Propagation Of Surface Waves Research Articles

Nonlinear Wave Evolution in Interaction with Currents and Viscoleastic Muds

A numerical model is extended to investigate the nonlinear dynamics of surface wave propagation over mud in the presence of currents. A phase-resolving frequency-domain model for wave-current interaction is improved to account for wave modulations due to viscoelastic mud of arbitrary thickness. The model compares well with published laboratory data and performs slightly better than the model with viscous mud-induced wave damping mechanism. Monochromatic and random wave simulations are conducted to examine the combined effect of currents, mud-induced wave dissipation and modulation, and nonlinear wave-wave interactions on surface wave spectra. Results indicate that current effects on wave damping over viscoelastic mud is not as straightforward as that over viscous mud. For example, while opposing currents consistently increase damping of random waves over viscous mud, they can decrease damping over viscoelastic mud due to high variations in frequency-dependent damping stemming from mud’s elasticity. It is shown that a model that assumes the mud layer to be thin for simplification can overestimate wave damping over thick mud layers.

High-isolation antenna array using SIW and realized with a graphene layer for sub-terahertz wireless applications

This paper presents the results of a study on developing an effective technique to increase the performance characteristics of antenna arrays for sub-THz integrated circuit applications. This is essential to compensate the limited power available from sub-THz sources. Although conventional array structures can provide a solution to enhance the radiation-gain performance however in the case of small-sized array structures the radiation properties can be adversely affected by mutual coupling that exists between the radiating elements. It is demonstrated here the effectiveness of using SIW technology to suppress surface wave propagations and near field mutual coupling effects. Prototype of 2 × 3 antenna arrays were designed and constructed on a polyimide dielectric substrate with thickness of 125 μm for operation across 0.19–0.20 THz. The dimensions of the array were 20 × 13.5 × 0.125 mm3. Metallization of the antenna was coated with 500 nm layer of Graphene. With the proposed technique the isolation between the radiating elements was improved on average by 22.5 dB compared to a reference array antenna with no SIW isolation. The performance of the array was enhanced by transforming the patch to exhibit metamaterial characteristics. This was achieved by embedding the patch antennas in the array with sub-wavelength slots. Compared to the reference array the metamaterial inspired structure exhibits improvement in isolation, radiation gain and efficiency on average by 28 dB, 6.3 dBi, and 34%, respectively. These results show the viability of proposed approach in developing antenna arrays for application in sub-THz integrated circuits.

Sustained Open Access Global Wave Observations for Science and Society

Abstract Studies of the generation and propagation of surface waves in the open ocean have been traditionally supported by sparse observations. Wave climatology is only known through data from expensive and heavy open ocean moorings, often not optimized for observing surface waves, coastal wave observing networks, or from satellites that can only measure the wave's amplitude. Yet, knowledge of wave physics is of fundamental importance to understand how the ocean and the atmosphere are coupled and to quantify, for example, exchanges of gas and momentum. Of similar importance is understanding how oceanic mesoscale, such as eddies and boundary currents, affect wave steepness and propagation; ultimately important to quantify, for example, hazards to navigation and to protect coastal communities from floods. Scientific advances in data assimilation and wave resolving models, which are supported by our visionary approach, are needed to improve coupled models to support extreme events modeling and forecasting and for improving climate assessment. In-situ global wave observations are one of the obviously missing key ingredients that are hampering progress in oceanography, meteorology, and climate sciences.

Terahertz surface plasmons propagation in semiconducting parallel plates waveguide configuration

In this study we theoretically and numerically demonstrated a 3-D plasmonic terahertz waveguide made up of two parallel plates of semiconductor sandwiching a thin region of vacuum/air. The semiconductor can reveal conductive properties at the THz regime, making it an appropriate replacement for structured metallic surfaces in plasmonic devices. The proposed waveguide configuration not only offers an extra degree of freedom to tailor the propagation of THz wave but also promises more confinement compared to the planar waveguide configuration. The dispersion relations of the terahertz surface plasmon polaritons as they propagate in the proposed configuration is calculated using the Drude model. It is observed that the dispersion behavior of the modes is altered by the carrier densities of the plates and the separation between them. We also numerically analyze the terahertz surface waves propagation in the proposed geometry and examine terahertz surface modes behavior in conjunction with the theory. For the tapered configuration, we observed that the transmission amplitude increases as the tapering angle increases for the same input width. The present study could be significant in the construction of terahertz active and passive devices that may utilize semiconductors instead of metals.

