FBG-based vibration sensor using gravity effects for large infrastructures

A simple mechanism for a vibration sensor based on fiber Bragg grating (FBG) is proposed. The mechanism utilizes the gravity force to allow the maximum sensitivity of the sensor into vertical direction while the minimum sensitivity for other two transverse directions. The sensor consists of a FBG cable and several masses to form a vibration system. The cable is extended to introduce a certain tensile force and acts as a spring. The sensitivity of the sensor is more than 1 μstrain/gal for vertical direction. This simple sensor has been developed for damage detection of large structures. Several prototypes were fabricated. And extensive shaking table tests were conducted to examine the performance.