Propagation Direction Of Surface Waves Research Articles

Compact Slotted Circularly Polarized Microstrip Patch Antenna with Surface Wave Suppressed Characteristics for WLAN Characteristics

Surface wave propagation in the dielectric substrate is one the dominant factors leading to power loss in microstrip patch antennas. The surface waves are radiated from the edges of the dielectric substrate and does not contribute to the radiation of the antenna. To mitigate this problem discontinuity is required to be introduced in the direction of surface wave propagation. In this paper, surface wave suppressed antenna structures with circularly polarized radiation characteristics have been proposed. A square patch antenna has been designed at 6 GHz. Slotted perturbations for the same patch has been done to achieve compactness and circular polarization in the design. Two variants of the slotted antenna with side patches and PTH pins embedded at specific locations have been presented. For the 1st antenna design the axial ratio bandwidth of 120 GHz, compactness of 32.58 % and gain of 10.5 dB been achieved at resonant frequency of 8.9 GHz. For the 2nd antenna design the axial ratio bandwidth of 110 GHz, compactness of 34.7 % and gain of 9.8 dB been achieved at resonant frequency of 9.2 GHz. The improvement in gain of the proposed designs as compared to simple square patch antenna has been observed to be around 3 - 4 dB.

Azimuthal multiple signal classification of dispersive and aliased surface waves recorded in 3D seismic acquisition

Irregular acquisition geometry causes discontinuities in the appearance of surface wave events, and a large offset causes seismic records to appear as aliased surface waves. The conventional method of sampling data affects the accuracy of the dispersion spectrum and reduces the resolution of surface waves. At the same time, “mode kissing” of the low-velocity layer and inhomogeneous scatterers requires a high-resolution method for calculating surface wave dispersion. This study tests the use of the multiple signal classification (MUSIC) algorithm in 3D multichannel and aliased wavefield separation. Azimuthal MUSIC is a useful method to estimate the phase velocity spectrum of aliased surface wave data, and it represents the dispersion spectra of low-velocity and inhomogeneous models. The results of this study demonstrate that the mode kissing affects dispersion imaging, and inhomogeneous scatterers change the direction of surface-wave propagation. Surface waves generated from the new propagation directions also are dispersive. The scattered surface wave has a new dispersion pattern different from that of the entire record. Diagonal loading is introduced to improve the robustness of azimuthal MUSIC, and numerical experiments demonstrate the resultant effectiveness of imaging aliasing surface waves. A phase-matched filter is applied to the results of azimuthal MUSIC, and phase iterations are unwrapped in a fast and stable manner. Aliased surface waves and body waves are separated during this process. Overall, field data demonstrate that the azimuthal MUSIC and the phase-matched filters can successfully separate aliased surface waves.

A magnon scattering platform

Scattering experiments have revolutionized our understanding of nature. Examples include the discovery of the nucleus [R. G. Newton, Scattering Theory of Waves and Particles (1982)], crystallography [U. Pietsch, V. Holý, T. Baumback, High-Resolution X-Ray Scattering (2004)], and the discovery of the double-helix structure of DNA [J. D. Watson, F. H. C. Crick, Nature 171, 737-738]. Scattering techniques differ by the type of particles used, the interaction these particles have with target materials, and the range of wavelengths used. Here, we demonstrate a two-dimensional table-top scattering platform for exploring magnetic properties of materials on mesoscopic length scales. Long-lived, coherent magnonic excitations are generated in a thin film of yttrium iron garnet and scattered off a magnetic target deposited on its surface. The scattered waves are then recorded using a scanning nitrogen vacancy center magnetometer that allows subwavelength imaging and operation under conditions ranging from cryogenic to ambient environment. While most scattering platforms measure only the intensity of the scattered waves, our imaging method allows for spatial determination of both amplitude and phase of the scattered waves, thereby allowing for a systematic reconstruction of the target scattering potential. Our experimental results are consistent with theoretical predictions for such a geometry and reveal several unusual features of the magnetic response of the target, including suppression near the target edges and a gradient in the direction perpendicular to the direction of surface wave propagation. Our results establish magnon scattering experiments as a platform for studying correlated many-body systems.

Surface wave direction control on curved surfaces

Transformation optics (TO) has been recognized as an established scheme that can precisely manipulate electromagnetic surface wave propagations. Utilising the advantages of the TO technique, we proposed a TO device which can control the propagation direction of surface waves. The device is based on a generalized Eaton lens and can be realized on curved surfaces. Such a device can be composed of stacked ring layers, where the refractive index of each ring segment can be individually engineered. By engineering the refractive index, the stacked ring structure can guide the propagation direction of the surface wave. It may open a new door to manipulate surface wave propagation on demand.

