Propulsion of microspheres in fluids using rotating magnetic fields

Abstract

Magnetic microspheres dispersed in fluids can be moved using static field gradients or by applying oscillating or rotating magnetic fields. Such separation methods are useful for many applications within biotechnology and medical technology as a tool to separate or extract cells or molecules. Efficient magnetic separation using field gradients usually requires having a strength of the source of the field of order B = 1 T. However, by applying alternating, or rotating, weak magnetic fields with field strength of order B = 1 mT, micron sized composite magnetic beads can be controlled and separated. This will happen since the beads are normally much heavier than the surrounding fluid. As the beads due to gravity approach the bottom surface of the sample cell, they may be propelled in a rolling/slipping motion due to a torque from the rotating magnetic field.