Fine separation of particles via the entropic splitter.

We investigate the fine separation of particles with different sizes in an asymmetric confined channel by directing them moving to the opposite directions. Besides redesigning the geometry of the channel, we add a general rectangular wave oscillating force to enlarge the velocity differences between particles with different radii, which is important to increase the separation speed and sort particles of similar radii. The separation process is guaranteed by choosing a small period of the oscillating force and a proper partition strategy of the device length sifting particles to the left and right. The optimal set of parameters for a fixed amplitude of the oscillating force is found by the above regime. We show that by this regime the separation efficiency is significantly improved compared to the classic square wave force.