[1] Stanislaw Staszic Univ Min & Met, Dept Elect, PL-30059 Krakow, Poland
[2] Inst Elect Mat Technol, PL-01919 Warsaw, Poland
[3] Polish Acad Sci, Inst Phys, PL-02668 Warsaw, Poland
[4] Univ Sheffield, Dept Phys, Sheffield S3 7RH, S Yorkshire, England