Effect of acoustic particle velocity gradient on the acoustic radiation force on microparticles

In this paper, effect of the acoustic particle velocity distribution on the acoustic radiation force on microparticles in a microfluidic system has been studied. Subwavelength acoustic modes generated in a PZT-driven, flexurally-vibrating glass capillary actuator enables formation of acoustic pressure and acoustic particle velocity gradients in two perpendicular axes. Since the subwavelength pressure coupling is frequency dependent, device enables monitoring of frequency dependent variation of the field terms. In agreement with the theoretical expectations, experimental results suggest that at low frequency regime radiation forces generated due to the acoustic particle velocity gradient can become up to two orders of magnitude higher than the forces due to acoustic pressure gradients.