Hard disk drives (HDD) with higher data density and faster access times rely heavily on the stability of the read-write head while flying over the magnetic media. Recognizing the importance of this stability, Hitachi development engineers
have studied the air bearing between the head and the media for a sequence of successively lower flying heights (gaps). This sequence of heights was produced by reducing the air pressure surrounding the HDD. A Polytec laser-Doppler
Vibrometer (LDV) was used to monitor the head response at each flying height. Once instabilities were known, methods were developed to dampen out excessive vibration levels that might damage the head-media interface.