Enhanced acoustic black hole effect using a modified thickness profile

The phenomenon of Acoustics Black Hole (ABH) takes place when bending waves propagate inside a think-walled structure with a power-law thickness profile. The phenomenon as well as its application potential in vibration damping enhancement, noise control and energy harvesting has also been demonstrated theoretically and experimentally by recent research. However, manufacturing an ideally tailored power-law profile can hardly be achieved in practice. The unavoidable truncation at the wedge tips of the structure can significantly weaken the ABH effect. On the premise of the minimum achievable truncation thickness by current manufacturing technology, ways to ensure and achieve better ABH effect need to be explored. In this paper, we investigate this issue using a previously developed wavelet-decomposed semi-analytical model on an Euler-Bernoulli beam with a modified power-law profile. As a continuation of the previous work, the model was first validated experimentally using a truncated conventional ABH profile. Then, the modified thickness profile is numerically investigated in terms of system loss factor and energy distribution. Compared with the conventional thickness profile with the same truncated wedge tip, it is shown that the modified thickness profile, along with the use of an extended plateau at the wedge tip, brings about a systematic increase in the ABH effect at mid-to-high frequencies, whilst providing rooms for possible low frequency applications.