Tunable Fluid-Type Metasurface for Wide-Angle and Multifrequency Water-Air Acoustic Transmission
The principle of the FAM. (a) Schematic illustration of the ideal FAM without solid structure. (b) The frequency of unity transmission () varying with and with the IMC calculation. (c) The maximum energy transmission coefficient () varying with (Note S4). (d) Schematic illustration of the real FAM. The cross-sectional area changes from to due to the solid structure. (e) The effect of solid properties on the shift. The parameters are and for the case without the solid, and and are added for the case with the solid. It suggests the effect of solid properties on can be neglected if the solid is harder than the rubber. The notation “hard” represents the hard boundary condition. (f) The varies with by the FEM calculations. When is small, the vibration of the water layer is confined by the solid structure, hence, decreases as decreases. This effect can be negligible when . The parameters are ,,, and , while and are variable with for satisfying . The analytical model always predicts that (about 500 Hz) regardless of because it does not consider the solid constraint effect.