Piezoelectret metamaterials with a double-V structure exhibiting tunable piezoelectric effect in a broad range

Piezoelectret metamaterials are a kind of piezoelectrets with distinctive properties such as negative Poisson's ratio and positive piezoelectric d31 coefficient. These materials hold significant promise for applications in sensing and mechanical energy harvesting. In this article, flexible piezoelectret metamaterials with a simple double-V cell structure are designed, and their properties are theoretically analyzed, simulated, and experimentally tested. The results indicate that the effective piezoelectric d33 and d31 coefficients can be tuned over a wide range by adjusting the geometric parameters of the cell. The experimental results are consistent with the theoretical prediction and simulation calculation. Differing from the piezoelectric d33 coefficient, which always has positive polarity, the sign of the piezoelectric d31 coefficient depends on Poisson's ratio of the material. In particular, d31 coefficients are negative for the materials with positive Poisson's ratio, while they have a positive sign when Poisson's ratio is negative. For a piezoelectret metamaterial sample prepared in this study, a large effective piezoelectric d31 coefficient up to 1200 pC/N is achieved experimentally. The significant piezoelectric effects in the piezoelectret metamaterials as well as their excellent mechanical adaptivity to irregular surface structures, such as the curved surfaces of humanoid robots and aircraft wings, introduce a novel solution for diverse applications.