An opposed migration classifier classifies particles suspended in a sample fluid that are passed through a classification channel defined by two permeable walls. Sample flow distribution input and output channels are located asymmetrically with respect to a center of the classification channel such that trajectories of the one or more particles in the sample fluid deviate from constant voltage operation trajectories. A cross-flow fluid enters the classification channel through a permeable wall and exits through the other permeable wall. An imposed field, created by a time varying filed imposed in a direction normal to the permeable walls, causes the particles to migrate in a direction opposite to that of the cross-flow fluid, such that the particles travel between the permeable walls. The particles in the sample are classified based on their mobility. The sample fluid enters and exists through or within a threshold distance of the permeable walls.