Surface waves in a Goubau line filled with nonlinear anisotropic inhomogeneous medium

The propagation of monochromatic nonlinear symmetric hybrid surface waves in a cylindrical nonlinear anisotropic inhomogeneous metal-dielectric waveguide is considered. The physical problem is reduced to solving a transmission eigenvalue problem for a system of ordinary differential equations. Spectral parameters of the problem are propagation constants of the waveguide. The setting is reduced to a new type of nonlinear eigenvalue problem and an analytical method of its solution is developed. The propagation modes are found that have not been previously reported in the literature. For the numerical solution, a method is proposed based on solving an auxiliary Cauchy problem (a version of the shooting method). As a result of comprehensive numerical modeling, new propagation regimes are discovered.

Gravity waves on a random bottom: exact dispersion-relation

In a recent paper [Cáceres MO, Comments on wave-like propagation with binary disorder. J. Stat. Phys. 2021;182(36):doi.org/10.1007/s10955-021-02699-0.], the evolution of a wave-like front perturbed by space-correlated disorder was studied. In addition, the generic solution of the field mean-value was presented as a series expansion in Terwiel's cumulants operators. This infinite series cuts due to the algebra of naked Terwiel's cumulants when these cumulants are associated to a space exponential-correlated symmetric binary disorder. We apply an equivalent approach to study the dispersion-relation for 1D surface gravity waves propagating on an irregular floor. The theory is based on the study of the mean-value of plane-wave-like Fourier modes for the propagation and damping of surface waves on a random bottom.

Nonreciprocal and Topological Plasmonics

Metals, semiconductors, metamaterials, and various two-dimensional materials with plasmonic dispersion exhibit numerous exotic physical effects in the presence of an external bias, for example an external static magnetic field or electric current. These physical phenomena range from Faraday rotation of light propagating in the bulk to strong confinement and directionality of guided modes on the surface and are a consequence of the breaking of Lorentz reciprocity in these systems. The recent introduction of relevant concepts of topological physics, translated from condensed-matter systems to photonics, has not only given a new perspective on some of these topics by relating certain bulk properties of plasmonic media to the surface phenomena, but has also led to the discovery of new regimes of truly unidirectional, backscattering-immune, surface-wave propagation. In this article, we briefly review the concepts of nonreciprocity and topology and describe their manifestation in plasmonic materials. Furthermore, we use these concepts to classify and discuss the different classes of guided surface modes existing on the interfaces of various plasmonic systems.

Surface waves in nonlocal transversely isotropic liquid-saturated porous solid

In this paper, propagation of surface waves in nonlocal transversely isotropic liquid-saturated porous solid half-space has been investigated. The model is proposed for two different situations of which one is for excluding fluid nonlocal effect, and the other is for including fluid nonlocal effect. The existence of a new wave that arises due to the presence of nonlocality parameter in the medium as well as some critical circular frequencies is derived. Dispersion equation for the propagation of Rayleigh-type surface waves and their conditions of existence at the free surface of transversely isotropic liquid-saturated porous solids has been obtained. The boundary may be opened surface pores or sealed surface pores. Dependence of the velocities of surface waves, Rayleigh wave type on the direction of propagation and frequency has been illustrated. These numerical results report the phenomena such as anomalous negative dispersion of wave velocities with frequency.

