Wave attenuation of a laminated acoustic black hole array in a load-bearing beam structure

Acoustic Black Hole (ABH) is a wedged taper in thin-walled structures that allows for a smooth and progressive retarding of bending wave speed. However, the application of ABH structures is mainly restricted by its inherent flaw, that is the impaired structural strength by digging holes. To this end, we reinvestigate the ABH concept to propose a compound layout conducive to both wave attenuation and load-bearing capacity. First, the void created by two ABH branches in a periodic double-leaf beam is filled with acoustically soft materials to retain the structural topology continuity. Based on the Rayleigh-Ritz method, a semi-analytical model considering the shear strain of the soft filler is then presented for bandgap computation and validated against finite element simulations. It is shown that the soft filler in the filled-ABH lattice could not only widen bandgaps below the characteristic frequency of ABH, but also preserve the structural bearing ability. Transmission spectra further indicate that reducing the ABH spacing will benefit to the local resonance of composite area, and the shape of ABH profile can be used to improve the broadband attenuation. We expect that this research promotes the engineering application of ABHs in vibration suppression dealing with the sub-wavelength frequencies.