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Ghulam Destgeer
Particle Separation and Chemical Gradient Control via
Focused Travelling Surface Acoustic Waves (F-TSAW)
Flow Control Laboratory, Department of Mechanical Engineering2013.06.10
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Contents
• Introduction
• Theory
• Device design and fabrication
• Experimental setup
• Results
• Summary
Introduction
Surface acoustic wave
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Particle separation
• The isolation and separation of micro particulate materials in a continuous flow are required for chemical syntheses and biological analyses.
• The separation and sorting of cells are critical in a variety of biomedicalapplications including:i. Diagnostics
ii. Therapeutics
iii. Cell biology
<Lee et al., 2010, Lab Chip> <Daniel et al., 2010, Anal Bioanal Chem>
Huang’s group
Sung’s group
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Particle manipulation by SSAW
• Particle separation:– Particle diameter: 0.87μm (Red), 4.16μm (Green)
• Experimental parameters:– Frequency: 12.6MHz
– Power: 15-22dBm (30-160mW)
– Flow rate: 0.6-2μl/min
<Shi et al., 2009, Lab Chip>
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Chemical gradient control
• Most methods are capable of generating linear chemical gradient profiles in a static manner.
• Generating pulsatile chemical gradients in microfluidic devices has important implications for the characterization of dynamic biological and chemical processes.
• Dynamic temporal control of chemical gradients is required.
<Ahmed et al., 2013, Lab Chip> <Daniel et al., 2006, Anal. Chem.> <Seidi et al., 2011, Biomicrofluidics>
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Chemical gradient control by oscillating bubbles
• Chemical solutions:– Dextran-FITC (stimulant)
– Phosphate buffered saline(buffer)
• Input voltage and frequency:– 12-16Vpp and 30kHz
<Ahmed et al., 2013, Lab Chip>
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Objective
• (a) Device schematic (b) Particle separation
• (c) Chemical gradient control and uniform micromixing
• (d) F-TSAW amplitude (e) Fabricated device
Theory
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Acoustic radiation force on compressible spheres
For TSAW:
<Yosioka & Kawasima, 1955, Acoustica>
𝐸𝑎𝑐 = (4π𝑓𝑢)2𝜌𝑓 𝐴 2 =2(4π𝑓𝑢)2
𝑘2= 8(𝑐𝑢)2𝐴 2 =
2 𝐸𝑎𝑐𝑘2𝜌𝑓
where, 𝐸𝑎𝑐 is acoustic energy density, 𝑢 is SAW amplitude, 𝑘 = 2πλ is
wavenumber, 𝑐 is speed of sound on wafer surface, 𝑓 is the frequency of SAW, Pin
is the input power and V is the input voltage.
where, 𝛼 =𝜌𝑓
𝜌𝑝, 𝛽 =
𝑐𝑓
𝑐𝑝, R is radius of μ-particles & A is complex amplitude
of the velocity potential.
