Magnetic Slab Research Articles

Magnetic superlens-enhanced inductive coupling for wireless power transfer

We investigate numerically the use of a negative-permeability “perfect lens” for enhancing wireless power transfer between two current carrying coils. The negative permeability slab serves to focus the flux generated in the source coil to the receiver coil, thereby increasing the mutual inductive coupling between the coils. The numerical model is compared with an analytical theory that treats the coils as point dipoles separated by an infinite planar layer of magnetic material [Urzhumov et al., Phys. Rev. B 19, 8312 (2011)]. In the limit of vanishingly small radius of the coils, and large width of the metamaterial slab, the numerical simulations are in excellent agreement with the analytical model. Both the idealized analytical and realistic numerical models predict similar trends with respect to metamaterial loss and anisotropy. Applying the numerical models, we further analyze the impact of finite coil size and finite width of the slab. We find that, even for these less idealized geometries, the presence of the magnetic slab greatly enhances the coupling between the two coils, including cases where significant loss is present in the slab. We therefore conclude that the integration of a metamaterial slab into a wireless power transfer system holds promise for increasing the overall system performance.

Microwave propagation in a magnetized inhomogeneous plasma slab using the Appleton–Hartree magnetoionic theory

Electromagnetic wave propagation in a nonuniform, collisional, magnetized plasma slab is investigated within magnetoionic theory. We allow for the presence of an ideal conductor at a distance d from the right transmissive plasma boundary, and derive the reflection, absorption, and transmission coefficients analytically for an arbitrary inhomogeneous plasma density profile. Dividing the inhomogeneous plasma slab into n thin layers allows for treating each layer as a homogeneous plasma and, therefore, the complex index of refraction of the magnetoionic theory is used to express the complex propagation vector of the waves in each layer. Upon matching the fields at all interfaces, a global matrix is formed that allows for the determination of the reflection, absorption, and transmission coefficients analytically. Results show that in the absence of the metallic wall, the reflected signal is a weak peak near ωce, while in the presence of the metallic wall this weak signal is overwhelmed by a strong transmitted...

Numerical analysis of the reflection and absorption of electromagnetic wave in nonuniform magnetized plasma slab

In this paper, a model for calculating the reflection and absorption powers of electromagnetic wave (EM wave) in nonuniform magnetized plasma slab is given out based on layer propagation theory. The effects of various plasma parameters and different values of magnetic field intensity on the reflected and absorbed powers are discussed. The results illustrate that the thickness of plasma seldom affects the reflection of radar wave, but it can broaden or reduce the absorption width. Meanwhile, the background magnetic field intensity has an influence upon the results, and it could change the resonance spectrum of magnetized plasma. We also find out that, with appropriate plasma density, collision frequency and magnetic field intensity, more than 90% of radar wave power can be absorbed and the resonant absorption band is about 2 GHz.

Switching properties of a tunneling junction connected to a spin valve

The switching properties of a prototype system containing a spin valve as well as a tunneling junction are investigated by means of a spin-polarized fully relativistic approach. Shown are the changes in the free energy and in the magnetoresistance when the orientation of the magnetization in the magnetic slabs of such a system is changed individually. It is demonstrated that the existence of a stable and a metastable state, a necessary condition for a switching device, is essentially determined by the free energy contributions of the interfaces of that magnetic slab that is part of the spin valve as well as of the tunneling junction. Furthermore, in estimating individual switching times, it is found that most of the gain in magnetoresistance occurs within a time range of about 20 ps, the time to achieve complete switching, however, being about 1.5 ns, which is close to what is found in recent experimental results.

Ab initiodescription of spin pumps and spin sinks in magnetic double layers with in-plane coupling

For magnetic double layers separated by a nonmagnetic metallic spacer the precession of the magnetization in only one magnetic slab (``spin pump'') and in both of them (``spin sink'') is described using the fully relativistic spin-polarized screened Korringa-Kohn-Rostocker method. It is found that both semiaxes of the ellipses that form the base planes of precessional cones can be identified with particular anisotropy energies. Slopes along particular paths of the obtained free energy hypersurfaces are then used to estimate in terms of the Landau-Lifshitz-Gilbert equation the minimal times to move from a chosen initial state to a particular final state. Furthermore, fully relativistic spin-polarized calculations by means of the Kubo equation of the corresponding zz-like elements of the conductivity tensor show that the current along the surface normal is bigger for ``spin pumps'' than for ``spin sinks.'' For moderately small external fields the time scale for the individual processes is in the femtoregime.

