Impressed Magnetic Field Research Articles

Reformulation of the Roy–Shafai Generalization of the Ludwig-3 Co-/Cross-Polarization Definition

The Roy-Shafai generalization of the Ludwig-3 polarization pattern definition is well-suited to the representation of the far electromagnetic field of a flanged aperture, either a perfect electric conductor (PEC)-flanged aperture with an impressed electric field as was shown by Roy and Shafai or a perfect magnetic conductor (PMC)-flanged aperture with an impressed magnetic field which can be similarly derived. We show that the Roy-Shafai generalization of the Ludwig-3 polarization definition is in fact equivalent to the transformed Ludwig-2 definition. The Ludwig-3 polarization is that of a Huygens source, while the Ludwig-2 polarization definition corresponds to either an electric or, with transformation, a magnetic dipole. That the Roy-Shafai polarization definition is equivalent to a transformed Ludwig-2 definition is reasonable as the rectangular PEC-flanged aperture with an impressed electric field behaves as a magnetic dipole in the low frequency limit and, subject to some restrictions, maintains the same polarization pattern for all frequency assuming the aperture field remains uniform. Likewise, the rectangular PMC-flanged aperture with an impressed magnetic field behaves like an electric dipole in the low-frequency limit and maintains the same polarization pattern for all frequency again, assuming that the aperture field remains uniform and, thus, exhibits a Ludwig-2 polarization pattern.

On Magnetic Inhibition Theory in Non-resistive Magnetohydrodynamic Fluids

We investigate why the non-slip boundary condition for the velocity, imposed in the direction of impressed magnetic fields, can contribute to the magnetic inhibition effect based on the nonhomogeneous magnetic Rayleigh--Taylor (abbr. NMRT) problem in non-resistive magnetohydrodynamic (abbr. MHD) fluids. Exploiting an infinitesimal method in Lagrangian coordinates, the idea of (equivalent) magnetic tension, and the differential version of magnetic flux conservation, we give an explanation of physical mechanism for the magnetic inhibition phenomenon in a non-resistive MHD fluid. Moreover, we find that the magnetic energy in the non-resistive MHD fluid depends on the displacement of fluid particles, and thus can be regarded as elastic potential energy. Motivated by this observation, we further use the well-known minimum potential energy principle to explain the physical meaning of the stability/instability criteria in the NMRT problem. As a result of the analysis, we further extend the results on the NMRT problem to the stratified MHD fluid case. We point out that our magnetic inhibition theory can be used to explain the inhibition phenomenon of other instabilities, such as thermal instability, magnetic buoyancy instability, and so on, by impressed magnetic fields in non-resistive MHD fluids.

Nonlinear stability and instability in the Rayleigh–Taylor problem of stratified compressible MHD fluids

We establish the stability/instability criteria for the stratified compressible magnetic Rayleigh–Taylor (RT) problem in Lagrangian coordinates. More precisely, under the stability condition $$\varXi <1$$ (under such case, the third component of impressed magnetic field is not zero), we show the existence of a unique solution with an algebraic decay in time for the (compressible) magnetic RT problem with proper initial data. The stability result in particular shows that a sufficiently large (impressed) vertical magnetic field can inhibit the growth of the RT instability. On the other hand, if $$\varXi >1$$ , there exists an unstable solution to the magnetic RT problem in the Hadamard sense. This in particular shows that the RT instability still occurs when the strength of an magnetic field is small or the magnetic field is horizontal. Moreover, by analyzing the stability condition in the magnetic RT problem for vertical magnetic fields, we can observe that the compressibility destroys the stabilizing effect of magnetic fields in the vertical direction. Fortunately, the instability in the vertical direction can be inhibited by the stabilizing effect of the pressure, which also plays an important role in the proof of the stability of the magnetic RT problem. In addition, we extend the results for the magnetic RT problem to the compressible viscoelastic RT problem, and find that the stabilizing effect of elasticity is stronger than that of the magnetic fields.

Coupling of Photoactive TiO2 and Impressed Magnetic Field for Phenol Highly Efficient Degradation

Synergistic effect of nanosized TiO2 and impressed magnetic field (MF) was studied by investigating the photocatalytic degradation of phenol at room temperature. The introducing of MF with relatively high intensity (>0.082 T) has obvious promotion effects on phenol degradation rate (C/C 0), while negative influences of MF on C/C 0 can be observed under low-intensity MF (<0.044 T). The yield of hydroxyl radicals (·OH) in reaction processes increases with the raising of MF intensity initially and reaches the maximum concentration when the magnetic intensity is 0.082 T. The photoinduced carriers initially decrease until the MF intensity reaches at 0.024 T, and then increase with the increasing of MF intensity. The effects of MF on photoinduced carriers can be explained in terms of the Δg mechanism together with the hyperfine coupling mechanism. Low-intensity MF accelerates the recombination of electrons and holes and suppresses the generation of photoinduced carriers, which further restricts the degradation of phenol. In contrast, the presence of high-intensity MF retards the recombination of hydroxyl radicals and thus enhances the production of ·OH radicals. The generation of hydroxyl radicals is the primary factor in determining the phenol degradation process in the high-intensity MF region.