Nonlinear surface wave measurements on aged and laser shock surface-treated Inconel 718 superalloy

Because of their ability to probe the material properties at different penetration depths, surface acoustic waves (SAW) are considered for nondestructively characterizing the near-surface properties of a component that has been previously modified. During long-term service, microstructural changes are unavoidable, which in many cases promote the formation of deleterious phases in a material that operates at elevated temperatures impacting the mechanical response of the component. This research investigates the behavior of the nonlinearity parameter (βR) measured using the second harmonic generation of Rayleigh surface waves propagating in the free surface of aged Inconel 718 (IN 718) superalloy specimens with and without laser shock processing (LSP). Also, microstructural and mechanical characterizations were conducted to track first the sole effect of aging time, and secondly, the combined effects of aging + LSP on microhardness, residual stress, and tensile properties of the samples. Our experimental results obtained from aged samples with and without LSP processing indicate that a superposition of different effects of aging and surface treatment in the material contribute to the βR parameter, including microstructure, compressive residual stress, and cold work effects. The experimental results also indicate that it is feasible to observe a perceivable change in the βR parameter of the SAW when the specimen is heat-treated at different temperatures, which has no perceivable effect on the surface roughness. The changes on the βR parameter in aged samples are due to the gradual precipitation of γ′ and γ" hardening phases and the further precipitation of δ-phase, and in aged samples with LSP, electron backscatter diffraction (EBSD) analysis showed that changes are due to microstructural, near-surface residual stresses and texture effects. These results indicate a distinctive trend that shows that the measured βR can be useful in tracking microstructural changes in this material during high-temperature operations.

Design of MIMO planar antenna at 24 GHz band for radar, communication and sensors applications

A MIMO antenna with adequate compactness for applications like sensor heads, automotive radars and communication systems etc. is presented here. Significant size reduction with overall dimensions of 40 mm×6 mm has been achieved. Substrate RT/duroid 5880 of 0.8 mm thickness was used for the fabrication of proposed antenna which has low dielectric constant (2.2) and low dielectric loss so it is suitable for high frequency applications. Incorporating two rectangular slots in the radiating patch has helped to reduced the coupling via surface wave propagation and use of defective ground as decoupling structure has contributed for significant isolation improvement. These were major design considerations in this work. Important parameters which enlighten the antenna characteristics e.g. S-Parameters, Total Active Reflection Coefficient (TARC), Radiation Patterns, Diversity Gain, Efficiency and Envelope Correlation Coefficient (ECC) were calculated, measured and compared. Isolation between multiple antenna is a paramount index for MIMO antenna, was achieved better than −35 dB. Adequate bandwidth of 4.44 GHz (21.43–25.87 GHz) with radiation efficiency up to 87% was optimized in this design. The efficiency plot has sharp dilapidation beyond the proposed band of interest which indicates a superior antenna performance for interference suppression. CST Microwave Studio has been used for modelling and simulation. Fabricated antenna was tested in an anechoic chamber and measured results were in agreement with the simulated results. Satisfactory results and miniaturized size make the proposed design highly suitable for radars, communication and sensor applications.

Improving Baltic Sea wave forecasts using modelled surface currents

Currents in the Baltic Sea are generally weak, but during strong winds they can grow high enough to affect the surface wave propagation and evolution. To evaluate the significance of wave-current interactions in the Baltic Sea, we conducted a study using the wave model WAM, comparing a run without surface currents to one with current forcing from a NEMO hydrodynamical model simulation. The overall changes to the wave field caused by currents were quite small. Changes of over 10 cm in significant wave height (SWH) or 1 s in the peak period (Tp) occurred only in some areas and typically less than 3% of the time. Current refraction changed the SWH annual mean by up to 2 cm, but changes up to 60 cm were seen in the maximum values. Tp had occasionally large changes due to shifts in the peak energy in two-peaked swell and wind-sea spectra. Including currents typically led to a stronger changes in swell energy compared to the changes in wind sea energy. A comparison with a wave buoy in the Gulf of Finland showed that this change in the swell energy improved the accuracy of the simulation in this narrow gulf. Current-induced refraction was most prominent near the coastal areas, where current speed occasionally exceeded 0.3 m/s. In general, SWH decreased in the coastal areas with strong currents and slightly increased in adjacent open sea areas. The current effects were most frequent in the Gulf of Finland, the Western Gotland Basin and the Åland Sea.

