Diffraction of Cylindrical Waves by a Transmissive Half-Plane

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Yusuf Ziya Umul
Keyword(s):  
Half Plane ◽  
Acoustic Waves ◽  
High Frequency ◽  
Line Source ◽  
Geometrical Optics ◽  
Cylindrical Waves ◽  
Uniform Theory Of Diffraction ◽  
The Waves

The scattered acoustic waves by a transmissive half-plane, which is illuminated by a line source, are investigated. The high-frequency diffracted wave expressions are obtained by taking into account a resistive half-screen that is defined in electromagnetics. The uniform diffracted fields are expressed in terms of the Fresnel cylinder functions. The behavior of the waves is compared with the case when the uniform theory of diffraction is considered. The geometrical optics and diffracted fields are examined numerically.

On cylindrical waves in stratified media: high frequency refraction and diffraction at a plane interface

1970 ◽  
Vol 67 (1) ◽  
pp. 133-161 ◽  
Author(s):  
I. Roebuck
Keyword(s):  
Exact Solution ◽  
Wave Equation ◽  
High Frequency ◽  
Line Source ◽  
Dielectric Medium ◽  
Plane Interface ◽  
Stratified Media ◽  
Cylindrical Waves ◽  
Cylindrical Obstacle ◽  
High Frequency Waves

Introduction. The problem of the scattering of high-frequency waves, which emanate from a line source in a homogeneous isotropic dielectric medium and impinge upon a cylindrical obstacle, has been attacked in a variety of ways. In certain cases, where both the shape of the obstacle and the conditions to be satisfied on its boundary are particularly convenient, an exact solution may be found by separation of the wave equation (see, for example, Marcuvitz (l)), but in general some form of approximation is necessary to obtain an explicit answer.

11.—High-Frequency Scattering in a Certain Stratified Medium. The Two-part Problem

1974 ◽  
Vol 72 (2) ◽  
pp. 149-178 ◽  
Author(s):  
W. G. C. Boyd
Keyword(s):  
High Frequency ◽  
Line Source ◽  
Geometrical Optics ◽  
Incident Field ◽  
Stratified Medium ◽  
Secondary Radiation ◽  
Shadow Region ◽  
Two Dimensional ◽  
Scalar Waves ◽  
Impedance Discontinuity

SynopsisThe propagation of scalar waves in a certain two-dimensional medium is considered. The incident field, which is due to the presence of a line source, is scattered by two coupled half-planes on each of which the impedance takes a constant value. The Wiener-Hopf technique is used to find a solution which is then examined asymptotically for high frequency. It is found that there is an illuminated region in which the solution is expressed in terms of geometrical optics rays, and a shadow region in which the solution is described by creeping modes. The point of impedance discontinuity may be regarded as producing secondary radiation. The nature of this secondary radiation is quite different according as the point of impedance discontinuity lies in the illuminated or shadow region of the geometrical optics field produced by the source.

scholarly journals Crack-Length Estimation for Structural Health Monitoring Using the High-Frequency Resonances Excited by the Energy Release during Fatigue-Crack Growth

Sensors ◽  
2021 ◽  
Vol 21 (12) ◽  
pp. 4221
Author(s):  
Roshan Joseph ◽  
Hanfei Mei ◽  
Asaad Migot ◽  
Victor Giurgiutiu
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Length ◽  
Crack Growth ◽  
Health Monitoring ◽  
Acoustic Waves ◽  
High Frequency ◽  
Fem Analysis ◽  
Signal Frequency ◽  
Propagation Pattern

Acoustic waves are widely used in structural health monitoring (SHM) for detecting fatigue cracking. The strain energy released when a fatigue crack advances has the effect of exciting acoustic waves, which travel through the structures and are picked up by the sensors. Piezoelectric wafer active sensors (PWAS) can effectively sense acoustic waves due to fatigue-crack growth. Conventional acoustic-wave passive SHM, which relies on counting the number of acoustic events, cannot precisely estimate the crack length. In the present research, a novel method for estimating the crack length was proposed based on the high-frequency resonances excited in the crack by the energy released when a crack advances. In this method, a PWAS sensor was used to sense the acoustic wave signal and predict the length of the crack that generated the acoustic event. First, FEM analysis was undertaken of acoustic waves generated due to a fatigue-crack growth event on an aluminum-2024 plate. The FEM analysis was used to predict the wave propagation pattern and the acoustic signal received by the PWAS mounted at a distance of 25 mm from the crack. The analysis was carried out for crack lengths of 4 and 8 mm. The presence of the crack produced scattering of the waves generated at the crack tip; this phenomenon was observable in the wave propagation pattern and in the acoustic signals recorded at the PWAS. A study of the signal frequency spectrum revealed peaks and valleys in the spectrum that changed in frequency and amplitude as the crack length was changed from 4 to 8 mm. The number of peaks and valleys was observed to increase as the crack length increased. We suggest this peak–valley pattern in the signal frequency spectrum can be used to determine the crack length from the acoustic signal alone. An experimental investigation was performed to record the acoustic signals in crack lengths of 4 and 8 mm, and the results were found to match well with the FEM predictions.

Parametric excitation of magnetoacoustic waves by a pump magnetic field in a high-β plasma

1977 ◽  
Vol 17 (1) ◽  
pp. 93-103 ◽  
Author(s):  
N. F. Cramer
Keyword(s):  
Magnetic Field ◽  
Parametric Excitation ◽  
Acoustic Waves ◽  
Magnetic Pressure ◽  
Gas Pressure ◽  
Alfven Wave ◽  
Fast Wave ◽  
Magnetoacoustic Waves ◽  
Background Magnetic Field ◽  
The Waves

The parametric excitation of slow, intermediate (Alfvén) and fast magneto-acoustic waves by a modulated spatially non-uniform magnetic field in a plasma with a finite ratio of gas pressure to magnetic pressure is considered. The waves are excited in pairs, either pairs of the same mode, or a pair of different modes. The growth rates of the instabilities are calculated and compared with the known result for the Alfvén wave in a zero gas pressure plasma. The only waves that are found not to be excited are the slow plus fast wave pair, and the intermediate plus slow or fast wave pair (unless the waves have a component of propagation direction perpendicular to both the background magnetic field and the direction of non-uniformity of the field).

High-frequency acoustic waves are not sufficient to heat the solar chromosphere

Nature ◽  
2005 ◽  
Vol 435 (7044) ◽  
pp. 919-921 ◽  
Author(s):  
Astrid Fossum ◽  
Mats Carlsson
Keyword(s):  
Acoustic Waves ◽  
High Frequency ◽  
Solar Chromosphere
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