Development of optical sensing systems for smart civil infrastructure

Abstract

This paper proposes an optical sensing system for smart civil infrastructure applications and reports on prototype development and preliminary experimental studies. The proposed optical sensors employ a vibrating wire whose tension can be modulated by external force, strain, or vibration and is translated into a change in the wire's vibration frequency. The wire's vibration frequency is detected by light sent to and reflected from the wire through an optical fiber cable. Compared to other existing optical fiber sensors, which tend to suffer from lack of reliability and robustness, the proposed sensors have 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 interference from miscellaneous effects; and the other is that wire vibration is a well understood physical phenomenon. In fact, with a high level of reliability, its frequency is optically measured and transmitted to recording and other devices through the optical fiber without attenuation or distortion. These advantages make the sensor system simple, reliable and robust, and hence more readily deployable in civil infrastructure applications. The experimental study with the prototype demonstrates its high performance as a sensor in terms of accuracy, high dynamic range and other characteristics. Such a sensor can be easily modified as a load cell, strain gauge, accelerometer and pressure sensor, and cost-effectively extended to a distributed sensing network with multiple sensor heads sharing the same optical components.