DESIGN OF SQUARE MICROSTRIP PATCH MULTI BAND ANTENNA FOR WIRELESS COMMUNICATION USING EBG STRUCTURE

Application of electromagnetic band-gap (EBG) structure and its use in the design of antenna and microwave integrated circuits is becoming more attractive. The recent electromagnetic band-gap structure method is capturing more importance in antenna design due to its uniqueness properties to suppress the propagation of surface waves in microstrip patch antenna. In this paper a square microstrip antenna is designed and its performance parameters are compared with geometry designed on EBG structure. The square antenna of 29 mm x29 mm size is designed at 2.455 GHz and analysis is done using IE3D simulation software. The proposed work mainly focuses on modification of antenna using electronic band gap structure (EBG). The antenna parameters such as Return loss, VSWR, Gain and Bandwidth, with and without EBG are obtained using IE3D simulation tool. The Electromagnetic band-gap structures have been used to improve the performance of the gain of the antennas and radiation patterns. One of the main advantages of electromagnetic band-gap structure is its ability to suppress the surface wave current present on the microstrip antenna. Combining the square patch with EBG structure, the bandwidth of the antenna has been increased by 34.66%, and attained gain of 44.44% at resonant frequency around 2.4 GHz as compared to the antenna without EBG..

Rayleigh waves on the impedance boundary of a rotating monoclinic half-space

The characteristic equations of Rayleigh waves in monoclinic materials have already been derived by various prominent researchers. This paper revisits all these studies with special attention on numerical solutions of the characteristic equation. In this work, the propagation of a Rayleigh surface wave in a rotating monoclinic half-plane is studied. The boundary conditions on the surface of the half-space are assumed in such a way that the normal and shear stresses are linearly proportional to the normal and tangential components, respectively. With the use of the polarization vector method, a non-dimensional characteristic equation of a Rayleigh wave is derived. The main aim of this work is to explore the numerical solutions of the characteristic equation. The analytical results are illustrated graphically to show the dependence of the Rayleigh wave speed upon the rotation, impedance, and material parameters.

Fundamental Study on Derivation of Elastic Modulus and Quality Estimate of Abrasive Layer of Super Abrasive Wheel Using Surface Wave Propagation Velocity

Fundamental Study on Derivation of Elastic Modulus and Quality Estimate of Abrasive Layer of Super Abrasive Wheel Using Surface Wave Propagation Velocity

Singular existence of a Dyakonov–Voigt surface wave: Proof

If Dyakonov surface-wave (DSW) propagation can be guided by the planar interface of an isotropic dielectric medium and a uniaxial dielectric medium with its optic axis lying wholly in the interface plane, then a Dyakonov–Voigt surface wave can propagate in at most one direction within the angular sector for DSW propagation.

Long-Range Spoof Surface Plasmons(LRSSP) on the Asymmetric Double Metal Gratings

Spoof surface plasmons (SSP) on the corrugated metal surfaces have been widely studied over the past decade in both microwave and Terahertz (THz) band. Previous studies show that SSP mode on the metal grating suffers from high dissipative losses in high THz band especially near asymptotic frequency which may limit its real applications. The issue can be addressed by utilizing long-range SSP mode (LRSSP). LRSSP is a special low-loss symmetric propagating surface wave mode along double-layer corrugated metallic waveguides. In this paper, the asymmetric double metal gratings are proposed to support LRSSP which can significantly reduce the damping losses of the other short-range SSP mode (SRSSP) on the conventional doubly-corrugated metallic surfaces, thus enabling new possibilities to utilizing this SRSSP mode within long-range manner. According to our dispersion theory and the numerical calculations, the propagation loss of LRSSP is still lower than that of SRSSP within asymmetric regime, which demonstrates good tolerance to the asymmetry of the double-layer corrugated structure. However, its long-range propagation superiority of LRSSP vanishes gradually as the degree of asymmetry is enlarged. This work provides an alternative approach to increase the propagation length of SRSSP mode on the doubly-corrugated metallic surfaces and can open up new avenues to develop some novel LRSSP-based plasmonic devices such as waveguides, filters, sensors and active powerful radiation sources induced by energy beam below optical spectrum.

