Patent ID: 8133371

Claim:
A method for causing motion of particles in a medium, the method comprising: applying a time-varying driving field to the particles, the driving field applying a time-varying driving force alternating in direction to the particles; and, applying a mobility-varying field to the particles, the mobility-varying field being one or both of: different in type from the driving field, and non-aligned with the driving field; wherein the driving field and mobility-varying field are applied simultaneously during a period and the mobility-varying field causes a mobility of the particles in the medium to be time dependent during the period, in a manner having a non-zero correlation with the driving field over the period; wherein the driving field applies a periodically varying driving force to the particles; wherein the mobility-varying field causes the mobility of the particles to vary periodically; wherein the driving force and the varying mobility of the particles have a substantially constant phase relationship.