Often, propagation of energy fluxes in conventional materials and structures is normally reciprocal and symmetric. Consequently, much effort has been devoted to exploring asymmetric acoustic/elastic-wave transmission in various structural designs. In addition, asymmetric manipulation of acoustic/elastic waves has attracted much attention due to the challenging one-way acoustic/elastic-wave transmission, as well as enormous application potential for various practical scenarios. As of now, various approaches have been proposed to realize asymmetric acoustic/elastic wave transmission. Based on whether an external energy is needed, these methods can be classified, in general, into two categories: active and passive designs.
A review of the existing plethora of literature shows that the propagation unidirectionality is normally confined to a narrow frequency band. Moreover, the frequency bandwidths for asymmetric transmission in such structures are normally confined to narrow frequency ranges, and the possibility to realize asymmetric elastic-wave transmission in multiple broadband frequency regions still needs more exploration.
A closer look on this topic reveals that very little has been published about the systematic study of damping effect on asymmetric wave transmission. In this view, Professor Bing Li at Northwestern Polytechnical University together University of Akron scientists, Professor K.T. Tan, Dr. Sagr Alamri, Dr. Garrett Mchugh and Professor Nicholas Garafolo developed a dissipative diatomic acoustic metamaterial with dual resonators with the aim being to realize asymmetric elastic-wave transmission in multiple broadband ranges. To be specific, the researchers focused on developing a dissipative acoustic metamaterial with diatomic resonators for broadband asymmetric elastic-wave propagation. This work is currently published in the research journal, Journal of Sound and Vibration.
To begin with, the team theoretically, numerically, and experimentally investigated the effect of damping on the asymmetric wave transmission. Further, numerical verifications were conducted using both mass-spring-damper lattice system and continuum models, and excellent agreements were obtained. Eventually, transient wave responses in time and frequency domains were also investigated.
The researchers reported that a systematic analytical discussion revealed that the frequency bandwidths of asymmetric transmission regions could be significantly enlarged by the merging effect of dissipative dashpots. Moreover, they further observed the asymmetric elastic-wave transmission in the proposed dissipative metamaterial structure experimentally. Of much importance, they highlighted that the enlarged asymmetric transmission bands could be analytically predicted and mathematically controlled by carefully designing and deliberately selecting the unit size parameters and material properties.
In summary, the study presented the in-depth assessment of the proposed dissipative diatomic acoustic metamaterial with dual resonators. Generally, the researchers noted that there was a specific damping range over which the ATB bandwidths could be increased. Overall, in an interview with Advances in Engineering, Professor Bing Li emphasized on how their work could be beneficial for a slew of applications in elastic-wave control and directional transmission devices.
Sagr Alamri, Bing Li, Garrett Mchugh, Nicholas Garafolo, K.T. Tan. Dissipative diatomic acoustic metamaterials for broadband asymmetric elastic-wave transmission. Journal of Sound and Vibration, volume 451 (2019) page 120-137.Go To Journal of Sound and Vibration