Waves In Slab Research Articles

Surface and waveguide Josephson plasma waves in slabs of layered superconductors

We discuss the propagation of symmetric and antisymmetric Josephson plasma waves in a slab of layered superconductor clad between two identical dielectrics. We predict two branches of surface waves in the terahertz frequency range, one above and another below the Josephson plasma frequency. Apart from this, there exists a discrete set of waveguide modes with electromagnetic fields oscillating across the slab thickness and decaying exponentially away from the slab. We consider the excitation of the predicted waves by means of the attenuated-total-reflection method. It is shown that for a specific set of the parameters of the structure, the excitation of the waveguide modes is accompanied by the total suppression of specular reflection.

COSMIC RAY TRANSPORT THROUGH GYRORESONANCE INSTABILITY IN COMPRESSIBLE TURBULENCE

We study the nonlinear growth of kinetic gyroresonance instability of cosmic rays (CRs) induced by large scale compressible turbulence. This feedback of cosmic rays on turbulence was shown to induce an important scattering mechanism in addition to direct interaction with the compressible turbulence. The linear growth is bound to saturate due to the wave-particle interactions. By balancing increase of CR anisotropy via the large scale compression and its decrease via the wave-particle scattering, we find the steady state solutions. The nonlinear suppression due to the wave-particle scattering limit the energy range of CRs that can excite the instabilities and be scattered by the induced slab waves. The direct interaction with large scale compressible modes still appears to be the dominant mechanism for isotropization of high energy cosmic rays (> 100 GeV).

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.

Surface wave modes in PEMC backed chiral slab

The characteristics of surface wave modes in a PEMC backed chiral slab are studied theoretically. First, the analytical solution of electromagnetic fields and dispersion relations are carried out. Then, the fractional field solutions are found using the fractional curl operator. The numerical results are given by assuming that wave numbers k and k ± are either real or imaginary. These results are also evaluated at real and imaginary values of fractional parameter describing the order of curl operator. The discussion contains fractional dispersion curves at various cut-off frequencies and the fractional surface waves in chiral-PEMC and achiral-PMC slabs respectively. For numerical analysis it is assumed that the fractional order of the curl operator is related to chiral admittance, thickness of the slab, and PEMC admittance. For the values of the fractional order equal to 0, 1, and 2 geometry corresponds to PMC backed ordinary dielectric slab, PEMC backed chiral slab, and PEC backed chiral slab respectively. Consequently TE, HE (even), and HE (odd) modes are produced in the respective geometries.

Nonlinear Wood anomalies in the reflectivity of layered superconductors

The excitation of nonlinear surface Josephson plasma waves in slabs of layered superconductors is studied theoretically by means of incident plane waves using the prism method in the Otto configuration. The bilateral excitation symmetric with respect to the magnetic field is considered. The excitation leads to the resonant suppression of the specular reflection, i.e. to the Wood anomalies. Due to the nonlinearity the reflectivity resonantly depends not only on the wave frequency ω and the incident angle θ but on the wave amplitude h as well. It is shown that total suppression of reflectivity can be attained by an appropriate choice of ω, θ, h, and other parameters of the problem. The results of the analytical calculations are supported by numerical simulations.

NUMERICAL MODELING AND MECHANISM ANALYSIS OF VHF WAVE PROPAGATION IN FORESTED ENVIRONMENTS USING THE EQUIVALENT SLAB MODEL

We study the radio wave propagation at VHF frequencies in a forested environment using a three-layer anisotropic slab model. The analytical solution to the slab model is implemented numerically to generate broadband data. The data are then transformed into the time domain. The various propagation mechanisms including the direct wave, the lateral wave, the multi-reflected slab waves and the multibounce lateral waves are investigated based on their respective timesof-flight. Our results show that the dominant propagation mechanisms are highly dependent on the effective permittivity and conductivity of the forest layer. We then utilize the numerical solution to extract the effective medium parameters of the forest based on the published measurement data of Hicks et al.. Good agreement between the fitted model and the measurement data is achieved. The extracted effective permittivity and conductivity of the forest layer show considerable anisotropy and frequency dependence.

Coupling characteristics between five-layer slab wave-guides including left-handed materials

To obtain the coupling characteristics between slab wave-guides including left-handed material, we modify the coupled wave equations by using Maxwell’s equations. First, we obtain new-coupled wave equations and new-coupling coefficient. Second, the coupling between two identical five-layer slab wave-guides where their cores are left-handed material, but their claddings are right-handed materials is studied. The coupling coefficient for even TE mode which is more complex than that of the riglt-handed material slab wave guides, is obtained.

