Optimal Faraday cage

Edward Quinn · 2010-02-25T22:31:04+00:00

I need a quiet environment for operating test instruments. Needs to beas close to full spectrum as practical, and about 1.5 metres square orequivalent internal space. From what I have read, this requires a combination of shielding types.With cost in mind, what is state-of-the-art homebrew for this?A few ideas:1. Aluminum foil on plywood box. Edges sealed with self-adhesivealuminum tape. I assume a solid surface is more effective than screenor mesh.2. Corrugated steel water tank. Thick metal may be better for lowerfrequencies(?) Corrugations may provide deflection(?)Of course, the unit would be earthed. For vents, etc. I would fit acurved section of flexible aluminum ducting a used in domesticheating/air con installations, with a metal screen over the opening.In addition, I would apply a thick paint with iron filings to theouter surface.Any feedback or analysis regarding the above would be appreciated.Ed Quinn

Feb 25, 2010 25 Replies

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MooseFET 16 years ago

es.

Foil is not much good for large shields. With larger shield cans and rooms the thickness needs to be greater to do much. It basically scales with size.

Doors are the biggest problem because there is always a clearance for it to be able to move. A large flap around the door helps a lot.

Pound for pound aluminum is better. For large shields, copper becomes impractical. Aluminum is far easier to support. The welding of the joints requires someone with skill to do. With copper, you can solder the joints.

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Phil Hobbs 15 years ago

Skin depth is the smaller of the two effects governing low frequency shielding. The bigger one is that the continuous conductor suppresses the B field in its neighbourhood. The leakage due to finite skin depth has to be calculated _after_ the field suppression.

Also it's hard to get the full effect of mu metal in a large fabrication, because it's so delicate--the mu drops like a rock if you bang it or bend it, and it has to be re-annealed. It's tough to anneal a shield room!

Cheers

Phil Hobbs

Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 email: hobbs (atsign) electrooptical (period) net http://electrooptical.net

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Adrian Jansen 15 years ago

Reminds me of a l-o-o-o-n-g time ago when we at Philips had the only large kiln around capable of holding a mu-metal shield about 1.5 m diameter and 1 m high, wanted for some scientific experiment by a defence department. They provided the shield, and told us the temperature profile they wanted for annealing, in pure nitrogen. No problem, it got done on night shift, when we were not using that kiln for production. Only problem was that someone got the instructions mixed up, and fired in pure oxygen. Was a bit of a surprise when they opened the kiln, and found a small pile of powder.

Regards, Adrian Jansen adrianjansen at internode dot on dot net Note reply address is invalid, convert address above to machine form.

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Tim Williams 15 years ago

Wow, I hope that person got...fired (use your imagination as to how)!

Tim

Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms

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Dave Platt 15 years ago

Ouch. The mere thought of it, makes my oyes glaze.

Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads!

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I AM THAT I AM 15 years ago

Pobably cost them the price of the item plus a penalty as well.

Several tens of $ks sounds likely.

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