Is very interesting but I'm not aware of any SOC that supports it.
> It would be really sweet to run something which speaks wifi even for short durations, if it recieves its energy from ephemeral radio.
One interesting source of power is a simple coil-and-diode to harvest radio waves, do this for a while until you have enough power to boot your device, take a reading and send off a sample.
A few mW for a few seconds every couple of hours or so would be a good target. 100's to 1000's of mWs would take so long to harvest that you'd likely never get there because of leakage.
And 'speaking' is the right term, I don't seen an easy way for such comms to be bi-directional without a lot more power to be consumed.
I wonder how much energy you can harvest from FM broadcast radios stations, those signals are pretty strong.
Edit: I calculated a power flux density of 2.648µW/cm^2 from 3.16mV/m (70 dBµ) which is the 'city-grade contour' in the US.
There seem to exist a patent for that, from a company called Freevolt (http://www.getfreevolt.com/).
Power law, so it's very much dependent on your distance to the transmitter.
In NL some clever person figured out that he could power his fluorescent tubes from the broadcasting tower across the street and promptly got sued for theft...
That's why IoT applications tend to use other, simpler and lower power radios and protocols.
https://en.wikipedia.org/wiki/IEEE_802.11ah
Is very interesting but I'm not aware of any SOC that supports it.
> It would be really sweet to run something which speaks wifi even for short durations, if it recieves its energy from ephemeral radio.
One interesting source of power is a simple coil-and-diode to harvest radio waves, do this for a while until you have enough power to boot your device, take a reading and send off a sample.
A few mW for a few seconds every couple of hours or so would be a good target. 100's to 1000's of mWs would take so long to harvest that you'd likely never get there because of leakage.
And 'speaking' is the right term, I don't seen an easy way for such comms to be bi-directional without a lot more power to be consumed.