TY - JOUR A1 - Altafim, Ruy Alberto Pisani A1 - Qiu, Xunlin A1 - Wirges, Werner A1 - Gerhard, Reimund A1 - Altafim, Ruy Alberto Pisani A1 - Basso, Heitor Cury A1 - Jenninger, Werner A1 - Wagner, Joachim T1 - Template-based fluoroethylenepropylene piezoelectrets with tubular channels for transducer applications N2 - We describe the concept, the fabrication, and the most relevant properties of a piezoelectric-polymer system: Two fluoroethylenepropylene (FEP) films with good electret properties are laminated around a specifically designed and prepared polytetrafluoroethylene (PTFE) template at 300 degrees C. After removing the PTFE template, a two-layer FEP film with open tubular channels is obtained. For electric charging, the two-layer FEP system is subjected to a high electric field. The resulting dielectric barrier discharges inside the tubular channels yield a ferroelectret with high piezoelectricity. d(33) coefficients of up to 160 pC/N have already been achieved on the ferroelectret films. After charging at suitable elevated temperatures, the piezoelectricity is stable at temperatures of at least 130 degrees C. Advantages of the transducer films include ease of fabrication at laboratory or industrial scales, a wide range of possible geometrical and processing parameters, straightforward control of the uniformity of the polymer system, flexibility, and versatility of the soft ferroelectrets, and a large potential for device applications e.g., in the areas of biomedicine, communications, production engineering, sensor systems, environmental monitoring, etc. Y1 - 2009 UR - http://jap.aip.org/ U6 - https://doi.org/10.1063/1.3159039 SN - 0021-8979 ER - TY - JOUR A1 - Sborikas, Martynas A1 - Qiu, Xunlin A1 - Wirges, Werner A1 - Gerhard, Reimund A1 - Jenninger, Werner A1 - Lovera, Deliani T1 - Screen printing for producing ferroelectret systems with polymer-electret films and well-defined cavities JF - Applied physics : A, Materials science & processing N2 - We report a process for preparing polymer ferroelectrets by means of screen printing-a technology that is widely used for the two-dimensional patterning of printed layers. In order to produce polymer-film systems with cavities that are suitable for bipolar electric charging, a screen-printing paste is deposited through a screen with a pre-designed pattern onto the surface of a polymer electret film. Another such polymer film is placed on top of the printed pattern, and well-defined cavities are formed in-between. During heating and curing, the polymer films are tightly bonded to the patterned paste layer so that a stable three-layer system is obtained. In the present work, polycarbonate (PC) films have been employed as electret layers. Screen printing, curing and charging led to PC ferroelectret systems with a piezoelectric d (33) coefficient of about 28 pC/N that is stable up to 100 C-a similar to. Due to the rather soft patterned layer, d (33) strongly decreases already for static pressures of tens of kPa. The results demonstrate the suitability of screen printing for the preparation of ferroelectret systems. Y1 - 2014 U6 - https://doi.org/10.1007/s00339-013-7998-3 SN - 0947-8396 SN - 1432-0630 VL - 114 IS - 2 SP - 515 EP - 520 PB - Springer CY - New York ER - TY - JOUR A1 - Kofod, Guggi A1 - Wirges, Werner A1 - Paajanen, Mika A1 - Bauer, Siegfried T1 - Energy minimization for self-organized structure formation and actuation N2 - An approach for creating complex structures with embedded actuation in planar manufacturing steps is presented. Self-organization and energy minimization are central to this approach, illustrated with a model based on minimization of the hyperelastic free energy strain function of a stretched elastomer and the bending elastic energy of a plastic frame. A tulip-shaped gripper structure illustrates the technological potential of the approach. Advantages are simplicity of manufacture, complexity of final structures, and the ease with which any electroactive material can be exploited as means of actuation. (c) 2007 American Institute of Physics. Y1 - 2007 UR - http://apl.aip.org/ U6 - https://doi.org/10.1063/1.2695785 SN - 0003-6951 ER - TY - JOUR