Analysis on sound absorption in Sonic Black Holes

Exploration of Acoustic black holes (ABHs) for sound wave manipulation is referred to as Sonic black holes (SBHs). Different from the ideal SBH structure with continuously varied wave propagation boundary formed by putting extensive number of rings inside, the wave trapping and energy dissipation mechanism of practically realized SBH structure with discrete varied wave propagation boundary formed by quite limited number of rings inside are still not clear. To fill the gap, finite element simulations are performed to assess the sound absorption performance of a practical discrete SBH structure and explore the sound absorption mechanism behind. The validity of the FEM results is demonstrated through comparisons with experimental data obtained through impedance tube tests. Analyses reveal that the physical mechanism underpinning the sound absorption of practically realized SBH device is attributed to the combined effects of the ABH-induced wave speed changes, energy trapping and the spatially graded local resonances of series cavities formed by the space between two adjacent rings. While shedding light on the underlying sound attenuation mechanism, studies provide guidelines for further investigations on SBH structures.