1. a Departments of Civil Engineering and Geodesy, and Research in Materials and Structures , University of Ljubljana , Ljubljana , Slovenia
2. b Bundesanstalt für Materialforschung und -prüfung (BAM), Division of Acoustical and Electrical Methods , Berlin , Germany
3. c BAM , Berlin , Germany
4. d BAM, Division of Non-Destructive Damage Assessment and Environmental Measurement Methods , Berlin , Germany