TY  - JOUR
A1  - Mellinger, Axel
A1  - Wegener, Michael
A1  - Wirges, Werner
A1  - Gerhard, Reimund
T1  - Thermally stable dynamic piezoelectricity in sandwich films of porous and non-porous amorphous fluoropolymer
Y1  - 2001
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  - 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
Y1  - 2006
ER  - 
TY  - JOUR
A1  - Pham, Cong Duc
A1  - Petre, Anca
A1  - Berquez, Laurent
A1  - Flores Suárez, Rosaura
A1  - Mellinger, Axel
A1  - Wirges, Werner
A1  - Gerhard, Reimund
T1  - 3D high-resolution mapping of polarization profiles in thin poly(vinylidenefluoride-trifluoroethylene) (PVDF- TrFE) films using two thermal techniques
N2  - In this paper, two non-destructive thermal methods are used in order to determine, with a high degree of accuracy, three-dimensional polarization distributions in thin films (12 mu m) of poly(vinylidenefluoride- trifluoroethylene) (PVDF-TrFE). The techniques are the frequency-domain Focused Laser Intensity Modulation Method (FLIMM) and time-domain Thermal-Pulse Tomography (TPT). Samples were first metalized with grid-shaped electrode and poled. 3D polarization mapping yielded profiles which reproduce the electrode-grid shape. The polarization is not uniform across the sample thickness. Significant polarization values are found only at depths beyond 0.5 mu m from the sample surface. Both methods provide similar results, TPT method being faster, whereas the FLIMM technique has a better lateral resolution.
Y1  - 2009
UR  - http://ieeexplore.ieee.org/servlet/opac?punumber=94
U6  - https://doi.org/10.1109/TDEI.2009.5128505
SN  - 1070-9878
ER  - 
TY  - JOUR
A1  - Qiu, Xunlin
A1  - Mellinger, Axel
A1  - Wegener, Michael
A1  - Wirges, Werner
A1  - Gerhard, Reimund
T1  - Barrier discharges in cellular polypropylene ferroelectrets : how do they influence the electromechanical properties?
Y1  - 2007
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  - Qiu, Xunlin
A1  - Mellinger, Axel
A1  - Wirges, Werner
A1  - Gerhard, Reimund
T1  - Dielectric barrier discharges during the generation of ferroelectrets : optical spectroscopy for process monitoring
Y1  - 2007
SN  - 978-1-4244-1482-6
ER  -