Elastic and electromechanical properties of polypropylene foam ferroelectrets

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.