Abstract
The ultrasonic manipulation of cells and bioparticles in a large population is a maturing technology. There is an unmet demand for improved theoretical understanding of the particle–particle interactions at a high concentration. In this study, a semi-analytical method combining the Jacobi–Anger expansion and two-dimensional finite element solution of the scattering problem is proposed to calculate the acoustic radiation forces acting on massive compressible particles. Acoustic interactions on arrangements of up to several tens of particles are investigated. The particle radius ranges from the Rayleigh scattering limit (ka«1) to the Mie scattering region (ka≈1). The results show that the oscillatory spatial distribution of the secondary radiation force is related to the relative size of co-existing particles, not the absolute value (for particles with the same radius). In addition, the acoustic interaction is non-transmissible for a group of identical particles. For a large number of equidistant particles arranged along a line, the critical separation distance for the attraction force decreases as the number of particles increases, but eventually plateaus (for 16 particles). The range of attraction for the formed cluster is stabilized when the number of aggregated particles reaches a certain value.
Highlights
Biological or biophysical detection of cells and macromolecules is essential for clinical diagnostics, while physical or chemical processing of particles in fluids plays another important role [1,2].Portable devices that keep the targets viable in a few cubic millimeters of nutrient medium offer advantages such as high sensitivity, short processing time and reduced sample volume
The direct effect of incident wave is the acoustic radiation force (ARF) field, which applies a time-averaged force on each particle
Once the momentum carried by the incident sound wave is changed by the scattering of an obstacle, the ARF arises according to the conservation law
Summary
Biological or biophysical detection of cells and macromolecules is essential for clinical diagnostics, while physical or chemical processing of particles in fluids plays another important role [1,2]. More accurate algorithms for the secondary ARF on elastic spheres have been proposed [27,28,55,56], in which the fully coupled scattering fields are simultaneously solved by the FEM, spontaneously including the high order scattering and multipole terms. With this numerical method, we successfully explained why particle agglomeration only happens at the pressure node and predicted the dominant range of attractive inter-particle force [55], which agreed well with the measurement. Considering that the secondary ARF overweighs the primary one only at the pressure node, we focus on the targets located there
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