Ghulam Destgeer

Graduate student

PARTICLE SEPARATION,

CHEMICAL GRADIENT CONTROL

AND MICROMIXING VIA

FOCUSED TRAVELLING SURFACE

ACOUSTIC WAVES (F-TSAW)

Prof. Hyung Jin Sung

Flow Control Laboratory

Department of Mechanical Engineering,

KAIST, Daejeon, South Korea.

2/18

Questions!

• How can we…

1. Separate particles!

2. Generate chemical gradient!

3. Mix fluids!

inside a PDMS microfluidic channel with continuous

flow… via focused travelling surface acoustic waves???

3/18

How surface acoustic waves work!

We do need…

1. Piezoelectric substrate (LiNbO3)

2. Interdigitated metallic (Au)

electrodes deposited on top of

LiNbO3 substrate

3. High frequency AC signal

4. Frequency of SAW = AC signal

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

Single phase unidirectional transducer (SPUDT)

λλ/4

SAW SAW

Interdigitated transducer (IDT)

• Surface acoustic wave (Rayleigh

wave) propagates on the surface of

solid piezoelectric substrate (LiNbO3)

<Animation courtesy of Dr. Dan Russell, Grad. Prog. Acoustics, Penn State>

LiNbO3 LiNbO3

4/18

Particle separation

Standing surface

acoustic waves (SSAW)

• Two IDTs are required

• Tight microchannel

alignment is needed

• Position of pressure

nodes is critical

Travelling surface

acoustic waves (TSAW)

• Single F-IDT is used

• Loosely aligned

microchannel can also

work

• Position of pressure

nodes is not important

<Shi et al., 2008, Lab Chip> <Destgeer et al., 2013, Lab Chip>

5/18

Particle separation via F-TSAW

• Continuous separation of particles in a PDMS

microfluidic channel via focused TSAW

<Destgeer et al., 2013, Lab Chip>

𝐹𝑇𝑆𝐴𝑊 ∝ 𝑅6

6/18

Particle separation via F-TSAW

• Acoustic streaming flow (ASF) vs.

acoustic radiation force (ARF)

• Polymer particles are dispersed in

DI water

<Destgeer et al., 2013, Lab Chip>

Particles’

diameter

1 and 5µm

• 1µm particles

are dominated

by ASF

• 5µm particles

are dominated

by ARF

Particles’

diameters

3 and

10µm

7/18

Particle separation via F-TSAW

• Experimental conditions:

– Frequency: 133.3MHz, Power:

225mW

– μ-channel h x w: 40 μm x 200 μm

– Flow rate (Q): 100μL/h (3.5mm/s)

– μ-particles diameter: 3 and 10μm

<Destgeer et al., 2013, Lab Chip>

500 µm

8/18

Particle separation efficiency

• TSAW OFF: all of the particles

are collected at the same

outlet

• TSAW ON: 100% of the 10µm

particles passed through a

separate outlet.

<Destgeer et al., 2013, Lab Chip>

For 10 µm particles

9/18

Particle separation comparison

• By focused IDT

– Flow: 3.5mm/s

– Input power: 235mW

– Power–Velocity ratio

(RF): 67mW/(mm/s)

• By straight IDT

– Flow: 4.6mm/s

– Input power: 870mW

– Power–Velocity ratio

(RS): 190mW/(mm/s)

• Comparison:

– RS/RF=2.84

– RS≈ 3 x RF

TSAW

TSAW

Flow

2. Separation

by straight

IDT

1. Separation by

focused IDT

10/18

Chemical gradient generators

<Jeon et al., 2000, Langmuir (a)> <Irimia et al., 2006, Anal Chem (b) & Lab Chip (c)> <Ahmed et al., 2013, Lab Chip (d)>

(b). Universal gradient generator

(d). Acoustofluidic oscillating bubbles

based gradient generator

(c). Microstructured membranes based

fast switching gradient generator (a). Premixing gradient

generator

11/18

Gradient generation via F-TSAW

• Adjustable, rapidly switching

microfluidic gradient

generation using F-TSAW

<Destgeer et al., Submitted>

12/18

Gradient generation via F-TSAW

• Characterization of the chemical

concentration gradient profiles

• Microchannel w x h: 500 x 140 µm

• Flow rate: 1,000 µL/h + 100 µL/h =

1,100 µL/h (4.37mm/s)

<Destgeer et al., Submitted>

Owl’s eyes vortices for gradient generation

13/18

Gradient generation via F-TSAW

• Temporal control over the gradient profile with a fast

switching frequency of 0.25 Hz.

• Gradient switching frequency is better then Ahmed

et al. 2013 (0.1 Hz) and Irimia et al. 2006

<Destgeer et al., Submitted>

14/18

Gradient generation

• The formation of acoustic streaming flow

in a stationary and moving fluid

• The generation of fast switching chemical

gradient profile

<Destgeer et al., Submitted>

Slowed down

15/18

Gradient generation & micromixing

• Chemical gradient generation and uniform mixing of

fluids inside a PDMS microfluidic channel.

• The plots indicate the normalized concentration of

DI water (white) or rhodamine (gray) at any

particular location in microchannel.

16/18

Summary

• The presented F-TSAW micro-chip combined

I. Label free continuous particle separation,

II. Adjustable, rapidly switching chemical gradient

generation and

III. Uniform micromixing

in a PDMS microfluidic channel.

• Particles are separated based upon their size

difference under the influence of ARF.

• ASF generated symmetrical vortices – responsible

for the controlled chemical gradient generation and

uniform mixing of two fluids.

• A straight IDT would not be able to form strong ASF

and separation would require higher power input.

17/18

Contributors

• Principal Investigator: Prof. Hyung Jin Sung

• Researchers: Ghulam Destgeer, Sunghyuk Im,

Byung Hang Ha, Jin Ho Jung, Hyun Wook Kang,

Kyung Heon Lee, Mubashshir Ahmad Ansari

• Collaborator: Dr. Anas Alazzam, KUSTAR, UAE

• Funding: Creative Research Initiative Project, Korea.

KAIST-KUSTAR Institute, Korea.

Research areas at Flow Control Lab (flow.kaist.ac.kr)

1. Turbulence 2. Flow-Flexible Body Interaction 3. Acouto/Opto Microfluidics 4. Microprinting

THANK YOU FOR YOUR

ATTENTION!!!