Propagation and attenuation of Rayleigh and pseudo surface waves in viscoelastic metamaterials

The development of seismic metamaterials has attracted much research interest in the past decade. Efforts have been made by using experimental and theoretical approaches to isolate buildings and structures susceptible to elastic surface wave damage. However, most seismic metamaterials were designed without considering the viscoelastic effect that widely exists in nature. In this work, we investigate the propagation and attenuation of the Rayleigh and pseudo surface waves (PSWs) in two types of viscoelastic seismic metamaterials, namely, pillared and inclusion-embedded metamaterials, by analyzing the complex band structures and transmission spectra. The complex band structure developed in this work reveals for the first time the existence of PSWs and their propagation properties in inclusion-embedded metamaterials at the surface. These PSW modes are hidden in the traditional ω(k) technique, therefore showing the usefulness of the complex band structure approach. Introducing viscosity to the substrate of both types of seismic metamaterials will enhance the attenuation of both the Rayleigh wave and PSW. For inclusion-embedded metamaterials, the viscoelastic effect in the soft coating layer can have a specific influence only on the PSW. PSWs show advantages to minimize the relative attenuating effect in general. The results in this work will open up great possibilities for designing and optimizing seismic metamaterials in practice.

A Consistent Scheme for the Precise FDTD Modeling of the Graphene Interband Contribution

The conductivity of graphene, due to interband electron transitions, is evaluated, in this article, as rational functions through an efficient iterative optimization of Padé polynomials. Then, the latter are straightforwardly imported in the text finite-difference text time-domain algorithm, as an equivalent surface current, by means of precise recursive convolution schemes. Numerical examples, considering an incident plane wave toward graphene, the extraction of the corresponding surface wave propagation attributes, and a plasmonic switch, successfully validate the consistent modeling of interband conductivity through the proposed technique.

Effect of surface waves in orthotropic crystal layer overlying an initial stressed elastic half-space due to point source

This paper implements the theoretical study of propagation of Rayleigh-type surface waves in an orthotropic crystal layer of finite thickness lying on an initially stressed elastic half-space due to a point source. The boundary conditions of the model are considered properly, and the displacement components are obtained in both layers using the substitution method and the matrix method for solution (non-trivial) of the system of homogeneous linear equation. The dispersion equation is found for the seismic wave propagation in a sixth-order determinant equation form. This equation is also derived for the initial stressed elastic half-space of the free boundary. Some particular cases are considered in a relevant manner. Dispersion curves for wave number versus phase velocity are traced for the model using Mathematica software. The curves conclude that the affecting parameters have a great effect on the surface wave propagation.

Impact of spatial variability of shear wave velocity on the lagged coherency of synthetic surface ground motions

The spatial incoherence of ground motion during an earthquake can have a significant effect on the dynamic response of engineering structures such as bridges, dams, nuclear power plants and lifeline facilities. The main objective of this paper is to study the effect of anisotropic heterogeneities in a soil layer overlying homogeneous bedrock on the lagged coherency of surface ground motion. A set of numerical experiments is performed based on 2D spatial variability of shear-wave velocities modeled as a homogeneous stationary random field and discretized by the EOLE method (Expansion Optimal Linear Estimation). Seismic ground motions were simulated using FLAC2D software in the 1–25 Hz band for a plane wave excitation with SV polarization. The soil is characterized by horizontal and vertical autocorrelation distances ranging between 5 and 20 m and 1 and 2 m, respectively, and a coefficient of variation of the shear-wave velocity varying between 5% and 40%. The synthetic seismograms calculated for 9 parameter sets (100 realizations each) clearly show seismic waves scattering and surface waves diffracted locally by the ground heterogeneities, generating large spatial variations in coherence mainly controlled by the coefficient of variation of shear-wave velocity. Consistently with existing models and experimental data, the numerical coherency curves decrease with frequency and receiver distance, however at a rate which is lower than that observed in the experimental data. This difference is probably due to intrinsic attenuation that is not accounted for in the simulations and/or to our 2D simulations that do not reproduce the complete wavefield. The numerical average coherency curves for each parameter set exhibit maxima within narrow frequency bands caused by the vertically trapped body waves and surface wave propagation properties within the average ground model. This interpretation is supported by experimental data recorded in the Koutavos-Argostoli valley (Greece).