Showing papers on "Reflection (physics) published in 2000"

Fundamentals of Physical Acoustics

Abstract: Detailed Development of the Acoustical Wave Equation. Reflection and Transmission of Normally Incident Plane Waves of Arbitrary Waveform. Normal Incidence Continued: Steady-State Analysis. Transmission Phenomena: Oblique Incidence. Normal Modes in Cartesian Coordinates: Strings, Membranes, Rooms, and Rectangular Waveguides. Horns. Propagation in Stratified Media. Propagation in Dissipative Fluids: Absorption and Dispersion. Spherical Waves. Cylindrical Waves. Waveguides. Radiation from a Baffled Piston. Diffraction. Arrays. Appendices. Index.

Elastic Wave Scattering by Periodic Structures of Spherical Objects: Theory and Experiment

Abstract: We extend the multiple-scattering theory for elastic waves by taking into account the full vector character. The formalism for both the band structure calculation and the reflection and transmission calculations for finite slabs is presented. The latter is based on a double-layer scheme which obtains the reflection and transmission matrix elements for the multilayer slab from those of a single layer. As a demonstration of applications of the formalism, we calculate the band structures of elastic waves propagating in a three-dimensional periodic arrangement of spherical particles and voids, as well as the transmission coefficients through finite slabs. In contrast with the plane-wave method, the multiple-scattering approach exhibits advantages in handling specialized geometries (spherical geometry in the present case). We also present a comparison between theory and ultrasound experiment for a hexagonal-close-packed array of steel balls immersed in water. Excellent agreement is obtained.

Bragg gratings in multimode and few-mode optical fibers

Abstract: Bragg gratings in optical fibers in multimode propagation are investigated experimentally and theoretically. Bragg gratings formed in optical fibers in multimode propagation show multiple reflection peaks or multiple transmission dips in the reflection or transmission spectra, respectively. For standard graded-index multimode fiber, the number of reflection peaks of a Bragg grating depends on excitation condition of propagating modes. The number of reflection peaks of a Bragg grating at around 1.55 /spl mu/m is 19 for highly multimode excitation and 3-4 for lower order mode excitation. We analyze the phase-matching conditions of the propagating modes and identify half of the reflection peaks as the reflection to the same mode and the rest as the reflection to the neighboring modes. In dispersion-shifted fiber, a Bragg grating at around 0.8 /spl mu/m in three-mode propagation shows three reflection peaks in the reflection spectrum. The temperature dependence of each reflection peak is similar to that of a conventional Bragg grating in single-mode fiber. Polarization dependence measured on a Bragg grating in multimode graded-index fiber is negligible. An advantage of Bragg gratings in multimode fiber (MMF) and the applications are discussed.

Geologic transect across the Grenville orogen of Ontario and New York

Abstract: Revised cross sections of the western Grenville Province incorporate new geologic results and reprocessed seismic reflection data. The geology is presented in terms of three tectonic elements: (1) ...

Fine-scale heterogeneity in the Earth's inner core

Abstract: The seismological properties of the Earth's inner core have become of particular interest as we understand more about its composition and thermal state1,2. Observations of anisotropy and velocity heterogeneity in the inner core are beginning to reveal how it has grown and whether it convects3,4. The attenuation of seismic waves in the inner core is strong, and studies of seismic body waves5,6 have found that this high attenuation is consistent with either scattering or intrinsic attenuation5. The outermost portion of the inner core has been inferred to possess layering and to be less anisotropic than at greater depths7,8,9,10. Here we present observations of seismic waves scattered in the inner core which follow the expected arrival time of the body-wave reflection from the inner-core boundary. The amplitude of these scattered waves can be explained by stiffness variations of 1.2% with a scale length of 2 kilometres across the outermost 300 km of the inner core. These variations might be caused by variations in composition, by pods of partial melt in a mostly solid matrix or by variations in the orientation or strength of seismic anisotropy.

