Angle-dependent broadband asymmetric acoustic transmission in a planar device

Asymmetric manipulation of acoustic transmission is of fundamental interest for wave physics, and has attracted rapidly-growing attentions owing to the potential applications in diverse scenarios. Here we propose to realize angle-dependent asymmetric acoustic transmission by designing a planar structure comprising a gradient-index layer and a layer of homogeneous medium with relatively-lower index. We analytically derive the working frequency and angle range of the device with unidirectional mechanism. And the simulated results show that the proposed device gives rise to high-efficiency broadband asymmetric transmission by allowing acoustic waves normally incident on one side to pass, while behaving as an acoustic barrier blocking waves obliquely incoming from both directions as angle of incidence exceeds a critical angle. Bearing the advantages of simple design, broad bandwidth and switchable functionality, our scheme opens a route to the design of novel acoustic devices capable of adapting various circumstances, and may find applications in noise control, medical detection, etc.