Question Faraday cage?

[perzy]

Now I am not an electrical engineer, but I have long thought that a computer box would work as a faraday cage so as not to let out or let in different frequencies. Therefore, there are hole patterns, etc.
But now when I look at replacing my old box, I see that all (?) New midi boxes have, among other things, no plate in the front. The front plate where the intake fans are maybe 10 inches x 4 inches. With such large holes, it can not work as a faraday cage? Does it shield radio radiation at all? Or is that not the point? I'm mostly curious.

 

[kanewolf]

Now I am not an electrical engineer, but I have long thought that a computer box would work as a faraday cage so as not to let out or let in different frequencies. Therefore, there are hole patterns, etc.
But now when I look at replacing my old box, I see that all (?) New midi boxes have, among other things, no plate in the front. The front plate where the intake fans are maybe 10 inches x 4 inches. With such large holes, it can not work as a faraday cage? Does it shield radio radiation at all? Or is that not the point? I'm mostly curious.

Are you trying to keep EMI in or out ?

 

[perzy]

Are you trying to keep EMI in or out ?

Well in I guess, because I use my computer a lot, working from home.

 

[kanewolf]

Well in I guess, because I use my computer a lot, working from home.

The key thing to remember is the square of the distance factor. The level of EMI falls of by the square of the distance from the source. You are much more likely to have an issue from a cell phone millimeters from your head, than from your PC 2 meters away.

 

[perzy]

Ok, but do modern boxes not shield anything? The Faraday box can not be working, so we could have plastic boxes or paper ones? I do not understand.

 

[kanewolf]

Ok, but do modern boxes not shield anything? The Faraday box can not be working, so we could have plastic boxes?

And we effectively do with glass panels everywhere.
But the voltages in a PC have gotten so low, EMI has dropped.

 

[hotaru.hino]

I'll leave this link here: https://physics.stackexchange.com/a/621402

Though I'll pull out an important bit:

I can vouch from my professional experience that interference still gets through both materials, having designed and EMI tested RF power enclosures made from both. (Silver-plated copper has high surface conductivity, but it is expensive and hence impractical for most applications. And it is non-magnetic, so the residual field still gets through). The trick is to ensure the residual interference is harmless, if necessary by hardening your circuit as required.

In the case of the modern ICT (Information and Communications Technology) you ask about, the signal levels penetrating a half-decent enclosure are so pathetic that there is not going to be a problem unless your circuit is a SQUID (superconducting quantum interference device) or similar super-sensitive toy.

 

[perzy]

No I have no problem, I’m just curious how computer cases that used to be pretty airtight with small holes, some with copper lignings along side edges etc etc , now cases are more or less open? Yet Power levels are incrising ?

 

[perzy]

Thank you, I’m not a tin foil hat thou,
I’ do however belive there can be health effects from radiation, and since I and many people spend thousands of hours next to a computer I want to be sure. So something in the computer industry has changed and cases are designed differently than 20 years ago when my old AOpen H600 case was made. Why?

 

[hotaru.hino]

No I have no problem, I’m just curious how computer cases that used to be pretty airtight with small holes, some with copper lignings along side edges etc etc , now cases are more or less open? Yet Power levels are incrising ?

If EMI was a problem, it would've been noticed years, possibly decades ago. Not only were there cases with windowed side panels, but you could also straight up buy acrylic cases. I would also argue that power consumption hasn't gone up too much since way back when. Pentium 4 Prescott CPUs were in the 80W-110W range, which isn't all that much different from say a Ryzen 9. High-end video cards were also creeping up into the 120W-200W range, which the upper range that much from a midrange to lower upper end video card.

Plus electronics have to get FCC tested to make sure they're not emitting gobs of EMI that could be "harmful" to other electronics.

 

[perzy]

Well my old AOpen is built like almost airtight tank with thick steel and small openings. Like a microwave owen. In contrast, todays cases are flimsy swiss cheese. Something fundamental designwise must have happened.

 

[kanewolf]

Well my old AOpen is built like almost airtight tank with thick steel and small openings. Like a microwave owen. In contrast, todays cases are flimsy swiss cheese. Something fundamental designwise must have happened.

Yes, the requirements for better airflow. A sealed box has very little.

 

[hotaru.hino]

And again, electronics have to be tested by the FCC or the equivalent in another territory if required to make sure they're not generating "harmful" EMI. So for the most part, computer hardware wasn't generating enough "harmful" EMI to begin with so there was no real need for metal enclosures. The only time I see EMI shielding is around parts that are actually designed to emit an RF signal, such as Wifi cards and RF audio/video outputs.

Also I say "harmful" in quotes for lack of a better word. It can cause problems, but it may not necessarily do so.

 

[perzy]

Ok, I hear what you are saying but I still don't get it. Steel isen´t cheap, and all the elaboret design 20 years ago was then unnecessary ?

 

[hotaru.hino]

Ok, I hear what you are saying but I still don't get it. Steel isen´t cheap, and all the elaboret design 20 years ago was then unnecessary ?

Aluminum costs more than steel.

And what elaborate designs? Cases back then were commonly steel boxes with plastic trim.

 

[perzy]

Elaborate designs in hoocks and fasteners to seal sides of cases tight, many screws (costs) , blocking plates etc. Only the outer parts were plastic and under it was steel. Built like a microwave owen.
Yes, there was acrylic cases to, I had one a short vile, but it had a thin steel sheet under and the acrilc cases was rare, 99% was the "steel tank"-type.

 

[hotaru.hino]

Elaborate designs in hoocks and fasteners to seal sides of cases tight, many screws (costs) , blocking plates etc. Only the outer parts were plastic and under it was steel. Built like a microwave owen.

Those aren't really that complicated to cut out and stamp. Plus rivets are used to put most of the case together.

 

[USAFRet]

And we've had plastic bodied laptops since forever.

 

[perzy]

"And we've had plastic bodied laptops since forever. "

Ah, low power, low freqvency parts and the plastic is coated with metal paint (inside).

 

[hotaru.hino]

Honestly I feel like the topic has run it's course.

Computer cases were not meant to be Faraday enclosures; the choice of metal is simply for structural support. Also, at least in the US and EU, every electronic device must go through EMI testing by the government agency that handles telecommunication and broadcasting so as to make sure the product doesn't emit enough EMI to cause problems.

If you want to remained convinced that computer cases way back then were supposed to be Faraday cages and somehow there's some shift in hardware design or manufacturing that makes this no longer needed because most modern cases have large gaping holes, then I'll let you remain convinced.