Nested dipolar Halbach arrays for the determination of magnetorheological properties at variable magnetic field

A new apparatus for the measurement of magnetorheological properties of magnetic fluids in a commercial strain-controlled rheometer is proposed. The new setup makes use of the concept of the Halbach cylinder to generate a homogeneous dipolar magnetic field, using only permanent magnets. Two of these Halbach cylinders are combined, allowing the magnetic field to be varied by simply rotating the cylinders relatively to one another. The magnetic field achieved in the middle of the cylinders varies from nearly zero to about 0.6 T without a significant variation on the high homogeneity (Δ B / B