For example, the wave impedance for a highly conductive material such as silver or copper is essentially zero, whereas that for a non-ferrous, non-conducting material such as dry concrete or soil is given by: ##EQU2## where ??0 is the permeability of free space (a constant), ??0 is the permittivity of free space (a constant), and ??r is the relative dielectric constant of the material in question.