Realization of Subwavelength Asymmetric Acoustic Transmission Based on Low-Frequency Forbidden Transmission

Asymmetric transmission devices that allow acoustic waves to propagate only along one direction receive significant attention because of the rich physics and many potential applications. However, most proposed designs, such as acoustic superlattices and nonlinear acoustic diodes, are much larger than the wavelength, which are impractical for aqueous applications that require unidirectionality at low frequencies. In this work, subwavelength asymmetric acoustic transmission (SAAT) is realized based on low-frequency forbidden transmission of solid-fluid acoustic superlattices. Our design is comprised of a 1D superlattice serving as a low-frequency forbidden transmitter and a periodic rectangular grating serving as the wave-front converter. The SAAT structure and superlattice constant are only 0.6λ and 0.128λ, respectively, where λ is the wavelength, while a very high rectifying efficiency of over 108 is achieved. This SAAT design breaks the size-wavelength limitation to allow unidirectional low-frequency acoustic wave transmissions, which is desirable for the miniaturization of integrated acoustic devices in unidirectional signal-transmission applications.