AN OPTICAL-FIBER SENSOR FOR MEASUREMENT OF DYNAMIC STRUCTURAL RESPONSE

This paper reports the development of and an experimental study on an optical fiber sensor for monitoring civil infrastructure systems. This optical sensor employs a vibrating wire whose tension can be modulate d by external force, strain, or vibration and transformed into the cha nge of frequency of wire vibration. The frequency of wire is detected by light sent to and reflected from the wire through an optical fiber cable. Compared to other optical fiber sensors developed so far, the p roposed sensor has two significant advantages: one is that the sensing head is a vibrating wire (rather than an optical fiber), which can se nse a specific physical quantity without being interfered by miscellan eous effects; the other is that the wire vibration is a well understoo d and reliable physical phenomenon and its frequency is optically meas ured and transmitted without attenuation or distortion through the opt ical fiber to recording and other devices. These advantages make the s ensor extremely simple, reliable and robust, and hence more readily de ployable in civil infrastructure applications. Three prototypes have b een developed and their static and dynamic characteristics have been e xperimentally tested. One of the prototypes was embedded into a concre te specimen to measure its strain and the result agrees with that from a conventional strain gauge. The experimental study with prototypes d emonstrates the high performance of the developed optical sensor in te rms of accuracy, high frequency range, and other characteristics.