Researchers at the University of Pennsylvania and the University of Michigan have achieved a significant milestone in robotics: creating fully autonomous, solar-powered robots that cost just one penny to manufacture. These machines, smaller than a grain of salt, overcome decades-old challenges in micro-robotics by harnessing electrical propulsion and novel circuit designs. The development opens doors for advancements in nanotechnology, medical research, and beyond.
The Decades-Long Challenge of Micro-Robotics
For 40 years, the robotics field has struggled with building independent robots at sub-millimeter scales. The problem isn’t just miniaturization; it’s physics. As objects shrink, inertia becomes less dominant while surface area effects like viscosity and drag take over. This means that traditional locomotive designs, such as legs or arms, become impractical at the micro-level—moving through fluids at this scale is akin to pushing through tar. The team’s solution bypasses the need for mechanical limbs altogether, relying instead on electrical fields to propel the robots.
How They Work: Electricity, Ions, and Water
Each robot, measuring approximately 200 x 300 x 50 micrometers, converts energy from tiny solar panels into an electrical field when submerged in a solution. This field pushes nearby ions, which then displace surrounding water molecules, creating movement. The robots aren’t limited to simple forward or backward motion; by adjusting the electrical field, they can move individually or in coordinated patterns, mimicking the behavior of a school of fish. The researchers explain it as the robot both being in a moving river and also causing the river to move.
Overcoming Power Constraints: Radical Circuit Design
Miniaturization presents another hurdle: limited space for power sources, memory, and circuitry. The robots operate on just 75 nanowatts—over 100,000 times less than a smartwatch consumes. To address this, engineers at the University of Michigan developed entirely new circuit designs that operate at low voltages, reducing the robot’s power needs by over 1,000 times. The solar panels take up most of the robot’s surface area, so the team had to radically condense the programming instructions.
Communication Through Movement: The “Wiggle Dance”
The micro-robots include sensors capable of detecting temperature with high accuracy (within a third of a degree Celsius). To report their findings, they use a unique communication method inspired by honeybees. They encode data into a “wiggle dance”—a specific pattern of movement that researchers can decode using a microscope and camera. This allows the robots to transmit information without requiring complex wireless systems.
Future Implications
The current robots can already sense temperature changes, potentially making them useful for tracking cellular activity and assessing cell health. But the foundation is now laid for even more advanced capabilities. With further refinement, these micro-robots could incorporate additional sensors and navigate increasingly complex environments, opening up possibilities in targeted drug delivery, environmental monitoring, or even precision manufacturing.
“We’ve shown that you can put a brain, a sensor, and a motor into something almost too small to see, and have it survive and work for months,” said Marc Miskin, lead engineer at the University of Pennsylvania. This breakthrough not only solves a long-standing robotics problem but also unlocks a new era of possibilities for ultra-small autonomous machines.
