@article{AltafimRychkovWirgesetal.2012,
  author    = {Altafim, Ruy Alberto Pisani and Rychkov, Dmitry and Wirges, Werner and Gerhard, Reimund and Basso, Heitor Cury and Altafim, Ruy Alberto Pisani and Melzer, Martin},
  title     = {Laminated tubular-channel ferroelectret systems from low-density Polyethylene Films and from Fluoroethylene-propylene Copolymer Films - A comparison},
  series = {IEEE transactions on dielectrics and electrical insulation},
  volume    = {19},
  journal   = {IEEE transactions on dielectrics and electrical insulation},
  number    = {4},
  publisher = {Inst. of Electr. and Electronics Engineers},
  address   = {Piscataway},
  issn      = {1070-9878},
  pages     = {1116 -- 1123},
  year      = {2012},
  abstract  = {A template-based lamination technique for the manufacture of ferroelectrets from uniform electret films was recently reported. In the present work, this technique is used to prepare similar ferroelectret structures from low-density polyethylene (LDPE) films and from fluoro-ethylene-propylene (FEP) copolymer films. A comparative analysis of the pressure-, temperature-, and frequency-dependent piezoelectric properties has been performed on the two ferroelectret systems. It is observed that the FEP ferroelectrets exhibit better piezoelectric responses and are thermally more stable. The difference between the piezoelectric d(33) coefficients of the two ferroelectret systems is partially explained here by their different elastic moduli. The anti-resonance peaks of both structures have been investigated by means of dielectric resonance spectroscopy and electroacoustic sound-pressure measurements. A difference of more than 10 kHz is observed between the anti-resonance frequencies of the two ferroelectret systems.},
  language  = {en}
}
@article{AssagraAltafimdoCarmoetal.2020,
  author    = {Assagra, Yuri A.O. and Altafim, Ruy Alberto Pisani and do Carmo, Joao P. and Altafim, Ruy A.C. and Rychkov, Dmitry and Wirges, Werner and Gerhard, Reimund},
  title     = {A new route to piezo-polymer transducers: 3D printing of polypropylene ferroelectrets},
  series = {IEEE transactions on dielectrics and electrical insulation},
  volume    = {27},
  journal   = {IEEE transactions on dielectrics and electrical insulation},
  number    = {5},
  publisher = {Inst. of Electr. and Electronics Engineers},
  address   = {Piscataway},
  issn      = {1070-9878},
  doi       = {10.1109/TDEI.2020.008461},
  pages     = {1668 -- 1674},
  year      = {2020},
  abstract  = {Here, a promising approach for producing piezo-polymer transducers in a one-step process is presented. Using 3D-printing technology and polypropylene (PP) filaments, we are able to print a two-layered film structure with regular cavities of precisely controlled size and shape. It is found that the 3D-printed samples exhibit piezoelectric coefficients up to 200 pC/N, similar to those of other PP ferroelectrets, and their temporal and thermal behavior is in good agreement with those known of PP ferroelectrets. The piezoelectric response strongly decreases for applied pressures above 20 kPa, as the pressure in the air-filled cavities strongly influences the overall elastic modulus of ferroelectrets.},
  language  = {en}
}
@article{QiuWirgesGerhard2014,
  author    = {Qiu, Xunlin and Wirges, Werner and Gerhard, Reimund},
  title     = {Polarization and Hysteresis in Tubular-Channel Fluoroethylenepropylene-Copolymer Ferroelectrets},
  series = {Ferroelectrics},
  volume    = {472},
  journal   = {Ferroelectrics},
  number    = {1},
  publisher = {Routledge, Taylor \& Francis Group},
  address   = {Abingdon},
  issn      = {0015-0193},
  doi       = {10.1080/00150193.2014.964603},
  pages     = {100 -- 109},
  year      = {2014},
  abstract  = {Polarization-vs.-applied-voltage hysteresis curves are recorded on tubular-channel fluoroethylene-propylene (FEP) copolymer ferroelectrets by means of a modified Sawyer-Tower circuit. Dielectric barrier discharges (DBDs) inside the cavities are triggered when the applied voltage is sufficiently high. During the DBDs, the cavities become man-made macroscopic dipoles which build up an effective polarization in the ferroelectret. Therefore, a phenomenological hysteresis curve is observed. From the hysteresis loop, the remanent polarization and the coercive field can be determined. Furthermore, the polarization can be related to the respective piezoelectric coefficient of the ferroelectret. The proposed method is easy to implement and is useful for characterization, further development and optimization of ferro- or piezoelectrets.},
  language  = {en}
}