It was well know that nature could produce massive output in narrow beams, so that always had to be one of the options.
Right... so why can't uBeam?
They do beam the energy. They actually say that much of their development work has been to build a high performance dynamic phased array beam forming system. They say they steer the beam continuously to focus on the target, with continuous feedback from the target to assist in this process. They also say they will cut the beam if anything gets in the way.
Physics (or maths, if you want to look at it that way) places limits on how much you can focus a beam, and the extent of the sidelobes you will get. This is a path trotten heavily by engineers in the sonar field for more than half a century, so most of the constraints are well understood - although better understood for water as a medium than air. However, it is engineering that places the final constraints. Engineers might find health and safety people annoying, but it would be a very poor engineer who doesn't build things to be safe and healthy to use. High levels of acoustic energy in the air are problematic for humans, and physics says too much of the energy will miss the target for engineers to consider this safe. Physics says this type of charging will be inefficient, but still allows us to use kilowatts to charge a phone. Engineering says the resulting energy bills would only allow the rich to use such a system. Some engineering constraints just won't go away with additional work.