“…To give accurate theoretical guidance for designing the piezoelectric stack, an improved theoretical model is of great significance. Piezo-elasticity theory has been successfully used to study piezoelectric composite structures, including piezoelectric curved actuators [51,52], multi-layer piezoelectric cantilever [4,6] and cement-based piezoelectric composites [15,53], functionally graded piezoelectric beams [54,55], and laminated piezoelectric hollow spheres [56]. In addition, assuming the electric field to be spatially varying rather than spatially constant is more accurate for describing the electric field [57,58], which is still not well-applied in the analysis of piezoelectric stacks.…”