A vibration monitoring system based on Sagnac interferometer with a novel algorithm

An economical and reliable fiber-optic vibration sensing system is proposed in this paper, which can eventually cooperate with distributed fiber sensing systems for long-span structural inspection. The system is designed to monitor the vibration state of the position to be measured, based on the principle of a Sagnac fiber-optic sensor. A novel algorithm of analyzing the strength ratio between a certain frequency band and the background frequency band of the signal is employed in this sensing system. Two sets of experiments were implemented to validate the reliability of the algorithm. In the first experiment, we tested whether the algorithm can recognize the sensing fiber was trampled. Application of the sensing system on a cast-iron pipeline detection was performed in the second experiment. Experimental results showed that the forced vibration frequency of the pipeline is between 170~230 Hz, and the sensing system is reliable for rapid recognizing the vibration state of the sensing fiber, which indicated that this system has a potential in application of field measuring as a part of traditional distributed optical fiber sensing system.