Plasma-Dielectric Traveling Wave Antenna

The paper investigates the efficiency of transformation of traveling wave into radiation in longitudinally inhomogeneous plasma cylinder. The plasma is limited by a dielectric shell of finite thickness. The investigation involves the use of the method of spectral field expansion in terms of a set of functions including the surface and spatial waves of plasma cylinder with dielectric shell. A system of integro-differential equations for expansion coefficients has been obtained. These coefficients determine the amplitudes of transmitted, reflected, and scattered waves and also radiation patterns (RP). The system of equations is solved for the case of strong longitudinal variation of plasma density. The relationships of the transformation coefficients of surface wave energy as a function of the plasma density gradient, electrical length of section of plasma inhomogeneity, the electric radius of plasma cylinder, dielectric permittivity, and the thickness of dielectric were calculated. The fraction of surface wave energy that is transformed into radiation at acute angles can amount to 35%. The resultant narrow-beam RPs have only one lobe. The radiation maximum fits into an angle of several degrees with respect to the direction of surface wave propagation. With an increase of plasma density gradient, the lobe width is reduced, while its position shifts to 0°. The impact of dielectric properties on radiation characteristics has been also investigated.

Surface wave analysis for heterogeneous geological formations in geothermal fields: effect of wave propagation direction

ABSTRACTWe applied advanced surface wave analysis for multichannel and multishot seismic data to estimate S-wave velocity structure with high lateral resolution. Although a horizontally layered structure is typically assumed in surface wave analysis, this assumption might be violated in environments such as geothermal fields because of their heterogeneous geological formation. The lateral variation of phase velocity can be effectively estimated with common midpoint (CMP) cross-correlation (CMPCC) analysis. In this study, we introduced two additional approaches into the CMPCC analysis workflow, to further improve lateral resolution of phase velocity estimates. One approach is window-controlled CMPCC analysis, which applies a spatial window for the CMP gathers while maintaining the accuracy of the phase velocity estimates. In this analysis, we found that it is difficult to improve phase velocity estimates at lower frequencies, as a wider spatial window must be kept to maintain the accuracy of the dispersion curve. Therefore, we introduced another approach in which we consider the direction of surface wave propagation from sources to receivers. Selection of cross-correlations based on source–CMP direction provides a significant improvement in dispersion curve resolution in the presence of lateral velocity variations, for a wide frequency range. We applied direction-controlled CMPCC analysis to seismic data acquired in the Yamagawa geothermal field, Kyushu Island, southwest Japan, and obtained dispersion curves in the heterogeneous geological setting. We then obtained S-wave velocity profiles by applying genetic algorithm inversion to the dispersion curves. The S-wave velocity profiles in the geothermal field resolve shallow and local heterogeneous structures (e.g. volcanic ash, pumice and igneous intrusions) that cannot be identified on reflection seismic profiles.

Anisotropic Quantum Well Electro-Optics in Few-Layer Black Phosphorus.

The incorporation of electrically tunable materials into photonic structures such as waveguides and metasurfaces enables dynamic, electrical control of light propagation at the nanoscale. Few-layer black phosphorus is a promising material for these applications due to its in-plane anisotropic, quantum well band structure, with a direct band gap that can be tuned from 0.3 to 2 eV with a number of layers and subbands that manifest as additional optical transitions across a wide range of energies. In this Letter, we report an experimental investigation of three different, anisotropic electro-optic mechanisms that allow electrical control of the complex refractive index in few-layer black phosphorus from the mid-infrared to the visible: Pauli-blocking of intersubband optical transitions (the Burstein-Moss effect); the quantum-confined Stark effect; and the modification of quantum well selection rules by a symmetry-breaking, applied electric field. These effects generate near-unity tuning of the BP oscillator strength for some material thicknesses and photon energies, along a single in-plane crystal axis, transforming absorption from highly anisotropic to nearly isotropic. Lastly, the anisotropy of these electro-optical phenomena results in dynamic control of linear dichroism and birefringence, a promising concept for active control of the complex polarization state of light, or propagation direction of surface waves.

