Design, fabrication, and validation of passive wireless resonant sensors for NDT/SHM

Detection of visible crack, delamination etc. in composite structures can be fulfilled by several techniques. However, the problem is of greater complexity in the case of nonvisible defects such as barely visible impact damage and microcracks. The objective of this research work was to create and validate a low cost smart-sensor for NDT and structural health monitoring (SHM) to be used for complex geometries. The smart-sensor presents a dual function, i.e. it determines the presence of delamination and cracks within the cross-section but it also provides information on surface damages due to fatigue or impacts. In the latter case the damage could induce the breakage of the sensor that could still work with a different resonant frequency. The sensor utilizes a passive wireless resonant telemetry scheme based on an inductor capacitor (LC). The use of a passive system eliminates the need for onboard power and exposed interconnects, increasing the life of the device and the reliability due to the continuous operation even in case of damage results from the sensor. The sensor design, the signal processing and the experimental setup that validate the remote interrogation of the antenna sensor are presented. Two different designs were investigated, one for conductive surface and one for nonconductive surface (fiberglass-composite).