Directional Acoustic Antennas Based on Valley‐Hall Topological Insulators

• Published in: Advanced materials (Weinheim) Vol. 30; no. 36; pp. e1803229 - n/a
• Main Authors: Zhang, Zhiwang, Tian, Ye, Wang, Yihe, Gao, Shuxiang, Cheng, Ying, Liu, Xiaojun, Christensen, Johan
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 06.09.2018
• Subjects: acoustic antennas; Acoustic insulation; Acoustic noise; Acoustics; Antennas; Background noise; Beamforming; Sound; Sound waves; superdirectivity; topological edge states; Topological insulators; Transducers; valley‐Hall phase; valley-Hall phase; acoustic antennas; topological edge states; superdirectivity
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.201803229

Realizing directional acoustic signal transmittance and reception robust against surrounding noise and competing signals is crucial in many areas such as communication, navigation, and detection for medical and industrial purposes. The fundamentally wide‐angled radiation pattern of most current acoustic sensors and transducers displays a major limitation of the performance when it comes to precise targeting and probing of sound particular of interest in human speaking and hearing. Here, it is shown how topological acoustic valley transport can be designed to enable a unique beamforming mechanism that renders a superdirective needle‐like sound radiation and reception pattern. The strategy rests on out‐coupling valley‐polarized edge states, whose beam is experimentally detected in the far‐field with 10° width and a sound‐intensity enhancement factor ≈10. Furthermore, anti‐interference communication is proposed where sound is received from desired directions, but background noise from other directions is successfully suppressed. This type of topological acoustic antenna offers new ways to control sound with improved performance and functionalities that are highly desirable for versatile applications. The valley degree of freedom has emerged to realize a topological state known as the valley‐Hall effect. The acoustic version of the valley refers to frequency extrema of the band structure in momentum space exhibiting topologically nontrivial properties. Along this frontier, it is demonstrated how a topological acoustic antenna enables a unique beam‐forming mechanism rendering a superdirective needle‐like sound radiation.