Repulsive Casimir forces with finite-thickness slabs

We use the extended Lifshitz theory to study the behaviors of the Casimir forces between finite-thickness effective medium slabs. We first study the interaction between a semi-infinite Drude metal and a finite-thickness magnetic slab with or without substrate. For no substrate, the large distance $d$ dependence of the force is repulsive and goes as $1/d^5$; for the Drude metal substrate, a stable equilibrium point appears at an intermediate distance which can be tuned by the thickness of the slab. We then study the interaction between two identical chiral metamaterial slabs with and without substrate. For no substrate, the finite thickness of the slabs $D$ does not influence significantly the repulsive character of the force at short distances, while the attractive character at large distances becomes weaker and behaves as $1/d^6$; for the Drude metal substrate, the finite thickness of the slabs $D$ does not influence the repulsive force too much at short distances until $D=0.05\lambda_0$.

Magnetoacoustic surface gravity waves at a spherical interface

Aims. The plasma structured by magnetic fields in the solar atmosphere is a perfect medium for the propagation of guided magnetic and magnetoacoustic waves. Geometrical restriction of wave propagation is known to confer a dispersive character for waves. In addition, waves propagating along discontinuities in the medium are known to remain localized. As an extension to theories of guided waves in magnetic slabs and cylinders under solar and stellar conditions, we aim to study the propagation of magnetoacoustic-gravity waves at a spherical interface in the low solar corona (considered here as a density discontinuity), modelling global waves recently observed in the corona in EUV wavelengths. Methods. Using conservation laws at the interface we derive the dispersion relation in spherical geometry with a radially expanding magnetic field in the presence of gravitational stratification. The obtained dispersion relation describing fast magnetoacoustic-gravity surface waves is derived using an approximative method taking into account that propagation takes place near the solar surface. Results. Theoretical results obtained in the present study are applied to investigate the propagation of EIT waves in the low corona. The frequency of waves is shown to increase with decreasing density contrast at the interface. We also show that, for a given azimuthal wavenumber, the magnetic field has a very small effect on the value of the frequency of waves. When plotted against the location of the interface (in the radial direction) the frequency varies inversely proportional to the distance, while for a fixed density ratio and location of the interface the frequency is obtained to be defined in a very narrow region.

The period ratio for kink and sausage modes in a magnetic slab

Aims. Increasing observational evidence of wave modes in the solar corona brings us to a closer understanding of that medium. Coronal seismology allows us to combine wave observations and theory to determine otherwise unknown parameters. The period ratio, P1/2P2, between the period P1 of the fundamental mode and twice the period P2 of its first overtone, is one such tool of coronal seismology and its departure from unity provides information about the structure of the corona. Methods. We consider analytically the period ratio for the fast kink and sausage modes of a magnetic slab, discussing both an Epstein density profile and a simple step function profile. Results. Transverse density structuring in the form of an Epstein profile or a step function profile may contribute to the shift of the period ratio for long thin slab-like structures.

Propagation of broadband terahertz pulses through a dense-magnetized-collisional-bounded plasma layer

The terahertz characteristics of a dense-magnetized-collisional-bounded plasma under normal incident are analyzed in this study, which is of practical significance in plasma diagnostics with electromagnetic waves. We theoretically calculate the reflection, absorption, and transmission coefficients for right- and left-handed polarized terahertz waves through a uniform, magnetized, and collisional plasma slab bounded by lossless transparent walls. The power absorption spectra in the frequency range of 0.1–2 THz are given with strong external magnetic fields and different plasma parameters such as plasma density and collisional frequency. Our numerical result is consistent with Jamison’s experimental result. It is found that plasma absorption is mainly caused by the collisional absorption and electron cyclotron resonance. Furthermore, the absorption heavily depends on the polarization mode of the terahertz waves when the external magnetic field B is high enough that the election gyrofrequency is near the incident wave frequency. The relationships between the corresponding parameters of the problem are studied numerically.

Resonant Absorption of Fast Magnetoacoustic Waves due to Coupling into the Slow and Alfvén Continua in the Solar Atmosphere

Resonant absorption of fast magnetoacoustic (FMA) waves in an inhomogeneous, weakly dissipative, one-dimensional planar, strongly anisotropic and dispersive plasma is investigated. The magnetic configuration consists of an inhomogeneous magnetic slab sandwiched between two regions of semi-infinite homogeneous magnetic plasmas. Laterally driven FMA waves penetrate the inhomogeneous slab interacting with the localised slow or Alfvén waves present in the inhomogeneous layer and are partly reflected, dissipated and transmitted by this region. The presented research aims to find the coefficient of wave energy absorption under solar chromospheric and coronal conditions. Numerical results are analysed to find the coefficient of wave energy absorption at both the slow and Alfvén resonance positions. The mathematical derivations are based on the two simplifying assumptions that i) nonlinearity is weak, and ii) the thickness of the inhomogeneous layer is small in comparison to the wavelength of the wave, i.e. we employ the so-called long wavelength approximation. Slow resonance is found to be described by the nonlinear theory, while the dynamics at the Alvén resonance can be described within the linear framework. We introduce a new concept of coupled resonances, which occurs when two different resonances are in close proximity to each other, causing the incoming wave to act as though it has been influenced by the two resonances simultaneously. Our results show that the wave energy absorption is heavily dependent on the angle of the incident wave in combination with the inclination angle of the equilibrium magnetic field. In addition, it is found that FMA waves are very efficiently absorbed at the Alvén resonance under coronal conditions. Under chromospheric conditions the FMA waves are far less efficiently absorbed, despite an increase in efficiency due to the coupled resonances.

