Theoretical Quantum Physics Laboratory, RIKEN Cluster for Pioneering Research, Wako-shi, Saitama 351-0198, Japan.
ITMO University, Birzhevaya liniya 14, St.-Petersburg 199034, Russia.
Phys Rev Lett. 2019 Nov 1;123(18):183901. doi: 10.1103/PhysRevLett.123.183901.
We examine acoustic radiation force and torque on a small (subwavelength) absorbing isotropic particle immersed in a monochromatic (but generally inhomogeneous) sound-wave field. We show that by introducing the monopole and dipole polarizabilities of the particle, the problem can be treated in a way similar to the well-studied optical forces and torques on dipole Rayleigh particles. We derive simple analytical expressions for the acoustic force (including both the gradient and scattering forces) and torque. Importantly, these expressions reveal intimate relations to the fundamental field properties introduced recently for acoustic fields: the canonical momentum and spin angular momentum densities. We compare our analytical results with previous calculations and exact numerical simulations. We also consider an important example of a particle in an evanescent acoustic wave, which exhibits the mutually orthogonal scattering (radiation-pressure) force, gradient force, and torque from the transverse spin of the field.
我们研究了小（亚波长）吸收各向同性粒子在单色（但通常不均匀）声波场中的声辐射力和力矩。我们表明，通过引入粒子的单极子和偶极子极化率，可以以类似于研究充分的偶极雷利粒子的光学力和力矩的方式来处理该问题。我们推导出了用于声学力（包括梯度力和散射力）和力矩的简单解析表达式。重要的是，这些表达式揭示了与最近为声学场引入的基本场特性之间的密切关系：正则动量和自旋角动量密度。我们将我们的分析结果与以前的计算和精确数值模拟进行了比较。我们还考虑了在消逝声波中的粒子的一个重要示例，该示例表现出来自场的横向自旋的相互正交的散射（辐射压力）力、梯度力和力矩。
