Direction Of Energy Propagation Research Articles

A Study on the Scattering Energy Properties of an Elastic Spherical Shell in Sandy Sediment Using an Improved Energy Method

An elastic wave is composed of compressional (longitudinal) waves and shear (transverse) waves which have different wave velocities in solids. The acoustic field presents complex interference patterns which means its phenomena and properties are difficult to reveal. Fortunately, the energy method is more accurate than the potential function approach in describing the physical properties of the acoustic field. However, the polarization state of particle vibration excited by an elastic wave is spatially periodic in the wave propagation direction. Therefore, the energy propagation direction is not consistent with the wave propagation direction using commonly used energy method. According to the polarization state of particle vibration, a time-space averaging method based on the spatial periodicity of energy flux in the solid is proposed. The method could eliminate the influence of the interference due to local energy exchange and retain the trend of energy propagation. Several conclusions are illustrated through the analysis of the scattering energy properties of a steel shell in sandy sediment. Sandy sediment can not be regarded as a fluid nor a general solid. Scattering energy excited by an incident shear wave mainly concentrates in the vicinity of the directions of backscattering and forward scattering. Especially, at low frequency, it plays an important role in the total scattering energy excited by an incident compressional and shear wave.

The giant dipole vortex

The field lines of energy flow of radiation emitted by an oscillating electric dipole in free space are either straight lines (linear dipole) or they form a vortex (rotating dipole). When the dipole is embedded in a material, the properties of the medium affect the direction of energy flow. Damping due to the imaginary part of the relative permittivity makes the field lines curve for the case of a linear dipole, and for a rotating dipole, the shape of the vortex is altered. In addition, a negative value of the real part of has the effect that the rotation direction of the vortex reverses for the case of a rotating dipole. The value of the relative permeability has in general not much effect on the redistribution of the direction of energy propagation. We show that a dramatic effect occurs when the embedding material is near-single-negative (both and approximately real, and the real parts of opposite sign). The curving of field lines is in general a sub-wavelength phenomenon. For near-single-negative materials, however, this curving extends over large distances from the dipole. In particular, the small free-space vortex of a rotating dipole becomes a vortex of enormous dimensions when the radiation is emitted into a near-single-negative material.

Simulated Global Swell and Wind-Sea Climate and Their Responses to Anthropogenic Climate Change at the End of the Twenty-First Century

Abstract The seasonal structure of the wind sea and swell is analyzed from the existing 29-yr surface gravity wave climatology produced using a coupled atmosphere–wave model. The swell energy fraction analysis shows that swell dominates most of the World Ocean basins for all four seasons, and the Southern Ocean swells dominate swell in the global ocean. The swells are loosely correlated with the surface wind in the midlatitude storm region in both hemispheres, while their energy distribution and propagation direction do not show any relation with local winds and vary significantly with season because of nonlinear interactions. The same coupled system is then used to investigate the projected future change in wind-sea and swell climate through a time-slice simulation. Forcing of the coupled model was obtained by perturbing the model sea surface temperatures and sea ice with anomalies generated by representative Working Group on Coupled Modelling (WGCM) phase 3 of the Coupled Model Intercomparison Project (CMIP3) coupled models that use the IPCC Fourth Assessment Report (AR4) A1B scenario late in the twenty-first century. Robust responses found in the wind seas are associated with modified climate indices. A dipole pattern in the North Atlantic during the boreal winter is associated with more frequent occurrence of the positive North Atlantic Oscillation (NAO) phases under global warming, and the wind-sea energy increase in the Southern Ocean is associated with the continuous shift of the southern annular mode (SAM) toward its positive phase. Swell responses are less robust because of nonlinearity. The only consistent response in swells is the strong energy increase in the western Pacific and Indian Ocean sector of the Southern Ocean during the austral winter and autumn.

Research of negative refractive direction of P-light in metal

This paper studies the light propagation in metal. Using the complex wave vector, we analyze the propagation direction of light energy in a metal, and find that P and S-polarized light propagate at a different refraction angle when a beam of light passes from the air to a metallic boundary at a certain angle. Especially, P-polarized light will be refracted at a negative angle, and the direction of P-polarized light is the same side of the incident light.

WITHDRAWN: Compositional Effects in Titan's Thermospheric Gravity Waves

AbstractIn Titan's upper atmosphere, the density profiles of several constituents (N2, CH4, H2 and 29N2) as measured by the Cassini Ion Neutral Mass Spectrometer (INMS) show periodical structures which we interpret as internal gravity waves. Compositional effects are frequently seen in the data, in which the wave structures in different constituents show different amplitudes and phase angles. We use a simple linearized wave perturbation theory to explain the observations, emphasizing their role as a useful diagnostic of the basic wave parameters. For the T39 flyby, the data‐model comparison constrains typical wavelength to be ~ 350 km, typical wave period to be ~ 64 min, and the direction of wave energy propagation to be primarily vertical. Our calculations also illustrate that wave‐induced diffusion is important for CH4 and H2.

