TRAPPING AND MANIPULATION OF PARTICLES （粒子的捕获和操纵）.pdf

TRAPPING AND MANIPULATION OF PARTICLES AND DROPLETS U SING MICRO-TOROIDAL CONVECTION CURRENTS * Amar S. Basu , and Yogesh B. Gianchandani Department of Electrical Engineering and Computer Science University of Michigan, Ann Arbor, USA ABSTRACT This paper introduces a technique for generating toroid- shaped convective vortices in thin (80-400 µm) layers of oil. Driven by micromachined heat sources suspended 5-250 µm above the oil surface, the vortices are used to trap weed pollen with 25 µm diameter and microdroplets of water with diameters ranging from 2-50 µm. The speed of the convective flow pattern can be controlled by the input power to the heat source and the air gap between the heat source and the oil surface, while the radius of the collection region is determined primarily by the thickness of the oil layer. Flow velocities up to 1700 µm/sec have been achieved in toroidal flows with radii ranging from 80-1120 µm. When the heat source is connected to an XY scanning stage, the vortex can be swept across the liquid, effectively collecting particles in the areas over which it travels. Keywords: Rayleigh-Benard convection cell, Benard- Marangoni convection, oil, microfluidic vortex, Fig 1: Device concept. (a) Cross section of the device operation, microdroplet, toroid, particle trap. illustrating convective currents beneath the heat source, outward