Figure 10.

Comparison of the Q_33−r /Q_33−a value for various k₃₁ values: (a) k₃₁ = 0.4; (b) k₃₁ = 0.7; (c) k₃₁ = 0.9. For unstiffened k₃₁-mode, the strong electromechanical coupling effect also introduces an obvious difference between the values of Q_31−r and Q_31−a, similar as the stiffened k₃₃-mode.