Flexural wave focalization in plates with imperfect two-dimensional acoustic black hole

Acoustic Black Hole (ABH) in thin-walled structures has been proved remarkably useful for broadband flexural wave focalization, in which the thickness profile or refractive index of the media gradually changes in the non-uniform part. Due to the extremely thin thickness of the indentation area, the ideal ABH effect will adversely be affected by geometrical and manufacturing uncertainties. This paper presents a plate-like structure with different tailored power-law-profiled indentations called imperfect two-dimensional ABH structures. With the new indentation profile, similar energy focalization phenomenon as the conventional ABH structure is produced on one hand; on the other hand, the stringent power-law thickness variation in ideal ABH structures can be relaxed, thus overcoming the structural problems of the ideal ABH structures to a certain extent. Numerical simulations were carried out to clarify the energy focalization phenomenon, the underlying physics as well as the evolution process of energy focalization in the non-uniform part in time domain. Finally, experiments were performed by using the laser ultrasonic scanning technique, which reconstructs the acoustic wave field in the whole area and validates the phenomenon of flexural wave focalization revealed in numerical simulations.