2016 Volume 37 Issue 5 Pages 221-230
In this work, we demonstrate the possibility of focusing a stream of microparticles to generate a matrixlike distribution using bulk acoustic standing waves. To achieve this goal, an axial acoustic excitation was performed on a suspension of spherical quasi-monodisperse microparticles in a flow through minichannel with a square cross section of 2 mm× 2 mm. The pair of transducer elements was also used for stimulation at several frequencies corresponding to its theoretical eigenmodes. The generation of the matrixlike tree-dimensional (3D) structures of focused particles was achieved by reflections of the acoustic radiation force associated with the square geometry. Particle positions were recorded by interferometric digital holographic microscopy, and the corresponding normalized distribution in the cross section was calculated for each experimental setting. The focusing efficiency was investigated through the variation of the acoustic energy density induced by the voltage applied to the piezo part and the injected flow rate. The acoustic field was numerically computed and compared with the experimental positions of particles in the cross section of the channel.