PERMANENT-MAGNET VARIABLE FLUX SOURCES

Rotatable transversely-magnetized magnet rods can be used to generate variable, uniform magnetic fields or field gradients. A four-rod devic e for use at the specimen stage of an optical microscope is described where the field can be in-plane or perpendicular to the stage. The max imum flux density ranges from 36 mT (360 G) for isotropic ferrite to 2 10 mT (2.1 kG) for sintered Nd-Fe-B. Calculated and measured field pro files are in good agreement. Homogeneity is better than 1 % of maximum in a region of diameter 7 mm or 3.5 mm at maximum and zero field, res pectively.