  We study the efficiency of frictional thermal ratchets driven by finite
frequency driving force and in contact with a heat bath. The efficiency
exhibits varied behavior with driving frequency. Both nonmonotonic and
monotonic behavior have been observed. In particular the magnitude of
efficiency in finite frequency regime may be more than the efficiency in the
adiabatic regime. This is our central result for rocked ratchets. We also show
that for the simple potential we have chosen, the presence of only spatial
asymmetry (homogeneous system) or only frictional ratchet (symmetric potential
profile), the adiabatic efficiency is always more than in the nonadiabatic
case.