Spectral decomposition for seismic interpretation

Abstract: The present invention is directed generally toward a method of processing seismic data to provide improved quantification and visualization of subtle seismic thin bed tuning effects and other sorts of lateral rock discontinuities. A reflection from a thin bed has a characteristic expression in the frequency domain that is indicative of the thickness of the bed: the reflection has a periodic sequence of notches in its amplitude spectrum, with the notches being spaced a distance apart that is inversely proportional to the temporal thickness of the thin bed. Further, this characteristic expression may be used to track thin bed reflections through a 3-D volume and estimate their thicknesses and lateral extent. The usefulness of this invention is enhanced by a novel method of frequency domain whitening that emphasizes the geologic information present within the spectrum. Although the present invention is preferentially applied to a 3-D seismic volume, it is alternatively applied to any collection of spatially related seismic traces.

Lighting apparatus, with high light directivity, liquid crystal display system using the same and electronic equipment using the same

Abstract: PCT No. PCT/JP96/03243 Sec. 371 Date Jul. 3, 1997 Sec. 102(e) Date Jul. 3, 1997 PCT Filed Nov. 6, 1996 PCT Pub. No. WO97/17631 PCT Pub. Date May 15, 1997A reflection layer is provided on a surface of a light guiding body on which projections are formed with intervals, except the side surfaces of the projections. A light emitting element is provided close to one end surface of a light guiding element. Most of the light from the light emitting element is input to the light guiding body through the light input surface. The light travels through the light guiding body to be output from the side surfaces of the projections. After passing through a directional change element, the light is input to the light receiving element in a direction substantially perpendicular to a light receiving element. Outside light passes through the light receiving element and is then input to a lighting apparatus. In the lighting apparatus, the outside light passes through the directional change element to be reflected by a reflection layer on the light-output-side surface of the light guiding body and then again passes perpendicularly through the directional change element toward the light receiving element. When the light passes through the light receiving element, a displayed image can be viewed. The reflection layer can reflect the light with a small loss. In addition, if the outside light is input at an angle of other than 90 DEG to the light receiving element at first, the light can be reflected by the reflection layer with a small loss.

Diffusion Waves and their Uses

Abstract: The concept of waves is an integral part of our scientific culture and has nourished physicists, pure and applied alike, for centuries. Many important discoveries in physics, including quantum mechanics, have involved wave phenomena. The wave concept owes some of its scientific success to its mathematical tractability. Linear wave equations—the sort that describe the transmission of sound and radio waves through air—contain a nonzero second‐order time derivative, which gives rise mathematically to the rich and familiar array of properties we associate with waves, such as wavefront propagation, reflection, and refraction.

Effects of target shape and reflection on laser radar cross sections

Abstract: Laser radar cross sections have been evaluated for a number of ideal targets such as cones, spheres, paraboloids, and cylinders by use of different reflection characteristics. The time-independent cross section is the ratio of the cross section of one of these forms to that of a plate with the same maximum radius. The time-dependent laser radar cross section involves the impulse response from the object shape multiplied by the beam's transverse profile and the surface bidirectional reflection distribution function. It can be clearly seen that knowledge of the combined effect of object shape and reflection characteristics is important for determining the shape and the magnitude of the laser radar return. The results of this study are of interest for many laser radar applications such as ranging, three-dimensional imaging-modeling, tracking, antisensor lasers, and target recognition.

