4: Review of Electrostrictive Materials

Chapter 4 reviews the characteristics of electrostrictive materials. Electrostriction is defined as the electromechanical coupling in all electrical-nonconductors (dielectric materials). Under the application of an electric field, these materials show deformation, strain, and stress. Generally speaking, all electrostrictive materials exhibit second-order nonlinear coupling between the elastic strains or stresses and the dielectric terms such that the strain tensor is given by a nonlinear product of the vectors of the electric fields. For a single uniaxial strain (deformation), the induced strain (deformation) is directly proportional to the square of the applied electric field (voltage). Electrostrictive materials in the form of polymers have been the subject of much interest and research in recent years, and much of the focus has been on actuator configurations and how to enhance electromechanical activities. When an electric field is applied to a dielectric material, the differential elements and domains of the material are polarized and opposite sides of these domains become differently charged and attract each other, reducing the materials thickness in the direction of the applied field (and increasing thickness in the orthogonal directions due to the Poisson's ratio). The resulting strain tensor S_ij (i, j=1, 2 3) is proportional to the product of the polarization vectors, P_k. For simple one-dimensional domains, the strain is proportional to the square of the applied electric field.