Nonlinear Focused Sound Field Measurement in Water Using the Laser Doppler Measurement Technique

摘要

Today, high intensity ultrasound is extensively used such as in diagnostic harmonic imaging and high intensity focused ultrasound therapy. Demands of the sound fields measuring technique for these applications become much higher. The usage of ordinary hydrophone suffers mechanical damage or nonlinear spurious response generated in the element. The optical measuring technique is thus expected to avoid the problems described above. As one of such method, authors proposed the laser Doppler measurement technique that detects the Doppler shift of the reflected light from the film reflector placed in the sound fields. However, the validities of the methods were only shown for the measurement of the linear acoustic wave field. In this paper, fundamental wave as well as second harmonic wave fields near the focal region of the uniformly plated concave sound source are measured by using the present optical method. They are compared with the results obtained by the hydrophone measurement and simulation calculation. As results, it is verified that the measured nonlinear harmonics wave amplitude using the present laser Doppler method is much satisfactory compared with the ones by the hydrophone.