Microwave response of magnetized hydrogen plasma in carbon nanotubes: multiple reflection effects

We derived simple sets of equations to describe the microwave response of the magnetized hydrogen plasma slab embedded inside carbon nanotubes, which were grown by iron-catalyzed high-pressure disproportionation. These equations, which are useful when interference effects due to multiple reflections between plasma film interfaces are small, were used to analyze the reflection, absorption, and transmission coefficients of the magnetized hydrogen plasma slab. A discussion on the effects of the continuously changing external magnetic field and hydrogen plasma parameters on the reflected power, absorbed power, and transmitted power in the system is presented.

Focusing of intense laser beam by a thin axially magnetized plasma lens

Focusing of intense laser beams by a thin magnetized plasma slab is investigated. A thin plasma slab is used as an optical element. The focal length is the distance between the plasma lens and the laser beam focus point. The external magnetic field is applied along the direction of the laser field propagation. The nonlinear current density induced in the plasma lens is derived up to the third order of perturbation and the evolution of the spot size for a Gaussian beam profile is determined by making use of the variational principle approach method. It is shown that the axially magnetic field decreases the minimum spot size and increases the focal length significantly.

ON THE INFLUENCE OF FLUCTUATIONS OF THE DIRECTION OF AN EXTERNAL MAGNETIC FIELD ON PHASE AND AMPLITUDE CORRELATION FUNCTIONS OF SCATTERED RADIATION BY MAGNETIZED PLASMA SLAB

Statistical characteristics of scattered electromagnetic waves by turbulent magnetized plasma slab with electron density and magnetic fleld ∞uctuations are considered via the perturbation method and boundary conditions. Magnetic fleld ∞uctuates both in magnitude and direction. Analytical expressions for the component of scattered electric fleld, correlation functions of the amplitude and phase ∞uctuations, and also the phase structure function for arbitrary correlation functions of ∞uctuating plasma parameters are derived. The obtained results are valid for near and far zones. Under equal conditions, at strong magnetic flelds, electron density ∞uctuations play the important role and in this case the imposed magnetic fleld decreases ∞uctuation intensity of the ordinary and extraordinary waves. Numerical calculations of statistical characteristics of scattered radiation were carried out for anisotropic Gaussian correlation function

Electromagnetic wave propagation through an overdense magnetized collisional plasma layer

The results of investigations into the feasibility of using a magnetic window to propagate electromagnetic waves through a finite-sized overdense plasma slab are described. We theoretically calculate the transmission coefficients for right- and left-handed circularly polarized plane waves through a uniform magnetized plasma slab. Using reasonable estimates for the plasma properties expected to be found in the ionized shock layer surrounding a hypersonic aircraft traveling in the earth’s upper atmosphere (radio blackout conditions), and assuming a 1 GHz carrier frequency for the radio communications channel, we find that the required magnetic field for propagation of right-handed circularly polarized, or whistler, waves is on the order of a few hundred gauss. Transmission coefficients are calculated as a function of sheath thickness and are shown to be quite sensitive to the electron collision frequency. One-dimensional particle-in-cell simulations are shown to be in good agreement with the theory. These simulations also demonstrate that Ohmic heating of the electrons can be considerable. Two- and three-dimensional particle-in-cell simulations using a simplified waveguide and antenna model illustrate the same general transmission behavior as the theory and one-dimensional simulations. In addition, a net focusing effect due to the plasma is also observed in two and three dimensions. These simulations can be extended to design and analyze more realistic waveguide and antenna models.

Characteristics of magnetoacoustic sausage modes

Aims: We perform an advanced study of the fast magnetoacoustic sausage oscillations of coronal loops in the context of MHD coronal seismology to establish the dependence of the sausage mode period and cut-off wavenumber on the plasma-beta of the loop-filling plasma. A parametric study of the ratios for different harmonics of the mode is also carried out. Methods: Full magnetohydrodynamic numerical simulations were performed using Lare2d, simulating hot, dense loops in a magnetic slab environment. The symmetric Epstein profile and a simple step-function profile were both used to model the density structure of the simulated loops. Analytical expressions for the cut-off wavenumber and the harmonic ratio between the second longitudinal harmonic and the fundamental were also examined. Results: It was established that the period of the global sausage mode is only very weakly dependent on the value of the plasma-beta inside a coronal loop, which justifies the application of this model to hot flaring loops. The cut-off wavenumber kc for the global mode was found to be dependent on both internal and external values of the plasma-beta, again only weakly. By far the most important factor in this case was the value of the density contrast ratio between the loop and the surroundings. Finally, the deviation of the harmonic ratio P1/2P2 from the ideal non-dispersive case was shown to be considerable at low k, again strongly dependent on plasma density. Quantifying the behaviour of the cut-off wavenumber and the harmonic ratio has significant applications to the field of coronal seismology.

