Reconstruction of sub-wavelength fractures and physical properties of masonry media using full-waveform inversion of proximal penetrating radar

High-frequency, ultra-wideband penetrating radar has the potential to be used as a non-invasive inspection technique for buildings, providing high-resolution images of structures and possible fractures affecting constructions. To test this possibility, numerical and laboratory experiments have been conducted using a proximal, stepped-frequency continuous-wave radar system operating in zero-offset mode, spanning the 3–8 GHz frequency range. The reconstruction of the material electrical properties is achieved by resorting to full-waveform inverse modeling. Numerical experiments showed that for typical electric permittivity and electrical conductivity values of concrete and plaster, it is possible to retrieve the physical properties of the material and to detect fractures less than 1 mm thick. Laboratory experiments were conducted on non-reinforced concrete and plaster test slabs in different configurations. The results showed the good potential of this method: (1) to provide a thorough fracture response model in buildings or artworks and (2) to non-invasively characterize the samples in terms of their electromagnetic properties.

Research Highlights
► Quantitative analysis for localization and characterization of hidden fractures.
► Exact model exploiting the magnitude and phase of the reflection coefficient.
► The ability to detect 1 mm planar fractures in building materials is shown.
► Fracture thickness retrieved in numerical and laboratory experiments.