FreeLists / si-list / [SI-LIST] Re: Help Explaining Microstrip

[steve weir <weirsi@xxxxxxxxxx>]

Paul, flux density and current are analagous.  For the wires in a 
solenoid configuration, ( current coming out of the page ):

<   high density
o
 > 
    low density due to cancellation
<
o
 > high density

In a microstrip the return current in the plane is into the page:

                       low     
                 >>>>>>>>>   
                 oooooooooo
                 <<<<<<<<<   
                      high
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
 >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
                     low

Regards,


Steve.

Paul Levin wrote:
> Dear SI-LIST'ers,
>
> I'm working on a presentation to explain transmission line to 
> non-engineers and I
> find myself stumbling over some of the basics. (There's nothing like 
> explaining
> something to bring out all of the glitches in what you were sure you 
> understood!)
> I'm hoping that one of you may be able to supply the missing link.
>
> Nearly two hundred years ago Oersted and Ampere figured out that if you 
> have
> two conductors carrying current in the same direction, they would would 
> to pull
> in close to each other whereas if you had two conductors carrying 
> current in
> opposite directions, they would want to separate.
>
> If one were to apply just these observations to microstrip, you would 
> expect to
> see all of the trace current bunched on the side away from the ground 
> plane and
> the return plane current in two bunches to either side of the trace and 
> as far away
> from the trace as possible, if not on the bottom.
>
> Of course, this is almost exactly opposite from what we know happens.
>
> What is the force that overcomes Oersted and Ampere and causes the trace and
> return currents to be so heavily attracted to each other?
>
> Thank you in advance.
>
> Regards,
>
> Paul Levin
> Senior Principal Engineer
> Xyratex
>
>
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