Tech Briefs

Simulation of a Piezoelectric Bimorph Motor

Piezoelectric materials deform when a voltage is applied to them. They are therefore used as micromechanical actuators in many applications. In this Brief, we feature one such application — a piezoelectric bimorph motor.

There are three main parts to this piezoelectric bimorph motor: two piezoelectric bimorph cantilevers and a drive shaft.  Each bimorph cantilever has two piezoelectric strips separated by a bond layer, as shown in Figure 1. When properly controlled and phase-shifted voltages are applied to the strips, the bimorph cantilevers bend, elongate, or shrink, moving the drive shaft. The above movie depicts such motion.

Figure 1  The piezoelectric bimorph motor studied: (a) bimorph assembly
(b) exploded view showing the various parts

The mechanical behavior of a piezoelectric bimorph motor is of interest to many designers, manufacturers and researchers. ADINA can be used to accurately predict this behavior.

In our example, an implicit dynamic analysis of the piezoelectric bimorph motor was performed, with a constant Coulomb friction coefficient between the contact surfaces of the mechanical head and the drive shaft. The electric field is coupled to the mechanical deformations.

A relatively soft piezoelectric material is used for the bimorph strips. The polarization directions of both strips in each bimorph are along the y-direction. The inner surfaces (surfaces B and D shown in Figure 1) are grounded (zero voltage) and time-dependent voltage signals are applied to the outer surfaces (surfaces A and C). The bond layer and the mechanical head are made of aluminum.

Two motors are considered, one with thick and one with thin bimorph cantilevers. The results of these analyses are shown in the movies above and below, respectively.

Of course, the motion of the drive shaft depends not only on the applied voltage, but also on the geometry of the bimorph cantilevers. For example, to activate the same displacement of the drive shaft, the motor shown in the movie below (with much thinner bimorph cantilevers) requires an input voltage of only 3V, whereas the motor shown in the movie above requires 100V.

This simulation demonstrates how ADINA can be used to analyze problems where the electric field is coupled to the mechanical deformations. The coupling can be performed in linear and nonlinear, static and dynamic analyses. As new piezoelectric materials are developed, with much higher piezoelectric coefficients than before, accurate simulation of these problems is becoming increasingly important.

For more examples of the powerful multiphysics capabilities of ADINA, see ADINA Multiphysics.

Piezoelectric, full coupling to solids, bimorph motor, nonlinear, implicit dynamics, contact, friction, multiphysics, MEMS