A twisted-graphene-like acoustic material created with vortex airflows

Twisted bilayer graphene (TBG) and allied materials have attracted significant attention in various fields owing to the remarkable performance achieved at a magic angle. However, because sound waves propagate freely in an acoustic system, the tight-binding theory, which is fundamental to studying TBG, cannot be directly applied in acoustic systems, which makes it challenging to create an acoustic material resembling TBG. Thus, in this work, we introduce vortex airflows into a bilayer structure to hinder free transmission of acoustic waves and provide the tight-binding condition in the system, which leads to the practical realization of a twisted-graphene-like acoustic material (TGAM). A theoretical model is established to study the frequency band of the TGAM. Theoretical analysis, numerical simulation, and experimental measurement demonstrate large magic angles over 3° validated by quasi-flatbands. Moreover, the acoustic system offers flexibility in design, in which the structural parameters can be readily adjusted to achieve distinct magic angles, quasi-flatband frequencies, and bandgap widths. This study is promising for advancing the design of two-dimensional acoustic materials in future applications.