1. Assistant Professor, School of Electrical and Nuclear Engineering, Sudan Univ. of Science and Technology, P.O. Box 407, Khartoum, Sudan (corresponding author).
2. Lecturer, School of Electrical and Nuclear Engineering, Sudan Univ. of Science and Technology, P.O. Box 407, Khartoum, Sudan.
3. Professor, Dept. of Electrical and Computer Engineering, Karary Univ., P.O. Box 12304, Omdurman, Sudan.