The system of monitoring falling stones on highway by means of an optical interferometer

Abstract

ABSTRACT The Cenozoic Geology of Taiwan rises from the ocean, and therefore many areas in Taiwan do not have solid rocks. Suffering from the rock fall induced by earthquakes and frequent flood disasters in recent years, the geology even shows the flimsiness. Falling stones are fre quently found on the highway, and sometimes disasters take place. Because the optical fiber has the features of low loss and wide bandwidth; it has replaced the coaxial cable and became the mainstream of the communication system in recent years. Owing to interferometer has high sensitivity characteristic is usually applied to long distance, weak signal detection. In general, weak signal is difficult to monitor if the vibration is located at far away place. The configuration of our sensing system is made of an interferometer and fiber Bragg Grating. A demodulation circuit is used as the signal processor to measure the phase difference caused by vibration. The fiber optic sensor is an all fiber system with good accuracy for low frequency vibration measurement. According to our test, the dynamic range detected by the optic fiber sensor is 38 dB where the frequency ranges between 50 ~ 400 Hz. The minimum detectable signal level is around 1.95 x 10