Monte Carlo simulation of seismogram envelopes in scattering media

Abstract: The analysis of the seismogram coda envelopes of local and regional earthquakes is one of the most effective strategies for investigating the heterogeneous lithospheric structure characterized by the seismic scattering and attenuation. In order to synthesize the coda envelope we introduce a numerical scheme called the direct simulation Monte Carlo method, which has been used in the field of the kinetic theory of gases. Because of the simplicity of the algorithm the method has several advantages over previous methods in terms of the flexibility of the numerical calculation to incorporate various factors required to construct realistic seismogram envelopes. On the basis of coda envelope simulations, including multiple scattering, we show that an increase of seismic velocity with depth severely affects the shape of the coda envelope. The effects of ray bending due to the velocity increase at the Moho and the reflection at the free surface are clearly found in the synthesized envelope for a shallow earthquake. Our simulation demonstrates that the amplitude of the envelope is magnified by stagnation of seismic energy at shallow depths due to the positive velocity gradient with depth. Because of this effect, for an a priori assumption of a homogeneous velocity model the measurement of the scattering coefficient by conventional methods may be overestimated.

Trapping and Generation of Waves by Vertical Porous Structures

Abstract: The trapping and generation of surface waves by submerged vertical permeable barriers or plates kept at one end of a semi-infinitely long channel of finite depth are investigated for various barrier and plate configurations. The various fixed barrier configurations are (1) a surface-piercing barrier; (2) a bottom-touching barrier; (3) a barrier with a gap; and (4) a fully submerged barrier. The different moving plate (or wavemaker) configurations are of types 1, 2, and 4, respectively. The boundary value problems are converted to dual/triple series relations by a suitable application of the eigenfunction expansion method and then the full solutions are obtained by the least-squares method. The variations of reflection coefficients are obtained and discussed for different values of the porous-effect parameter, the normalized distance between the barrier and the channel end-wall, and the length of submergence of barriers for all types of barrier configurations. The dynamic pressure distributions for various...

Electromagnetic propagation into reinforced-concrete walls

Abstract: A rigorous method for analyzing building construction materials, using finite-element techniques and an expansion of fields in Floquet's modes, is presenteded in this paper. It allows us to precisely study the electromagnetic properties of buildings walls in terms of transmission and reflection characteristics, which can be useful in the design of wireless communication systems. First, we present the influence of the wall's parameters, namely, its thickness, the square side length, and the steel diameter of a concrete grid. The influence of the angle of arrival of the incident wave and the effect of considering the diffused field on the electromagnetic properties are then presented.

A seismic-based cross-section of the Grenville Orogen in southern Ontario and western Quebec

Abstract: A schematic crustal cross-section is presented for the southwestern Grenville Province based on reprocessed Lithoprobe near-vertical incidence seismic reflection data and compiled seismic refractio...

Bulk acoustic wave filter

Abstract: The invention describes a filter arrangement as well as an electronic component, each with a bulk acoustic wave resonator unit which is present on a carrier substrate ( 1 ) A reflection element ( 2 ) is provided between the carrier substrate ( 1 ) and the bulk acoustic wave resonator unit for the purpose of acoustic insulation of the generated oscillations This reflection element ( 2 ) may consist either of several layers of alternately high and low impedance or, if the acoustically reflecting substance has a sufficiently low impedance, of a single layer In addition, a mobile telephone device, a transmitter, a receiver, and a wireless data transmission system as well as a method of manufacturing an electronic component are described

Reflection and Transmission of Waves near the Localization Threshold

Abstract: A theory is presented for propagation of waves in bounded media near the mobility edge, based on the self-consistent theory for localization. It predicts a spatially inhomogeneous diffusion constant that leads to scale dependence in enhanced backscattering and transmission.

Multidimensional Monte Carlo Simulation of Short-Pulse Laser Transport in Scattering Media

Abstract: The Monte Carlo technique is used to simulate the two-dimensional transient radiative heat transfer in scattering and absorbing media The transient behavior of transmissivity and reflectivity, subject to short-pulse laser radiation incident on highly scattering media, is investigated The influences of medium dimensions, anisotropic scattering characteristics, incident pulse width and spatial and temporal Gaussian distributions, and the effect of Fresnel reflection resulting from refractive index changes at the boundaries are discussed It is found that the temporal distribution shape and spread of the predicted transmissivity and reflectivity are significantly influenced by the incident pulse width and the dimensions of the media Forward scattering increases the magnitude of maximum transmissivity and reduces the transmitted pulse width Neglecting the boundary reflection results in overestimated transmissivity and reflectivity and shortens the transmitted pulse width

