scholarly journals On the acoustic scattering amplitude for a multi-layered Scatterer

1998 ◽  
Vol 39 (4) ◽  
pp. 431-448 ◽  
Author(s):  
Christodoulos Athanasiadis
Keyword(s):  
Scattering Amplitudes ◽  
General Theory ◽  
Plane Wave ◽  
Boundary Value Problems ◽  
Cross Section ◽  
Scattering Amplitude ◽  
Boundary Value ◽  
Acoustic Scattering ◽  
Scattering Cross ◽  
Time Harmonic

AbstractWe consider the boundary-value problems corresponding to the scattering of a time-harmonic acoustic plane wave by a multi-layered obstacle with a sound-soft, hard or penetrable core. Firstly, we construct in closed forms the normalized scattering amplitudes and prove the classical reciprocity and scattering theorems for these problems. These results are then used to study the spectrum of the scattering amplitude operator. The scattering cross-section is expressed in terms of the forward value of the corresponding normalized scattering amplitude. Finally, we develop a more general theory for scattering relations.

Analysis of Threshold-Induced Bias Inherent in Acoustic Scattering Cross-Section Estimates of Individual Fish

1975 ◽  
Vol 32 (12) ◽  
pp. 2547-2551 ◽  
Author(s):  
R. T. Weimer ◽  
J. E. Ehrenberg
Keyword(s):  
Cross Section ◽  
Stock Assessment ◽  
Acoustic Scattering ◽  
Operating Conditions ◽  
Scattering Cross Section ◽  
Fish Stock ◽  
Small Fish ◽  
Scattering Cross ◽  
Electronic Circuitry ◽  
Fish Stock Assessment

During acoustic fish stock assessment surveys, it is often desirable to measure the distribution of the acoustic scattering cross-section of single fish. One of the problems in such measurements is that a threshold in the electronic circuitry discriminates against small fish. This effect is analyzed in detail, and an expression is derived for the threshold-induced bias in the mean scattering cross-section estimate. Results are plotted for a typical set of operating conditions.

Acoustic Scattering Cross Sections of Smart Obstacles: A Case Study

2011 ◽  
Vol 10 (3) ◽  
pp. 672-694
Author(s):  
Lorella Fatone ◽  
Maria Cristina Recchioni ◽  
Francesco Zirilli
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Space Shuttle ◽  
Scattering Problem ◽  
Plane Waves ◽  
Acoustic Scattering ◽  
Scattering Cross Section ◽  
Scattering Cross ◽  
Scattering Cross Sections

AbstractAcoustic scattering cross sections of smart furtive obstacles are studied and discussed. A smart furtive obstacle is an obstacle that, when hit by an incoming field, avoids detection through the use of a pressure current acting on its boundary. A highly parallelizable algorithm for computing the acoustic scattering cross section of smart obstacles is developed. As a case study, this algorithm is applied to the (acoustic) scattering cross section of a “smart” (furtive) simplified version of the NASA space shuttle when hit by incoming time-harmonic plane waves, the wavelengths of which are small compared to the characteristic dimensions of the shuttle. The solution to this numerically challenging scattering problem requires the solution of systems of linear equations with many unknowns and equations. Due to the sparsity of these systems of equations, they can be stored and solved using affordable computing resources. A cross section analysis of the simplified NASA space shuttle highlights three findings: i) the smart furtive obstacle reduces the magnitude of its cross section compared to the cross section of a corresponding “passive” obstacle; ii) several wave propagation directions fail to satisfactorily respond to the smart strategy of the obstacle; iii) satisfactory furtive effects along all directions may only be obtained by using a pressure current of considerable magnitude. Numerical experiments and virtual reality applications can be found at the website: http://www.ceri.uniromal.it/ceri/zirilli/w7.

Modification of scattering of waves by central loading

1968 ◽  
Vol 46 (24) ◽  
pp. 2755-2763 ◽  
Author(s):  
Chin-Lin Chen
Keyword(s):  
Plane Wave ◽  
Cross Section ◽  
Cross Sections ◽  
Normal Incidence ◽  
Physical Explanation ◽  
Lumped Element ◽  
Scattering Cross ◽  
Back Scattering ◽  
Conducting Wire ◽  
Scattering Cross Sections

The problem of the scattering of a plane wave by a long, thin, perfectly conducting wire is studied. The scatterer is loaded at its center by a lumped element. The effects of the loading on the scattering of waves are investigated. Numerical results are obtained for the case of normal incidence. The results show that for relatively short wires, the back-scattering cross sections may be modified effectively by central loading, while for longer wires, the modification is rather difficult to achieve. To nullify the back-scattering cross section completely, it is necessary to use active loading if kh > 3.6. A physical explanation is also presented.

