1. Basis of Electronics Department, Faculty of Electronics, Telecommunication and Information Technology, University of Cluj-Napoca, 400114 Cluj-Napoca, Romania
2. Applied Physics Department, Escuela Politécnica Superior, University of Zaragoza, Crta. de Cuarte s/n, 22071 Huesca, Spain
3. Applied Physics Department, Engineering Research Institute of Aragon (I3A), Faculty of Science, University of Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza, Spain