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I have a Faraday cage and inside there is a WIFI router whose RF I am trying to contain. The cage is made of aluminium mesh with hole sizes of 3 mm or so.

What happens to the RF electricity coming from the RF WIFI router and hitting the Faraday cage (from inside) if I don't ground the cage?

Would the electricity "build up" inside/on the cage and in what form since it will cease to be RF?

I have had the RF WIFI router emitting for few hours however I cannot detect any voltage increase on the cage's surface.

I measured for DC and AC using a multimeter and the values remain constantly the same - about 4 volts AC.

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No, radio waves are not "electricity" in that sense. Electromagnetic waves are produced by electric charges moving inside a conductor (the antenna), but the charges never actually leave the conductor and go somewhere else.

The RF power emitted by the router reflects from the inner surface of the cage, and bounces around until it encounters something that can absorb it, such as the plastic case of the router and other nonmetallic items inside the cage. These items will get slightly warmer as a result.

The router itself consumes a significant amount of electrical power while operating. A small fraction of this power gets emitted as radio waves, but the vast majority of it gets turned directly into heat within the components of the router.

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  • \$\begingroup\$ Mmm I know that EMF specialists who use conductive paint to shield an apartment from external RF sources, will also ground the conductive paint. Are you saying they are grounding it NOT to discharge any charge resulting from RF ? \$\endgroup\$ – Zertix.net Sep 9 '17 at 23:02
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    \$\begingroup\$ Yes. Grounding the shield has no effect on its effectiveness for stopping RF (electromagnetic waves), but it does allow the shield to prevent capacitive (electric field) coupling as well, which is particularly important at low frequencies. \$\endgroup\$ – Dave Tweed Sep 9 '17 at 23:08
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RF doesn't "build-up" on conductive objects. The RF will bounce between walls with finite reflection coefficient, with wave scattered and randomized, and each act of absorption will create so-called eddy currents in the bulk of surface and around your holes, and these currents will dissipate into heat. Eventually all RF will dissipate. If you have a 1W radio, your cage should behave as a small heater, and ambient air will cool it off, so you might notice no difference.

If you don't connect the cage to ground, it will "float" and might get charged by accidental touching by charged hands or by convective air flow, to any potential, theoretically, just as one part of a capacitor.

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  • \$\begingroup\$ Hi, thanks for your answer. But I know that EMF specialists who use conductive paint to shield an apartment from external RF sources, will also ground the conductive paint. Are you saying they are grounding it NOT to discharge any charge resulting from RF ? \$\endgroup\$ – Zertix.net Sep 9 '17 at 23:04
  • \$\begingroup\$ @Zertix.net, I am saying that floating (ungrounded) conductive structure may accumulate charge, which is unrelated to the RF. For safety reasons metal cages should be connected to ground. For example, high-voltage industrial capacitors must be stored with their terminals shorted, otherwise there were cases when unattended capacitors, having nearly no leakage, would accumulate a serious charge just from air flowing around, and people can be killed. \$\endgroup\$ – Ale..chenski Sep 9 '17 at 23:12
  • \$\begingroup\$ @Zertix.net, there could be a possibility that imperfections in metal construction act as rectifiers, but you need to work really hard to make these charged to accumulate. \$\endgroup\$ – Ale..chenski Sep 9 '17 at 23:19
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You need to step back and understand some basic theory. This site is about electrical engineering, where we expect people to know the basics, or that be the topic of their question.

"Electricity", whatever that really means, doesn't come out of the WiFi router somehow. The WiFi router emits radio waves. When those waves hit the wall of your Faraday cage, most will be reflected, some absorbed, and some will cause currents in the metal of the cage since it acts in part like a antenna. Some of the radio signal being conducted by the metal of the cage will be re-radiated by that metal. The fraction that gets re-radiated to outside will make it appear as if the cage leaks.

The amount that leaks out this way will be significantly less than the amount that would be radiated past the cage if the cage wasn't there. The net result is that the cage will appear to significantly attenuate the radio signals both from and to the WiFi router.

This means the effective range of the router will be significantly dimished.

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  • \$\begingroup\$ I am sure you are right. There is now a prototype of a mobile phone that charges by absorbing RF from a WIFI Router. You can google it. I don't know maybe it uses the heat from RF.. \$\endgroup\$ – Zertix.net Sep 9 '17 at 23:31
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    \$\begingroup\$ For fairly laughable values of 'charges', LOTS of hucksters playing in the wireless charging startup space, and I would hate to be in the same room as a phone charging at a reasonable rate from far field 2.4GHz.... Think microwave oven with the door jammed open as a transmitter! There are a surprising number of these clowns who at least get a write up on Bloomberg or such with no actual involvement of a physicist. \$\endgroup\$ – Dan Mills Sep 9 '17 at 23:39
  • \$\begingroup\$ @Zertix.net, please don't fall for idiocy of crooks. A WiFi router emits maximum 1-2W of RF, which gets radiated evenly into space, and field intensity drops horribly with distance. A mobile phone can get a few microwatts of power at best, which would be barely enough to do anything, and even if some circuit can "harvest" this power, it will take millions of hours to charge phone battery \$\endgroup\$ – Ale..chenski Sep 9 '17 at 23:39
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Insert an insulated straight wire through one of the 3mm holes, the wire of length wavelength/2. Push the wire in 50%. Thus wv/4 is inside and wv/4 is outside. You'll have a fine internal pickeup and fine external radiator. Use insulated wire.

A prior question, quoting Feynman, showed the attenuation being 2.718^6.28 or about 500:1 (54dB) for every 3mm you back off the holes in the mesh.

Why are many IR receivers in metal cages?

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If you are asking where does the "Power" that the router consumes actually go, absolutely all the electricity consumed by the router is turned into heat, radio waves, and light with the vast majority being converted directly to heat (Conservation of power, there is no other magic place for the power to go). Ultimately all of the power consumed by the router ends up as heat (Unless it escapes the earth as light or other EM radiation).

Of the tiny amount of power that actually goes into the radio waves--without the cage it would go out to heat antennas and metal conductors ever so slightly (and a tiny fraction would even wander out into the universe), but with the cage in place, most of it would heat the cage itself or be reflected back to heat the air inside the cage and the metal components in the router.

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