Magnetic Interaction Force Research Articles

Self-organization of local magnetoplasma structures in the upper layers of the solar convection zone

Self-organization and evolution of magnetoplasma structures in the upper layers of the solar convection zone are discussed as a process of diffuse aggregation of magnetic flux tubes. Equations describing the tube motion under the action of magnetic interaction forces, hydrodynamic forces, and random forces are written explicitly. The process of aggregation of magnetic flux tubes into magnetic flux clusters of different shapes and dimensions is simulated numerically. The obtained structures are compared with the observed morphological types of sunspot groups. The quantitative comparison with the observational data was performed by comparing the fractal dimensions of the photospheric magnetic structures observed in solar active regions with those of structures obtained in the numerical experiment. The model has the following free parameters: the numbers of magnetic flux tubes with opposite polarities on the considered area element (Nn and Ns), the average radius of the cross section of the magnetic flux tube (a), its effective length (l), the twist factor of the tube field (k), and the absolute value of the average velocity of chaotic tube displacements (d). Variations in these parameters in physically reasonable limits leads to the formation of structures (tube clusters of different morphological types) having different fractal dimensions. Using the NOAA 10488 active region, which appeared and developed into a complicated configuration near the central meridian, as an example, it is shown that good quantitative agreement between the fractal dimensions is achieved at the following parameters of the model: Nn = Ns = 250 ± 50; a = 150 ± 50 km; l ∼ 5000 km, and d = 80 ± 10 m/s. These results do not contradict the observational data and theoretical estimates obtained in the framework of the Parker “spaghetti” model and provide new information on the physical processes resulting in the origin and evolution of local magnetic plasma structures in the near-photospheric layers of the solar convection zone.

Simulation of magneto-induced rearrangeable microstructures of magnetorheological plastomers

Magneto-induced microscopic particulate structures of magnetorheological plastomers (MRP) are investigated using particle-level dynamics simulation, as this is a basis for studying the macroscopic physical or mechanical properties of MRP. In the simulation, a modified magnetic dipolar interaction force model is proposed to describe the magnetic interaction of two close magnetized iron particles. Other microscopic analytical models of particle–particle and particle–matrix interactions are also constructed. The simulation results show that chain-like and column-like particulate structures are formed when MRP is placed into a steady uniform magnetic field. When MRP is subjected to a stepwise in-plane rotating magnetic field, the microstructure rearranges to form a layered structure parallel to the rotation plane. Moreover, some other patterns or complex magneto-induced rearrangeable microstructures can be achieved by spatially changing the external magnetic field. With the evolution of the microscopic particulate structure in every changing step of the external magnetic field, the microstructure dependent magnetic potential energy and stress state vary sharply at the beginning and then approach respective stable values gradually.

Probing of pair interaction of magnetic microparticles with optical tweezers

Magnetic interaction of paramagnetic Brownian submicron-sized particles is studied by optical tweezers technique. Correlation analysis allows one to extract magnetic interaction of two particles 0.4 μm in size, which are optically trapped at the distance of 3 μm one from each other and placed in a static magnetic field of 30 Oe, from the background of their Brownian motion. The magnetic interaction force is estimated to be of approximately 100 fN. Two configurations of the mutual orientation of the magnetic field vector and the line connecting two centers of optical traps are used in the experiment. For field vector orientation parallel/perpendicular to this line, the magnetic interaction is detected by the cross-correlation function increase/decrease in comparison with the absence of magnetic field on the time scales of 1 ms.

Magnetic Micro Actuator Using Interactive Force between Magnetic Elements

In micro electro mechanical system (MEMS) field, there have been used many kinds of actuators. Among them, the magnetic actuator has some advantages. As magnetic micro actuators do not need electric wiring for energy supply, the structure can be simple and be downsized easily. However, the magnetic force would be very small with downsizing, which is the main problem for conventional magnetic actuators. We propose a new type actuator using magnetic interaction force between magnetic elements to solve this matter. This actuator can work even if it gets smaller, because the interaction force is dominant in a microscopic region. We fabricated the actuator by a casting process with photolithography using the SU-8 resist material. Then, the structure was fabricated by casting the mixture of poly(dimethylsiloxane) (PDMS) and a magnetic powder material. The beam type actuator works successfully and also shows interesting behavior. We can control the behavior of this actuator by changing the arrangement of magnetic elements on the structure. We also show theoretical evaluation of the deformation of the present actuator.

