凹面で受波された集束音波の第2高調波成分

概要

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To develop a measurement method for acoustic nonlinearity parameter B/A using an acoustic microscope, the second harmonic component of a focused Gaussian beam observed with a concave receiver, with an aperture large enough to cover the whole beam, set within the post focal region has been investigated. The theory based on the successive approximation solution for the Khokhlov-Zabolotskaya-Kuznetsov equation is validated through the experiment employing a 1. 9-MHz focused ultrasound and a concave receiver. Both the fundamental and second harmonic amplitudes attain the maxima at the position where the multiple reflection signal produced between the source and receiver is well detected by the concave receiver. The phase of the second harmonic component relative to the fundamental is the same as that of the axial pressure in particular at this position. These are true even in the case with the insertion of a different liquid layer. The generation of the second harmonic, which corresponds to the linear and nonlinear acoustic properties of the different liquid, is observed with the concave receiver. This suggests that the B/A measurement utilizing the axial pressure of the focused beam may be extended to the data obtained with the concave receiver.
社団法人日本音響学会の論文