From: Sean Murray ([email protected])
Date: Thu May 11 2000 - 12:31:32 PDT
Is there a way to change the si-list from 1000 emails a day to digest
form where we just receive one huge email? Since joining, my monthly
email total has gone from about 100 or so to 3000 a month.
M&M Specialties Inc.
1236 W. Southern Ave. #106
Tempe, AZ. 85282-4518
Phone: (480) 858-0393 x105
Cell: (602) 684-7859
Fax: (480) 858-1882
Email: [email protected]
> -----Original Message-----
> From: Barry Ma [mailto:[email protected]]
> Sent: Thursday, May 11, 2000 9:42 AM
> To: [email protected]
> Subject: RE: [SI-LIST] : May 9th Presentation: "Radiation
> from Edge Eff
> Thanks for the nice summarization. Please allow me to raise
> some more questions.
> The intention of 20H rule is to reduce the radiation from the
> space between pwr plane and gnd plane. However, "The
> simulations presented showed that 20H structures actually
> resulted in more emission at the board edge." Did anybody
> measure the radiation from the board edge to validate the 20H
> rule yet?
> I would do my best to reduce common mode voltage in pwr/gnd
> planes when designing PCB, and pay less attention to
> differential mode voltage between pwr and gnd planes. Does
> the radiation from board edge come from CM or DM voltage? If
> DM, does it make main contribution to the radiation of the
> whole board?
> Barry Ma
> [email protected]
> -----Original Message-----
> From: [email protected]
> Sent: Wednesday, May 10, 2000 9:39 AM
> To: '[email protected]'
> Subject: RE: [SI-LIST] : May 9th Presentation: "Radiation from Edge
> Effects in Printe...
> Here is what I think I heard at the EMC society presentation. The
> simulations presented showed that 20H structures they
> examined actually
> resulted in more emission at the board edge. However, the
> presenters were
> neutral on whether this was detrimental to compliance for the
> system as a
> whole, pointing out that EMC solutions are rarely universally
> applicable. I
> hope they post this on the web, I found it most instructive.
> The main points I remember:
> 1) Time-varying currents on vias can inject radial TEM-mode
> waves into the
> space between planes.
> 2) The energy thus injected bounces around the cavity volume
> between the
> planes. The board edge is a discontinuity in the medium and
> so results in
> partial reflection of the propagating wave and partial
> transmission, i.e.
> radiation from the board edge.
> 3) Fencing the board edge with grounded vias is equivalent to
> changing the
> PCB-edge discontinuity to a short to ground, so the
> reflection coefficient
> becomes -1 and all energy is kept inside of the fenced area.
> 4) By contrast, a 20H-rule example showed that that
> structure, which looks a
> little like a patch antenna, allows for more efficient
> radiation from the
> edge. The exposed area allows a propagation mode where energy
> can travel
> around the outside edges of the board also. Thus less energy
> is trapped
> within the board area and more gets radiated.
> 5) Is this good? Energy bouncing around between planes can be
> picked up by
> structures like the one that initially injected it, e.g.
> vias, and then
> travel along conductors to outside surface components where it can be
> emitted. This is not especially desirable. On the other hand, the more
> efficient radiatiing edge (20H) puts more energy into the
> system chassis,
> which moves the problem one level higher.
> 6) Closely spaced ground vias all across the board had the
> effect of fencing
> in the injected energy to a small area. This seems to cut
> radiation from the
> edges drastically. I would like to know more about this
> particular case.
> The data was obtained from an FDTD simulation of a small
> board with a single
> off-center via as the point of injection. Excitation was with both a
> continuous sine-wave at 1GHz and also a Gaussian-derivative pulse.
> Dielectric losses were included in the FR4 model. The results
> of lengthy
> simulations were presented as captivating animations, with
> color variation
> showing the magnitude of the Poynting vector across the whole
> board. The
> test setup was of necessity rather artificial but it did help
> to give a feel
> for the physical behavior underlying radiation from board edges.
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