Acoustophoresis separation of particles based on motion modes via tilted-angle standing surface acoustic wave driven by a unidirectional transducer

Acoustophoresis separation technique has attracted great attention due to its superior properties, such as biocompatibility, non-contact, label-free and high-efficiency. In this paper, separation of particles based on motion modes via tilt angle standing surface acoustic wave (TaSSAW) driven by a unidirectional transducer is developed theoretically. It is verified that the designed electrode width controlled unidirectional transducers are effective to improve the intensity of the acoustic field and the acoustic radiation force of the particles in the channel. The results show that when the density and compressibility of the particles are close to those of the fluid and the particle shape is close to spherical, the influences of fluid viscosity and particle shape on the acoustic radiation force are negligible. It is found that in the TaSSAW system the motion modes of the particles are divided into locked mode and drift mode, and they depend on the fluid velocity, acoustic field intensity and tilt angle. polystyrene (PS) particles with radii of 4 and 5 µm are separated based on the differences of motion modes. For further smaller size difference (4.5 and 5 µm) particles, the separation is also realized successfully by making particles move in the same drift mode.