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Monday, 5 April 2021

A smart race

Nanorobot swarms are the stuff of sci-fi films, but smart dust is being developed now.

Johan Oomen.
An assembly of microelectromechanical systems or “MEMS”, smart dusts consist of a party of tiny robots that detect light, temperature, vibration, magnetism, or chemicals. They talk to each other via wireless network and employ radio-frequency sensors. Smart dust particles are just a few millimetres across – much like intelligent grains of rice. A dependent species, they have to operate together, like bees, ants, or other colony creatures. And they have their weaknesses too: smart dusts are vulnerable to microwaves, which could electromagnetically disable them.

How did they come about?


Originally, by accident. A silicon chip shattered – and a new idea was born: the idea that all the tiny fragments could work in unison as if they were still part of the bigger chip, signalling away, self-assembling, and working to deliver drugs, attack tumours, or monitor the environment. They have potential uses from ecosystem health monitoring to faster earthquake detection or chasing mobile pollutants. For instance, programmed to detect a toxin, the microscopic fragments will join together upon finding it, the sensor equivalent of waving a flag.

What are they made of?

 

By Vidsplay.
 
Computational scientists are still arguing about what smart dust is, since the sci-fi story and reality are so divergent. Currently, they are functionalised photonic crystals made of porous silicon. They’re made by electrochemically etching two mirrors into the silicon on top of each other, and thermally modifying one by oxidation. The crystals are then fractured into small particles by sonication to produce asymmetric particles driven to spontaneously assemble, orient, and undergo microshifts in electronic properties as they sense changes in their surroundings[1][2]. Control circuitry, signal processing, optical receivers and power sources have to be tacked on.
 

What are the challenges?


By flightzone.
 
The military are investigating ways to make smart dusts even smaller (sand grain sized) and ultra secretive – so that dropping them over a zone leaves no environmental footprint behind. Sorry, Bond, but smart dusts will be tomorrow’s spies. However, at the moment they tend to be pretty big – about the size of an old VHS tape once they have a protective casing – so there’s still some way to go. Tiny smart dust computers, of course, do raise ethical questions. The idea of microelectromechanical spies necessarily terrifies people, and alongside the technical development there has to be governance and legal documentation. But different countries do things differently, and the race to develop these things is ongoing.

There’s also the problem of the dead bodies left at the scene. Not only would they perform sensing activities, but it would be great to develop self-monitoring smart dusts, so they could report back when they’re running out of energy. After experimenting a lot with batteries, researchers found they kept dying out and the smart dust would get left behind, and so they developed the idea of energy-scavenging smart dust – or ones carrying solar panels. This, of course, could still be problematic. Remember Philae?, the Rosetta spacecraft robot that landed in a hole on Comet 67P following a 10 year 8 month journey, whereupon its solar panels promptly died and it eventually ran out of power. Another challenge of mounting solar panels is that it would make the robots bigger, counter to current plans. And so the challenges continue.


References
why don't all references have links?

[1] Link, J.R., and Sailor, M.J. Smart dust: Self-assembling, self-orienting photonic crystals of porous Si. Proceedings of the National Academy of Sciences 100.19 (2003): 10607-10610.
[2] Sailor, M.J., and Link, J.R. Smart dust: nanostructured devices in a grain of sand. Chemical Communications 11 (2005): 1375-1383.

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