Magneto Binary Nanofluid Convection in Porous Medium

The effect of an externally impressed magnetic field on the stability of a binary nanofluid layer in porous medium is considered in this work. The conservation equations related to the system are solved using normal mode technique and Galerkin method to analyze the problem. The complex expressions are approximated to get useful results. Mode of heat transfer is stationary for top heavy distribution of nanoparticles in the fluid layer and top heavy nanofluids are very less stable than regular fluids. Oscillatory motions are possible for bottom heavy distribution of nanoparticles and they are not much influenced by properties of different nanoparticles. A comparative analysis of the instability of water based nanofluids with metallic (Cu, Ag) and semiconducting (TiO2, SiO2) nanoparticles under the influence of magnetic field is examined. Semiconducting nanofluids are found to be more stable than metallic nanofluids. Porosity destabilizes the layer while solute difference (at the boundaries of the layer) stabilizes it. Magnetic field stabilizes the fluid layer system significantly.

Quantum collapse in ground-state Fermi-Dirac-Landau plasmas

In this paper, it is revealed that in a relativistically degenerate dense highly magnetized electron-ion plasma, the effective quantum-potential due to the quantum-force acting on fermions may vanish causing a quantum transverse collapse in the ground-state Fermi-Dirac-Landau (GSFDL) plasma. The condition for the plasma transverse collapse is found to be restricted to the minimum relativistic degeneracy parameter and minimum impressed magnetic field strength values satisfied for some superdense astrophysical objects such as white dwarfs and neutron stars. In such objects, the magnetization pressure is shown to cancel the lateral electron degeneracy pressure counteracting the existing gravitational pressure. Furthermore, using the Sagdeev pseudopotential method in the framework of quantum magnetohydrodynamics model, including magnetization, it is confirmed that the quantum pressure due to spin-orbit polarization and the electron relativistic degeneracy has crucial effects on the existence criteria and the propagation of localized magnetosonic density excitations in GSFDL plasmas. Current findings can have important implications for the density excitation mechanism and hydrostatic stability of the highly magnetized astrophysical relativistically dense objects such as white-dwarfs, neutron stars, magnetars, and pulsars.

Influence of magnetic field on wave propagation at liquid-microstretch solid interface

The reflection and refraction of a longitudinal wave at an interface between a perfectly conducting nonviscous liquid half-space and a perfectly conducting microstretch elastic solid half-space are studied. The appropriate solutions to the governing equations are obtained in both the half-spaces satisfying the required boundary conditions at the interface to obtain a system of five non-homogeneous equations in the amplitude ratios of various reflected and transmitted waves. The system is solved by a Fortran program of the Gauss elimination method for a particular example of an interface between water and aluminum-epoxy composite. Numerical values of the amplitude ratios are computed for a certain range of the incidence angle both in the presence and absence of an impressed transverse magnetic field. The effects of the presence of the transverse magnetic field on the amplitude ratios of various reflected and transmitted waves are shown graphically.

Smart composites with controlled anisotropy

The new generation of magnetic elastomers represents a new type of composites, consisting of small (mainly nano- and micron-sized) magnetic particles dispersed in a high elastic polymeric matrix. The combination of polymers with magnetic materials displays novel and often enhanced properties. The magnetic particles couple the shape of the elastomer to the external magnetic field. All of the forces acting on the particles are transmitted directly to the polymer chains resulting in either locomotion or deformation. Shape distortion occurs instantaneously and disappears abruptly when external field is applied or removed, respectively. Combination of magnetic and elastic properties leads to a number of striking phenomena that are exhibited in response to impressed magnetic field. Giant deformational effect, tuneable elastic modulus, non-homogeneous deformation and quick response to magnetic field open new opportunities for using such materials for various applications. Elastic materials with tailor-made anisotropy can also be prepared under external field. The anisotropy manifests itself in both direction dependent elastic modulus as well as direction dependent swelling.

