It's not just a problem of the transducers. It's not just the energy lost in the conversion of electricity to sound and back to electricity. That's actually the least of uBeam's worries. Their big problem is that 93% to 97% of ultrasonic energy is absorbed by 12 feet of air! That's a fundamental physics barrier that can never be crossed. Of the remaining 3% to 7% energy, most of that gets lost in the conversion to and from sound.
Even if all the above problems did not exist, uBeam has the fundamental usability issue of the requirement for a clear line-of-sight. Nobody wants to use a product that requires a bulky receiver that forces the screen to face down.
Yup. It's plainly and demonstrably impractical to anyone with a clue.
But there continues to be believers.
The efficiency is a problem from an environmental point of view as well.
Take their claimed 1.5W, and be generous on the efficiency, let's say 2% total system efficiency. That's 75W to charge a phone at 1.5W.
Let's assume that 1/10th the population of the US will charge their phone, say 30M phones. 30M x 75W = 2250MW of power required.
And that's being generous.
That's an awful amount of waste. And a huge step backward given the EnergyStar and other efficiency measures the world has been taking up.
Yet uBeam want to revolutionise the whole world with this rubbish!
Look at their website of what they want to use this with :
It's outright disgusting to champion a power technology with such wastage!
They should change that slogan to "Waste At 100%"