The invention relates to a roller shutter for opening and closing a doorway having a door leaf and side rails for guiding the door leaf, and having a coiling device for selectively rolling up the door leaf for opening the doorway and unrolling the door leaf for closing the doorway. An annular member and a ring foil are provided between the separators. The fired kaolin is preferably surface-treated with a silane coupling agent. Each layer of dielectric material has a thickness that is an integral number of half-waves of the centre wavelength. The invention also relates to kits for carrying out this method and to the cell preparations prepared by this method. The carrier plug removeably couples with the plug of the docking assembly.