Bessel驻波对椭球形液滴的声辐射转矩

Acoustic radiation torque on a spheroidal droplet in standing Bessel beams

在实际的声操控中,由于声辐射力、表面张力和重力的共同作用,液滴往往呈现出椭球的形状,在螺旋声场中会受到力矩的作用而发生转动。从声波的散射理论出发,根据部分波展开法求解得到了椭球形液滴在Bessel驻波场中的声散射系数,并给出了其受到的声辐射转矩的解析式。在此基础上,对椭球形不可压缩液滴和椭球形可压缩液滴分别进行数值计算。仿真结果表明,不可压缩液滴的声辐射转矩与声束半锥角的关系更密切,而可压缩液滴则更依赖于特定的频率;提升Bessel驻波场的阶数有利于增强声辐射转矩的峰值,但在中低频处较难对可压缩液滴产生明显的力矩。该研究结果预期对利用螺旋声场进行液滴的操控具有理论指导作用。

In the actual acoustic manipulation,a droplet often takes the shape of a spheroid due to the combined effects of the acoustic radiation force,surface tension and gravitational force,which can be rotated by the torque in helicoidal sound fields.Based on the theory of acoustic scattering,the scattering coefficients of a spheroidal droplet in standing Bessel beams are solved using the partial wave series expansion method,and the analytical expression of the acoustic radiation torque is also provided.On this basis,the results for spheroidal incompressible droplets and compressible droplets are both calculated numerically.The simulated results show that the acoustic radiation torque on incompressible droplets is more closely related to the half-cone angle of the beam,while compressible droplets are more dependent on specific frequencies.The growth of the beam order will increase the peaks of the acoustic radiation torque,but it is difficult to obtain an obvious radiation torque for compressible droplets at low and medium frequencies.The results of this study are expected to provide a theoretical guide for manipulating droplets using helicoidal acoustic beams.