Strong magnetic field effects on solid–liquid and particle–particle interactions during the processing of a conducting liquid containing non-conducting particles

The behavior of micrometer-sized weak magnetic insulating particles migrating in a conductive liquid metal is of broad interest during strong magnetic field processing of materials. In the present paper, we develop a numerical method to investigate the solid–liquid and particle–particle interactions by using a computational fluid dynamics (CFDs) modeling. By applying a strong magnetic field, for example, 10 Tesla, the drag forces of a single spherical particle can be increased up to around 15% at a creeping flow limit. However, magnetic field effects are reduced when the Reynolds number becomes higher. For two identical particles migrating along their centerline in a conductive liquid, both the drag forces and the magnetic interaction will be influenced. Factors such as interparticle distance, Reynolds number and magnetic flux density are investigated. Shielding effects are found from the leading particle, which will subsequently induce a hydrodynamic interaction between two particles. Strong magnetic fields however do not appear to have a significant influence on the shielding effects. In addition, the magnetic interaction forces of magnetic dipole–dipole interaction and induced magneto-hydrodynamic interaction are considered. It can be found that the induced magneto-hydrodynamic interaction force highly depends on the flow field and magnetic flux density. Therefore, the interaction between insulating particles can be controlled by applying a strong magnetic field and modifying the flow field. The present research provides a better understanding of the magnetic field induced interaction during liquid metal processing, and a method of non-metallic particles manipulation for metal/ceramic based materials preparation may be proposed.

Use of a magnetic force exciter to vibrate a piezocomposite generating element in a small-scale windmill

A piezocomposite generating element (PCGE) can be used to convert ambient vibrations into electrical energy that can be stored and used to power other devices. This paper introduces a design of a magnetic force exciter for a small-scale windmill that vibrates a PCGE to convert wind energy into electrical energy. A small-scale windmill was designed to be sensitive to low-speed wind in urban regions for the purpose of collecting wind energy. The magnetic force exciter consists of exciting magnets attached to the device’s input rotor and a secondary magnet fixed at the tip of the PCGE. The PCGE is fixed to a clamp that can be adjusted to slide on the windmill’s frame in order to change the gap between exciting and secondary magnets. Under an applied wind force, the input rotor rotates to create a magnetic force interaction that excites the PCGE. The deformation of the PCGE enables it to generate electric power. Experiments were performed with different numbers of exciting magnets and different gaps between the exciting and secondary magnets to determine the optimal configuration for generating the peak voltage and harvesting the maximum wind energy for the same range of wind speeds. In a battery-charging test, the charging time for a 40 mA h battery was approximately 3 h for natural wind in an urban region. The experimental results show that the prototype can harvest energy in urban regions with low wind speeds and convert the wasted wind energy into electricity for city use.

On the Magnetic Forces in Magnetic Cooling Machines: Numerical Calculations and Experimental Investigations

In this paper, we present a detailed study of the magnetic interaction forces encountered in magnetic cooling machines between magnetocaloric (MC) refrigerants and a magnetic field source. Numerical calculations have been performed using different magnetocaloric materials. The obtained results have been analyzed and compared with experimental measurements. In order to reduce the magnetic forces in reciprocating magnetic cooling systems and as a consequence increase their thermodynamic performances, a special configuration of the MC refrigerants is proposed. Numerical investigations have been carried out to analyze the resulting magnetic force. The obtained results are confirmed by measuring directly the involved forces on our recent developed magnetic refrigerator. The preliminary calculations demonstrate that more than 90% of the energy absorbed by the cooling machine can be saved with the new design, and consequently, a high coefficient of performance can be obtained.

Particles size effects of single domain CoFe2O4 on suspensions stability

Single domain magnetic CoFe2O4 nanoparticles with spinel structure were prepared by the coprecipitation method. Particles with size of 16, 20, 40 and 60nm were synthesized by sintering the precursor at 500, 600, 800 and 900°C, respectively. The magnetic hysteresis measurement of CoFe2O4 particles showed that particles were single domain particles with similar saturation magnetization (∼300emu/cm3) at room temperature. The zeta potential study of suspensions (CoFe2O4–acetylacetone system) with various particle sizes showed the suspension systems had similar zeta potential values (∼40mV). The effects of magnetic particle size on the suspension stability characterized by electrophoretic deposition yields and sediment volumes were studied. The suspension stability decreased with an increase in particle size and a flocculation threshold of particle radius a was found at 30nm. A suspension stability theory approaching to the phenomenon was established. The theory based on the DLVO theory was developed by introducing an extra magnetic interaction force. Dormann model was adopted, in which the magnetic interactions of two spherical nanoparticles were investigated in terms of dipole–dipole interactions. Compared to DLVO, suspension's physical parameters not only zeta potential ζ and the Debye length 1/κ, but also particles' radius a brought about stable to flocculation transition in the theory.