Estimates of Surface Waves Using Subsurface EM-APEX Floats under Typhoon Fanapi 2010

AbstractSeven subsurface Electromagnetic Autonomous Profiling Explorer (EM-APEX) floats measured the voltage induced by the motional induction of seawater under Typhoon Fanapi in 2010. Measurements were processed to estimate high-frequency oceanic velocity variance associated with surface waves. Surface wave peak frequency fp and significant wave height Hs are estimated by a nonlinear least squares fitting to , assuming a broadband JONSWAP surface wave spectrum. The Hs is further corrected for the effects of float rotation, Earth’s geomagnetic field inclination, and surface wave propagation direction. The fp is 0.08–0.10 Hz, with the maximum fp of 0.10 Hz in the rear-left quadrant of Fanapi, which is ~0.02 Hz higher than in the rear-right quadrant. The Hs is 6–12 m, with the maximum in the rear sector of Fanapi. Comparing the estimated fp and Hs with those assuming a single dominant surface wave yields differences of more than 0.02 Hz and 4 m, respectively. The surface waves under Fanapi simulated in the WAVEWATCH III (ww3) model are used to assess and compare to float estimates. Differences in the surface wave spectra of JONSWAP and ww3 yield uncertainties of <5% outside Fanapi’s eyewall and >10% within the eyewall. The estimated fp is 10% less than the simulated before the passage of Fanapi’s eye and 20% less after eye passage. Most differences between Hs and simulated are <2 m except those in the rear-left quadrant of Fanapi, which are ~5 m. Surface wave estimates are important for guiding future model studies of tropical cyclone wave–ocean interactions.

Nonlinear evolution of the jet‐flow‐associated Kelvin‐Helmholtz instability in MHD plasmas and the formation of Mach‐cone‐like plane waves

Kelvin‐Helmholtz (K‐H) instability triggered by a jet flow along a magnetohydrodynamic (MHD) tangential discontinuity (TD) is studied by means of the two‐dimensional MHD simulations. In addition to the vortex structures and the undulant surface waves, we also found fast‐mode and slow‐mode Mach‐cone‐like plane waves at the saturation stage of the jet‐flow‐associated K‐H instabilities. Fast‐mode Mach‐cone‐like plane waves are launched in pairs from the ridges of the surface waves when the fast‐mode Mach numbers of the surface waves on both sides of the jet flow are greater than one. Slow‐mode Mach‐cone‐like plane waves are found for the first time in a limited range of MSL0y, θ0, and β0, where MSL0y is the slow‐mode Mach number of the surface disturbances observed in the ambient plasma rest frame, θ0 is the angle between the surface wave propagation direction and the direction of the ambient magnetic field, and β0 is the plasma β of the ambient plasma. The flaring angle of the fast‐mode Mach‐cone‐like plane wave is less than or equal to 90°, but the flaring angle of the slow‐mode Mach‐cone‐like plane wave is greater than or equal to 90°. A theoretical model is proposed to explain the formation and the characteristics of the slow‐mode Mach‐cone‐like plane waves. The flaring angles of the slow‐mode Mach‐cone‐like plane waves measured from the simulation results are in good agreement with the flaring angles predicted by the theoretical model. Applications of our results to the observations in the space plasma are discussed.

A simple method of representing azimuthal anisotropy on a sphere

SUMMARY We describe a method of expressing azimuthally anisotropic surface wave velocities on the Earth using a local and smooth spherical-spline parametrization. Anisotropy in the Earth leads to azimuthally varying Love and Rayleigh wave velocities that can be expressed as (cos 2ζ , sin 2ζ ) and (cos 4ζ , sin 4ζ ) perturbations to the isotropic velocities, where ζ is the direction of surface-wave propagation. The strength of the perturbations varies laterally, and a current goal of seismic tomography is the detailed global mapping of these variations. Several parametrizations have previously been used to describe azimuthally varying velocities. The representation proposed here uses spherical splines and is designed to describe smooth variations in both the strength and geometry of azimuthal anisotropy. The method builds on a simple geometrical approximation for the local azimuth of propagation expressed at the defining spline knot points. It avoids the singularities at the poles that result when azimuthal variations are parametrized using traditional scalar spherical harmonics. Compared with a generalized spherical-harmonic expansion of the tensor fields that represent 2ζ and 4ζ azimuthal variations smoothly on a sphere, the new method offers the advantages of local geographical support and simplicity of implementation.

