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Calculating phase velocity in a material

  1. Nov 30, 2011 #1
    Calculating wavelength in a media

    Hi

    Trying to get how to calculate the wavelength of an electromagnetic wave in a media and I am getting confused about the permittivity.

    I know the formula:

    vphase = c/(sqrt(εrr))

    where vphase is the phase velocity.
    c is the speed of light in a vacuum.
    εr is the relative permittivity.
    μr is the relative permability.

    Then to get the wavelength we do like this:

    λ = vphase/f

    where λ is the wavelength and f the frequency.

    This is all well and good, but isn't there a real and imaginary part to the permittivity? Is only the real part used or is the entire complex number used in which case you end up with a complex distance??
     
    Last edited: Nov 30, 2011
  2. jcsd
  3. Nov 30, 2011 #2

    NascentOxygen

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    Staff: Mentor

    Re: Calculating wavelength in a media

    I've never heard of it being anything but real? Can you cite something that causes you to think it is a complex number?
     
  4. Nov 30, 2011 #3
    Re: Calculating wavelength in a media

    http://www.random-science-tools.com/electronics/water_dielectric.htm

    One of many but shows the principle nicely.

    The dielectric constant is for most (all?) dielectric materials frequency dependant and is often written as εr=ε'-iε''

    where ε' is the real part and is related to the stored energy inside the medium
    ε'' is the imaginary part and related to the loss inside the medium

    https://en.wikipedia.org/wiki/Permittivity
     
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