Dynamic magnetic information storage or retrieval – Monitoring or testing the progress of recording
Reexamination Certificate
2007-09-18
2007-09-18
Wellington, Andrea (Department: 2627)
Dynamic magnetic information storage or retrieval
Monitoring or testing the progress of recording
C360S025000
Reexamination Certificate
active
10975259
ABSTRACT:
A method for determining whether a spike in a read back signal from a read head positioned over a perpendicular recording disk having a magnetically soft underlayer (SUL) is caused by a defect in the SUL or by a thermal asperity (TA). A first read back signal with the spike is obtained in the absence of a local magnetic field near the read head. Then, a permanent magnet or electromagnet is used to induce a small local magnetic field by the read head, and a second signal is obtained. If the signals are substantially similar, a thermal asperity is indicated. Otherwise a defect in the 13 magnetically soft underlayer of the disk is indicated.
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Duan Shanlin
Shi Zhupei
Tang Li
Zhang Jane Jie
Hitachi Global Storage Technologies - Netherlands B.V.
Kapadia Varsha A.
Rogitz John L.
Wellington Andrea
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