Magnetostatic waves in the gap between two ferromagnetic films that move relative to each other

The propagation of a magnetostatic gap wave in a gap between two ferromagnetic films with opposite magnetizations is considered under the conditions for relative longitudinal displacement. When the velocity of one film is reversed, the transformation of spectra is similar to the transformation in which each spectrum of magnetostatic wave with corresponding symmetry is split into two branches. It is demonstrated that significant modification of the magnetic field distribution in the gap structure occurs when the film moves along the energy propagation direction of the gap-wave mode.

Effects of the 2010 Chile and 2011 Japan tsunamis on the Antarctic coastal waters as detected via online mooring system

AbstractSea level oscillations associated with both the 2010 Chile and 2011 Japan tsunamis were recorded in the coastal waters of King George Island off the west coast of Antarctica with an online coastal mooring system. The Chile tsunami arrived at the detection site within around five hours of the earthquake. The largest wave (84.4 mm) was measured 27 hours after the first arrival. In contrast, the Japan tsunami was detected around 26 hours after the earthquake, and the maximum wave height (180.8 mm) was observed around 11 hours after the initial wave. The energy level of the earthquake and the direction of energy propagation are probably the two most significant causes of the comparatively high amplitudes of the 2011 Japan tsunami, despite the fact that its epicentre was much further away than that of 2010 Chile tsunami. The sea level oscillations associated with the tsunami increased the level of mixing of seawater in the shallow Antarctic coastal waters and influenced the environment temporarily.

Wave spectra assimilation in typhoon wave modeling for the East China Sea

The East China Sea is a hot area for typhoon waves to occur. A wave spectra assimilation model has been developed to predict the typhoon wave more accurately and operationally. This is the first time where wave data from Taiwan have been used to predict typhoon wave along the mainland China coast. The two-dimensional spectra observed in Taiwan northeast coast modify the wave field output by SWAN model through the technology of optimal interpolation (OI) scheme. The wind field correction is not involved as it contributes less than a quarter of the correction achieved by assimilation of waves. The initialization issue for assimilation is discussed. A linear evolution law for noise in the wave field is derived from the SWAN governing equations. A two-dimensional digital low-pass filter is used to obtain the initialized wave fields. The data assimilation model is optimized during the typhoon Sinlaku. During typhoons Krosa and Morakot, data assimilation significantly improves the low frequency wave energy and wave propagation direction in Taiwan coast. For the far-field region, the assimilation model shows an expected ability of improving typhoon wave forecast as well, as data assimilation enhances the low frequency wave energy. The proportion of positive assimilation indexes is over 81% for all the periods of comparison. The paper also finds that the impact of data assimilation on the far-field region depends on the state of the typhoon developing and the swell propagation direction.

Characteristics of Gravity Waves over the Tibetan Plateau during the PRC-Japan Cooperative JICA Project in 2008

Using wind and temperature data with high vertical resolution obtained from Global Positioning System (GPS) radiosondes which were launched four times a day at Gerze (32.2°N, 84.4°E) and Litang (30.0°N, 100.3°E) stations during the People’s Republic of China (PRC)-Japan cooperative JICA project in 2008, the characteristics of gravity waves such as vertical energy propagation directions, intrinsic frequencies, vertical wave-lengths, and horizontal propagation directions over the Tibetan Plateau are investigated by hodograph method. The statistic characteristics of the gravity waves show that the activities of the gravity waves over the western and eastern Tibetan Plateau have significant spatial variations except for horizontal propagation directions, and that the gravity waves over the eastern Tibetan Plateau are easier to be triggered. The energy propagates upward for almost half of the observed gravity waves, and the energy propagation is downward for the other half of the gravity waves, indicating that the wave sources in lower and upper troposphere are equally important over the Tibetan Plateau. The dominant gravity wave frequencies lie in the frequency range of 2-2.5 times of Coriolis parameter f at Gerze station, while the dominant gravity wave frequencies are in the range of 1.5-2 times of f at Litang station. The dominant vertical wavelengths are 1.5-2.5 km over Gerze and Litang. For Gerze station, the dominant gravity waves propagate along the west-southwestward directions, while the dominant gravity wave propagating directions are north-northwestward for Litang station.

