Subwavelength asymmetric transmission device for underwater acoustic waves with multiple incident directions

Abstract

Asymmetric acoustic transmission devices with less restrictions on incident waves, i.e. incident direction and wavelength, are an inevitable trend of its future development. In this study, we reveal the mechanism for the subwavelength asymmetric transmission for underwater sound with multiple incident directions in an assembly system, constituting of a cascade solid-fluid superlattice coupled with an acoustic grating (AG) immersed in water. Theoretical analysis and numerical simulations verified that acoustic waves are almost totally reflected for negative incidence with multiple incident directions, while having a high transmission for positive cases. Moreover, our design can work within a remarkable broad bandwidth and possesses a preserved waveform in the subwavelength region. The unique feature is attributed to the extraordinary ultra-wide forbidden transmission of the cascade structure, as well as the diffraction effect of AG at low frequencies. The perfect subwavelength performance of our design suggests its potential practical application in underwater communication and signal transmission.