szczys writes: Transmitting power through the air using sound above the range of human hearing: that's the gist of ultrasonic power transfer. The promise is that you can sit in a coffee shop and use your phone like normal while it's recharged by invisible waves of energy. That's a future we all want — and one that uBeam has been promoting, but hasn't backed it up with proof. Physics is a cruel mistress, and this is no exception. Using the data found in uBeam's patent filings you can see that ultrasonic power transfer is a brutal engineering challenge. It's probably not impossible, but looking at what it would take for a widespread rollout of the tech makes it highly improbable.