Abstract
A FOD (Fiber Optic Doppler) sensor that can measure AE (Acoustic Emission) has been invented and developed. The measuring principle is completely different from that of the conventional PZT type AE sensor. The FOD sensor is made by looping a optical fiber and it is glued on object to measure vibration. It measures the vibration as the frequency changes of laser light due to the Doppler effect. The FOD sensor has the following advantages; (1) small diameter and small weight, (2) immunity from the electromagnetic noises, (3) durability and corrosive resistance, (4) usability under high temperature, (5) long-range transmission, and (6) low cost. In order to examine applicability of the FOD sensor to monitoring of rock structures, the authors compared the sensitivity and the frequency response of the FOD sensor to those of the convertional PZT type sensor in laboratory experiments. The results indicated that the FOD sensor has strong possibility to be used for real rock structures.
