1. Faculty of Information Technology and Communication Sciences, Tampere University, Korkeakoulunkatu, 3, 33720 Tampere, Finland
2. Department of Electrical and Electronics Engineering, College of Technology, University of Buea, P.O. Box 63, Buea, Cameroon
3. Faculty of Engineering and Natural Sciences, Tampere University, P.O. Box 692, FI-33014 Tampere, Finland
4. Tampere Microscopy Center, Tampere University, Korkeakoulunkatou, 3, 33720 Tampere, Finland
5. Department of Electrical & Computer Engineering, The Ohio State University, Columbus, Ohio 43210