Structural design of low-frequency broadband adaptive nonlinear underwater acoustic absorption metasurface

• The metasurface exhibits low-frequency, broadband acoustic absorption capabilities. • Conform to the curved surfaces of underwater vehicles. • The design methodology for rotating steel frame and folding fan element. • Passive acoustic absorption in marine equipment. • The impact of adaptivity. To date, most underwater metasurface units are designed with rigid connections, which limit their ability to conform perfectly to the complex curved surfaces of medium- and small-sized vehicles. This challenge is addressed by introducing degrees of freedom among the units. In this paper, we propose four absorptive elements integrated into a steel framework that can rotate around an axis, thereby forming a unit of the adaptive metasurface. Simulations and experiments demonstrate that the proposed underwater acoustic absorption metasurface, with a subwavelength thickness of λ/154, achieves a sound absorption coefficient exceeding 0.8 across the frequency ranges of 309–2202 Hz and 3292–10,000 Hz. Furthermore, low-frequency acoustic absorption is enhanced as the bending angles between the metasurface units increase. This design approach not only broadens the low-frequency acoustic absorption bandwidth of the adaptive metasurface but also provides a reference for its more effective application in engineering contexts.