## 4aSA6. Scattering by elastic elliptical cylinders of different aspect ratio.

### Session: Thursday Morning, May 16

### Time: 9:30

**Author: Jacques Lanfranchi**

**Author: Gerard Maze**

**Location: Lab. d'Acoust. Ultrason. et d'Electron., LAUE URA CNRS 1373, Univ. du Havre, Pl. Robert Schuman, 76610 Le Havre, France**

**Abstract:**

The scattering of elliptical cylinders of infinite length insonified by an
incident beam perpendicular to their axis is investigated. The method of
isolation and identification of resonances (MIIR) allows one to plot resonance
spectra. These spectra are obtained from three targets characterized by their
major radius/minor radius ratio equal to 4/3, 4/2, 4/1. The resonance spectra
obtained from a circular cylinder excited in the same conditions show peaks
related to circumferential waves which, for particular frequencies, constitute
standing waves. In this case, the phase velocity depends only on the frequency.
Contrary to the circular cylinder, resonance spectra obtained by an experimental
monostatic method depend on the azimuthal position of the transducer. Some
resonances vanish at certain positions. In this case, the phase velocity and the
coupling coefficient are a function of the curvature radius and the frequency.
The wavelength is not identical on the circumference of the elliptical cylinder.
To explain the experimental results, a phase-matching model is developed to
determine the resonance frequencies [H. Uberall et al., J. Acoust. Soc. Am. 81,
312--315 (1987)]. This method allows one to represent the vibration state on the
circumference. An integral calculus applied on the latter result gives the
far-field pressure.

from ASA 131st Meeting, Indianapolis, May 1996