A rotating ultrasonic waveguide for studying acoustic radiation forces on particles.
An apparatus was designed to allow a suspension of biological cells to be subjected to a well-defined, 160-kHz standing ultrasonic field while being viewed through a stereo microscope. Cell positions were recorded either photographically or by means of a video camera. The chamber cavity, which has a square cross section and pressure-release walls, acts as a single-mode acoustic waveguide. The well-defined single-mode field is achieved through use of a special design involving air-filled chamber windows. Aqueous metrizamide solution is used to fill the ultrasonic chamber because it has a unique combination of properties, including low viscosity, low osmolarity, and high density. The chamber rotates about its axis (whose inclination can be varied) producing the centripetal force necessary to contain the buoyant cells in the axial region. Observations were made on stroboscopically illuminated suspensions both of latex microspheres and of red blood cells. The particles formed groups at half-wavelength intervals along the rotation axis near positions of acoustic pressure-amplitude minima. The position and shape of these groupings are explained by a scalar-potential theory for noninteracting particles that considers gravitational, rotational, and acoustic radiation forces on the particles.
Whitworth
G
G
Department of Physics, University of Vermont, Burlington 05405.
Nyborg
W L
WL
D004912:Erythrocytes / Q000502:physiology*; D006801:Humans; D010316:Particle Size; D014465:Ultrasonics; D014463:Ultrasonography / Q000295:instrumentation