A Brownian Ratchet is a device that can rectify the random Brownian
motion of particles to yield a directed steady-state flow.
We can imagine a thermo-fluid field of particles which
interact with the ratchet. The laws of thermodynamics imply that the
ratchet must use energy from some other source.
The dynamics of continuous-time Brownian ratchets are determined by a
stochastic partial differential equation. We have used a simplified
discrete-time model of a Brownian ratchet called ``Parrondo's games''
which are governed by a difference equation. In their original form,
Parrondo's games are a finite set of simple games of chance. An
indefinite pure sequence of any single game is neutral or even
losing. A periodic or randomised sequence of mixed games can be
winning. There is a steady state flow of probability in the preferred
We have been able to design a feasible and consistent device, by
mapping the conservation law of total probability onto the law of
conservation of charge. This device can absorb energy from a
mechanical field to produce a directed flow of charge. The fundamental
architecture is based on a ``bucket-brigade'' device. The capacitors
are 2-port MEMS devices. We use CMOS transmission gates to connect the
capacitors in the required topology.
We present an analysis and simulation of the MEMS Brownian ratchet and
suggest some possible applications.