Innovative ultrasonic fiber optic sensors offer an opportunity for early-stage, localized detection of defects (e.g., steel corrosion) in reinforced concrete (RC) structures. The use of optical fibers enables engineers to develop small size sensors used inside RC structures without creating significant interfacial effects. Recently, a new ultrasonic fiber optic sensor using gold nanocomposite and utilizing the photoacoustic effect has been proposed for the early stage surface corrosion detection in RC structures. By generating and receiving surface ultrasonic waves at the tip of the sensor using gold nanocomposite, presence of surface corrosion can be detected and located. In this study, wave propagation behavior of the proposed ultrasonic fiber optic sensor inside steel specimens is investigated in order to optimize the design of such sensors for civil infrastructure monitoring. Finite element (FE) simulations using ABAQUS were conducted on a steel plate specimen where one side was excited by the fiber optic sensor and the other was measured by a lead zirconate titanate (PZT) transducer. A wide-bandwidth impulse signal in the frequency range of 0~25 MHz was applied. Multiple reflections generated by the photoacoustic excitation and measured by the PZT transducer were experimentally collected and numerically simulated. From our result, it is found that the simulated response of the proposed ultrasonic fiber optic sensor verifies the fidelity of the FE model. Such FE models provide the basis for future research such as surface rust detection of steel rebars in concrete.

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