- Researchers have created fully autonomous robots smaller than a grain of sand
- The robots swim by using electric fields to manipulate ions in the surrounding liquid.
- The propulsion system provides coordinated movement and speed of up to one body length per second.
Researchers from the University of Pennsylvania and the University of Michigan claim to have created the world's smallest fully programmable autonomous robots.
Each robot measures approximately 200 by 300 by 50 micrometers, which is smaller than a grain of salt, and operates at the level of biological microorganisms.
The robots operate without tethers, magnetic fields or external joysticks, making them the first truly autonomous devices of their size.
Swimming through microscopic physics
The team faced challenges in creating propulsion systems suitable for such small robots, as forces such as drag and viscosity dominate at this scale, making traditional limbs or body flexion ineffective.
Instead, the robots use electric fields to manipulate ions in the surrounding liquid. These ions, in turn, push the water molecules, creating movement.
This approach allows robots to swim in complex patterns and even coordinate their actions in groups, reaching speeds of up to one body length per second.
Because the field-generating electrodes have no moving parts, the robots are extremely durable and can be moved between samples repeatedly without damage.
Another challenge was placing the computer, memory, sensors and tiny solar panels on a chip less than a millimeter in size.
Solar panels take up most of the robot's surface, producing just 75 nanowatts of energy, more than 100,000 times less than a smartwatch.
To operate under such tight power constraints, the Michigan team condensed software instructions into extremely efficient circuits, reducing power consumption by more than a thousand times.
This allows each robot to store a program, sense its environment, and autonomously adjust its movement over several months.
The robots are equipped with electronic sensors that can measure temperature to within a third of a degree Celsius.
They can move to warmer areas or report measurements using data encoded in the “wiggling” of a small dance.
Researchers observe these movements under a microscope and decipher the signals, similar to how honey bees communicate.
Each robot can be programmed with light pulses, giving unique instructions to individual robots and allowing coordinated tasks across multiple robots.
This sub-millimeter robotic platform is the basis for future advances: its propulsion, electronics and power systems can be scaled to include more complex programs, additional sensors, faster movement and operation in more challenging environments.
This achievement shows that it is now possible to integrate computation, measurement and actuation on microscopic scales.
This could also have implications for medicine, allowing the monitoring of individual cells, as well as for the production of microscale devices.
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