Dispersion Properties Of Surface Waves Research Articles

Surface wave propagation along a narrow transition layer in a slab Voigt geometry

The dispersion properties of electromagnetic surface waves, which propagate along a slab narrow transition layer separating two magnetoactive plasma uniform half spaces, are studied. Voigt geometry is considered, in which the waves propagate perpendicularly to an external uniform static magnetic field, which in turn is parallel to the interfaces between the plasmas and the transition layer. Electromagnetic power absorption within local resonances inside the transition layer is out of scope of the study. The influence of the plasma particle density profile smoothness on the surface wave dispersion properties is emphasized.

Dispersion Properties of Surface Waves Decaying in Red-Shifted and Blue-Shifted Gaps in Photonic Hypercrystals

The dispersion characteristics of surface waves for transverse electric and magnetic polarization modes of photonic hypercrystals (PHC) are theoretically explored. PHC are composed of a dielectric and hyperbolic metamaterial (HMM) with thin layers of both metal and dielectric surface waves that decay inside red-shifted gaps have a negative group velocity, whereas surface waves that decay inside traditional blue-shifted gaps have more typical characteristics. Curve plotting is used to elucidate on how these surface waves depend on several other structural properties such as filling factor, widths of HMM and dielectric, frequency range and angle of incidence etc.

Probabilistic neural network tomography across Grane field (North Sea) from surface wave dispersion data

SUMMARYSurface wave tomography uses measured dispersion properties of surface waves to infer the spatial distribution of subsurface properties such as shear wave velocities. These properties can be estimated vertically below any geographical location at which surface wave dispersion data are available. As the inversion is significantly non-linear, Monte Carlo methods are often used to invert dispersion curves for shear wave velocity profiles with depth to give a probabilistic solution. Such methods provide uncertainty information but are computationally expensive. Neural network (NN) based inversion provides a more efficient way to obtain probabilistic solutions when those solutions are required beneath many geographical locations. Unlike Monte Carlo methods, once a network has been trained it can be applied rapidly to perform any number of inversions. We train a class of NNs called mixture density networks (MDNs), to invert dispersion curves for shear wave velocity models and their non-linearized uncertainty. MDNs are able to produce fully probabilistic solutions in the form of weighted sums of multivariate analytic kernels such as Gaussians, and we show that including data uncertainties as additional inputs to the MDN gives substantially more reliable velocity estimates when data contains significant noise. The networks were applied to data from the Grane field in the Norwegian North sea to produce shear wave velocity maps at several depth levels. Post-training we obtained probabilistic velocity profiles with depth beneath 26 772 locations to produce a 3-D velocity model in 21 s on a standard desktop computer. This method is therefore ideally suited for rapid, repeated 3-D subsurface imaging and monitoring.

Dyakonov surface waves at the interface of nanocomposites with spherical and ellipsoidal inclusions

The dispersion properties of different types of surface electromagnetic waves which are supported by the interface of two nanocomposite materials with inclusions of different shape are studied theoretically and numerically. Both nanocomposites are made of doped n-type semiconductor inclusions which are evenly distributed in a transparent dielectric matrix. First nanocomposite contains semiconductor inclusions of spherical shape and can be represented as isotropic material with scalar effective dielectric permittivity. Second nanocomposite contains semiconductor inclusions of ellipsoidal shape and can be modeled as a uniaxial anisotropic crystal with two different principal effective permittivity components. Influence of physical and geometrical parameters of the nanocomposites on dispersion properties of surface waves is studied. It is shown that when dissipations in the semiconductor inclusions are taken into account the angular spectrum of Dyakonov surface wave existence becomes wider, and several dispersion curves of surface modes can simultaneously exist.

