A series of electromechanical measurements for determination of piezoelectric, dielectric and elastic tensor components in porous polypropylene electrets

The electromechanical properties of porous polypropylene electrets were studied by means of linear and nonlinear dielectric measurements. The second and the third order nonlinear permittivity ε₂ and ε₃ were measured by two measurement methods. The ε₂ and ε₃ depend on the piezoelectric constant d₃₃ and the elastic compliance s₃₃ respectively when the nonlinear permittivity is induced by the electrostriction generated by the Maxwell force. The value of s₃₃ determined by ε₃ was about two times larger than the value determined by the dielectric resonance. The result suggests an existence of frequency dependence of s₃₃. On the other hand, the value of d₃₃ determined by ε₂ showed a good agreement with the result of the dielectric resonance. This result means that the piezoelectric response of the p-PP electret is mainly induced by the size effect.