1. Institute of Nuclear and Physical Engineering, Faculty of Electrical Engineering and Information Technology, Slovak University of Technology in Bratislava, Ilkovičova 3, 812 19 Bratislava, Slovakia
2. Department of Physics, South Ukrainian National Pedagogical University, 65020-Odessa, Ukraine
3. Institute of Electrical Engineering, Slovak Academy of Science, Dúbravská cesta 9, 841 04 Bratislava, Slovakia