[londons_explore]

The metal tin box will have had varnish and paint on it's surfaces.

That means at the junction between the tin and the lid (and maybe other joins), there isn't an electrical connection all along.

Having two metal surfaces next to eachother, but with an insulator in between, acts like a 'choke flange'[1]. However, they only work at one specific frequency - at all other frequencies they will leak either a little signal or a lot/all the signal.

The same technique is used on a microwave door edge to keep the microwaves in. It's why keeping the microwave door edge clean is critical to safety - a small bit of food there isn't an insulator like the paint, and energy leaks out.

[1]: https://en.wikipedia.org/wiki/Waveguide_flange#Choke_connect...

[coldacid]

I wonder how many of us are going to end up cleaning our microwaves today after seeing this comment.

[PeterisP]

What I hear from you is that soldering a wire connection between the tin can and its lid should improve it's function as a Faraday cage?

[rubylark]

That's interesting! As far as improvised faraday cages go, I always heard that microwave ovens are a good solution. Does this mean that microwave ovens wouldn't be any better as they would only block the specific microwave frequency they're designed for?

[londons_explore]

Correct. In fact, you can easily verify this by putting a phone in an unpowered microwave and calling it. It'll usually get both 4G (frequencies range, but 800Mhz in my area) and Wifi (over 5GHz).

[op00to]

TIL! Thanks!