The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Sep. 18, 2007
Filed:
Oct. 28, 2004
Zhupei Shi, San Jose, CA (US);
LI Tang, Fremont, CA (US);
Jane Jie Zhang, San Jose, CA (US);
Shanlin Duan, Fremont, CA (US);
Zhupei Shi, San Jose, CA (US);
Li Tang, Fremont, CA (US);
Jane Jie Zhang, San Jose, CA (US);
Shanlin Duan, Fremont, CA (US);
Hitachi Global Storage Technologies Netherlands B.V., Amsterdam, NL;
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.