Analog and Digital Deformable Diffractive Optics Actuated by Inter-Nanomagnet Forces

In this paper, we present a novel actuation technique of diffractive optics based on magnetic interaction forces, permitting a fine resolution tuning as well as a tuning in discrete steps. This actuation combines advantages of “analog” and “digital” tuning in conventional diffractive optics. The application of a magnetic field perpendicularly to the beams of a freestanding grating coated with magnetic material generates intermagnet forces causing these beams to deform slightly or to clump together. A theoretical analysis of the forces has been carried out, followed by actuation simulations in both linear and nonlinear regimes for different types of gratings, showing examples of exponential and parabolic chirp profiles in addition to beam clumping. In experiment, the diffraction patterns of distinct fabricated gratings have shown both a continuous shift and smear as well as a discrete change in the diffracted angles proving the concept of analog and digital tuning.

Recent Patents in Magnetic Transmission and Applications

Magnetic transmission is a special kind of transmission. It is mainly used in the special occasions of non-contact power and movement transmission utilizing the characteristics of the non-contact of magnetic force interaction. It can be divided into three types according to different forms of movement: rectilineal motion transmission, rotational motion transmission and complex motion transmission. This paper reviews various recent patents in all types of magnetic transmission and various applications. The patents reviewed concern a period extending from the year 2000 up to date. The applications concern mainly integrated all types of motion transmission covering the area connected with the production of pump, stirrer and other industrial mechanism using modernization that has reached by material replacing, geometry, and embedding additional units into main design. The list of patents reviewed is by no means complete or extensive it shows however the extent of the subjects covered in patents in this area during the last five years. The paper concludes with a description of the future developments expected in the subjects covered.

Dynamic rheology of sphere- and rod-based magnetorheological fluids

The effect of particle shape in the small amplitude oscillatory shear behavior of magnetorheological (MR) fluids is investigated from zero magnetic field strengths up to 800 kA/m. Two types of MR fluids are studied: the first system is prepared with spherical particles and a second system is prepared with rodlike particles. Both types of particles are fabricated following practically the same precipitation technique and have the same intrinsic magnetic and crystallographic properties. Furthermore, the distribution of sphere diameters is very similar to that of rod thicknesses. Rod-based MR fluids show an enhanced MR performance under oscillatory shear in the viscoelastic linear regime. A lower magnetic field strength is needed for the structuration of the colloid and, once saturation is fully achieved, a larger storage modulus is observed. Existing sphere- and rod-based models usually underestimate experimental results regarding the magnetic field strength and particle volume fraction dependences of both storage modulus and yield stress. A simple model is proposed here to explain the behavior of microrod-based MR fluids at low, medium and saturating magnetic fields in the viscoelastic linear regime in terms of magnetic interaction forces between particles. These results are further completed with rheomicroscopic and dynamic yield stress observations.

Magnetohydrodynamic simulation of the protoplanetary disk of the Sun

In the framework of the basic cosmogony problem related with the reconstruction of the solar protoplanetary disk at the early stages of its existence, a closed system of magnetohydrodynamic equations with the scale of average motion is formulated in the approximation of single-fluid magnetic hydrodynamics; this system is designated for setting and numerically solving various problems on the self-consistent simulation of the structure and evolution of the disk and related corona. The influence of both the axially symmetric magnetic field of the proto-Sun and the large-scale field generated by the turbulent dynamo mechanism on the disk structure formation is analyzed. A new approach to the simulation of the turbulent transport coefficient in the weakly ionized disk is developed. This approach provides an account of the effects of the influence of the generated magnetic field and the processes of convective heat transport on turbulence development in the stratified layer with finite thickness and, thus, rejects the Shakura-Sunyaev α formalism widely used in astrophysical literature. The mathematical model of a thin (but optically thick) non-Keplerian disk taking into account the turbulence dissipation due to kinematical and magnetic viscosity, medium opacity, accretion from ambient space, the action of a turbulent αω dynamo on the magnetic field generation, the magnetic force and energy interaction between the disk and its corona, etc., is discussed. This study is the continuation of the stochastic-thermodynamic approach to the description of turbulence of astro-geophysical systems developed by us in a number of papers [Kolesnichenko 2000, 2001, 2003, 2004, 2005; Kolesnichenko, Marov 2006, 2007, 2008; Marov, Kolesnichenko 2002, 2006].

