Abstract:

Separation of particles by their acoustomechanical properties can be accomplished by acoustophoresis, which depends on both primary and secondary acoustic radiation forces. In an acoustic standing wave, particles are moved either toward the pressure nodes or the antinodes depending on the relative contrasts in the particle density and compressibility with the surrounding host liquid. Because particles reradiate the sound waves, there are secondary interparticle forces as well. These secondary forces can either hinder or enhance the separation process. If two species which are to be separated attract each other because of interparticle forces, the separation will be compromised. But if several like particles aggregate, then primary forces are much stronger and the separation occurs more rapidly. When flow is superimposed on the system, as is common in practical applications, then drag forces must also be accounted for. In the present work, novel field configurations have been explored, and the trajectories of particles have been computed for a number of frequencies, flow speeds, field strengths, and property contrasts. Based on these simulations, experiments have been designed to optimize the efficiency of acoustophoresis, especially for biotechnology applications. [Work supported by NASA through Grant NAG8-1351.]