Silence of the Fins

Blend in like a chameleon, and you will see the world reveal itself to you. When you observe from the shadows, without drawing attention to yourself, you minimize the observer effect — that phenomenon where the very act of observation alters the behavior of the observed. Being an unobtrusive observer is especially important in the sciences, where the goal is to understand natural phenomena in their purest form. In fields like ecology, researchers strive to be flies on the wall, witnessing behaviors and patterns without influencing them.

Unfortunately, this is not always easy to accomplish. The technologies we use to help us make observations are very often highly disruptive. Consider the floating and swimming robots that are used to monitor the health of aquatic ecosystems. They are typically powered by propellers, which stir up the water and alter the behavior of nearby animals. And that, of course, results in abnormal observations being collected, which, in turn, can lead researchers to draw incorrect conclusions.

Yet we can hardly do without assistance from technology. Manual observation is very labor-intensive and does not scale well. And anyway, we can be a bunch of bumbling fools ourselves, greatly disrupting the systems we wish to observe.

To address this challenge, researchers at the Swiss Federal Institute of Technology Lausanne and the Max Planck Institute for Intelligent Systems have developed a new kind of swimming robot that moves stealthily. Instead of noisy and disruptive propellers, the device relies on soft, undulating fins inspired by marine flatworms. This novel propulsion system allows the robot to glide effortlessly through water without disturbing its surroundings, making it an ideal tool for ecological monitoring, pollution tracking, and precision agriculture.

Smaller than a credit card and weighing just six grams, the robot’s compact size allows it to navigate tight spaces, such as rice paddies or densely vegetated lake shores. Despite its small frame, it is exceptionally strong, capable of pushing objects 16 times its own weight. Furthermore, the robot’s ability to move in multiple directions — including forward, backward, and sideways — gives it an agility rarely seen in aquatic robotics.

The robot’s soft electrohydraulic actuators are the key to its stealth and agility. These ultra-thin artificial muscles generate traveling waves along the flexible fins, propelling the robot through water with precision. By oscillating its fins up to 10 times faster than the flatworms that inspired it, the robot reaches speeds of 12 centimeters per second — that is roughly 2.6 times its body length each second.

Equipped with a compact electronic control system, the robot operates autonomously using only 500 milliwatts of power — four times less than an electric toothbrush. Light sensors serve as rudimentary eyes, enabling the robot to detect and follow light sources, giving it basic navigational capabilities through aquatic environments.

Future versions of the robot may incorporate solar energy harvesting for prolonged missions or additional sensors for real-time environmental monitoring. With its silent, natural movements and minimal impact on its surroundings, this new robotic swimmer has the potential to make a significant impact in ecological research, bringing scientists closer to understanding aquatic ecosystems as they really are.