Uniform Magnetic Field Research Articles

A magnetic pendulum for demonstrating Mathieu-type parametric resonance

Abstract We describe a magnetic pendulum apparatus designed for studying and demonstrating Mathieu-type parametric resonance. The apparatus features a T-shaped rigid arm with a neodymium (NdFeB) magnet bob, suspended by double V-shaped thread suspensions. It is parametrically driven by an alternating uniform magnetic field produced by Helmholtz coils. The pendulum is structurally simple and easy to implement, and its parameter-driven mechanism is transparent in terms of physics. The use of electromagnetic driving allows for precise control over both the frequency and amplitude of parameter modulation, enabling quantitative studying on parametric resonance. We have observed the first and second instability region of parametric resonance. We also theoretically analyze the impact of non-uniformity in the Helmholtz coils' magnetic field on the pendulum motion, revealing that the non-uniformity can significantly alter the pendulum's nonlinearity, influencing both the magnitude and the sign of the coefficients of the nonlinear terms. However, under the parameters of our experimental setup, the nonlinearity effect is mainly manifested in large swing angle motions. For small swing angle within 5\textsuperscript{$\circ$}, the impact of magnetic field non-uniformity on parametric resonance is negligible. The experiment reported here is appropriate for undergraduates to carry out experimental research, helping them develop a more intuitive and quantitative understanding of parametric resonance.

Reverse-Bent Modular Coil Structure with Enhanced Output Stability in DWPT for Arbitrary Linear Transport Systems

Dynamic wireless power transfer (DWPT) systems with segmented transmitters suffer from output pulsations during the moving process. Although numerous coil structures have been developed to mitigate this fluctuation, the parameter design process is complicated and restricted by specific working conditions (e.g., air gaps). To solve these problems, a novel reverse-bent modular transmitter structure is proposed for DWPT in industrial automatic application scenarios such as linear transport systems. Considering the heterogeneous current density distribution in the adjacent region between two coils which causes a drop in magnetic field, the proposed coil structure attempts to eliminate the effects of the adjacent region by bending the terminal parts of each coil reversely to the ferrite layer for shielding. Compared to traditional planar couplers, this structure array can generate a uniform magnetic field over various air gaps. A 100 W laboratory prototype was built to verify the feasibility of the proposed system. The experimental results show that the proposed system achieved a constant output voltage, and the output pulsation was within ±2.3% in the dynamic powering process. The average efficiency was about 88.29%, with a 200 mm transfer distance. When the air gap varied from 20 mm to 30 mm, the system could still retain constant voltage output characteristics.

Impacts of Buoyancy and Joule Heating on Unsteady MHD Fluid Flow Along a Semi‐Infinite Vertical Porous Plate With Dufour, Chemical Reaction, and Radiation Effect

ABSTRACTAn analytical solution for unsteady, incompressible, laminar MHD fluid flow involving mass and heat transfer along a semi‐infinite vertical moving flat plate in a porous medium have been studied in this paper. Effects of heat radiation and absorption, Joule heating, Dufour, thermal and solutal buoyancy, and first order chemical reaction of are discussed under suitable physical conditions. It is postulated that the plate will migrate in the fluid's motion's direction due to the presence of a uniform magnetic field normal to the porous surface. The regular perturbation technique is used to solve the dimensionless governing equations. The mathematical derivations for fluid velocity, temperature, and concentration are evaluated; apart from that, skin friction, rate of mass and heat transfer at the plate are also expressed. The present outcomes are compared with previously obtained results and are found to be in excellent agreement. It is observed that the fluid velocity and temperature enhanced with thermal and solutal buoyancy forces as well as the Dufour effect. Also, with an increase in chemical reaction parameter, there is a decrease in fluid velocity, temperature, and concentration. Skin friction and Nusselt number increase with higher heat absorption parameter values. Schmidt number and chemical reaction parameter both lead to a rise in Sherwood number. Applications for these models have been observed in a number of industrial and technical methods.

