shimage
100+ Head-Fier
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Agreed, but in practice nearly all Faraday cages aren't totally closed. In fact, most are just enclosures made with metal screens (so you can look into them). At least for static fields (yes, I know that radiation isn't a static field), a box with one open end blocks most of the fields, even if your source is on the open side.
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Leakage of what? Magnetic fields are essentially static in good conductors. I have not calculated it, but the skin depth of aluminum in the frequency range of interest should be ... small. I'm too lazy to look it up, but I guarantee you it's a lot less than the thickness of the aluminum foil. As for crappy conductors letting less radiation through, why stop at tin? why not use a paper napkin? or air? those are much poorer conductors than tin. You'll notice that they also don't do much to impede radiation.
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density has nothing to do with conductivity.
edit: [If you really wanted to damp radiation (instead of reflecting it), you'd want to match the resonance of the electrons (in the "conductor") with the frequency of radiation. That is, match the plasma frequency with the radiation frequency.] <- This is for conducting fluids... I want to say that a complex index of refraction is necessary for dissipation in solids, but I'm not sure.
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Fair enough, but anecdotal evidence is just that. What's easier is to line a cardboard box (and the cover too) with the foil. I remember a demo in 7th or 8th grade when they did this, and the radio went quiet. I don't know how many layers they used, though (at the time I had assumed there was only one layer, but I never checked it out). I would try it myself at home, except that 1) I don't have enough foil (of either kind), and 2) I don't care enough.
| Originally Posted by VitaminJosh A Faraday Cage is closed on all ends, and inside of your computer with a PCI card that's near impossible to do. |
Agreed, but in practice nearly all Faraday cages aren't totally closed. In fact, most are just enclosures made with metal screens (so you can look into them). At least for static fields (yes, I know that radiation isn't a static field), a box with one open end blocks most of the fields, even if your source is on the open side.
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| There are a few reasons that tin would be better for this application. Skin-effect. Aluminum foil is up to 98% pure, so I agree to you it makes a great conductor; but what about leakage? EMI causes a magnetic field in the metal because there is a current flowing through it, which in turn would create the audio disturbance. The less conductive your shield, the less that is going to flow through it. |
Leakage of what? Magnetic fields are essentially static in good conductors. I have not calculated it, but the skin depth of aluminum in the frequency range of interest should be ... small. I'm too lazy to look it up, but I guarantee you it's a lot less than the thickness of the aluminum foil. As for crappy conductors letting less radiation through, why stop at tin? why not use a paper napkin? or air? those are much poorer conductors than tin. You'll notice that they also don't do much to impede radiation.
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| Tin foil is much more dense than aluminum, and will act like a dampener rather than an antenna. |
density has nothing to do with conductivity.
edit: [If you really wanted to damp radiation (instead of reflecting it), you'd want to match the resonance of the electrons (in the "conductor") with the frequency of radiation. That is, match the plasma frequency with the radiation frequency.] <- This is for conducting fluids... I want to say that a complex index of refraction is necessary for dissipation in solids, but I'm not sure.
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| I ran an experiment with my Sony SRF-83 before replying to this post - it took me 4 layers of aluminum foil wrapped around it before I lost tune to a station and it turned into fuzz. It took me 1 layer of tin foil. Just to make sure it wasn't the qualities of the tin filtering lower signals than the aluminum; I then tried it on my cell phone. ATTWS GSM, Nokia 6800. It still took more aluminum than tin foil. I heard the disconnect after 6 coverage sheets for aluminum, and 2 for tin. (it was on speaker phone with a locked keypad dialed into my home line) |
Fair enough, but anecdotal evidence is just that. What's easier is to line a cardboard box (and the cover too) with the foil. I remember a demo in 7th or 8th grade when they did this, and the radio went quiet. I don't know how many layers they used, though (at the time I had assumed there was only one layer, but I never checked it out). I would try it myself at home, except that 1) I don't have enough foil (of either kind), and 2) I don't care enough.
