When exposed to sufficiently high electric fields, polymer-foam electret materials with closed cells exhibit ferroelectric-like behavior and may therefore be called ferroelectrets. In cellular ferroelectrets, the influence of the cell size and shape distributions on the application-relevant properties is not yet understood. Therefore, controlled inflation experiments were carried out on cellular polypropylene films, and the resulting elastical and electromechanical parameters were determined. The elastic modulus in the thickness direction shows a minimum with a corresponding maximum in the electromechanical transducer coefficient. The resonance frequency shifts as a function of the elastic modulus and the relative density of the inflated cellular films. Therefore, the transducer properties of cellular ferroelectrets can be optimized by means of controlled inflation.

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Internally charged closed-cell polymer electrets exhibit ferroelectric-like behavior and have been called ferroelectrets. They are attractive for soft electroactive transducers, the high compressibility leads to d33 transducer coefficients exceeding those of ferroelectric polymers. A technique for the measurement of the elastic modulus and the transducer coefficient of ferroelectrets is reported. The elastic behavior of ferroelectretic polypropylene foams is correlated with the piezoelectric-like properties. Prestress treatments linearize the transducer properties.

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