Uniform Magnetic Field Research Articles

Numerical Simulation and Neural Network Model for Hydromagnetic Nanofluid Convection in a Porous Wavy Channel with Thermal Non-Equilibrium Model

Abstract The present study aims to analyze the nonfluid MHD convective heat transfer in a porous wavy channel with a local thermal non-equilibrium (LTNE) model. Such a model finds applications related to enhancement in thermal performance, increasing the heat transfer coefficient in the compact design of heat exchangers for the aerospace and automotive industries and elevation in the efficiency of the solar collector. A sinusoidal porous wavy LTNE channel containing nanofluid and subjected to the induced and applied magnetic fields is considered. A uniform magnetic field is applied orthogonal to the channel and the induced magnetic field effects are considered due to the large magnetic Reynolds number. The momentum, continuity, energy, and nanoparticle volume fraction equations constitute the coupled nonlinear system of differential equations and are solved using the Galerkin finite element method. The reliability of the technique is assessed by comparing the proposed procedure with the results from earlier sources. A detailed analysis is presented to determine the effects of different physical parameters arising in the system on temperature, nanoparticle concentration, and velocity profiles. As an illustration, the findings exhibit that increasing the modified diffusivity ratio increases the values of the nanoparticle volume fraction whereas, reducing the modified diffusivity ratio enhances the temperature distribution. A higher value of thermal Rayleigh number presents a significant involvement of buoyancy forces, potentially resulting in the development of convective currents. A higher Nield number indicates more effective heat transport from the solid surface to the nanofluid. Consequently, there is a minimal thermal difference between the solid surface and the bulk nanofluid. Effective heat transmission enhances the nanofluid ability to absorb heat and generates a more consistent dispersion of temperature inside the fluid. The performance of the designed algorithms of the artificial neural network, namely, the Levenberg – Marquardt algorithm, in the problem under consideration is evaluated and the methodology is found reasonably precise with the matching of order around 6 to 7 decimal places of accuracy.

On the Piezomagnetism of Magnetoactive Elastomeric Cylinders in Uniform Magnetic Fields: Height Modulation in the Vicinity of an Operating Point by Time-Harmonic Fields.

Soft magnetoactive elastomers (MAEs) are currently considered to be promising materials for actuators in soft robotics. Magnetically controlled actuators often operate in the vicinity of a bias point. Their dynamic properties can be characterized by the piezomagnetic strain coefficient, which is a ratio of the time-harmonic strain amplitude to the corresponding magnetic field strength. Herein, the dynamic strain response of a family of MAE cylinders to the time-harmonic (frequency of 0.1-2.5 Hz) magnetic fields of varying amplitude (12.5 kA/m-62.5 kA/m), superimposed on different bias magnetic fields (25-127 kA/m), is systematically investigated for the first time. Strain measurements are based on optical imaging with sub-pixel resolution. It is found that the dynamic strain response of MAEs is considerably different from that in conventional magnetostrictive polymer composites (MPCs), and it cannot be described by the effective piezomagnetic constant from the quasi-static measurements. The obtained maximum values of the piezomagnetic strain coefficient (∼102 nm/A) are one to two orders of magnitude higher than in conventional MPCs, but there is a significant phase lag (35-60°) in the magnetostrictive response with respect to an alternating magnetic field. The experimental dependencies of the characteristics of the alternating strain on the amplitude of the alternating field, bias field, oscillation frequency, and aspect ratio of cylinders are given for several representative examples. It is hypothesized that the main cause of observed peculiarities is the non-linear viscoelasticity of these composite materials.

Magnetic field simulation and analysis of superconducting magnetic separator with different magnetic matrices

Superconducting magnetic separation technology leverages strong magnetic fields to separate magnetic from non-magnetic materials, vital for industries like mining, recycling, and water treatment. This study aims to elucidate the impact of various magnetic gathering media on the magnetic field distribution within superconducting magnetic separators through detailed modeling and simulation. Using Infolytica MagNet software, we simulate the magnetic field distribution of a JS-6-102 pilot-scale superconducting magnetic separator, both without media and with different magnetic matrices, such as mesh and rod media. Our results reveal that the presence of magnetic matrices significantly alters the magnetic field distribution, enhancing magnetic induction intensity and affecting field uniformity. We demonstrate that smaller mesh sizes yield more uniform magnetic fields, while larger rod diameters increase magnetic field distortion. These findings contribute to optimizing the design and efficiency of superconducting magnetic separation systems.