Magnetic nanoparticle migration in microfluidic two-phase flow

Continuous separation of superparamagnetic nanoparticles in a microfluidic system has numerous applications, especially in novel sensors based technology platforms. We have studied a simple microfluidic system with two fluidic inlets, resulting in two-phase flow of identical aqueous fluids. Magnetic nanoparticles were entrained in de-ionized water entering one inlet channel, while the other inlet channel had only de-ionized water input. The application of a magnetic field using a simple permanent magnet causes increased migration of nanoparticles into the pure fluid channel. In the absence of the magnetic field, the particles are able to diffuse into the particle free phase. A steady state convection diffusion model describes the transport of nanoparticles in the microchannel. Particle velocities are estimated from magnetic and hydrodynamic interaction forces. It is shown how particle separation is affected by Péclet number, channel length to width ratio, and magnetic field strength and field gradient. Experiments were conducted with three particle sizes, 1000, 500, and 100 nm. Results revealed a significant discrepancy between theoretical and experimental particle separations under the applied magnetic field. A correction term was introduced into the magnetic force equation. Experiment and theory could be reconciled with the insight that the correction term scales linearly with the volume of the nanoparticle core.

Bounds on the dynamic magnetic properties of multiresonant nanostructure composites in exchange resonance model

Existing bounds expression established on the sum of the gyromagnetic losses is limited by static magnetic interactions. In this paper, we deduce a bounds relation from the Bloch–Bloembergen theorem to depict both the uniform resonance and exchange resonance. It is shown to agree with experiments, of particular relevance to the competition between static magnetic force and exchange interaction. An analytic explanation on favorable multiresonance phenomenon in nanocrystalline iron flakes is achieved.

Magnetic Interaction Force and a Couple on a Superconducting Sphere in an Arbitrary Dipole Field

The calculation of the magnetostatic potential and levitation force due to a point magnetic dipole placed in front of a superconducting sphere in the Meissner state is readdressed. Closed-form analytical expression for the scalar potential function that yields the image system for an arbitrarily oriented magnetic dipole located in the vicinity of a superconducting sphere is given. Analytic expression for the lifting or levitation force acting on the sphere is extracted from the solution for a general dipole. A special case of our expression where the initial magnetic dipole makes an angle with the z-axis is derived. Our expression for the force in this particular case shows that a recently obtained result (J. Supercond. Nov. Magn. 21:93–96, 2008) for an arbitrary dipole is incorrect. A brief discussion of another erroneous result (J. Supercond. Nov. Magn. 15:257–262, 2002) for a transverse/tangential dipole–sphere configuration, corrected elsewhere recently, is reproduced. Correct expressions for the interaction energy with some limiting cases are also provided. The result derived here demonstrates that the value of the levitation force for a dipole that makes an angle with z-axis lies between the values for a radial dipole–sphere and transverse dipole–sphere configurations providing upper and lower bounds. It is found that for a magnetic dipole making an angle with z-axis, there exits a second force component along the negative y-direction, which influences a couple acting on the superconducting sphere. It is also shown that the couple is proportional to the second force component and that both the couple and second force components vanish for a radial dipole–sphere and transverse dipole–sphere configurations, respectively. These results appear to be new and have not had received due attention in the context of superconductivity.

