[SI-LIST] Re: (no subject)
- From: "Scott McMorrow" <scott@xxxxxxxxxxxxx>
- To: jeff.loyer@xxxxxxxxx
- Date: Tue, 10 Dec 2002 14:21:06 -0800
Jeff,
The assumption that is often unstated or weakly stated is that the
materials are "ideal" , have no losses and have uniform properties at
all frequencies. Then dispersion is not possible. For real materials,
as Steve Corey has pointed out, we have dielectric loss, which then
requires that dielectric constant will change across frequency. We also
have non-perfect conductors with finite conductivity, which requires
that resistance and inductance are also functions of frequency.
The reality is that all real conductors in all real media have losses
and have dispersion across the frequency spectrum. Even for stripline
traces in a homogenous media with extremely low losses, the conductance
of the trace gives rise to "skin effect" losses and wildly changing
inductance (and therefore wave propagation velocity) in the
mid-frequency band of 100 kHz to 100 MHz.
best regards,
scott
--
Scott McMorrow
Teraspeed Consulting Group LLC
2926 SE Yamhill St.
Portland, OR 97214
(503) 239-5536
http://www.teraspeed.com
Loyer, Jeff wrote:
>Thanks for the information. I'm still a bit confused. For further =
>clarification:
>
>In your first point, you imply that, for a homogenous medium, dispersion =
>is not possible (and Pozar implies this same thing for a TEM plane wave =
>on page 170 of his book). Is that correct? =20
>
>I thought Er could vary with F. For instance, in optics, v =3D c/n, =
>where v is the phase velocity of a wave, c is the speed of light in a =
>vacuum, and n is the refractive index of the material. For light, this =
>refractive index is a function of frequency (hence prisms work). If Er =
>varied with F, wouldn't you get dispersion?
>
>What am I missing?
>
>Jeff Loyer
>
>
>
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