Unsteady Two-Dimensional Drift of a Viscoelastic Fluid with Magnetic and Thermal Effects: A Perturbation Approach

This study explores the unsteady, two-dimensional flow of an electrically conductive, viscoelastic, and incompressible fluid past a uniformly moving, infinite, non-conducting vertical plate, in the presence of a uniform first-order chemical process involving mass and heat transfer. A uniform magnetic field is applied perpendicular to the flow, with the magnetic Reynolds number assumed small to neglect the induced magnetic field. The governing equations are solved using a regular perturbation method, yielding approximate solutions for concentration, velocity, temperature, and shear stress at the plate. Additionally, mass and heat transfer rates are determined, with the influence of viscoelasticity and other physical parameters emphasized. Where applicable, results are graphically represented.

Nonlinear dust ion acoustic solitary waves propagation in a magnetized plasma with Tsallis electron distribution

Abstract We have done a theoretical investigation into the propagation of nonlinear dust ion acoustic solitary waves and their soliton properties in a three-component magnetized collisionless plasma consisting of inertial positively charged ions, noninertial electrons following a Tsallis q–distribution, and stationary negatively charged dust grains. We consider a uniform external magnetic field along the z–direction, and the wave propagation occurs obliquely to the magnetic field direction. It is observed that the two types of wave modes namely slow and fast modes, are appears in the linear analysis. By employing the reductive perturbation method, the Korteweg-de Vries (KdV) and modified KdV equations are determined to describe the small amplitude dust ion acoustic soliton. The dependence of several physical plasma parameters including nonextensive q–parameter, magnetic field strength etc. of our plasma on the propagating dust ion acoustic solitary waves potential are numerically examined. This study shows the simultaneous existence of compressive and rarefactive solitons due to the variation of first order nonlinearity coefficient represented by the KdV equation and it is found that there is a critical point for the plasma parameters where the amplitude of the soliton of KdV equation become diverges. The mKdV equation with second order nonlinearity coefficient is derived from there and observed the solitons only with finite amplitude. The present study could be helpful for understanding the nonlinear travelling waves propagating in laboratory and space plasma environments.

Zastosowanie Metody Elementów Skończonych do analizy metody określania rozmiaru buta na podstawie pomiarów pola magnetycznego

Paper presents utilization of Finite Element Method (FEM) for analysis of usefulness of shoe size assessment method, based on magnetovision measurements. Measurement method based on disturbances of the uniform magnetic field (e.g. Earth’s magnetic field) is presented. Disturbances are caused by loose material of high magnetic permeability placed inside the tested shoe, which adapts to the insides of the shoe. The disturbed magnetic field is measured by the matrix of magnetometers. The values of magnetic field are an input into inverse transformation algorithm which fits the position of matrix sensors into the reference (obtained by FEM) distribution of magnetic field. Based on the fitted parameters of sensors matrix a ratio between the measured and reference shoe size was determined. A FEM-based forward transformation is presented, which allows for generation of three-dimensional array of magnetic field distribution. Initial tests of inverse transformation were conducted successfully. Next steps consisted of tests of inverse transformation method with an inclusion of the typical measurement noise. A FEM-based forward transformation was conducted of a modified shoe model (including simplified screw model). Inverse transformation was conducted but both influence of measurement noise, as well as the presence of additional high permeability material, resulted that the presented shoe size assessment method is not suitable for practical implementation.

Axial, planar-diagonal, body-diagonal fields on the cubic-spin spin glass in d=3: A plethora of ordered phases under finite fields.

