Optimal magnet shape design for wideband magnetic bias torque in a hard disk drive

In order to prevent the swing arm parked on the ramp from rotating due to a rotary shock, a wideband magnetic bias torque is generated on a retract pin. This paper presents the optimal magnet shape to generate a wideband magnetic bias torque. To find the optimal magnet shape, the standard shape optimization is employed. The physics behind why the optimized shape of the magnet yielded better performance is briefly explained using numerical simulation. To verify the effectiveness of the optimized magnet, the actual experiment was conducted. Experimental result shows that the optimized magnet shape generates a wideband magnetic bias torque while maintaining the maximum magnetic bias torque compared to a nominal magnet shape.