GPS–Cellular Drifter Technology for Coastal Ocean Observing Systems

Abstract A drifter for observing small spatial and temporal scales of motion in the coastal zone is presented. The drifter uses GPS to determine its position, and the Mobitex terrestrial cellular communications system to transmit the position data in near–real time. This configuration allows position data with order meter accuracy to be sampled every few minutes and transmitted inexpensively. Near-real-time transmission of highly accurate position data enables the drifters to be retrieved and redeployed, further increasing economy. Drifter slip measurements indicate that the drifter follows water to within ∼1–2 cm s−1 during light wind periods. Slip values >1 cm s−1 are aligned with the direction of surface wave propagation and are 180° out of phase, so that the drifter “walks” down waves. Nearly 200 drifter tracks collected off the Santa Barbara, California, coast show comparisons with high-frequency (HF) radar observations of near-surface currents that improve by roughly 50% when the average drifter values are computed from more than 25 observations within a 2-km square HF radar bin. The improvement is the result of drifter resolution of subgrid-scale eddies that are included in time–space-averaged HF radar fields. The average eddy kinetic energy on 2-km space and hour time scales is 25 cm2 s−2, when computed for bins with more than 25 drifter observations. Comparisons with trajectories that are computed from HF radar data show mean separation velocities of 5 and 9 cm s−1 in the along- and across-shore directions, respectively. The drifters resolve scales of motion that are not present in HF radar fields, and are thus complementary to HF radar in coastal ocean observing systems.

Saw filter having electrodes for relaxation of electric field concentration

An SAW filter includes an SAW substrate and input and output IDTs which are arranged on the SAW substrate at a prescribed distance from each other. The IDTs are provided on outer end portions along the surface wave propagation direction with electric field concentration relaxation electrodes extending from pairs of bus bars inwardly along oblique directions.

3D particle motion trajectories: Direct observation of Love‐Rayleigh coupling

We present observations of severe particle motion distortion due to Love‐Rayleigh wave coupling (e.g., between 0L and 1R) using a display of 3D particle motion trajectory for records obtained at GDSN station HON. Though effects of lateral heterogeneity are yet to be examined carefully, phase velocity dispersion curves, calculated for a multilayered oceanic model with azimuthal anisotropy, predict this type of coupling in the period range between 20 and 30 s depending on the propagation direction of surface waves.

Magnetoelastic Rayleigh waves propagating along a tangential bias field on a YIG substrate

The propagation characteristics of magnetoelastic (ME) Rayleigh waves on a YIG substrate are treated for the parallel bias configuration, wherein the bias field is tangential to the substrate and parallel to the direction of propagation. The YIG surface is considered to be mechanically free and either adjoined to vacuum (unmetallized configuration) or electrically shorted by a thin perfectly conducting metallic film (metallized configuration). The ME Rayleigh waves are found to be bound surface waves outside of a spectrum of frequencies given approximately by the magnetostatic bulk-wave spectrum, and of the leaky type within it. By varying the frequency (or equivalently the bias field) over the leaky-wave spectrum, the direction of energy leakage into the substrate may be controlled over an angle of 180° from the direction of surface-wave propagation.

Coherent and Incoherent Radiation from Optically Excited Surface Plasmons on a Metal Grating

Excitation of surface charge waves (surface plasmons) produces intensity anomalies in the light reflected from a metal grating. We demonstrate that coupling occurs for both $s$- and $p$-polarized light if the grating lines are oblique to the plane of incidence, provided there is a component of the incident electric field along the direction of surface-wave propagation. We have measured the magnitude, phase, and direction of the plasmon electric field, and find Fano's theory confirmed. Underlying the coherent radiation we observe a small incoherent component resulting from spontaneous emission by the surface plasmons.

Elastic wave propagation in layered anisotropic media

This is an analysis of the dispersive properties of transversely isotropic media. This kind of anisotropy is exhibited by hexagonal crystals, sediments, planar igneous bodies, ice sheets, and rolled metal sheets where the unique axis is perpendicular to the direction of surface wave propagation and the other axes are distributed randomly in the plane of the layers. Period equations are derived for waves of Rayleigh, Stoneley, and Love types, and comparisons are made, in certain cases, with ray theoretical and plane stress solutions. Anisotropy can have a pronounced effect on both the range of existence and the shape of the dispersion curves and can lead to an apparent discrepancy between Love and Rayleigh wave data. Attention is focused in this initial paper on a single solid layer in vacuo (i.e. a free plate) and a solid layer in contact with a fluid halfspace. The single layer solutions are generalized to n-layer media by the use of Haskell matrices.