A nematic phase, previously seen in the d=3 classical Heisenberg spin-glass system, occurs in the n-component cubic-spin spin-glass system, between the low-temperature spin-glass phase and the high-temperature disordered phase, for number of spin components n≥3, in spatial dimension d=3, thus constituting a liquid-crystal phase in a dirty (quenched-disordered) magnet. Furthermore, under application of a variety of uniform magnetic fields, a veritable plethora of phases is found. Under uniform magnetic fields, 17 different phases and two spin-glass phase diagram topologies (meaning the occurrences and relative positions of the many phases), qualitatively different from the conventional spin-glass phase diagram topology, are seen. The chaotic rescaling behaviors and their Lyapunov exponents are calculated in each of these spin-glass phase diagram topologies. These results are obtained from renormalization-group calculations that are exact on the d=3 hierarchical lattice and, equivalently, approximate on the cubic spatial lattice. Axial, planar-diagonal, or body-diagonal finite-strength uniform fields are applied to n=2 and 3 component cubic-spin spin-glass systems in d=3.

Effective quantum dynamics for magnetic fermions

We show how to derive an effective nonlinear dynamics, described by the Hartree-Fock equations, for fermionic quantum particles confined to a two-dimensional box and in presence of an external, uniform magnetic field. The derivation invokes the Dirac-Frenkel principle. We discuss the validity of this effective description with respect to the many-body Schr\"odinger dynamics for small times and for weak interactions, and also in regards to the number of particles.

Numerical investigation of synergistic effects of magnetic fields and bluff bodies on heat transfer enhancement and pressure drop reduction in microchannels

Efficient thermal management is essential for designing compact and high-performance heat sinks and heat exchangers. This study addresses the challenge of optimizing heat transfer while minimizing pressure losses in systems exposed to concentrated heat flux by proposing a novel approach that employs both active and passive vortex generators. Specifically, a uniform magnetic field generated by permanent magnets and a bluff body are utilized within a microchannel containing a 2 vol% ferrofluid. Numerical simulations were performed across Reynolds numbers ranging from 100 to 500 and magnetic field intensities up to 0.5 T to evaluate the system's performance. The results demonstrate that the combination of magnetic fields and a bluff body induces vortex generation, alters velocity distribution, and enhances flow mixing, resulting in a 30 % increase in heat transfer efficiency and an 11 % reduction in pressure drop under optimal conditions. Although the introduction of barriers led to a 3 % rise in pressure drop, the uniform magnetic field effectively mitigated friction by reducing flow separation and limiting surface contact. These findings highlight the potential of this method for improving the design of advanced thermal management systems.

A hybrid, nonlinear programming approach for optimizing passive shimming in MRI.

In magnetic resonance imaging (MRI), maintaining a highly uniform main magnetic field (B0) is essential for producing detailed images of human anatomy. Passive shimming (PS) is a technique used to enhance B0 uniformity by strategically arranging shimming iron pieces inside the magnet bore. Traditionally, PS optimization has been implemented using linear programming (LP), posing challenges in balancing field quality with the quantity of iron used for shimming. In this work, we aimed to improve the efficacy of passive shimming that has the advantages of balancing field quality, iron usage, and harmonics in an optimal manner and leads to a smoother field profile. This study introduces a hybrid algorithm that combines particle swarm optimization with sequential quadratic programming (PSO-SQP) to enhance shimming performance. Additionally, a regularization method is employed to reduce the iron pieces' weight effectively. The simulation study demonstrated that the magnetic field was improved from 462 to 3.6ppm, utilizing merely 1.2kg of iron in a 40cm diameter spherical volume (DSV) of a 7T MRI magnet. Compared to traditional optimization techniques, this method notably enhanced magnetic field uniformity by 96.7% and reduced the iron weight requirement by 81.8%. The results indicated that the proposed method is expected to be effective for passive shimming.

Magnetic Torque-Driven All-Terrain Microrobots.

All-terrain microrobots possess significant potential in modern medical applications due to their superior maneuverability in complex terrains and confined spaces. However, conventional microrobots often struggle with adaptability and operational difficulties in variable environments. This study introduces a magnetic torque-driven all-terrain multiped microrobot (MTMR) to address these challenges. By coupling the structure's multiple symmetries with different uniform magnetic fields, such as rotating and oscillating fields, the MTMR demonstrates various locomotion modes, including rolling, tumbling, walking, jumping, and their combinations. Experimental results indicate that the robot can navigate diverse terrains, including flat surfaces, steep slopes (up to 75°), and gaps over twice its body height. Additionally, the MTMR performs well in confined spaces, capable of passing through slits (0.1 body length) and low tunnels (0.25 body length). The robot shows potential for clinical applications like minimally invasive hemostasis in internal bleeding and thrombus removal from blood vessels through accurate cargo manipulation capability. Moreover, the MTMR can carry temperature sensors to monitor environmental temperature changes in real time while simultaneously manipulating objects, displaying its potential for in-situ sensing and parallel task implementation. This all-terrain microrobot technology demonstrates notable adaptability and versatility, providing a solid foundation for practical applications in interventional medicine.

