Crumpling electret films for a stronger macroscopic flexoelectric response

Flexoelectricity is a universal phenomenon in all dielectrics, which couples electrical polarizations with strain gradients. However, limited by the size effects, the intensity of the flexoelectric effect becomes appreciable at the micro-and nano-scale, which suppresses its applications at the macroscale. To amend this inconvenience in applications, we innovatively propose replacing the traditional pure dielectric film with flexoelectret film containing quasi-permanent electrical charges in crumpling deformation. The crumpled flexoelectret film can give a considerable flexoelectric-like response at the macroscale. Specifically, we establish a theoretical model for the crumpled flexoelectret film, derive the analytical solution of the electromechanical coupling under the bi-directional bending conditions, and analyze the flexoelectric-like response under different thicknesses, charge densities, and scales. The results show that when the flexoelectret film's thickness H = 1 mm and the charge density q = -0:2mC . m(-2), the intensity of its flexoelectric-like response is nearly 100 times of that of pure dielectric film's intrinsic flexoelectricity.