Measurement and Simulation of Millimeter Wave Scattering Cross-sections from Steel-Reinforced Concrete
Ahmed M. Hassan, Edward J. Garboczi, Robert D. McMichael, Jack T. Surek, Mark D. Stiles, David F. Plusquellic, Virgil Provenzano, Paul E. Stutzman, Shuangzhen S. Wang, Sung Kim, Michael D. Janezic, Jason B. Coder, Nicos Martys, David R. Novotny
Some iron oxide corrosion products exhibit antiferromagnetic magnetic resonances (AFMR) at around 100 GHz at normal temperatures. AFMR can be detected in laboratory conditions, which serves as the basis for a new non-destructive spectroscopic method for detecting early corrosion. When attempting to measure the steel corrosion in reinforced concrete in the field, the actual local rebar geometry must be taken into account. Experiments and numerical simulations have been developed at around 100 GHz to sort out these effects. The experimental setup involves a network analyzer with converter heads to up-convert the output frequency, which is then connected to a horn antenna followed by a 7.5 cm diameter polymer lens to focus the waves on the sample. Two sets of samples were studied: uniform cylindrical rods and genuine rebars with different kinds of coatings. The electromagnetic scatterings from uniform rods were calculated numerically using classical modal expansion. A finite-element electromagnetic solver was used to model more complex rebar geometry and non-uniform corrosion layers. Experimental and numerical data were compared to help quantify and understand the anticipated effect of local geometrical features on AFMR measurements.