Wave Propagation In Media Research Articles

High-order generalized screen propagator migration based on particle swarm optimization

Various migration methods have been proposed to image high-angle geological structures and media with strong lateral velocity variations; however, the problems of low precision and high computational cost remain unresolved. To describe the seismic wave propagation in media with lateral velocity variations and to image high-angle structures, we propose the generalized screen propagator based on particle swarm optimization (PSO-GSP), for the precise fitting of the single-square-root operator. We use the 2D SEG/EAGE salt model to test the proposed PSO-GSP migration method to image the faults beneath the salt dome and compare the results to those of the conventional high-order generalized screen propagator (GSP) migration and split-step Fourier (SSF) migration. Moreover, we use 2D marine data from the South China Sea to show that the PSO-GSP migration can better image strong reflectors than conventional imaging methods.

FOCUSING THE VERTICAL ELECTRIC DIPOLE RADIATION BY THE PENDRY LENS

The flat lens conception was considered in the pioneering work of V.G. Veselago, who considered the possibility of electromagnetic waves propagation in media with simultaneously negative permittivity and permeability (according to modern terminology − in the left-handed metamaterials). Later, J.B. Pendry put forward the idea of the so-called "superlens", the resolution of which would exceed the diffraction limit. In view of the prospects for the practical applications it has caused a discussion on the possibility of anti-parallelism of phase and group velocities and the actual super-resolution implementation for the source in the form of a monopole. However, using the ray theory approximation reduced the generality of the results, neglecting losses radically distorted them, and errors in the theoretical analysis led to the wrong physical interpretation. In this paper, we obtained a rigorous solution to the problem of focusing radiation from elementary electric dipole located perpendicularly to the plane layer of finite thickness made of the left-handed metamaterial with absorption. Spatial distribution of the electromagnetic field in the layer, as well as the incident and reflected fields at various heights of the dipole, layer thickness and losses in each medium are numerically simulated. The analysis of the calculated spatial structure of the electromagnetic field confirmed the focusing ability of the interfaces between ordinary and left-handed media, as well as a flat lens.

Breaking time reversal symmetry with coriolis mean flow systems

One way to break time reversal symmetry is to have a moving wave propagation medium. If the acoustic wave vector and the moving fluid velocity are collinear, such as the one created by Fluery et al. (Science, 343, 2014) we can use the wave vector shift caused by the fluid flow to break reciprocity. An alternative approach we have taken is to use a fluid velocity field which enters the differential equation of the system as a cross product term with the wave vector. A circular field in which the fluid velocity increases radially has a Coriolis acceleration term. In this system, the acoustic wave enters from the central wall and exits from the perimeter wall. Equations of conservation of mass and momentum, after linearization can be simplified to: (∂/∂t+V.▽)P+ρC2▽.(u+V) = 0, ρ∂/∂t(u+V)+ρ(V.▽)u+ρ(u.▽)V+ρ(V.▽)V+▽P = 0, in which u is the particle acoustic velocity and V = rωeθis the fluid velocity due to the rotational velocity field. It can be shown that the third term in the second equation can be simplified as:ρωek×u. This term Coriolis acceleration induces nonreciprocity. In this work, we solved the differential equation numerically and investigated the effect of fluid velocity on the nonreciprocity factor.

Numerical modeling of wave processes in layered media in the Arctic region

The aim of this work is the numerical simulation of wave propagation in media with linear-elastic and acoustic layers as exemplified by the seismic prospecting problems in the Arctic region and the explosive impact on an iceberg. The complete system of equations describing the state of a linearly elastic body and the system of equations describing the acoustic field are solved. The grid-characteristic method is used to provide the contact and boundary conditions, including the contact condition between acoustic and linear-elastic layers, to be correctly described.

Propagation Characteristics of Acoustic Emission in Plate Structure with Various Materials and Multilayer Medium

Acoustic emission signal is a kind of elastic wave which is caused by the release of internal energy of materials when the structure changes. The propagation characteristics of acoustic emission is important to the testing technology of a structure by acoustic emission signal. The finite element method is introduced to analyze elastic wave propagation in plate structure in the article, which mainly contains the discretization techniques of the area and time domain. The structure plate with different materials ,style and coating metal are selected in finite element simulation, the displacement contours and wave curve resulted from simulation are used to analyze the interface reflection, refraction and diffraction process as well as the wave type conversion in different medium of the elastic wave propagation . The mechanical pencil lead fracture experiment is done to verify the transient simulation of elastic wave propagation in plate structure.

