Researchers have developed a low-voltage, muscle-like actuator that powers autonomous insect-scale robots with unprecedented force, speed, and efficiency.
Study: Muscle-inspired elasto-electromagnetic mechanism in autonomous insect robots. Image Credit: miroha141/Shutterstock.com
Published in Nature, the study introduces an elasto-electromagnetic (EEM) artificial muscle that mimics biological muscle contractions to drive soft robotic systems. This actuator delivers high force (210 newtons per kilogram), 60% contraction, fast response (60 Hz), and low-voltage operation (<4 volts), all within a compact footprint.
These features enable insect-sized robots to crawl, swim, and jump autonomously, tackling the limitations of traditional rigid actuators in miniaturized designs. The approach improves energy efficiency and adaptability, with promising applications in disaster response, environmental sensing, and biomedical devices.
Background
Biological muscles, especially those found in insects, are exceptional in their ability to produce powerful, adaptive movement at small scales. They achieve force-to-mass ratios over 230 N/kg and can dynamically contract to support efficient locomotion. Replicating this performance in robotics has proven difficult, particularly for small systems.
Most existing actuators—such as electric motors—are rigid, complex, and prone to issues like friction and mechanical wear. They also struggle to scale down effectively. Meanwhile, soft actuators based on smart materials often require impractical inputs like high voltages, extreme temperatures, or continuous external stimuli, limiting their usefulness for untethered or autonomous robots.
The EEM actuator addresses these limitations by combining soft elastomeric materials with strategically placed magnetic components. The result is a compact, energy-efficient system capable of producing muscle-like motion under conditions suitable for small, mobile robots.
How it Works
At the core of the EEM actuator are three key components: a hard magnet (NdFeB), soft magnetic iron spheres embedded within copper coils, and a flexible PDMS (Polydimethylsiloxane) elastomer structure. These parts are fabricated using a scalable 2D molding process, supporting a wide range of sizes.
What sets the EEM design apart is its use of magnetic and elastic interactions to create multi-stable states—bistable or even tristable configurations that allow the actuator to hold positions without constant power. This dramatically reduces energy consumption while enabling precise, responsive motion.
The bistable design takes inspiration from mollusk catch muscles, which maintain tension with minimal energy. In the EEM actuator, transitions between states require only a 6-millisecond pulse at 38 milliwatts (at 1 Hz), cutting energy usage by over 95 % compared to monostable systems. This efficient switching, combined with high force output and rapid response, allows the actuator to replicate biological muscle dynamics more closely than conventional approaches.
Centimeter-scale prototypes have demonstrated impressive capabilities:
- Forces up to 0.38 N (210 N/kg)
- Contraction ratios of 30–60 %
- Operating frequencies up to 60 Hz
These figures outperform many conventional systems—including piezoelectric actuators (0.05 N) and even combustion-based mechanisms (0.3 N)—all while maintaining low voltage requirements.
Durability is another major strength. Thanks to the hyperelasticity of PDMS, the actuators can endure over 4.7 million actuation cycles and survive drops from up to 30 meters. The system is also thermally stable at operating frequencies up to 15 Hz, aided by adaptive current modulation that minimizes heat buildup.
Scalability and Versatility
A standout feature of the EEM system is its scalability. Researchers have demonstrated versions ranging from millimeter-scale actuators requiring just 0.43 milliwatts of power, to decimeter-scale models capable of producing 27 N of force. This versatility opens the door to integration across a wide variety of soft robotic platforms.
Its planar, 2D geometry simplifies manufacturing and integration into soft-bodied systems. Flexure linkages convert the actuator’s linear motion into rotation—up to 65°—enabling robots with diverse gaits and movement strategies.
Compared to Lorentz-force actuators, which need continuous current, the EEM design operates through static magnetic interactions, activated by short pulses of current. This eliminates the need for bulky, rigid transmission systems and allows for lightweight, autonomous robots that are more robust and responsive.
What This Means for Soft Robotics
By achieving muscle-like performance in a soft, scalable, and energy-efficient package, the EEM actuator addresses a long-standing challenge in soft robotics: enabling autonomous motion at small scales without sacrificing power or precision.
The technology has already been demonstrated in insect-scale robots capable of crawling, swimming, and jumping on their own. Its robustness, low power needs, and compatibility with soft materials make it particularly suited for applications where size, weight, and mobility are critical.
While challenges remain, particularly in terms of thermal management and further miniaturization, the EEM actuator sets a new benchmark for robotic actuation at small scales and offers a solid foundation for next-generation systems in fields ranging from rescue operations to medical devices.
Journal Reference
Xu, C., Cao, Y., Zhao, J. et al. Muscle-inspired elasto-electromagnetic mechanism in autonomous insect robots. Nat Commun 16, 6813 (2025). DOI:10.1038/s41467-025-62182-2. https://www.nature.com/articles/s41467-025-62182-2
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