Ultrathin coding metasurface for underwater wave focusing, branching and self-bending generation with one single actuator

A novel metasurface is proposed that aims to generate underwater acoustic waves with various functions by only one actuator. Each metasurface unit consists of an air cavity sandwiched on one side by a vibration plate and connecting rubber supports. By properly selecting the ratio of the plate to unit lengths, a phase shift of π can be attained to constitute a binary coding metasurface. Three demonstrations, including focusing, branching and self-bending waves, are chosen to validate the functionality of the design. The design is also shown to work over a wide frequency range by changing the ratio. In addition, the design is extremely compact, with the thickness only about 1/100 of the target wavelength. Compared with commonly used phased array transducers that are utilized to generate underwater acoustic waves, this design offers has the advantage of needing only a single actuator as opposed to needing a lumped electrical control system.