Experimental investigation of damping flexural vibrations in plates containing tapered indentations of power-law profile

In the present paper, experimental results are reported on damping flexural vibrations in rectangular plates containing tapered indentations (pits) of power-law profile, with the centres of the indentations covered by a small amount of absorbing material. In the case of quadratic or higher-order profiles, such indentations materialise two-dimensional acoustic ‘black holes’ for flexural waves that can absorb almost 100% of the incident elastic energy. In the present investigation, pits have been made in different locations of rectangular plates, and the corresponding frequency response functions have been measured. It has been found that basic power-law indentations, with no or very small central hole, result in rather low reduction in resonant peak amplitudes, which may be due to the relatively small effective absorption area in this case. To increase the damping efficiency of power-law profiled indentations, this absorption area 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. When multiple indentations are used, the resultant damping increases substantially, as expected, and may become comparable if not greater than that achieved by one-dimensional wedges of power-law profile.