Let’s read a bit more:
”the power levels beamed are more than 50 times lower than the lowest ultrasound imaging exposure limits set by the FDA for medical imaging”
The lowest limits I could find in http://www.fda.gov/RegulatoryInformation/Guidances/ucm070856... is 20 mW/cm^2 (“A simple conservative approach for pulsed Doppler FHR monitors is to use 20 mW/cm2 as a guide for the maximum spatial-average pulse-average intensity at the transducer face”)
Dividing by 50 for the ”more than 50 times lower than the lowest ultrasound imaging exposure limits”, and multiplying for (ballpark) 100 cm^2 receiver area (about what one can get in a mobile phone), I get 40 mW of power received.
http://www.fda.gov/downloads/MedicalDevices/DeviceRegulation... gives 17 mW/cm^2 for ophthalmic use, so 20 mW/cm^2 isn’t even strictly the lowest limit set by the FDA.
There may be a useful product here, but if so, I don’t see how all of what they say can be true.
Then you have to contend with any orientation offset. If the receiver is off by 90 degrees or more, there is zero energy received. If your hand blocks half the surface area, that's another 50% power loss.
If you boost the power above 140 dB safety limit, you can burn your hands or cause other problems. At 140 dB at 2 meters, the theoretical best case with 100% efficiency transmitter and receiver will deliver 0.85 watts. You obviously lose even more than that.
Part of the problem not discussed here is the 'Absorption conflict': for efficient power transmission you need materials that are able to absorb very well the given form of power; but at the same time you want nothing to interact in the path of the unconfined flux. This can only be dealt with up to a point, since our everyday objects' configuration and atomic composition are not so different from the composition of a receiver. This applies to all technologies: even for resonant EM power transfer you are relying on a specific conductor geometry; thankfully there's no strong conductor in our bodies, but you will have to deal with metal parts everywhere.
Wireless information gets around this kind of limitation because power ceases to important for the capacity of a channel [1] past a threshold (roughly when the signal PSD equals the noise PSD), while the determining factor is bandwidth. So you just use a few Ghz+ radiation and you have enormous bandwidth available; once that becomes insufficient we can move to Thz+ light; and so on without much environmental concerns (just medium concerns -- atmosphere gets opaque), since power levels will be kept constant or lower.
[1] https://en.wikipedia.org/wiki/Channel_capacity#Example_appli...
https://en.m.wikipedia.org/wiki/Crystal_radio
RFID are often a short range example of the same idea.
So, it's less that wireless power is useless As it is modern devices needing lots of power.
Remember that's for a (usually) 50kW station -- that's 1e-9 efficiency, or 0.0000001%. Realistically I'd expect you to be able scale this to 10k's receivers to up to about 0.001%. It's not realistic to increase this power significantly due to health/electronics concerns for persons living close to the source and massive consumption -- bringing the power near a single station to 4W would consume 5GW, about 1% of total US power consumption!
Interesting to imagine a system with sightly higher frequencies (20Mhz?) dedicated to power transmission. It'd essentially be a hugely wasteful system (and expensive with high powered antennas everywhere to mitigate invsq law) which however might be able to power ultra low power sensors and gadgets. Some clever phase distribution (pseudorandom modulation should do it) system would allow location with ~15m accuracy too (even working indoors, although building refraction and reflections might be a little troublesome).
PS: I suspect the real issue is making a receiver fit into a reasonable cellphone case.