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Chapter V Dielectric Study of ……
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Here, D0 and E0 are amplitudes of the displacement and electrical fields,
respectively. The response of a medium to static electric fields is described by
the low frequency limit of permittivity (also called the static permittivity) or
dielectric constant r or s.
S = lim ω → 0 * (ω) (5.16)
At high frequency limit, the complex permittivity is commonly preferred
to as ∞. At plasma frequency and above, dielectric behave as ideal metals,
with electron gas behavior. The static permittivity is a good approximation for
the low frequency altering fields but as the frequency increases a measurable
phase difference δ comes in to the picture between D and E. The frequency at
which the phase shift becomes noticeable depends on the temperature and
the details of the medium. For the moderate field strength (E0), D and E
remain proportional, therefore,
* = =
i
. e
(5.17)
As the response of the materials to alternating fields is characterized
by a complex permittivity, it is needed to isolate the real and imaginary parts,
and hence
* (ω) = ’(ω) - i”(ω) = (5.18)
Where, ’ is the real part of the permittivity and ” is the imaginary part of the
permittivity. The ” is related to the rate at which energy is absorbed by the
medium and converted into thermal energy [5].
The complex permittivity is generally a complicated function of
frequency, because it is a superimposed description of dispersion phenomena
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