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PaperclipPerfector  2mo ago (text post)   2901 thread views

Small-Scale Question Sunday for September 15, 2024

Do you have a dumb question that you're kind of embarrassed to ask in the main thread? Is there something you're just not sure about?

This is your opportunity to ask questions. No question too simple or too silly.

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I get that encasing something in aluminum with no gaps would shield it. Aluminum is the fourth most conducive metal and a good shielding design made out of aluminum would work.

But merely wrapping something in aluminum foil would leave small gaps that I think would defeat the shield. I get that you'd overlap the aluminum layers and not have large gaping holes, but I don't think that's good shielding. I sometimes deal with EMI issues at work and it is much harder than you'd think to shield parts. "Wrap it in foil" is not a clear path to success. I have literally seen parts wrapped in foil in misguided attempts to shield them. They were really quite leaky from an EMI point of view. "Put it in a metal enclosure whose lids or openings are sealed with metal EMI gaskets" is what actually works.

I think if the typical person tried shielding a radio with aluminum foil, they would screw it up.

Aluminum is the fourth most conducive metal

It depends on how you're counting it. Resistivity is usually measured by dimensions, and aluminium's #4 by that measure, but aluminium is far less dense than copper/silver/gold, so if your limiting factor is weight (often the case) aluminium is the best.

But merely wrapping something in aluminum foil would leave small gaps that I think would defeat the shield.

There's leakage, yes. But everything I've read suggests that you can achieve very high reduction with enough layers, and "very high" suffices (one only needs to bring the voltage inside below that needed to destroy the device, after all - it doesn't have to be brought to zero).

your limiting factor is weight (often the case) aluminium is the best

I didn't think about that. That's actually a good point.

"With enough layers" would be the key. Not merely wrapping with a bit of overlap, which I think the typical person would mistakenly do. Multiple layers offset or wrapped in different directions. And having a DC path to ground would defeat charge buildup.

I my work I seal things correctly by putting copper tape over the cracks and joints. 3M sells it. The conductive adhesive is only good for one or maybe two sticks though. EMI shielding goes to shit if the tape is even slightly lifted or the adhesive not quite sticking on well.

And also bare metal boxes with EMI gaskets. Which if you really wanted to shield your stuff you should use.

"With enough layers" would be the key. Not merely wrapping with a bit of overlap, which I think the typical person would mistakenly do. Multiple layers offset or wrapped in different directions.

Yes, there's a reason I bought 60 metres of the stuff. Still under 10 bucks.

But merely wrapping something in aluminum foil would leave small gaps

I wouldn't worry about small gaps.

No, he's at least partially right.

Nuclear EMP is not the same thing as an electric arc; it's a massive burst of radio waves that induces currents inside devices. Gaps do matter. That's why you need multiple layers, so that there's metal connected between any two given directions (ideally closed circuits, to cancel the magnetic component as well as the electrical one).

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