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Distributed Strain Sensing with FO Bragg Gratings

  1. Mar 14, 2006 #1
    Not really something I would expect most people to know so I will keep it out of the Homework help section (it is not homework)

    I am working on distributed strain sensing with fibre optic Bragg gratings for aircraft.

    For those that dont know, FO Bragg gratings are a periodic variation in refractive index along an optical fiber. Light who's wavelength is equal to the spacing between variations will be reflected via Bragg reflection. Any slight change in the period of the index variations means the wavelength of light reflected changes. You can therefore meansure strain by monitoring the peak wavelength that is reflected due to a strain change(1.22pm/micostrain)

    Unfortunatly, that technique only works for point sensing and will not work unless a crack or whatever effects the exact location of the grating. So, we want a distrobuted strain sensor that can cover a larger length. Just monitoring the reflection data will tell you if there is a change in strain but it will not tell you where it is along the grating.

    This can be found outby finding the phase information as well as the reflection data. In my case, we are using what is called Layer Peeling to extract the strain infroamtion from the phase and reflection. It works quite well but my predesessor who was developing the measurment system left the strain profile in dφ/dλ and not in any strain units.

    None of the papers he kept and no amount of searching through the mountain of papers on strain sensing on the internet seem to give the linear scaing factor needed to convert dφ/dλ to strain.

    My part involves taking the system that he has produced and testing it against existing systems. I do not know the full details of the matematics involved and I can not understand what might need to be done to convert dφ/dλ to strain.

    If anyone could help me out on this it would save me a whole lot more searching. it is out there somewhere I just dont know where to look. It is a simple linear factor I am told.
  2. jcsd
  3. May 11, 2011 #2
    I'm four years behind on this post, but is this something you are still working on? I could help you out and would like to hear more about what you're working with.
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