Research on controllability of radiation direction of nondiffiracting ultrasonic beam by non-concentric annular array sound source

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The purpose of this research is forming the ultrasonic beam without diffracting, by constructing sound source using non-concentric annular array, and making the radiation direction of beams controllable.At first, by conducting decentering for the annular array in which clearances exist between elements, it was confirmed that changing the direction of radiated beam becomes possible. By numerical analyses, it is shown that the beam radiated to the direction of 15 degrees from the sound axis, by the array with ten elements, still keeps a sharp profile. And, it was shown that the radiation of narrow beams was possible for the direction deviated from the sound axis, even when the number of array element was small. In addition, effects caused by the fluctuation of the decentering ratio in each element were verified, and relations between actually decentered element and vertical distance where the direction of beams deviates were found.Continuously, examinations on the configuration of source element, for effectively changing of the beam direction, were carried out, and it was confirmed that the direction of beams propagated without diffraction was variable, when the number of decentering element was minimized, and that the possibility as a precise parallel scanning method of the beam was found. Besides, the technique for setting the propagation path of beam more in detail was examined, and the technique that obtains beams with the twisted propagation path was found.Furthermore, as a means for carrying out measurement experiments, techniques for measuring sound fields were also examined. Noncontact and noninvasive measuring systems for sound fields were constructed based on the optical technique using two kinds of interferometers. Measurement experiments using general sound sources were carried out, and in the visualization of two-dimensional complex distribution of radiated fields, results with the tendency that agreed with numerical results well were obtained.