Scattering and wave-blocking characteristics of composite ABHs in steel plate

Drawing upon the advantages of lightweight nature and highly efficient energy harvesting capabilities, acoustic black holes (ABHs) serve as local resonator units with significant potential in constructing phononic plates. In this paper, we introduce a novel composite ABH structure made of different materials, and extends this composite concept to the infinite plate model. Analytical results reveal that the composite ABH exhibits a stronger local resonance effect and more localized trapped modes compared to traditional homogeneous types. By employing linear algebraic equation systems derived from boundary conditions and utilizing the closed-form solutions of the varying-thickness Kirchhoff plate, we compare the wave propagating behaviors of different ABH scatterers. Numerical results highlight that the enhanced trapped modes resulting from material inhomogeneity lead to more pronounced peaks in scattering energy. Moreover, we address the multiple scattering problem for composite ABH array in the infinite plate using the T-matrix relationship between the scattering and exciting energy. Displacement spectra and wave field results demonstrate that the larger impedance mismatch and increased interaction caused by periodic composite ABHs in the plate result in more effective vibration isolation. Our discussion on array configurations concludes that the ABH square array, incorporating both rows and columns, produces a significant bandgap for flexural vibration, while also expanding the larger and more efficient vibration-attenuated region.