Headline: Advancing miniature underwater robotics: innovations in actuation and locomotion

Miniature Underwater Robots (MURs) are revolutionizing how humans explore aquatic environments. However, achieving efficient propulsion in highly resistive underwater conditions remains a formidable challenge. Unlike aerial and terrestrial robots, MURs operate in a medium with significant drag forces, making propulsion efficiency a primary concern.

Propulsion mechanisms are categorized into conventional approaches, such as propellers and jet propulsion, and bio-inspired methods that mimic marine organisms’ swimming patterns. While conventional propulsion systems are well-established, they often struggle with miniaturization and energy efficiency. In contrast, bio-inspired propulsion techniques—including fish-like undulatory motion and jellyfish-like pulsation—offer enhanced maneuverability, stealth, and energy efficiency. The development of soft-bodied actuators and shape-adaptive propulsors has opened new possibilities, enabling robots to adapt more effectively to dynamic environments. Recent advances in soft robotics have facilitated the integration of compliant materials, making bio-inspired designs an attractive alternative to traditional propulsion systems.

Despite recent advancements, several key challenges persist. Miniaturizing actuation systems without compromising power output remains a significant hurdle, as smaller robots have limited onboard energy storage capacity. Additionally, energy efficiency is a critical bottleneck, since underwater robots often operate in environments where recharging or refueling is impractical. This constraint has driven research into ultra-low-power actuators and innovative energy-harvesting technologies. Another major challenge lies in achieving precise control and stable locomotion in unpredictable underwater currents, which can introduce disturbances that affect navigation accuracy. To overcome these issues, researchers are exploring advanced control strategies, including reinforcement learning-based adaptive control and distributed swarm intelligence, enabling MURs to operate autonomously in complex environments.

The study identifies several promising directions for future MUR research. The integration of artificial intelligence and real-time environmental perception is expected to significantly enhance autonomy, allowing robots to make intelligent navigation decisions without human intervention. AI-driven motion planning algorithms could enable MURs to optimize their trajectories while minimizing energy consumption. Additionally, advancements in soft robotics and biohybrid actuation may lead to robots that seamlessly adapt to varying underwater conditions, mimicking marine organisms with unprecedented fluidity. These developments could also facilitate swarm robotics, where multiple MURs coordinate for collective exploration and monitoring.

Beyond marine exploration, MURs have vast potential applications in environmental monitoring, underwater infrastructure inspection, and even biomedical fields such as targeted drug delivery in aquatic environments. Their ability to maneuver in confined spaces makes them well-suited for pipeline inspection, ship hull maintenance, and deep-sea ecological surveys. As demand grows for compact, efficient, and intelligent underwater robots, further innovations in actuation mechanisms and control strategies will drive the field forward.

This research provides a comprehensive review of actuation methods, categorizing and evaluating various propulsion techniques used in MURs while highlighting their advantages, limitations, and potential for future development. It also analyzes emerging trends in soft-bodied actuators and biohybrid swimming mechanisms, demonstrating their potential for improving energy efficiency and adaptability. Furthermore, it outlines key challenges in miniaturization, power efficiency, and control, offering valuable insights into future research directions that could revolutionize underwater robotics.

The advancements in miniature underwater robot technologies pave the way for innovative applications across marine science, industry, and healthcare. By integrating soft robotics, AI-driven control, and energy-efficient propulsion systems, researchers aim to develop next-generation MURs capable of autonomous operation in complex underwater environments. These robots could play a transformative role in protecting marine ecosystems, assisting in search-and-rescue missions, and improving underwater infrastructure maintenance—ultimately reshaping how humans interact with and explore the underwater world.

The paper “Actuation and Locomotion of Miniature Underwater Robots: A Survey,” authored by Panbing Wang, Xinyu Liu, and Aiguo Song. Full text of the open access paper: https://doi.org/10.1016/j.eng.2024.10.022. For more information about the Engineering, follow us on X (https://twitter.com/EngineeringJrnl) & like us on Facebook (https://www.facebook.com/EngineeringJrnl).