I'm a little leary of transmitting focused RF power. On the other hand you could put your burrito on top of your phone so it would receive some of that focused power to heat it up.
On a more serious note, I've always wondered if a tiny, very-low-power device could harvest power from all the RF being broadcast all over the place these days: WiFi at 2.4GHz, 5GHz, all the various cell frequencies, even the old UHF,VHF radio and television.
Certainly it is possible to build a tank circuit to capture some of this power. I'm just wondering if it is enough to do anything with. Maybe you could have a sensor that just collects miscellaneous RF power for a few hours, then it could broadcast its data for a few microseconds.
RF for powering remote sensor networks is an extended topic. IMEC in Belgium, for example, are driving research since quite a bit, now.
WSN can work with less than mW, in duty cycle mode. Anyway, charging-up your mobile telephone is another story, you need Watts for decent recharge time, and since there is FDA regulation, you can't send RF anywhere, so you need to focus in a small spot, avoiding humans and pets.
Further, 2.4 GHz is the frequency of WiFi, but maybe other frequencies would be better for remote powering. Your WiFi EIRP has legal limitation (500mW EIRP MAX or 4W at 15% duty-cycle). To charge your phone-up you need to broadcast Watts over distance, so focusing becomes paramount to cope with health regulation.
RF power transfer is the way to go, no doubt, anyway I'd like to carefully see at how good we are in focusing energy in a very limited spot, not touching at people walking around. Any additional data would be appreciated.
I didn't find anywhere that it says that the power being broadcast is going out at 2.4GHz (which would seem to be a less-than-ideal frequency, agreed). It does, however, use the two aforementioned frequencies (2.4/5 GHz) to locate participating devices.
For example, PowerCast has been at this for a few years, and they use 915MHz.
Besides the safety issues regarding exposure, I wonder what objects will block the signal and prevent charging. Most people probably don't want to be carefully checking the line-of-sight to their charging home base. I'd think it would be less trouble to connect the phone to a charging cord or a charging dock than to seek out the compatible remote charger (only 15 feet away) and ensure that the devices are coordinating properly to recharge the phone.
Agreed, I imagine the objects in a room could potentially prevent easy charging. If the technology could be as accurate in sending a signal as wifi (and we all know wifi is never 100%), perhaps this could really take off. What do you see as ways around this conundrum?