Evaluating vibration characteristics of a disk media substrate

This paper describes an objective test procedure to evaluate vibration char acteristics of disk media at different spin speeds. In this new approach, f requency response functions of a disk-spindle system were measured experime ntally at different speeds through an automatic hammer and a capacitance pr obe. In addition, the experiments were conducted in vacuum to eliminate aer odynamic excitations, and a large number of averages was used to reduce the bearing runouts. To evaluate the disk substrate, three vibration character istics were extracted from the frequency response functions: modal damping, resonance amplitude (quality factor), and integrated energy spectrum. Thre e substrate materials were tested: NiPAl (nickel phosphorus aluminum), AlBC (aluminum boron carbide), and glass ceramics. Both 84-mm and 95-mm substra te materials were tested. The results show that AlBC disks have the best vi bration characteristics (i.e., highest damping and smallest amplitude) and that glass disks have the poorest vibration characteristics.