Claude Belleville

White-light interferometric multimode fiber-optic strain sensor

A white-light interferometric extrinsic Fabry-Perot strain sensor that uses a multimode fiber is demonstrated. The Fabry-Perot cavity length is measured with the help of a Fizeau interferometer. The sensor is described, and some results obtained at this time are given. The strain measurements are absolute and perfectly linear, with a sensitivity of 0.25 micrometers per meter (micro). the design of a thermally autocompensated strain sensor is also presented.

SMART SKINS - A STEP TOWARD A PRACTICAL FIBRE-OPTIC SENSOR

Intelligent structures are those which highly integrate sensors to provide information on the state of the structure1. The complete sensing of the structure may require strain, pressure, thermal, chemical or electrical sensors, while a mechanically intelligent structure is sensed mainly by strain sensors. In recent years, many efforts have been devoted to develop a fibreoptic strain sensor with characteristics suitable for intelligent structures. We have developed a white-light interferometric multimode fibre-optic sensor with great potential for use in smart structures. This sensor is very versatile since the gauges can be configured so as to be sensitive to different parameters such as strain, temperature, pressure, humidity, etc2. In the specific case of strain, our sensor is perfectly linear, can be thermally self-compensated, is not sensitive to transverse strain, and provides precise, absolute and stable measurements over long periods of time, at a cost competitive with conventional techniques. 54 Fabry-Perot strain gauges, configured as 18 strain rosettes, have been embedded inside a propeller blade of a Polar Class icebreaker. The large number of gauges serves to monitor the distribution of load induced by the impact of ice on the propeller. In this paper, the basic principle of operation of our sensor is described, and some preliminary results obtained with the smart blade are presented.