[SI-LIST] Re: Skin Effect on Power/ground Plane

Jongbae,
   
  I agree with Orin Laney. Ideally, if the power planes are infinite large and 
infinite thick, there shouldn't have any field outside the power plane. In that 
case, connecting the probe on the outer side of the power planes, we shouldn't 
see any noise wave. Skin effect means the attenuation is 8.69 dB at the skin 
depth, it doesn't mean nothing penetrating the plane.
   
  Thanks,
   
  Shaohua
   
  olaney@xxxxxxxx wrote:
  Consider the idea that resonant cavities (spherical, cylindrical,
whatever) can have intense internal fields that are undetectable at the
outside of the cavity. Simply because you have a high impedance
measuring instrument does not imply that you can get a meaningful reading
of what is happening on the other side. At DC, you can connect a
voltmeter anywhere for an accurate reading because then the skin depth is
infinite. For metal that is not too many multiples of the skin depth for
a particular frequency, you get an attenuated, low pass filtered version
of the signal right through the metal. Every skin depth adds 8.686 dB,
and skin depth scales as inverse root frequency. An infinite plane of 1
oz. copper (.0014" thk) will attenuate 1 MHz by 4.7 dB, 10 MHz by 14.9
dB, 100 MHz by 47.2 dB, and 1 GHz by 149.2 dB (might as well be infinite)
between one side and the other. The fact that you see good signal
fidelity on both sides of a PCB plane is due to the fact that the plane
is not solid and infinite, but pierced by vias, slots, and everything
else. The top and bottom sides of the metal plane are electrically
connected wherever a hole or plane edge occurs. Virtually all of the
high frequency content is forced to go the long way around rather than
straight through the metal.

Orin Laney

On Fri, 15 Feb 2008 10:28:29 +0900 jbtera77@xxxxxxxxx writes:
> Hi, all
> Assuming there is a significant high frequency power/ground noise 
> inside a
> power/ground plane pair, which size is infinite, (Plane is thick 
> enough)
> when we probe (for measurement) the power/ground noise at the inner 
> side
> of power/ground plane, we can observe the power/gound noise waveform
> generated inside the plane pair.
> How do you think if we probe the power/ground noise at the outer 
> side of
> power/ground plane? Can we still get the same waveform? or we cannot 
> oberve
> any voltage because of skin effect?
> I think we can have almost same waveform because, even if there is 
> no any
> current at the outer side of power/ground plane due to skin effect, 
> the
> noise potential is still effective at the outer side of planes. am i 
> wrong?
> 
> Please give me your advice.
> 
> Thanks in advance,
> Jongbae.
> 
> 
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