Zhijian Ren

Mr. Zhijian Ren

orcid

Research Focus & Metrics

Academic Career Length

5Years (2022-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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22 March 2023 in Science Robotics
Verified
Journal Article
Closed access
SKSuhan Kim
Suhan Kim
YHYi-Hsuan Hsiao
Yi-Hsuan Hsiao
YLYounghoon Lee
Younghoon Lee
WZWeikun Zhu
Weikun Zhu
ZRZhijian Ren
Zhijian Ren
Yufeng (Kevin) ChenYufeng (Kevin) Chen
Yufeng (Kevin) Chen
Insects maintain remarkable agility after incurring severe injuries or wounds. Although robots driven by rigid actuators have demonstrated agile locomotion and manipulation, most of them lack animal-like robustness against unexpected damage. Dielectric elastomer actuators (DEAs) are a class of muscle-like soft transducers that have enabled nimble aerial, terrestrial, and aquatic robotic locomotion comparable to that of rigid actuators. However, unlike muscles, DEAs suffer local dielectric breakdowns that often cause global device failure. These local defects severely limit DEA performance, lifetime, and size scalability. We developed DEAs that can endure more than 100 punctures while maintaining high bandwidth (>400 hertz) and power density (>700 watt per kilogram)—sufficient for supporting energetically expensive locomotion such as flight. We fabricated electroluminescent DEAs for visualizing electrode connectivity under actuator damage. When the DEA suffered severe dielectric breakdowns that caused device failure, we demonstrated a laser-assisted repair method for isolating the critical defects and recovering performance. These results culminate in an aerial robot that can endure critical actuator and wing damage while maintaining similar accuracy in hovering flight. Our work highlights that soft robotic systems can embody animal-like agility and resilience—a critical biomimetic capability for future robots to interact with challenging environments.

15 January 2025 in Science Robotics
Verified
Journal Article
Closed access
SKSuhan Kim
Suhan Kim
YHYi-Hsuan Hsiao
Yi-Hsuan Hsiao
ZRZhijian Ren
Zhijian Ren
JHJiashu Huang
Jiashu Huang
Yufeng (Kevin) ChenYufeng (Kevin) Chen
Yufeng (Kevin) Chen
Aerial insects are exceptionally agile and precise owing to their small size and fast neuromotor control. They perform impressive acrobatic maneuvers when evading predators, recovering from wind gust, or landing on moving objects. Flapping-wing propulsion is advantageous for flight agility because it can generate large changes in instantaneous forces and torques. During flapping-wing flight, wings, hinges, and tendons of pterygote insects endure large deformation and high stress hundreds of times each second, highlighting the outstanding flexibility and fatigue resistance of biological structures and materials. In comparison, engineered materials and microscale structures in subgram micro–aerial vehicles (MAVs) exhibit substantially shorter lifespans. Consequently, most subgram MAVs are limited to hovering for less than 10 seconds or following simple trajectories at slow speeds. Here, we developed a 750-milligram flapping-wing MAV that demonstrated substantially improved lifespan, speed, accuracy, and agility. With transmission and hinge designs that reduced off-axis torsional stress and deformation, the robot achieved a 1000-second hovering flight, two orders of magnitude longer than existing subgram MAVs. This robot also performed complex flight trajectories with under 1-centimeter root mean square error and more than 30 centimeters per second average speed. With a lift-to-weight ratio of 2.2 and a maximum ascending speed of 100 centimeters per second, this robot demonstrated double body flips at a rotational rate exceeding that of the fastest aerial insects and larger MAVs. These results highlight insect-like flight endurance, precision, and agility in an at-scale MAV, opening opportunities for future research on sensing and power autonomy.

11 April 2025 in Science Advances
Verified
Journal Article
Open access
YHYi-Hsuan Hsiao
Yi-Hsuan Hsiao
SBSongnan Bai
Songnan Bai
ZGZhongtao Guan
Zhongtao Guan
SKSuhan Kim
Suhan Kim
ZRZhijian Ren
Zhijian Ren
Yufeng (Kevin) ChenYufeng (Kevin) Chen
Yufeng (Kevin) Chen
Insect-scale robots face two major locomotive challenges: constrained energetics and large obstacles that far exceed their size. Terrestrial locomotion is efficient yet mostly limited to flat surfaces. In contrast, flight is versatile for overcoming obstacles but requires high power to stay aloft. Here, we present a hopping design that combines a subgram flapping-wing robot with a telescopic leg. Our robot can hop continuously while controlling jump height and frequency in the range of 1.5 to 20 centimeters and 2 to 8.4 hertz. The robot can follow positional set points, overcome tall obstacles, and traverse challenging surfaces. It can also hop on a dynamically rotating plane, recover from strong collisions, and perform somersaults. Compared to flight, this design reduces power consumption by 64 percent and increases payload by 10 times. Although the robot relies on offboard power and control, the substantial payload and efficiency improvement open opportunities for future study on autonomous locomotion.

18 July 2022 in Micromachines
Verified
Journal Article
Open access
PDF file
Yufeng (Kevin) ChenYufeng (Kevin) Chen
Yufeng (Kevin) Chen
CACathleen Arase
Cathleen Arase
ZRZhijian Ren
Zhijian Ren
Pakpong ChirarattananonPakpong Chirarattananon
Pakpong Chirarattananon
Dragonflies are agile and efficient flyers that use two pairs of wings for demonstrating exquisite aerial maneuvers. Compared to two-winged insects such as bees or flies, dragonflies leverage forewing and hindwing interactions for achieving higher efficiency and net lift. Here we develop the first at-scale dragonfly-like robot and investigate the influence of flapping-wing kinematics on net lift force production. Our 317 mg robot is driven by two independent dielectric elastomer actuators that flap four wings at 350 Hz. We extract the robot flapping-wing kinematics using a high-speed camera, and further measure the robot lift forces at different operating frequencies, voltage amplitudes, and phases between the forewings and hindwings. Our robot achieves a maximum lift-to-weight ratio of 1.49, and its net lift force increases by 19% when the forewings and hindwings flap in-phase compared to out-of-phase flapping. These at-scale experiments demonstrate that forewing–hindwing interaction can significantly influence lift force production and aerodynamic efficiency of flapping-wing robots with passive wing pitch designs. Our results could further enable future experiments to achieve feedback-controlled flights.

1 October 2026 in IEEE Robotics and Automation Letters
Verified
Journal Article
Closed access
ZRZhijian Ren
Zhijian Ren
SKSuhan Kim
Suhan Kim
YHYi-Hsuan Hsiao
Yi-Hsuan Hsiao
Yufeng (Kevin) ChenYufeng (Kevin) Chen
Yufeng (Kevin) Chen