Fireflies became the inspiration of the researchers from the Massachusetts Institute of Technology (MIT) to develop insect-scale robots that have electroluminescent soft artificial muscles for flying in which the tiny artificial muscles that control the robots’ wings could emit the coloured light during flight.
The robots could communicate with each other using electroluminescence. If a robot is sent on a search-and-rescue mission into a collapsed building, for example, it can use lights to signal others and call for help.
“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,” said Kevin Chen, Assistant Professor, Department of Electrical Engineering and Computer Science (EECS), MIT and the senior author of the study.
The ability to emit light also brings these microscale robots, which weigh no more than a paper clip, one step closer to flying independently outside of the lab. Because these robots are so light, they can’t carry sensors, so researchers must track them with bulky infrared cameras that don’t work well outdoors. They’ve recently demonstrated that they can precisely track the robots using the light they emit and only three smartphone cameras.
Large-scale robots can communicate using a variety of tools, such as Bluetooth and wireless, but the researchers were forced to consider new modes of communication for a tiny, power-constrained robot. This was accomplished by embedding tiny electroluminescent particles into the artificial muscles. The process adds only 2.5 per cent more weight to the robot without affecting its flight performance.
These scientists have previously shown how to construct soft actuators or artificial muscles, that move the robot’s wings. These robust actuators are created by stacking and rolling alternating ultrathin layers of elastomer and carbon nanotube electrodes. The electrodes on that cylinder squeeze the elastomer when a voltage is provided, and the mechanical strain causes the wing to flap.
The team incorporated electroluminescent zinc sulphate particles into the elastomer to create a glowing actuator, but they encountered several challenges along the way. Moreover, the researchers had to make an electrode that wouldn’t stop light from getting through. They made it with carbon nanotubes that are only a few nanometers thick and are very clear. This lets light pass through.
But the zinc particles only light up when a very strong and high-frequency electric field is nearby. This electric field gets the electrons in the zinc particles excited, which causes them to send out photons, which are subatomic particles of light. The researchers use high voltage to make a strong electric field in the soft actuator. They then drive the robot at a high frequency, which makes the particles light up brightly.
Adding zinc particles to the actuator prototype lowered its quality and made it break more easily while chemically combining zinc particles affects light colour that results in each actuator having a solid green, orange, or blue glow.
They altered the fabrication method so actuators could emit multicoloured, patterned light. After fine-tuning the fabrication process, they examined the actuators’ mechanical qualities and measured the light’s intensity.
They then conducted flight tests with a specially designed motion-tracking system. They intend to improve that motion tracking system in the future so that it can track robots in real-time. The team is working on incorporating control signals so that the robots can turn on and off their lights during flight and communicate more like real fireflies.
The study was supported by the Research Laboratory of Electronics at MIT and joining Kevin’s team are Suhan Kim, lead author and Yi-Hsuan Hsiao; Yu Fan Chen SM ’14, PhD ’17; and Ningxia University associate professor, Jie Mao.
