Li Wei, Wang Mingsheng
School of Naval Architecture and Ocean Engineering, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China.
J Acoust Soc Am. 2018 Jun;143(6):3676. doi: 10.1121/1.5043422.
In this study, the authors use the partial-wave series expansion method in the spherical coordinate system and provide a theoretical formula for the off-axis acoustical scattering by rigid prolate and oblate spheroids illuminated by an arbitrary-order Bessel beam to explore the physical characteristics of the off-axis far-field scattering (the axis of the Bessel beam is parallel to the axis of the spheroids). The proposed method is verified and several three-dimensional far-field directivity patterns of rigid spheroids illuminated by zeroth- and first-order Bessel beams are depicted to explore the off-axis scattering. A special emphasis is placed on the geometry size of the prolate and oblate spheroids, the half-cone angle of the Bessel beam, the order of the Bessel beam, and the offset position. Compared with the on-axis scattering, the derivation and calculation of the off-axis scattering takes into account the spherical harmonic function using a numerical integral procedure. In addition, no symmetry was observed in the patterns of the far-field acoustic scattering form function for the zeroth- and higher-order Bessel beams with the off-axis illumination. This investigation provides a tool for the exploration of the complex scattering problems of underwater non-spherical particles under the illumination of the Bessel beam.
在本研究中，作者在球坐标系中使用分波级数展开法，给出了任意阶贝塞尔光束照射下刚性长椭球体和扁椭球体的离轴声散射理论公式，以探究离轴远场散射的物理特性（贝塞尔光束的轴与椭球体的轴平行）。对所提方法进行了验证，并绘制了零阶和一阶贝塞尔光束照射下刚性椭球体的几个三维远场方向图，以探究离轴散射。特别强调了长椭球体和扁椭球体的几何尺寸、贝塞尔光束的半锥角、贝塞尔光束的阶数以及偏移位置。与轴上散射相比，离轴散射的推导和计算使用数值积分程序考虑了球谐函数。此外，对于零阶及更高阶贝塞尔光束离轴照射的远场声散射形式函数的方向图，未观察到对称性。本研究为探索贝塞尔光束照射下水下非球形粒子的复杂散射问题提供了一种工具。
