Flexoelectric effect, materials, and structures

Flexoelectricity defines the linear coupling between the mechanical strain gradient with the electric polarization or the mechanical response under the electric field gradient. This unique electromechanical coupling mechanism allows the measurement of strain gradient information in mechanical structures electrically, which is regarded as a sensitive indicator of the structural health status. Application of such an effect is based on the understanding of the related principle, materials, and structures. In this chapter, the constitutive equation of the flexoelectric structure is provided by including coupling with piezoelectricity. The nontrivial flexoelectric coefficients of materials in various symmetry groups are presented. The measurement methods of main flexoelectric coefficients and flexoelectric structures corresponding to each mode are introduced. Finally, flexoelectricity in liquid crystals, polymers, and biomembranes are compared with that of solid materials.