[sdiy] case shielding properties

[Paul Higgins]

Isn't there also an issue with steel actually conducting magnetic 
fields, say from very large transformers, and injecting it into the 
circuit?  I think I remember reading something like this in an old book 
on tube amplifier construction.  It is not surprisingly the biggest 
problem in low-level signal paths, especially those that use magnetic 
materials (e.g. microphone input transformers).

-PRH

On Thursday, May 27, 2004, at 05:24 PM, Tim Parkhurst wrote:

> As a mechanical designer, I would have to go with the steel for the 
> best
> shielding properties, followed by the thick aluminum and then the thin
> aluminum. Some other factors will influence the 'quality' of the shield
> (rectangular is better than square, use fewer parallel surfaces, round
> openings are better than squared-off openings, etc.), but if you look 
> at the
> material used in RFI shielding you will find a lot of beryllium-copper,
> plated copper, nickel-steel, or steel with various platings, and brass 
> with
> various platings. Aluminum is rarely, if ever, used for shielding 
> purposes.
> Unfortunately, most of the shielding materials I mentioned above are 
> not
> suitable for making enclosures, but given the choice between steel and
> aluminum, I'd have to go with steel.
>
> Another choice would be an aluminum case with internal shields made of 
> thin
> steel, copper, or brass. I've done this quite a bit for RF amplifiers,
> receivers and the like (I've designed enclosures for a lot of gear like
> this). This is a very common industry practice.


Paul Higgins
email: higg0008 at tc.umn.edu