Subject Area

Mechanical Engineering

Abstract

Micro-scale robotic systems have garnered significant interest for applications in micromanufacturing and biosensing, yet quantitative design rules linking geometry, stiffness distribution, and magnetic actuation to locomotion performance at low Reynolds number remain limited. This thesis investigates magnetically actuated rod-like soft robots composed of hydrogel filaments with embedded micro-magnets and tunable hard:soft length ratios. Four- and eight-magnet swimmers with hard:soft ratios ranging from 1:1 to 2.5:1 and 4:3:1 are fabricated using a simple molding-and-insertion process and tested in water and silicone oil. A triaxial Helmholtz coil system generates rotating magnetic fields from 1 to 10 Hz, and a custom image-processing pipeline extracts time-averaged propulsion speeds and stability metrics from recorded trajectories. Experiments show propulsion speeds on the order of 0.1-1.0 mm/s depending on fluid viscosity, magnet count, and stiffness ratio. In water, eight-magnet swimmers with 1:1 and 4:3:1 stiffness distributions exhibit the most efficient and stable locomotion in the 7-9 Hz band, achieving substantially higher speeds than their four-magnet counterparts. In silicone oil, stiffer 2:1 and 4:3:1 designs exhibit optimal responses at lower frequencies (approximately 2-7 Hz), while softer swimmers require higher driving frequencies to reach comparable speeds. Overall, increasing tail stiffness shifts the optimal frequency to lower values and enhances performance in highly viscous media, whereas softer designs support broader high-frequency plateaus in low-viscosity environments. These results provide experimentally grounded design guidelines connecting stiffness, magnet distribution, and actuation frequency to swimming performance, supporting rod-like soft robots as tunable microrobots for microfluidic transport and sensing tasks.

Degree Date

Fall 12-20-2025

Document Type

Thesis

Degree Name

M.S.M.E.

Department

Mechanical Engineering

Advisor

MinJun Kim

Acknowledgements

I would like to thank my advisor, Professor Minjun Kim, my committee members, and my lab colleagues for their guidance and support throughout this work.

Number of Pages

111

Format

.pdf

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