Looks like there are some figures to work with on the website now:
WHAT IF SOMEONE WERE TO STAND DIRECTLY IN FRONT OF THE BEAM?
uBeam's ultrasound energy will not beam to the skin, and the power levels beamed are more than 50 times lower than the lowest ultrasound imaging exposure limits set by the FDA for medical imaging, making the system inherently safe and within all existing regulatory constraints.
Bingo. If someone can find out what the FDA exposure limits are, then it's 50 times less than that at maximum.
I think the only FDA figures will relate to the direct injection of ultasound into flesh, and for frequencies well above 1MHz. Things like ear damage aren't an issue there.
and:
The "holy grail" experience of true wireless power is one where multiple devices can simply charge in the air as they're moving and as they're being used. It's like the experience of Wi-Fi, but for power. In order to achieve this type of experience, you need a system that can achieve the following - simultaneously:
TRANSMIT LARGE AMOUNTS OF POWER SAFELY
(> 1 WATT PER PHONE)...
So presumably the uBeam is at least 1W output? (but under what conditions?)
The whole article is written to carefully avoid saying anything important. Things like "99.9% of uBeam's emitted ultrasound will bounce off the skin" ignore what it will do to your ears. Most of the safety related comments dodge the real issues like that. The whole thing about shutting down when line of sight is blocked is pretty funny. The writer seems to imagine an ultrasound beam as a hard edged beam, like a collimated light source.
It originally seemed like they were using a frequency only just above human hearing. The article makes it sound like they are now taking the hearing of animals into account, and have pushed the frequency much higher. That won't be good for efficiency. Above 100kHz the losses in air are massive.
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