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Light waves travelling in a material.

  1. Jun 9, 2013 #1
    Hi all.

    I am doing a project in which I have a 99%clear transparent Silicone sheet. LEDs make light pass through this material which is than picked up by phototransistors on the other side. when someone/something touches the Silicone, this deforms and the phototransistors pick up different light signals. I need to understand how light behaves when a touch on the Silicone is made. Could someone help me please?
  2. jcsd
  3. Jun 10, 2013 #2


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    What tells you that the silicone alters the light transmission when it deforms?
  4. Jun 10, 2013 #3
    I assumed it since the phototransistors change the voltage they produce
  5. Jun 10, 2013 #4


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    Just to be clear, you've already tested this and seen the voltage change when you press on the sheet?
  6. Jun 10, 2013 #5
    Yes i did. I just wish to understand how it is happening..
  7. Jun 11, 2013 #6
    Thanks! This is a photo of the silicone being touched. Do you kindly have any good links where I can learn more about this please?

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  8. Jun 11, 2013 #7


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    Does it really have to do with silicone or is the "touch" deforming the surface slightly? That would change the direction of the light beam through the silicone and so (assuming the light beam was originally aimed at the phototransistors) reduce the light hitting the phototransistor.
  9. Jun 11, 2013 #8
    yes it does but also I reckon that by a touch, physical properties change in the silicone and there might be some more internal reflections, dispersion and refractive index in the material.
  10. Jun 14, 2013 #9

    Claude Bile

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    If the light source is incoherent (which I am assuming is the case since you have a LED source), then surface deformation is the only plausible explanation.

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