In a study, Cornell researchers installed electronic "brains" in solar-powered robots that are 100 to 250 micrometers in size, so the tiny robots could walk autonomously without being externally controlled. The size of robots is smaller than an ant's head. 

Cornell researchers and others have previously developed microscopic machines that can crawl, swim, walk and fold themselves up. To generate motion, wires were used to provide electrical current, or laser beams had to be focused directly onto specific locations of the robots. According to Itai Cohen, professor of physics in the College of Arts and Sciences, before, they had to manipulate these wires to get any response from the robot. But with their recent study, it is like taking the strings off the marionette with the brains on board.  

The innovation sets the stage for a new generation of microscopic devices that can track bacteria, sniff out chemicals, restring pollutants, conduct microsurgery and sub the plaque out of arteries.  

The "brain" in the new robots is a complementary metal-oxide-semiconductor clock circuit containing a thousand transistors and an array of diodes, resistors and capacitors. The integrated CMOS circuit generates a signal that produces a series of phase-shifted square wave frequencies that, in turn, set the robot's gait. The legs of the robot are platinum-based actuators. The circuit and the legs are powered by photovoltaics. 

The team created three robots to demonstrate the CMOS integration: a two-legged Purcell bot, named in tribute to physicist Edward Purcell, who proposed a similarly simple model to explain the swimming motions of microorganisms, a more complicated six-legged antibot, which was with an alternating tripod gait, like that of an insect; and a four-legged doubt that can vary the speed with which it walks. The robot has chemical detectors to photovoltaic "eyes" that help it to navigate by sensing changes in light. 

The team's paper, "Microscopic Robots with Onboard Digital Control", was published in Science Robotics on September 21. The project brought together researchers from the labs of Cohen, Alyosha Molnar, associate professor of electrical and computer engineering at Cornell Engineering, and Paul McEuen, the John A. Newman Professor of Physical Science (A&S).