Multichannel surface wave analysis of reinforced concrete pipe segments using longitudinal and circumferential waves induced by a point impact

In this paper, we extend the multichannel surface wave (MASW) analysis method for non-destructive testing (NDT) of medium to large diameter concrete pipe segments. In a typical MASW investigation, experimentally obtained surface wave records from an elastic medium are transformed into dispersion curves and compared with the appropriate theory to inversely determine the unknown parameters of the medium. We extend this procedure for the lengthwise and circumferential inspection of an individual concrete pipe segment by employing longitudinal and circumferential waves. These waves are generated by a point impact applied perpendicular to the pipe surface. Using finite element based simulations, it is first shown that the dispersion properties of surface waves traveling along two orthogonal cross-sections of a pipe segment, which intersect the impact point, agrees with the corresponding theoretical properties of longitudinal modes in an infinite hollow cylinder and circumferential Lamb wave modes in a circular annulus. This forms the basis for implementing the MASW method along the lengthwise and angular directions of the pipe, independently. Using the lessons learned from numerical study, an experimental demonstration of the proposed angular MASW implementation is carried out in a reinforced concrete pipe segment held under laboratory conditions. Equations for a cylindrical version of the phase-shift based wavefield transform given in [1] is presented for use in this process and its effectiveness to extract the angular phase velocity spectra from an actual record is demonstrated. Finally, it is shown that multi-modal dispersion curves can be extracted from an actual reinforced concrete pipe segment and its unknown elastic properties can be determined using the proposed method. The numerical models developed in this paper are validated by comparing its results against the measured data.

Near-field radiative heat transfer between metasurfaces: A full-wave study based on two-dimensional grooved metal plates

Metamaterials possess artificial bulk and surface electromagnetic states. Tamed dispersion properties of surface waves allow one to achieve controllable super-Planckian radiative heat transfer (RHT) process between two closely spaced objects. We numerically demonstrate enhanced RHT between two 2D grooved metal plates by a full-wave scattering approach. The enhancement originates from both transverse magnetic spoof surface plasmon polaritons and a series of transverse electric bonding- and anti-bonding waveguide modes at surfaces. The RHT spectrum is frequency-selective, and highly geometrically tailorable. Our simulation also reveals thermally excited non-resonant surface waves in constituent materials can play a prevailing role for RHT at an extremely small separation between two plates, rendering metamaterial modes insignificant for the energy transfer process.

Resolution equivalence of dispersion-imaging methods for noise-free high-frequency surface-wave data

A key step in high-frequency surface-wave methods is to acquire the dispersion properties of surface waves. To pick dispersion curves, surface-wave data is required to be transformed from the time–space (t–x) domain to the frequency–phase velocity (f–v) domain. In constructing accurate multi-mode dispersion curves, it is necessary to generate a reliable and high-resolution image of dispersion energy in the f–v domain. At present, there are five methods available for imaging dispersion energy: the τ-p transformation, the f-k transformation, the phase shift, the frequency decomposition and slant stacking, and the high-resolution linear Radon transformation. Among them, resolution of the high-resolution linear Radon transformation is the highest. We proposed a processing step to enhance resolution of the other four methods. Resolution of the four enhanced methods and high-resolution linear Radon transformation is compared by imaging dispersion energy of the same synthetic data. As a result, the four enhanced methods generated dispersion images with the same resolution, which revealed that the resolution of the five dispersion-imaging methods is essentially equivalent for noise-free data.

Surface Waves Supported by Metasurfaces With Self-Complementary Geometries

This paper investigates the fundamental dispersion properties of surface waves (SWs) supported by a class of metasurfaces (MTSs) that consists of a planar layer made of metal patches and apertures with self-complementary geometries. When the MTS is suspended in free space, the supported SW is ${\rm TM}$ or ${\rm TE}$ depending on whether the vertexes of the metallic parts are interconnected or not, whereas the phase velocity is equal in the two cases. A simple analytical model, that depends only on the geometry, is derived to predict the dispersion curves for a quite general class of geometries. The proposed model is also extended to cases in which the MTSs are printed on a grounded or ungrounded dielectric slab, by using an equivalent dielectric constant. Comparisons with dispersion curves obtained through full-wave simulations confirm the accuracy of the model all over the Brillouin region. Finally, it is shown that connecting or disconnecting the metal patches along a given path allows for a confinement of the SWs on such a path. An experimental validation of this concept is also presented. This feature provides the possibility of controlling the wave's direction of propagation by changing the vertexes status by means of miniaturized switches or optical control.