𝐹𝑇𝑆𝐴𝑊 = 2𝜋𝜌𝑓 𝐴2(𝑘𝑅)6φ𝑇𝑆𝐴𝑊
φ𝑇𝑆𝐴𝑊 =
1 −𝛼 2 + 𝛼 𝛽2
3
2
+2 1 − 𝛼 2
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(2 + 𝛼)2
TSAW
Flo
w
𝐹𝑇𝑆𝐴𝑊 ~ 𝑉2𝑓6𝑅6 ~ Pin 𝑓6𝑅6
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F-TSAW amplitude
• Acoustic wave amplitude is estimated as:
• Acoustic wave amplitude qualitative measure:
𝑢(𝑥, 𝑧) ≈1
𝑍1/4
−∞
+∞
𝐺 𝑡 exp 𝑗 𝑡4 +𝑍′𝑡2 +𝑋′𝑡 𝑑𝑡
𝑍′ =(0.145𝑍 − 𝑅𝑘0/2)
4.98𝑍𝑋′ =
−𝑋44.98𝑍
𝑡 =44.98𝑍𝐾1 𝑍 = 𝑘0𝑧 𝑋 = 𝑘0𝑥 𝐾1 = 𝑘1/𝑘0
<Fang and Zhang, 1989, IEEE Transactions on Ultrasonic> <Wu et al., 2005, IEEE Transactions on Ultrasonic>
Wu et al. 2005 Calculated
θ
R
A A’
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F-TSAW amplitude
5R 5R 5R
5R 5R 5R
5R 5R 5R
Am
plit
ud
eA
mp
litu
de
Am
plit
ud
e
Am
plit
ud
eA
mp
litu
de
Am
plit
ud
e
Am
plit
ud
eA
mp
litu
de
Am
plit
ud
e
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F-TSAW amplitude
Freq
ue
ncy
(M
Hz)
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SAW amplitude calculation
F𝑇𝑆𝐴𝑊~ (Eac/k2) (kR)6φ𝑇𝑆𝐴𝑊
E𝑎𝑐~ u2 f2 ρ
Energy density (Eac) – J/m3
SAW displacement (u) – nmFrequency (f) – MHzDensity (ρ) – kg/m3
Wave number (k) – (μm)-1
Particle radium (R) – (μm)Constant (φ)
Contour plots of SAW displacement square (u2) – m2
Top – f =133.3MHzBottom – f = 40.0MHz
x
z
Device design and fabrication
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F-TSAW device design
• Two salient features: (i) unidirectional (ii) focused
• Interdigitated transducer(IDT): Two interlocking comb-shaped metallic electrodes on top of a piezoelectric substrate.
• Frequency of applied AC signal = frequency of SAW (fSAW)– fSAW = c/λ, c is speed of sound in the piezoelectric
substrate
Maximum energy is transmitted in the forward direction.
Very little energy is transmitted in the backward direction.
SAW
λ
λ/8
λ/43λ/16
SAW
Unidirectional transducer
λλ/4
SAW SAW
IDT
F-TSAW amplitude by a focusing transducer
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Fabrication of micro-chip
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Microfluidic channels
150µm 500µm200µm
1st 2nd 3rd
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Focused IDTs
40MHz 133.3MHz
1st 2nd
Experimental setup
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Experiment schematicSignal generator, N5181A [3GHz]
μ-pump, neMESYS
Microscope, BX51
Camera, DP26
Power amplifier, ZHL-1-2W
DC power supply, E3634A
Micro Chip
PDMSLiNbO3
Au electrodes
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Experimental setup
Power supply
Amplifier
Signal generator
Microscope
Microchip
Micropump
Display screen
Oscilloscope
Camera
Results
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Experimental parameters
PARAMETERS Device #1 Device #2 Device #3 Device #4Frequency (MHz) 40 133.3 133.3 133.3Input power 0.25µW 0.45mW 0.07mW ---After amplification 0.175mW 275mW 63mW 60–200mWRadius of FUT (mm) 6 4 4 4Distance from FUTto microchannel
1.25R 2.5R 2.5R 2.5R
µ-channel cross section (µm×µm)
150×110 150×45 200×40 500×90
Particles diameter (µm) 30 and 10 10 and 3 10 and 3 ---
Fluid/media DI water DI water DI waterDI water, rhodamine
Total flow rate (µl/hr) 50 150 100 100Average velocity (mm/s) 0.84 6.17 3.5 0.6
FunctionParticle Separation
Particle Separation
Particle Separation
GradientGeneration
Names CAPS-1 CAPS-2 CAPS-3 CAGG
*CAPS: Cross-type Acoustic Particle Separator*CAGG: Cross-type Acoustic Gradient Generator
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CAPS-1: Particle trajectory and separation
• Experimental conditions:– Frequency (f): 40MHz (Low)
– Input power: 725µW
– Flow rate (Q): 50μl/h (0.84mm/s)
– μ-channel cross-section: 150x110μm
– μ-particles diameter: 10, 30μm
• Equation of particle motion:
• Acoustic radiation force:
• Stokes drag force:
• Particle trajectory:– Left figure: Theoretical
– Center figure: Experimental
• Particle separation on right
𝑚 𝑧 = 𝐹𝑇𝑆𝐴𝑊 − 𝐹𝐷
𝐹𝑇𝑆𝐴𝑊 = 4π𝐸𝑎𝑐𝑘4𝑅6φ𝑇𝑆𝐴𝑊
𝐹𝐷 = 6πη𝑅 𝑧
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CAPS-2: Particle trajectory and separation
• Experimental conditions:– Frequency (f): 133.3MHz (High)
– Input power: 1.36W
– Flow rate (Q): 150μl/h (6.17mm/s)
– μ-channel cross-section: 150x45μm
– μ-particles diameter: 10, 3μm
• (a) Schematic diagram of a PDMS microchannel.
