Acoustic black hole duct with damping material

Abstract

Acoustic black holes have a tapering thickness profile to create the idealized phenomenon of zero reflection and transmission. The phenomenon entails wave propagation in an ideal medium where the profile tapers according to the power law shortening the wavelength and decreasing the wave speed. Consequently, the wave’s travel time tends to infinity so that the wave never reaches the end of the acoustic black hole and cannot be reflected or transmitted. For the application of a duct, thin annular rings of inner radii decrease with the power law to control pressure levels. An infinite number of rings and a final cross sectional area of zero is needed to create the ideal case and is impossible to manufacture. A common method to compensate for imperfections is to use damping material, such as in the experiment [El-Ouahabi et al, in International Conference InterNoise 2015 (2015)], though their results did not show that adding damping to the termination made an improvement. This work aims to find which areas of the acoustic black hole duct are most beneficial to add damping to in order to reduce the reflection and transmission coefficients by measuring the properties of different damping configurations. [Approved for Public Release Distribution Statement A.]