Specification of the bump on the disk surface by deviation of impulse force

The spacing between a magnetic head and a magnetic disk has been decreasing, as the areal recording density increase. Recently the flying height is less than lOnm, and it is necessary to detect the low bumps several nm or less. In order to detect the low bumps, it is required to maintain the low surfacing state of glide height head. But it is unstable, the vibration of the head is excited by the interaction between the head and the disk, and the contact occurs by remarkable waviness. So, to understand contact specifications is important in hard disk manufacturing. Therefore, we study the identification method of the contact force from PZT signal. Using this method, we can detect the contact of a head and a bump by SNR higher 3dB than the conventional method. Moreover, we have distinguished the interaction between the head and the surface from that between the head and the bump.