Effect of reinforcement, gravity and liquid loading on Rayleigh-type wave propagation

In the present time, self-reinforced materials are the basic requirement for civil engineering construction. These constructions encounter surface wave propagation during earthquakes and similar disturbances. Therefore, the study of surface wave propagation in such material is of great significance. The present paper, in the light of practical situation like dams, canals etc. aims to study the effect of gravity on the propagation of Rayleigh-type surface wave in a self-reinforced semi-infinite medium bounded and loaded by an inviscid liquid layer. Secular equation for the propagation of Rayleigh-type wave has been derived in closed form. The effect of gravity, reinforcement and liquid loading on phase velocity of Rayleigh-type wave has been distinctly observed. Numerical computation has been carried out and graphical illustration is provided for analysis of the presented study. Moreover, the effect of reinforced semi-infinite medium is compared to the effect of reinforced free semi-infinite medium on the phase velocity of Rayleigh-type surface wave to unravel the reinforcement effect. The effect of presence and absence of liquid loading on self-reinforced semi-infinite medium for Rayleigh-type wave propagation is also analysed and depicted by means of graphs.

Prestack elastic generalized-screen migration for multicomponent data

An efficient prestack depth migration method based on the elastic one-way wave equation was developed using an improved elastic generalized-screen propagator, which effectively describes the behavior of elastic waves with mode conversion at the interfaces and efficiently computes wave propagation in media with lateral velocity variations. The elastic propagator presented in this study was improved from the elastic generalized-screen propagator. Several terms of the vertical slowness right symbol with orders are corrected from the original formulation, and the vertical slowness operator in the propagator was expanded up to the 2nd order which yields a more accurate approximation. In each screen propagation step, the multicomponent wavefields are automatically separated into the P and S wavefields by the P–S decomposition operator included in the elastic generalized-screen propagator. This process facilitates the imaging of the P and S waves separately without any additional P and S separation process after the wavefield extrapolation. Impulse response tests of the improved elastic generalized-screen propagator in a uniform-property medium proved that propagation accuracy increases with order, even when large medium perturbations are assigned. Migration tests using the developed algorithm on a simple layered model and two complex models (the SEG/EAGE salt and elastic Marmousi-2 model) demonstrated the functional advantages and capabilities of the algorithm compared with elastic migration using the scalar wave equation.

Wave propagation in two-dimensional block media with viscoelastic layers (Theory and experiment)

A model of a medium consisting of parallel layers of elastic rectangular blocks separated by deformable viscoelastic interlayers is considered. The model is proposed for describing the lowfrequency part of the spectrum in waves propagating in media with such a structure. For a twodimensional assembly consisting of 36 blocks, the results of numerical calculations are compared with experimental data.

Modeling of Seismic Wave Propagation at Tiris Geothermal Area Using 2D Spectral Element Method (SEM)

The spectral-element method (SEM) has been applied to simulate seismic wave propagation in 2D tentative geological model of Geothermal Area in Tiris, East Java Indonesia. we used 2-D model with 36 km x 5 km dimensions and discretized into 720 × 80 rectangular elements (mesh). We computed 8000 time steps with a sampling interval of 0.001 s using 10 Hz Ricker wavelet. The snapshots of seismic wave propagation along Tiris 2D geological model illustrate that SEM could accurately modeling seismic wave propagation. The seismic event that triggers a vibration in rock layers not only depend on the characteristics of the seismic earthquake source parameters and seismic wave propagation media, but also influenced by geometry of the media, such as topography and geological setting. The influence of ground topography, difference media, and structural geology were demonstrated by different time of wave arrival and different amplitudes. Therefore, SEM could be applied as preliminary study in geothermal exploration.

