TY  - THES
A1  - Voronina, Olena
T1  - Structure-property relations in polymer ferroelectrets
Y1  - 2007
CY  - Potsdam
ER  - 
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  - Wirges, Werner
A1  - Wegener, Michael
A1  - Voronina, Olena
A1  - Zirkel, Larissa
A1  - Gerhard, Reimund
T1  - Optimized preparation of elastically soft, highly piezoelectric, cellular ferroelectrets from nonvoided poly(ethylene terephthalate) films
N2  - Electrically charged cellular polymer films can exhibit very high piezoelectric activity and are therefore more and more often employed in advanced electromechanical and electro-acoustical transducers. In this paper, we report an optimized sequence of steps for preparing such ferroelectrets from commercial nonvoided ploy(ethylene terephthalate) (PETP) films by means of foaming with CO2 biaxial mechanical stretching, controlled void inflation, and bipolar electric charging. The nonvoid PETP films foamed with supercritical CO2 at a suitably high pressure and subsequently annealed for stabilization. The cellular foam structure was further optimized by means of well controlled biaxial stretching in a commercial stretcher and sometimes subsequent inflamation in a pressure chamber. Bipolar electric charging of the internal voids was achieved through the application of high electric fields in an SF0 atmosphere. The new optimized PETP ferroelectric exhibit quite large piezoelectric coefficients up to almost 500 pCN(-1), for which unusually low elastic stiffness of only around 0.3 MPa are essential. The PETP foam ferroelectrics posses unclamped thickenss-extension resonance frequences between approximately 120 and 250 kHz, and are thus highly suitable for several established as well as novel ultrasonic-transductant applications.
Y1  - 2007
UR  - http://onlinelibrary.wiley.com/doi/10.1002/adfm.200600162/pdf
U6  - https://doi.org/10.1002/adfm.200600162
ER  -