1D Phononic Lattice with Periodic Compound Acoustic Black Hole Indentations for the Generation of Ultra-wide Energy Attenuation Bands

The Acoustics Black Hole (ABH) effect exhibits unique features in vibrational energy focalization and structural damping enhancement. The phenomenon, proven both theoretically and experimentally, occurs during the bending wave propagation in a thin-walled structure with its thickness tailored according to a power-law variation. Most of previous work mainly focuses on elementary ABH configurations with conventional single layer ABH indentations, which inevitably suffers from the inherent structural strength problem to suit practical applications. In this paper, we investigate the flexural vibrations of beams with periodically embedded compound double-leaf ABH indentations. While ensuring the structural integrity and enhancing the structural strength, the proposed 1D lattice is shown to produce the duel effect of local resonances and Bragg scattering, resulting in exceptionally broad band gaps in a lattice of infinite length. Both finite element analyses and experimental results show that, with only a few elements embedded in a beam of finite length, considerable energy attenuation can be achieved within an ultra-broad frequency band, starting from low frequencies. With the use of an additional strengthening stud to connect the two ABH branches, the attenuation bands can cover as much as 90% of the entire frequency range of interest. Meanwhile, the maximum attenuation bands as well as their frequency locations can be tuned through adjusting various ABH parameters and the length of the strengthening stud. With its improved structural property and high energy attenuation performance, the proposed configuration shows promise for various vibration control applications.