Say you have a Faraday cage mesh with holes small enough to reflect the radio waves. What happens to radiation when it is emitted from inside the Faraday cage?

Does it keep reflecting off of the inside of the cage forever?

No. Unless the cage is a perfect conductor (which it is impossible in real life to make or find), a portion of the energy of the waves will get absorbed by the walls of the cage on each reflection, eventually causing the wave to attenuate or "die out". Given the incredible speed of light, these reflections happen close to a billion times each second in a cage around $$1\, \mathrm{m}^3$$ in volume, so the attenuation happens really quickly.

The absorbed radiation (electromagnetic energy) gets transformed into another form of energy, usually heat. The walls of the conductor heat up slightly as a result.

Typically, the radiation penetrates a characteristic distance called the "skin depth" inside the material of the conductor, before falling to around $$1/3$$ of its initial strength. For example, copper has a skin depth of around $$8.5 \, \mathrm{mm}$$ for a radiation of frequency $$60\, \mathrm{Hz}$$. The conductor will get heated up as the wave is attenuating; it is a continuous process.

• What happens to the radiation absorbed by the inside walls of the cage?
– Masu
Jan 5, 2021 at 3:50
• @Masu It is transformed to another form of energy, usually heat. The walls of the cage heat up and expand ever so slightly. Jan 5, 2021 at 3:56
• Thank you for your help.
– Masu
Jan 5, 2021 at 4:00
• Would the absorbed radiation travel through the walls of the cage for any reason? Or would it just immediately be dissipated into heat?
– Masu
Jan 5, 2021 at 4:05