1. Department of Physics, Faculty of Mechanical Engineering, University of Technology and Humanities in Radom, E. Stasieckiego 54, 26-600 Radom, Poland
2. Institute of Experimental Physics SAS, Watsonova 47, 040 01 Košice, Slovakia
3. Department of Electrical Power Engineering, Technical University of Košice, Faculty of Electrical Engineering and Informatics, Mäsiarska 74, 041 20 Košice, Slovakia