Converting RF to power, changes the (original) RF signal somehow?

[onesixright]

Hey Guys,

I have seen a few projects that claim to convert RF signals into usable power. 

Examples:

http://www.nowi-energy.com

http://www.ibtimes.co.uk/iphone-6-case-downloads-power-air-by-converting-radio-signals-into-electricity-1499696

I always understood, there is no such thing as a free lunch. So, if you convert RF energy back to "some" current, would that effect (as in absorb?) the RF signal itself (i.e. less distance?) ? If it would not be the case, you could put a ton of these box and endless generate energy from the same source. I would think you can never, ever, generate more then you would output. Now im pretty sure, it doesn't work like that.

Anybody that could "shine some light" on this?

Thanks!

[ataradov]

Yes, you are absorbing part of the signal energy, and whatever is located behind you (if you are looking at the source) will not receive that power.

Every TV antenna "shadows" the signal for further consumers, but typically it is not noticeable, since its area is very small.

Imagine complete absorbent sphere around the source, there is no way signal can get outside, and it will be entirely absorbed by the sphere. Individual antenna (or mentioned harvesting devices) is a very tiny part of this sphere.

[CJay]

There are, probably urban legend, stories of farmers near to radio masts causing 'odd' radiation patterns from the discovery that their cow sheds lighting would stay lit with no power due to the wiring being of some sub wavelength.