An eel-like robot was developed that can swim silently in salt water without an electric motor. Instead, the robot uses artificial muscles filled with water to propel itself. The foot-long robot, which is connected to an electronics board that remains on the surface, is also virtually transparent.
The robot is an important step toward a future when soft robots can swim in the ocean alongside fish and invertebrates without disturbing or harming them. Today, most underwater vehicles designed to observe marine life are rigid and submarine-like, and powered by electric motors with noisy propellers.
One key innovation was using the salt water in which the robot swims to help generate the electrical forces that propel it. The bot is equipped with cables that apply voltage to both the salt water surrounding it and to pouches of water inside its artificial muscles. The robot's electronics then deliver negative charges in the water just outside the robot, and positive charges inside the robot that activate the muscles. The electrical charges cause the muscles to bend, generating the robot's undulating swimming motion. The charges are located just outside the robot's surface and carry very little current so they are safe for nearby marine life.
Previously, other robots with similar technology were powered using materials that need to be held in constant tension inside semi-rigid frames.
The robot was tested inside salt water tanks filled with jellyfish, coral, and fish. The conductive chambers inside the robot's artificial muscles can be loaded with fluorescent dye; in the future, the fluorescence could be used as a signaling system.
Next steps also include improving the robot's reliability and its geometry. Researchers need to improve ballast, equipping the robot with weights so that it can dive deeper. For now, engineers have improvised ballast weights with a range of objects such as magnets. In future work, researchers envision building a head for the eel robot to house a suite of sensors.