Characterization of disk vibrations on aluminum and alternate substrates

Aluminum disk platters in 3.5 inch disk drives have been shown to vibrate at their natural frequencies due to air flow excitation. This causes track misregistration that can limit the tracks per inch (TPI). This was shown to be a characteristic behavior of 95 x 0.8 mm aluminum disks [1]. Measurement methods which are useful in characterizing disk vibrations are described. A laser doppler vibrometer, focused on the disk surface, is used as a velocity sensor to measure force hammer excited frequency response functions, spin-up waterfall plots, and constant speed power spectra. These measurement methods were used to characterize disk platter vibrations on aluminum and alternate substrates in 3.5 inch disk drives. Alternate substrates which have significantly higher stiffness to density ratios (specific stiffness), dramatically reduce the amplitude of these disk vibrations and may provide higher TPI capability.