1. University of Yaoundé I, Faculty of Science, Department of Physics, Materials Science Laboratory, P.O. Box 812, Yaoundé, Cameroon
2. University of Dschang, IUT Bandjoun, Department of General and Scientific Studies, P.O. Box 134, Bandjoun, Cameroon
3. University of Bamenda, National Higher Polytechnic Institute, Department of Electrical and Electronic Engineering, P.O. Box 39, Bambili, Cameroon