Diffraction of Elastic Waves by a Cylindrical Nanohole

2014 ◽  
Vol 526 ◽  
pp. 145-149 ◽  
Author(s):  
Li Wang ◽  
Pei Jun Wei ◽  
Xi Qiang Liu ◽  
Gui Zhang
Keyword(s):  
Plane Wave ◽  
Cross Section ◽  
Elastic Waves ◽  
Surface Stress ◽  
Scattering Amplitude ◽  
Expansion Method ◽  
Plane Wave Expansion ◽  
Plane Wave Expansion Method ◽  
Stress Effects ◽  
Diffraction Of Elastic Waves

Diffraction of in-plane wave and out-plane wave by a cylindrical nanohole is investigated. The surface elastic theory is used to consider the surface stress effects and to derive the boundary condition on the surface of the nanohole. The plane wave expansion method is applied to obtain the scattering waves. The scattering cross section and far-field scattering amplitude are numerically evaluated. The influences of surface stress are discussed based on the numerical results.

REALISTIC AND CORRECT MODELS OF IMPRESSED SOURCES FOR TIME-HARMONIC ELECTROMAGNETIC BOUNDARY VALUE PROBLEMS INVOLVING METAMATERIALS

2013 ◽  
Vol 04 (03) ◽  
pp. 1350012 ◽  
Author(s):  
PAOLO FERNANDES ◽  
MIRCO RAFFETTO
Keyword(s):  
Finite Element ◽  
Boundary Value Problems ◽  
Boundary Value ◽  
Numerical Noise ◽  
Time Harmonic ◽  
Effective Media ◽  
Ill Posed ◽  
Well Posed

The aim of this work is to analyze the role of the impressed sources in determining the well or ill-posedness of time harmonic electromagnetic boundary value problems involving isotropic effective media. It is shown, in particular, that, even if all interfaces are regular, the class of ill-posed problems can be very large in the presence of general square-integrable impressed sources. However, when a simple and realistic constraint is enforced on these sources, requiring that the support of the sources does not include any interface between a traditional medium and a metamaterial, among the problems here considered just those involving an interface between complementary materials remain ill-posed. These considerations have a very significant impact also on the approximability of the solution of well-posed problems since the numerical noise can introduce small fictitious sources even where the sources to be simulated are not present. These effects on finite element simulators are fully analyzed. Finally, we propose an algorithm that allows to obtain much better approximations of the solutions of the most critical well-posed problems.

Scattering of drift waves by drift vortices

1997 ◽  
Vol 58 (1) ◽  
pp. 1-10 ◽  
Author(s):  
T. A. DAVYDOVA ◽  
V. M. LASHKIN
Keyword(s):  
Scattering Amplitudes ◽  
Cross Section ◽  
Scattering Cross Section ◽  
Drift Waves ◽  
Vortex Interaction ◽  
Scattering Cross ◽  
Wide Range

The scattering of free drift waves by drift vortices is investigated analytically in the Born and eikonal approximations. Scattering amplitudes and scattering cross-section are found for a wide range of parameters of the vortex and wave. It is shown that under certain conditions the wave–vortex interaction becomes very strong; that is, the scattering cross-section is much more than the vortex radius.

The low frequency scalar diffraction by an elliptic disc

1967 ◽  
Vol 63 (4) ◽  
pp. 1273-1280 ◽  
Author(s):  
B. D. Sleeman
Keyword(s):  
Plane Wave ◽  
Cross Section ◽  
Scattered Field ◽  
Low Frequency ◽  
Field Amplitude ◽  
Wave Number ◽  
Series Expansions ◽  
Far Field ◽  
Scalar Diffraction ◽  
Scattering Cross

SummaryThe problem of scalar Dirichlet diffraction of a plane wave by an elliptic disc is discussed. A scheme is given whereby the low frequency expansion of the scattered field may be readily obtained. Series expansions are obtained for the far-field amplitude up to and including the second order in the wave number. The first two terms of the scattering cross-section are also derived.

scholarly journals The scattering of slow neutrons by ortho - and para -hydrogen

1955 ◽  
Vol 230 (1180) ◽  
pp. 19-32 ◽  
Keyword(s):  
Scattering Amplitudes ◽  
Cross Section ◽  
Cross Sections ◽  
Scattering Amplitude ◽  
Coherent Scattering ◽  
Para Hydrogen ◽  
Cavendish Laboratory ◽  
Proton Interaction ◽  
Scattering Cross Sections ◽  
Slow Neutrons

The neutron velocity selector of the Cavendish Laboratory has been used to measure the scattering cross-sections of ortho- and para -hydrogen for slow neutrons. The triplet and singlet scattering amplitudes of the neutron-proton interaction may be deduced from these cross-sections. The values obtained are a t = (0·537 ± 0·004) x 10 -12 cm, a s = -(2·373 ±0·007) x 10 -12 cm, where a t and a s are the triplet and singlet scattering amplitudes respectively. The values of the coherent scattering amplitude ƒ = 2(3/4 a +1/4 a ), and of the free proton cross-section σ ƒ = 4π(3/4 a 2 t + 1/4 a 2 s given by the above values of a t and a s , are ƒ = -(0·380 ± 0·005) x 10 -12 cm, σ ƒ = (20·41 ± 0·14) x 10 -24 cm 2 .

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