic field signals in high-noise environments; therefore, a comprehensive comparison of the noise reduction effectiveness of five common signal processing techniques in stress-distorted regions was conducted, an in-depth analysis of the limitations of different methods was performed, and a hybrid noise reduction framework combining wavelet threshold denoising (WTD) and sequential variational modal decomposition (SVMD) was established. Concurrently, the whale optimization algorithm (WOA), which possesses global search capabilities and demonstrates good adaptability to multi-parameter coupling issues in hybrid denoising frameworks, was innovatively proposed for key parameter optimization. Using fuzzy entropy (FE) as an evaluation metric, the experimental results demonstrated that magnetic field signals in all directions achieved at least a 1.03% reduction in FE and a minimum increase of 33.1% in integrated side lobe ratio (ISLR). This provided effective technical support for reliably detecting stress-distortion zones on coiled-tubing surfaces and established the engineering necessity of implementing preventive maintenance. Full article

External stray magnetic fields from permanent magnet synchronous motors (PMSMs) may cause electromagnetic interference to nearby equipment and limit their application in space-constrained systems. To address this issue, this paper investigates the use of laminated Co-based amorphous ribbon shields for stray-field suppression. An efficient equivalent modeling method is proposed for the simulation of such multilayer thin shielding structures, in which the laminated shield is replaced by an equivalent single-layer model while preserving its macroscopic shielding behavior. The method is first assessed in 2-D through comparisons between refined laminated and simplified equivalent models under both linear permeability and nonlinear magnetization-curve descriptions, and is then extended to 3-D PMSM shielding analysis under static and rotating no-load conditions with experimental validation. Results show that the 10-layer amorphous ribbon shield, with a total thickness of 420 μm, achieves a maximum shielding effectiveness of 7.9 dB at a measurement distance of two motor radii. The maximum deviation between simulation and experiment is 7.4%, and the equivalent model reduces computation time by 28% relative to the refined model. This method provides an accurate and efficient approach for the analysis and design of compact low-frequency magnetic shields for PMSMs. Full article