Mini Generator Using Electromagnetic Field

After reading Dan Brown's Deception Point, i was pondering over the mini remote controlled UAV mentioned(don't know if it's fiction or not). It is described that it recharges its battery when it's places in an electromagnetic field.
I do not have any in-depth knowledge about physic (only took the subject in "O" levels last year and luckily got an "A"). I will like to know how much electricity is generated this way when the device is placed in electromagnetic fields created by household appliances or others, and what kind of product can make use of this small amount of electricity.

[edit on 21-4-2005 by NotheRaGe]

[edit on 21-4-2005 by NotheRaGe]

Since the equation E=f.h (where E=energy, f=frequency and h is plancks constant which is (6.626*10^-34) and represents the amount of joules per second. Because there is an inverse relationship between frequency and wavelength in the EM spectrum (because c is constant) we can deduce that the shorter wavelengths will produce more energy.
So, to answer your question: 1) radio waves
2) microwaves
3) IR
4) visible light
5) UV
6) X-ray
7) Gamma

The least energetic being radio waves and the most energetic being Gamma. Gamma and x-rays would be far to dangerous so they would probably use microwaves or something but i am not really sure.
As for harnessing this power i am not sure, an aerial could do it but the further away it gets the power starts droping very fast (inverse square law) so the flying insect would have to have a very low power consumption.

BTW i thought it was a great read.

yes higher frequency -> more energy

But the question is how the mechanism works? I mean the normal generator makes use of a rotating magnet so there is a change in the magnetic flux, but what the device uses to generate electricity?

[edit on 22-4-2005 by NotheRaGe]