Engineers Create the First Dust-Sized Wireless Implantable Human Sensors
sciencenewsjournal.com
sciencenewsjournal.com
Though 1 cubic millimeter is significantly more volume than something 300 microns long (1000 microns = 1mm)
These things will fall on the ground and you'll hear them hit the floor in a quiet room.
These things will not float on windless air, suspended in a sunbeam.
They are not saw dust, either. They are not iron filings. They are not crushed slivers of glass. They are something more.
Look at the picture. Maybe relative to other implantable electronics, they are certainly very small. But qualitatively speaking, not soot, not smoke, not powder, not dust.
NSA: heavy breathing intensifies
You could feed it electromagnetic energy - but then all you really have is a smaller version of the Great Seal bug https://en.wikipedia.org/wiki/The_Thing_(listening_device). I wouldn't be surprised if those already exist in about this size and the paper linked to from the web page talks about several such devices (and how they are not as well suited for implantation).
It seems that you could do a lot more with it if you added a battery and some memory so that it can record signals when the ultrasonic is not present? I am thinking of things like the Michigan Mote which was also about a cubic millimetre. http://www.eecs.umich.edu/eecs/about/articles/2015/Worlds-Sm...
I made an arm which moves in a a similar way but i didnt make fingers which is the hardest part actually. Human fingers are an amazing boon from nature to us. Theyre incredibly accurate and sensitive tools with so many sensors on them which is what makes them so hard to replicate.