In complex systems like aircraft engines and oil refinery machines, pipeline inspection is an essential task for ensuring safety. Here, we proposed a type of smart material–driven pipeline inspection robot (weight, 2.2 grams; length, 47 millimeters; diameter, <10 millimeters) that could fit into pipes with sub-centimeter diameters and different curvatures. We adopted high–power density, long-life dielectric elastomer actuators as artificial muscles and smart composite microstructure–based, high-efficiency anchoring units as transmissions. Fast assembling of components using magnets with an adjustable number of units was used to fit varying pipeline geometries. We analyzed the dynamic characteristics of the robots by considering soft material’s unique properties like viscoelasticity and dynamic vibrations and tuned the activation voltage’s frequency and phase accordingly. Powered by tethered cables from outside the pipe, our peristaltic pipeline robot achieved rapid motions horizontally and vertically (horizontal: 1.19 body lengths per second, vertical: 1.08 body lengths per second) in a subcentimeter-sized pipe (diameter, 9.8 millimeters). Besides, it was capable of moving in pipes with varying geometries (diameter-changing pipe, L-shaped pipe, S-shaped pipe, or spiral-shaped pipe), filled media (air or oil), and materials (glass, metal, or carbon fiber). To demonstrate its capability for pipeline inspection, we installed a miniature camera on its front and controlled the robot manually from outside. The robot successfully finished an inspection task at different speeds.

Dielectric elastomer actuators (DEAs) as a typical class of electroactive polymers have been developed rapidly in the last two decades due to their advantages such as large strain, high energy density, and fast response. The high‐frequency characteristics of DEAs enable them to be applied in a wider range of fields. In this review, the high‐frequency (>10 Hz) characteristics and applications of DEAs are focused on. The basic concepts and metrics for high‐frequency DEAs are first given. Next, the commercial and synthesized dielectric and electrode materials of DEAs used in high‐frequency applications are reviewed. Following materials, strategies for extending the lifetime of DEAs are introduced. Subsequently, the dynamic modeling approaches for DEAs are presented, considering damping, inertia, and the electrical loss. Building on the fundamental research, some important applications are summarized based on the high‐frequency motions of DEAs including loudspeakers, active vibration suppression, pumps/valves, haptic devices, and high‐speed mobile robots. Finally, the conclusions and future perspectives are given. This review will give readers a clearer understanding of how to design and use high‐frequency DEAs.

Fluidic Elastomer Actuators (FEAs) provide new opportunities for developing agile, adaptive, and strong mobile robots for field explorations. In this letter, we propose a soft-rigid coupled linear FEA with a bio-comparable energy density of 10.9 J/kg at 50 kPa. This actuator achieves an increased blocked force output (318%), increased energy density (183%), and increased power density (358%) by incorporating a rigid carbon-fiber telescopic shaft within its elastomeric skin. Based on this new FEA, we develop an untethered crawling robot with enhanced capability of forward locomotion and vertical load-bearing. We analyze and demonstrate how the proposed actuators increase the crawling robot's payload and terrain adaptivity. Experiments demonstrate that the robot's crawling speed with a payload of 6 kg (8.8 times of its own weight) is effectively increased compared with robot with purely soft actuators. Furthermore, we have demonstrated the robot can adapt to terrains with a wide range of roughnesses. Our design of coupling soft and rigid components provides a feasible strategy for building FEAs with higher energy density and constructing FEA-based, untethered mobile robot with better locomotion and payload performance driven by low-power pumps.

Mobile robots that can adapt to an extensive range of terrains play essential roles in many applications. Millipedes are one of the most terrain-adaptive creatures in nature due to their multi-legged locomotion and flexible body. Inspired by natural millipedes, we report an untethered robotic millipede with a 6-segments soft-rigid hybrid body that can actively bend and 24 legs driven by low-pressure microfluidic actuators. The 24 microfluidic actuators are driven by two independent low-pressure sources from miniature pumps, which allows the untethered locomotion of the robotic millipede in small size (length, 23 cm; width, 5 cm; height, 4 cm) and lightweight (150 g). Using a pre-defined gait for the multi-legs, the robotic millipede can locomote with a maximum speed of 30.96 cm/min (1.35 body length per minute) and a minimum turning radius of 15 cm (0.65 body length). Experiments also demonstrated that the robot was able to locomote effectively in various uneven terrains. Utilizing its passive or active mode of its flexible body, the robot could also achieve adaptive moves. The robotic millipede has the potential to perform a variety of environment exploration tasks by remotely controlling and transmitting real-time images wirelessly.