Periodic plates with tunneled Acoustic-Black-Holes for directional band gap generation

Research in Acoustic Black Holes (ABHs) attracts increasing interests for its potential applications in vibration control. ABH effect features the energy focalization of flexural waves within a confined area inside a structure with a reducing power-law profiled thickness. With conventional design of ABH structures, however, systematic broadband ABH effects can only be achieved at relatively high frequencies while the mid-to-low frequency application can hardly be envisaged without prohibitively large ABH dimensions. We propose a kind of periodic plates carved inside with tunneled ABHs to achieve directional broad band gaps for flexural waves at mid-to-low frequencies. Analyses on the band structures and mode shapes show the generation of the band gaps through locally resonant effects of the ABH cells. With additional strengthening studs connecting the two ABH branches, Bragg scattering is produced due to its large impedance mismatch with the residual thickness of ABH profile. With the two effects combined, wide band gaps are achieved over a large frequency range for flexural waves travelling along the direction perpendicular to the tunneled ABHs. Both numerical and experimental results show significant attenuation gaps in finite plates with only three ABH cells. The proposed periodic plates with 1D tunneled ABHs and strengthening studs point at potential applications in wave filtering and vibration isolation applications.