INFLUENCE OF SURFACE ROUGHNESS ON AXIAL ACOUSTIC ENERGY DISTRIBUTION IN A PARABOLIC REFLECTOR
INFLUENCE OF SURFACE ROUGHNESS ON AXIAL ACOUSTIC ENERGY DISTRIBUTION IN A PARABOLIC REFLECTOR

Summary/Abstract: This paper analyzes the effect of surface roughness of an acoustic parabolic reflector on the scattering of acoustic energy outside the focal region. First, a formulation for calculating the gain of a parabolic reflector is presented as a function of its geometrical parameters, including the reflector depth H, aperture radius R, and focal position zF. The gain is then evaluated as a function of the acoustic wavelength λ for reflectors constructed in the courtyard of the Academy of Technical and Educational Applied Studies in Niš, Serbia. The reflecting surface of the reflector is not smooth but rough, which leads to a degradation of acoustic energy concentration E at the focus, i.e., to increased scattering of acoustic energy along the axial z-direction. In the second part of the paper, an experiment is described in which the spatial distribution of acoustic energy E(zi) is determined from measurements of acoustic impulse responses along the z-axis. Subsequently, by applying statistical parameters (the energy centroid zeff, standard deviation σ, position of the maximum zmax, full width at half maximum (FWHM), focusing efficiency η, and entropy H) the influence of surface roughness on the scattering of acoustic energy outside the focal region is quantified.

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