PhD Oral Exam - Holden Li

Holden Li holdenli at stanford.edu
Wed Jul 20 20:49:56 PDT 2005


DEPARTMENT OF MECHANICAL ENGINEERING

UNIVERSITY PhD DISSERTATION DEFENSE



Speaker:                Holden Li



Research Advisor: Professor Tom Kenny



Title:          Study of High Speed Acoustic Separation of Particles in 
Micro-channels


Date :          July 25, 2005

Time:           9:30 a.m.

Place:           CIS-X Auditorium



ABSTRACT



Doctors and engineers have long envisioned that a handheld portable blood 
diagnosis device would be able to give an accurate measurement of chemical 
content based on a very small sample in the shortest time possible. One of 
the immediate applications of such device is the Point Of Care (POC) 
diagnosis system, whereby a single drop of human blood would determine 
his/her health status. However, a major technical challenge lies in the 
ability to separate different particles in micro-scale, which in the case of 
human blood, is to separate red and white blood cells and plasma in a quick, 
cheap, reliable device with low power consumption (less than 100mW).


A robust and high-speed separation mechanism of using acoustic separation is 
proposed for blood cells separation.  This study is a continuation work of 
the fundamental research done more than half a century ago when the first 
experiment of using ultrasonic standing waves to separate particles in a 
suspended liquid medium was successfully carried out.  This current research 
covers the study of ultrasonic standing waves behavior in micro-channels, 
scaling effects and most importantly to separate different particles based 
on their sizes differences as in the case of blood cells.



A method called Micro Particle Image Velocimetry (micro-PIV) is used to 
understand the mechanism of acoustic separation in the micro-channels, and 
polystyrene beads of similar densities to the blood cells, are used to 
represent red and white blood cells in the whole blood.  This has enabled 
the image capturing of the separation process in microfluidic regimes and 
further demonstrates the impact of acoustic potential energy in the overall 
separation mechanism, and the promising future of implementation of this 
technology in Lab-On-A-Chip application.  Comparison with the most 
conventional centrifugation method of separation shows that acoustic 
separation running at megahertz frequencies exhibits promising results as it 
produces only a small fraction of the force (less than 50G force) acting on 
the blood cells compared to the order of 10,000G forces exerted by 
centrifuges to achieve the goal.






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