Experimental investigation of damping flexural vibrations using two-dimensional acoustic ‘black holes’

In the present paper, we report the results of the experimental investigation of damping flexural vibrations in rectangular plates containing tapered indentations (pits) of power-law profile, with the addition of a small amount of absorbing material. In the case of quadratic or higher-order profiles, such indentations materialise two-dimensional ‘black holes’ for flexural waves. In the present investigation, pits have been made in different locations of rectangular plates. It has been found that basic power-law indentations that are just protruding over the opposite surface cause rather small reduction in resonant peak amplitudes, which may be due to their relatively small absorption crossection. To increase damping in the present investigation, the absorption crossection has been enlarged by increasing the size of the central hole in the pit, while keeping the edges sharp. As expected, such pits, being in fact curved power-law wedges, result in substantially increased damping comparable with that achieved by one-dimensional wedges of powerlaw profile.