1. Laboratory of Condensed Matter, Electronics and Signal Processing, Department of Physics, University of Dschang, P.O. Box 67, Dschang, Cameroon
2. Laboratory of Modelling and Simulation in Engineering, Biomimetics and Prototypes, Department of Physics, Faculty of Science, University of Yaoundé 1, P.O. Box 812, Yaoundé, Cameroon
3. Applied Physics Research Group (APHY), Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
4. GeorgiaTech-CNRS Joint International Laboratory (UMI 2958), Atlanta Mirror Site, School of Electrical and Computer Engineering, 777 Atlantic Dr NW, Atlanta, Georgia 30332, USA