> I am building a project that has some high gain, low noise 
> amplifiers and
> will need to be in a shielded housing.  My first choice was to buy a 
> metal
> enclosure but I could not find one that fit other requirements.  I 
> ended up
> building it around a Hammond mfg 1598J plastic enclosure.  Can 
> anyone suggest
> a way to shield the inside of the box?  Is there some type of spray 
> that I
> could spray inside to do this?  The only requirement of the 
> shielding
> material is that it has to be non-ferrous.  I will be discarding the 
> plastic
> end panels and having some aluminum ones machined.  Thanks so much 
> for any
> suggestions.

You can (or could and almost certainly still can) buy Nickel loaded 
spray specifically sold for shielding purposes. Non ferrous shields 
(whether sprayed or solid material) will provide electrostatic 
shielding but for electromagnetic shielding you need the real deal.  I 
haven't tried it for shielding but you can or could but zinc loaded 
paint for "cold galvanising" and if the weight of the tin is anything 
to go buy the metal content is reasonably high. You'll note that some 
Hammond plastic enclosures already have a shielding spray on the inner 
surfaces.

For especially problematic equipment that demands electromagnetic 
shielding you can build shields out of sheet steel which may be 
masquerading as tin-plate wedding cake slice boxes (probably nowadays 
as rare as Dodo teeth), stove element protectors (pretty round things 
with pictures on), suitably sized "tin cans" or just good old 
galvanised sheet steel (which is generally thicker and so harder to 
cut). Most of these do a good job of cutting unwary fingers when cut 
and bent to suit. Tin cans and tinplate in general has the advantage 
of being reasonably possible to solder without a blow torch. (A Weller 
etc will almost do). Galvanised steel is usually less easy.

For really demanding applications mu-metal is the super miracle 
material, can be bought currently and has the super miracle price to 
match. Some old surplus valve equipment has mumetal valve shields but 
this is also probably getting down to the Dodo teeth level.


        Russell

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