I was really interested in Witricity and read a few related papers on their technology. There are a few problems that they are not so keen to publicize: (1) I

I was really interested in Witricity and read a few related papers on their technology. There are a few problems that they are not so keen to publicize: (1) If the receiver loop isn't "inside" the transmitter loop along the normal of the loop area then efficiency falls a bit (2) Efficiency depends a lot on the orientation of the device being charged. If the receiver loop isn't very nearly coplanar with the transmitter loop, efficiency bombs (3) Range is fairly limited (4) When you have multiple devices charging concurrently, efficiency falls for every individual device being charged as magnetic resonance cannot be achieved nearly as well for more complicated multi-body flux loops Witricity has been trying to push electric car charging as for that application these downsides don't matter as much. But even there, you get something like 50% efficiency. Do you want to nearly double your electricity costs just to avoid plugging in a cable? Interesting technology, but it doesn't see like a worthwhile proposition to me. General purpose wireless power transmission is a really difficult problem. I was interested in the ultrasonic acoustic approach that uBeam is pursuing but that has its own slew of problems.