Welded mesh for Faraday cage

[Mark Miller]

Would a welded steel cage like the ones shown here function as a
Faraday cage for frequencies up to 4GHz?

http://www.meshproducts.com.au/Page/welded-mesh-cages

What degree of attenuation might I expect with this approach?

Most people assume something as fine as flyscreen is needed, but this
is far below the wavelengh I intend to block. I have even heard of
some success with chicken wire.

Also, given the opening size in the steel mesh, is a continuous door
seal really needed? Or, could there simply be a series of contact
points with the same opening size as the mesh.

Mark Miller

 

[Mark Miller]

Would a welded steel cage like the ones shown here function as a
Faraday cage for frequencies up to 4GHz?

http://www.meshproducts.com.au/Page/welded-mesh-cages

What degree of attenuation might I expect with this approach?

Most people assume something as fine as flyscreen is needed, but this
is far below the wavelengh I intend to block. I have even heard of
some success with chicken wire.

Also, given the opening size in the steel mesh, is a continuous door
seal really needed? Or, could there simply be a series of contact
points with the same opening size as the mesh.

Mark Miller

Of course, there is always this material, which could be substituted
for cage wire mesh.

http://www.wire-mesh-cloth.com/wire-mesh/expanded-metal-series/expanded-steel-mesh.htm

Given it is fairly stiff, I was thinking it could be bent into an oval
shape and two ends added. That would eliminate the corners, thereby
reducing seams to seal.

Any thoughts please?

Mark Miller

 

[TheQuickBrownFox]

Of course, there is always this material, which could be substituted
for cage wire mesh.

http://www.wire-mesh-cloth.com/wire-mesh/expanded-metal-series/expanded-steel-mesh.htm

Given it is fairly stiff, I was thinking it could be bent into an oval
shape and two ends added. That would eliminate the corners, thereby
reducing seams to seal.

Any thoughts please?

Mark Miller

It would need to be of a finer "mesh size" than 2" x 3" rectangular
holes.

You'll need to line it with another mesh of copper. Think "macrome".

Then conductive epoxy at each node to attach it to the cage frame.

Then, you're a little closer.

 

[Jon Danniken]

For VHF instruments (wavelength 1 or 2 meters) we commonly use mesh of
2mm. It can be effective at the 40dB level but door gaps and hinges
are big leakage sources. BeCu spring contacts are standard but still
most of the leakage at that point is coming from the seams.

Die-cast aluminum boxes (even with overlapping lips on the seams) are
markedly inferior (due to leakage at the seams) to a box made out of
printed circuit board material and soldered shut.

At some point you'll give up with the mesh and hinges and BeCu
springs, and just build a box out of unetched printed circuit board
soldered shut at all the seams. Printed circuit board is cheap. Use
fiber optics and/or good quality feedthrough caps for all input/
output. Really, do skip all the intermediate screwing around with mesh
if you need serious (as opposed to cosmetic) attenuation.

<thread hijack>

Here's something I've been wondering about for a long time:

I put my cellphone inside of a steel cookie tin, sealed the lid with
aluminum tape, and put the cellphone inside of the cookie tin into the
microwave.

When I called my cellphone, it still rang.

Why didn't the steel cookie tin + microwave oven block the signal?

Jon

</thread hijack>

 

[Spurious Response]

<thread hijack>

Here's something I've been wondering about for a long time:

I put my cellphone inside of a steel cookie tin, sealed the lid with
aluminum tape, and put the cellphone inside of the cookie tin into the
microwave.

When I called my cellphone, it still rang.

Why didn't the steel cookie tin + microwave oven block the signal?

Jon

</thread hijack>

I don't know, but I would throw the microwave oven away. You probably
already have cancer if it leaks that badly.

Does it make your smoke alarm chirp too (for a split second)?

Not a complete hijacking though. Call it a tangent.

You should power off the cell phone, and power it on while it is in the
tin, and in the mw cavity. Turn it on and drop it in the tin quickly and
seal it, then the oven door.

THEN try to call it.

Previously, the phone had recently been pinged by the node it was
currently hooked in with. After going in the box, it may have lost that
hook, but still got the ring packet from the tower.

How it made it in is a different story.

 

[John - KD5YI]

How it made it in is a different story.

Yeah. And you have no clue about how. Jeez, wot a dolt.

 

[OutsideObserver]

Yeah. And you have no clue about how. Jeez, wot a dolt.

I was working with magnetics before you knew what a magnet was.

 

[John - KD5YI]

I was working with magnetics before you knew what a magnet was.

No doubt. That steel plate in your head must have had a real impact on
you. When they had the top of your skull open did they dig out the
atrophied brain and replace it with feces?

 

[SoothSayer]

The glue isn't conductive and the microwave is defective.

More like the tin isn't mu metal and the microwave is defective.

 

[Rich Grise]

The glue isn't conductive and the microwave is defective.

The microwave isn't necessarily defective - the door seals are tuned
to the freq. of the maggie, and cell phones aren't.

You're probably right on the cookie tin - I wonder if the phone
would still ring if the lid were soldered on.

Speaking of cell phones, has anybody not seen this gag yet?

Cheers!
Rich

 

[Sum Ting Wong]

You're probably right on the cookie tin - I wonder if the phone
would still ring if the lid were soldered on.

Yer an idiot. The lid seals fine to the level it needs to. Far
smaller than a 4mm mesh, which was already referred to.