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Electrokinetic Propulsion for Electronically Integrated Microscopic Robots

Lucas C. Hanson, William H. Reinhardt, Scott Shrager, Tarunyaa Sivakumar, Marc Z. Miskin

Abstract

Semiconductor microelectronics are emerging as a powerful tool for building smart, autonomous robots too small to see with the naked eye. Yet a number of existing microrobot platforms, despite significant advantages in speed, robustness, power consumption, or ease of fabrication, have no clear path towards electronics integration, limiting their intelligence and sophistication when compared to electronic cousins. Here, we show how to upgrade a self-propelled particle into an an electronically integrated microrobot, reaping the best of both in a single design. Inspired by electrokinetic micromotors, these robots generate electric fields in a surrounding fluid, and by extension propulsive electrokinetic flows. The underlying physics is captured by a model in which robot speed is proportional to applied current, making design and control straightforward. As proof, we build basic robots that use on-board circuits and a closed-loop optical control scheme to navigate waypoints and move in coordinated swarms at speeds of up to one body length per second. Broadly, the unification of micromotor propulsion with on-robot electronics clears the way for robust, fast, easy to manufacture, electronically programmable microrobots that operate reliably over months to years.

Electrokinetic Propulsion for Electronically Integrated Microscopic Robots

Abstract

Semiconductor microelectronics are emerging as a powerful tool for building smart, autonomous robots too small to see with the naked eye. Yet a number of existing microrobot platforms, despite significant advantages in speed, robustness, power consumption, or ease of fabrication, have no clear path towards electronics integration, limiting their intelligence and sophistication when compared to electronic cousins. Here, we show how to upgrade a self-propelled particle into an an electronically integrated microrobot, reaping the best of both in a single design. Inspired by electrokinetic micromotors, these robots generate electric fields in a surrounding fluid, and by extension propulsive electrokinetic flows. The underlying physics is captured by a model in which robot speed is proportional to applied current, making design and control straightforward. As proof, we build basic robots that use on-board circuits and a closed-loop optical control scheme to navigate waypoints and move in coordinated swarms at speeds of up to one body length per second. Broadly, the unification of micromotor propulsion with on-robot electronics clears the way for robust, fast, easy to manufacture, electronically programmable microrobots that operate reliably over months to years.
Paper Structure (16 sections, 12 equations, 7 figures)

This paper contains 16 sections, 12 equations, 7 figures.

Table of Contents

  1. Supplementary Data
  2. Full Fabrication Protocol
  3. Estimating field strength and mobility coefficient
  4. Modeling Microrobot Propulsion
  5. Model for predicting $\kappa$
  6. Control Laws
  7. Scaling up to more robots
  8. Supplementary Video 1
  9. Supplementary Video 2
  10. Supplementary Video 3
  11. Supplementary Video 4
  12. Supplementary Video 5
  13. Supplementary Video 6
  14. Supplementary Video 7
  15. Supplementary Video 8
  16. ...and 1 more sections

Figures (7)

  • Figure S1: Speed vs. current density and conductivity. Top: Robot speed as a function of current density for a fixed solution conductivity of 300 nS/cm in 5 mM hydrogen peroxide. Bottom: Robot speed as a function of conductivity in 5 mM hydrogen peroxide. Here current density also varies due to the changes in conductivity.
  • Figure S2: Speed vs. intensity. Robot speed as a function of light intensity, i.e. optical power. For speeds below approximately 200 $\mu$m/s we find a linear relationship.
  • Figure S3: Fabrication of a single motor. Steps (1)-(4) form discrete PVs through a series of doping and etching steps, Steps (5)-(7) deposit the electrical interconnects and actuator electrodes, and Steps (8)-(11) encapsulate and release the motors.
  • Figure S4: PV I-V sweeps. Current vs voltage sweeps of a single PV under various illumination intensities, normalized to the maximum intensity of our light source.
  • Figure S5: Open circuit voltage. Open circuit voltage at maximum intensity as a function of the number of PVs wired in series.
  • ...and 2 more figures