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Abstract
This paper presents the results of an experimental study on an innovative electro-optical fiber sensor developed for measuring the dynamic response of civil structures such as buildings and bridges, which can be used for non-destructive evaluation of structural systems. This electro-optical sensor employs an electric circuit, LC oscillator, in which inductance and capacitance are connected in parallel. The resonant frequency of the LC oscillator is modulated by the external displacement transmitted through the core of the induction solenoid. This frequency is detected from the optically-transmitted oscillatory signal and the LC oscillator is optically powered. Compared to the conventional optical fiber sensors developed so far, the proposed sensor has two significant advantages: 1) the sensing head is an electric circuit (rather than an optical fiber cable), which can sense a specific physical quantity without interference from miscellaneous effects and is expected to be much more durable than the sensing head made of optical fiber cable as seen in usual extrinsic optical fiber sensors; 2) the LC oscillator is a well understood and reliable circuit with its resonant frequency measurable and transmittable without attenuation or distortion through an optical fiber cable over a long distance to recording and other devices. These advantages make the sensor extremely simple to design and manufacture, durable, reliable, robust to use, and hence, more readily deployable in civil structural applications. A prototype electro-optical strain sensor has been developed and its static and dynamic characteristics were experimentally tested. This sensor was also installed on a steel frame to measure the dynamic strain response when subjected to seismic ground motions during a shaking table test. The experimental study using the prototype demonstrated excellent performance of the electro-optical sensor in terms of accuracy, wide frequency range, and other advantageous characteristics for civil structural applications.
