1. Electrical Engineering Dept., Czestochowa University of Technology, Armii Krajowej 17, Czestochowa, Poland
2. Institut Charles Gerhardt, University Montpellier 2 and CNRS, Pl. E. Bataillon, Montpellier, France
3. Condensed Matter Physics Department, University of Geneva, 21 Quai E. Ansermet, Geneva, Switzerland
4. Electronic Department, Military University of Technology, Kaliskiego 2, 00-908, Warsaw, Poland