1. Institute for Electronics; Swiss Federal Institute of Technology; Gloriastrasse 35 Zurich 8092 Switzerland
2. Division of Engineering and Applied Science; California Institute of Technology; Pasadena CA 91125 USA
3. Institute of Mechanical Systems; Swiss Federal Institute of Technology; Leonhardstrasse 21 Zurich 8092 Switzerland
4. Sensor Technology Research Center School of Engineering and Informatics; University of Sussex; Richmond 3A7 Brighton BN1 9QT UK