Extension of the multilevel radiative transfer code PyRaTE to model linear polarization of molecular lines

Linear polarization of spectral lines, commonly known as the Goldreich-Kylafis effect within the star formation community, is one of the most underutilized techniques for probing magnetic fields in the dense and cold interstellar medium. In this study, we implement linear polarization of molecular spectral lines into the multilevel, non-local thermodynamic equilibrium radiative transfer code PyRaTE Different modes of polarized radiation are treated individually, with separate optical depths computed for each polarization direction. Our implementation is valid in the so-called strong magnetic field limit and is exact for either a system satisfying the large-velocity-gradient approximation, and/or for any system with a uniform magnetic field. We benchmark our implementation against analytical results and provide tests for various limiting cases. In agreement with previous theoretical results, we find that in the multilevel case the amount of fractional polarization decreases when compared to the two-level approximation, but this result is subject to the relative importance between radiative and collisional processes. Finally, we post-process an axially symmetric, nonideal magnetohydrodynamic chemo-dynamical simulation of a collapsing prestellar core and provide theoretical predictions regarding the shape (as a function of velocity) of the polarization fraction of $ CO $ during the early stages in the evolution of molecular clouds.

A reverse Faber-Krahn inequality for the magnetic Laplacian

We consider the first eigenvalue of the magnetic Laplacian in a bounded and simply connected planar domain, with uniform magnetic field and Neumann boundary conditions. We investigate the reverse Faber-Krahn inequality conjectured by S. Fournais and B. Helffer, stating that this eigenvalue is maximized by the disk for a given area. Using the method of level lines, we prove the conjecture for small enough values of the magnetic field (those for which the corresponding eigenfunction in the disk is radial).

Numerical study of effective parameters on deformation and coalescence of ferrofluid droplets under uniform magnetic field

This research examines different numerical techniques for modeling ferrofluids in a non-magnetic liquid subjected to homogeneous and steady magnetic field. It particularly compares the conservative level set method with the Volume of Fluid (VOF) and Simple Coupled Level Set and Volume of Fluid (SCLSVOF) methods. By comparing these methods with experimental data, we established the superiority of the utilized method in this study. Several case studies were conducted to evaluate how a homogeneous magnetic actuation affects ferrofluid dynamics, considering parameters such as initial droplet size, surface tension coefficient, and magnetic susceptibility. Additionally, the study explored the coalescence of two falling ferrofluid droplets under the combined effects of an external magnetic field and gravity. The conservative level set method was shown to be extendable to three-dimensional environments, unlike the standard level set method. The novelty of this work lies in demonstrating that the conservative level set method is particularly effective for ferrofluids, accurately capturing their complex dynamics. The main novelty of this article lies in demonstrating the precision of Conservative Level Set Method while utilizing a reduced number of equations compared to other works. This reduction in complexity enhances the method's efficiency without compromising precision, making it especially suited for applications requiring both speed and accuracy, such as model-based control systems.

Orbits of particles with magnetic dipole moment around magnetized Schwarzschild black holes: Applications to the S2 star orbit

This study provides a comprehensive analytical investigation of the bound and unbound motion of magnetized particles orbiting a Schwarzschild black hole immersed in an external asymptotically uniform magnetic field, which includes all conceivable types of bounded and unbounded orbits. In particular, for planetary orbits, we perform a comparative analysis of our findings with the observed position of the S2 star carrying magnetic dipole moment around Sagittarius A*. We found maximum and minimum values for the parameter of magnetic interaction between the magnetic dipole of the star and the external magnetic field, as well as the energy and angular momentum of the S2 star. As a result, we obtain estimations of the magnetic dipole of the star in the order of 106 G·cm3. Additionally, we explore deflecting trajectories akin to gravitational Rutherford scattering. In obtaining the solutions for the orbital equations, we articulate the elliptic integrals and Jacobi elliptic functions, and illustrative figures and simulations augment our study. Published by the American Physical Society 2024

