Size-dependent effect of the flexoelectronics in a composite beam

In this paper, a sandwich composite structure consisting of two piezoelectric layers and a flexoelectric semiconductor layer is proposed, where piezoelectric layers are poled in opposite direction, either tail-to-tail (T-T) or head-to-head (H-H). The macroscopic theory for piezoelectric and flexoelectric semiconductors is utilized to establish the field equations and constitutive relations of the composite beam. For the composite beam with T-T design, the electromechanical behaviors of the flexoelectric semiconductor exhibit a significant size-dependent effect. In this design, the piezoelectric field competes with the flexoelectric field, resulting in a net electric field reversal at a certain thickness. For the composite beam with H-H design, the electromechanical response of the semiconductor is enhanced due to the synergistic interaction of these two polarization fields. Furthermore, this study shows that flexoelectric-like effect from piezoelectric mimicry can induce highly appreciable electromechanical responses at both macroscopic and microscopic scales. It could be foreseen that this research provides fundamental guidance for the structural design of flexoelectric-like semiconductor devices.