Direct calculation of energy streamlines in near-field thermal radiation

Accurate prediction of the energy propagation direction and the associated lateral shift is very important for the design of efficient energy conversion devices and sensors based on nanoscale thermal radiation. This paper concerns the direction of energy flow during near-field radiative transfer between two parallel plates separated by a vacuum gap. An improved formulation, fully consistent with fluctuational electrodynamics, is developed to correctly trace the energy streamlines inside the emitter, receiver, and the vacuum gap. The influence of surface waves on the direction of energy propagation as well as on the lateral shift of energy streamlines is elucidated. An important finding with the improved formulation is that the lateral shift in the emitter may exceed that in the vacuum gap. The method can be extended for tracing the energy streamlines in multilayered structures.

Analysis of a diffractive microlens using the finite-difference time-domain method

The finite-difference time-domain (FDTD) method is used as rigorous electromagnetic analysis model to calculate the field for a diffractive microlens (DML). The FDTD is used for the entire solution rather than using a near- to far-field propagation method to obtain the far-field energy distribution; thus, all the results are vector based. We derived a formula to calculate the magnitude of electric field, which is time dependent and can be used to graphically show the light wave propagation and focusing process through a DML. Both the comparison and the integral methods are presented to obtain wave amplitude in full solution space, and the distribution of light energy behind a DML is illustrated based on the wave amplitude. The formula of diffractive efficiency of the DML is derived from a time-averaged Ponyting vector, which can indicate the propagation direction of light energy. Application of these formulations in the analysis of a DML example demonstrates the high accuracy and efficiency of our method.

SH Waves in a Transversely Isotropic Medium-I

Summary In a transversely isotropic medium plane SH waves, polarized parallel to the plane of isotropy, are propagated with phase velocity (normal to the wave front) I/ = (v,,~ cos2c+ v,’ sin2e), where V, and V, are shear wave velocities perpendicular and parallel to the plane of isotropy, and e is the angle of incidence on that plane. The direction of energy propagation, on the other hand, is in general not normal to the wave front but in the direction of the radius vector from the origin to the wave surface, which is the envelope, at time t = 1, of plane waves which all passed through the origin at time t = 0. The velocity of energy propagation, which is here the group velocity, has magnitude u = (vV4 cos2e+ v,,~ sin2e)f/V. Expressions for I/ and U in terms of ray direction are derived, and also the modified form of Snell’s Law for refraction. We show that when the seismic velocity is calculated from travel times and hypocentral distances it is U, not V, which is obtained.

An Estimation Method of Poynting Vector with Near-Magnetic-Field Measurement

A new technique to estimate the Poynting vector distribution from near-magnetic-field measurement is proposed. To calculate the Poynting vector, both electric and magnetic field should be known. In the proposed method, only magnetic-field measurement of three orthogonal axes is required. Electric field is estimated from the measured magnetic field by using the Maxwell's equation. The modified Yee cell is employed to estimate electric field from the measured magnetic field. Finally, the Poynting vector is calculated from the measured magnetic field and the estimated electric field. Since the proposed method enables us to understand propagation direction of electro-magnetic energy, it can be utilized to locate an emission source and to investigate a mechanism of undesired emission. Experiments are carried out to discuss the accuracy and to validate practical usefulness.

Variations of the nonlinear equation for diffracting beams in fluids to study different modes of propagation in elastic media.

Four variations of the equation for nonlinear acoustic beam propagation derived originally for a fluid will be reviewed. These variations describe finite amplitude beam propagation in isotropic elastic solids and in crystals, influence of diffraction on nonlinear Rayleigh waves, and nonlinear shear wave beams. The distinguishing features of each case will be discussed. The equation for nonlinear longitudinal wave beams in isotropic solids is based on nonlinear theory of elasticity and is close to the original equation for fluids. The equation for sound beams in crystals takes into account that the direction of energy propagation does not coincide with the direction normal to wavefronts. Nevertheless, the general form of the equation is similar to that of the original equation for fluids. Distinguishing features of Rayleigh waves are that they are two-dimensional and their nonlinearity is nonlocal. Because of the nonlocal nonlinearity, the evolution equation for this case was derived in the frequency domain using Hamiltonian formalism. The equation for nonlinear shear wave beams was derived in the cubic approximation in terms of particle displacement and it accounts for any polarization. Solutions of these evolution equations will be presented to illustrate phenomena specific to each case.

Diurnal and intraseasonal variation of UTLS vertical wind disturbance in the equatorial region and its relation to tropospheric convective activities

Abstract Vertical wind variations in the Upper Troposphere and Lower Stratosphere (UTLS) measured by the Equatorial Atmosphere Radar (EAR) at Kototabang, Sumatra, between 2003 and 2005 but mainly in 2004, have been statistically analyzed to study the characteristics of wind variances associated with convective activity, which is related to gravity wave generation and propagation. The analyses are intended to characterize relatively short period disturbances of less than 12 hours and an energy propagation direction of a relatively high elevation angle, and to relate vertical wind variations to convective activity close to the EAR. Correlation analyses between vertical wind variations and rainfall show that the wind variances have a clear diurnal variation indicating probable effects of tropospheric convection. They also show some intraseasonal variation. However, there are no significant correlations with the Out-going Long-wave Radiation (OLR) anomaly. The correlations between variances at UT and LS suggest that the UTLS coupling of vertical wind variation through upward propagation of gravity wave is similarly evident in the afternoon during both the active and the inactive phase of OLR that is a proxy of large-scale convective activity.

