A sonic black hole structure with perforated boundary for slow wave generation

Abstract

Sonic black hole (SBH) allows for effective and broadband sound absorption in a retarding duct structure, in which two indispensable physical processes take place: wave retarding and energy dissipation. In this study, an SBH structure with perforated boundary (SBH-PB) is investigated, in which perforated acoustic boundaries are incorporated into the SBH to enhance the black hole effects through a simplified structural design. To predict acoustic performance and understand the physical mechanisms, this paper employs the transfer matrix method (TMM) to model and analyze the physics characteristics of an SBH-PB. Compared to the original form of SBH, the proposed SBH-PB is shown to entail better sound absorption owing to the increased energy dissipation by the small holes, while requiring a smaller number of inner rings. The validity of the TMM prediction is verified by experiments. Finally, the slow wave phenomenon in the retarding structure is also further studied and visualized by numerical simulation and experiment. The proposed structure holds promise for sound wave manipulation and the development of acoustic noise control devices.