Electromagnetic properties of iron oxide corrosion product powders at radio frequencies

We calculated the refractive index from Sparameter data for corrosion samples tested in waveguide from 12.4 GHz to 110 GHz. This approach minimizes the modal noise often seen in derived permittivity and permeability for low-loss samples in this range. Also, any resonance absorption due to atomic structure is made clearly discernible. We are interested in observing spectral signatures with network analyzer measurements to quantify corrosion in reinforcing steel embedded in concrete. Here, we report room-temperature measurements of the refractive index for magnetite, maghemite, goethite, hematite, calcium ferroaluminate, and bridge girder corrosion powders, all of which exhibit flat spectral responses.