Computational dynamics of acoustically-driven microsphere systems

TL;DR

This paper introduces a computational framework combining molecular dynamics and integral equations to simulate the self-consistent dynamics of microspheres driven by pulsed acoustic fields, capturing interactions and trapping behaviors.

Contribution

It presents a novel integrated computational approach for modeling microsphere dynamics under acoustic driving, including field-induced interactions and trapping effects.

Findings

Field-induced interactions are effectively dipolar, based on microsphere velocities.

Ultrasound pulses mainly translate the microsphere cloud, with possible expansion or contraction.

The framework accurately describes non-dissipative drag forces in microsphere systems.

Abstract

We propose a computational framework for the self-consistent dynamics of a microsphere system driven by a pulsed acoustic field in an ideal fluid. Our framework combines a molecular dynamics integrator describing the dynamics of the microsphere system with a time-dependent integral equation solver for the acoustic field that makes use of fields represented as surface expansions in spherical harmonic basis functions. The presented approach allows us to describe the inter-particle interaction induced by the field as well as the dynamics of trapping in counter-propagating acoustic pulses. The integral equation formulation leads to equations of motion for the microspheres describing the effect of non-dissipative drag forces. We show (1) that the field-induced interactions between the microspheres give rise to effective dipolar interactions, with effective dipoles defined by their velocities, and (2) that the dominant effect of an ultrasound pulse through a cloud of microspheres gives rise mainly to a translation of the system, though we also observe both expansion and contraction of the cloud determined by the initial system geometry.