Building a Faraday's cage ?

Almost. The currents induced in the conductor take energy off the field and thus attenuate it.

Rene

--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net

"Meindert Sprang - Dutch Fuckwit "

** Sorry for the tautology.

** Exactly.

** Crapology.

........ Phil

It takes a good deal of copper, several mm roughly as I recall, to produce enough eddy-current effects to cut a 60 Hz magnetic field in half. Skin depth in copper is about 8 mm at 60 Hz, so that sort of brackets the attenuation numbers. 1 oz copperclad FR4 starts being a useful shield at some 10's of KHz.

John

London

In the USAF, in avionics, they were routine. At one base where I worked, the whole shop was a screen room, (which they called 'shield room') to the extent that they used incandescent lights and the air conditioning was woefully inadequate. The wall paneling, ceiling, and floor were sheet metal.

It was pretty quiet (electrically), however. :-)

Cheers! Rich

Well, the only thing is, he's wrong[1]. A "Faraday" cage does _not_ shield you from magnetic fields - electrostatic, yes, if it's properly grounded, and _electromagnetic_ (not magnetic), more commonly known as RF radiation.

And if you use window screen, it's transparent above the wavelengths on the order of the screen mesh size or so.

Cheers! Rich

1. Although it could have been a translation error.

Just make the box out of CoNetic:

Cheers! Rich

Not easily. These alloys are fragile (bending wrecks the permeability), seams will leak magnetically, and you still need an absurd wall thickness/box size ratio to get good shielding. And they cost a fortune.

John

"John Larkin" "Phil Allison"

** Kindly calculate the attenuation figure at 50Hz for a box the size of a toilet cubicle made from aluminium or copper fly screen.

That is what the game is here.

....... Phil

So true !

Copper foil makes a decent 'belly band' for transformers though. It's only recently I had occasion to get into that side of things.

Graham

"Eeyore"

** Wot - fit a copper flux shorting strap around an R-core ??

Least it can be done, I suppose.

Unlike with a toroidal.

........ Phil

Actually I was thinking of one on a ferrite 'E-E' core I did a while back. Reminded me of some I've seen wrapped round E-I 50Hz transformers though - typically those out of Asia.

Very true. Haven't ever needed it but that's a good point.

Hmmm... Quite.

Graham

The use of "screen" is a new stipulation. Of course, screen isn't very conductive, so the eddy currents will be far lower than for a solid sheet of metal.

Still, the magnetic attenuation isn't "** exactly" "ZERO" as someone has recently claimed.

John

"John Larkin"

** No it is NOT !!!!!

Read the OP's first post.

" I'm planning to build a 2m x 2m Faraday's cage/booth to protect active electric guitar pickups from external electrostatic and electromagnetic noise 20hz-96khz "

What the HECK did YOU imagine such a booth is like ??

** So low as to be insignificant at 50 Hz.

** Wot a pedant !

Maybe you can say how to make a usable guitarist's booth with 150 dB attenuation as was claims by that Rene idiot.

" For the lower frequencies, iron would be the choice. I'd expect an attenuation in the order of 150dB or better. "

...... Phil

Well, we did discuss using copper sheet and aluminum foil. And I did suggest that sub-mm layers wouldn't attenuate 60 Hz fields much. Even foil would be usefully effective against h-fields at his high end, if he indeed had any floating around.

Actually, I'm an engineer, and I like to understand (and predict, when it comes down to it) numbers no matter their magnitude. I suppose that when you say...

"There is ZERO attenuation of low frequency magnetic induction."

and clarify that with

"** Exactly"

then I'm being a pedant to assume you actually meant it.

You didn't actually mean it?

John

Why not?

John

Not very practical to apply one due to mechanical issues.

Graham

"John Larkin"

** Try answering the damn question - asshole.

See the word "cage " in the heading ??????

Mean anything to you ?

** And just like so many of them, a useless, PITA autistic pedant.

...... Phil

It means pretty much this to me...

"Faraday stated that the charge on a charged conductor resided only on its exterior, and had no influence on anything enclosed within it. To demonstrate this fact he built a room coated with metal foil,..."

So the original Faraday "cage" was in fact made of metal foil.

Does that answer the damn question?

John

Whatever - it'll be like a red rag to a bull as far as Phil's concerned you mischeivious person !

Graham