Abstract
Much effort has been devoted to exploring asymmetric acoustic/elastic-wave transmission in various structural designs. However, the propagation unidirectionality is normally confined to a narrow frequency band. This work presents the development of a dissipative diatomic acoustic metamaterial with dual resonators to realize asymmetric elastic-wave transmission in multiple broadband ranges. We theoretically, numerically, and experimentally investigate the effect of damping on the asymmetric wave transmission. A systematic analytical discussion shows that the frequency bandwidths of asymmetric transmission regions can be significantly enlarged by the merging effect of dissipative dashpots. Numerical verifications are conducted using both mass-spring-damper lattice system and continuum models, and excellent agreements are obtained. We further observe the asymmetric elastic-wave transmission in the proposed dissipative metamaterial structure experimentally. Transient wave responses in time and frequency domains are also investigated. The enlarged asymmetric transmission bands can be analytically predicted and mathematically controlled by carefully designing and deliberately selecting the unit size parameters and material properties. This work could be potentially beneficial for applications in elastic-wave control and directional transmission devices.