1. a Department of Electrical and Electronic Engineering, Faculty of Engineering , Shinshu University , Wakasato 500, Nagano, 380, Japan
2. b Department of Physics, Faculty of Science , Shinshu University , Asahi 3-1-1, Matsumoto, 390, Japan
3. c Department de Physique, Fuculte des Siences , Universite Ibn Tofail , Kenitra, Morocco