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

本研究的目的是通过非同心环形阵列构建声源，形成无衍射的超声波束，并使波束的辐射方向可控。首先，通过对元件间存在间隙的环形阵列进行偏心，证实了改变辐射波束方向是可能的。数值分析表明，十元阵向声轴15度方向辐射的波束仍能保持清晰的轮廓。结果表明，即使阵列单元数较少时，窄波束在偏离声轴方向上仍有可能产生辐射。验证了各单元离心比波动的影响，得到了实际离心单元与光束偏离方向处垂直距离的关系。为了有效地改变光束的方向，对源元件的结构进行了连续的检验，证实了当离心元件的数量最小时，光束在无衍射情况下的传播方向是可变的，并发现了光束作为一种精确平行扫描方法的可能性。此外，研究了更详细地设置光束传播路径的技术，找到了获得具有扭曲传播路径的光束的技术。此外，作为进行测量实验的手段，还研究了测量声场的技术。基于光学技术，利用两种干涉仪构建了声场非接触式、非侵入式测量系统。利用一般声源进行了测量实验，在二维复杂辐射场分布的可视化中，得到了与数值结果较为吻合的结果。

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.