### ASA 125th Meeting Ottawa 1993 May

## 4pPA2. Acoustic nonlinearity parameter inversion from harmonic
interaction.

**T. J. Plona
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S. Kostek
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C. V. Kimball
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R. D'Angelo
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*Schlumberger-Doll Res., Ridgefield, CT 06877-4108
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This paper is concerned with the measurement of the acoustic nonlinearity
parameter of fluids ((beta)=1+B/2A) using harmonic interactions of finite
amplitude acoustic waves. The data consist of the on-axis pressure field
emanating from a planar circular transducer, measured by a small probe. The
source is excited by either a single frequency signal (f) or by a composite
signal of two frequencies (f[sub 1] and f[sub 2]). The attenuation of the fluid
is measured independently by a standard linear wave propagation technique. The
model for predicting the finite amplitude pressures is the
Kuznetsov--Zabolotskaya--Khokhlov equation (KZK), which has been used
extensively to model nonlinear acoustic beam fields. By taking the pressure
measurements just beyond the Rayleigh distance, and providing that the sound
pressure level is not too high such that the measurements are taken within one
shock formation distance, a quasilinear approximation to the KZK equation is
used, which is sufficiently accurate to represent the first-order interactions
(2f, f[sub 1]+f[sub 2], f[sub 1]-f[sub 2], etc.) and computationally efficient,
thus rendering the one-parameter inversion problem manageable. The accuracy of
the inversion technique will be discussed for data consisting of both
second-harmonic and difference frequency signals. Results for various fluids
will be shown and discussed.