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30 March 2010 Piezoelectric polymer foams: transducer mechanism and preparation as well as touch-sensor and ultrasonic-transducer properties
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Different materials provide a mechanical-electrical energy conversion and are thus interesting candidates for piezoelectric sensors and actuators. Beside ferroelectric ceramics and polymers, also polymer foams, so-called ferroelectrets, are developed as piezoelectric active materials. Their piezoelectricity originates from optimized structural and elastic-foam properties accompanied with an optimized charge trapping at the polymer layers within the foam structure. The piezoelectric activity arises if mechanical stimuli lead to a thickness variation of the electrically charged voids which results in an electrical signal between the connected electrodes on the film surfaces due to the change of internal electric fields. The concept of such a piezoelectric transducer was developed by investigating cellular polypropylene films with different foam structures and thus different elastic properties. Recently, ferroelectrets were prepared from other polymers following the same concept. Different kind of new foaming procedures are developed in order to broaden the range of usable materials as well as to optimize the adjustment of piezoelectric and ultrasonictransducer properties. The paper provides an overview about ferroelectrets, their underlying working mechanism as well as their preparation possibilities. In detail, piezoelectric properties of polypropylene ferroelectrets are described which are usable for pushbutton or touch-pad applications as well as in ultrasonic-transducer applications.
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M. Wegener "Piezoelectric polymer foams: transducer mechanism and preparation as well as touch-sensor and ultrasonic-transducer properties", Proc. SPIE 7644, Behavior and Mechanics of Multifunctional Materials and Composites 2010, 76441A (30 March 2010);

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