Surface Waves

Faraday waves are standing waves which arise through a parametric instability on the surface of a vertically oscillated fluid layer. They can emerge with various symmetries, simply square to N-fold rotationally symmetric, which for N > 3 are quasi-crystalline. In an experiment with a very large aspect ratio we determine the boundaries of the stability regions of waves with different rotational symmetries in the driving frequency amplitude parameter plane. We find a remarkable agreement with a recent theory by Chen & Viñals (1999) who predict the stability boundaries at the onset amplitude. We argue why such agreement can only be observed in a very large experiment. The main nonlinear damping mechanism of the waves is a three-wave resonance. We devise a simple model that captures this mechanism and that can explain quantitatively the change of the symmetry of the waves with fluid depth. Detailed information about the surface is obtained by scanning the wave field and measuring the phase of subharmonic and harmonic components. Also the results of these measurements compare very favourably to the theoretical predictions.

When the mechanisms of fading channels were first modeled in the 1950s and 1960s, the ideas were primarily applied to over-the-horizon communications covering a wide range of frequency bands. The 3-30 MHz high-frequency (HF) band is used for ionospheric communications, and the 300 MHz-3 GHz ultra-high-frequency (UHF) and 3-30 GHz super-high-frequency (SHF) bands are used for tropospheric scatter. Although the fading effects in a mobile radio system are somewhat different than those in ionospheric and tropospheric channels, the early models are still quite useful to help characterize fading effects in mobile digital communication systems. This tutorial addresses Rayleigh fading primarily in the UHF band. That affects mobile systems such as cellular and personal communication systems (PCS). Part I of the tutorial itemizes the fundamental fading manifestations and types of degradation

This paper investigates the enhancement of the sensitivity and adsorption efficiency of a localized surface plasmon resonance (LSPR) biosensor that includes a layer of graphene sheet on top of the gold layer. For this purpose, biomolecular interactions of biotin-streptavidin with the graphene layer on the gold thin film are monitored. The performance of the LSPR graphene biosensor is theoretically and numerically assessed in terms of sensitivity and adsorption efficiency under varying conditions, including the thickness of biomolecule layer, number of graphene layers and operating wavelength. Enhanced sensitivity and improved adsorption efficiency are obtained for the LSPR graphene biosensor in comparison with its conventional counterpart. It is found that the LSPR graphene biosensor has better sensitivity with lower operating wavelength and larger number of graphene layers.

A compact multiple-input-multiple-output (MIMO) antenna with very high isolation is proposed for ultrawideband (UWB) applications. The antenna with a compact size of 30.1 × 20.5 mm 2 (0.31λ 0 × 0.21λ 0) consists of two planar-monopole antenna elements. It is found that isolation of more than 25 dB can be achieved between two parallel monopole antenna elements. For the low-frequency isolation, an efficient technique of bending the feed-line and applying a new protruded ground is introduced. To increase isolation, a design based on suppressing surface wave, near-field, and far-field coupling is applied. The simulation and measurement results of the proposed antenna with the good agreement are presented and show a bandwidth with S 11 ≤ −10 dB, S 12 ≤ −25 dB ranged from 3.1 to 10.6 GHz making the proposed antenna a good candidate for UWB MIMO systems.

A gas sensor was developed by depositing polythiophene nanofibers on the surface of ZnO/36° YX LiTaO3 layered surface acoustic wave (SAW) transducer and tested towards different concentrations of hydrogen gas in synthetic air. Polythiophene nanofibers were synthesized by using a template-free method through the introduction of an initiator into the reaction mixture of a rapidly mixed reaction between the monomer (thiophene) and the oxidant. The yield of the reaction was characterized using scanning electron microscopy (SEM) as well as Ultraviolet-visible (UV-vis) and Fourier Transform Infrared (FTIR) spectroscopies. The frequency shift due to the sensor response was ~17 kHz towards 1% of H2. All tests were conducted at room temperature. The sensor performance was assessed over a two day period and a high degree of repeatability was obtained.

In this paper, we present the WCIP iterative procedure (wave concept iterative procedure) for solving continuity conditions in terms of waves rather than in term of tangential fields providing a mixed resolution in spatial and spectral domain taking the best advantage of each resolution domain and lower computation time. The spiral inductor with patterned ground shield is taken as an example of multi-layer structures; the results are in reasonably good agreement with the experimental data.

