MS Thesis Presentation by Alexis Dumortier
Thursday, June 17, 2004
(David Trivett, Chair)
"Investigation of a Medium with a Large, Negative Parameter of Nonlinearity and its Application to the Enhancement of a Compact, Omni-directional, Parametric Source"
Nonlinear acoustic media for implementations of parametric generation of low frequencies has so far been restricted to small values of the parameter B/A, typically between 3 and 13.
Parametric amplification, defined as the generation of a low difference frequency signal resulting from the nonlinear interactions of two higher frequency fundamentals is enhanced by medium with a large coefficient of nonlinearity and low sound speed. The acoustic properties of a highly nonlinear medium were estimated and introduced in a numerical model, to evaluate the parametric amplification induced by a thin layer of such material in contact with a spherical transducer.
The numerical model predicted a significant enhancement of the sound pressure
level for the difference frequency component relative to that obtained when
the transducer is driven linearly at the difference frequency. A source was
then constructed to compare the theoretical predictions with experimental values
and an enhancement of 17dB compared to the linear operation of the transducer
was measured. The difference between the parametric amplification achieved with
the nonlinear medium and the parametric amplification that would be obtained
in water is 73dB.