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 modulated by external force, strain, or vibration and transformed into the change 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 proposed sensor has two significant advantages: one is that the sensing head is a vibrating wire (rather than an optical fiber), which can sense a specific physical quantity without being interfered by miscellaneous effects; the other is that the wire vibration is a well understood and reliable physical phenomenon and its frequency is optically measured and transmitted without attenuation or distortion through the optical fiber to recording and other devices. These advantages make the sensor extremely simple, reliable and robust, and hence more readily deployable in civil infrastructure applications. Three prototypes have been developed and their static and dynamic characteristics have been experimentally tested. One of the prototypes was embedded into a concrete specimen to measure its strain and the result agrees with that from a conventional strain gauge. The experimental study with prototypes demonstrates the high performance of the developed optical sensor in terms of accuracy, high frequency range, and other characteristics.