ÉTUDE EXPÉRIMENTALE DE LA DIFFRACTION ACOUSTIQUE PAR UNE CIBLE RIGIDE : CYLINDRE TERMINÉ PAR DEUX HÉMISPHÈRES

Abstract
This study was carried out with the aim of bringing some experimental results to valid theorical results [1] computed with programmes using the 'Geometrical Theory of Diffraction' [2]. A bistatic geometry is used, a broadband sphérical impulsive wave impinges on the rigid target in air. At a distance r=10a (a : characteristic parameter of the target), the signal of the diffracted wave is measured. After signal processing (time averaging, time filtering, FFT, ...) one can observe, for several geometries : -The signal of the diffracted wave : It consists of the reflected wave and also of a main creeping wave which can be shown. For particular geometries, a secondary creeping wave coming from the hemispheres and a weak echo due to the discontinuity of curvature can be isolated. -The frequency responses : They are carried out for [MATH], [MATH] ; from these, diagrams of scattering of sound are deduced. The time filtering enables us to get the 'reflection coefficient of the target' . Analysis of the results shows the importance of creeping waves and also of echos dues to the discontinuity in curvatuve.