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27 July 2004 Dynamic demodulation of long-gauge interferometric strain sensors
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Long-guage interferometric SOFO sensors have been in use for the last 10 years for the monitoring of civil, geotechnical, oil & gas and other structures. The sensors are based on an all-fiber Mechelson interferometer with one arm mechanically coupled to the structure and one used as reference. The original demodulation system is based on low-coherence interferometry. The path-matching readout unit features excellent long-term stability and preceision, but is not suitable for dynamic measurements because the scanning mirror requires about 7 seconds to acquire a complete interferogram. In order to allow the use of the same sensors for the measurement of dynamic events, a new demodulator was developed. It is based on the coherent demodulation of a coherence-colloapsed laser source and is able to demodulate 8 SOFO sensors at frequencies of up to 1 kHz with resolutions of 0.01 microns. This system is particularly adapted for the analysis of dynamic structural deformations produced by traffic, wind, seismic and impacts. The use of long-gauge sensors allows a direct measurement of the dynamic strains and the calculation of modal strains and curvatures. This paper presents the optical setup of the SOFO dynamic demodulation system and discusses its performances through the presentation of laboratory and field tests.
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Daniele Inaudi and Daniele Posenato "Dynamic demodulation of long-gauge interferometric strain sensors", Proc. SPIE 5384, Smart Structures and Materials 2004: Smart Sensor Technology and Measurement Systems, (27 July 2004);

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