Page 1. AD-A256 672 :. / " PL-TR-92-2108 PHYSICAL CONSTRAINTS ON SEISMIC WAVES FROM CHEMICAL AND NUCLEAR EXPLOSIONS Brian Stump Lane Johnson Robert Reinke Sharon Reamer Ken Olsen Klaus-G. Hlnzen Southern Methodist University ._ ...

A new effective approach to analytical description of electromagnetic waves in nonmagnetic anisotropic media is proposed. Analytical formulas for refraction and reflection of the waves at the interface between an isotropic and an anisotropic media are obtained. Beam splitting at reflection and refraction is reviewed, and the generation of surface waves is examined. Conditions for the D'yakonov surface waves creation and a method of these waves observation are discussed. Analytical and numerical calculations of the reflection and trasmission of plane parallel uniaxial plates are outlined.

El tema central del estudio se presenta como un análisis de la metodología de caracterización mecánica no destructiva de morteros de edad temprana (proceso de endurecimiento), mediante la técnica no destructiva, flexible y rentable, de Análisis Espectral de Ondas Superficiales (Código ACI 228.2R-98 “Nondestructive Test Methods for Evaluation of Concrete in Structures”) que recurre al estudio de la curva de dispersión para obtener las velocidades de fase en función de la longitud de onda, mediante el procesamiento de señales generadas por impacto a bajas frecuencias con martillos calibrados, dos transductores piezoeléctricos y un equipo de vibración analizador de Brüel&Kjaer adquirido y puesto a punto para el desarrollo del método AEOS en morteros a edad temprana.
  Como objetivo principal del trabajo se ha determinado la información necesaria de modelos estructurales de morteros dosificados de distinta forma (simulando perfiles heterogéneos y dispersivos debido a la diferente forma de curado de los especímenes), mediante el citado método de ensayo no destructivo de propagación de ondas superficiales [AEOS o SASW]: técnica idónea para definir directamente la curva de dispersión proporcionando la velocidad de onda superficial en función de la longitud de onda, variable valiosa dentro del perfil de capas de un material, ya que a través de este valor se derivan parámetros importantes estructurales (resistencias, módulos…) en morteros a edad temprana, presentando sus propiedades según proceso de curado, espesor y profundidad desde la superficie.
  Conocido como método de caracterización no invasivo, desarrollado por Jones (1958) y evolucionado por Stokoe & Nazarian (1980) en geotecnia y pavimentos en su origen, hoy día, debido a sus posibilidades, se constituye como una alternativa significativa, más rápida, limpia y económica por su naturaleza no destructiva, en comparación a otras metodologías normalmente utilizadas.
La investigación se ha centrado principalmente en la aplicación de la teoría de propagación de la onda Rayleigh en un medio heterogéneo viscoelástico lineal basado en modelos reales tipo placa de morteros fabricados en laboratorio con diferentes dosificaciones para determinar mediante impactos a bajas frecuencias (alta longitud de onda y alcance en profundidad) la velocidad de onda en cada capa interna a diferentes edades de fraguado. Basado en el principio de que los diversos componentes de la longitud de onda en la superficie de impacto penetran a diferentes profundidades en un medio dispersivo de ondas R, las frecuencias de la onda se propagan a diferentes velocidades de fase.
Por tanto, se analizan y discuten las diferentes bases/etapas/resultados experimentales, del método explorando en detalle, su alcance, limitaciones, desarrollo computacional e implementación de la rutina como programa con aplicabilidad próxima a hormigones. Para validar el método los resultados se contrastaron con otras dos metodologías complementarias no destructivas, las técnicas de Frecuencia-Resonancia (FFRC) y de Impacto-Eco (IE).

In this paper a detailed investigation of slot waveguides for optical sensing in near-IR wavelength region is carried out, assuming Silicon-on-Insulator technology. Optimized guided-wave structures are found in terms of high sensitivity (Sh) and low propagation losses (αprop) and design guidelines are clearly selected. A number of possible application fields for environmental monitoring are covered, including gas sensing (gas identification or measure of their physical parameters as pressure) and liquid sensing (as pollutants in water). Influence of fabrication tolerances and wavelength dependence are also studied.

