The MIT inventors of tiny artificial muscles that flap the wings of robotic insects have now added electroluminescent particles that enable them to emit colored light during flight, similar to fireflies.

The artificial muscles, called actuators, are made by alternating ultrathin layers of elastomer and carbon nanotube electrode material and then rolling the stack of layers into a squishy cylinder. When a voltage is applied, the electrodes squeeze the elastomer, and the mechanical strain flaps the wing.

To make them glow, electrical engineering and computer science professor Kevin Chen and his team embedded zinc sulfate particles into the elastomer and used a very thin layer of nanotubes to avoid blocking the light. Because the particles light up only in the presence of a strong, high-frequency electric field, they use a high voltage to create such a field in the actuator and then drive the robot at a high frequency. It ends up just 2.5% heavier, and flight performance isn’t compromised.

This capability could enable the robo-bugs to communicate with each other, and it brings microscale robots closer to flying on their own outside the lab. Such lightweight devices can’t carry sensors, so researchers must track them using infrared cameras that don’t work well outdoors. Now the scientists have shown that they can track these robots using the emitted light and three smartphone cameras.

The team is working to incorporate control signals so the robots could turn their lights on and off during flight to communicate. On a search-and-rescue mission, for instance, they could signal for help.

Larger robots can use tools like Bluetooth or wireless to communicate, “but for a tiny, power-­constrained robot, we are forced to think about new modes of communication,” Chen says. “This is a major step toward flying these robots in outdoor environments where we don’t have a well-tuned, state-of-the-art motion tracking system.”