Implications of the theory of turbulent mixing for wave propagation in media with fluctuating coefficient of refraction

Implications of the theory of turbulent mixing for wave propagation in media with fluctuating coefficient of refraction

An analog extremely-low-frequency-very-low-frequency atmospheric noise spectrum analyzer on programmable integrated circuits

A functional diagram of the analog extremely-low-frequency-very-low-frequency atmospheric noise spectrum analyzer is presented and its characteristics and spectrum record examples are given. The joint use of programmable analog and digital integrated circuits allows a unit being in the operating state to change in real time such basic parameters of the analyzer as the number of analysis points, characteristics of the analyzing filter, and scanning time of the frequency spectrum. Studying the signals of the lightning generator (of atmospheric noises) provides important information for studying both the atmospheric electricity and the electromagnetic wave propagation medium (earth-ionosphere waveguide).

A comparison of finite-difference and spectral-element methods for elastic wave propagation in media with a fluid-solid interface

The numerical simulation of wave propagation in media with solid and fluid layers is essential for marine seismic exploration data analysis. The numerical methods for wave propagation that are applicable to this physical settings can be broadly classified as partitioned or monolithic: The partitioned methods use separate simulations in the fluid and solid regions and explicitly satisfy the interface conditions, whereas the monolithic methods use the same method in all the domain without any special treatment of the fluid-solid interface. Despite the accuracy of the partitioned methods, the monolithic methods are more common in practice because of their convenience. In this paper, we analyse the accuracy of several monolithic methods for wave propagation in the presence of a fluid-solid interface. The analysis is based on grid-dispersion criteria and numerical examples. The methods studied here include: the classical finite-difference method (FDM) based on the second-order displacement formulation of the elastic wave equation (DFDM), the staggered-grid finite difference method (SGFDM), the velocity-stress FDM with a standard grid (VSFDM) and the spectral-element method (SEM). We observe that among these, DFDM and the first-order SEM have a large amount of grid dispersion in the fluid region which renders them impractical for this application. On the other hand, SGFDM, VSFDM and SEM of order greater or equal to 2 yield accurate results for the body waves in the fluid and solid regions if a sufficient number of nodes per wavelength is used. All of the considered methods yield limited accuracy for the surface waves because the proper boundary conditions are not incorporated into the numerical scheme. Overall, we demonstrate both by analytic treatment and numerical experiments, that a first-order velocity-stress formulation can, in general, be used in dealing with fluid-solid interfaces without using staggered grids necessarily.

On finding exact solutions of the two-dimensional eikonal equation when the front of the wave propagating in a medium is a circle

Wave propagation in a two-dimensional medium is considered in the case when the wave front is a circle with the center (a(t), 0) and radius r(t). A question is posed: What is the distribution of velocity in the medium? General characteristics and examples of such media are given.

Experimental investigation of bifurcation induced bandgap reconfiguration

By applying an asymmetric on-site restoring force in a 1D chain of oscillators, we demonstrate experimentally that a morphing in the bandgap structure or passive bandgap reconfiguration can be triggered by an increase in environmental excitation amplitude. Recent studies on wave propagation have focused on new capabilities and behaviors resulting from intrinsic nonlinearities. This paper details a bistable experimental design that achieves amplitude dependent filtering through passive bandgap reconfiguration, which is triggered by a bifurcation. The system studied comprises a 1D chain of axially aligned pendulums in dimer unit cells with geometrically nonlinear nearest neighbor coupling where bistability is induced through repulsive magnets. When the bistability is asymmetric, each potential well has a different linear spectra. Though this paper uses mechanically coupled oscillators as an example, the phenomenon itself could be used in any wave propagation media where asymmetric bistability can be implemented.

Determination of trace glyphosate in water with a prism coupling optical waveguide configuration

We herein discuss a prism coupling hollow-core metal-cladded waveguide (HCMW) sensor that uses ultrahigh-order modes (UHM) for sensitive absorption detection of glyphosate. In our method, modified chromogenic glyphosate in the hollow-core serves as guiding medium for high-power wave propagation. Prism coupling is employed to generate attenuated total reflection (ATR) dips of the UHM. The depths of the dips are closely related to the extinction coefficient of chromogenic glyphosate. A glyphosate detection limit below1.4nm/l is experimentally demonstrated with low consumption and solution-free operation. The calibration curve has been found linear in the concentration range of 0.0−5.0nm/l.

