Abstract
As known, ultrasonic standing waves can be used to concentrate particles and biological cells into separated bands. Acoustical separation based on plane standing waves is limited to particles of few microns and larger. This presentation concerns using acoustic radiation force (ARF) produced by cylindrical standing waves for detection of high-density submicron-size particles (bacterial cells) in pressure nodes and low-density particles (fat globules) in antinodes. Theoretical calculations show that in a cylindrical ultrasonic chamber, ARF near the central node can exceed the force at the chamber periphery by about 20 times. In a cylindrical standing wave, ARF may induce movement of bacteria with a speed of the order of a few millimeter per second at a frequency of 2 MHz and pressure amplitude of 100 kPa, whereas the speed of bacteria in plane standing wave does not exceed 0.2 mm/s under the same conditions. The cylindrical standing wave system performance was tested for the E. coli bacteria in water and for a multi-component system containing fat globules and somatic cells in milk. Dilute suspensions of bacteria or fat globules were concentrated by at least 2 orders of magnitude.
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