Nonlinear signal mixing in a ratchet device

The nonlinear signal mixing of two, generally incommensurate, rectangular driving forces is used to control overdamped transport in Brownian ratchet devices. The interplay between the relative phase and the frequency ratio of the two driving forces is sufficient to generate an intriguing transport action that can be put to work to optimize shuttling and separation of particles in a variety of physical and technological applications. Analytic results for a striking multiple current reversal behavior are obtained for doubly rocked and rocked-pulsating Brownian ratchets. This tunable signal mixing can readily be implemented and exhibits an even richer behavior than those realized by the hard-to-implement, modifiable ratchet profiles.