> That means you will need some very cutting edge focused ultrasound beam transducers (not cheap) that can mechanically track phones (not cheap) which must be pointed by something like a kinnect (not cheap) and a clear line of sight to the phone (completely unlike WiFi)

Note: I'm not in any way in the following saying uBeam will work. I'm just speculating on ways that one might work around some of the objections that have been raised. Here's an idea that combines the tracking and the pointing and I don't think uses anything expensive.

One way to do focused ultrasound beams is by using a phased array of transducers. That reminded me of a phased array demo I saw a film of at Caltech in the early '80s. I was taking the introductory optics class, which was taught by William Bridges [1]. Before he came to Caltech, he worked at Hughes Research, where he did such interesting things as invent ion lasers. After he came to Caltech, he split his time between Caltech and Hughes, and when I took his class he showed us a film of something his Hughes group was working on. (Note: I saw this film once over 30 years ago. The description below of what I saw is correct. I may not have the technology exactly right)

It had an array of optical radiators whose phase could be varied. If you got the phase right, you could get constructive interference at a target, and destructive interference off the target, and so deliver your energy to the target. Get the phase wrong, and you just deliver a bunch of light to a large area in the general direction of the target.

In the film, you saw a black background, and you saw a bunch of of vague overlapping blobs of light moving around. Someone then dangled a shiny model of the starship Enterprise in front of the background. Then they started modulating the phases of the radiators, with each being modulated at a different frequency. They had a light sensor pointed toward the target area, so that it picked up light reflected from the Enterprise.

The signal from the light sensor was sent through a set of parallel filters, one for each of the frequencies being used to modulate the radiators, and the output of those filters was used to control the phase of the radiator associated with that frequency. It was designed to try to set the phase to minimize that frequency in the reflected flight.

The idea is that if a given radiator is contributing to a maximum at the target, then slight changes in the phase of that radiator won't make much difference, and so the modulation frequency of that radiator should be weak in the reflected light. If, on the other hand, a given radiator is contributing toward a minimum, slight changes in phase will make big changes, and so the modulation of that radiator should be strong in the reflected light.

When they turned on this feedback circuit that filtered the reflected signal and adjusted the phase, those drifting blobs all pretty much instantly disappeared, replaced with a beam that was focused on the Enterprise, and tracked it as they waved the Enterprise around.

Could something like this work for an ultrasonic charger? Suppose the transmitter uses a phased array of transducers in order to get a focused ultrasonic beam. Suppose we include in the receiver some kind of wireless communication mechanism, such as ZigBee (IEEE 802.15.4). Now perhaps we can modulate the phases of the transducers, and have the receiver report back on how strong the modulation is at its end, and then we can adjust the phases back at the transmitter side to focus the beam on the receiver and follow it, doing with ultrasound what Bridges' group at Hughes was doing with light.

[1] http://en.wikipedia.org/wiki/William_B._Bridges