Showing papers on "Standing wave published in 2009"

A subwavelength coupler-type MIM optical filter.

Abstract: A novel subwavelength surface plasmon polaritons optical filter based on an incompletely directional coupler is proposed and numerically simulated by using the finite difference time domain method with perfectly matched layer absorbing boundary condition. An analytical solution for the resonant condition of the structure is derived by means of the cavity theory. Both analytical and simulative results reveal that the resonant wavelengths are proportional to the length of the slit segment, inversely proportional to the antinode number of a standing wave in the segment, and are related to the slit width and the gap between the two slits. The analytical solution being consistent with the numerical simulation verifies the feasibility of the concept of the new filter structure.

Wireless energy transfer system

Abstract: A system for transmitting power without wires or with no more than one connection, wherein communication is provided between an unlimited number of electronic devices, or to connect these devices to an unlimited number networks that are located externally to the system to thereby enable high speed voice and data communications over a single resonant connection At least one transmitter and one receiver are utilized, which may have the same or different configurations, such that an induced oscillating electπc current, which occurs at the resonant frequency of a transmitter, induces a standing wave The standing wave is tuned and “tapped” by a receiver having a coil or set of plates and receivers that are tuned to oscillate at the same frequency or one of its harmonics and, thus, absorb an electrical current and/or signals at the receiver

Properties of magnetohydrodynamic waves in the solar photosphere obtained with hinode

Abstract: We report the observations of the magnetohydrodynamic (MHD) waves propagating along magnetic flux tubes in the solar photosphere. We identified 20 isolated strong peaks (8 peaks for pores and 12 peaks for intergranular magnetic structure) in the power spectra of the line-of-sight (LOS) magnetic flux, the LOS velocity, and the intensity for 14 different magnetic concentrations. The observation is performed with the spectro-polarimeter of the Solar Optical Telescope aboard the Hinode satellite. The oscillation periods are located in 3-6 minutes for the pores and in 4-9 minutes for the intergranular magnetic elements. These peaks correspond to the magnetic, the velocity, and the intensity fluctuation in time domain with root-mean-square amplitudes of 4-17 G (0.3%-1.2%), 0.03-0.12 km s–1, and 0.1%-1%, respectively. Phase differences between the LOS magnetic flux ( B ), the LOS velocity ( v ), the intensities of the line core ( I,core), and the continuum intensity ( I,cont) have striking concentrations at around –90° for B – v and v – I,core, around 180° for I,core – B , and around 10° for I,core – I,cont. Here, for example, B – v ~ –90° means that the velocity leads the magnetic field by a quarter of cycle. The observed phase relation between the magnetic and the photometric intensity fluctuations would not be consistent with that caused by the opacity effect, if the magnetic field strength decreases with height along the oblique LOS. We suggest that the observed fluctuations are due to longitudinal (sausage-mode) and/or transverse (kink-mode) MHD waves. The observed phase relation between the fluctuations in the magnetic flux and the velocity is consistent with the superposition of the ascending wave and the descending wave reflected at chromosphere/corona boundary (standing wave). Even with such reflected waves, the residual upward Poynting flux is estimated to be 2.7 × 106 erg cm–2 s–1 for a case of the kink wave. Seismology of the magnetic flux tubes is possible to obtain various physical parameters from the observed period and amplitude of the oscillations.

Properties of Magneto-Hydrodynamic Waves in the Solar Photosphere with Hinode

Abstract: We report the observations of the magneto-hydrodynamic waves propagating along magnetic flux tubes in the solar photosphere. We identified 20 isolated strong peaks (8 peaks for pores and 12 peaks for inter-granular magnetic structure) in the power spectra of the l.o.s. (line-of-sight) magnetic flux, the l.o.s. velocity, and the intensity for 14 different magnetic concentrations. The observation is performed with the spectro-polarimeter of the Solar Optical Telescope aboard the \emph{Hinode} satellite. The observed phase relation between the magnetic and the photometric intensity fluctuation would not be consistent with that caused by the opacity effect, if the magnetic field strength decreases with height along the oblique line of sight. We suggest that the observed fluctuations are due to longitudinal (sausage mode) and/or transverse (kink mode) MHD waves. The observed phase relation between the fluctuations in the magnetic flux and the velocity is consistent with the superposition of the ascending wave and the descending wave reflected at chromosphere/corona boundary (standing wave). Even with such reflected waves, the residual upward Poynting flux is estimated to be $2.7 \times 10^{6}$ erg cm$^{-2}$ s$^{-1}$ for a case of the kink wave. Seismology of the magnetic flux tubes is possible to obtain various physical parameters from the observed period and amplitude of the oscillations.

