THE LIMIT OF MAGNET REMANENCE BR IN MOVING COIL ACTUATORS FOR DISK DRIVES

The expected future limit on a magnet's residual flux density B, due to decreased size in disk drive form factor is presented. Because, historically, the energy products of magnets have been increasing while the flux carrying capacity of steels has remained the same, one may expect a limit on further increase in B(r). For numerical illustration, the force exerted by the moving coil actuators in 2.5'' and 1.8'' disk drives is calculated as a function of B(r). These calculations show that one may expect no limit on B(r) for any practical, future scenarios, but that the ratio of an increase in force for an increase in B(r) diminishes.