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Research Article

Tunable Fluid-Type Metasurface for Wide-Angle and Multifrequency Water-Air Acoustic Transmission

Figure 4

Preparation of the FAM and its stability. (a) The prepared FAM using the 3D printed solid structures. (b) The enlarged image of a shows trapped bubbles in the cells. (c) The FEM simulation for the bubble formation. See the Movie S2 for the full process. (d) The analysis of bubble formation process for the horizontal immersion method. The is the atmospheric pressure, and is the advancing angle on the solid surface. The is the thickness of the water above the solid structure due to the balance of hydrophobic effect and gravity. is the pressure in the bubble. (e) The critical state that the trapped bubbles will depart from the solid cell under a relative speed of between water and the solid structure. The critical state for the bottom boundary is the contact angle larger than , and that for the upper boundary is the curvature radius equals . (f) The vertical immersion method can be used for the large , and the corresponding FEM simulation (g). See the Movie S6 for details. (h) When the temperature decreases, the will increase and will decrease due to the contraction of air, and will shift slightly. (i) The temperature dependence of the FAM. The analytical solution and the FEM agree well.