Influence of an external magnetic field on the dispersion properties of surface waves in the 1-D periodic biaxial metamaterial

This paper analyzes surface waves (SW) supported by a biaxial metamaterial layer placed between two semi-infinite isotropic media. The metamaterial fabricated by periodic alternating semiconductor and dielectric layers and subjected to an external magnetic field. The magnetic field is applied parallel to the layers. We consider such structure in the long-wave limit so that we apply the effective medium theory to describe the electrodynamic properties. The necessary conditions of SW existence were found in terms of anisotropy of the structure. The dependences of penetration depth and attenuation constant (AC) of SW on the external magnetic field and thicknesses of the layers were examined analytically and numerically.

Propagation of a TE surface mode in a relativistic electron beam–quantum plasma system

The dispersion properties of a transverse electric (TE) surface waves propagating along the interface between a magneto-quantum plasma–relativistic beam system and vacuum are studied by using the quantum hydrodynamic model. The general dispersion relations are derived and analyzed in some special cases of interest. Moreover, the effects of density gradients for the beam and plasma on the dispersion properties of surface waves are investigated. The kind of dispersion relations depends strongly on the ambient magnetic field B o via the gyro-frequency ω c , the quantum parameters, and the width of the plasma layer as well as the relativistic factor for the electron beam. It is found that the quantum effects play a crucial role to facilitate the propagation of TE surface waves.

High-frequency surface waves at a plasma-metal interface: II. Dispersion of a nonlinear wave

A study is made of the dispersion properties of nonlinear surface waves propagating along a plasma-metal interface under conditions corresponding to the formation of a space charge sheath that equalizes the electron and ion fluxes to the wall. Oscillations of the plasma boundary under the action of the surface wave field are taken into account. It is shown that these oscillations are the main nonlinear mechanism for generating wave field harmonics and are analogous to the nonlinearity in the current-voltage characteristic of the space charge sheath. The effect of the nonlinearity on the dispersion properties of surface waves due to the relationship between the sheath thickness and wave amplitude is calculated with allowance for harmonic generation. The energy transported by surface waves under conditions typical of RF and microwave discharges is calculated.

High-frequency surface waves at a plasma-metal interface: I. Linear model

A study is made of the dispersion properties of surface waves at a plasma-metal interface under thermodynamically nonequilibrium conditions such that a space charge sheath forms at the plasma boundary. In the simplest model, the sheath is described as a dielectric with a given permittivity. The wave parameters in a highly collisional plasma are discussed. The effect of interaction between waves propagating near the opposite plasma boundaries is considered, in particular, for space charge sheaths of different thicknesses. Conditions are determined under which the parameters of surface waves are substantially altered by the plasma-sheath geometric resonance.

True surface waves guided by metamaterials

The dispersion properties of surface waves propagating along the interface between a resonant metamaterial and vacuum have been studied. It is shown that such an interface can support both forward and backward waves. The case of degeneracy, where an infinite number of waves with arbitrary retardation correspond to one frequency, has been investigated.