Overcoming the Challenges of Hyperpolarizing Substrates with Parahydrogen‐Induced Polarization in an MRI System

Hyperpolarization of 13C nuclei in biomolecules and their administration as imaging agents enables in‐vivo monitoring of metabolism. This approach has demonstrated potential for deriving imaging biomarkers for cancer detection, differentiation, and therapy efficacy assessment. The in situ generation of polarized substrates using a permanent addition of parahydrogen to an unsaturated precursor inside the bore of an MRI system used for subsequent imaging circumvents the need for a dedicated external polarizer. This approach reduces polarization loss associated with sample transfer, minimizes hardware requirements and cost, and results in reduced spatial requirements. However, performing INEPT‐like pulsed sequences for heteronuclear spin‐order transfer in the bore of an MRI system is challenged by poor uniformity of static and excitation magnetic field and molecular convection during the polarization transfer. Therefore, here we characterize these effects, implement a robust modification to the pulse sequence, and measure experimentally the polarization improvement upon modification of the sequence. After rigorous optimization of the parameters, we obtained a 13C polarization of 44.5% for 50 mM of the 1‐13C site of ethyl acetate‐d6. Our parahydrogen‐induced polarization approach enhances the accessibility to hyperpolarized MRI, circumventing the need for an external polarizer.

Semiclassical Scattering by Edge Imperfections in Topological Insulators Under Magnetic Field

We study the scattering of edge states of 2D topological insulator in the uniform external magnetic field due to edge imperfections, common in realistic 2D topological insulator samples. The external magnetic field breaks time-reversal symmetry, opening the possibility of the scattering of otherwise topologically protected fermionic edge states. The scattering happens to be always an over-barrier event, irrespective of the shape of the edge deformation and magnitude of the magnetic field. We use the advanced Pokrovsky–Khalatnikov semiclassical approach, which allows us to obtain analytically both the main exponential and pre- exponential factors of the scattering amplitude for wide classes of analytic deformation profiles.

Establishment of Theoretically Guided Understanding for Magneto‐Optical Interactions through Ferromagnetic Fluids in Uniform, Static Magnetic Field

Prior magneto‐optical transmission models through ferrofluids are limited by oversimplifications which hinder accuracy and generalizability. To overcome this challenge, this study models the magnetic field effect on the magneto‐optical transmission through hematite ferrofluid using the method of invariant embedding. Optical coherence tomography (OCT) is used to extract the changes in the refractive index, enabling a discovery of a magnetodielectric effect for the hematite ferrofluid. To establish a basis for control and understanding, the influence of the magnetic field on the spatial transmission profile at different wavelengths, optical propagation lengths, and the effect of variation of each size parameter on the optical transmission have been investigated. Further parametric studies allowed finding out an analogy to nonuniform, cascade, volume holographic diffraction gratings, which is crucial for a wide range of optical and bioimaging applications. Compared to the experimental results, the presented model achieves 99% accuracy over the wavelength range (300–1100) nm under uniform static magnetic field (0–6.5) mT. Besides, the conspicuous lead of evidentiary understanding of magneto‐optical interactions with magnetic fluids, the structural milestones of the model can be further utilized to model similar challenging constructs in complex media. The innumerable applications of study extend to involve communication engineering, biomedical, optical, and security applications.

Dispersive and Strichartz Estimates for Schrödinger Equation with One Aharonov–Bohm Solenoid in a Uniform Magnetic Field

Dispersive and Strichartz Estimates for Schrödinger Equation with One Aharonov–Bohm Solenoid in a Uniform Magnetic Field

Tunable magnonic crystal in a hybrid superconductor–ferrimagnet nanostructure

One of the most intriguing properties of magnonic systems is their reconfigurability, where an external magnetic field alters the static magnetic configuration to influence magnetization dynamics. In this paper, we present an alternative approach to tunable magnonic systems. We studied theoretically and numerically a magnonic crystal induced within a uniform magnetic layer by a periodic magnetic field pattern created by the sequence of superconducting strips. We showed that the spin-wave spectrum can be tuned by the inhomogeneous stray field of the superconductor in response to a small uniform external magnetic field. Additionally, we demonstrated that modifying the width of superconducting strips and separation between them leads to the changes in the internal field which are unprecedented in conventional magnonic structures. The paper presents the results of semi-analytical calculations for realistic structures, which are verified by finite-element method computations.