A1 - Wegener, Michael A1 - Wirges, Werner A1 - Tiersch, Brigitte T1 - Porous polytetrafluoroethylene (PTFE) electret films : porosity and time dependent charging behaviour of the free surface N2 - Electrically charged porous polytetrafluoroethylene (PTFE) films are often discussed as active layers for electromechanical transducers. Here, the electric charging behavior of open-porous PTFE films with different porosities is investigated. Optimized electric charging of porous PTFE films is determined by variation of charging parameters such as electric fields and charging times. Maximum surface potentials are depending on the porosity of the PTFE films. Suitable charging leads to high surface potentials observed on non-stretched or slightly stretched porous PTFE films. Further increase of charging fields yields decreasing values of the surface potential accompanied with an increase of conductivity. Y1 - 2006 UR - http://www.springerlink.com/content/601u86x365560515/ U6 - https://doi.org/10.1007/s10934-006-9015-0 ER - TY - JOUR A1 - Wang, Feipeng A1 - Frübing, Peter A1 - Wirges, Werner A1 - Gerhard, Reimund A1 - Wegener, Michael T1 - Enhanced Polarization in Melt-quenched and Stretched Poly(vinylidene Fluoride-Hexafluoropropylene) Films N2 - beta-phase poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) copolymer films were prepared by uniaxially stretching solution-cast or melt-quenched samples. Different preparation routes lead to different amounts of the crystalline alpha and beta phases in the films, as detected by means of Fourier-transform infrared spectroscopy and X-ray diffractometry. The beta phase is significantly enhanced in melt-quenched and stretched films in comparison to solution-cast and stretched films. This is particularly true for copolymer samples with higher HFP content. The beta- phase enhancement is also observed in ferroelectric-hysteresis experiments where a rather high polarization of 58 mC/ m(2) was found on melt-quenched and stretched samples after poling at electric fields of 140 MV/m. After poling at 160 MV/m, one of these samples exhibited a piezoelectric d(33) coefficient as high as 21 pC/N. An electric-field-induced partial transition from the alpha to the beta phase was also observed on the melt-quenched and stretched samples. This effect leads to a further increase in the applications-relevant dipole polarization. Uniaxially stretched ferroelectric- polymer films are highly anisotropic. Dielectric resonance spectroscopy reveals a strong increase of the transverse piezoelectric d(32) coefficient and a strong decrease of the transverse elastic modulus c(32) upon heating from 20 to 50 degrees C. Y1 - 2010 UR - http://ieeexplore.ieee.org/servlet/opac?punumber=94 U6 - https://doi.org/10.1109/TDEI.2010.5539679 SN - 1070-9878 ER - TY - JOUR A1 - Wirges, Werner A1 - Raabe, Sebastian A1 - Qiu, Xunlin T1 - Dielectric elastomer and ferroelectret films combined in a single device how do they reinforce each other? JF - Applied physics : A, Materials science & processing N2 - Dielectric elastomers (DE) are soft polymer materials exhibiting large deformations under electrostatic stress. When a prestretched elastomer is stuck to a flat plastic frame, a complex structure that can be used as an actuator (DEA) is formed due to self-organization and energy minimization. Here, such a DEA was equipped with a ferroelectret film. Ferroelectrets are internally charged polymer foams or void-containing polymer-film systems combining large piezoelectricity with mechanical flexibility and elastic compliance. In their dielectric spectra, ferroelectrets show piezoelectric resonances that can be used to analyze their electromechanical properties. The antiresonance frequencies ( ) of ferroelectret films not only are directly related to their geometric parameters, but also are sensitive to the boundary conditions during measurement. In this paper, a fluoroethylenepropylene (FEP) ferroelectret film with tubular void channels was glued to a plastic frame prior to the formation of self-organized minimum-energy DEA structure. The dielectric resonance spectrum (DRS) of the ferroelectret film was measured in-situ during the