  When active matter particles such as swimming bacteria are placed in an
asymmetric array of funnels, it has been shown that a ratchet effect can occur
even in the absence of an external drive. Here we examine active ratchets for
two dimensional arrays of funnels or L-shapes where there is also an externally
applied dc drive or drift. We show that for certain conditions, the ratchet
effect can be strongly enhanced, and that it is possible to have conditions
under which run-and-tumble particles with one run length move in the opposite
direction from particles with a different run length. For the arrays of
L-shapes, we find that the application of a drift force can enhance a
transverse rectification in the direction perpendicular to the drift. When
particle-particle steric interactions are included, we find that the ratchet
effects can be either enhanced or suppressed depending on barrier geometry,
particle run length, and particle density.
