4 ms·
I attended the EM wave propagation lectures years ago at my Uni, so my knowledge is rusty, and the following might not be something that is true in practice.
by jagrsw 4y ago
I attended the EM wave propagation lectures years ago at my Uni, so my knowledge is rusty, and the following might not be something that is true in practice.
The faraday cage tries to equalize electrical field potential over space. It does so by allowing electrons to move more or less freely, typically inside a metal mesh.
But
a). metals (unless we use superconductors) have electrical resistance
b). electrons themselves have rest masses (i.e. don't accelerate infinitely quickly in response to force).
So, the movement of electrons is not instantaneous, therefore the electrical field cannot be equalized ideally. in effect we achieve attenuation of the signal, and not its complete blockage.
Secondly, the mesh must have some relation to the signal frequency (the wave-length), probably at 1:1 or 1:2 ratio. At some frequencies (terahertz, infra-red, visible, xray) you'll need pretty much a solid box to attenuate those.
And there's obviously tech which you cannot block/attenuate, like neutrinos. Producing and receiving such signals is however non-trivial and requires particle accelerators and large cavities filled with mineral oil and bulky detectors, so we can probably skip this :). Gravity waves belong to the same category.
You can also probably try to send and receive particles, like electrons or alpha particles if you use non-solid meshes.
- aqme28 4y ago> At some frequencies (terahertz, infra-red, visible, xray) you'll need pretty much a solid box to attenuate those. The width of the walls scales relative to the wavelength of the frequency you're trying to stop. So it doesn't take much to block all useful signals. You should realize that aluminum foil blocks visible light signals.
- jagrsw 4y ago> You should realize that aluminum foil blocks visible light signals. Yup, I mentioned the solid box earlier - a non-mesh metal container. Reading through some more material, it seems that there are ways around it - one can use a static electric field to send signals, e.g. switching it on/off or changing its intensity. I suppose the differing el. charge of the opposing walls of such a cage/box would create en electrical field gradient within such box, which is easy to detect, if one's goal is sending some low-bitrate signals. It's detectable (i.e. the fact of using it), but the communication scheme itself can be encrypted or encoded, so plausible deniability can be employed.
- planede 4y agoElectron rest mass is negligible to other effects. Notably electron rest mass adds to the same effect as inductance. You can calculate the effective inductance of a piece of wire coming from the electron's rest mass, and it is several magnitudes smaller coming from the actual inductance coming from generated magnetic of the same electrons.