Acoustic radiation force for rapid detection of particles in biological liquids

As known, ultrasonic standing waves can be used to concentrate particles and biological cells into separated bands. Acoustic separation in plane standing waves is limited to particles of few microns and larger. This presentation concerns using acoustic radiation force (RF) produced by cylindrical standing waves, for detection of high-density standing waves in pressure nodes and low-density particles (fat globules) in antinodes. Theoretical calculations show that in a cylindrical ultrasonic resonator RF near the central node can exceed the force at the periphery by about 20 times. In a cylindrical standing wave, RF can induce movement of bacteria with a speed of a few mm/s at frequency of 2 MHz and pressure amplitude of 100 kPa, whereas the speed of bacteria in a 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 two orders of magnitude.