Windowed-Transform Processing of Acoustic Beam Scattering From Fluid-Immersed Elastic Structures

1995 ◽  
Author(s):  
Smaine Zeroug ◽  
Leopold B. Felsen
Keyword(s):  
Specular Reflection ◽  
Incident Beam ◽  
Window Size ◽  
Domain Modeling ◽  
Acoustic Beam ◽  
Elastic Structures ◽  
Present Contribution ◽  
Hybrid Beam ◽  
Beam Scattering ◽  
Local Wavenumber

Abstract Acoustic beam scattering from submerged bulk and layered elastic structures is of interest for applications ranging from determining material properties to locating and identifying interior defects. Nonspecular reflection, which occurs when the incident beam is phase matched to leaky waves (LW) supported by the structure, constitutes an effective sensor for such applications. Forward frequency domain modeling based on a robust asymptotic hybrid beam-LW algorithm [Zeroug and Felsen, 1992] has shown that the nonspecular data, which is established by interference between specular reflection and LWs, depends strongly on the collimation of the incident beam, the number and leakage strengths of the excited LWs, and the curvature of the insonified structure. The present contribution addresses the inverse problem of extracting this phenomenology via wave-oriented processing, which is implemented by subjecting the scattered field data to a Gaussian-windowed Fourier transform (GWT) along spatial tracks parallel to the fluid-structure interface. For the fluid-immersed elastic configurations of: 1) solid half-spaces, 2) plates, 3) solid cylinders, and 4) cylindrical shells, the GWT-generated local wavenumber phase-space distributions footprint the correct wave physics, but with resolutions that are limited by the configuration-spectrum tradeoff. Examples demonstrate how the resolution is influenced by the GWT window size. The paper also includes preliminary results on application of a Prony superresolution algorithm for extraction of LW phase velocities and leakage rates.

Determination of the Elastic Properties of a Solid Sphere Based on the Results of Acoustic Beam Scattering

2021 ◽  
Vol 67 (4) ◽  
pp. 360-374
Author(s):  
L. M. Kotelnikova ◽  
D. A. Nikolaev ◽  
S. A. Tsysar ◽  
O. A. Sapozhnikov
Keyword(s):  
Elastic Properties ◽  
Solid Sphere ◽  
Acoustic Beam ◽  
Beam Scattering

Rocking curves for specular reflection from crystal surfaces in the TEM

1983 ◽  
Vol 41 ◽  
pp. 320-321
Author(s):  
P. S. Turner ◽  
J. A. Eades
Keyword(s):  
Electron Beam ◽  
Specular Reflection ◽  
Bragg Reflection ◽  
Incident Beam ◽  
Bragg Condition ◽  
Beam Angle ◽  
Crystal Surfaces ◽  
High Quality ◽  
Rocking Curve ◽  
Transmission Electron

In transmission electron microscopy, electron diffraction is most frequently undertaken in the “Laue condition” (i.e. the electron beam entering one surface of a parallel sided slab and leaving through the opposite surface) or some approximation to it. In contrast, surfaces studies by RHEED are carried out in the “Bragg condition” (i.e. the electron beam enters and leaves through the same surface of the crystal and the Bragg reflection is from planes parallel rather than perpendicular to the surface).Now that high quality images from surfaces are being obtained in reflection e.g., Yagi, it is appropriate to develop diffraction techniques for the Bragg condition in the electron miroscope; there are many examples of such work in RHEED equipment e.g. The symmetric Bragg condition is obtained when the incident and diffracted beams make the same angle with the specimen surface; this is specular reflection. Thus to obtain a rocking curve in the symmetric Bragg case requires variation of both the incident beam angle and the take off angle. This is not practical in an unmodified microscope.

Characterization of rutile (110) surface structure by REM

1992 ◽  
Vol 50 (2) ◽  
pp. 1462-1463
Author(s):  
L. Wang ◽  
J. Liu ◽  
J. M. Cowley
Keyword(s):  
Resonance Condition ◽  
Specular Reflection ◽  
Azimuthal Angle ◽  
Incident Beam ◽  
High Energy ◽  
Surface Cleaning ◽  
Pure Oxygen ◽  
Surface Resonance ◽  
Cleaning Procedures ◽  
Reflection Electron Microscopy

Single crystal TiO2 (rutile) (110) surface has been characterized by several experimental techniques. In this paper, we report the investigations of “optically polished” as well as high temperature oxygen annealed rutile (110) surfaces by using reflection electron microscopy (REM) and reflection high energy electron diffraction (RHEED) techniques.The crystal was purchased, “optically polished” as-received, from Commercial Crystal Laboratories, Inc.. The details in specimen cutting and surface cleaning procedures have been reported previously. The samples were annealed in pure oxygen at 1425°C for 36 h. The experimental observations were carried out in a Philips 400T microscope operated at 120 kV. The REM images were obtained by selecting the specular reflection spots satisfying surface resonance conditions.Figure 1 is a REM image of as-received rutile (110) surface. The corresponding RHEED pattern is shown in the inset. The azimuthal angle of the incident beam was at 3.9° away from [001] zone axis and the image was formed by choosing (440) specular reflection spot under surface resonance condition.