Nanoparticle positioning effect on the percolation phenomenon of the polyethylene oxide/iron nanocomposite films

AbstractIn this research, we demonstrate the influence of compelled iron nanoparticles (FeNPs) up to the surface on the percolation phenomenon and the electrical conductivity of the PEO/FeNPs nanocomposite films by applying a uniform magnetic field. The electrical conductivity of the PEO/FeNPs nanocomposite films exhibits a sharp increase from to 390 S∙cm−1 as the FeNPs volume fraction rises from 0.12 to 0.24, where the FeNPs form percolating networks and interparticle contacts. Applying a magnetic field drives the FeNPs towards the surface of the PEO/FeNPs nanocomposite films and consequently increases the electrical conductivity of the PEO/FeNPs nanocomposite films up to 1960 S∙cm−1. The morphological features of the PEO/FeNPs nanocomposite films with different concentrations of FeNPs upon applying a magnetic field towards the surface were investigated. Finally, the corrosion protection efficiency of PEO/FeNPs nanocomposite films increases as FeNPs increase from an insulating zone to a conductive zone. On the other hand, applying a magnetic field drives the FeNPs towards the PEO/FeNPs nanocomposite surfaces, increasing the corrosion protection efficiency from 92.67% to 98.09%.Highlights The nanoparticle positioning effect on nanocomposite films is investigated. The electrical conductivity of PEO/FeNPs nanocomposite film reaches 390 S∙cm−1. Electrical conductivity increases to 1960 S∙cm−1 upon nanoparticle positioning. Corrosion protection efficiency increases to 98.09% after nanoparticle positioning.

Investigating new aspects of Bocharova–Bronnikov–Melnikov–Bekenstein spacetime: ionized thin accretion disk model

Accretion processes near black hole candidates are associated with the high-energy emission of radiation from relativistic particles and outflows. It is widely believed that the magnetic field plays a crucial role in explaining these high-energy processes near these astrophysical sources. In this work, we analyze thin accretion disks in the Bocharova–Bronnikov–Melnikov–Bekenstein (BBMB) spacetime framework using the Novikov–Thorne model. Our study examines the thermal and optical characteristics of these disks, including their emission rate and luminosity in the specified spacetime. Later, we extend the Novikov–Thorne model to ionized thin accretion disk. We propose that the black hole is embedded in an asymptotically uniform magnetic field. We investigate the dynamics of charged particles near a weakly magnetized black hole. Our findings show that, in the presence of a magnetic field, the radius of the marginally stable circular orbit (MSCO) for a charged particle is close to the black hole’s horizon. The orbital velocity of the charged particle, as measured by a local observer, has been computed in the presence of the external magnetic field. We also present an analytical expression for the four-acceleration of the charged particle orbiting around black holes. Finally, we determine the intensity of the radiation emitted by the accelerating relativistic charged particle orbiting the magnetized black hole.

Computational outline on heat transfer analysis and entropy generation in hydromagnetic squeezing slip flow of hybrid nanofluid

PurposeThe current work investigates an unsteady squeezed flow of hybrid-nanofluid between two parallel plates in occurrence with a uniform transverse magnetic field. Water is used as base fluid mixed with Graphene Oxide (GO) and Copper (Cu) nanoparticles. The flow considered here is under slip boundary conditions.Design/methodology/approachThe governing PDEs are transmuted into ODEs by applying an appropriate similarity transformation and then solved numerically using the 4th order R-K method with shooting technique. Graphical illustrations for velocity, temperature, entropy generation (NG), Bejan number (Be), streamline etc. are presented and discussed in detail from the physical point of view. The nature of the Nusselt number is also studied numerically through contour plots for different flow parameters.FindingsThere is no funding obtained for the research work.Social implicationsThis kind of study may be used in various fields including polymer processing, lubrication apparatus, compression including hydrodynamical machines compression, food processing etc.Originality/valueIt is observed that very little investigation has yet been made about the movement of hybrid nanofluid between two analogous plates.