Diffraction of quasi-nondiffracting Bessel beam by an impedance disc in an anisotropic plasma

The diffraction of the so-called nondiffracting Bessel beam by an impedance disc immersed in an anisotropic medium is examined. The external uniform magnetic field, which makes the plasma anisotropic, is taken to be rotational as opposed to being parallel to the edge of the problem geometries in the literature. Thus, the appropriate dielectric matrix that models the anisotropic region under the rotational dc external magnetic field is derived for the first time, to the best of our knowledge. Upon considering the geometric optics waves, the total scattered waves are obtained with the diffracted waves by using the definition of high-frequency asymptotic expressions associated with the scattered waves at the transition regions. The results are expressed in terms of the Fresnel functions so that the wave behaviors in the transition regions are uniform. The solutions are compared numerically with existing studies in the literature, including limit values.

Landau quantization under effects of torsion and confinement potentials

In this paper, we have investigated the nonrelativistic limit of a quantum particle, subjected to a uniform magnetic field and in the presence of some confinement potentials, immersed in a background with a cosmic string and a screw dislocation. We separately examined four models, constructed the energy spectrum and cyclotron frequency for each of them, and checked the consistency of the results by considering the limit of some characteristic parameters of the potentials.

Target-field design of surface permanent magnets

We present a target-field approach to analytically design magnetic fields using permanent magnets. We assume that their magnetization is bound to a two-dimensional surface and is composed of a complete basis of surface modes. By posing the Poisson’s equation relating the magnetic scalar potential to the magnetization using Green’s functions, we derive simple integrals that determine the magnetic field generated by each mode. This approach is demonstrated by deriving the governing integrals for optimizing axial magnetization on cylindrical and circular-planar surfaces. We approximate the governing integrals numerically and implement them into a regularized least-squares optimization routine to design permanent magnets that generate uniform axial and transverse target magnetic fields. The resulting uniform axial magnetic field profiles demonstrate more than a tenfold increase in uniformity across equivalent target regions compared to the field generated by an optimally separated axially magnetized pair of rings, as validated using finite element method simulations. We use a simple example to examine how two-dimensional surface magnetization profiles can be emulated using thin three-dimensional volumes and determine how many discrete intervals are required to accurately approximate a continuously varying surface pattern. Magnets designed using our approach may enable higher-quality bias fields for electric machines, nuclear fusion, fundamental physics, magnetic trapping, and beyond. Published by the American Physical Society 2024

Fermion self-energy and effective mass in a noisy magnetic background

In this article, we consider the propagation of QED fermions in the presence of a classical background magnetic field with white-noise stochastic fluctuations. The effects of the magnetic field fluctuations are incorporated into the fermion and photon propagators in a quasiparticle picture, which we developed in previous works using the . By working in the very strong-field limit, here we explicitly calculate the fermion self-energy involving radiative contributions at first order in αem, in order to obtain the noise-averaged mass of the fermion propagating in the fluctuating magnetized medium. Our analytical results reveal a leading double-logarithmic contribution ∼[ln(|eB|/m2)]2 to the mass, with an imaginary part representing a spectral broadening proportional to the magnetic noise autocorrelation Δ. While a uniform magnetic field already breaks Lorentz invariance, inducing the usual separation into two orthogonal subspaces (perpendicular and parallel with respect to the field), the presence of magnetic noise further breaks the remaining symmetry, thus leading to distinct spectral widths associated with fermion and antifermion, and their spin projection in the quasiparticle picture. Published by the American Physical Society 2024