Efficient Optical to Microwave Conversion

Modern-day communications often involve the use of specially designed fiber-optic channels as a guided wave propagation medium. Information is carried through this medium as a modulated light beam, which can then be received and utilized in a manner similar to traditional analog signaling. However, engineers are increasingly finding a greater use for fiber-optic communications in place of traditional, analog communications, mainly because of the significantly higher bandwidth, lower losses, and lack of interference possibility in fiber-optic channels.

Simulations of P-SV wave scattering due to cracks by the 2-D finite difference method

We simulate P-SV wave scattering by 2-D parallel cracks using the finite difference method (FDM). Here, special emphasis is put on simplicity; we apply a standard FDM (second-order velocity-stress scheme with a staggered grid) to media including traction-free, infinitesimally thin cracks, which are expressed in a simple manner. As an accuracy test of the present method, we calculate the displacement discontinuity along an isolated crack caused by harmonic waves using the method, which is compared with the corresponding results based on a reliable boundary integral equation method. The test resultantly indicates that the present method yields sufficient accuracy. As an application of this method, we also simulate wave propagation in media with randomly distributed cracks. We experimentally determine the attenuation and velocity dispersion induced by scattering from the synthetic seismograms, using a waveform averaging technique. It is shown that the results are well explained by a theory based on the Foldy approximation, if the crack density is sufficiently low. The theory appears valid with a crack density up to at least 0.1 for SV wave incidence, whereas the validity limit appears lower for P wave incidence.

Immersive experimentation in a wave propagation laboratory.

A wave propagation laboratory is proposed which enables the study of the interaction of broadband signals with complex materials. A physical experiment is dynamically linked to a numerical simulation in real time through transmitting and recording transducer surfaces surrounding the target. The numerical simulation represents an arbitrarily larger domain, allowing experiments to be performed in a total environment much greater than the laboratory experiment itself. Specific applications include the study of non-linear effects or wave propagation in media where the physics of wave propagation is not well understood such as the effect of fine scale heterogeneity on broadband propagating waves.

Dyakonons in hyperbolic metamaterials

We have analyzed surface-wave propagation that takes place at the boundary between an isotropic medium and a semi-infinite metal-dielectric periodic medium cut normally to the layers. In the range of frequencies where the periodic medium shows hyperbolic space dispersion, hybridization of surface waves (dyakonons) occurs. At low to moderate frequencies, dyakonons enable tighter confinement near the interface in comparison with pure SPPs. On the other hand, a distinct regime governs dispersion of dyakonons at higher frequencies. Full Text: PDF References Z. Ruan, M. Qiu, "Slow electromagnetic wave guided in subwavelength region along one-dimensional periodically structured metal surface", Appl. Phys. Lett. 90, 201906 (2007). CrossRef A. Yariv, P. Yeh,"Electromagnetic propagation in periodic stratified media. II. Birefringence, phase matching, and x-ray lasers", J. Opt. Soc. Am. 67, 438 (1977). CrossRef D.R. Smith, D. Schurig, "Electromagnetic Wave Propagation in Media with Indefinite Permittivity and Permeability Tensors", Phys. Rev. Lett. 90, 077405 (2003). CrossRef I.I. Smolyaninov, E. Hwang, E. Narimanov, "Hyperbolic metamaterial interfaces: Hawking radiation from Rindler horizons and spacetime signature transitions", Phys. Rev. B 85, 235122 (2012). CrossRef Z. Jacob, E.E. Narimanov, "Optical hyperspace for plasmons: Dyakonov states in metamaterials", Appl. Phys. Lett. 93, 221109 (2008). CrossRef M.I. D'yakonov, "New type of electromagnetic wave propagating at an interface", Sov. Phys. JETP 67, 714 (1988). DirectLink I.I. Smolyaninov, Y.J. Hung, C.C. Davis, "Magnifying Superlens in the Visible Frequency Range", Science 315, 1699 (2007). CrossRef J. Elser, V.A. Podolskiy, I. Salakhutdinov, I. Avrutsky, "Nonlocal effects in effective-medium response of nanolayered metamaterials", Appl. Phys. Lett. 90, 191109 (2007). CrossRef E. Popov, S. Enoch, "Mystery of the double limit in homogenization of finitely or perfectly conducting periodic structures", Opt. Lett. 32, 3441 (2007). CrossRef B. Wood, J.B. Pendry, D.P. Tsai, "Directed subwavelength imaging using a layered metal-dielectric system", Phys. Rev. B 74, 115116 (2006). CrossRef

