How to EMI shield a custom quiet-pc case?

Ephemeron · Post by **Ephemeron** » Fri May 06, 2005 5:52 pm

Case materials could be aluminum, Cu, or wood. I can't say which alloys or types of wood. Any way to do this?

ilh · Post by **ilh** » Fri May 06, 2005 7:11 pm

Are there suitably conductive paints?

This whole shielding has me wondering. I have a SLK3000B, all steel. I currently have a Radio Shack wireless thermometer sitting inside it down in the bottom of the 5-1/4" drive bays. Up on my desk, about 2-3ft from the PC is the display for the thermometer. It reads the signal just fine coming from inside the case. So much for a steel case and shielding.

BTW, this is a very convenient way to monitor case temperatures.

mco_chris · Post by **mco_chris** » Fri May 06, 2005 7:50 pm

This is a complex subject! What problem are you trying to solve/prevent?

There's a copper/steel alloy called TI-Shield that's fairly easy to use. I've used it before with mixed results - the problem is that you really need to know what you're doing to use it effectively. .01" of TI shield is supposed to attenuate 35db (H field, ~100dB E field) at 1kHz to over 100db at 100kHz.

You may also have luck with copper shielding tape - easy to apply, but harder to make effective.

Of course you'll need a way to measure the effectiveness of your shielding. This can get very expensive.

Ephemeron · Post by **Ephemeron** » Fri May 06, 2005 8:16 pm

I end up with numerous electronic devices near my current puter, and this is a pattern of placing I'll likely continue if I go ahead with my custom case. Things like my digicam with compact flash, cell, etc. Frankly I 'm not even sure EMI could damage these devices or bork sensitive data, but if there was an easy way to do it I was just going to go ahead with it... are my concerns just FUD?

mathias · Post by **mathias** » Fri May 06, 2005 8:23 pm

That copper tape seems really useful. Besides EMI shielding, it could be used to give wires that aren't soldered together a better connection, and maybe it would work for some CPU mods and the like.

Would adding some of this tape to the inside of a case reduce EMI considerably?

tay · Post by **tay** » Fri May 06, 2005 8:50 pm

The best way to deal with this whole EMI business, is to forget about the fact that you ever heard of it in the first place unless you begin to have EMi problems of course.

The copper tape will work if it encloses the EMI generating device or the EMI susceptible device. Google Faraday cage + EMI for how to get around any EMI problems.

mathias · Post by **mathias** » Fri May 06, 2005 9:58 pm

What are those problems anyway, besides screwed up radio and TV reception? Wouldn't it mess up Wi-Fi too?

mco_chris · Post by **mco_chris** » Sat May 07, 2005 5:35 am

Ephemeron wrote:...are my concerns just FUD?

I think so, but it would be fun to experiment making an EMI "silent" PC. Without a way to measure your success, I'd think you'd be wasting your time and money.

If you have an electronic device near your PC that dosen't work now due to EMI (never heard of this though) then you could use that as a way to measure your shielding success.

I've used radios, cellphones, phones, ISDN, DSL, GPS, camcorders, PDA's, digital cameras, FLASH, TV's, etc w/o problems near my PC. Not many PC cards are shielded, so I don't think PC EMI it's a problem.

But then do a search on TEMPEST

Katharsis · Post by **Katharsis** » Mon May 09, 2005 4:56 pm

one of my best friends has a plexiglass case, no metal in the entire thing except for the screws. he has his entertainment system right next to it on one side. a 3 foot tall speaker on the other side. his crate amp for his guitar about 5 foot away with all its assorted pedals and crap. and we haven't percieved any problems with anything yet. this does not mean that the comp isn't slowly dying from emi. just that we haven't noticed any problems from any screens or speakers in the room. and the comp still runs prime95 and memtest86+ without errors.

now you won't catch me using a case like that, but fan blowholes and giant windows don't bother me as long as the board and components are grounded to the frame. i'm sure an electronics major could tell you better, but as far as i remember the radiation drops off exponentially. so for every x inches you take from the comp the field drops in half. it doesnt take much distance to have the field be effectively nil.

monkeh · Post by **monkeh** » Fri May 13, 2005 1:00 pm

i couldnt turn my tv on with the remote, when i used a plexi case... lol had to bin it in the end

i think i was just unlucky, as i havent heard of many people who have had that serious a problem

alglove · Post by **alglove** » Fri May 13, 2005 1:21 pm

Well, just because you have a properly EMI shielded case does not mean you will be free from electromagnetic interference. I remember working on a computer that had such a horrible power supply (supposedly rated FCC Class B), it made an AM radio located 10 meters away totally unintelligible.

On the other hand, I had a fully decked out computer on the bench next to it, but all its components were outside the case. In other words, it was naked on the bench. That setup caused no discernable interference... at least, not as far as the AM radio was concerned.

I guess what I am trying to say is that a lot of EMI depends on the individual components used, and the case is just one part of the puzzle.

m0002a · Post by **m0002a** » Fri May 13, 2005 1:45 pm

I read somewhere that if you want effective EFI shielding of a computer, the metal shielding should be grounded to the Power Supply (where the PSU screws are attached is fine). Some have also suggested that grounding the motherboard to the same shielding also helps (where the mb mounting holes are located).

I don't have any personal expertise in this area, and just repeating what I have read.

Gorsnak · Post by **Gorsnak** » Fri May 13, 2005 2:22 pm

monkeh wrote:i couldnt turn my tv on with the remote, when i used a plexi case... lol had to bin it in the end

i think i was just unlucky, as i havent heard of many people who have had that serious a problem

Since your remote uses IR light to carry its signal, it's hard to imagine how your case was the issue, unless it was getting in the way physically.

StarfishChris · Post by **StarfishChris** » Fri May 13, 2005 3:17 pm

Gorsnak wrote:
monkeh wrote:i couldnt turn my tv on with the remote, when i used a plexi case... lol had to bin it in the end

i think i was just unlucky, as i havent heard of many people who have had that serious a problem
Since your remote uses IR light to carry its signal, it's hard to imagine how your case was the issue, unless it was getting in the way physically.

Oh, but I thought that's why you got cases with windows!

tay · Post by **tay** » Fri May 13, 2005 4:42 pm

Hehe starfrish, I have IR, UV, and blue light!!! Beat that!
Anyway, heres some links by the amateur radio folks.
http://www.arrl.org/tis/info/rficomp.html