Rebar diameter and rebar orientation using different antenna polarizations

It is well known, that the antenna polarization is a relevant parameter for the inspection of different orientations of rebars. In particular, an electric field that is parallel to the rebar orientation will result in a reflection that is much stronger than one caused by an electric field that is orthogonal to the rebar orientation. When horn antennas are used, it can be shown that both rebar orientations can be inspected even when driving in one direction only, because of the geometry of the ray path. This is not true for coupled antennas. This paper describes the basics of the influence of the antenna polarization and the raypath of horn antennas when compared to ground coupled antennas. This is followed by the description of a field test on a real bridge combined with extensive destructive testing. Both rebar orientations were mapped successfully by collecting data along lines parallel to the bridge axis. In addition, the diameter of the top orientation of rebars was successfully estimated by a comparison of the results for the concrete cover for the two orientations.