TY  - JOUR
A1  - Saarimäki, Eetta
A1  - Paajanen, Mika
A1  - Savijärvi, Ann-Mari
A1  - Minkkinen, Hannu
A1  - Wegener, Michael
A1  - Voronina, Olena
A1  - Schulze, Robert
A1  - Wirges, Werner
A1  - Gerhard, Reimund
T1  - Novel heat durable electromechanical film : processing for electromechanical and electret applications
N2  - New ferroelectrets were developed on the basis of foams from cyclo-olefin polymers and copolymers. The results obtained on the cyclo-olefin polymer foam demonstrate a significant improvement of the service temperature for ferroelectret transducer materials. Suitable compounding and preparation led to cyclo-olefin ferroelectrets with an electromechanical activity of around 15 pC/N, which is thermally stable at least up to 110 degrees C. The properties in sensor and actuator applications are strongly dependent on the processing parameters related to film-making, sensor and actuator preparation, gas content and electric charging. The processing window for the film stretching was very narrow compared to the earlier developed polypropylene ferroelectrets. The film porosity, softness and thus the electromechanical activity are adjusted by gas-diffusion expansion. The activity of the electromechanically operating sensors and actuators was increased by stacking several layers of cellular cyclo-olefin film. For applications such as flat loudspeakers, the foamed films are tuned by tensioning them on a support frame. Correct tensioning was essential also for reducing the distortion levels.
Y1  - 2006
ER  - 
TY  - JOUR
A1  - Wegener, Michael
A1  - Wirges, Werner
A1  - Gerhard, Reimund
A1  - Dansachmüller, M.
A1  - Schwödiauer, R.
A1  - Bauer-Gogonea, Simona
A1  - Bauer, Siegfried
A1  - Paajanen, Mika
A1  - Minkkinen, Hannu
A1  - Raukola, J.
T1  - Controlled inflation of voids in cellular polymer ferroelectrets : optimizing electromechanical transducer properties
N2  - 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. (C) 2004 American Institute of Physics
Y1  - 2004
ER  -