Surface acoustic waves in finite slabs of three-dimensional phononic crystals

We study theoretically, by means of layer-multiple-scattering techniques, the propagation of elastic waves through finite slabs of phononic crystals consisting of metallic spheres in a polyester matrix, embedded in air. In particular, we focus on the study of modes localized on the surfaces of the structure. Their origin and behavior, as well as the physical parameters that influence and determine their appearance, are investigated in detail. Our results reveal the existence of absolute phononic frequency gaps in these finite structures, and point out the possibility, under an appropriate choice of the parameters, of tunable regions of frequency free of propagating and/or surface-localized modes.

Nonlinear Josephson plasma waves in slabs of layered superconductors

For layered superconductors, we study the specific nonlinear Josephson plasma waves (NJPWs) propagating along thin superconducting slabs and damping away from them. Two cases are considered, when the superconductor is surrounded by either vacuum or metals. The magnetic field of the NJPW is distributed symmetrically with respect to the middle of the sample and can change its sign inside the slab. The impedance ratio of the tangential electric and magnetic field amplitudes for NJPWs can be of the order of unity. For the case of a superconductor surrounded by the vacuum, this results in a non-monotonic dispersion relation, ω(k), strongly sensitive to the NJPW amplitudes. Therefore, the “stopping light” phenomenon can be observed at frequencies where dω(k)/dk=0. Resonance excitations of the NJPWs should produce anomalies in the amplitude dependence of the reflectivity and transmissivity of the incident THz waves, which could be useful for THz devices. Animations illustrating the results presented here, are available online at dml.riken.go.jp/nonlinear.

Leaky modes of a left-handed slab

Using complex plane analysis we show that left-handed slab may support either leaky slab waves, which are backward because of negative refraction, or leaky surface waves, which are backward or forward depending on the propagation direction of the surface wave itself. Moreover, there is a general connection between the reflection coefficient of the left-handed slab and the one of the corresponding right-handed slab (with opposite permittivity and permeability) so that leaky slab modes are excited for the same angle of incidence of the impinging beam for both structures. Many negative giant lateral shifts can be explained by the excitation of these leaky modes.

Effects of external magnetic field on propagation of electromagnetic wave in uniform magnetized plasma slabs

A simple method is proposed to describe the propagation of electromagnetic waves in magnetized uniform plasma slabs. Using this method, the reflection, absorption and transmission coefficients of such plasmas for right-hand circularly waves are studied and the effects of the continuously changing external magnetic field on the power of the electromagnetic waves propagated in magnetized plasma slabs with fixed parameters are presented. Our method enables more detailed numerical analyses which are useful in practical applications pertaining to the control of the reflection or absorption coefficients of electromagnetic wave through a uniform magnetized plasma slab by adjusting the external magnetic field.

Propagation of an Electromagnetic Beams in Non-Linear Dielectric Slab Wave Guides

Propagation of an Electromagnetic Beams in Non-Linear Dielectric Slab Wave Guides

Photonic amorphous silicon device technology

Optically smooth hot-wire deposited films were characterized with respect to the photonic application by examination of the slab wave guiding of the room temperature bulk photoluminescence. Films displayed strong photoluminescence as well as strong slab wave guiding of the light to the edge. These properties are consistent with materials suitable for photonic engineering. Waveguide structures were prepared using previously described hydrogen implantation techniques and tested using novel methods. We report the first successful demonstration of refractive index engineered amorphous silicon devices.

Approximate estimates of fracture speeds for dry slab avalanches

Dry slab avalanches release by propagating shear fractures. It has been suggested that slab wave or fracture speed on horizontal terrain is consistent with the propagation of a flexural wave in the slab. In this note, an alternate proposal is made. Namely, it is proposed that the fracture speed is consistent with dynamic crack propagation speeds from other materials. The theory is compared with an in situ measurement of speed associated with shear fracture propagation in a weak snow pack layer sensed by geophones placed on the surface of a horizontal snow pack. The theory is shown to be consistent with the mechanical properties of alpine snow and known characteristics of slab avalanche release.

Spectral analysis of surface waves in single and multi-layer slabs with finite thickness using finite element modelling

This paper presents the numerical modelling of spectral analysis of surface waves (SASW) method to find the surface wave velocities and to investigate if the numerical modelling of a multi-layer slab system can show the dispersive characteristics. In the modelling of a single-layer slab, the average surface wave velocities obtained from the finite element mode superposition analysis are reasonably close to the experimental value. The refinement of the finite element mesh from element size of 25.4×25.4 mm to 12.7×12.7 mm improves the surface wave velocity results. The numerical modelling of a three-layer slab shows that the dispersive characteristics of surface wave exist in the layer system and can be modelled by the finite element analysis. This study further advances the application of the SASW method to the assessment of existing concrete slab structures.