actuation of the DEA under applied voltage. It is found that the antiresonance frequency is a monotropic function of the bending angle of the actuator. Therefore, the actuation of DEAs can be used to modulate the of ferroelectrets, while the can also be taken for in-situ diagnosis and for precise control of the actuation of the DEA. Combination of DEAs and ferroelectrets brings a number of possibilities for application. Y1 - 2012 U6 - https://doi.org/10.1007/s00339-012-6833-6 SN - 0947-8396 SN - 1432-0630 VL - 107 IS - 3 SP - 583 EP - 588 PB - Springer CY - New York ER - TY - JOUR A1 - Mellinger, Axel A1 - Wegener, Michael A1 - Wirges, Werner A1 - Mallepally, Rajendar Reddy A1 - Gerhard, Reimund T1 - Thermal and temporal stability of ferroelectret films made from cellular polypropylene/air composites N2 - Ferroelectrets are thin films of polymer foams, exhibiting piezoelectric properties after electrical charging. Ferroelectret foams usually consist of a cellular polymer structure filled with air. Polymer-air composites are elastically soft due to their high air content as well as due to the size and shape of the polymer walls. Their elastically soft composite structure is one essential key for the working principle of ferroelectrets, besides the permanent trapping of electric charges inside the polymer voids. The elastic properties allow large deformations of the electrically charged voids. However, the composite structure can also possibly limit the stability and consequently the range of applications because of, e. g., penetration of gas and liquids accompanied by discharge phenomena or because of a mechanical pre-load which may be required during the application. Here, we discuss various stability aspects related to the piezoelectric properties of polypropylene ferroelectrets. Near and below room temperature, the piezoelectric effect and the stability of the trapped charges are practically independent from humidity during long-time storage in a humid atmosphere or water, or from operating conditions, such as continuous mechanical excitation. Thermal treatment of cellular polypropylene above -10 degrees C leads to a softening of the voided structure which is apparent from the decreasing values of the elastic modulus. This decrease results in an increase of the piezoelectric activity. Heating above 60 degrees C, however, leads to a decrease in piezoelectricity Y1 - 2006 ER - TY - JOUR A1 - Qiu, Xunlin A1 - Mellinger, Axel A1 - Wirges, Werner A1 - Gerhard, Reimund T1 - Spectroscopic study of dielectric barrier discharges in cellular polypropylene ferroelectrets N2 - The transient light emission from the dielectric barrier discharges (DBDs) in cellular polypropylene ferroelectrets subjected to high electric poling fields was spectroscopically measured. The spectrum shows strong emission from the second positive system of molecular nitrogen, N-2(C (3)Pi(u))-> N-2(B (3)Pi(g)), and the first negative system of N-2(+), N-2(+)(B (2)Sigma(+)(u))-> N-2(+)(X (2)Sigma(+)(g)), consistent with a DBD in air. When a dc voltage is applied stepwise to the ferroelectret film, light emission starts above a threshold, coinciding with the threshold voltage in obtaining piezoelectricity. From selected vibronic band strength ratios, the electric field in the discharge was determined and found to agree with Townsend breakdown. Y1 - 2007 UR - http://apl.aip.org/ U6 - https://doi.org/10.1063/1.2786597 ER - TY - JOUR A1 - Mellinger, Axel A1 - Flores Suárez, Rosaura A1 - Singh, Rajeev A1 - Wegener, Michael A1 - Wirges, Werner A1 - Lang, Sidney B. A1 - Gerhard, Reimund T1 - High-resolution space-charge and polarization tomography with thermal pulses N2 - Die Arbeit wurde am 13.03.2006 mit dem "BEST PAPER AWARD" des deutschen IEEE Instrumentation and Measurement (I&M) Chapter ausgezeichnet. Y1 - 2006 SN - 3-8007-2939-3 ER - TY - JOUR A1 - Basso, Heitor Cury A1 - Altafim, Ruy Alberto Pisani A1 - Altafim, Ruy Alberto Pisani A1 - Mellinger, Axel A1 - Fang, Peng A1 - Wirges, Werner A1 - Gerhard, Reimund T1 - Three-layer ferroelectrets from perforated Teflon-PTFE films fused between two homogeneous Teflon-FEP films Y1 - 2007 SN - 978-1-4244-1482-6 ER -