Impaired sound radiation in plates with periodic tunneled Acoustic Black Holes

Acoustic Black Hole (ABH) effects offer remarkable possibilities to manipulate bending waves inside light weight structures. The effective frequency range of conventional ABH structures, however, is limited by the so-called characteristic/cut-on frequency, only above which can systematic ABH effects be systematically obtained, which seriously hampers practical applications. In this paper, plates with periodic tunneled double-leaf ABHs are studied to achieve reduced sound radiation in the low frequency range below the characteristic frequency. Upon showing the band structure of an infinite ABH lattice, the vibration and sound radiation of a finite plate with four ABH cells are investigated through FE analyses after experimental validations of the model. Results show that, apart from the expected ABH-induced benefit at high frequencies with damping treatment, it is also possible to draw acoustic benefit in the low frequency range, which is far below the characteristic frequency of the structure. It is shown that, within the ABH-induced locally resonant band gaps, the designed plates exhibit low sound radiation without additional damping treatment. Supersonic intensity and wavenumber analyses confirm that the observed phenomena are attributed to the impaired sound radiation efficiency generated by the ABH-induced high energy localization inside the inactive sound radiation regions of the plate, alongside a structural wavenumber and vibration energy transport effect from supersonic to subsonic components when comparing to a uniform plate.