Ultrasonic is DOA, sorry, but that just won't do. It's already a nuisance to have all these switching supplies that mess up your hearing (and some can be surprisingly loud), using it for power delivery is really a non-starter.
There was a company that planned on using ultrasonic for power delivery to smart phones, every engineer with some ultrasonic experience said it wasn't going to work and they just kept going until they - predictably - went out of business.
https://en.wikipedia.org/wiki/SonicEnergy (formerly Ubeam).
Just wishing it exists does not mean it is possible or practical, that's right up there with Theranos (and I think Theranos actually had a better chance of working even though that chance was extremely slim).
There are interesting start-ups around the theme of energy scavenging though, that's a far more realistic but still extremely challenging proposition.