Over the years, the downsizing of robotics has presented a persistent challenge. Despite significant advancements in miniaturizing electronics, the creation of fully autonomous miniature robots smaller than one millimeter has remained elusive. Fragility of tiny mechanical limbs and the drastic shift in physical forces at microscopic scales—where drag and viscosity dominate rather than gravity and inertia—have hindered progress. Recently, researchers from two American institutions have reported a breakthrough in this area, overcoming a challenge that has persisted for four decades. They introduced a robot smaller than a grain of salt, measuring just 200 by 300 by 50 micrometers, with its longest dimension being merely 0.3 millimeters, well beneath the critical 1-millimeter mark. Remarkably, this minuscule robot can independently sense its environment, make decisions, and navigate through water without relying on external controls like wires or magnetic fields, all while being produced at a cost approximating one cent per unit.
The propulsion mechanism developed signifies a significant leap forward compared to traditional robotics. While larger aquatic creatures generate forward movement by pushing water backward, a method ineffective at microscopic scales due to the overwhelming water viscosity, the research team implemented an innovative tactic. Instead of mechanical movement, the robot generates an electric field that moves charged particles in the surrounding liquid, creating currents that effectively move the robot. This approach mimics a scenario where it is not the robot that moves but the fluid around it flows. Powered by LED light, the robot can traverse its own body length in up to one second, and by varying the electric field, it can follow intricate paths or swim collectively like a school of fish. Crucially, the absence of moving parts ensures exceptional durability, enabling the robot to swim continuously over extended periods.
Achieving autonomy required more than just efficient propulsion; the robot needed sensing and decision-making capabilities on a similarly miniature scale. A team led by a scientist at the second institution tackled this by integrating the world’s smallest computer, which had been previously developed. When the two research groups collaborated, combining the propulsion and computing expertise took five years to materialize fully. One major obstacle was power supply; the robot’s minuscule solar panels generate a mere 75 nanowatts—less than one hundred-thousandth of typical smartwatch power consumption. The team countered this with specially designed circuitry operating at ultra-low voltages, drastically reducing energy consumption to a viable level. Additionally, space limitations on the robot’s surface mandated a radical simplification of the control program from numerous instructions into a single, highly specialized instruction that fit the scant memory available.
For communication, the tiny robot integrates a sensor that detects subtle temperature variations but lacks the capacity for traditional data transmission owing to its size. Instead, inspired by insect communication methods, the robot encodes sensor information into distinctive movements or “dance moves,” which researchers decode visually under a microscope. Each unit also carries a unique identifier and can receive different programmed commands, enabling a swarm of such robots to undertake complex, coordinated tasks simultaneously. This development marks the first instance of a complete computer—processor, memory, and sensors—being incorporated into a sub-millimeter robot. Functioning on a scale akin to microbes, these micro-robots hold promise for precise applications such as monitoring individual cells in medicine or assembling tiny devices in engineering.