Wireless interrogation of passive crack sensor

This study aims to apply passive wireless (PW) sensors for structural bridge inspections. In this paper, an innovative passive wireless sensor consisting of an interdigital capacitor (IDC) and a loop inductor antenna is proposed for crack monitoring. The crack sensing element is fabricated using photolithography processes consisting of a polyimide composite film on a substrate and rolled-annealed copper foil. The proposed inductive coil consists of a coated copper wire with circular geometry. The abovementioned components work together as an LC resonator whose resonant frequency was designed to change correspondingly with the size, shape, orientation, and propagation of the monitored crack. The capacitance value of the IDC sensor depends on the crack initial position, orientation, and crack length. The LC frequency reader detects the frequency variation by monitoring the impedance across the terminals of the wide bandwidth reader antenna. Thereafter, the crack growth is retrieved and interpreted based on the received signal from the reader by the resonant frequency shift. The sensor was experimentally validated showing an increase in its resonant frequency with an increase in crack size. The comparison with physical damage of a steel specimen showed that the system is capable to wirelessly monitor crack propagation.