Elastic Wave Modulation of Metamaterial Beams in Bidirectional Asymmetric Acoustic Black Holes: Finite Element Method and Experiment

Purpose Acoustic black hole (ABH) is a passive vibration damping technique that can efficiently mitigate vibrations in beam structures. However, the bandgap performance in most conventional periodic ABH structures is constrained to the flexural direction, and the unit cell possesses a single symmetric configuration. Therefore, this paper proposes a bidirectional asymmetric ABH metamaterial beam to investigate its bandgap characteristics in both the flexural and longitudinal directions. Method The finite element method was employed to predict the bandgap structure of the bidirectional asymmetric ABH metamaterial beam in various directions, along with the attenuation of evanescent waves within the bandgaps, which was subsequently validated by experimental results. Additionally, the influence of geometric parameters and material damping on the bandgap performance of this metamaterial beam was also examined. Results The results suggest that, compared to conventional unidirectional metamaterial beams, this metamaterial beam exhibits a wider unidirectional bandgap, several comparatively broader complete bandgaps, and a higher evanescent wave attenuation factor. The formation of flexural bandgaps can be attributed to the combined effects of the ABH effect and Bragg scattering, whereas the formation of longitudinal bandgaps results solely from the Bragg scattering effect. It was further observed that the formation of complete bandgaps arises from the coupling and decoupling of these two effects. Parametric analysis demonstrates that tunable bandgaps in various directions can be realized through uniform changes in geometric parameters. Material damping has a negligible effect on bandwidth but significantly improves the attenuation of flexural waves, while having only a minor influence on the attenuation of longitudinal waves. Conclusion Numerical analysis and experimental results demonstrate the superior vibration damping performance of this metamaterial beam in both the flexural and longitudinal directions. The proposed structure could provide a novel perspective on the design of multi-directional vibration beams.