In this paper, a novel hybrid damage detection system is proposed, which utilizes piezoelectric actuators for guided wave excitation and a new fibre optic (FO) sensor based on Fabry-Perot (FP) and Fiber Bragg Grating (FBG). By replacing the FBG sensors with FBG-based FP sensors in the hybrid damage detection system, a higher strain resolution is achieved, which results in higher damage sensitivity and higher reliability in diagnosis. To develop the novel sensor, optimum parameters such as reflectivity, a wavelength spectrum, and a sensor length were chosen carefully through an analytical model of the sensor, which has been validated with experiments. The sensitivity of the new FBG-based FP sensors was compared to FBG sensors to emphasize the superiority of the new sensors in measuring micro-strains. Lastly, the new FBG-based FP sensor was utilized for recording guided waves in a hybrid setup and compared to the conventional FBG hybrid sensor network to demonstrate their improved performance for a structural health monitoring (SHM) application.

In a guided-wave-based damage detection hybrid system which combines piezoelectric transducers (PZT) and fiber Bragg grating (FBG) sensors, changes of temperature will affect both the propagation of Lamb waves and the fiber optic (FO) sensor’s spectrum. These variations will mask the changes caused by the occurrence of damage and thus make the damage detection unreliable, if not compensated for. This paper addresses the temperature effect calibration for Lamb wave signals measured by FBG-based Fabry Perot (FP) sensors. First, the temperature effect on the sensor’s spectrum is investigated, and a corresponding calibration method is derived and validated experimentally. After that, FBG-based FP sensor’s capability in measuring both Lamb wave signal (i.e. strain wave) and temperature separately is demonstrated. Finally, a validation test is conducted in which the current state signals are measured under a random temperature, different from that of the baseline temperature. Temperature effect on both sensor sensitivity and guided wave is calibrated based on the proposed calibration algorithm. The compensated signal is then tested with different types of damage index and its reliability in damage detection after applying the compensation algorithm is demonstrated.