Pedagogical models of surface mechanical wave propagation in various materials

We report on a teaching approach oriented to the understanding of some relevant concepts of wave propagation in solids. It is based on simple experiments involving the propagation of shock mechanical waves in solid slabs of various materials. Methods similar to the generation and propagation of seismic waves are adopted. Educational seismometers, interfaced with computers, are used to detect and visualize the shock waves and to analyse their propagation properties. A qualitative discussion of the results concerning the propagation and the attenuation of the waves allows us to draw basic conclusions about the response of the matter to solicitation impacts and their propagation.

Linear and nonlinear wave propagation in rarefied plasmas

Small-amplitude magnetohydrodynamic waves are studied in a dilute collisionless plasma with an anisotropic plasma pressure. The parallel and perpendicular pressure components are defined by two polytropic pressure laws. Previous results obtained within the framework of the Chew–Goldberger–Low double-adiabatic and double-isothermal models are recovered for specific values of the polytropic indices. The double-polytropic model can be considered as an extension of its single-polytropic counterpart model. Dispersion relations for the linear waves are derived and analyzed in the presence of pressure anisotropy. Particular cases of linear and nonlinear waves in a magnetic slab with double-polytropic plasma are investigated. The presence of the effective parallel and perpendicular sound speeds in the slab gives rise to a complicated interplay between kink and sausage modes supported by the slab. The behavior of weakly nonlinear waves in the slab are governed by the Benjamin–Ono equation. The soliton-like solution of this equation may be accelerated or retarded depending on the values of parallel and perpendicular sound speeds. The solitons are always accelerated in the magnetically dominated slab.

Excitation of coupled TM-TE focus wave modes in biisotropic media

We prove that two kinds of coupled TM-TE focus wave modes can propagate in a biisotropic medium, and we consider what happens when a TM or TE focus wave mode impinges from a vacuum on a slab made of a biisotropic material. We get the amplitudes of the reflected and refracted waves in a chiral slab.

VIBRATIONAL ENERGY ANALYSIS OF GROUND/STRUCTURE INTERACTION IN TERMS OF WAVE TYPE

The vibrational interaction of underground structures such as tunnels or building foundations with the ground involves different types of waves both in structures and in ground. In this paper, a wave approach is used to study these waves in the simple case of an infinite slab laying on a half-space homogeneous soil. The results are expressed in terms of energy quantities such as input line mobility and radiated power in the case of line force excitation of the slab and power injected to the slab in the case of forced vibration by an incoming ground borne wave. It is shown that in the case of line force excitation of the slab, the radiation loss factors obtained are 10 times higher than common values of structural loss factors, showing that the energy losses of an underground structure are mainly radiated into the ground. In the case of forced vibration by an incoming ground-borne wave, the slab wave type depends on the type of incident ground-borne waves: P waves mainly generate quasi-longitudinal waves in the slab at low frequencies and bending waves at higher frequencies; SV waves generate both bending and quasi-longitudinal waves with a percentage depending on the type of ground.

Power transfer and current generation of fast ions with large-kθ waves in tokamak plasmas

The direction and magnitude of power and momentum exchange between fast ions and electrostatic waves in slab and toroidal systems are obtained from global Monte Carlo simulations that include the quasilinear wave-induced ion diffusion both in velocity space and through a radially localized (lower hybrid) wave structure with propagation in one preferential poloidal direction in tokamaks. The model considers a full linearized collision model, finite fast ion orbits, and losses in toroidal geometry, and can properly treat the boundary effects on the particle–wave interaction in the configuration space. For an isotropic steady ion source, reduction of wave Landau damping but no wave amplification by wave localization is found for a Gaussian wave intensity distribution in radius, irrespective of the steepness of the radial gradient of the fast ion source rate. Enhanced wave-driven fast ion current, with magnitude, direction, and profile determined by the boundary conditions, net power transfer, and fast ion radial transport, is found to follow from the asymmetry in the parallel wave number spectrum created by the finite poloidal magnetic field. In the presence of intense well-penetrated waves the current carried by fusion α particles can be controlled by the choice of the poloidal wave number spectrum and the total current can greatly exceed the neoclassical bootstrap current of the α particles in a reactor.