For an idea of exactly how small the FCC limits maximum transmitter output power (as fed into the antenna) for the band to 1 Watt. I.e. the low numbers in the results are expectations not early previews for much larger numbers in the future.

In practice even high power WiFi APs tend to top out around 300mW. Multiply by free space power loss and the inefficiencies of the system and the total available power is approximately bupkis.

Those tiny solar cells that power cheap calculators are a far more practical solution.

Exactly, moreover they speak about WIFI band, but in the experiment they didn't use an Access Point but a signal generator with the test device at * 2.5cm (0.9 inch) * from the antenna, if I've understood: "For the energy harvesting, we used the 2.45 GHz resonant patch antenna with a return loss of more than −35 dB at 2.45 GHz and a gain of 7 dBi. The antenna is fed by the signal generator at 0 dBm. The antenna is placed at ~2.5 cm away from the MTJ array". Let's try to measure at 2.5 meters. That is a laboratory experiment not intended to prove that you can give power to something moving around. They speak about neuromorphic computing: I know there are devices implanted int the brain of blind people receiving power from a radio device installed very not inside the cranium but at the outside, on the skin. That kind of application is more credible.

And WIFI is total bullshit. They say "WIFI frequency" aka 2.4 GHZ because, as we all know, that is the deregulated frequency reserved for consumer application. So, IMHO the researcher shouldn't have used that term, is confusing ! From there to say that the experiment involve the problem of powering cordless devices in the sense of electronic gadget with an access point is a complete misunderstanding of the sense of that research. They intend to power something very close to the emitter in medical/niche applications with a dedicated emitter. This is an important clarification because WIFI data transmission delivered power is NOT constant and too weak, differently from the one from a signal generator near the device.

Some conspiracy theorist freak want transform a legitimate scientific paper in some kind of proof of alien technology existance, maybe ! :-)