We present the concept of a feedback-based topological acoustic metamaterial as a tool for realizing autonomous and active guiding of sound beams along arbitrary curved paths in free two-dimensional space. The metamaterial building blocks are acoustic transducers, embedded in a slab waveguide. The transducers generate a desired dispersion profile in closed-loop by processing real-time pressure field measurements through preprogrammed controllers. In particular, the metamaterial can be programmed to exhibit analogies of quantum topological wave phenomena, which enables unconventional and exceptionally robust sound beam guiding. As an example, we realize the quantum valley Hall effect by creating, using a collocated pressure feedback, an alternating acoustic impedance pattern across the waveguide. The pattern is traversed by artificial trajectories of different shapes, which are reconfigurable in real-time. Due to topological protection, the sound waves between the plates remain localized on the trajectories, and do not back-scatter by the sharp corners or imperfections in the design. The feedback-based design can be used to realize arbitrary physical interactions in the metamaterial, including non-local, nonlinear, time-dependent, or non-reciprocal couplings, paving the way to new unconventional acoustic wave guiding on the same reprogrammable platform. We then present a non-collocated control algorithm, which mimics another quantum effect, rendering the sound beams uni-directional.
Fully manipulate the power intensity pattern in a large space-time digital metasurface: from arbitrary multibeam generation to harmonic beam steering scheme
Chiral Landau levels induced by two in-plane pseudomagnetic fields in underwater acoustic metamaterials
Jiangsu Key Laboratory for Design and Manufacturing of Precision Medicine Equipment, School of Mechanical Engineering, Southeast University（东南大学机械工程学院精密医疗器械设计与制造江苏省重点实验室）；Key Laboratory of Underwater Acoustic Signal Processing (Southeast University), Ministry of Education（教育部水下声学信号处理重点实验室（东南大学））；Advanced Ocean Institute of Southeast University Nantong（东南大学南通海洋研究院）；State Key Laboratory of Acoustics and Marine Information, Institute of Acoustics, Chinese Academy of Sciences（中国科学院声学研究所声学与海洋信息国家重点实验室）；Modern Matter Laboratory and Advanced Materials Thrust, The Hong Kong University of Science and Technology (Guangzhou)（香港科技大学（广州）现代物质实验室先进材料课题组）
