3-D Acoustic Trapping With Standing Waves

TL;DR

This paper presents an experimental and theoretical study of 3-D acoustic trapping of air microbubbles in oil using standing ultrasound waves, including modeling, validation, and force analysis.

Contribution

It introduces a comprehensive model for 3-D acoustic trapping with experimental validation, highlighting limitations of simple standing wave models.

Findings

Pressure field reconstructed with Lorenz-Mie Theory and FEM validation

Minimum trapping force ranged from 3 nN to 780 nN

Standing wave interference model cannot fully explain 3-D trapping

Abstract

In this work, we will describe an experimental setup for a standing--wave ultrasound trap for air microbubbles in oil. We develop a model for the finite acoustic beam using the angular spectrum technique, and reconstruct the pressure field using the General Lorenz-Mie Theory framework, which was validated using a finite elements method (FEM) simulation. Using Stokes' drag law, we were able to obtain the radius of the trapped bubbles and estimate the minimum acoustic force necessary to trap them, which ranged from 3 nN to 780 nN. We also present the force profile as a function of distance for different bubble that were trapped experimentally, and show that a standing wave formed by interfering infinite plane waves cannot explain the observed acoustic trapping of bubbles in 3-D.