Ultra-high-Q tunable whispering-gallery-mode microresonator

Abstract: Optical microresonators hold great potential for many fields of research and technology. However, due to their small dimensions typical microresonators exhibit a large frequency spacing between resonances and a limited tunability. This impedes their use in a large class of applications which either require a resonance of the microcavity to coincide with a predetermined frequency, e.g., an optical transition in atoms, or a tailored frequency spacing between resonances, e.g., for the generation of optical frequency combs. Here, we present a fully tunable ultra-high-Q whispering-gallery-mode “bottle microresonator”, fabricated from standard optical glass fibres. Due to its highly prolate shape, the bottle microresonator gives rise to a class of whispering-gallery-modes (WGMs) with advantageous properties, see Fig. 1. In addition to the radial confinement by continuous total internal reflection at the resonator surface, the light in these “bottle modes” oscillates back and forth along the resonator axis between two turning-points which are defined by an angular momentum barrier [1]. The resulting axial standing wave structure can be compared to the one observed in Fabry-Perot microresonators.

Formation and manipulation of two-dimensional arrays of micron-scale particles in microfluidic systems by surface acoustic waves

Abstract: The two-dimensional concentration and manipulation of micron-scale particles by orthogonal, surface acoustic, standing waves is demonstrated. The particles are organized by liquid pressure waves in a microfluidic system over a piezoelectric substrate and form a uniform two-dimensional array with a spacing governed by the mechanical nodes of the two orthogonal, surface acoustic, standing waves. The nodal spacing can be controlled in each orthogonal direction independently by adjustment of the radio frequency applied to the separate acoustic wave transducers. This technique could be used to enhance the particle concentrations at sensing locations in DNA or protein array detectors.

Confining standing waves in optical corrals.

Abstract: Near-field scanning optical microscopy images of solid wall, circular, and elliptical microscale corrals show standing wave patterns confined inside the structures with a wavelength close to that of the incident light. The patterns inside the corrals can be tuned by changing the size and material of the walls, the wavelength of incident light, and polarization direction for elliptical corrals. Finite-difference time-domain calculations of the corral structures agree with the experimental observations and reveal that the electric and magnetic field intensities are out of phase inside the corral. A theoretical modal analysis indicates that the fields inside the corrals can be attributed to p- and s-polarized waveguide modes, and that the superposition of the propagating and evanescent modes can explain the phase differences between the fields. These experimental and theoretical results demonstrate that electromagnetic fields on a dielectric surface can be controlled in a predictable manner.

Generation and Propagation of Inertia–Gravity Waves from Vortex Dipoles and Jets

Abstract: This study investigates gravity wave generation and propagation from jets within idealized vortex dipoles using a nonhydrostatic mesoscale model. Two types of initially balanced and localized jets induced by vortex dipoles are examined here. These jets have their maximum strength either at the surface or in the middle levels of a uniformly stratified atmosphere. Within these dipoles, inertia–gravity waves with intrinsic frequencies 1–2 times the Coriolis parameter are simulated in the jet exit region. These gravity waves are nearly phase locked with the jets as shown in previous studies, suggesting spontaneous emission of the waves by the localized jets. A ray tracing technique is further employed to investigate the propagation effects of gravity waves. The ray tracing analysis reveals strong variation of wave characteristics along ray paths due to variations (particularly horizontal variations) in the propagating environment. The dependence of wave amplitude on the jet strength (and thus on the ...

Prediction of Multipactor Breakdown Thresholds in Coaxial Transmission Lines for Traveling, Standing, and Mixed Waves

Abstract: In this paper, we present a numerical model for predicting the multipactor breakdown effect in coaxial transmission lines. To validate this method, we have first compared our results with numerical data from other theoretical studies and with experimental measurements. Then, we have investigated the multipactor phenomena in coaxial lines considering three kinds of RF signals: traveling, standing, and mixed waves. From this paper, we conclude that different breakdown thresholds are obtained for any of the considered RF excitations under high values of frequency times gap product. This effect is attributed to the existence of regions with zero (or very low levels) electric field amplitude in the propagation direction, where electrons are absorbed before the discharge occurs.

Analysis of Kapitza-Dirac diffraction patterns beyond the Raman-Nath regime

Abstract: We study Kapitza-Dirac diffraction of a Bose-Einstein condensate from a standing light wave for a square pulse with variable pulse length but constant pulse area. We find that for sufficiently weak pulses, the usual analytical short-pulse prediction for the Raman-Nath regime continues to hold for longer times, albeit with a reduction of the apparent modulation depth of the standing wave. We quantitatively relate this effect to the Fourier width of the pulse, and draw analogies to the Rabi dynamics of a coupled two-state system. Our findings, combined with numerical modeling for stronger pulses, are of practical interest for the calibration of optical lattices in ultracold atomic systems.

Effective mixing of laminar flows at a density interface by an integrated ultrasonic transducer.

