We're used to thinking of robots as mechanical entities, but at very small scales, it sometimes becomes easier to use existing structures (like microorganisms that respond to magnetic fields or even swarms of bacteria) instead of trying to design and construct one (or lots) of teeny tiny artificial machines. Aaron Ohta's lab at the University of Hawaii at Manoa has come up with a novel new way of creating non-mechanical microbots quite literally out of thin air, using robots made of bubbles with engines made of lasers.
To get the bubble robots to move around in this saline solution, a 400 mW 980nm (that's infrared) laser is shone through the bubble onto the heat-absorbing surface of the working area. The fluid that the bubbles are in tries to move from the hot area where the laser is pointing towards the colder side of the bubble, and this fluid flow pushes the bubble towards the hot area. Moving the laser to different sides of the bubble gives you complete 360 degree steering, and since the velocity of the bubble is proportional to the intensity of the laser, you can go as slow as you want or as fast as about 4 mm/s.
This level of control allows for very fine manipulation of small objects, and the picture below shows how a bubble robot has pushed glass beads around to form the letters "UH" (for University of Hawaii, of course):
Besides being able to create as many robots as you want of differing sizes out of absolutely nothing (robot construction just involves a fine-tipped syringe full of air), the laser-controlled bubbles have another big advantage over more common microbots in that it's possible to control many different bubbles independently using separate lasers or light patterns from a digital projector. With magnetically steered microbots, they all like to go wherever the magnetic field points them as one big herd, but the bubbles don't have that problem, since each just needs its own independent spot of light to follow around.
The researchers are currently investigating how to use teams of tiny bubbles to cooperatively transport and assemble microbeads into complex shapes, and they hope to eventually develop a system that can provide real-time autonomous control based on visual feedback. Eventually, it may be possible to conjure swarms of microscopic bubble robots out of nothing, set them to work building microstructures with an array of thermal lasers, and then when they're finished, give each one a little pop to wipe it completely out of existence without any mess or fuss.
Cooperative Micromanipulation Using Optically Controlled Bubble Microrobots by Wenqi Hu, Kelly S. Ishii, and Aaron T. Ohta of the the Department of Electrical Engineering, University of Hawaii at Manoa, was presented last week at the 2012 IEEE International Conference on Robotics and Automation in St. Paul, Minn.