Magnetic field-mediated ferrofluid droplet deformation in extensional flow

Extensional flow is vital in droplet dynamics, influencing their formation, size, stability, and functionality across diverse applications from industrial processes to biomedical technology. Ferrofluid droplets are pivotal in many such applications, where magnetic fields enable non-contact manipulation without undesirable heating effects. However, controlling ferrofluid droplet dynamics in magnetically influenced extensional flows is challenging due to the complex interplay of induced magnetization, intrinsic magnetic properties, and flow kinematics. Here, we present a first-principle-based theory delving into the morphology of a ferrofluid droplet under the combined influence of an external magnetic field and extensional flow. Unlike previous studies, we employ an asymptotic analysis that delves on the shape alterations by considering local magnetization as dependent on magnetic field intensity. Additionally, we develop a numerical model based on phase-field hydrodynamics to establish the practical applicability of the asymptotic solution and to explore large droplet-deformation regimes. The study demonstrates that increasing the magnetic field intensity, the saturation magnetization of the ferrofluid, and the initial magnetic susceptibility each independently improve droplet deformation. Additionally, we found that in a uniform magnetic field, the extensional viscosity of a ferrofluid emulsion is influenced by the strain rate, leading to strain-thickening behavior in the dilute emulsion. Our findings offer new insights into field-assisted manipulation of ferrofluid droplets, emphasizing their potential in applications ranging from process engineering to biomedical technology.

Influence of magneto-hydrodynamic and couple stress squeeze film lubrication on conical bearing-a slip velocity model

This paper explores the impact of MHD couple stress and slip velocity over a conical bearing in the presence of magnetic field. The flow is considered as incompressible. A uniform magnetic field is imposed perpendicular to the bearing alongy-axis. The modified Reynolds equation is solved using appropriate boundary conditions in dimensionless form to find the pressure distribution which is then used to obtain the expression for load carrying capacity paving the way for the calculation of response time. Numerical computations of the results show that the MHD couple stress on the conical bearings indicates that enhances the pressure distribution, load carrying capacity and squeeze film time of the conical bearings. Further, decrease in these characteristics was observed for the increased values of slip velocity and cone angle.

The Effect of Noisy Magnetic Fields on Electrons

Abstract In this work, we study the behavior of an electron in the presence of a constant and uniform magnetic field, which is subjected to white noise fluctuations with an autocorrelation of magnitude Δ B . Starting from the Schwinger representation for a propagator in the presence of a constant magnetic field, we use the method of replicas to determine the effect of the magnetic noise on the shape of the renormalized quasi-particle parameters. Leading to an effective charge and an effective refraction index that depend not only on the energy scale, as usual, but also on the magnitude of the noise ΔB and the average field B.

Linear instability of a resting state of the magnetohydrodynamic flows of polymeric fluid in a cylindrical channel (generalized Vinogradov–Pokrovski model)

We study a linear stability of a resting state for flows of incompressible viscoelastic fluid in an infinite cylindrical channel under the influence of an external uniform magnetic field directed parallel to the cylinder axis (we use a generalized rheological Vinogradov–Pokrovski model as mathematical model) in a class of axisymmetric periodic along the axial variable flows. We establish that for some values of the parameters in the case of an absolute conductivity bm=0, the magnetic field can substantially lessen the real part of an exponent for perturbations of the radial velocity component, which is the main element of the instability development. For general case bm≠0, we justify the possibility of removing the instability based on the performed calculations.

Comparison of Skin Effects in Ferromagnetic and Nonferromagnetic Metals in Eddy Current Testing

ABSTRACT In eddy current (EC) testing, skin effect is a constraint factor of detecting subsurface defects and skin depth is an important parameter for probe design and frequency setup. This paper compares the skin effects in ferromagnetic and nonferromagnetic metals. It is well known that the high permeability of ferromagnetic metal makes the attenuation of EC faster due to the greater EC loss. In this paper, the other role of the high permeability of ferromagnetic metal on the skin effect is reported. The EC distributions in both the radial and depth directions in the two types of materials excited by pancake coils are computed. It shows that the EC is more dispersed in the radial direction in high-permeability material. More importantly, the high permeability of ferromagnetic metal makes the skin depth of EC under the excitation of pancake coil close to the standard skin depth of EC under the excitation of uniform magnetic field, whereas there is a big discrepancy in the skin depths of ECs under the two types of excitations. This difference is explained by the radial dispersion of EC based on the EC diffusion-cancellation theory. Finally, the EC distributions in ferromagnetic Q235 steel and nonferromagnetic brass are compared, and the simulation results are qualitatively verified by experiments.