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 - Singh, Rajeev A1 - Wegener, Michael A1 - Wirges, Werner A1 - Gerhard, Reimund A1 - Lang, Sidney B. T1 - Three-dimensional mapping of polarization profiles with thermal pulses N2 - High-resolution, large-area three-dimensional mapping of polarization profiles in electret polymers was carried out by means of a fast thermal pulse technique with a focused laser beam. A lateral resolution of 38 mu m and a near- surface depth resolution of less than 0.5 mu m was achieved. At larger depths, fast thermal diffusion in the metal electrode rather than the laser spot size becomes the limiting factor for the lateral resolution. (c) 2005 American Institute of Physics Y1 - 2005 SN - 0003-6951 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 - 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 - 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 - Flores Suárez, Rosaura A1 - Mellinger, Axel A1 - Wegener, Michael A1 - Wirges, Werner A1 - Gerhard, Reimund A1 - Singh, Rajeev T1 - Thermal-pulse tomography of polarization distributions in a cylindrical geometry JF - IEEE transactions on dielectrics and electrical insulation N2 - Fast, three-dimensional polarization mapping in piezoelectric sensor cables was performed by means of the novel thermal-pulse tomography (TPT) technique with a lateral resolution of 200 mum. The active piezoelectric cable material (a copolymer of polyvinylidene fluoride with trifluoroethylene) was electrically poled with a point-to-cable corona discharge. A focused laser was employed to heat the opaque outer electrode, and the short-circuit current generated by the thermal pulse was used to obtain 3D polarization maps via the scale transformation method. The article describes the TPT technique as a fast non-destructive option for studying cylindrical geometries. Y1 - 2006 U6 - https://doi.org/10.1109/TDEI.2006.258210 SN - 1070-9878 VL - 13 IS - 5 SP - 1030 EP - 1035 PB - IEEE CY - Piscataway 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 - 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 - 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 - 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 -