Abstract: An acoustic mixer for glass channel microfluidic systems is presented. An acoustic standing wave, perpendicular to the fluid flow, is generated by the excitation of a miniaturized piezoelectric transducer operated around 10 MHz. The transducer is fabricated into a planar printed circuit board structure, constituting the bottom channel wall, which makes the mixer simple to integrate with a wide selection of microfluidic channel designs. The mixing occurs at a fluid-fluid density interface due to the acoustic radiation force; an analytical expression is derived to qualitatively describe this phenomenon. Only a small density difference in the range of 2–5% is required to achieve 150–270% peak broadening of a fluorescent sample between sheath flows, which we use as a measure of the mixing efficiency. The mixing efficiency is measured with regard to its sensitivity to the density difference, the fluid velocity and the transducer driving frequency. Transducers at different positions along the microchannel make it possible to compare the mixing of straight versus diagonal flows across the transducer surface. We finally demonstrate enhanced chemical lysis of E. coli K12 cells in the device due to active fluid mixing.

Magic wavelength to make optical lattice clocks insensitive to atomic motion.

Abstract: In a standing wave of light, a difference in spatial distributions of multipolar atom-field interactions may introduce atomic-motion dependent clock uncertainties in optical lattice clocks. We show that the magic wavelength can be defined so as to eliminate the spatial mismatch in electric dipole, magnetic dipole, and electric quadrupole interactions for specific combinations of standing waves by allowing a spatially constant light shift arising from the latter two interactions. Experimental prospects of such lattices used with a blue magic wavelength are discussed.

Filtration Combustion of Methane in High-Porosity Micro-Fibrous Media

Abstract: Filtration combustion of lean methane-air mixtures in inert, high-porosity micro-fibrous media was studied experimentally in quartz tubes with different diameters. First, an overall stability diagram was obtained. Between the upstream and downstream propagating regimes, a specific rigid standing wave regime was observed, whereas only one standing wave point existed in other ordinary porous media. A specific instability phenomenon of a combustion wave splitting into two or more parts during wave propagation downstream was also observed in smaller diameter tubes at high filtration velocities. In principle, the results of a conventional two-temperature 1D analytical model captured the main feature of the process obtained in the experiment, but failed to explain the process of flame anchoring to the porous carcass that was observed under variation of the mass flow rate. The possible causes of the failure of the conventional modeling approach were presented.

Two-dimensional quantum gas in a hybrid surface trap

Abstract: We demonstrate the realization of a two-dimensional (2D) quantum gas in a smooth optical surface trap. Using a combination of evanescent wave, standing wave, and magnetic potentials, we create a long-lived quantum gas deep in the 2D regime at a distance of a few microns from a glass surface. To realize a system suitable for many-body quantum simulation, we introduce methods such as broadband ``white'' light to create evanescent and standing waves to realize a smooth potential with a trap frequency aspect ratio of 300:1:1. We are able to detect phase fluctuations and vortices, and we demonstrate cooling to degeneracy and low disorder in the 2D configuration.

Improved estimates and a limit case for the electrostatic Klein-Gordon-Maxwell system

Abstract: We study the class of nonlinear Klein-Gordon-Maxwell systems describing a standing wave (charged matter field) in equilibrium with a purely electrostatic field. We improve some previous existence results in the case of an homogeneous nonlinearity. Moreover, we deal with a limit case, namely when the frequency of the standing wave is equal to the mass of the charged field; this case shows analogous features of the well known "zero mass case" for scalar field equations.

Thin resonant structures for angle and polarization independent microwave absorption

Abstract: We present a microwave absorbing structure comprised of an array of subwavelength radius copper disks, closely spaced from a ground plane by a low loss dielectric. Experiments and accompanying modeling demonstrate that this structure supports electromagnetic standing wave resonances associated with a cylindrical cavity formed by the volume immediately beneath each metal disk. Microwave absorption on resonance of these modes, at wavelengths much greater than the thickness of the structure, is dictated almost entirely by the radius of the disk and permittivity of the dielectric, being largely independent of the incident angle and polarization.

On Asymptotic Stability of Standing Waves of Discrete Schrödinger Equation in $\mathbb{Z}$

Abstract: We prove an analogue of a classical asymptotic stability result of standing waves of the Schrodinger equation originating in work by Soffer and Weinstein. Specifically, our result is a transposition on the lattice $\mathbb{Z}$ of a result by Mizumachi [J. Math. Kyoto Univ., 48 (2008), pp. 471–497] and it involves a discrete Schrodinger operator $H=-\Delta+q$. The decay rates on the potential are less stringent than in [J. Math. Kyoto Univ., 48 (2008), pp. 471–497], since we require $q\in\ell^{1,1}$. We also prove $|e^{itH}(n,m)|\le C\langle t\rangle^{-1/3}$ for a fixed C requiring, in analogy to Goldberg and Schlag [Comm. Math. Phys., 251 (2004), pp. 157–178], only $q\in\ell^{1,1}$ if H has no resonances and $q\in\ell^{1,2}$ if it has resonances. In this way we ease the hypotheses on H contained in Pelinovsky and Stefanov [On the Spectral Theory and Dispersive Estimates for a Discrete Schrodinger Equation in One Dimension, http://arxiv.org/abs/0804.1963v1], which have a similar dispersion estimate.

