2016年3月10日，我实验室张宇教授课题组在物理学领域TOP期刊PRA(Physical Review Applied，ISSN:2331-7019, IF:4.06，物理类1区) 发表了题为“Realization of Subwavelength Asymmetric Acoustic Transmission Based on Low-Frequency Forbidden Transmission”的研究论文。论文第一作者和通讯作者单位均为水声通信与海洋信息技术教育部重点实验室。
该论文设计了由一维周期性流固声栅和第II 类流固超晶格耦合而成的水声非对称传输亚波长结构，并分析了该亚波长结构实现水声非对称传输效应的物理机制。研究表明，当声波以特定入射角度从声栅结构一侧入射时，声栅引起低频声波衍射，衍射波的波矢方向偏离入射波方向进入流固超晶格的第一通带，形成正向导通；当声波从第II 类流固超晶格一侧以同样角度入射时，入射波受流固超晶格低频禁带传输效应的影响，无法激发固体板中的低频S0 模式，形成反向截止。此外，论文从实验角度证实了提出的亚波长结构具有明显的非对称传输效应。
论文的第一作者为张宇教授指导的博士研究生张赛，合作者包括美国宾夕法尼亚大学的曹文武教授等，作为一项跨机构的研究工作，该研究还得到了国家自然科学基金(41276040)和福建自然科学基金(2012J06010)的大力资助。
此项最新研究成果的发表标志着张宇教授课题组在超材料研究及国际化合作方面取得重要进展。其中，水声亚波长结构的非对称传输效应研究为研制小型化和集成化水声能流控制结构奠定了理论基础，具有潜在的科学意义及应用价值，不仅有利于提升我水声部重实验室的学术影响力，同时能推动该领域日后相关研究工作的有力开展。
Figure 1. (a) The schematic illustration of the SAAT device. The FI and BI are indicated by arrows. The wavelength of the incident acoustic wave is much larger than the thickness of the structure. (b) Schematic presentation of a unit cell of the SAAT structure. (c) Three-dimensional illustration of the SAAT structure.
Figure 2. Transmission coefficient as a function of frequency and incident angle of the four-layered PMMA-water SL. Low-frequency forbidden transmission is indicated by the arrow. For reference, the first Bragg band gap of the superlattice for normal incidence is also shown.
Figure 3. (a),(b) Simulated acoustic pressure and displacement distributions for the BI and FI cases at the frequency of 65 kHz. Dashed black hollow arrows indicate the propagation directions. (c),(d) show the pressure distributions at y=0.002 m.
Abstract: 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.
Citation：Zhang S, Zhang Y, Guo Y, et al. Realization of Subwavelength Asymmetric Acoustic Transmission Based on Low-Frequency Forbidden Transmission[J]. Physical Review Applied, 2016, 5(3).
Link to full text：http://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.5.034006