Nonlinear resonant absorption of fast magnetoacoustic waves in strongly anisotropic and dispersive plasmas

The nonlinear theory of driven magnetohydrodynamics (MHD) waves in strongly anisotropic and dispersive plasmas, developed for slow resonance by Clack and Ballai [Phys. Plasmas 15, 2310 (2008)] and Alfvén resonance by Clack et al. [Astron. Astrophys. 494, 317 (2009)], is used to study the weakly nonlinear interaction of fast magnetoacoustic (FMA) waves in a one-dimensional planar plasma. The magnetic configuration consists of an inhomogeneous magnetic slab sandwiched between two regions of semi-infinite homogeneous magnetic plasmas. Laterally driven FMA waves penetrate the inhomogeneous slab interacting with the localized slow or Alfvén dissipative layer and are partly reflected, dissipated, and transmitted by this region. The nonlinearity parameter defined by Clack and Ballai (2008) is assumed to be small and a regular perturbation method is used to obtain analytical solutions in the slow dissipative layer. The effect of dispersion in the slow dissipative layer is to further decrease the coefficient of energy absorption, compared to its standard weakly nonlinear counterpart, and the generation of higher harmonics in the outgoing wave in addition to the fundamental one. The absorption of external drivers at the Alfvén resonance is described within the linear MHD with great accuracy.

Surface waves in a magnetized ferrite slab filled with a wire medium

Novel metamaterial, based on wire medium embedded into magnetized ferrite, is studied. Waves in unbounded ferrites filled with wire media, surface wave at the interface of this metamaterial and the air as well as waves in a ferrite slab adjacent to a wire medium are considered. Different geometries of wires arrangement and different magnetization directions are discussed. Effective permeability was introduced for the case where both plasma and magnetic properties take place. Dispersion diagrams and applicability of the Drude model for the description of the wire medium in a host matrix, possessing high permittivity and permeability, are discussed.

Anomalous transmission of an intense short-pulse laser through a magnetized overdense plasma

A short-pulse laser having Gaussian radial intensity distribution and incident normally on a magnetized overdense plasma slab undergoes anomalous transmission. The laser induces a large oscillatory velocity on electrons, raising their mass and lowering the plasma frequency. The cyclotron resonance enhances this effect. Moreover, the ponderomotive force-driven electron cavitation lowers the plasma frequency further. These effects are most pronounced near the laser axis; hence, the central portion of the beam tunnels through the magnetized plasma slab, while marginal rays suffer reflection. The output beam thus has a smaller spot size. It also possesses a curvature in the wavefront that may help diagnostics.

Slow magnetoacoustic standing waves in a curved solar coronal slab

<i>Aims. <i/>We consider a model of a two-dimensional solar coronal arcade to explore the effects of a curved magnetic field topology on excitation and attenuation of slow magnetoacoustic standing waves.<i>Methods. <i/>The time-dependent ideal magnetohydrodynamic equations are solved numerically to find the spatial and temporal signatures of these waves.<i>Results. <i/>A pulse in gas pressure initially launched at a loop footpoint excites the fundamental mode of slow magnetoacoustic standing waves. The typical excitation time of such a wave mode is 2.5 wave periods, with a similar attenuation timescale. These values are remarkably similar to those recovered from observations by SOHO/SUMER in an Fe XIX line.<i>Conclusions. <i/>Slow magnetoacoustic standing waves are excited and attenuated more efficiently in curved magnetic field lines than in a straight magnetic slab topology. The waves supported by the magnetic arcade are in far closer agreement with observations.

Slab thickness and magnetic field effects on dust ion–acoustic surface waves on a thin magnetized dusty plasma slab

The effects of slab thickness and magnetic field on the propagation of dust ion–acoustic surface waves are investigated on a thin magnetized dusty plasma slab. The symmetric and anti-symmetric dispersion modes of the dust ion–acoustic surface wave are obtained by the plasma dielectric function with the kinetic dispersion model for the slab geometry. It is shown that the phase velocity increases with an increase in the strength of the magnetic field. It is also interesting to note that the frequency increases with an increase of the thickness in the plasma slab.