Study on Arc Movement in Hollow Electrode Plasma Generators with Impressed Double Magnetic Fields

In order to prolong cathode lifetime of hollow electrode plasma generators, a method of impressed double magnetic fields with an alternating frequency is presented in this paper. The alternating frequency of the double magnetic fields is an important factor that influences the erosion rate on the area between the two coils' central planes. By analyzing the arc movement in the hollow cathode with a simplified theoretical model, the spiral curve shape of the radial arc and the relationship between the optimal alternating frequency and the intensity of magnetic fields are obtained. A photoelectric method is employed to measure the arc root rotation speed in the hollow cathode, and then the optimal alternating frequency is calculated as 319 Hz for the experimental conditions. The life testing with this alternating frequency showed that the cathode lifetime could be prolonged significantly.

Smart nanocomposite polymer gels

AbstractThe combination of polymers with nanomaterials displays novel and often enhanced properties compared to the traditional materials. They can open up possibilities for new technological applications. The magnetic polymer gel represents a new type of composites consisting of small magnetic particles, usually from the nanometer range to the micron range, dispersed in a highly elastic polymeric gel matrix. Combination of magnetic and elastic properties leads to a number of striking phenomena that are exhibited in response to impressed magnetic fields. Giant deformational effects, high elasticity, anisotropic properties, temporary reinforcement and quick response to magnetic field open new opportunities for using such materials for various applications.

Adaptive compensation of magnetic fields inside an open cylindrical magnetic shield

For the development of a magnetic field compensation system suited for the open end of the cylindrical magnetic shell, magnetic field distributions were characterized on the axis of the magnetic shell for the externally impressed low-frequency AC magnetic field and for the compensating magnetic field generated by a set of ring coils. Based on this observation, a system for actively compensating the magnetic field leakage through the opening is proposed. A cylindrical magnetic shield of desk-top size was constructed by combining an axial shell made of 2 in wide Metglas 2705M amorphous tapes encircling the outer surface of a cylindrical body in its axial direction, with a magnetic shaking coil, and then a proposed compensation system was built on top of the structure. The axial shielding factor was improved with this active compensation system by 55 times for a 2 Hz impressed magnetic field, 20 times for a 10 Hz impressed field, ten times for a 30 Hz impressed field, and five times for a 50 Hz impressed field. An interesting phenomenon observed during the characterization of the magnetic fields is that the magnetic field in the space inside the axial magnetic shell leads in phase with respect to that of the impressed magnetic field, unlike the case with a helical shell where the magnetic field is lagging in phase. A model for explaining this phenomenon is also given.

705 ローレンツ力にもとづいた磁気ダンパ

In general, a magnetic field generated by a magnet is not constant in a certain direction but distributed over the space. In the case of a magnet moving through a impressed magnetic field, a magnetic damping force based on Lorentz force works on a conductor because of the component in the right direction of a magnetic field to the moving direction of a conductor. Authors report experimental results about the influence of a conductor thickness and of a distance between a magnet and a conductor to both type I magnetic damper which has a mechanism that a circular magnet plate and a conductor disk moves relatively and parallel to each other, and type II magnetic damper which has a mechanism that they are facing and moves relatively to each other.

이중원관내 자성유체의 자연대류에 대한 전열특성

자성유체는 고액혼상유체로 뉴턴유체와 달리 자기력에 반응하는 유체이다. 본 연구에서는 금속과 유체의 특성을 겸비한 자성유체의 열전달 특성을 밀도 있게 연구함을 목적으로, 그 대상을 이중원관으로 하여 열대류현상을 고찰하기 위해 내부원관을 가열하고, 외부원관을 냉각하면서, 또한 외부에서 인가자장의 세기와 방향에 따라 자연대류 현상의 변화 및 열전달 특성을 수치해석적으로 연구하여, 실험결과와 비교 검토하였다. 자성유체의 자연대류현상은 인가자장에 따라 제어할 수 있었고, 평균 뉴셀트수를 구한 결과로서 자장을 가하지 않았을 경우와 비교해 보면 열전달은 자장을 중력방향으로 가하거나 중력과 반대방향으로 그세기를 -14 mT이상 가했을 때 증가하였고, 중력과 반대방향으로 감했을 때 감소하였다. 특히 자장의 세기가 -14 mT가 되면 열전달은 최소가 되었다. Compared with Newtonial fluids, magnetic fluids have effects on magnetic force. In this study, the purpose is to research the heat transfer characteristic of magnetic fluids which have metalic and fluid characteristics as the external pipe is being cooled and internal pipe is heated. This study found the experimental results from the study of the variety of natural convection for magnetic fluids and the characteristics of the heat transfer by using numerical analysis according to the strength and direction of the magnetic fields from being imposed from the outside. Natural convection of magnetic fluids was controlled by the impressed magnetic fields, and the result of mean nusselt number was calculated. If the impressed magnetic field is in the direction of gravity or the strength of impressed magnetic field is more than -14 mT in the opposite direction, the heat transfer is more than that without the impressed magnetic field. If the strength of impressed magnetic field is less than -14 mT in the opposite direction, it is smaller than that without the impressed magnetic field. Especially, when the strength of the magnetic field is -14 mT, the heat transfer was at the minimum.

