零阶Bessel驻波场中任意粒子声辐射力和力矩的Born近似

Born approximation of acoustic radiation force and torque for an arbitrary particle in a zero-order standing Bessel beam

声辐射力和声辐射力矩的计算是实现粒子精准操控的重要基础.基于经典声散射理论的偏波级数展开法较难直接用于复杂模型的研究,而纯数值的方法则不利于进行系统的参数化分析.基于Born近似的基本原理,推导了低频情况下零阶Bessel驻波场中心任意粒子的声辐射力和力矩表达式.在此基础上,以球形粒子、椭球形粒子和柱形粒子为例进行详细地计算,并考虑声参数的非均匀性对声辐射力和力矩的影响.仿真结果表明,在低频范围内Born近似具有很高的精度,随着频率的增加和粒子与流体的阻抗匹配变差,Born近似的精度逐渐下降.对于倾斜放置于零阶Bessel驻波场中的椭球形粒子和柱形粒子,非对称性会导致其受到声辐射力矩的作用.在粒子尺寸远小于波长的情况下,声辐射力特性与粒子的具体形状几乎无关,但声辐射力矩不然.最后,引入周围流体的黏滞效应并对声辐射力的表达式进行了修正.该研究预期可以为生物医学、材料科学等领域利用驻波场声镊子实现微小粒子的精准操控提供一定的理论指导.

The calculation of acoustic radiation force and acoustic radiation torque is an important basis for the precise manipulation of particles.It is difficult to directly apply the partial-wave series expansion method based on the classical acoustic scattering theory to the study of complicated models,while pure numerical methods are not conducive to the parametric analyses of the system.Based on the basic principle of Born approximation,the expressions of acoustic radiation force and torque acting on an arbitrary particle located in the center of a zeroorder Bessel standing wave field are derived at low frequencies.On this basis,the numerical simulations are systematically performed by taking spherical,spheroidal and cylindrical particles as examples.The effects of inhomogeneity on the acoustic radiation force and torque are also investigated.The simulation results show that the Born approximation method has a high accuracy in the low frequency range.As the frequency increases and the impedance matching between the particle and the fluid becomes worse,the accuracy of Born approximation will gradually decrease.An acoustic radiation torque caused by asymmetry will be exerted on spheroidal and cylindrical particles obliquely positioned in a zero-order Bessel standing wave field.When the particle size is much smaller than the wavelength,the acoustic radiation force is nearly independent of the particle shape,but this is not the case for acoustic radiation torque.Finally,viscous effect of the surrounding fluid is introduced and the expression of acoustic radiation force is corrected accordingly.The study is expected to provide a theoretical guide for the precise manipulation of small particles using standing wave acoustic tweezers in biomedicine and material sciences.