Scattering and radiation of water waves by permeable barriers

Abstract: The two-dimensional problems of scattering and radiation of small-amplitude water waves by thin vertical porous plates in finite water depth are considered using the linear water wave theory. Applying the method of eigenfunction expansion, these boundary value problems are converted to certain dual series relations. Solutions to these relations are then obtained by a suitable application of the least squares method. For the scattering problem, four different basic configurations of the barriers are investigated, namely, (I) a surface-piercing barrier, (II) a bottom-standing barrier, (III) a totally submerged barrier, and (IV) a barrier with a gap. The performance of these types of barriers as a breakwater are examined by studying the variation of their reflection and transmission coefficients, hydrodynamic forces and moments for different values of the porous effect parameter defined by Chwang [J. Fluid Mech. 132, 395–406 (1983)], or the Chwang parameter. For the radiation problem, three types of wavemakers, which resemble types (I), (II), and (III) of the above-mentioned configuration, are analyzed. The dependence of the amplitude to stroke ratio on other parameters is also investigated to study the features of these wavemakers.

Selective laser-induced heating of biological tissue

Abstract: The invention features methods and systems for selectively delivering or coupling laser radiation into a first material or substrate, e.g., a first biological tissue, having a first index of refraction and not into a second material or substrate, e.g., a second biological tissue, having a second index of refraction. The system determines whether a target area corresponds to the first material or the second material by monitoring the reflection of a probe beam incident on the target area through an optical coupler at a non-normal incident angle. The monitored reflection of the probe beam is a control signal for a feedback controller that causes a treatment beam to be delivered to the target area based on the monitored reflection.

Reflection-type 2×2 optical waveguide switch using the Goos–Hänchen shift effect

Abstract: We have designed a structure for a 2×2 silica-based optical waveguide switch that is based on a thermocapillarity effect. This switch can use the reflection walls on both sides of the slit, because the Goos–Hanchen shift effect was taken into account when the structure of the waveguides and the slit was designed. This switch can provide a cross/bar function through a single element, and the measured reflection losses in the reflection walls on both sides of the slit were consistent. The loss was comparable to the insertion loss of a Mach–Zender-interferometer-type thermo-optic switch.

Chromatic dispersion compensation

Abstract: An optical waveguide (11, 71) provided with a linearly chirped Bragg reflective grating (13, 73) can be employed as a device that provides linear dispersion compensation. The amount of the linear dispersion thereby provided can be rendered adjustable by adjustment of the magnitude of axial strain imposed upon the grating. If the chirp is purely linear, and if also, the strain is at all times uniform along the length of the grating, adjustment of the strain magnitude will have no such effect. This requires the presence of a quadratic chirp term, but such a term introduces its own transmission penalty. This penalty is compensated at least in part by causing the light to make a reflection in a further Bragg reflection grating (14, 74) whose quadratic component of chirp has the opposite sign to that of the other Bragg reflection grating, but a substantially matched modulus. The effect of the strain is to scale the effective pitch of the Bragg reflection grating by scaling its physical pitch. An alternative way of achieving a similar effect is to change the effective refractive index of the waveguide in which the grating is formed, for instance by changing its temperature.