Electromagnetic waves in a suddenly created magnetized Lorentz medium (transverse propagation)

The interaction of electromagnetic waves in a suddenly created Lorentz medium with impressed steady uniform magnetic field is considered. It was shown that for the case of the incident electric field normal to the static magnetic field, the source wave splits into six new extraordinary waves whose frequencies are different from the incident waves. Three of those six new waves are transmitted waves, and the other three are reflected waves. The dispersion relation, power transmission, and reflection coefficients are derived and discussed.

A system for measuring magnetic core noise as a function of the magnetization level

The problem of magnetic core noise is considered in terms of non-repeatability of the hysteresis loop trace for any repetition of the magnetization process. The examination condition is that the effect of eddy currents is reduced to as low a level as possible. Based on such premises, this paper presents a system which periodically extracts the fluctuation voltage, induced at an arbitrary but specified point of the impressed magnetic field, as an instantaneous value. The minimum extraction interval is mainly determined by the integration time of the digital voltmeter used to measure the voltage and by the time required for transferring the extracted data to a personal computer. Therefore, the upper limit of the repetition frequency for the magnetization is restricted to less than 1 Hz. The serially extracted time data is dealt with in a statistical manner and is arranged in order as a magnitude distribution. Two kinds of cores are tested, one is a Fe-Ni-based amorphous core and the other a supermalloy. The results reveal that each core has distinctive noise features.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

FEM computation of the forces on the arc of a DC-furnace

A finite element model of a DC arc furnace is investigated in order to predict the forces acting on the arc due to the magnetic field. The currents have an a priori unknown distribution in the steel tank wall, in the anode, in the melt and in the cathode, so a current flow problem is analysed in the first step. The current density is solved for in terms of a current vector potential whose edge element representation is used in the subsequent nonlinear magnetic field calculation to act as impressed magnetic field. The current dependence of the shielding provided by the steel tank is investigated. It is shown that by providing an asymmetrical feed of the current, the force on the arc can be reduced substantially.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Conduction system ablation using ferrite rod for cardiac arrhythmia

A disorder of the conduction system causes cardiac arrhythmia. At present, electromagnetic waves such as radiofrequency waves are generally used for the ablation. However, the radiofrequency ablation often accompanies fatal side effects. We developed the new method of catheter ablation using a temperature-sensitive ferrite rod and a nonmagnetic metal ring as a heating device. The device generates heat in an impressed magnetic field that does not generate heat in the body itself. The maximum temperature is determined by the Curie temperature of the ferrite rod. The clinical application of the method was discussed experimentally. The results suggest the usefulness of this method for conduction system ablation in the treatment of ventricular arrhythmia.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Oscillations in the current-voltage characteristics of inter-grain Y-Ba-Cu-O junctions

I-V curves of bulk Y-Ba-Cu-O samples show Josephson tunnelling characteristics comprising finite pair current and quasi-particle tunnelling regions. The authors report here the first observations of oscillatory structures superposed on these curves under impressed microwave or small DC magnetic fields. A possible explanation of these oscillations is believed to be tunnelling of individual electrons charging and discharging the capacitance of a large number of inter-grain Josephson junctions.

強制磁界を用いた埋設金属管の塗覆装損傷位置の検出法

強制磁界を用いた埋設金属管の塗覆装損傷位置の検出法

On the stability of a thermally stratified conducting fluid under the action of aligned magnetic field

The stability of a thermally stable stratified viscous electrically conducting shear flow is investigated in the presence of an impressed uniform aligned magnetic field. Only two-dimensional disturbances are studied in this paper because Squire's theorem does not apply in general, owing to the presence of the aligned magnetic field. The analysis is partly analytical and partly numerical. The asymptotic solutions for non-viscous fluid are first obtained analytically and they are then improved by introducing viscous and thermal diffusion terms (but only for σ=1) to get a uniformly valid solution. The neutral stability curves are numerically computed for a range of values of Richardson and Stuart numbers, which show that the flow is completely stabilized when a Stuart number exceeds a certain value for a given R i>0. It is shown that the combined effects of magnetic field and stratification is to make the system stable to two-dimensional disturbances at lower Stuart number than the one given by Stuart (1954) in the absence of thermal stratification.