Influence of inserted sample on second harmonic component in a finite-amplitude focused sound

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The influence of a liquid sample layer on the nonlinearly generated second harmonic component is examined by computations and experiments. The sample with plane surfaces is inserted in the focal region normal to the axis, whose acoustical properties are different from those of surrounding medium(water). The theory is based on the quasilinear parabolic approximation, valid for the case of weak distortion and small concavity. A linear transmission through the boundaries is also applied for the second harmonics. The analysis for a source with a Gaussian profile excitation shows that, in the case of a lossless sample, the second harmonic component generated at the sample can be the greater part of the second harmonic sound propagating in the post focal region. In the case of a lossy sample, a newly introduced quantity C_s evaluated from the waveform at the post focal region corresponds well to the sample properties excepting the linear absorption. The experimental results suggest the usefulness of the quantity C_s.
社団法人日本音響学会の論文