Ultra-wide Band Gaps in Periodic Beams with Multi-acoustic Black Holes Indentations

The acoustic black hole (ABH) effect can reduce structural vibrations by efficiently trapping flexural waves. Phononic crystals (Pcs) are artificial materials with a periodic structure that can create stopbands on the propagation of elastic waves. However, even Pcs with ABH structures have difficulty in solving the problem of needing impractical large dimensions or extremely thin truncation to attain low-frequency band gaps. In this paper, a type of ABH beam coupled with additional ABH profile of studs is proposed to achieve ultra-wide band gaps at low and medium frequencies by incorporating the local resonance effect and Bragg scattering effect as well as the wave aggregation effect of ABH studs. By varying the length of the ABH studs, the band gap can be adjusted up to 87% of the entire frequency range of interest. The results show that the beam can achieve significant vibration attenuation at the low and medium frequencies with only three units. Meanwhile, the structure has a flat appearance and is easy to process, which makes it highly promising in the applications of vibration control.