New Technique Capable Of Investigating Ultra-Miniature Flow Fields

September 04, 1998

CHAMPAIGN, Ill. -- A system for measuring fluid velocities on the scale of a single cell has been developed at the University of Illinois. The system, capable of measuring flow fields in micron-scale fluidic devices, utilizes an epifluorescent microscope, seed particles 100 to 300 nanometers in diameter, and an intensified CCD camera to record high-resolution particle-image fields.

"Over the past ten years, significant progress has been made in the development of microfluidic devices based on micro-electromechanical systems (MEMS) technologies," said David Beebe, a U. of I. professor of electrical and computer engineering and a researcher at the Beckman Institute for Advanced Science and Technology. "While the scientific community has witnessed an explosive surge of miniaturization schemes and designs, the measurement of fluid flow has not kept pace."

Since the flow passages of MEMS microfluidic devices have dimensions on the order of 1 to 100 microns, traditional flow-diagnostic tools cannot be used, Beebe said. To address this need, Beebe, research scientist Juan Santiago, professor of theoretical and applied mechanics Ronald Adrian, and colleagues Steve Wereley and Carl Meinhart at the University of California at Santa Barbara developed a micron-resolution particle image velocimetry (PIV) system capable of measuring miniature flow fields. The micro-PIV system is designed specifically for measuring velocity fields in bioanalysis systems where low-light level imaging is critical.

"Micro-PIV can be used to study the physics and performance of a wide range of fluid-flow devices including micro-flow sensors, micro-valves and micro-pumps," Santiago said.

Images of submicron fluorescent particles are magnified by a microscope and recorded with an intensified CCD camera. By analyzing sequential snapshots using statistical correlations, the researchers can track the motion of groups of particles, yielding fluid flow velocity vectors.

"We have currently refined the technique to provide velocity-field measurements with spatial resolutions approaching 1 micron," Santiago said.

Adrian is a leading developer of the PIV technique and has used it to study turbulence in larger-scale flow fields. By combining the PIV technique with epifluorescence microscopy and an intensified CCD camera, the researchers have opened a new door to making biological flow-field measurements. They will be implementing this technique in MEMS-based micro-pumps, miniature fluid mixers and sub-millimeter rocket nozzles.The researchers describe the new measurement technique in the September issue of the journal Experiments in Fluids.

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University of Illinois at Urbana-Champaign

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