Off-Transition Noise Characterization During Head Thermal Protrusion

This paper characterizes the read-back off-transition noise (OTN) in spectral, spatial, and time domains during the thermal protrusion of a magnetic head. In perpendicular recording, the OTN is typically lower than the background noise, and shows bathtub-like cross-track profile. The spatial and spectral characteristics of the read-back OTN make it sensitive to the head positing change in cross-track, down-tack, and vertical directions. In contrast to the conventional on-transition signal reading, the OTN monitoring reverses the usage of signal and noise and lowers the requirement on signal quality. Monitoring OTN during head's thermal control can detect air bearing's stability, head's fly-ability, and head-lube/disk contact without Fourier transform (FT) related techniques. A single-track and single read-frequency head-lube/disk contact detection method with high simplicity, high sensitivity, and high repeatability is introduced.