1. Department of Physics, Faculty of Sciences, University of Yaounde 1, Yaounde, Cameroon
2. Department of Electrical and Telecommunications Engineering, Ecole Nationale Supérieure Polytechnique, University of Yaounde 1, Yaounde, Cameroon
3. Department of Electrical and Power Engineering, University of Bamenda, Bamenda, Cameroon
4. CRIStAL Laboratory, CNRS-UMR, University of Lille, Nord, France