Analytical model of mechanically excited piezoelectric unimorph beams.

A model is presented of a composite beam with one elastic and one piezoelectric layer. A reduced set of piezoelectric equations of state that has only the longitudinal components of stress and strain and the transverse components of electric field and charge density is consistently used to include the effect of piezoelectric coupling in all the equations. The equi-potential boundary conditions on the electrodes, the open-circuit condition, and the Gauss condition are satisfied. The position of the neutral axis and the dynamic equilibrium equation are derived after including the effect of piezoelectric coupling. All equations are combined to derive an equation of motion that contains only the displacement and the mechanical excitation. The solution to the equation is expressed in terms of a complete set of functions and an auxiliary function that contains the electric potential. The latter is needed to satisfy piezoelectric boundary conditions at the ends of the beam. The electric potential varies along the length of the beam and has a quadratic variation between the electrodes. Analytical expressions for displacement and potential, and numerical results at low frequencies and in the neighborhood of resonance, are presented for certain sets of boundary conditions.