[SI-LIST] Re: Loss Tangent question
- From: Peter Fekete <thefekete@xxxxxxxxx>
- To: doug@xxxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Mon, 28 Mar 2005 15:46:54 -0800 (PST)
One more step, since you asked for conductance, and
assuming you know the capacitance:
G=C*sigma/Kr
Which comes from the fact that G and C are calculated
by same relation, with sigma replaced by Kr.
If you use the loss tangent that gives you
G=omega*C*tand
--- Peter Fekete <thefekete@xxxxxxxxx> wrote:
>
> Doug,
>
> They have to give the same value of the imaginary
> part
> of the dielectric constant.
> A simplified deduction form Maxwell:
> curl H=J+j*omega*D = sigma*E +j*omega*Kr*E =
> j*omega*(Kr+sigma/j*omega)*E = j*omega*(Kr-j*Ki)*E
>
> Kr, Ki ? real, imaginary part of the dielectric
> constant (equivalent or effective)
> Thus:
> Ki=sigma/omega
> And also by definition Ki=Kr*tand which gives:
> tand=sigma/Kr*omega
> Sigma=2*pi*f*Kr*tand
> (include eps0 in Kr when calculating
> this,Kr=eps0*epsrelative)
>
>
> Note that from the physics point of view, the term
> loss tangent includes more than actual conductive
> losses, like for example losses due to reorientation
> of the crystal domains in feroelectric materials and
> various other loss mechanisms at atomic and
> molecular
> level.
> But for Maxwell?s equations they are equivalent to
> some frequency dependent conductivity, and that is
> the
> convention I used above (ie equivalent or effective
> conductivity).
>
> Agree with Steve on the frequency dependence.
>
>
>
> Peter
>
> --- steve weir <weirsi@xxxxxxxxxx> wrote:
> > Doug, yes, you can solve this as a phase plane
> > problem:
> >
> > The loss tangent expresses the ratio of the
> > conductance to the reciprocal
> > capacitive reactance at the test frequency.
> >
> > Loss tangent is frequency dependent, but changes
> > slowly. So, DC to
> > daylight is out. You will want the loss tangent
> for
> > the frequency range of
> > interest.
> >
> > Steve.
> >
> > At 12:05 PM 3/26/2005 -0800, Doug Brooks wrote:
> > >The model for a "lossy" (microstrip or stripline)
> > transmission line has
> > >terms for series resistance (skin effect) and
> > parallel conductance
> > >(dielectric losses.) If I have a specification
> for
> > loss tangent (at a
> > >particular frequency), is there a straightforward
> > way to get from loss
> > >tangent to conductance? That is, how do I
> calculate
> > conductance given a
> > >loss tangent?
> > >
> > >Secondly, if I know the loss tangent at one
> > frequency, can I therefore
> > >derive it for all other frequencies? Or are there
> > too many variables involved?
> > >
> > >Thanks for your input.
> > >
> > >Doug Brooks
> > >
> > >
> >
>
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