Isn't that effectively wireless power, thus inefficient, and not purpose-designed wireless power, thus even even less efficient?

It's interesting regardless; I'm just trying to understand some of its potential (and maybe these things can be overcome or become irrelevant for certain uses).

Oh there’s almost certainly a ton of loss, that said it’s definitely still super fun to play with. And makes me excited for better advancements in that field.

The chip I’m playing with is the NAC1080 - supposedly designed for small lock motors but I’m using it to update an eink display on tap

Cool, you just pointed me to a interesting thing! I did not know about NFC energy harvesting. I've been thinking about a eink project. Thanks!

Yeah, there are plenty of use cases for which overall energy efficiency doesn't matter, because the actual energy demands are so low.

If you can run a microcontroller on a fraction of a milliwatt (which is entirely feasible) then it might not matter that you're wasting another 10 milliwatts on wireless power delivery. Depends what your energy source is.

For reference, one can buy 486 / Pentium "compatible ISA" from Intel that use 0.025W, 25mW. ~14mA!

And that's TDP!