Flexoelectricity represents the linear relationship between the strain/electric gradient field and the induced electric polarization/mechanical stress in dielectric materials. This electro-mechanical behavior is important for prospective applications due to its size effect and other advantages. In this work, a converse flexoelectric effect is generated by the designed permittivity gradient with Ba0.67Sr0.33TiO3 ceramic powder and the substrate. The equivalent piezoelectric effect of the gradient composite is obviously increased by converse flexoelectricity. This study opens up an avenue for prospective sensing and actuating approaches for both piezoelectric and non-piezoelectric dielectric materials with relative permittivity gradients and uniform geometric structures.

Stretchable materials are expected in next-generation devices as examples of soft electronics and wearable healthcare. Elastomers are stretchable and well-applied in various electromechanical applications as substrate and functional materials. Elastomers are believed to have substantial electromechanical response of flexoelectricity, due to their large deformation range and hence large strain gradient capability. Flexoelectricity is an electromechanical coupling effect in dielectrics, describing the linear relation between its strain gradient and its induced electric polarization. In this work, we propose a phenomenological model to study the flexoelectricity of elastomers, where cross-linking density is the key. The flexoelectric coefficient is increased by enlarging the cross-linking density of the elastomer. This model is experimentally verified by measuring transverse flexoelectric response of two typical elastomers. This work shows a fundamental understanding on tunable flexoelectricity of elastomers, and opens up possibilities in material designs for flexoelectric-based applications with elastomers.

Converse flexoelectricity describes the linear relationship between an electric field gradient and the mechanical stress in dielectric materials. It is not restricted by the Curie temperature limit, does not require advanced electrical poling and a wide range of candidate materials exist; hence, there is growing interest in converse flexoelectricity for application in actuators. In this work, a biconcave beam structure and actuation method based on the converse flexoelectric effect is presented. Theoretical and finite element analyzes were developed for the relationship between the electric field gradient and the geometric parameters. A non-piezoelectric dielectric material, polyvinylidene fluoride, was experimentally applied to validate the designed effect. The experimental results show that the designed structure outputs markedly larger displacements magnitudes than the control specimens. This work provides a design method for converse flexoelectric actuators and further enhances the application prospects of converse flexoelectricity in all solid dielectric materials.

Recent advancements in electromechanical coupling effects enable the electromechanical materials in soft and stretchable formats, offering unique opportunities for biomimetic applications. However, high electromechanical performance and mechanical elasticity hardly coexist...

All dielectric materials exhibit flexoelectricity defined as a strain gradient-induced electric polarization. The flexoelectric coefficient measures electric polarization induced by strain gradient in dielectric materials. In this work, an approach to measure the 1123 component of the flexoelectric coefficient of polymeric materials is presented. Theoretical analysis and finite element analysis are performed on an un-polarized polyvinylidene fluoride rectangular beam. When deformation occurs in the specimen, a normal strain gradient is generated. The consistency of the elastic deformation determined through calculations and experimental measurements under applied loads was good. The experimental system was set up as follows: a circular sine wave load with bias value was applied to the specimen and the strain gradient-induced electric charge curve was measured. The flexoelectric coefficient μ1123 was obtained and was consistent with our theoretical calculations of the electric polarization induced by the strain gradients. This study provides experimental support for further theoretical investigations of flexoelectricity in polymers and may expand the range of applications of flexoelectric effects.