Fabrication of Protein Chip by Magnetic Force

This research describes a new immobilizing method of many kinds of biomaterials (enzyme, antibody, and DNA) on a transducer array using magnetic force interaction as the short-range force. The method composes two immobilizing steps. In the first step, same biomaterials are immobilized on metal particles. In the second step, the particles are arranged by the fluidic self-assembly method at random on an array. An array immobilized many kinds of the particles become multichannel biosensor. The biosensor can apply to DNA chip, protein chip, multienzyme electrode, and so on. The metal particles and the array were fabricated by micromachining manufacture. The metal particles were multilayer structure (gold, titanium, and nickel). In the array case, sidewalls of patterning nickel dots on an array were covered by thick negative photoresist (SU-8), and the array was magnetized. The array and the particles were mixed in buffer solution, and were arranged by magnetic force interaction. A quarter of total nickel dots were covered by the particles. The binding direction of the particles was controllable, and condition of particles was almost with gold surface on top. The immobilization of the biomaterials to metal particles was able to materialize it by using 3-CPD. This confirmed an activity by the luminol radiation.

Magnetoelastic modelling of composites containing randomly dispersed ferromagnetic particles

Coupled magnetoelastic behaviour is investigated for two-phase composites containing randomly dispersed ferromagnetic particles under both magnetic and mechanical loading. The pair-wise particle interactions for magnetic field and elastic field are first defined by the solution for two particles embedded in the infinite domain, which is explicitly solved by the Green's function technique. By integrating the interactions from all other particles in the representative volume element, the homogenized magnetic and elastic fields are then obtained. Effective magnetostriction due to the magnetic interaction force is further derived. Without consideration of magnetic loading, this micromechanical model provides an effective elasticity with the pair-wise particle interactions. By dropping the interaction term, this model is reduced into Mori–Tanaka's model. Finally, magnetoelasticity is numerically solved by considering the magnetomechanical coupling effect. It is predicted that the effective Young's modulus and shear modulus decrease along with the increase of magnetic loading for random composites.

Numerical Simulation of Magnetic Field Distribution in MAF

Magnetic field distribution (MFD) plays an important role in magnetic abrasive finishing (MAF). The mathematical models of the MFD in MAF have been established, and forced behavior of magnetic abrasive (MA) in the magnetic field has been analyzed in this paper. The MFD characteristics of the grooved poles have been numerically simulated, and the distribution law of magnetic force, interaction force and interface pressure have been investigated based on a single particle. The calculated results show that the MFD in the finishing zone is directly affected by the pole structure and working gap. The mapping function of interaction force and interface pressure corresponds to corner-effect in the peak point of the pole, and the magnetic brush stiffness is changed by the diameter and magnetization characteristics of MA, and the magnetic flux intensity (MFI). The numerical simulations are in a good agreement with the experiments. All of results mentioned above will offer an important method to study further on the finishing mechanism.

Magneto-elastic modeling of composites containing chain-structured magnetostrictive particles

Magneto-elastic behavior is investigated for two-phase composites containing chain-structured magnetostrictive particles under both magnetic and mechanical loading. To derive the local magnetic and elastic fields, three modified Green's functions are derived and explicitly integrated for the infinite domain containing a spherical inclusion with a prescribed magnetization, body force, and eigenstrain. A representative volume element containing a chain of infinite particles is introduced to solve averaged magnetic and elastic fields in the particles and the matrix. Effective magnetostriction of composites is derived by considering the particle's magnetostriction and the magnetic interaction force. It is shown that there exists an optimal choice of the Young's modulus of the matrix and the volume fraction of the particles to achieve the maximum effective magnetostriction. A transversely isotropic effective elasticity is derived at the infinitesimal deformation. Disregarding the interaction term, this model provides the same effective elasticity as Mori–Tanaka's model. Comparisons of model results with the experimental data and other models show the efficacy of the model and suggest that the particle interactions have a considerable effect on the effective magneto-elastic properties of composites even for a low particle volume fraction.

Numerical Simulation of Carrier Behavior Around a Magnet Roll in a Two-Component Developer Unit in Electrophotography

A new particle simulator to analyze the behavior of carrier beads around a magnet roll in a two-component developer unit in electrophotography has been developed. The simulator, which is based on the Discrete Element Method, including the magnetic interaction force among particles in a magnetic field, adopts parallel processing with MPI and/or OpenMP. Parallel processing of the particle simulator with several processors provides excellent performance to simulate the behavior of a realistic amount of particles in a practical time. The simulation results obtained for tens of thousands of carrier beads reveals not only realistic particle behavior around a magnet roll but also the quantitative relation between the stress on the carrier and the amount of carrier beads that passes through a gap between the doctor blade and the magnet roll. These are very important parameters to obtain high-quality images in a two-component developer unit.