Wiederhold Curtis P, Sounas Dimitrios L, Alù Andrea
Department of Mechanical Engineering, The University of Texas at Austin, Austin, Texas 78712, USA.
Department of Electrical and Computer Engineering, The University of Texas at Austin, 1 University Station C0803, Austin, Texas 78712, USA.
J Acoust Soc Am. 2019 Jul;146(1):802. doi: 10.1121/1.5115018.
Isolators, devices with unidirectional wave transmission, are integral components in computing networks, enabling a one-way division of a large system into independent subunits. Isolators are created by breaking the inversion symmetry between a source and a receiver, known as reciprocity. In acoustics, a steady flow of the background medium in which sound travels can break reciprocity, but significant isolation is typically achieved only for large, often impractical speeds. This article proposes acoustic isolator designs enabled by duct flow that do not require large flow velocities. A basic isolator design is simulated based on the acoustic analogue of a Mach-Zehnder interferometer, with monomodal entry and exit ports. The simulated device footprint is then reduced by using bimodal ports. Further, a nonuniform velocity profile combined with a grating to induce phononic transitions is considered, which, combined with filters, can provide significant isolation. By coupling a waveguide with flow to free space through an array of small apertures, largely nonreciprocal leaky-wave radiation is demonstrated, breaking the symmetry between reception and transmission patterns of an acoustic linear aperture array. These investigations open interesting pathways towards efficient acoustic isolation, which may be translated into integrated acoustic and surface acoustic waves, as well as phononic technology.
隔离器，即具有单向波传输功能的器件，是计算网络中的重要组件，能将大型系统单向划分为独立的子单元。隔离器是通过打破源与接收器之间的反转对称性（即互易性）来实现的。在声学中，声音传播所依赖的背景介质的稳定流动会破坏互易性，但通常只有在极高的、往往不切实际的速度下才能实现显著的隔离效果。本文提出了由管道流实现的声学隔离器设计，该设计不需要大的流速。基于马赫 - 曾德尔干涉仪的声学模拟，设计了一种具有单模入口和出口端口的基本隔离器。然后通过使用双模端口减小了模拟器件的尺寸。此外，还考虑了结合光栅以诱导声子跃迁的非均匀速度分布，其与滤波器相结合可提供显著的隔离效果。通过一系列小孔将带有流动的波导与自由空间耦合，展示了基本上非互易的漏波辐射，打破了声学线性孔径阵列接收和传输模式之间的对称性。这些研究为实现高效声学隔离开辟了有趣的途径，这可能会转化为集成声波和表面声波以及声子技术。
