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The preparation and characterization of novel piezoelectric and pyroelectric electrets is discussed with respect to their electret properties. Charged heterogeneous electrets, like closed-cell microporous polypropylene (pp) foams and 'soft-hard' fluoropolymer hybrids are shown to yield large quasi-static and dynamic piezoelectric responses, indistinguishable from true piezoelectricity. Piezoelectric coefficients comparable to that of ceramic counterparts have been achieved. For the investigation of the piezoelectric and pyroelectric properties of the electret materials, the thermal-pulse technique has been extended towards temperature-dependent investigations and measurements on planar, cylindrical or spherical samples. The potential of the thermal-pulse technique not only for the measurement of electric-field and polarization distributions, but also for acoustical, electromechanical and pyroelectric properties is outlined.
Schwödiauer et al. (2000) studied this question.