| A constitutive theory of ferroelectrets is developed to analyze the electromechanical coupling properties and stability with large deformation. The equations of equilibrium and condition of stability are hereby derived from the nonlinear theory. Piezoelectricity with static mechanical and electric loads and stability are investigated. In addition, a composite structure of ferroelectrets and liquid crystal elastomer (LCE) is proposed to obtain the photoelectric conversion and their photoelectric properties are studied.Results show the reciprocity of piezoelectricity of ferroelectrets with external loads. The piezoelectric coefficient d33is proportional to the charge density and decreases with the relative dielectric constant of the polymer substrate. Subjected to a small external force, the piezoelectric coefficient d33is almost independent with the external force. When the external force is big enough, the piezoelectric coefficient d33increases with the external force. The value of d33increases almost linearly with the dc voltage at small deformation, but possesses nonlinear response at large deformation. To ensure that the ferroelectret is in a stable equilibrium, the corresponding Hessian should be positive definite. Two critical voltages exist and they decrease with the pre-applied pressure.As for the composite structure of ferroelectrets and LCE, theoretical analysis demonstrates that the induced charge is proportional to the intensity of the light. Moreover, the photoelectric coefficient is proportional to the piezoelectric coefficient of ferroelectrets, the photomechanical coefficient of LCE and the width of the LCE beam. When the thickness of LCE beam is fixed, the photoelectric coefficient first increases with the attenuation length and then decreases. The maximum value is obtained when the ratio of the thickness of LCE beam to the attenuation length equals2.688. The photoelectric coefficient decreases with the length of LCE beam, but increases with the Young’s modulus of LCE. |
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