Please define "middle of the plane" first before continuing with this
discussion.
Are you talking about middle in the x-y, or z direction?
Thanks,
Arpad
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-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Doug Brooks
Sent: Monday, December 9, 2019 2:20 PM
To: shlepnev@xxxxxxxxxxxxx; 'SI' <si-list@xxxxxxxxxxxxx>
Subject: [SI-LIST] Re: Skin effect on ground plane?
Yuriy
OK Upon closer look at your demo-video, I see what you are saying.
However I am not sure I agree about something.
Given a trace, without an underlying plane, as the frequency increases, the
current density is higher around the surfaces (top, bottom and
sides) than it is in the middle of the trace. Absent any external influence,
the current density decays exponentially from a surface to the centerline of
the trace. In general, the current density pattern would be symmetrical around
the trace (top to bottom, side to side).
Now, bring a plane adjacent to the trace. This introduces an effect typically
called a proximity or a ground effect. The opposite sign attraction causes some
of the current flowing on the top (far) surface to migrate to the bottom
(close) surface. So the current density shifts a little --- higher on the
bottom surface, not as high on the top surface, but still smallest along the
middle or centerline of the trace.
The mutual inductance effect that causes the skin effect in the first place
dominates the opposite sign attraction of the proximity effect, so the current
is still smallest at the centerline.
All of this is true, at any frequency.
It seems to me your simulation at around 2:45 starts to support that, on both
the trace and the plane.
Do you agree with me so far?
If so, why is it that "current density is not lower in the middle of the plane."
Doug
Yuriy Shlepnev wrote:
Hi Doug,
The current density is not lower in the middle of the plane - it is just
visual impression. Smaller number of arrows is used in the middle of the
metal layer and it may create impression that the density values are lower in
the middle (same for power flow densities). Each arrow and color presents the
Current Density value in A/m^2 at a particular location within the metal.
Density of the arrows does not correlate with the current density (see more
at webinar #7 at https://www.simberian.com/Webinars.php).
The value of the current density is actually lower on the opposite
side of planes and gradually decreases from one side to another - it
is obvious on the color or blanket plots shown at
https://www.simberian.com/AppNotes/PlaneCurrentDensity.gif
It would be different if trace is at the edge of the plane or near a cut-out
in the plane. You will see current higher at the edges and on the opposite
side of the plane - I think I visualized it at some demos.
Best regards,
Yuriy
-----Original Message-----
From: Doug Brooks [mailto:dbrooks9@xxxxxxxxxxxxxxx]
Sent: Sunday, December 8, 2019 12:59 PM
To: shlepnev@xxxxxxxxxxxxx; 'SI'
Subject: Re: [SI-LIST] Skin effect on ground plane?
Hi Yuriy
Your simulation is exactly what I was looking for. But I have one question.
You show that at moderate frequencies there is current density on both
the top and bottom surfaces of the plane, with a lower current density
down the centerline of the plane. But at very high frequencies the
current density only exists on the top surface of the plane (closest
to the trace) with effectively no current density on the bottom surface.
What causes the difference in the two conditions, and why?
Thanks
Doug
Yuriy Shlepnev wrote:
Hi Doug,
Yes, there is proximity as well as skin effects on the planes - the
area where signal power flow is shrinking with the frequency and
current flowing in thinner and thinner surface layer (result of
absorption by the metal). And all signal power is in dielectric and
air! :) See illustrations for microstrips at
https://www.simberian.com/ScreenCasts.php?id=38 and in some other ;
demo-videos at https://www.simberian.com/ScreenCasts.php?view=table ;
or at Simbeor channel at https://www.youtube.com/user/simbeor/videos
Best regards,
Yuriy
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Doug Brooks
Sent: Friday, December 6, 2019 10:32 AM
To: SI
Subject: [SI-LIST] Skin effect on ground plane?
We all know what the skin effect is on a trace. And we all know the
return signal path is on the plane directly under the trace.
The question is, is there a corresponding skin effect on the ground plane?
Doug Brooks
