**From:** Sainath Nimmagadda (*[email protected]*)

**Date:** Mon Jun 04 2001 - 09:01:03 PDT

**Next message:**[email protected]: "Re: [SI-LIST] : Antenna Problem on the Board"**Previous message:**Charles Grasso: "RE: [SI-LIST] : Antenna Problem on the Board"**In reply to:**Daniel, Erik S.: "RE: [SI-LIST] : Re: Antenna Problem on the Board"

1. Can we apply the physics/math of circular motion to motion of an electron

along a right angle, even curved, bend of a trace ?

2. If the "radiation due solely to change in direction of the electron in a

right angle bend of a trace would be similarly small", how much would it be?

Thanks,

Sainath

"Daniel, Erik S." wrote:

*> Mary, Prasad -
*

*>
*

*> > Be careful how you mix quantum and classical EM theory.
*

*> > Using this line of reasoning, we would expect a loop
*

*> > of wire carrying DC current to radiate.
*

*>
*

*> Classically, a loop of wire carrying DC current does radiate, but only a
*

*> very very tiny amount. For a single electron traveling in a small circle of
*

*> a 1 mil radius (say) at 10^5 m/s (a generously high drift velocity for a
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*> metal), the Larmor formula yields a radiated power of ~10^-24 watts.
*

*> Radiation due solely to change in direction of the electron in a right angle
*

*> bend of a trace would be similarly small -- much smaller than radiation due
*

*> to an RF current in the trace (which may still be small in many cases --
*

*> several others have commented on this).
*

*>
*

*> None of these considerations are quantum mechanical unless the dimensions
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*> are tiny (e.g., electron orbits around an atomic nucleus). Relativity can
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*> play a significant role if the velocities are large, in which case the
*

*> radiation increases dramatically.
*

*>
*

*> - Erik
*

*>
*

*> ==================================================================
*

*> Erik Daniel, Ph.D. Voice: (507) 538-5461
*

*> Mayo Foundation Fax: (507) 284-9171
*

*> 200 First Street SW E-mail: [email protected]
*

*> Rochester, MN 55905 Web: www.mayo.edu/sppdg/
*

*> ==================================================================
*

*>
*

*> > -----Original Message-----
*

*> > From: [email protected]
*

*> > [mailto:[email protected]]On Behalf Of Doug McKean
*

*> > Sent: Friday, June 01, 2001 10:57 AM
*

*> > To: Signal Integrity
*

*> > Subject: Re: [SI-LIST] : Re: Antenna Problem on the Board
*

*> >
*

*> >
*

*> > Prasad,
*

*> >
*

*> > Yes, and thanks. Again, this is only my opinion.
*

*> >
*

*> > When you apply the vector definition of acceleration to
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*> > include directional change of a vector field such as an
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*> > electric or magnetic field, then you should get emission.
*

*> >
*

*> > Aside from all this theoretical talk, how this results in
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*> > actual practice, I haven't seen an increase in emissions
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*> > to be significant.
*

*> >
*

*> > Now, concerning bends in traces with regard to crosstalk,
*

*> > I think I can say there is concern.
*

*> >
*

*> > - Doug McKean
*

*> >
*

*> >
*

*> >
*

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