  Due to the reversibility of viscous flow it is not expected to obtain a
fluidic rectifier simply from geometrical asymmetry without any moving
mechanical parts. Here, we found a counter example by using spatial asymmetry
combined with electric field to inject memory effects that render the flow
irreversible. This stems from the strong dependency of the electrorheological
(ER) fluid particle chaining on the flow direction. A funnel-shaped
microfluidic rectifier with ER fluid has been shown to be easily and rapidly
tuned via the applied electric field to achieve more than an order of magnitude
rectification along with pressure oscillations. These findings are of
importance for realization of fluidic diodes, rectifiers and ratchets.
