Grain-of-salt microrobots swim, sense and compute for months

The robots move without joints or limbs. Instead, electrodes on each device generate an electrical field that pushes ions in the surrounding fluid; those ions drag water and create propulsion. Because there are no mechanical motors, the electrodes tolerate repeated handling and transfer between samples.

Power comes from tiny solar cells producing about 75 nanowatts. Engineers at the University of Michigan redesigned circuits to run at very low voltages and cut energy use by more than 1,000 times. Software was compressed so key behaviors fit within the microrobots’ minimal memory.

Each microrobot contains a processor, memory, sensors, and motor control—making it the first sub-millimeter device with a full computer stack. They detect temperature changes to within one-third of a degree Celsius and can swim toward warmer regions or signal readings by encoding data in small motion patterns observers decode under a microscope.

Robots are powered and programmed by light pulses; each unit has a unique address so different programs can be loaded. They can act alone or coordinate in groups, swim up to one body length per second, and researchers say the design is a platform for adding sensors or more complex programs. “This is really just the first chapter,” said Marc Miskin, and “Once you have that foundation, you can layer on all kinds of intelligence and functionality.”