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Faraday cage, shielding and grounding

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ricko_uk:
Hi,
I need to protect a small experimental space so that it is immune to external noise as much as possible. I had few ideas which then raised a few questions:

1) what is the best material? Copper mesh, metal mesh, solid copper, solid steel, other?

2) is placing a Faraday cage inside another more effective? Or would it create some capacitor (or other) undesired effect?

3) if yes to (2) above should they be connected to each other? Of would connecting each other create some waves bouncing around inside between them and create other effects that ultimately affect the inner most space?

4) should I be grounding it or leave it floating? Or perhaps if (2) is a better solution should I ground perhaps the external one and leave floating the inner one?

Thank you :)

Henrik_V:
Two cases, isolated by 10-20 mm styrofoam , outer to earth, inner to guard 

outer case 5mm Aluminium ... and good contact of the plates...   also will shield magnetic fields ...

Another construction used here: two boxes made of transformer iron 'foil' (~2mm) , like shoe box , isolation again 10-20 mm

If you place heat generating parts in there add forced ventilation ... (aluminium mesh..)   temperature monitoring is a good idea anyway

ricko_uk:
Thank you Henrik for your suggestions/solutions,

few questions:
1) why styrofoam and not just "empty space"?
2) puraly out of curiosity, why 10-20mm gap and not less or more? Just practical construction or is it related to some waves/physics phenomenon?
3) you mentioned "outer case 5mm Aluminium ... and good contact of the plates...   also will shield magnetic fields ..." I don't think aluminium blocks magnetic fields. Are you referring to some special aluminium alloy perhaps?

Many thanks :)

ahbushnell:

--- Quote from: Henrik_V on June 09, 2020, 12:37:02 pm ---Two cases, isolated by 10-20 mm styrofoam , outer to earth, inner to guard 

outer case 5mm Aluminium ... and good contact of the plates...   also will shield magnetic fields ...

Another construction used here: two boxes made of transformer iron 'foil' (~2mm) , like shoe box , isolation again 10-20 mm

If you place heat generating parts in there add forced ventilation ... (aluminium mesh..)   temperature monitoring is a good idea anyway

--- End quote ---
Aluminum is bad because it forms an oxide. 

Copper is probably best.  You can solder the seams.  Place an FM radio inside the box and you can test for leaks.  I have used copper sheet or copper screen.  The screen is nice because you can see inside the enclosure.  It also provides some ventilation.

What frequencies are you trying to shield?

The  door needs to make a good connection all the way around.  Maybe multiple latches. 

Double shielding works better but is it worth it? 

Do you need to bring signals our power into your screen box?  That's always a weak point for shielding. 

ricko_uk:
Thank you Ahbushnell :)


--- Quote from: ahbushnell on June 09, 2020, 02:14:26 pm ---What frequencies are you trying to shield?

--- End quote ---

As broadband as possible, from Hz to GHz (WifI etc). It needs to be as quiet as we can make it without spending thousands of dollars.


--- Quote from: ahbushnell on June 09, 2020, 02:14:26 pm ---Double shielding works better but is it worth it? 

--- End quote ---

If it contributes then definitely yes, especially if the materials cost is only few tens of dollars.

Any feedback on Henrik suggestion about styrofoam and connecting?


--- Quote from: ahbushnell on June 09, 2020, 02:14:26 pm ---Do you need to bring signals our power into your screen box?  That's always a weak point for shielding.

--- End quote ---

Yes, but an analog one not a power one (battery is inside the enclosure for that reason). I just posted another post exactly about this if you have any suggestions they are very much appreciates, you might want to have a look at it here: https://www.eevblog.com/forum/projects/optically-transparent-electrical-isolation-of-analog-signal/?topicseen

Thank you :)

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