"
It's certainly possible to pick up a useful quantity of energy from ambient electromagnetic waves - an old band I VHF antenna connected to a capacitor via rectifying diodes will give you enough charge to light an LED after a while, and you could probably power a small CMOS circuit from it.
"
No, not enough energy to be all that useful unless you are extremely close to a high power transmitter. An exceptionally strong signal into a full-size aerial would give you 100mV at the aerial socket, which assuming a 75 ohm load impedance would amount to 100uW of power.
Biting the hand that feeds IT
