@article{WegenerWirgesTiersch2006,
  author    = {Michael Wegener and Werner Wirges and Brigitte Tiersch},
  title     = {Porous polytetrafluoroethylene (PTFE) electret films : porosity and time dependent charging behaviour of the free surface},
  doi       = {10.1007/s10934-006-9015-0},
  url       = {http://www.springerlink.com/content/601u86x365560515/},
  year      = {2006},
}