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

2

Contents

• Introduction

• Theory

• Device design and fabrication

• Experimental setup

• Results

• Summary

Introduction

Surface acoustic wave

4

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>

6

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>

7

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>

8

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

13

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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