• (b-c) Once the TSAW was turned ON, a distinct separation distance could be observed.
• (d) Trajectory followed by a 10 µm particle influenced by acoustic streaming.
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CAPS-3: Particle trajectory and separation
• Experimental conditions:– Frequency: 133.3MHz
– Input power: 225mW
– μ-channel cross-section:
• h x w: 40 x 200 μm
– Flow rate (Q):
• Sample+ Sheath: 25μl/h + 75μl/h = 100μl/h
• Average speed: 3.5mm/s
– μ-particles diameter: 3μm and 10μm
• Left: TSAW OFF, all the particles flowing together with the laminar flow.
• Right: TSAW ON, larger particles are pushed towards the opposite wall resulting in separation
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Particle separation efficiency
• (a) TSAW OFF: all of the particles are collected at the same outlet
• (b) TSAW ON: 3µm particles are collected at same outlet whereas almost 100% of the 10µm particles passed through a separate outlet.
(a) (b)
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CAPS-3: Particle deflection vs. input power
• Flow rate is kept constant:– Sheath + Sample = 80 + 20 = 100 µlh-1
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CAPS-3: Deflection vs. input power and flow rate
• For particles with diameter 10µm:
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CAPS-3: Deflection (µm) vs. Input Power (mW)
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CAGG
• Acoustic streaming flow induced via F-TSAW
• Flow is traced by 1µm polymer microspheres dispersed in DI water.
• On smaller particles, drag force is dominant compared to acoustic radiation force.
• Three microchannels 150µm x 45µm, 200µm x 40µm and 500µm x 90µm from left to right, respectively, are tested.
• Microchannel 500µm x 90µm can produce strong and large vortices appropriate for mixing and gradient control.
F-TSAW
F-TSAW
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Chemical gradient control and micromixing
• Acoustic streaming flow– Generate chemical gradient
– Uniformly mix fluids.
• Microchannel– w×h: 500µm×90µm
• Flow rate: 100µl/h (0.6mm/s)– Fluid 1: rhodamine: 50µl/h
– Fluid 2: DI water: 50 µl/h
• Power input– Gradient control: 60–200mW (18–
23dBm)
– Uniform mixing: 800mW (29dBm)
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Chemical gradient control and micromixing
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Summary
• Four types of devices are tested:– First three are Cross-type Acoustic Particle Separator (CAPS)
– Fourth is Cross-type Acoustic Gradient Generator (CAGG)
• A single micro-chip is capable to be used as CAPS or CAGG
• Particles are successfully separated with efficiency close to 100%:– 10μm particles from 3μm and 30μm particles from 10μm
• Particle deflection is plotted against input power which shows:– 3μm, 7μm and 10μm are separated
• Low amplitude and high frequency (40 and 133.3MHz) waves are used.
• Chemical gradient control and uniform mixing is also shown using F-TSAW without trapping any micro-bubble.
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