Wave energy control using asymmetric dual acoustic black holes with width variation

The acoustic black hole (ABH), a wedge-type structure with power-law thickness, has been developed for light-weight vibration damping in thin structures. Recently, a space efficient concept of a spiral ABH was reported based on a geometrical modification on the ABH baseline into the spiral shape. In this study, we propose another two simple modifications and investigate advantages of using the modified ABHs. One of the modifications is attaching dual ABHs to a beam, which results in enhancement of the damping performance compared to the conventional case of the single ABH. The other is gradually decreasing the width-profile of the ABH to zero towards the ABH tip, and the width-varying ABH focalize the elastic waves near the tip with higher energy density than that of the standard ABH. Numerical results show that the resonant peaks of vibration response in the dual ABHs case are reduced up to 4.3 dB compared to the single ABH case. In addition, the damping performance of the dual ABHs can be more increased by making a difference in the ABH length between the dual ABHs. In the case of the width-varying ABH, the highly focused waves are near-perfectly attenuated by only a small amount of damping material and it could achieve damping performance similar to the standard one, so the installation weigth of the ABH can be saved by modifying the width-profile. When we utilize the width-varying ABH for vibration amplification, the vibration response in a beam only are increased up to 30.1 dB, indicating that the width-varying ABH can be applied to ultra-sensitive vibration detection by focalizing the elastic waves in the original structure into the ABH tip.