  In conventional Deterministic Lateral Displacement (DLD), the migration
behavior of a particle of specific size is determined by the critical diameter
(Dc), which is predefined by the device's geometry. In contrast to the typical
approach that alters the angle between the pillar array and fluid streamlines
by modifying the geometrical parameters, this study introduces a novel
perspective that focuses on changing the direction of the streamlines. The
proposed technique enables the fabrication of a tunable DLD chip that is both
easy to manufacture and design. This chip features one completely horizontal
pillar array with two bypass channels on the top and bottom of the DLD chamber.
The width of these bypass channels changes linearly from their inlet to their
outlet. Two design configurations are suggested for this chip, characterized by
either parallel or unparallel slopes of the bypass channels. This chip is
capable of generating a wide range of Dc values by manipulating two distinct
control parameters. The first control parameter involves adjusting the flow
rates in the two bypass channels. The second control parameter entails
controlling the slopes of these bypass channels. Both of these parameters
influence the direction of particle-carrying streamlines resulting in a change
in the path-line of the particles. By changing the angle of streamlines with
pillar array, the Dc can be tuned. Prior to determining the Dc for each case,
an initial estimation was made using a Python script that utilized the
streamline coordinates. Subsequently, through FEM modeling of the particle
trajectories, precise Dc values were ascertained and juxtaposed with the
estimated values, revealing minimal disparities. This innovative chip enables
the attainment of Dc values spanning from 0.5 to 14 {\mu}m.
