(1) allowing a solution containing flexible particles to flow through a microfluidic device, said flexible particles being nano- or micron-sized particles with deformation properties, said device comprising:

a fluid channel having an inlet and an outlet;

one or more ultra-high frequency (UHF) bulky acoustic wave resonators provided on a wall of said fluid channel, said ultra-high frequency bulky acoustic wave resonators being capable of generating bulk acoustic waves in said fluid channel with a frequency of about 0.5-50 GHz and transmitted to the opposite side of said fluid channel;

(2) said UHF bulky acoustic wave resonator emitting a bulky acoustic wave transmitted to said wall on the opposite side of said fluid channel, producing a vortex channel in the solution defined by the boundary of the bulky acoustic wave generating region of the UHF resonator;

(3) by the setting of the shape or position of the bulky acoustic wave action region of the UHF bulky acoustic wave resonator, allowing the flexible particles in the solution enter and move along the vortex channel and leave the vortex channel at a set position, which is called the release point,

wherein a boundary line of the bulky acoustic wave generation region of said UHF resonator are set to be suitable for keeping the target flexible particles in the vortex channel while moving down along the vortex channel to the release point, by reducing the presence of a turn or curvature change in the boundary line of the bulky acoustic wave generation region.