Abstract
An optical fiber sensing system integrating a fiber Bragg grating (FBG) sensor, a long-period fiber grating (LPFG) optical filter and a photodetector is presented to monitor the dynamic response of a structure subjected to base excitation and impact loading. The FBG sensor is attached to a test specimen and connected to an LPFG filter. As the light reflected from the FBG sensor is transmitted through the long-period fiber grating filter, the intensity of the light is modulated by the wavelength, which is affected by the strain of the FBG. By measuring the intensity of the light using a photodetector, the wavelength reflected from the FBG sensor can be demodulated, thus leading to the determination of the strain in the structure. To demonstrate its effectiveness, the proposed sensing system was employed to measure the dynamic strain of a beam subjected to mechanical testing. The mechanical tests comprised three load scenarios: base excitation by a shaker at resonant frequency, impact loading by a hammer and shock test on a drop table. To monitor the dynamic strain during the test and validate the accuracy of the measurement of the FBG sensor, strain gauge was used as reference. Experimental results show good correlation between the measurements of FBG sensor and strain gauge. The present work provides a fast response and easy-to-implement optical fiber sensing system for structural health monitoring based on real-time dynamic strain measurements.
Highlights
Sensing technologies for real-time monitoring of engineering structures are very important, since in-service monitoring can lead to the improved safety and performance of engineering structures.Traditional sensors such as the strain gauge and the load cell are mostly based on electrical working principles to measure physical quantities such as strain, force or temperature
Zou et al [32] measured dynamic strain using two wavelength-matched Fiber Bragg grating (FBG) sensors interrogated with a cascaded Long-period fiber gratings (LPFG)
An FBG sensor is attached at the center of the cantilever beam
Summary
Sensing technologies for real-time monitoring of engineering structures are very important, since in-service monitoring can lead to the improved safety and performance of engineering structures. Zou et al [32] measured dynamic strain using two wavelength-matched FBG sensors interrogated with a cascaded LPFG. An FBG sensor with a constant grating period index will reflect light at a single Bragg λ B = and 2 n 0 refractive. Change in the grating period and index of refraction due to the strain and temperature will lead to a shift of the Bragg wavelength. Using Equation (3), the refractive index with a grating period on the order of hundreds of microns along the core of a singlelongitudinal strain in the sensor can be determined by the measured Bragg wavelength shift. Since the coupling is wavelength-selective, LPFG acts as a wavelengthrefractive index with a grating period on the order of hundreds of microns along the core of a single-mode dependent band stop filter.
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