自由空间中球形粒子的负向声辐射力

The negative acoustic radiation force on a spherical particle in free space

针对一定声场作用下自由空间中的球形粒子,首先分析了声散射过程中的吸收声功率、散射声功率和损失声功率以及三者之间的关系,并通过计算发现了由于参数选取不当导致的负吸收现象。接着从动量守恒定律出发推导了声辐射力的一般表达式,阐释了声辐射力与声能流之间的关系,并从理论和计算两方面验证了负向声辐射力的存在。当负向声辐射力产生时,声波的背向散射被抑制。在此基础上,进一步研究了粒子的偏心特性和流体的黏度这两种常见因素对负向声辐射力的影响。利用球函数的加法公式推导了偏心球的散射系数和声辐射力公式,结果显示偏心距离、粒子的材料等都会显著改变负向声辐射力的产生条件。在低频近似下,由于流体黏度附加的正向声辐射力是否能完全抵消原来的负向声辐射力将决定最终的声辐射力方向。该结果对利用负向声辐射力制成单行波声学镊子来实现对特定粒子的操控有着理论指导意义。

The absorption power,scattering power and extinction power during the acoustic scattering process as well as the relationship between the three are analyzed.The negative absorption phenomenon caused by improper parameter selection is found through calculation.Moreover,the general expression of acoustic radiation force is derived based on the conservation law of momentum.The relationship between acoustic radiation force and acoustic energy flow is illustrated and the existence of negative acoustic radiation force is verified from both theoretical and computational aspects.The backscattering acoustic field is suppressed when the radiation force is negative.On this basis,the influence of the two common factors,the eccentricity of the particle and the viscosity of the fluid,on the negative acoustic radiation force is further studied.Using the additional theorem for spherical functions,the scattering coefficients and the acoustic radiation force expression for an eccentric sphere are derived.The results show that the eccentric distance and the particle material both significantly affect the conditions for generating the negative radiation force.Under the low frequency approximation,the sign of the final radiation force is determined by whether the positive radiation force caused by the fluid viscosity can completely offset the original negative one.The results are expected to provide a theoretical guide for developing single beam acoustic tweezers using negative radiation force to manipulate certain particles.