eli5: How do the factors of a faraday cage work?


I understand faraday cages block EM waves by creating it’s own EM field in response to the original EM waves, and I know faraday cages can have holes, but what parameters mean what? How does wall thickness play in? Hole size? Distance between the wall of the cage and objects that are supposed to be shielded? Does grounding the cage electrically do anything? I’ve searched around a bit and found little information into the parameters, and I’d like to hear all that others can provide for info relating to faraday cages.

In: 2

Firstly, the way the cage works is that the electrons in the metal of the cage move, in response to the electromagnetic (EM) wave. This in-turn results in a field which cancels out the original wave.

So, with that in mind…

Does **wall thickness** play a role: yes, but practically only if you’re trying to protect against very strong EM fields/ pulses. The issue is whether enough electrons in the cage, can move fast enough in response to the wave, without burning the cage itself. Also cages of materials with higher conductivity can afford to be thinner. So copper/ silver cages can be thinner than aluminum..

**Hole size**: needs to be smaller than the minimum wavelength across the part of the EM spectrum that you’re trying to block. A cage really starts working at holes smaller than half the wavelength, and recommended engineering guidelines is holes smaller than a tenth of the wavelength.

**Distance between wall and cage**: theoretically doesn’t matter for a perfect Faraday cage. Practically, would really matter only in extreme (very strong EM fields) situations, where arcing/ currents between cage and internal objects could be a concern.

**Grounding**: again only matters if the EM field is strong enough, or components nearby sensitive enough for arcing, stray currents to be a problem. If the EM field is strong enough, you should definitely ground the cage to avoid getting a shock when you touch the cage.

Edit: this is based on basic engineering knowledge and reading. Happy to be corrected on practicalities by any working engineers.

Wall thickness mostly helps more current pass through the metal and drain to the ground. Cause wires that are too thin will melt.

Hole size is about blocking [EM waves](https://en.wikipedia.org/wiki/Electromagnetic_spectrum); higher frequency waves have a smaller wavelength, and “smaller waves” could pass through the holes.

Distance between cage and object [doesn’t really have an effect](https://i.ytimg.com/vi/QqEesFaboV4/maxresdefault.jpg). Electricity will follow the much easier path of going through the metal, to the ground.