This Autonomous Aquatic Robot Is Smaller Than a Grain of Salt

Miniaturization has been around for a long time been a challenge in the history of robotics.

While engineers have made great strides in miniaturizing electronics in recent decades, builders of miniature autonomous robots have not been able to achieve the goal of making them less than a millimeter in size. Indeed, small arms and legs are fragile and difficult to manufacture. Above all, the circumstances of the laws of physics change in the microscopic world. Instead of gravity and inertia, drag and viscosity become dominant.

In this context, American researchers announced the results of a study that addresses a 40-year-old challenge. A team of researchers from the University of Pennsylvania and the University of Michigan have developed a new robot smaller than a grain of salt, measuring just 200 x 300 x 50 micrometers. At 0.3mm on its longest side, it’s well below the 1mm threshold. However, it can sense its surroundings, make decisions for itself, swim and move in water.

This experimental robot is smaller than a grain of salt.

Photograph: Marc Miskin/University of Pennsylvania

In addition, it operates completely autonomously and does not depend on any external controls such as wires or magnetic fields. The cost of production would be as low as 1 cent per unit.

“We were able to miniaturize an autonomous robot to 1/10,000th the size of a conventional robot,” says Mark Miskin, one of the researchers and an assistant professor of power systems engineering at the University of Pennsylvania. “This opens up a whole new scale for programmable robots.”

The electric slide

The propulsion system developed by Miskin and his team represents a major advance in conventional robotics. Fish and other large aquatic organisms move forward due to the reaction of water pushing backward, in accordance with the third law of motion of Newtonian mechanics. But pushing water on a microscopic scale is like pushing muddy tar. The viscosity of water is so great that little arms and legs can never compete with it.

The researchers therefore adopted a completely new approach. Instead of swimming by moving parts of its body, the new robot moves by generating an electric field around itself and gently pushing charged particles into the liquid. The robot exploits the phenomenon that moving charged particles drag nearby water molecules, creating a current of water around the robot. It’s as if the robot itself isn’t moving, but the ocean or river is.

This image shows the movement of charged particles generated around a robot moving in a liquid.

Photograph: Lucas Hanson/William Reinhardt/University of Pennsylvania