Interaction of guided electromagnetic waves with defects emerging in metallic plates

Ultra-wideband guided electromagnetic waves have been recently adopted to detect damage in structures. Transmission and reflection coefficients are indeed sensitive to any defect within the waveguide and can potentially warn the presence of hidden failures. Within this context, the paper shows a detection and localization approach for a structural health monitoring system based on elctromagnetic sensors permanently integrated with the structure to be monitored. A metallic plate is equipped with a dielectric waveguide patch attached to the structure's surface and a multi-input multi-output approach is adopted to interrogate the host component characterized by a reversible defect in different position. The findings show the sensitivity of transmission and reflection loss to the defect presence in between 3-20 GHz. Furthermore, an optimal frequency band beyond 12-15 GHz can be generally found. Based on wave spectrum changes, damage indicators result reliable means of detection. On top of that, they can be further elaborated to reconstruct and localize the defect. Both the amplitude and the phase of the signals are worth being investigated as detection and localization features.