3D-printed meta-slab for focusing flexural waves in broadband

Focusing of elastic waves by meta-structures is of considerable significance in energy harvesting. However, meeting both high transmission and wide bandwidth for these meta-structures is a challenge. In this paper, we propose a 3D-printed meta-slab with shuttle-like subunits with gradually varying thickness to focus incident flexural waves in broadband. Shuttle-like subunits have high transmission performance and frequency-dependent phase shifts. Based on these subunits, the meta-slab is designed by the mechanism of phase compensation, which makes the focal position unchanged with the incident frequencies. The wave fields of the transmitted region are obtained by the phased array theory and measured by the experiments. Their results are consistent and demonstrate well the focus ability of the meta-slab. Our design effectively concentrates the energy of broadband flexural waves, providing a new approach for energy harvesting.