A new wavelet analysis methodology is proposed to estimate the statistics of steep waves. The method is applied to open ocean wave height data from the Southern Ocean Waves Experiment (1992) and from a field experiment conducted at Duck, North Carolina (1997). Results show that high wave slope crests appear over a wide range of wavenumbers, with a large amount being much shorter than the dominant wave. At low wave slope thresholds, all wave fields have roughly the same amount of wave crests regardless of wind forcing. The steep wave statistic decays exponentially with the square of the wave slope threshold, with a decay rate that is larger for the low wind cases than the high wind cases. Comparison of the steep wave statistic with independent measurements of the breaking wave statistic suggests a breaking wave slope threshold of about 0.12. The steep wave statistic does not scale with the cube of the wind speed, suggesting that other factors besides the wind speed also affect its level. Comparison of the steep wave statistic to the saturation spectrum reveals a reasonable correlation at moderate wave slope thresholds.

Microstrip antenna arrays have found broad applications in recent years and the reduction of mutual coupling is an important criterion in their design. The FDTD method is applied to analyze probe fed patch antennas and the simulated results agree well with the experimental results of R.P. Jedlicka et al. (see IEEE Trans. Antennas Propagat., vol.29, p.147-9, 1981). The mutual coupling of patch antennas on a high dielectric constant substrate, which is of growing interest due to its compact size and conformability with MMIC, is characterized in detail. Such antennas have larger mutual coupling than antennas on a low permittivity substrate because of the pronounced surface waves. The electromagnetic band-gap structure introduced by D. Sievenpiper et al. (see IEEE Trans. MTT, vol.47, p.2059-74, 1999) is then employed to inhibit the surface waves so that the mutual coupling is greatly reduced.

Rotational components of seismic waves have been estimated using the strong motion array in Taiwan, SMART-1. The inner rings of accelerographs, covering an approximately circular area of 3 km2, permit a decomposition of travelling waves with wavelengths in the range 0.5 to 5.0 km and frequencies from 0.1 to 5 Hz.Rotational components of the strain field, obtained from station pairs and averaged over the array using stacking techniques, were computed for five different earthquakes with Ms magnitude 5.7 to 7.8, and epicentral distances 6 to 84 km. The results indicate peak rotation values about a vertical axis on the order of 4 × 10−5 rad at an approximately 2.5 s period. The measured values for pure rotation and rocking are in agreement with the spatial coherency structure observed in these earthquakes. For comparison, significant effects to engineered structures generally appear when curl u > 10−4 rad. The estimates are important for design of scaled engineered models for soil-structure interaction experiments.

Radar imaging of deserts suffers from insufficient radar backscatter at low microwave frequencies due to the low permittivity of dry sand and relatively smooth sand surface roughness. Operating at millimeter-wave (MMW) frequencies, however, rectifies this deficiency as significant radar backscatter is generated by surface and volume scattering. This is due to the fact that sand surface roughness is electrically large and signal penetration into the dry sand, which is a homogeneous mixture of air and sand particles with dimensions comparable to a fraction of a wavelength, generates considerable volume scattering. This paper investigates both surface and volume scattering from dry sand surfaces, subject to the peculiar physical properties of sand surfaces found in sand dune-covered regions. An incoherent model is proposed that characterizes the angular dependence of volume scattering from dry sand in the presence of a 1-D rippled air/sand surface. A set of indoor experiments conducted on smooth and 1-D rippled sand surfaces at Ka-band confirms that significant volume scattering is present at MMW frequencies and that the proposed model correctly captures the observed angular dependence when 1-D surface ripples are present.

ABSTRACT Metasurfaces are thin metamaterial layers characterized by unusual dispersion properties of surface/guided wave and/or reflection properties of otherwise incident plane waves. At the scales intervening in their design, metasurfaces can be described through a surface impedance boundary condition. The impedance, possibly tensorial, is often “modulated,” i.e., it can vary from place to place on the surface (by design). We investigate on different integral equation formulations of the problem, with special attention to the stability properties of the resulting system matrix.