Experimental evidence of the acoustic black hole effect for flexural waves in tapered plates

A new efficient method of reducing edge reflections of flexural waves in plates or bars based on the 'acoustic black hole effect' has been recently proposed and described theoretically by one of the present authors [1] (see also [2-4]). The method utilises a gradual change in thickness of a plate or bar, partly covered by thin damping layers, from the value corresponding to the thickness of the basic plate or bar (which is to be damped) to almost zero. The present paper describes the results of the experimental investigation of the damping system consisting of a steel plate (wedge) of quadratic shape covered on one side by a strip of absorbing layer. The results of the measurements of point mobility in such a system show that for the wedge covered by an absorbing layer there is a significant reduction of resonant peaks, in comparison with the uncovered wedge or with the covered plate of constant thickness. Thus, the measurements confirm the existence of the acoustic black hole effect for flexural waves and demonstrate the possibility of its use in practice.