### ASA 125th Meeting Ottawa 1993 May

## 4pPA1. An experimental investigation of the nonlinear interaction of
noncollinear sound beams.

**Ronald A. Roy
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*Appl. Phys. Lab., Univ. of Washington, Seattle, WA 98105
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**Junru Wu
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*Univ. of Vermont, Burlington, VT 05405
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The nonlinear interaction between two pulsed, Gaussian ultrasonic beams
propagating through degassed and filtered water was studied. One beam had a
center frequency of 3.5 MHz and a peak pressure amplitude (in the interaction
region) of 450 kPa. The other possessed a center frequency and peak pressure
amplitude given by 3.0 MHz and 320 kPa, respectively. With the axes of the
beams intersecting perpendicularly in the near-field, no sum-frequency
scattered pressure amplitude greater than 0.03 Pa was detected outside the
interaction region. The insertion of a brass sphere into the center of the
interaction region resulted in the generation of two partially collinear
scattered beams, and a sum-frequency scattered signal level of 0.9 Pa was
subsequently detected at a 45(plus or minus)0.5(degrees) scattering angle.
Experiments with collinear beams generated using a single projector driven by
two electrically summed tone bursts (center frequencies=3.0 and 3.5 MHz)
indicate the production of sum and difference frequencies in quantitative
agreement with Westervelt's theory for the parametric end-fire array [J.
Acoust. Soc. Am. 32, 934A (1960)]. [Work supported by APL IR Funds.]