[jodrellblank]

WiFi -> electric current rectennas announced a year ago[1] were in the range of 40 microwatts, and the blog post says this NFC system runs at 1.4 Watts, that feels a long way away. But years ago LCD calculators could run on a solar cell the size of a finger and powered by ambient room lighting - surely must be some close to crossover level available.

[1] http://news.mit.edu/2019/converting-wi-fi-signals-electricit...

[Smoosh]

I'm wondering if that was a constant 40 microwatts, and if that could be stored in capacitors so that every 4-5 seconds (the refresh rate of the panel) there would be enough energy accumulated to power the circuitry for an update.

[eyegor]

Yes is the answer, but it would be much slower. Assuming 1w for 6 seconds (4s refresh + 2s transfer), it would take about 42 hours for a lossless storage + regulator circuit. 40uw is an incredibly small amount of power.

[abiogenesis]

It doesn't say that the e-Paper requires 1.4 Watts. The board that can be used as an alternative to a mobile device provides 1.4 Watts.