Ultrasound focuser: A multi-cylindrical source configuration and entrapped particles dynamics

Abstract

We aim to introduce the proof of concept of a 3D ultrasound Focuser with possible advanced applications in living-matter/cell entrapment, particle focusing, transportation through virtual channel and drug, agent or material delivery systems. The proposed mechanism is assumed to be fully submerged in a fluidic environment and composed of three parallel acoustic line sources which are located in such a way that form a triangular right prism. By approximating the wave field of each cylindrical source as a progressive plane wave field whose amplitude decreases with respect to the travelling distance from the source, the acoustic radiation force exerted on a single particle is analytically derived. It is shown that when each source has a π/3 phase different from other sources, an attracting zone around the axis of the triangular prism is formed for wavelengths in the order of the size scale, λ/l∼O(1), where l denotes the distance between each two sources. The optimal operating situation (the largest attracting zone) is found for the case where λ≈l. The theoretical study is supported by stability analysis of dynamics of the entrapped particle which located on the axis of the prism; and validated by computing the trajectories of migration of the test particle. The stability analysis is performed by considering the unsteady solution of Stokes equations and the possible flow of environmental fluid medium. In addition, the required settling time and required length scales to focus the particle to the center line of the prism for different size scale ratios are estimated and discussed. Compared to other 3D focusing techniques, this method is non-invasive, robust, easy to implement, applicable to nearly all types of micro-particles and does not need any specific pre-designed channel for focusing process.