Optical sheets suitable for spreading light

Abstract: An optical sheet (25) for spreading light has a substantially smooth surface (27), and a structured surface (28) comprising an array of prisms (30, 31). A beam of light that is to be spread is directed through the film from the smooth surface. Some of the prisms (termed 'refraction prisms') deviate normally-incident light only by refraction at a prism facet as the light leaves the film while others (termed 'reflection prisms') deviates normally-incident light by total internal reflection within the prism before the light leaves the film. There are a plurality of reflection prisms (30) selected to deviate normally-incident light through different angles and plurality of refraction prisms (31) selected to deviate the normally-incident light through different angles, and they are arranged, preferably in a non-ordered manner, so that successive reflection prisms are separated by at least one refraction prism. In alternative embodiments, the structured surface comprises an non-ordered arrangement of a plurality of reflection prisms selected to deviate normally-incident light through different angles, or a non-ordered arrangement of a plurality of refraction prisms selected to deviate normally-incident light through different angles.

Dielectric frequency-selective structures incorporating waveguide gratings

Abstract: In this paper, a frequency-selective structure based on guided-mode resonance effects in all-dielectric waveguide gratings is demonstrated theoretically and verified experimentally. Reflection (band-stop) filters with high efficiency, extended low-sideband reflection, and symmetric line shapes are designed by embedding gratings in layered antireflection structures. Reflection filter examples employing common dielectric materials illustrate linewidth control by grating modulation. An additional mechanism for linewidth control is demonstrated with phase-shifted gratings. Double-line reflection filters are obtained in structures containing two gratings with different grating periods. High-efficiency transmission (bandpass) filters are demonstrated using multilayer waveguide gratings in a high-reflectance thin-film configuration with a single grating in the center layer bordered by dielectric mirrors composed of high/low quarter-wave layers. Single-layer and multilayer waveguide gratings operating as reflection and transmission filters, respectively, were built and tested in the 4-20-GHz frequency range. The presence of guided-mode resonance notches and peaks is clearly established by the experimental results, and their spectral location and line shape is found to be in excellent agreement with the theoretical predictions.

Image pickup device

Abstract: PROBLEM TO BE SOLVED: To obtain images of stable brightness, even when the brightness of a light source is suddenly changed by arranging n half mirrors and (n+1) image pickup parts, for receiving reflected light or transmitted light from respective half mirrors and dividing input light from a lens by respective half mirrors. SOLUTION: On the optical path of a lens 2, n (n is an integer >=1) half mirrors 22a, 22b are arranged in states respectively inclined 45 deg. from the vertical direction to the optical axis of the lens 2 mutually in vertical directions, and these half mirrors 22a, 22b have respectively different transmission/reflection factors. In addition, (n+1) image pickup parts 23a to 23c are respectively arranged on the optical paths of reflected beams from respective half mirrors 22a, 22b and the optical path of transmitted light from all the half mirrors 22a, 22b. Since in this way input light from the lens 2 is split into three beams by the half mirrors 22a, 22b, plural images of respective different luminance values can be obtained in one time via respective image pickup parts 23a to 23c, and moreover each of the geometric conditions of these images become identical.

Free Boundary Problems for the Unsteady Transonic Small Disturbance Equation: Transonic Regular Reflection

Abstract: We formulate and solve a transonic regular reflection problem for the unsteady transonic small disturbance equation, using a free boundary problem approach. Our method applies to self-similar shock reflection when the incident shock angle is large enough to permit a regular reflection configuration with a subsonic state behind the reflected shock. For the small-disturbance approximation in weak shock reflection, this corresponds to relatively large wedge angles. One contribution of this paper is the development of an asymptotic formula for the reflected shock, far from the reflection point, and for the subsonic state far downstream. These asymptotic series are valid for the small-disturbance approximation, for any incident shock angles. The main result in the paper is an existence theorem for the nonuniform subsonic flow behind the reflected shock. The flow velocity satisfies a quasilinear elliptic equation which is coupled to the Rankine-Hugoniot equations for the reflected shock, forming a free boundary problem on part of the boundary. Because the equation is not uniformly elliptic in the entire domain, we introduce a cut off to give a bounded domain, and also cut offs to the coefficients. Our result is incomplete in the following sense: we have been unable to remove the cut offs entirely. However, we prove that the flow we have constructed solves the original problem in a domain of finite size around the reflection point.