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 media gradually changes in non-uniform part. Due to extremely thin thickness of the indentation area, ideal ABH structures are difficult to realize and suffer from potential structural integrity problems for practical applications. This paper presents a plate-like structure with different tailored power-law-profiled indentations called imperfect two-dimensional ABH. With the new indentation profile, similar energy focalization phenomenon as the conventional ABH is produced on one hand; on the other hand stringent power-law thickness variation in ideal ABH structures can be relaxed and it overcomes the structural problems of the ideal ABH structures in a certain degree. Numerical simulation was carried out to clarify the energy focalization phenomenon, the underlying physics as well as the dependence of the focal positions on various system parameters. The evolution process of energy focalization in non-uniform part is investigated in time domain. Finally, experiments have been performed by using the laser ultrasonic scanning technique, which reconstruct the acoustic wave field in the whole area and validate phenomenon of flexural wave focalization in numerical calculations.