Waves in asymmetric hyperbolic media

In this paper, a homogenization model is applied for analysis of the spectrum of natural modes in s finite-thickness slab of tilted metallic carbon nanotubes. Tilted anisotropy axis causes a difference between normal wave vector components for waves, propagating upward and downward with respect to slab interfaces. This asymmetry effects becomes very strong for hyperbolic media and it results in appearance of backward waves and accumulation points in spectra of natural waves. Full Text: PDF References D. R. Smith and D. Schurig, "Electromagnetic Wave Propagation in Media with Indefinite Permittivity and Permeability Tensors", Phys. Rev. Lett. 90, 077405 (2003). CrossRef P. A. Belov, et al., "Strong spatial dispersion in wire media in the very large wavelength limit", Phys. Rev. B 67, 113103 (2003). CrossRef I. S. Nefedov, "Electromagnetic waves propagating in a periodic array of parallel metallic carbon nanotubes", Phys. Rev. B 82, 155423 (2010). CrossRef Z. Jakob, I. Smolyaniniv, and E.E. Narimanov, "Broadband Purcell effect: Radiative decay engineering with metamaterials", Appl. Phys. Lett. 100, 181105 (2012). CrossRef N. Poddubny, et al., "Microscopic model of Purcell enhancement in hyperbolic metamaterials", Phys. Rev. B 86, 035148 (2012). CrossRef V. N. Ivanov, et al., "Waves in a tangentially magnetized ferrite layer (electrodynamic calculation and uniform asymptotes)", Izvestiya Vysshikh Uchebnikh Zavedenii Radiofizika (Radiophysics and Quantum Electronics), 32, 764 (1989). CrossRef A. Yakovlev, et al., "Characterization of Surface-Wave and Leaky-Wave Propagation on Wire-Medium Slabs and Mushroom Structures Based on Local and Nonlocal Homogenization Models", IEEE Trans. Microw. Theory Tech. 57, 2700 (2009). CrossRef I. S. Nefedov and S. A. Tretyakov, "Ultrabroadband electromagnetically indefinite medium formed by aligned carbon nanotubes", Phys. Rev. B 84, 113410 (2011). CrossRef I. S. Nefedov and C. R. Simovski, "Giant radiation heat transfer through micron gaps", Phis. Rev. B 84, 195459 (2011). CrossRef S.-A. Biehs, M. Tschikin, and P. Ben-Abdallah, "Hyperbolic Metamaterials as an Analog of a Blackbody in the Near Field", Phys. Rev. Lett. 109, 104301 (2012). CrossRef Yu Guo, C. L. Cortes, S. Molesky, and Z. Jacob, "Broadband super-Planckian thermal emission from hyperbolic metamaterials", Appl. Phys. Lett. 101, 131106 (2012). CrossRef S.-A. Biehs, M. Tschikin, R. Messina and P. Ben-Abdallah, "Super-Planckian near-field thermal emission with phonon-polaritonic hyperbolic metamaterials", Appl. Phys. Lett. 102, 131106 (2013). CrossRef B. Liu and S. Shen, "Broadband near-field radiative thermal emitter/absorber based on hyperbolic metamaterials: Direct numerical simulation by the Wiener chaos expansion method", Phys. Rev. B 87, 115403 (2013). CrossRef G. Y. Slepyan, S. A. Maksimenko, A. Lakhtakia, O. Yevtushenko, A.V. Gusakov, "Electrodynamics of carbon nanotubes: Dynamic conductivity, impedance boundary conditions, and surface wave propagation", Phys. Rev. B 60, 17136 (1999). CrossRef S. M. Hashemi and I. S. Nefedov, "Wideband perfect absorption in arrays of tilted carbon nanotubes", Phys. Rev. B 86 195411 (2012). CrossRef