Generalized acoustic impedance metasurface

• Published in: Communications physics 2024-01, Vol.7 (1), p.34-9, Article 34
• Main Authors: Tian, Yu-Ze, Wang, Yan-Feng, Laude, Vincent, Wang, Yue-Sheng
• Format: Article
• Language: English
• Subjects: 639/705/1041; 639/766/25/3927; Acoustic impedance; Acoustic waves; Acoustics; Boundary conditions; Engineering Sciences; Equivalence principle; Impedance matrix; Materials; Metasurfaces; Micro and nanotechnologies; Microelectronics; Physics; Physics and Astronomy; Power flow; Sound fields
• ISSN: 2399-3650; 2399-3650
• DOI: 10.1038/s42005-024-01529-5

Impedance theory has become a favorite method for metasurface design as it allows perfect control of wave properties. However, its functionality is strongly limited by the condition of strict continuity of normal power flow. In this paper, it is shown that acoustic impedance theory can be generalized under the integral equivalence principle without imposing the continuity of power flow. Equivalent non-local power flow transmission is instead realized through local design of metasurface unit cells that are characterized by a passive, asymmetric impedance matrix. Based on this strategy, a beam splitter loosely respecting local power flow is designed and demonstrated experimentally. It is concluded that arbitrary wave fields can be connected through arbitrarily shaped boundaries, i.e. transformed into one another. Generalized impedance metasurface theory is expected to extend the possible design of metasurfaces and the manipulation of acoustic waves. Impedance theory grants insight to design metasurfaces for controlling acoustic fields, but such theory imposes great limitation on boundary conditions. The authors propose a generalized acoustic impedance theory connecting arbitrarily conservative acoustic fields, and design a beam splitter as an example of power flow processing.