Nonlinearly generated second harmonic sound in a focused beam reflected from free surface

概要

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By providing a phase reversal at the focal region, another phase reversal due to diffraction is compensated and as a result, an enhancement of the second harmonic generation is expected. To attain this, the reflection of the focused beam at a water surface being set in the focal region is experimentally observed using a focusing source to receive the reflected second harmonic sound by itself, which employs a LiNbO_3 plate with a ferroelectric inversion layer. The experimental result is compared with the theoretical calculation based on the Khokhlov-Zabolotskaya-Kuznetsov equation, where the condition of the phase reversal for both the fundamental and second harmonic components is assumed to be at the free surface. The expenmental result agrees reasonably well with the predicted increase in the second harmonic amplitude by 20 times. Since this growth rate is sensitive to the velocity dispersion that occurs in different liquid media, such a measurement of second harmonic component may be potentially useful for estimating the dispersion.
社団法人日本音響学会の論文