Acoustic simulation of the complete L-CMUT structure. Nodal plots obtained by the three-dimensional FEM: (A) pressure and (B) particle velocity in z (“y” axis in the ANSYS code). Comparison of (C) the equivalent friction coefficient, c_eq, and (D) the equivalent piston area, S_eq, according to the simplified analytical model, the two-dimensional FEM, and the three-dimensional FEM.