Re: Farady Cage

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

chicken wire's not that great a magnetic shield
1) Steel has a fairly high coercivity (it's not magnetically "soft"), and 
the odds of the steel being already magnetized (albeit randomly) is pretty 
high, given the temperatures and mechanical stresses involved in the 
manufacture.

2) It needs to be a continuous sheet (substantially thicker than a skin 
depth, by the way) to be a shield. Think of it this way, a field on one 
side of the "wall" induces a current in the conductor in the wall.  That 
current has a field that, effectively, just matches the field inducing the 
current.  However, if it's just a wire, the field extends all the way 
around the wire, so, on the other side, it radiates a field.

(of such calculations are radar cross section and scattering calculations 
done..)

It is true that a grid of wires, sufficiently close together, could act as 
a shield (by the same mechanism as the "proximity effect" squeezing the 
magnetic field out between windings in a coil), but, off hand, I'd suspect 
that you need the wires to be quite close together (on the order of the 
wire diameter) for this to work.

It's sort of the inverse problem to designing Litz wire.

At 04:59 PM 12/18/2002 -0700, you wrote:
>Original poster: "Harold Weiss by way of Terry Fritz <twftesla-at-qwest-dot-net>" 
><hweiss-at-new.rr-dot-com>
>
>Hi All,
>
>Wouldn't the steel chicken wire serve to knock down the magnetic 
>fields?  I can understand penetration of a copper wall, due to the copper 
>being dimagnetic.  That's why the CIA uses both copper and mu metal walls 
>to keep bugs out.  I would think that the magnetic field would tend to 
>follow the steel mesh, and not radiate much beyond it.
>
>David E Weiss