Design and optimization of a novel solenoid with high magnetic uniformity

Currently, solenoids are extensively utilized in various research fields due to their flexibility of fabrication and high magnetic field strength. However, the internal magnetic field of the solenoid itself exhibits some non-uniformity defects, which limits its application in some domains. This article proposes a novel single winding tightly wound solenoid structure with an improved magnetic field uniformity. To optimize the magnetic field near the aperture of the conventional solenoid, an auxiliary solenoid with a gradually changing diameter is included at each end of the solenoid. By adjusting different parameters of the auxiliary solenoid, the edge effect of the solenoid was reduced, and its overall magnetic field uniformity was improved. The optimization of the auxiliary solenoids is achieved through GA-KAN network techniques. Finite element simulation results with the optimized parameters show that the proportion of uniform areas can be improved by more than five times. The research results are a reference for high-precision electromagnetic sensing applications based on solenoids.

Magnetic polarizability of octet baryons via lattice QCD

Drawing on recent advances in lattice QCD background-field techniques, the magnetic polarizability of octet baryons is calculated from the first principles of QCD. The results are presented in the context of new constituent quark model calculations providing a framework for understanding the lattice results and a direct comparison with simulation results at unphysical quark masses. Using smeared quark sources, low-lying Laplacian eigenmode projection and final-state Landau-mode projection, considerable attention is devoted to ensuring single-state isolation in the lattice correlation functions. We also introduce new weighting methods to reduce the sensitivity to correlation-function fits, averaging over many fits based on merit drawn from the full correlated χ2 of the fits. The techniques are implemented on the 323×64, 2+1-flavor dynamical-fermion lattices provided by the PACS-CS Collaboration following the introduction of uniform magnetic fields quantized to the lowest nontrivial values available. After some scaling of the constituent quark model parameters, we find the model captures the patterns observed in the lattice QCD results very well, providing important insights into the physics underpinning the magnetic polarizabilities. Finally, comparison with the most recent results from experiment proceeds through an effective field theory formalism which incorporates estimates of finite-volume corrections and small electroquenching corrections as the results are brought to the physical point. We find excellent agreement with experiment where available, including the proton and neutron polarizabilities. Published by the American Physical Society 2024

Entropy analysis of mixed convective electro-magnetohydrodynamic couple-stress hybrid nanofluid flow with variable electrical conductivity in a porous channel

The paper presents a novel study to examine the irreversibility of quadratically mixed convective electro-magnetohydrodynamic (EMHD) flow of a couple-stress hybrid nanofluid (CSHNF) with variable properties in a vertical porous channel. The channel walls are exposed to an applied electric field effect and a uniform transverse magnetic field. The hybrid nanofluid considered is an ethylene glycol (C 2 H 6 O 2) base mixed with multi-walled carbon nanotubes (MWCNT) and silver (Ag) nanoparticles (NPs), assuming the base fluid and nanoparticles to be in a state of thermal equilibrium following the Tiwari-Das nanofluid model. The potential applications of the study can be in microfluidics to nanofluidics, particularly in developing cooling technologies, EMHD pumps, high-end microelectromechanical systems (MEMS), and lab-on-a-chip (LOC) devices used in bioengineering. A constant pressure gradient acting in the flow direction and the buoyancy effect under the quadratic Boussinesq approximation drive the flow. The governing momentum and energy equations are nondimensionalized using pertinent dimensionless parameters and solved by the semi-analytical homotopy analysis method (HAM). The entropy generation and the Bejan numbers are derived to examine the irreversibilities in the system. To investigate the rate of shear stresses and heat transfer, skin friction coefficients and Nusselt numbers on the channel walls are determined. The analysis emphasizes the influence of nanoparticle concentration and electromagnetic field on the flow dynamics, temperature distribution, and system irreversibilities in the presence of porous media. It reveals the enhancement of fluid velocity and temperature degradation for higher concentrations. In contrast, both reduce for higher magnetic and electrical strength. With the enhancement of electrical joule heating and quadratic convection, a higher entropy generation rate is attained with a low rate of heat transfer irreversibility. However, it reduces with higher nanoparticle concentration, electrical strength, porosity, and variable electrical conductivity parameters under the dominance of heat transfer irreversibility.

