Inhomogeneous soliton ratchets under two ac forces.

We extend our previous work on soliton ratchet devices [L. Morales-Molina, Eur. Phys. J. B 37, 79 (2004)] to consider the joint effect of two ac forces including nonharmonic drivings, as proposed for particle ratchets by Savele'v [Europhys. Lett. 67, 179 (2004); Phys. Rev. E 70, 066109 (2004)]. Current reversals due to the interplay between the phases, frequencies, and amplitudes of the harmonics are obtained. An analysis of the effect of the damping coefficient on the dynamics is presented. We show that solitons give rise to nontrivial differences in the phenomenology reported for particle systems that arise from their extended character. A comparison with soliton ratchets in homogeneous systems with biharmonic forces is also presented. This ratchet device may be an ideal candidate for Josephson junction ratchets with intrinsic large damping.