Free-layer damping influence on the evanescent wave in a strip containing periodic acoustic black holes

Abstract

This work demonstrates the transformation of wave motions in a periodic two-dimensional (2D) ABH structure with one-dimensional (1D) lattice subject to the damping dissipation. The free-layer damping (FLD) treatment is employed to achieve the damping dissipation. Numerical results, alongside analyses based on the local dispersion relation model, expose the effect of dissipation on bandgap (BG), which is always accompanied by the ABH-featured local resonance. Analyses show that the dissipative periodic ABH strip enables comparable attenuation intensity as that in its corresponding non-dissipation periodic ABH strip due to fact that the periodic ABH strip has two types of BG: (i) one shows infinite group velocity and constant lattice phase; (ii) another is accompanied by the discontinuous dispersion curves for the same flexural wave. The minimal attenuation inside these two BGs is less affected by the dissipation level. The discontinuity phenomenon inside the BG is attributed to the coupling between different flexural wave evanescent modes. As a result, the reduction of minimal attenuation inside the BG is less sensitive to the dissipation level. This attenuation variation subject to the damping dissipation inside the BG is distinguished from the weakened attenuation in traditional local resonance BG, in which there always exists a phase jump by π/a. Along with the ABH-enhanced dissipation, the dissipative periodic ABH strip enables broadband attenuation by inducing wide complex waves, while obtaining considerable attenuation intensity.