Ray theory in mode models: Demonstration of high‐frequency collective‐mode interference effects

1996 ◽  
Vol 100 (4) ◽  
pp. 2833-2833
Author(s):  
Jason F. Manning ◽  
Evan K. Westwood ◽  
Eric Smith
Keyword(s):  
High Frequency ◽  
Collective Mode ◽  
Ray Theory ◽  
Interference Effects ◽  
Mode Interference

Dynamic properties of reflected and head waves near the critical point

1979 ◽  
Vol 16 (7) ◽  
pp. 1388-1401 ◽  
Author(s):  
Larry W. Marks ◽  
F. Hron
Keyword(s):  
Exact Solution ◽  
High Frequency ◽  
Classical Problem ◽  
Plane Boundary ◽  
Head Wave ◽  
Disk File ◽  
Ray Theory ◽  
Computational Point ◽  
Spherical Waves ◽  
Head Waves

The classical problem of the incidence of spherical waves on a plane boundary has been reformulated from the computational point of view by providing a high frequency approximation to the exact solution applicable to any seismic body wave, regardless of the number of conversions or reflections from the bottoming interface. In our final expressions the ray amplitude of the interference reflected-head wave is cast in terms of a Weber function, the numerical values of which can be conveniently stored on a computer disk file and retrieved via direct access during an actual run. Our formulation also accounts for the increase of energy carried by multiple head waves arising during multiple reflections of the reflected wave from the bottoming interface. In this form our high frequency expression for the ray amplitude of the interference reflected-head wave can represent a complementary technique to asymptotic ray theory in the vicinity of critical regions where the latter cannot be used. Since numerical tests indicate that our method produces results very close to those obtained by the numerical integration of the exact solution, its combination with asymptotic ray theory yields a powerful technique for the speedy computation of synthetic seismograms for plane homogeneous layers.

Comparison of seismic anisotropy of sedimentary strata at low- and high-frequency limits

Geophysics ◽  
2019 ◽  
Vol 85 (1) ◽  
pp. MR1-MR10 ◽  
Author(s):  
Fuyong Yan ◽  
De-Hua Han ◽  
Tongcheng Han ◽  
Xue-Lian Chen
Keyword(s):  
High Frequency ◽  
Seismic Anisotropy ◽  
Sedimentary Rocks ◽  
Low Frequency ◽  
Layered Media ◽  
Ray Theory ◽  
Frequency Limit ◽  
Anisotropic Properties ◽  
Velocity Anisotropy ◽  
Backus Averaging

The layer-induced seismic anisotropy of sedimentary strata is frequency-dependent. At the low-frequency limit, the effective anisotropic properties of the layered media can be estimated by the Backus averaging model. At the high-frequency limit, the apparent anisotropic properties of the layered media can be estimated by ray theory. First, we build a database of laboratory ultrasonic measurement on sedimentary rocks from the literature. The database includes ultrasonic velocity measurements on sandstones and carbonate rocks, and velocity-anisotropy measurements on shales. Then, we simulate the sedimentary strata by randomly selecting a certain number of rock samples and using their laboratory measurement results to parameterize each layer. For each realization of the sedimentary strata, we estimate the effective and apparent seismic anisotropy parameters using the Backus average and ray theory, respectively. We find that, relative to Backus averaging, ray theory usually underestimates the Thomsen parameters [Formula: see text] and [Formula: see text], and overestimates [Formula: see text]. For an effective layered medium consisting of isotropic sedimentary rocks, the differences are significant. These differences decrease when shales with intrinsic seismic anisotropy are included. For the same sedimentary strata, the seismic wave should perceive stronger seismic anisotropy than the ultrasonic wave.

scholarly journals Experimentelles FMCW-Radar zur hochfrequenten Charakterisierung von Windenergieanlagen

2017 ◽  
Vol 15 ◽  
pp. 1-9
Author(s):  
Karsten Schubert ◽  
Jens Werner ◽  
Fabian Schwartau
Keyword(s):  
Renewable Energy ◽  
High Frequency ◽  
Renewable Energy Sources ◽  
Cost Effective ◽  
Energy Sources ◽  
Interference Effects ◽  
Fmcw Radar ◽  
Weather Radars ◽  
Radar Systems ◽  
Radar Echoes

Abstract. During the increasing dissemination of renewable energy sources the potential and actual interference effects of wind turbine plants became obvious. Turbines reflect the signals of weather radar and other radar systems. In addition to the static radar echoes, in particular the Doppler echoes are to be mentioned as an undesirable impairment Keränen (2014). As a result, building permit is refused for numerous new wind turbines, as the potential interference can not be reliably predicted. As a contribution to the improvement of this predictability, measurements are planned which aim at the high-frequency characterisation of wind energy installations. In this paper, a cost-effective FMCW radar is presented, which is operated in the same frequency band (C-band) as the weather radars of the German weather service. Here, the focus is on the description of the hardware design including the considerations used for its dimensioning.

Modeling of N×N Optical Switch Based on Two-demionsional Multi-mode Interference Effects

2011 ◽  
Vol 40 (12) ◽  
pp. 1789-1792
Author(s):  
叶新威 YE Xin-wei ◽  
马卫东 MA Wei-dong ◽  
黄晓东 HUANG Xiao-dong ◽  
赵建宜 ZHAO Jian-yi
Keyword(s):  
Optical Switch ◽  
Interference Effects ◽  
Multi Mode ◽  
Mode Interference

High frequency collective mode in a Heisenberg ferromagnet

1970 ◽  
Vol 32 (1) ◽  
pp. 11-12 ◽  
Author(s):  
C.R. Natoli ◽  
J. Ranninger
Keyword(s):  
High Frequency ◽  
Collective Mode ◽  
Heisenberg Ferromagnet

scholarly journals Asymptotics of near-cloaking

2020 ◽  
pp. 1-21
Author(s):  
J. R. OCKENDON ◽  
H. OCKENDON ◽  
B. D. SLEEMAN ◽  
R. H. TEW
Keyword(s):  
Asymptotic Analysis ◽  
Acoustic Waves ◽  
High Frequency ◽  
Ray Theory ◽  
Elastic Materials ◽  
Eigenfunction Expansions ◽  
Linear Elastic

This paper describes how asymptotic analysis can be used to gain new insights into the theory of cloaking of spherical and cylindrical targets within the context of acoustic waves in a class of linear elastic materials. In certain cases, these configurations allow solutions to be written down in terms of eigenfunction expansions from which high-frequency asymptotics can be extracted systematically. These asymptotics are compared with the predictions of ray theory and are used to describe the scattering that occurs when perfect cloaking models are regularised.

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