3-D numerical simulations of coronal loops oscillations

Abstract: We present numerical results of 3-D MHD model of a dipole active region field containing a loop with a higher density than its surroundings. We study different ways of excitation of vertical kink oscillations by velocity perturbation: as an initial condition, and as an impulsive excitation with a pulse of a given position, duration, and amplitude. These properties are varied in the parametric studies. We find that the amplitude of vertical kink oscillations is significantly amplified in comparison to horizontal kink oscillations for exciters located centrally (symmetrically) below the loop, but not if the exciter is located a significant distance to the side of the loop. This explains why the pure vertical kink mode is so rarely observed in comparison to the horizontally polarized one. We discuss the role of curved magnetic field lines and the pulse overlapping at one of the loop's footpoints in 3-D active regions (AR's) on the excitation and the damping of slow standing waves. We find that footpoint excitation becomes more efficient in 3-D curved loops than in 2-D curved arcades and that slow waves can be excited within an interval of time that is comparable to the observed one wave-period due to the combined effect of the pulse inside and outside the loop. Additionally, we study the effect of AR topology on the excitation and trapping of loop oscillations. We find that a perturbation acting directly on a single loop excites oscillations, but results in an increased leakage compared to excitation of oscillations in an AR field by an external source.

Trapping of particles by the leakage of a standing wave ultrasonic field

Abstract: This paper presents a method of trapping particles by the acoustic leakage from a low frequency standing wave ultrasonic field. The standing wave ultrasonic field is generated in a triangular air gap between two vibrating V-shaped metal strips. Particles are trapped to the lower outlet of the standing wave ultrasonic field. The acoustic radiation force acting on the particles in this method is opposite to the direction of the acoustic leakage. Particles such as medicine pills with a weight up to 256 mg per particle can be trapped. A physical model is developed to analyze the trapping phenomena. The effects of the vibration displacement amplitude at the tip of the V-shaped metal strip, particle’s shape and weight, and size of standing wave ultrasonic field on the trapping capability are investigated theoretically and experimentally.

Instability of Standing Waves for a System of Nonlinear Schrodinger Equations with Three-Wave Interaction

Abstract: We consider a three-component system of nonlinear Schrodinger equations related to the Raman amplification in a plasma. In dimension N ≤ 3, we study the orbital instability of standing wave solution of the form (0,0,e2iωtψ), where ψ is a ground state of scalar nonlinear Schrodinger equation. Using time derivative instead of space derivatives to estimate nonlinear terms, we improve an instability result in our previous paper [4], and also give a simpler proof.

Resonance shifts of counterpropagating whispering-gallery modes: degenerate perturbation theory and application to resonator sensors with axial symmetry

Abstract: A theory is presented that considers the resonance shift of degenerate whispering-gallery modes (WGMs) in sensor applications. The theory is then applied to a pair of counterpropagating waves in a spheroidal resonator. Adsorption of a particle lifts the twofold degeneracy, resulting in a pair of standing waves with a symmetric field around the particle, a standing symmetric wave (SSW) and an antisymmetric wave (ASW). The shift for a SSW is twice as large as the one for a nondegenerate WGM when the particle radius is sufficiently smaller than the wavelength, whereas the shift for an ASW is nearly zero. The ratio of the split to the mean shift gives an estimate of the particle size, whereas the mean shift is sensitive to its polarizability. With an increasing particle radius, the ratio of the split to the mean shift decreases. There is a particle radius that maximizes the split.

Optical generation of long-lived surface vibrations in a periodic microstructure

Abstract: We use the laser-induced transient grating technique for the excitation and detection of surface vibrational modes of a periodic microstructure on a silicon substrate forming a one-dimensional phononic crystal. Two standing wave eigenmodes with zero-group velocity corresponding to the top and bottom of the bandgap in the dispersion of the zone-folded Rayleigh waves are produced by setting the spatial period of the excitation pattern to twice the structure period. These modes do not radiate acoustic energy into the substrate, yielding an enhanced lifetime. We show that the relative amplitude of the two modes is controlled by the spatial phase of the excitation pattern, and discuss the dependence of the confinement time of the acoustic oscillations within the excitation area on the curvature of the dispersion surface.