This article is part of our exclusive IEEE Journal Watch series in partnership with IEEE Xplore.
Fish are able to dart quickly through the water and turn on a dime with a flick of their tail. Researchers have been trying to achieve similar results with aquatic robots. In fact, one group in China has made progress using a flexible electromagnetic fin that propels an underwater robot at 405 millimeters—or 1.66 body lengths—per second. The team’s robotic swimmer can also make turns over just a 0.86 body-length radius.
Fanghao Zhou, an assistant professor at the State Key Laboratory of Ocean Sensing at Zhejiang University in Zhejiang, China, helped guide the research. Zhou notes that fish are agile, efficient, and adaptive—and robotically mimicking these qualities is a challenge.
“Traditional robotic fins powered by motors can generate strong thrust, but they’re often bulky and rigid,” he says. “Soft actuators, on the other hand, are flexible but usually too weak to be practical. Our goal was to combine the best of both fields—a compact actuator that’s powerful yet flexible, like real muscle.”
Making a New Kind of Fin
So the research team designed a flexible electromagnetic fin with an elastic joint that swishes back and forth with little friction. It’s built with two small coils and spherical magnets. When alternating current flows through the coils, it creates an oscillating magnetic field that makes the fin flap back and forth, much like a fish’s tail. When the magnetic field isn’t oscillating, the fin returns to a neutral position at rest.
In their study, the researchers tested their bionic fin in a pool. Zhe Wang, a Ph.D. student in Zhou’s lab, emphasizes that the team not only successfully piloted the bionic fin in water, but they also built a mathematical model connecting electrical input to hydrodynamic thrust output. “That means we can predict how the fin will behave underwater just from the input current, which is rare in soft robotics,” he says.
A new robotic fish design reveals different swimming behaviors at different fin oscillation speeds. Zhe Wang et al.
In their experiments, the researchers used a high-speed camera and precision force sensor to measure the trajectory of the fin and the thrust it generated—achieving a peak thrust of 0.493 newtons, despite the fin weighing just 17 grams.
Zhou notes the robotic system is small, lightweight, and powerful, and it will also be easy to scale into multi-fin systems. However, he adds that the current design consumes a lot of energy. “The electromagnetic coils draw a lot of current, so the swimming duration is relatively short,” he explains. “We are exploring ways to reduce energy loss, for example [by] optimizing coil geometry, using energy recovery circuits, and applying smart control strategies that don’t require continuous excitation.”
The researchers anticipate this robotic system could have a range of applications, including perhaps in underwater exploration, ecological monitoring, and inspection—such as safely interacting with coral reefs and marine life.
“Our next step is to study multi-fin coordinated motion, enabling the robot to perform more flexible and lifelike swimming behaviors,” Wang says. “We are also exploring ways to improve energy efficiency, extend operation time, and further miniaturize the system for small autonomous underwater platforms.”
The researchers’ bionic fin is described in a study published 4 September in IEEE Robotics and Automation Letters.
The post “Robotic Fish Zips Through Water With Flexible Electromagnetic Fin” by Michelle Hampson was published on 11/04/2025 by spectrum.ieee.org