A penta-hybrid approach for modeling the nanofluid flow in a spatially dependent magnetic field

Abstract The penta-hybrid nanofluid is a nanofluid that contains five different types of nanoparticles. It can achieve higher heat transfer rates than conventional hybrid nanofluids due to the synergistic effects of the nanoparticles. It also has more diverse physical and thermal properties, which make it more adaptable for various applications. Therefore, this research examines the influence of localized magnetic fields on the vortex dynamics in a penta-hybrid nanofluidic flow in a vertical cavity with an aspect ratio of 1:10, driven by a top and bottom lid moving in the opposite direction. The stream-vorticity formulation is used to solve the dimensionless governing partial differential equation. A confined magnetic field in the form of horizontal and vertical strips has been applied instead of a uniform magnetic field throughout the flow domain, which is more realistic. Moreover, MATLAB codes developed by the authors are used to investigate how these parameters affect the flow and thermal properties of the nanofluids. The results suggest that magnetic fields have an impact on how stress, flow patterns, and temperature are distributed. Moreover, the presence of a magnetic field influences the spacing of isotherms, indicating a more even temperature distribution. It has also been observed that stress distribution is affected by the magnetic field, with higher stress levels near walls and regions with velocity-induced stress. However, in certain areas, the magnetic field can decrease shear stress depending on its strength and orientation. These study findings have implications for designing and operating nanofluidic devices. For instance, utilizing a magnetic field can help regulate flow patterns, temperature distribution, and stress distribution within nanofluidic channels. This capability could prove beneficial for a range of applications, such as cell separation, drug delivery, and nanofluidic heat exchange systems.

Effect of metallic materials on magnetic resonance image uniformity: a quantitative experimental study.

To assess quantitatively the effect of metallic materials on MR image uniformity using a standardized method. Six types of 1cm cubic metallic materials (i.e., Au, Ag, Al, Au-Ag-Pd alloy, Ti, and Co-Cr alloy) embedded in a glass phantom filled were examined and compared with no metal condition inserted as a reference. The phantom was scanned five times under each condition using a 1.5-T MR superconducting magnet scanner with an 8-channel phased-array brain coil and head and neck coil. For each examination, the phantom was scanned in three planes: axial, coronal, and sagittal using T1-weighted spin echo (SE) and gradient echo (GRE) sequences in accordance with the American Society for Testing and Materials (ASTM) F2119-07 standard. Image uniformity was assessed using the non-uniformity index (NUI), which was developed by the National Electrical Manufacturers Association (NEMA), as an appropriate standardized measure for investigating magnetic field uniformity. T1-GRE images with Co-Cr typically elicited the lowest uniformity, followed by T1-GRE images with Ti, while all other metallic materials did not affect image uniformity. In particular, T1-GRE images with Co-Cr showed significantly higher NUI values as far as 6.6cm at maximum equivalent to 11 slices centering around it in comparison with the measurement uncertainty from images without metallic materials. We found that MR image uniformity was influenced by the scanning sequence and coil type when Co-Cr and Ti were present. It is assumed that the image non-uniformity in Co-Cr and Ti is caused by their high magnetic susceptibility.