The antenna is way too small for 2.4GHz. It makes sense for higher frequency (60GHz or whatever he said in the video). You can power harvest RF waves straight u

The antenna is way too small for 2.4GHz. It makes sense for higher frequency (60GHz or whatever he said in the video). You can power harvest RF waves straight up but what you absorb gives you very little to rebroadcast again. There are others doing work on this for sensors you could embed into say a wall to give you the pressure reading of the concrete (a simple piezo say) but those usually modulate an RF wave (similar to NFC) instead of rebroadcasting.