CONCENTRATION AND FRACTIONATION OF SMALL PARTICLES IN LIQUID BY ULTRASOUND

The efficacy of the ultrasonic standing plane wave in concentrating sm all particles was theoretically evaluated and compared with experiment al results. Acoustic energy density was estimated by measuring the ult rasonic absorption, and particle distribution was observed by dark-fie ld microscopy. The theory predicts that diffusion is negligible in con centrating polystyrene spheres larger than 5 mu m in diameter when the y are subjected to 2J/m(3) ultrasound. The half-width of the steady-st ate particle distribution was of the same order of magnitude as the th eoretical value for the particles of 1 mu m and 2 mu m diameter. We al so applied this concentrating technique to fractionation of polystyren e spheres 10 mu m in diameter, and more than 90% of the particles in t he laminar flow were successfully collected.