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Optical Radiation vs Radio Frequencies

Discussion in 'Lighting' started by Roger Breton, Jan 16, 2004.

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  1. Roger Breton

    Roger Breton Guest

    Visible light rays can be reflected or refracted or otherwise controlled
    through lenses. Not gamma rays I read. They will go through any material.
    Same as cosmic rays I guess. What happens at the longer end of the EM
    spectrum: do EM radiations with wavelengths longer than visible light keep
    behaving as visible light in that they can be reflected by mirrors,
    rectified by lenses? For example, let's say that I am inside a building. How
    do the waves from the radio or TV station I listen to reach my receptor? I
    guess they must travel through walls, get attenuated at some point. But
    visible light does not have these properties, obviously. What is it,
    physically, in the nature of wavelengths other than visible that allow them
    to traverse inpune any material?

    If this is not the right forum for these kinds of questions please let me
    know kindly ;-)

    Roger Breton
     
  2. Don Stauffer

    Don Stauffer Guest

    All em waves can exhibit effects we see with light. Gamma rays actually
    can be reflected or bent, if you have the right setup, like special
    gratings. Same for X-rays. Most cosmic rays are high energy particles
    rather than EM radiation (photons).

    One can make radio wave antennas that work just like lenses, though for
    longer wave RF they would have to be huge. However, this is common with
    shorter wavelength microwaves. It is very possible, and commonly done,
    to make radar antennas out of dielectric materials. And hills, ridges,
    buildings, etc., diffract radio waves, which is why it is possible to
    receive FM broadcasts even when you are out of direct line of site of
    transmitting antenna.
     
  3. The physics is the same for all types of EM radiation. the trick is to
    find materials that have the required proprieties at the wavelength of
    interest. Radio waves can and very often are reflected using "mirrors"
    made from metal or other electrical conductive material. Just look at
    any satellite TV dish. It is also possible to use dielectric materials
    to make "lenses" to focus long wave EM radiation such as radio and TV
    signals.
     
  4. ddwyer

    ddwyer Guest

    Possible now to produce microwave lenses with -ve refractive index
    (negative phase delay?) moves to produce optical eq.
    Dont think there will be binoculars to se in the future though!
     
  5. There are plasma waves where the phase velocity is in the opposite
    direction than the group velocity. Since the group velocity is always
    directed away from the antenna used to launch the wave, this means the
    phase velocity is directed toward the antenna.
     
  6. That is OK. There is no reason why the phase velocity of a wave cannot
    be faster than the speed of light. Information is carried at the group
    velocity, and THAT cannot exceed the speed of light.
     
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