1 University of Mons, Department of Theoretical Mechanics, Dynamics and Vibrations, Mons, Belgium. Electronic address: georges.kouroussis@umons.ac.be.
2 University of Thessaly, Department of Civil Engineering, Laboratory of Transportation Environmental Acoustics (L.T.E.A.), Pedion Areos, 38334 Volos, Greece. Electronic address: kvogiatz@uth.gr.
3 University of Ioannina, Department of Physics, University Campus, GR-45110 Ioannina, Greece. Electronic address: pkassom@uoi.gr.