Figure 2.

Velocity variations of 0.28- and 0.87-μm-diameter polystyrene beads (empty symbols for numerical modeling results and solid symbols for experimental data) along the microchannel constriction at various U_dc. The magnitude of the U_{ac_1} (τ=10s) and U_{ac_2} (f=30 kHz) were maintained at 50 V and 800 V, respectively. The error bars indicate the standard deviation of average velocity obtained at each U_dc by tracking 60 or 300 individual trajectories from the experimental or the simulation results, respectively. At the applied U_dc conditions from 0 to + 30 V in both the experiment and the numerical modeling, the average velocities of 0.87 μm particles were in the opposite direction to the applied U_dc, showing apparent ratchet migration, whereas 0.28 μm particles showed the normal response with positive migration velocities according to the sign and magnitude of U_dc.