Internal stress and structural geometry calculations of a rainbow actuator

The performance of the Reduced And INternally Biased Oxide Wafer (RAINBOW) actuator developed by Haertling, as explained by many authors, mainly owes to the special behaviors of domains under the high internal stress status. The finite element method (FEM) was the one used by Haertling's group to si mulate the internal stress in RAINBOW and its dome shape of RAINBOW and the ir FEM simulation results can explain some experimental results of RAINBOW actuator. In this paper, a simple model is presented to evaluate the intern al stress and dome shape of RAINBOW actuator on the basis of the two step f ormation of RAINBOW structure. The internal radius stress and structural de formation of RAINBOW actuators with different geometrical dimensions were c alculated by the present model. The results show good agreements with that of FEM simulation by Haertling and by us. Moreover, the optimal thickness r atio (the reduced layer/total) of the RAINBOW actuator. which represents th e highest displacement induced by an electric field in its symmetric axial, can be directly determined from this model (the optimal thickness ratio is about 0.33, close to that calculated by FEM). This model has a clear physi cal meaning, explaining easily the non-uniform stress in the RAINBOW actuat ors from the physical point view, and is very useful for the RAINBOW actuat or designs. These advantages are not so easily obtained by FEM. From the po int of view of the presented model, the origin of the strain-amplifying mec hanism of the RAINBOW was preliminarily considered to be due to the structu ral geometry of the unique dome shape.