Flexoelectric metamaterials design based on anti-trichiral structure

Flexoelectricity is characterized by the polarization in response to strain gradients. Since the flexoelectric effect is not restricted by crystalline symmetry and exists in all dielectrics, flexoelectric metamaterials offer a promising approach to achieve apparent piezoelectricity in non-piezoelectric materials through structural design. In this work, a bending-dominated anti-trichiral structure is utilized to design a flexoelectric metamaterial. Theoretical analysis and finite element simulations reveal that external axial compression enable the rotation of solid cylinders and consequently leads to a bending deformation in ligaments. The superposition of the flexoelectric charges of the bent ligaments makes the anti-trichiral structure exhibit apparent piezoelectricity. The effective piezoelectric coefficient is theoretically predicted to exceed 3000 pC/N by optimizing the structural parameters, such as reducing the ligament thickness to hundreds of micrometers. Resin- and unpoled lead zirconium titanate-based metamaterials are fabricated by 3D printing and laser cutting, respectively. Both specimens exhibit apparent piezoelectricity subjected to axial dynamic loads. The measured piezoelectric coefficient is consistent with the theoretical predictions, verifying the design strategy. This work offers insights into the design of flexoelectric metamaterials and highlights the potential of mechanical metamaterials for high-performance sensing and energy harvesting applications utilizing the flexoelectric effect.