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Re: What is proximity effect? (was:litz)



> 
> Proximity effect has been mentioned before, as a reason not to use thich
> wire in secondary coils. I have come to understand it as that the HF
> will not flow in the parts of the wire, that is close to each other. (As
> if it was repelled, like magnetic lines of equal polarity)

precisely... The changing in field in one wire induces a voltage in the
adjacent wires (or conductor) that opposes the flow.  If you imagine 7
wires in a hexagonal bundle, the middle wire gets the effects of the 6
surrounding ones.

> 
> If the wires are divided into 4 quadrants, this would mean that there
> would be little current flowing in quadrants 1 and 3, like indicated in
> ASCI below.

Except that the effect is uniform, so the current flowing in 1, would
reduce the current flowing in 2,3,4, etc...


> 
> But if this is true for a litz wire too, and the litz is twisted, then
> the current will have to jump from wire to wire along the turns, making
> the litz wire an undesirable choise on a level with braided shield.

In litz wire, the strands are insulated, a big difference from braid.  The
insulation forces a separation between the strands, reducing the coupling. 
 The weaving means that each strand spends an equal amount of time on the
outside of the bundle.

The ideal would be to have the woven effect on the outside of a hollow (or
nonconducting) core.

Litz wire isn't supposed to be perfect, just better than an equivalent
bundle of bare stranded wires with the same cross sectional conductor area.
What you have done is trade off the physical density for inductance.  If
you had some scheme for physically separating the strands without
insulating them, it would work just as well.  An example would be bundled
conductors on HV power lines, where it also has the benefit of reducing
corona losses. Note that for the same conductor area, a thin walled tube or
thin flat strip is even better than litz wire, although physically larger.

Now, if you want a nifty transmission line, think of two litz conductors
interwoven. Almost no external field.

> 
> Is this true, or false?
> 
> Cheers, Finn Hammer
> 
>