Accession Number:

ADA171220

Title:

Effects of Strong Diffraction on the Focusing and Scattering of Acoustic Waves.

Descriptive Note:

Technical rept.,

Corporate Author:

PENNSYLVANIA STATE UNIV UNIVERSITY PARK APPLIED RESEARCH LAB

Personal Author(s):

• Gabrielson,T. B.
• McDaniel,S. T.
• Thomson,D. W.

Report Date:

1986-06-01

Pagination or Media Count:

164.0

Abstract:

In many wave propagation problems, diffraction is considered to be a second order effect that diffuses the sharp shadows and focal surfaces predicted by ray theory. However, if the frequency is low enough so that the wavelength is comparable to the size of the focusing region, structured fields of significant level can be found in classical shadows and smooth, featureless enhancement can replace the sharp, multiple convergences common at higher frequencies. This study examines the effects of strong diffraction on refractive focusing of acoustic waves. In addition, signal fluctuations caused by perturbations of the refractive index are considered where the spatial extent of a particular perturbation patch is comparable to the wavelength. Consequently, the perturbation mechanism is primarily diffractive also.

Descriptors:

• *ACOUSTIC WAVES
• *DIFFRACTION ANALYSIS
• TIME DEPENDENCE
• REFRACTIVE INDEX
• EIGENVALUES
• FINITE DIFFERENCE THEORY
• ASYMPTOTIC SERIES
• FOCUSING
• RAY TRACING
• UNDERWATER ACOUSTICS
• SHADOWS
• CAUSTICS

Subject Categories:

• Acoustics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE