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 ε
₂
and ε
₃
were measured by two measurement methods. The ε
₂
and ε
₃
depend on the piezoelectric constant d
₃₃
and the elastic compliance s
₃₃
respectively when the nonlinear permittivity is induced by the electrostriction generated by the Maxwell force. The value of s
₃₃
determined by ε
₃
was about two times larger than the value determined by the dielectric resonance. The result suggests an existence of frequency dependence of s
₃₃
. On the other hand, the value of d
₃₃
determined by ε
₂
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.