Post-Doc (Since February 2003)
This post-doc work is currently conducted at the Applied Mechanics and Reliability Analysis Laboratory in EPFL, the collaboration group during my Ph.D. work. My responsibilities have been to build a second OLCR apparatus for their needs, instruct the people how to use it and improve the method more specifically for strain sensing. I currently help my colleagues in measuring strains in diverse mechanical problems. We have very interesting results that will be available soon in publications.
Course at LMAF
I have organized in January 2004 a complete course on the retrieval of strain profiles with the combination of FBG gauges and reconstruction from the OLCR measurements. A Web version of the presentation is available.
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The main points treated in the course are enumerated hereafter. The course focused on issues for mechanical engineers, concretely how to reach the best resolution and S/N in strain measurements.
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Mechanics Point of View
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Mapping 3D stress or strain fields in samples
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Embedded FBG’s gauges
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Main problems
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Opto-mechanical models
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Opto-mechanical equations
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Understanding FBG’s
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Light / Material Interaction
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Single-mode fibers
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FBG description
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Representation Domains for FBG’s
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Example : Spatial / Time / Frequency Domains
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FBG Parameters and Relations between Parameters
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External influence (Naked FBG / Embedded FBG)
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Understanding OLCR
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Optical Low Coherence Reflectometry
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Fiber OLCR and FBG’s
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OLCR Set-up
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Signal Generation
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Detection Scheme
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Polarization Problems
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Time constants
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OLCR Properties
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Performing Measurements
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Measuring Intensity Spectral Response
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OLCR : Preliminary Tests
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Choosing the Parameters
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Judging a measurement
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Retrieving the Local Bragg Wavelength
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Quick View
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Methods for Switching Representation Domains
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Model : Spatial Description
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Model : Frequency Description
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Model : Time Description
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Time Domain to Spatial Domain Algorithm
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Calibration (Frequency Domain to and from Time Domain)
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Filtering (Wavelets)
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From Local Bragg to Strain Distribution
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Basic Equations (Simple Model)
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Remaining problem
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Interesting links
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Applied Mechanics and Reliability Analysis Laboratory (LMAF) : lmaf.epfl.ch
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