A MAGNETIC FORCE DRIVEN

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A MAGNETIC FORCE DRIVEN CHAOTIC MICRO-MIXER
Hiroaki Suzuki, The University of Tokyo Chih-Ming
Ho, UCLA
Website
http//ho.seas.ucla.edu
http//www.thtlab.t.u-tokyo.ac.jp
Last updated Jan 25, 2002
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OBJECTIVES
Magnetic beads based cell separation
device Magnetic Beads specifically attach to the
target cell Chaotic mixing of beads and
biomolecules Mixing in very low Reynolds number
flow
Diffusion time (100 mm channel) Iron/Dye 10
sec Biomolecules/Beads(110 mm) 103 104 sec
Spherotech, 1mm beads
Concept of micro magnetic separator
CHAOTIC ADVECTION
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MAGNETIC MICRO-MIXER

• - Embedded conductors as a magnetic field source
• Large sectional area allows large current
• Flat surface for the micro-channel fabrication
  on top
• - Micro-channel formed on the substrate/electrodes
  
• Magnetic beads in the channel are attracted
  toward the center of two conductors
• Chaotic mixing is explored with time-varying
  control signal

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FABRICATION (3 masks)
Top view
biofluid inlet
beads inlet
mixture outlet
Fabricated Structure
Embedded Conductor
Micro-Channel
(i) KOH etching from backside followed by DRIE to
define electrode pattern, (ii) Cu seed layer
evaporation, (iii) Lift off, (iv) Cu
electroplating, (v) SU-8 channel structure, (vi)
Cover glass bonding, (vii) Packaging
200mm
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PRELIMINARY TEST
1 mm Magnetic Beads
Current Off RELEASE
Current On (500 mA, 12) HOLD
Magnetic field 40 gauss Magnetic force
0.3 pN
Flow (80mm/s)
Magnetic force is strong enough to manipulate
beads
http//ho.seas.ucla.edu/
http//www.thtlab.t.u-tokyo.ac.jp
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NUMERICAL SIMULATION OF CHAOTIC FLOW
Chaos in Laminar Flow
System in which initially nearby trajectories
diverge exponentially fast
Cavity Flow (Ottino, 1989)
In OPEN FLOW SYSTEMS
Pressure perturbation (Y.K. Lee, 2001) DEP force
(J. Deval, 2002)
Magnetic Force (ATTRACTIVE FORCE ONLY)
Coil
Low Velocity
push
pull
pull
No Repulsive Force
Flow
Flow
Coil
High Velocity
Saddle Point

• With pressure or DEP force, chaotic mixing is
  created by pushing and pulling material lines
  between low and high velocity region
• It is not possible with magnetic force, since
  only attractive force can be achieved

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SERPENTINE CHANNEL PHASE SHIFT CONTROL
Serpentine Channel with Perpendicular Electrodes
Driving Signal (Phase Shift Control)
Re UH/v 3.2 x 10-3
NUMERICAL SIMULATION
2-D Steady Velocity Field Lagrangian Particle
Tracking with Fluidic/Magnetic Force
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http//www.thtlab.t.u-tokyo.ac.jp
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FLOW VISUALIZATION
No Disturbance
Phase Shift Control (after 5 forcing periods)
vx, max / U 1.34 StU 0.54
Shaded area, initial condition
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http//www.thtlab.t.u-tokyo.ac.jp
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EVIDENCE OF CHAOS
(2) Lyapunov Exponent
(1) Poincaré Map
Exponential rate at which initially nearby
trajectories diverge
Plot (mapping) of particles at each forcing period
No Disturbance
POSITIVE s CHAOTIC
Frequency Dependence
Amplitude Dependence
Phase Shift Control
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http//www.thtlab.t.u-tokyo.ac.jp
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STRETCHING AND FOLDING, SIGN OF CHAOS
Conductor 12 on
shear
folding
Stretching
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FEEDBACK TO THE EXPERIMENT
Serpentine Channel
DI water
160mm
FLOW
Water with beads
Channel width 160mm, Height 30mm, Electrode width
40mm
No Control No mixing
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http//www.thtlab.t.u-tokyo.ac.jp
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PAIRS OF ELECTRODES, ON OFF
Stretching (ON)
Folding (OFF)
Flow rate 0.1 mL/min Current 0.7 A Frequency
1/8 Hz
Similar pattern is observed
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CONCLUSIONS

• Magnetic beads can be manipulated by simple
  design of conductors
• Serpentine Channel with Phase Shift Control
  produces Chaos
• Matching of time constants of flow field and
  control makes chaotic mixing
• Experiment shows similar patterns to the
  numerical results

http//ho.seas.ucla.edu/
http//www.thtlab.t.u-tokyo.ac.jp