1. Fraunhofer Institute for Biomedical Engineering, Invalidenstrasse 42, 10115 Berlin, Germany
2. University of Freiburg, Department of Microsystems Engineering, Laboratory for MEMS Applications, G.-Koehler-Allee 106, 79110 Freiburg, Germany
3. Institut fuer Mikro- und Informationstechnik der Hahn-Schickard-Gesellschaft, W.-Schickard-Strasse 10, 78052 Villingen-Schwenningen, Germany