Geometrical explanation of parabolas and resonance in electron diffraction

1989 ◽  
Vol 47 ◽  
pp. 498-499
Author(s):  
M. Gajdardziska-Josifovska ◽  
J. M. Cowley
Keyword(s):  
Focal Point ◽  
Specular Reflection ◽  
Incident Beam ◽  
Simple Geometry ◽  
Line Parallel ◽  
Surface Resonance ◽  
Reflection Electron Microscopy ◽  
Diffraction Patterns ◽  
Geometrical Explanation ◽  
Transmission And Reflection

Reflection electron microscopy (REM) relies on the surface resonance (channeling) conditions for enhancement of the intensity of the specular reflection from a flat surface of a single crystal. The two most frequently cited geometries for attaining surface resonance conditions are: i) tilting the incident beam such that the specular beam in the RHEED pattern falls on an intersection of a K-line parallel to the surface with some oblique K-line; ii) positioning the specular beam on an intersection of a K-Iine parallel to the surface with some of the surface resonance regions bound by parabolas. Parabolas are also observed in the transmission diffraction patterns and have been explained as Kikuchi envelopes. Recent studies indicated a similarity between the CBED transmission and reflection patterns. We will describe a simple geometry which can be used to interpret the above observations.A parabola is by definition a curve of equal distance from a point (called focus) and a line (called directrix; see Fig.1 ).Simple previously unnoticed facs are that the zone axis is a focal point of all the parabolas belonging to a given zone, and that the directrix of each parabola corresponds to a K-line.

Beam-Induced Motion of Adatoms in the Transmission Electron Microscope

2013 ◽  
Vol 19 (2) ◽  
pp. 479-486 ◽  
Author(s):  
R.F. Egerton
Keyword(s):  
Incident Energy ◽  
Room Temperature ◽  
Incident Beam ◽  
Atomic Motion ◽  
Displacement Rate ◽  
Transmission Electron ◽  
Beam Scattering ◽  
Induced Motion ◽  
Surface Translation ◽  
Analytical Expressions

AbstractEquations governing the elastic scattering of electrons are applied to the knock-on displacement of atoms along a substrate, yielding analytical expressions for the surface-translation energy, threshold incident energy, and displacement rate. For a surface perpendicular to the incident beam, scattering angles around 90° contribute most to the kinetic energy of surface atoms. Tilting the specimen lowers the threshold incident energy for displacement and leads to anisotropy in the atomic motion but has little effect on the directionally-averaged displacement rate. The rate of beam-induced adatom motion is predicted to exceed that of room-temperature thermal motion when the surface-diffusion energy is greater than about 0.5 eV.

On obtaining high spectral resolution in extreme ultraviolet/soft X-ray monochromators operating off-plane diffraction in a divergent incident beam

2020 ◽  
Vol 27 (6) ◽  
pp. 1499-1509
Author(s):  
Werner Jark
Keyword(s):  
Spectral Resolution ◽  
Extreme Ultraviolet ◽  
Specular Reflection ◽  
Incident Beam ◽  
Diffraction Order ◽  
Source Size ◽  
Resolving Power ◽  
High Spectral Resolution ◽  
Radiation Beam ◽  
X Ray

When the trajectory of an incident beam is oriented parallel to the grooves of a periodic grating structure the radiation beam is diffracted off-plane orthogonal to the plane of incidence. The diffraction efficiency in this condition is very high and in a grating with a sawtooth profile it can approach the reflection coefficient for a simple mirror, when the diffraction order of interest follows the direction for specular reflection at the flat part of the steps. When this concept is used in a plane grating in a monochromator for synchrotron radiation sources, the incident beam is almost always collimated in order to minimize any deterioration of the beam properties due to aberrations, which will be introduced in the diffraction process when an uncollimated beam is used. These aberrations are very severe when the groove density is constant. It will be shown that the effect of these aberrations can be corrected after the diffraction by the use of astigmatic focusing. The latter can be provided by a crossed mirror pair with different focal lengths in the corresponding orthogonal directions. Then a monochromator based on this concept can provide source size limited spectral resolution in an uncollimated incident beam. This is identical to the spectral resolution that can be provided by the same grating when operated at the same position in a collimated incident beam. The source size limited spectral resolution in this case corresponds to a high spectral resolving power of better than ΔE/E = 10 000 for photon energies around 300 eV in the soft X-ray range.

Sign in / Sign up

Export Citation Format

Share Document