@article{BassoAltafimAltafimetal.2007,
  author    = {Basso, Heitor Cury and Altafim, Ruy Alberto Pisani and Altafim, Ruy Alberto Pisani and Mellinger, Axel and Fang, Peng and Wirges, Werner and Gerhard, Reimund},
  title     = {Three-layer ferroelectrets from perforated Teflon-PTFE films fused between two homogeneous Teflon-FEP films},
  isbn      = {978-1-4244-1482-6},
  year      = {2007},
  language  = {en}
}
@article{FloresSuarezGanesanWirgesetal.2010,
  author    = {Flores Su{\´a}rez, Rosaura and Ganesan, Lakshmi Meena and Wirges, Werner and Gerhard, Reimund and Mellinger, Axel},
  title     = {Imaging liquid crystals dispersed in a ferroelectric polymer matrix by means of thermal-pulse tomography},
  issn      = {1070-9878},
  doi       = {10.1109/TDEI.2010.5539683},
  year      = {2010},
  abstract  = {A new arrangement of the optical elements in a Thermal-Pulse-Tomography (TPT) setup allows to scan micrometer structures in composite and heterogeneous samples such as polymer-dispersed liquid crystals (PDLCs). The non-destructive TPT technique allows the determination of three-dimensional profiles of polarization and space charge in dielectrics. The samples under study were 12 mu m thick films of a copolymer of vinylidene fluoride with trifluoroethylene P(VDF- TrFE) (65/35) with embedded liquid-crystal droplets. The poling process was performed in direct contact well above the coercive field of the copolymer. The 3D map obtained from scanning with a 10 mu m wide spot shows elliptically shaped areas with liquid-crystal droplets. Considering the droplets as oblate spheroids, their major axis lies in the x-y plane, while their minor axis in the z direction measures 0.5 mu m or more. This result is in good agreement with scanning electron micrographs. It is believed that the major axis is overestimated due to imaging of liquid-crystal clusters.},
  language  = {en}
}
@article{FloresSuarezMellingerWegeneretal.2006,
  author    = {Flores Su{\´a}rez, Rosaura and Mellinger, Axel and Wegener, Michael and Wirges, Werner and Gerhard, Reimund and Singh, Rajeev},
  title     = {Thermal-pulse tomography of polarization distributions in a cylindrical geometry},
  series = {IEEE transactions on dielectrics and electrical insulation},
  volume    = {13},
  journal   = {IEEE transactions on dielectrics and electrical insulation},
  number    = {5},
  publisher = {IEEE},
  address   = {Piscataway},
  issn      = {1070-9878},
  doi       = {10.1109/TDEI.2006.258210},
  pages     = {1030 -- 1035},
  year      = {2006},
  abstract  = {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.},
  language  = {en}
}
@article{MellingerFloresSuarezSinghetal.2007,
  author    = {Mellinger, Axel and Flores Su{\´a}rez, Rosaura and Singh, Rajeev and Wegener, Michael and Wirges, Werner and Gerhard, Reimund},
  title     = {Zerst{\"o}rungsfreie Tomographie von Raumladungs- und Polarisationsverteilungen mittles W{\"a}rmepulsen},
  issn      = {0171-8096},
  doi       = {10.1524/teme.2007.74.9.437},
  year      = {2007},
  abstract  = {Non-destructive, three-dimensional imaging of space-charge and polarization distributions in electret materials has been implemented by means of laser-induced thermal pulses. In pyroelectric films of poled poly(vinylidene fluoride), images of up to 45 x 45 pixels with a depth resolution of less than 0.5 mu m and a lateral resolution of 40 mu m were recorded, the latter being limited by fast thermal diffusion in the absorbing metallic front electrode. Initial applications include the analysis of polarization distributions in corona-poled piezoelectric sensor cables and the detection of patterned space-charge distributions in polytetrafluoroethylene films.},
  language  = {de}
}
@article{MellingerFloresSuarezSinghetal.2006,
  author    = {Mellinger, Axel and Flores Su{\´a}rez, Rosaura and Singh, Rajeev and Wegener, Michael and Wirges, Werner and Lang, Sidney B. and Gerhard, Reimund},
  title     = {High-resolution space-charge and polarization tomography with thermal pulses},
  isbn      = {3-8007-2939-3},
  year      = {2006},
  abstract  = {Die Arbeit wurde am 13.03.2006 mit dem "BEST PAPER AWARD" des deutschen IEEE Instrumentation and Measurement (I\&M) Chapter ausgezeichnet.},
  language  = {en}
}
@article{MellingerSinghWegeneretal.2005,
  author    = {Mellinger, Axel and Singh, Rajeev and Wegener, Michael and Wirges, Werner and Gerhard, Reimund and Lang, Sidney B.},
  title     = {Three-dimensional mapping of polarization profiles with thermal pulses},
  issn      = {0003-6951},
  year      = {2005},
  abstract  = {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},
  language  = {en}
}
@article{MellingerWegenerWirgesetal.2001,
  author    = {Mellinger, Axel and Wegener, Michael and Wirges, Werner and Gerhard, Reimund},
  title     = {Thermally stable dynamic piezoelectricity in sandwich films of porous and non-porous amorphous fluoropolymer},
  year      = {2001},
  language  = {en}
}
@article{MellingerWegenerWirgesetal.2006,
  author    = {Mellinger, Axel and Wegener, Michael and Wirges, Werner and Mallepally, Rajendar Reddy and Gerhard, Reimund},
  title     = {Thermal and temporal stability of ferroelectret films made from cellular polypropylene/air composites},
  year      = {2006},
  abstract  = {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},
  language  = {en}
}
@article{MellingerWegenerWirgesetal.2006,
  author    = {Mellinger, Axel and Wegener, Michael and Wirges, Werner and Mallepally, Rajendar Reddy and Gerhard, Reimund},
  title     = {Thermal and temporal stability of ferroelectret films made from cellular polypropylene/air composites},
  year      = {2006},
  language  = {en}
}
@article{PhamPetreBerquezetal.2009,
  author    = {Pham, Cong Duc and Petre, Anca and Berquez, Laurent and Flores Su{\´a}rez, Rosaura and Mellinger, Axel and Wirges, Werner and Gerhard, Reimund},
  title     = {3D high-resolution mapping of polarization profiles in thin poly(vinylidenefluoride-trifluoroethylene) (PVDF- TrFE) films using two thermal techniques},
  issn      = {1070-9878},
  doi       = {10.1109/TDEI.2009.5128505},
  year      = {2009},
  abstract  = {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.},
  language  = {en}
}