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Programmable rheotaxis of magnetic rollers in time-varying fields
Yiyang Wu1, Guzhong Chen1, April Ramos2
1Department of Chemical Engineering, Columbia University, New York, NY, USA. kyle.bishop@columbia.edu.
Soft Matter
|September 3, 2025
Summary
Magnetic microrobots can navigate fluids using field-programmable rheotaxis. Time-periodic magnetic fields enable directional migration of magnetic particles in shear flows, offering a feedback-free alternative for microrobot guidance.
Area of Science:
- Physics
- Engineering
- Materials Science
Background:
- Microrobot navigation in complex fluids often requires real-time feedback for control.
- Existing methods for magnetic microrobot guidance are limited by the need for continuous external field adjustments.
Purpose of the Study:
- To investigate field-programmable rheotaxis as a feedback-free method for controlling magnetic particle migration in shear flows.
- To demonstrate the ability to program diverse rheotactic behaviors (downstream, upstream, cross-stream) using tailored magnetic fields.
Main Methods:
- Development of a deterministic model coupling magnetic torques and hydrodynamic interactions near a surface.
- Analysis of particle migration in simple shear flows under time-periodic magnetic fields.
- Design and simulation of complex magnetic field waveforms to optimize migration speed and direction.
Main Results:
- The frequency, magnitude, and waveform of applied magnetic fields dictate the rheotactic behavior of ferromagnetic particles.
- Achieved programmable downstream, upstream, and cross-stream migration relative to the fluid flow.
- Identified a performance-robustness tradeoff: high-performance upstream motion is sensitive to parameters, while robust designs offer modest gains.
Conclusions:
- Field-programmable rheotaxis offers a general strategy for programming flow-guided navigation in magnetic colloids.
- This approach enables predictable microrobot responses to fluid environments without external feedback.
- Suggests pathways for developing self-guided microrobots capable of autonomous navigation.
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