[slow_typist]

RFID tags are powered wirelessly, one could imagine powering smaller particles when operating on higher frequencies (RFID is on 13.something MHz requiring relatively large coils). A directional antenna could send a pulsed beam to power a subset of the particles in the area and afterwards receive their signals.

[regularfry]

It needs to be in the infrared spectrum at least to be useful for smart dust, otherwise the package size is still dominated by the size of the antenna. Even mm-wave radar is marginal here.

[volemo]

So... smart dust powered by the sun? Cool!

[slow_typist]

Okay if you take dust literally. The important part is that the particles fly. Like dandelion seeds.