Surface waves in inversely dispersive media

ABSTRACTThe dispersion of surface waves in inversely dispersive media where the shear‐wave velocity decreases with depth is studied. Theoretical dispersion curves are calculated in the complex wavenumber domain. Excitability and attenuation due to leakage are calculated for each point on the dispersion curves. These additional parameters are critical for a correct understanding of the dispersion properties of surface waves. Mode shapes are included in the study to visualize displacements inside the medium. The results of the study show that, for inversely dispersive media, the Rayleigh‐wave assumption is not valid, and other types of interface waves and leaky Lamb waves contribute to the surface wavefield. They also show that, in this case, true theoretical dispersion curves can be approximated by Lamb‐wave dispersion curves for a free plate in a vacuum, provided that the stiffness contrast between the top layer and the underlying half‐space is large, and also that the shear‐wave velocity of the stiff layer is greater than the compressional‐wave velocity in the underlying media. The error in the phase velocity resulting from this approximation is investigated and it is shown that the error does not exceed 5% for the fundamental antisymmetric Lamb‐wave dispersion curve. Because of the numerical simplicity of calculating its theoretical dispersion curves, the Lamb‐wave approximation can provide an effective evaluation method to resolve the thickness and elastic parameters of the stiff top layer. This is exemplified using a set of field data.

Characteristics of Surface Wave Propagation at Nanouneter Range of Wave Length.

It is very important to know the characteristics of wave propagating on the surface of anisotropic materials for estimating the property of materials. It is known that crystal structures near the surface are different from those in bulk. The author deduced the boundary condition taking into consideration of surface density and surface stresses of materials in a previous paper. In the present paper, the boundary condition is used for examining the velocity of the surface wave against wave number. The dispersion of the surface wave in an isotropic material is first investigated, and it is shown that the wave velocity decreases with decreasing the wavelength in the case where the surface density and the surface stresses are taken into account. The dispersion properties of surface wave in anisotropic materials, in particular, Ni (001) and W (110) are next investigated, and the dispersion relationship obtained by a continuum approach is compared to the experimental results of surface phonon. The theoretical results considering the surface density and the surface stresses are almost agreed with the experimental ones. In this analysis, the surface density plays an important role for the explanation of behavior of surface phonon against the wave number.

611 連続体力学による表面フォノン伝播解析

It is known that crystal structures near the surface are different from those in bulk. In the present paper, the boundary condition taking into consideration of surface density and surface stresses is used for examining the velocity of the surface wave against wave number. The dispersion of the surface wave in an isotropic material is first investigated, and it is shown that the wave velocity decreases with decreasing the wavelength in the case where the surface density and the surface stresses are taken into account. The dispersion properties of surface wave in anisotropic materials, in particular, Ni(001) and W(110) are next investigated, and the dispersion relationship obtained by a continuum approach is compared to the experimental results of surface phonon. The theoretical results considering the surface density and the surface stresses are almost agreed with the experimental ones. In this analysis, the surface density plays an important role for the explanation of behavior of surface phonon against the wave number.

Azimuthal surface waves in a magnetized plasma

A theoretical analysis is made of the dispersion properties of surface waves propagating along the azimuth in magnetized cylindrical plasma waveguides. It is shown that surface oscillations of the ion component may propagate in these waveguides.

Surface waves on the harmonics of the electron cyclotron frequency propagating along a plasma - metal interface

Dispersion properties of slow electromagnetic surface waves propagating on the harmonics of the electron cyclotron frequency across the external steady magnetic field are studied in the case when the magnetic field is parallel to the plasma - metal interface. Theoretical investigation of these surface modes is carried out using the kinetic description under the condition of weak plasma spatial dispersion, when the radii of the charged plasma particles' Larmor rotation are much less than the spatial scale of the considered wave perturbation. The effect of the plasma density transverse inhomogeneity, of plasma particles' concentration and of the external magnetic field value on the dispersion properties of the surface waves on electron cyclotron harmonics (SWCH) is researched.

Wave properties of a cylindrical antenna immersed in a magneto-active plasma

The dispersion properties and electromagnetic field topography of surface waves propagating along and in the azimuthal direction with respect to a cylindrical metal antenna immersed in a magneto-active plasma are investigated. The external magnetic field is directed along the antenna axis. The presence of a vacuum-gap sheath region separating the antenna from the plasma is assumed. The sheathless case is also considered. The dependence of the surface-wave dispersion properties on magnetic field intensity, plasma density, antenna radius and sheath thickness is presented for structure parameters close to experimental data. The results show qualitative agreement between our theory and experiment. The antenna surface impedance is calculated as well.