Tunable low-frequency broadband metamaterial beams composed of hierarchical annular cantilevers

Abstract

Tuning the resonance frequency of the local resonators in an active way and obtaining a broad bandgap at low frequency is a long-lasting challenge for traditional elastic metamaterials. This work proposes a kind of tunable metamaterial beam to isolate flexural waves, which are composed of hierarchical annular cantilevers with a steel mass block embedded in the center of each unit cell. To obtain a broad low-frequency bandgap, a genetic algorithm-based size optimization is utilized to determine the optimal geometry parameters of the unit cell. The tunability of the metamaterial beam is realized by attaching different numbers of permanent magnets to the embedded mass block. Such a tuning approach makes the change of the resonator’s mass available. Moreover, based on the rainbow effect, ultra-broadband flexural wave attenuation is realized by forming a gradient metamaterial beam. Both numerical and experimental results verify the good flexural wave attenuation ability of our proposed tunable metamaterial beam.