# RE: [SI-LIST] : Re: Antenna Problem on the Board

From: Daniel, Erik S. (Daniel.Erik@mayo.edu)
Date: Sun Jun 03 2001 - 15:40:05 PDT

> 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
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
are tiny (e.g., electron orbits around an atomic nucleus). Relativity can
play a significant role if the velocities are large, in which case the

- Erik

==================================================================
Erik Daniel, Ph.D. Voice: (507) 538-5461
Mayo Foundation Fax: (507) 284-9171
200 First Street SW E-mail: daniel.erik@mayo.edu
Rochester, MN 55905 Web: www.mayo.edu/sppdg/
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> -----Original Message-----
> From: owner-si-list@silab.eng.sun.com
> [mailto:owner-si-list@silab.eng.sun.com]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
>
>
>
> Yes, and thanks. Again, this is only my opinion.
>
> When you apply the vector definition of acceleration to
> include directional change of a vector field such as an
> electric or magnetic field, then you should get emission.
>
> Aside from all this theoretical talk, how this results in
> actual practice, I haven't seen an increase in emissions
> 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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