Inferring Propagation Direction of Nonlinear Internal Waves in a Vertically Sheared Background Flow

Abstract Internal waves heave the background flow through which they propagate. If the background flow is vertically sheared, the high-pass-filtered velocity field will thus contain signals of both the wave velocity and the heaved flow. Under conditions of large wave amplitude and large background shear—a common situation for nonlinear internal waves in coastal waters—the velocity fluctuations caused by wave heaving of the background flow can be comparable to the wave velocity itself. This complicates the inference of wave properties such as energy flux and propagation direction. The present study deals with methods to infer propagation direction in such situations. Attention is given to three methods that may be applied to acoustic Doppler current profiler measurements: a “filtering” method that estimates wave signals from high-pass-filtered time series, a “beamwise” method that infers wave direction from lagged correlations of echo intensity between the spatially separated acoustic beams of the profiler, and a “modal” method that separates background and wave signals by regressing the high-pass-filtered velocity field onto a normal-mode wave model. The methods are tested using synthetic datasets. The results suggest that the filtering method is biased by wave heaving of the background shear, while the beamwise and modal methods are resistant to heaving. The beamwise method provides accurate predictions of wave propagation angle for cases in which the measurements have high temporal resolution and the environment exhibits no depth-averaged background flow. The limitation on depth-averaged flow is relaxed for the modal method, but it requires the measurement of stratification. These issues are illustrated, and the applicability of these methods is explored with a series of sensitivity tests, and it is found that the different methods perform well under different circumstances.

Lateral Shifts in Near-Field Thermal Radiation with Surface Phonon Polaritons

It is well known that radiative heat transfer in the near field regime can be greatly enhanced because of photon tunneling, during which the classical radiation theory fails to predict the energy propagation direction. In the present article, we investigate the lateral shifts of energy pathways in near-field thermal radiation between two SiC plates separated by a vacuum gap. The energy streamline (ESL) method can be combined with fluctuational electrodynamics to trace the Poynting vector at a fixed parallel wavevector component β. The spectral energy flux exhibits nearly monochromatic enhancement with the excitation of surface phonon polaritons. In the spectral region important for radiative energy transfer, there exist considerable lateral shifts depending on the values of β. The range of β dominantly contributing to the spectral energy flux is identified for different wavelengths by examining the Poynting vector equation. With the use of ESLs, the effect of coupled surface polaritons on the lateral shift is also investigated. Furthermore, the lateral dimension for the SiC plates to be treated as infinitely extended is estimated based on the lateral shifts in the wavelength region that mostly contributes to the total energy flux.

Design of electromagnetic refractor and phase transformer using coordinate transformation theory

We designed an electromagnetic refractor and a phase transformer using form-invariant coordinate transformation of Maxwell's equations. The propagation direction of electromagnetic energy in these devices can be modulated as desired. Unlike the conventional dielectric refractor, electromagnetic fields at our refraction boundary do not conform to the Snell's law in isotropic materials and the impedance at this boundary is matched which makes the reflection extremely low; and the transformation of the wave front from cylindrical to plane can be realized in the phase transformer with a slab structure. Two dimensional finite-element simulations were performed to confirm the theoretical results.

Mixed phase and absorption thin gratings diffraction

AbstractThe coupled wave theory of Raman and Nath diffraction is extended to the case of thin anisotropic holographic media with grating vector parallel to the medium boundaries. Solutions for the wave amplitudes, diffraction efficiencies, and angular mismatch sensitivities are given in transmission geometries for the case of mixed dielectric and absorption modulations. For an apparent distinction, the results are given only for dielectric modulation. The main difference of the new results, with respect to the expressions valid for isotropic media, arises due to the walk-off between the wave-front and energy propagation directions. The difference is particularly important in materials with large birefringence, such as organic crystals, ordered polymers, and liquid crystalline cells.

The Theory of Light Diffraction in Thin Anisotropic Medium

The coupled wave theory of Raman and Nath diffraction is extended to the case of thin anisotropic holographic media with grating vector parallel to the medium boundaries. Solutions for the wave amplitudes, diffraction efficiencies, and angular mismatch sensitivities are given in transmission geometries for the case of dielectric modulation. The main difference of the new results with respect to the expressions valid for isotropic media arises due to the walk-off between the wave-front and energy propagation directions. The difference is particularly important in materials with large birefringence, such as organic crystals, ordered polymers, and liquid crystalline cells.