Interaction of Sound With Sound by Novel Mechanisms: Ultrasonic Four-Wave Mixing Mediated by a Suspension and Ultrasonic Three-Wave Mixing at a Free Surface.
WASHINGTON STATE UNIV PULLMAN DEPT OF PHYSICS
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Two mechanisms of sound interacting with sound are experimentally and theoretically investigated ultrasonic four-wave mixing in a dilute particle suspension, analogous to optical four-wave mixing in photorefractive materials, involves the interaction of three ultrasonic wavefields that produces a fourth scattered wavefield. The experimental configuration consists of two ultrasonic 800 kHz pump waves that are used to produce a grating in a suspension of 25 mm diameter polymer particles in salt water. The pump waves are counter-propagating, and form a standing wavefield in the suspension. The less compressible particles are attracted to the pressure nodes in response to the time averaged radiation pressure. A higher frequency 2-10 MHz ultrasonic wavefield is used to probe the resulting grating. The ultrasonic Bragg scattering is then measured. The scattering depends strongly on the response to the pump wave and is an unusual class of acoustical nonlinearity. Ultrasonic three-wave mixing at a free surface uses a high amplitude 400 kHz plane wavefield incident at 330 on a water-air interface to interact with a normally incident high frequency 4.6 MHz focused probe wavefield. The 400 kHz pump wavefield reflects from the surface and produces oscillating surface displacements that form a traveling phase grating.
- *RADIATION PRESSURE
- BRAGG SCATTERING
- HIGH FREQUENCY
- SALT WATER